com.unity.netcode.gameobjects@1.3.1

The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).

## [1.3.1] - 2023-03-27

### Added

- Added detection and graceful handling of corrupt packets for additional safety. (#2419)

### Changed

- The UTP component UI has been updated to be more user-friendly for new users by adding a simple toggle to switch between local-only (127.0.0.1) and remote (0.0.0.0) binding modes, using the toggle "Allow Remote Connections" (#2408)
- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.3. (#2450)
- `NetworkShow()` of `NetworkObject`s are delayed until the end of the frame to ensure consistency of delta-driven variables like `NetworkList`.
- Dirty `NetworkObject` are reset at end-of-frame and not at serialization time.
- `NetworkHide()` of an object that was just `NetworkShow()`n produces a warning, as remote clients will _not_ get a spawn/despawn pair.
- Renamed the NetworkTransform.SetState parameter `shouldGhostsInterpolate` to `teleportDisabled` for better clarity of what that parameter does. (#2228)
- Network prefabs are now stored in a ScriptableObject that can be shared between NetworkManagers, and have been exposed for public access. By default, a Default Prefabs List is created that contains all NetworkObject prefabs in the project, and new NetworkManagers will default to using that unless that option is turned off in the Netcode for GameObjects settings. Existing NetworkManagers will maintain their existing lists, which can be migrated to the new format via a button in their inspector. (#2322)

### Fixed

- Fixed issue where changes to a layer's weight would not synchronize unless a state transition was occurring.(#2399)
- Fixed issue where `NetworkManager.LocalClientId` was returning the `NetworkTransport.ServerClientId` as opposed to the `NetworkManager.m_LocalClientId`. (#2398)
- Fixed issue where a dynamically spawned `NetworkObject` parented under an in-scene placed `NetworkObject` would have its `InScenePlaced` value changed to `true`. This would result in a soft synchronization error for late joining clients. (#2396)
- Fixed a UTP test that was failing when you install Unity Transport package 2.0.0 or newer. (#2347)
- Fixed issue where `NetcodeSettingsProvider` would throw an exception in Unity 2020.3.x versions. (#2345)
- Fixed server side issue where, depending upon component ordering, some NetworkBehaviour components might not have their OnNetworkDespawn method invoked if the client side disconnected. (#2323)
- Fixed a case where data corruption could occur when using UnityTransport when reaching a certain level of send throughput. (#2332)
- Fixed an issue in `UnityTransport` where an exception would be thrown if starting a Relay host/server on WebGL. This exception should only be thrown if using direct connections (where WebGL can't act as a host/server). (#2321)
- Fixed `NetworkAnimator` issue where it was not checking for `AnimatorStateTtansition.destinationStateMachine` and any possible sub-states defined within it. (#2309)
- Fixed `NetworkAnimator` issue where the host client was receiving the ClientRpc animation updates when the host was the owner.(#2309)
- Fixed `NetworkAnimator` issue with using pooled objects and when specific properties are cleaned during despawn and destroy.(#2309)
- Fixed issue where `NetworkAnimator` was checking for animation changes when the associated `NetworkObject` was not spawned.(#2309)
- Corrected an issue with the documentation for BufferSerializer (#2401)

CHANGELOG.md

@@ -1,4 +1,3 @@
-
 # Changelog
 
 All notable changes to this project will be documented in this file.
@@ -7,6 +6,69 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
+## [1.3.1] - 2023-03-27
+
+### Added
+
+- Added detection and graceful handling of corrupt packets for additional safety. (#2419)
+
+### Changed
+
+- The UTP component UI has been updated to be more user-friendly for new users by adding a simple toggle to switch between local-only (127.0.0.1) and remote (0.0.0.0) binding modes, using the toggle "Allow Remote Connections" (#2408)
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.3. (#2450)
+- `NetworkShow()` of `NetworkObject`s are delayed until the end of the frame to ensure consistency of delta-driven variables like `NetworkList`.
+- Dirty `NetworkObject` are reset at end-of-frame and not at serialization time.
+- `NetworkHide()` of an object that was just `NetworkShow()`n produces a warning, as remote clients will _not_ get a spawn/despawn pair.
+- Renamed the NetworkTransform.SetState parameter `shouldGhostsInterpolate` to `teleportDisabled` for better clarity of what that parameter does. (#2228)
+- Network prefabs are now stored in a ScriptableObject that can be shared between NetworkManagers, and have been exposed for public access. By default, a Default Prefabs List is created that contains all NetworkObject prefabs in the project, and new NetworkManagers will default to using that unless that option is turned off in the Netcode for GameObjects settings. Existing NetworkManagers will maintain their existing lists, which can be migrated to the new format via a button in their inspector. (#2322)
+
+### Fixed
+
+- Fixed issue where changes to a layer's weight would not synchronize unless a state transition was occurring.(#2399)
+- Fixed issue where `NetworkManager.LocalClientId` was returning the `NetworkTransport.ServerClientId` as opposed to the `NetworkManager.m_LocalClientId`. (#2398)
+- Fixed issue where a dynamically spawned `NetworkObject` parented under an in-scene placed `NetworkObject` would have its `InScenePlaced` value changed to `true`. This would result in a soft synchronization error for late joining clients. (#2396)
+- Fixed a UTP test that was failing when you install Unity Transport package 2.0.0 or newer. (#2347)
+- Fixed issue where `NetcodeSettingsProvider` would throw an exception in Unity 2020.3.x versions. (#2345)
+- Fixed server side issue where, depending upon component ordering, some NetworkBehaviour components might not have their OnNetworkDespawn method invoked if the client side disconnected. (#2323)
+- Fixed a case where data corruption could occur when using UnityTransport when reaching a certain level of send throughput. (#2332)
+- Fixed an issue in `UnityTransport` where an exception would be thrown if starting a Relay host/server on WebGL. This exception should only be thrown if using direct connections (where WebGL can't act as a host/server). (#2321)
+- Fixed `NetworkAnimator` issue where it was not checking for `AnimatorStateTtansition.destinationStateMachine` and any possible sub-states defined within it. (#2309)
+- Fixed `NetworkAnimator` issue where the host client was receiving the ClientRpc animation updates when the host was the owner.(#2309)
+- Fixed `NetworkAnimator` issue with using pooled objects and when specific properties are cleaned during despawn and destroy.(#2309)
+- Fixed issue where `NetworkAnimator` was checking for animation changes when the associated `NetworkObject` was not spawned.(#2309)
+- Corrected an issue with the documentation for BufferSerializer (#2401)
+
+## [1.2.0] - 2022-11-21
+
+### Added
+
+- Added protected method `NetworkBehaviour.OnSynchronize` which is invoked during the initial `NetworkObject` synchronization process. This provides users the ability to include custom serialization information that will be applied to the `NetworkBehaviour` prior to the `NetworkObject` being spawned. (#2298)
+- Added support for different versions of the SDK to talk to each other in circumstances where changes permit it. Starting with this version and into future versions, patch versions should be compatible as long as the minor version is the same. (#2290)
+- Added `NetworkObject` auto-add helper and Multiplayer Tools install reminder settings to Project Settings. (#2285)
+- Added `public string DisconnectReason` getter to `NetworkManager` and `string Reason` to `ConnectionApprovalResponse`. Allows connection approval to communicate back a reason. Also added `public void DisconnectClient(ulong clientId, string reason)` allowing setting a disconnection reason, when explicitly disconnecting a client. (#2280)
+
+### Changed
+
+- Changed 3rd-party `XXHash` (32 & 64) implementation with an in-house reimplementation (#2310)
+- When `NetworkConfig.EnsureNetworkVariableLengthSafety` is disabled `NetworkVariable` fields do not write the additional `ushort` size value (_which helps to reduce the total synchronization message size_), but when enabled it still writes the additional `ushort` value. (#2298)
+- Optimized bandwidth usage by encoding most integer fields using variable-length encoding. (#2276)
+
+### Fixed
+- Fixed `IsSpawnedObjectsPendingInDontDestroyOnLoad` is only set to true when loading a scene using `LoadSceneMode.Singleonly`. (#2330)
+- Fixed issue where `NetworkTransform` components nested under a parent with a `NetworkObject` component  (i.e. network prefab) would not have their associated `GameObject`'s transform synchronized. (#2298)
+- Fixed issue where `NetworkObject`s that failed to instantiate could cause the entire synchronization pipeline to be disrupted/halted for a connecting client. (#2298)
+- Fixed issue where in-scene placed `NetworkObject`s nested under a `GameObject` would be added to the orphaned children list causing continual console warning log messages. (#2298)
+- Custom messages are now properly received by the local client when they're sent while running in host mode. (#2296)
+- Fixed issue where the host would receive more than one event completed notification when loading or unloading a scene only when no clients were connected. (#2292)
+- Fixed an issue in `UnityTransport` where an error would be logged if the 'Use Encryption' flag was enabled with a Relay configuration that used a secure protocol. (#2289)
+- Fixed issue where in-scene placed `NetworkObjects` were not honoring the `AutoObjectParentSync` property. (#2281)
+- Fixed the issue where `NetworkManager.OnClientConnectedCallback` was being invoked before in-scene placed `NetworkObject`s had been spawned when starting `NetworkManager` as a host. (#2277)
+- Creating a `FastBufferReader` with `Allocator.None` will not result in extra memory being allocated for the buffer (since it's owned externally in that scenario). (#2265)
+
+### Removed
+
+- Removed the `NetworkObject` auto-add and Multiplayer Tools install reminder settings from the Menu interface. (#2285)
+
 ## [1.1.0] - 2022-10-21
 
 ### Added
@@ -157,6 +219,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `ClientNetworkTransform` from the package samples and moved to Boss Room's Utilities package which can be found [here](https://github.com/Unity-Technologies/com.unity.multiplayer.samples.coop/blob/main/Packages/com.unity.multiplayer.samples.coop/Utilities/Net/ClientAuthority/ClientNetworkTransform.cs) (#1912)
 
 ### Fixed
+
 - Fixed issue where `NetworkSceneManager` did not synchronize despawned in-scene placed NetworkObjects. (#1898)
 - Fixed `NetworkTransform` generating false positive rotation delta checks when rolling over between 0 and 360 degrees. (#1890)
 - Fixed client throwing an exception if it has messages in the outbound queue when processing the `NetworkEvent.Disconnect` event and is using UTP. (#1884)
@@ -210,10 +273,12 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ## [1.0.0-pre.6] - 2022-03-02
 
 ### Added
+
 - NetworkAnimator now properly synchrhonizes all animation layers as well as runtime-adjusted weighting between them (#1765)
 - Added first set of tests for NetworkAnimator - parameter syncing, trigger set / reset, override network animator (#1735)
 
 ### Fixed
+
 - Fixed an issue where sometimes the first client to connect to the server could see messages from the server as coming from itself. (#1683)
 - Fixed an issue where clients seemed to be able to send messages to ClientId 1, but these messages would actually still go to the server (id 0) instead of that client. (#1683)
 - Improved clarity of error messaging when a client attempts to send a message to a destination other than the server, which isn't allowed. (#1683)
@@ -265,6 +330,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `FixedQueue`, `StreamExtensions`, `TypeExtensions` (#1398)
 
 ### Fixed
+
 - Fixed in-scene NetworkObjects that are moved into the DDOL scene not getting restored to their original active state (enabled/disabled) after a full scene transition (#1354)
 - Fixed invalid IL code being generated when using `this` instead of `this ref` for the FastBufferReader/FastBufferWriter parameter of an extension method. (#1393)
 - Fixed an issue where if you are running as a server (not host) the LoadEventCompleted and UnloadEventCompleted events would fire early by the NetworkSceneManager (#1379)
@@ -279,6 +345,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Fixed network tick value sometimes being duplicated or skipped. (#1614)
 
 ### Changed
+
 - The SDK no longer limits message size to 64k. (The transport may still impose its own limits, but the SDK no longer does.) (#1384)
 - Updated com.unity.collections to 1.1.0 (#1451)
 - NetworkManager's GameObject is no longer allowed to be nested under one or more GameObject(s).(#1484)

Components/AssemblyInfo.cs

@@ -1,10 +1,15 @@
 using System.Runtime.CompilerServices;
 
 #if UNITY_EDITOR
-[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#endif // UNITY_EDITOR
-#endif
+
+#if UNITY_INCLUDE_TESTS
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#endif // UNITY_INCLUDE_TESTS

Components/NetworkAnimator.cs

@@ -23,12 +23,6 @@ namespace Unity.Netcode.Components
         /// </summary>
         private void FlushMessages()
         {
-            foreach (var clientId in m_ClientsToSynchronize)
-            {
-                m_NetworkAnimator.ServerSynchronizeNewPlayer(clientId);
-            }
-            m_ClientsToSynchronize.Clear();
-
             foreach (var sendEntry in m_SendParameterUpdates)
             {
                 m_NetworkAnimator.SendParametersUpdateClientRpc(sendEntry.ParametersUpdateMessage, sendEntry.ClientRpcParams);
@@ -64,9 +58,10 @@ namespace Unity.Netcode.Components
                         }
 
                         // Everyone applies any parameters updated
-                        foreach (var parameterUpdate in m_ProcessParameterUpdates)
+                        for (int i = 0; i < m_ProcessParameterUpdates.Count; i++)
                         {
-                            m_NetworkAnimator.UpdateParameters(parameterUpdate);
+                            var parameterUpdate = m_ProcessParameterUpdates[i];
+                            m_NetworkAnimator.UpdateParameters(ref parameterUpdate);
                         }
                         m_ProcessParameterUpdates.Clear();
 
@@ -80,20 +75,6 @@ namespace Unity.Netcode.Components
             }
         }
 
-        /// <summary>
-        /// Clients that need to be synchronized to the relative Animator
-        /// </summary>
-        private List<ulong> m_ClientsToSynchronize = new List<ulong>();
-
-        /// <summary>
-        /// When a new client is connected, they are added to the
-        /// m_ClientsToSynchronize list.
-        /// </summary>
-        internal void SynchronizeClient(ulong clientId)
-        {
-            m_ClientsToSynchronize.Add(clientId);
-        }
-
         /// <summary>
         /// A pending outgoing Animation update for (n) clients
         /// </summary>
@@ -157,13 +138,6 @@ namespace Unity.Netcode.Components
             m_SendTriggerUpdates.Add(new TriggerUpdate() { AnimationTriggerMessage = animationTriggerMessage, SendToServer = true });
         }
 
-        private Queue<NetworkAnimator.AnimationMessage> m_AnimationMessageQueue = new Queue<NetworkAnimator.AnimationMessage>();
-
-        internal void AddAnimationMessageToProcessQueue(NetworkAnimator.AnimationMessage message)
-        {
-            m_AnimationMessageQueue.Enqueue(message);
-        }
-
         internal void DeregisterUpdate()
         {
             NetworkUpdateLoop.UnregisterNetworkUpdate(this, NetworkUpdateStage.PreUpdate);
@@ -226,31 +200,12 @@ namespace Unity.Netcode.Components
             }
         }
 
-        /// <summary>
-        /// Creates the TransitionStateInfoList table
-        /// </summary>
-        private void BuildTransitionStateInfoList()
-        {
 #if UNITY_EDITOR
-            if (UnityEditor.EditorApplication.isUpdating)
+        private void ParseStateMachineStates(int layerIndex, ref AnimatorController animatorController, ref AnimatorStateMachine stateMachine)
         {
-                return;
+            for (int y = 0; y < stateMachine.states.Length; y++)
-            }
-            TransitionStateInfoList = new List<TransitionStateinfo>();
-            var animatorController = m_Animator.runtimeAnimatorController as AnimatorController;
-            if (animatorController == null)
             {
-                return;
+                var animatorState = stateMachine.states[y].state;
-            }
-
-            for (int x = 0; x < animatorController.layers.Length; x++)
-            {
-                var layer = animatorController.layers[x];
-
-                for (int y = 0; y < layer.stateMachine.states.Length; y++)
-                {
-                    var animatorState = layer.stateMachine.states[y].state;
-                    var transitions = layer.stateMachine.GetStateMachineTransitions(layer.stateMachine);
                 for (int z = 0; z < animatorState.transitions.Length; z++)
                 {
                     var transition = animatorState.transitions[z];
@@ -263,19 +218,32 @@ namespace Unity.Netcode.Components
                     foreach (var condition in transition.conditions)
                     {
                         var parameterName = condition.parameter;
+
                         var parameters = animatorController.parameters;
+                        // Find the associated parameter for the condition
                         foreach (var parameter in parameters)
                         {
+                            // Only process the associated parameter(s)
+                            if (parameter.name != parameterName)
+                            {
+                                continue;
+                            }
+
                             switch (parameter.type)
                             {
                                 case AnimatorControllerParameterType.Trigger:
                                     {
-                                            // Match the condition with an existing trigger
+
-                                            if (parameterName == parameter.name)
+                                        if (transition.destinationStateMachine != null)
+                                        {
+                                            var destinationStateMachine = transition.destinationStateMachine;
+                                            ParseStateMachineStates(layerIndex, ref animatorController, ref destinationStateMachine);
+                                        }
+                                        else if (transition.destinationState != null)
                                         {
                                             var transitionInfo = new TransitionStateinfo()
                                             {
-                                                    Layer = x,
+                                                Layer = layerIndex,
                                                 OriginatingState = animatorState.nameHash,
                                                 DestinationState = transition.destinationState.nameHash,
                                                 TransitionDuration = transition.duration,
@@ -284,6 +252,11 @@ namespace Unity.Netcode.Components
                                             };
                                             TransitionStateInfoList.Add(transitionInfo);
                                         }
+                                        else
+                                        {
+                                            Debug.LogError($"[{name}][Conditional Transition for {animatorState.name}] Conditional triggered transition has neither a DestinationState nor a DestinationStateMachine! This transition is not likely to synchronize properly. " +
+                                                $"Please file a GitHub issue about this error with details about your Animator's setup.");
+                                        }
                                         break;
                                     }
                                 default:
@@ -295,6 +268,30 @@ namespace Unity.Netcode.Components
             }
         }
 #endif
+
+        /// <summary>
+        /// Creates the TransitionStateInfoList table
+        /// </summary>
+        private void BuildTransitionStateInfoList()
+        {
+#if UNITY_EDITOR
+            if (UnityEditor.EditorApplication.isUpdating || UnityEditor.EditorApplication.isPlayingOrWillChangePlaymode)
+            {
+                return;
+            }
+            TransitionStateInfoList = new List<TransitionStateinfo>();
+            var animatorController = m_Animator.runtimeAnimatorController as AnimatorController;
+            if (animatorController == null)
+            {
+                return;
+            }
+
+            for (int x = 0; x < animatorController.layers.Length; x++)
+            {
+                var stateMachine = animatorController.layers[x].stateMachine;
+                ParseStateMachineStates(x, ref animatorController, ref stateMachine);
+            }
+#endif
         }
 
         public void OnAfterDeserialize()
@@ -488,8 +485,17 @@ namespace Unity.Netcode.Components
         private int[] m_AnimationHash;
         private float[] m_LayerWeights;
         private static byte[] s_EmptyArray = new byte[] { };
+        private List<int> m_ParametersToUpdate;
+        private List<ulong> m_ClientSendList;
+        private ClientRpcParams m_ClientRpcParams;
+        private AnimationMessage m_AnimationMessage;
         private NetworkAnimatorStateChangeHandler m_NetworkAnimatorStateChangeHandler;
 
+        /// <summary>
+        /// Used for integration test purposes
+        /// </summary>
+        internal List<AnimatorStateInfo> SynchronizationStateInfo;
+
         private unsafe struct AnimatorParamCache
         {
             internal int Hash;
@@ -519,75 +525,44 @@ namespace Unity.Netcode.Components
             }
         }
 
-        private void Cleanup()
+        /// <summary>
+        /// Only things instantiated/created within OnNetworkSpawn should be
+        /// cleaned up here.
+        /// </summary>
+        private void SpawnCleanup()
         {
             if (m_NetworkAnimatorStateChangeHandler != null)
             {
                 m_NetworkAnimatorStateChangeHandler.DeregisterUpdate();
                 m_NetworkAnimatorStateChangeHandler = null;
             }
-
-            if (m_CachedNetworkManager != null)
-            {
-                m_CachedNetworkManager.OnClientConnectedCallback -= OnClientConnectedCallback;
         }
 
+        public override void OnDestroy()
+        {
+            SpawnCleanup();
+
             if (m_CachedAnimatorParameters != null && m_CachedAnimatorParameters.IsCreated)
             {
                 m_CachedAnimatorParameters.Dispose();
             }
+
             if (m_ParameterWriter.IsInitialized)
             {
                 m_ParameterWriter.Dispose();
             }
-        }
-
-        public override void OnDestroy()
-        {
-            Cleanup();
             base.OnDestroy();
         }
 
-        private List<int> m_ParametersToUpdate;
+        private void Awake()
-        private List<ulong> m_ClientSendList;
-        private ClientRpcParams m_ClientRpcParams;
-        private AnimationMessage m_AnimationMessage;
-
-        /// <summary>
-        /// Used for integration test to validate that the
-        /// AnimationMessage.AnimationStates remains the same
-        /// size as the layer count.
-        /// </summary>
-        internal AnimationMessage GetAnimationMessage()
-        {
-            return m_AnimationMessage;
-        }
-
-        // Only used in Cleanup
-        private NetworkManager m_CachedNetworkManager;
-
-        /// <inheritdoc/>
-        public override void OnNetworkSpawn()
         {
             int layers = m_Animator.layerCount;
-
             // Initializing the below arrays for everyone handles an issue
             // when running in owner authoritative mode and the owner changes.
             m_TransitionHash = new int[layers];
             m_AnimationHash = new int[layers];
             m_LayerWeights = new float[layers];
 
-            if (IsServer)
-            {
-                m_ClientSendList = new List<ulong>(128);
-                m_ClientRpcParams = new ClientRpcParams();
-                m_ClientRpcParams.Send = new ClientRpcSendParams();
-                m_ClientRpcParams.Send.TargetClientIds = m_ClientSendList;
-
-                // Cache the NetworkManager instance to remove the OnClientConnectedCallback subscription
-                m_CachedNetworkManager = NetworkManager;
-                NetworkManager.OnClientConnectedCallback += OnClientConnectedCallback;
-            }
             // We initialize the m_AnimationMessage for all instances in the event that
             // ownership or authority changes during runtime.
             m_AnimationMessage = new AnimationMessage();
@@ -612,6 +587,7 @@ namespace Unity.Netcode.Components
             var parameters = m_Animator.parameters;
             m_CachedAnimatorParameters = new NativeArray<AnimatorParamCache>(parameters.Length, Allocator.Persistent);
             m_ParametersToUpdate = new List<int>(parameters.Length);
+
             for (var i = 0; i < parameters.Length; i++)
             {
                 var parameter = parameters[i];
@@ -652,39 +628,75 @@ namespace Unity.Netcode.Components
 
                 m_CachedAnimatorParameters[i] = cacheParam;
             }
+        }
+
+        /// <summary>
+        /// Used for integration test to validate that the
+        /// AnimationMessage.AnimationStates remains the same
+        /// size as the layer count.
+        /// </summary>
+        internal AnimationMessage GetAnimationMessage()
+        {
+            return m_AnimationMessage;
+        }
+
+        /// <inheritdoc/>
+        public override void OnNetworkSpawn()
+        {
+            if (IsServer)
+            {
+                m_ClientSendList = new List<ulong>(128);
+                m_ClientRpcParams = new ClientRpcParams();
+                m_ClientRpcParams.Send = new ClientRpcSendParams();
+                m_ClientRpcParams.Send.TargetClientIds = m_ClientSendList;
+            }
+
+            // Create a handler for state changes
             m_NetworkAnimatorStateChangeHandler = new NetworkAnimatorStateChangeHandler(this);
         }
 
         /// <inheritdoc/>
         public override void OnNetworkDespawn()
         {
-            Cleanup();
+            SpawnCleanup();
         }
 
         /// <summary>
-        /// Synchronizes newly joined players
+        /// Wries all parameter and state information needed to initially synchronize a client
         /// </summary>
-        internal void ServerSynchronizeNewPlayer(ulong playerId)
+        private void WriteSynchronizationData<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
         {
-            m_ClientSendList.Clear();
+            // Parameter synchronization
-            m_ClientSendList.Add(playerId);
+            {
-            m_ClientRpcParams.Send.TargetClientIds = m_ClientSendList;
+                // We include all parameters for the initial synchronization
-            // With synchronization we send all parameters
                 m_ParametersToUpdate.Clear();
                 for (int i = 0; i < m_CachedAnimatorParameters.Length; i++)
                 {
                     m_ParametersToUpdate.Add(i);
                 }
-            SendParametersUpdate(m_ClientRpcParams);
+                // Write, apply, and serialize
+                WriteParameters(ref m_ParameterWriter);
+                var parametersMessage = new ParametersUpdateMessage
+                {
+                    Parameters = m_ParameterWriter.ToArray()
+                };
+                serializer.SerializeValue(ref parametersMessage);
+            }
 
+            // Animation state synchronization
+            {
                 // Reset the dirty count before synchronizing the newly connected client with all layers
                 m_AnimationMessage.IsDirtyCount = 0;
 
                 for (int layer = 0; layer < m_Animator.layerCount; layer++)
                 {
-                AnimatorStateInfo st = m_Animator.GetCurrentAnimatorStateInfo(layer);
+                    var synchronizationStateInfo = m_Animator.GetCurrentAnimatorStateInfo(layer);
-                var stateHash = st.fullPathHash;
+                    if (SynchronizationStateInfo != null)
-                var normalizedTime = st.normalizedTime;
+                    {
+                        SynchronizationStateInfo.Add(synchronizationStateInfo);
+                    }
+                    var stateHash = synchronizationStateInfo.fullPathHash;
+                    var normalizedTime = synchronizationStateInfo.normalizedTime;
                     var isInTransition = m_Animator.IsInTransition(layer);
 
                     // Grab one of the available AnimationState entries so we can fill it with the current
@@ -739,23 +751,40 @@ namespace Unity.Netcode.Components
                 }
                 // Send all animation states
                 m_AnimationMessage.IsDirtyCount = m_Animator.layerCount;
-            SendAnimStateClientRpc(m_AnimationMessage, m_ClientRpcParams);
+                m_AnimationMessage.NetworkSerialize(serializer);
+            }
         }
 
         /// <summary>
-        /// Required for the server to synchronize newly joining players
+        /// Used to synchronize newly joined clients
         /// </summary>
-        private void OnClientConnectedCallback(ulong playerId)
+        protected override void OnSynchronize<T>(ref BufferSerializer<T> serializer)
         {
-            m_NetworkAnimatorStateChangeHandler.SynchronizeClient(playerId);
+            if (serializer.IsWriter)
+            {
+                WriteSynchronizationData(ref serializer);
+            }
+            else
+            {
+                var parameters = new ParametersUpdateMessage();
+                var animationStates = new AnimationMessage();
+                serializer.SerializeValue(ref parameters);
+                UpdateParameters(ref parameters);
+                serializer.SerializeValue(ref animationStates);
+                HandleAnimStateUpdate(ref animationStates);
+            }
         }
 
         /// <summary>
         /// Checks for changes in both Animator parameters and state.
         /// </summary>
+        /// <remarks>
+        /// This is only invoked by clients that are the owner when not in server authoritative mode
+        /// or by the server itself when in server authoritative mode.
+        /// </remarks>
         internal void CheckForAnimatorChanges()
         {
-            if (!IsOwner && !IsServerAuthoritative() || IsServerAuthoritative() && !IsServer)
+            if (!IsSpawned || (!IsOwner && !IsServerAuthoritative()) || (IsServerAuthoritative() && !IsServer))
             {
                 return;
             }
@@ -817,6 +846,11 @@ namespace Unity.Netcode.Components
                 }
                 else
                 {
+                    // Just notify all remote clients and not the local server
+                    m_ClientSendList.Clear();
+                    m_ClientSendList.AddRange(NetworkManager.ConnectedClientsIds);
+                    m_ClientSendList.Remove(NetworkManager.LocalClientId);
+                    m_ClientRpcParams.Send.TargetClientIds = m_ClientSendList;
                     SendAnimStateClientRpc(m_AnimationMessage);
                 }
             }
@@ -824,10 +858,7 @@ namespace Unity.Netcode.Components
 
         private void SendParametersUpdate(ClientRpcParams clientRpcParams = default, bool sendDirect = false)
         {
-            m_ParameterWriter.Seek(0);
+            WriteParameters(ref m_ParameterWriter);
-            m_ParameterWriter.Truncate();
-
-            WriteParameters(m_ParameterWriter, sendDirect);
 
             var parametersMessage = new ParametersUpdateMessage
             {
@@ -961,8 +992,10 @@ namespace Unity.Netcode.Components
         /// This uses the m_ParametersToUpdate list to write out only
         /// the parameters that have changed
         /// </summary>
-        private unsafe void WriteParameters(FastBufferWriter writer, bool sendCacheState)
+        private unsafe void WriteParameters(ref FastBufferWriter writer)
         {
+            writer.Seek(0);
+            writer.Truncate();
             // Write how many parameter entries we are going to write
             BytePacker.WriteValuePacked(writer, (uint)m_ParametersToUpdate.Count);
             foreach (var parameterIndex in m_ParametersToUpdate)
@@ -1049,7 +1082,7 @@ namespace Unity.Netcode.Components
         /// <summary>
         /// Applies the ParametersUpdateMessage state to the Animator
         /// </summary>
-        internal unsafe void UpdateParameters(ParametersUpdateMessage parametersUpdate)
+        internal unsafe void UpdateParameters(ref ParametersUpdateMessage parametersUpdate)
         {
             if (parametersUpdate.Parameters != null && parametersUpdate.Parameters.Length != 0)
             {
@@ -1067,6 +1100,16 @@ namespace Unity.Netcode.Components
         /// </summary>
         internal void UpdateAnimationState(AnimationState animationState)
         {
+            // Handle updating layer weights first.
+            if (animationState.Layer < m_LayerWeights.Length)
+            {
+                if (m_LayerWeights[animationState.Layer] != animationState.Weight)
+                {
+                    m_Animator.SetLayerWeight(animationState.Layer, animationState.Weight);
+                }
+            }
+
+            // If there is no state transition then return
             if (animationState.StateHash == 0)
             {
                 return;
@@ -1114,7 +1157,6 @@ namespace Unity.Netcode.Components
                     m_Animator.Play(animationState.StateHash, animationState.Layer, animationState.NormalizedTime);
                 }
             }
-            m_Animator.SetLayerWeight(animationState.Layer, animationState.Weight);
         }
 
         /// <summary>
@@ -1134,7 +1176,7 @@ namespace Unity.Netcode.Components
                 {
                     return;
                 }
-                UpdateParameters(parametersUpdate);
+                UpdateParameters(ref parametersUpdate);
                 if (NetworkManager.ConnectedClientsIds.Count > (IsHost ? 2 : 1))
                 {
                     m_ClientSendList.Clear();
@@ -1183,7 +1225,6 @@ namespace Unity.Netcode.Components
                     UpdateAnimationState(animationState);
                 }
 
-                m_NetworkAnimatorStateChangeHandler.AddAnimationMessageToProcessQueue(animationMessage);
                 if (NetworkManager.ConnectedClientsIds.Count > (IsHost ? 2 : 1))
                 {
                     m_ClientSendList.Clear();
@@ -1196,6 +1237,18 @@ namespace Unity.Netcode.Components
             }
         }
 
+        internal void HandleAnimStateUpdate(ref AnimationMessage animationMessage)
+        {
+            var isServerAuthoritative = IsServerAuthoritative();
+            if (!isServerAuthoritative && !IsOwner || isServerAuthoritative)
+            {
+                foreach (var animationState in animationMessage.AnimationStates)
+                {
+                    UpdateAnimationState(animationState);
+                }
+            }
+        }
+
         /// <summary>
         /// Internally-called RPC client receiving function to update some animation state on a client
         /// </summary>
@@ -1211,15 +1264,7 @@ namespace Unity.Netcode.Components
                 }
                 return;
             }
-
+            HandleAnimStateUpdate(ref animationMessage);
-            var isServerAuthoritative = IsServerAuthoritative();
-            if (!isServerAuthoritative && !IsOwner || isServerAuthoritative)
-            {
-                foreach (var animationState in animationMessage.AnimationStates)
-                {
-                    UpdateAnimationState(animationState);
-                }
-            }
         }
 
         /// <summary>
@@ -1319,7 +1364,7 @@ namespace Unity.Netcode.Components
                     m_NetworkAnimatorStateChangeHandler.QueueTriggerUpdateToClient(animTriggerMessage);
                     if (!IsHost)
                     {
-                        InternalSetTrigger(hash);
+                        InternalSetTrigger(hash, setTrigger);
                     }
                 }
                 else
@@ -1328,7 +1373,7 @@ namespace Unity.Netcode.Components
                     m_NetworkAnimatorStateChangeHandler.QueueTriggerUpdateToServer(animTriggerMessage);
                     if (!IsServerAuthoritative())
                     {
-                        InternalSetTrigger(hash);
+                        InternalSetTrigger(hash, setTrigger);
                     }
                 }
             }

Components/NetworkTransform.cs

@@ -451,6 +451,33 @@ namespace Unity.Netcode.Components
             return m_LastSentState;
         }
 
+        /// <summary>
+        /// This is invoked when a new client joins (server and client sides)
+        /// Server Side: Serializes as if we were teleporting (everything is sent via NetworkTransformState)
+        /// Client Side: Adds the interpolated state which applies the NetworkTransformState as well
+        /// </summary>
+        protected override void OnSynchronize<T>(ref BufferSerializer<T> serializer)
+        {
+            // We don't need to synchronize NetworkTransforms that are on the same
+            // GameObject as the NetworkObject.
+            if (NetworkObject.gameObject == gameObject)
+            {
+                return;
+            }
+            var synchronizationState = new NetworkTransformState();
+            if (serializer.IsWriter)
+            {
+                synchronizationState.IsTeleportingNextFrame = true;
+                ApplyTransformToNetworkStateWithInfo(ref synchronizationState, m_CachedNetworkManager.LocalTime.Time, transform);
+                synchronizationState.NetworkSerialize(serializer);
+            }
+            else
+            {
+                synchronizationState.NetworkSerialize(serializer);
+                AddInterpolatedState(synchronizationState);
+            }
+        }
+
         /// <summary>
         /// This will try to send/commit the current transform delta states (if any)
         /// </summary>
@@ -1065,10 +1092,9 @@ namespace Unity.Netcode.Components
         /// <param name="posIn"></param> new position to move to.  Can be null
         /// <param name="rotIn"></param> new rotation to rotate to.  Can be null
         /// <param name="scaleIn">new scale to scale to. Can be null</param>
-        /// <param name="shouldGhostsInterpolate">Should other clients interpolate this change or not. True by default</param>
+        /// <param name="teleportDisabled">When true (the default) the <see cref="NetworkObject"/> will not be teleported and, if enabled, will interpolate. When false the <see cref="NetworkObject"/> will teleport/apply the parameters provided immediately.</param>
-        /// new scale to scale to.  Can be null
         /// <exception cref="Exception"></exception>
-        public void SetState(Vector3? posIn = null, Quaternion? rotIn = null, Vector3? scaleIn = null, bool shouldGhostsInterpolate = true)
+        public void SetState(Vector3? posIn = null, Quaternion? rotIn = null, Vector3? scaleIn = null, bool teleportDisabled = true)
         {
             if (!IsSpawned)
             {
@@ -1092,16 +1118,16 @@ namespace Unity.Netcode.Components
                 {
                     m_ClientIds[0] = OwnerClientId;
                     m_ClientRpcParams.Send.TargetClientIds = m_ClientIds;
-                    SetStateClientRpc(pos, rot, scale, !shouldGhostsInterpolate, m_ClientRpcParams);
+                    SetStateClientRpc(pos, rot, scale, !teleportDisabled, m_ClientRpcParams);
                 }
                 else // Preserving the ability for server authoritative mode to accept state changes from owner
                 {
-                    SetStateServerRpc(pos, rot, scale, !shouldGhostsInterpolate);
+                    SetStateServerRpc(pos, rot, scale, !teleportDisabled);
                 }
                 return;
             }
 
-            SetStateInternal(pos, rot, scale, !shouldGhostsInterpolate);
+            SetStateInternal(pos, rot, scale, !teleportDisabled);
         }
 
         /// <summary>

Editor/AssemblyInfo.cs

@@ -1,3 +1,7 @@
 using System.Runtime.CompilerServices;
 
+#if UNITY_INCLUDE_TESTS
+#if UNITY_EDITOR
 [assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+#endif // UNITY_EDITOR
+#endif // UNITY_INCLUDE_TESTS

Editor/CodeGen/INetworkMessageILPP.cs

@@ -102,15 +102,19 @@ namespace Unity.Netcode.Editor.CodeGen
         private PostProcessorAssemblyResolver m_AssemblyResolver;
 
         private MethodReference m_MessagingSystem_ReceiveMessage_MethodRef;
+        private MethodReference m_MessagingSystem_CreateMessageAndGetVersion_MethodRef;
         private TypeReference m_MessagingSystem_MessageWithHandler_TypeRef;
         private MethodReference m_MessagingSystem_MessageHandler_Constructor_TypeRef;
+        private MethodReference m_MessagingSystem_VersionGetter_Constructor_TypeRef;
         private FieldReference m_ILPPMessageProvider___network_message_types_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_MessageType_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_Handler_FieldRef;
+        private FieldReference m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef;
         private MethodReference m_Type_GetTypeFromHandle_MethodRef;
         private MethodReference m_List_Add_MethodRef;
 
         private const string k_ReceiveMessageName = nameof(MessagingSystem.ReceiveMessage);
+        private const string k_CreateMessageAndGetVersionName = nameof(MessagingSystem.CreateMessageAndGetVersion);
 
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
@@ -126,6 +130,7 @@ namespace Unity.Netcode.Editor.CodeGen
             TypeDefinition listTypeDef = moduleDefinition.ImportReference(typeof(List<>)).Resolve();
 
             TypeDefinition messageHandlerTypeDef = null;
+            TypeDefinition versionGetterTypeDef = null;
             TypeDefinition messageWithHandlerTypeDef = null;
             TypeDefinition ilppMessageProviderTypeDef = null;
             TypeDefinition messagingSystemTypeDef = null;
@@ -137,6 +142,12 @@ namespace Unity.Netcode.Editor.CodeGen
                     continue;
                 }
 
+                if (versionGetterTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.VersionGetter))
+                {
+                    versionGetterTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
                 if (messageWithHandlerTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.MessageWithHandler))
                 {
                     messageWithHandlerTypeDef = netcodeTypeDef;
@@ -157,6 +168,7 @@ namespace Unity.Netcode.Editor.CodeGen
             }
 
             m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(messageHandlerTypeDef.GetConstructors().First());
+            m_MessagingSystem_VersionGetter_Constructor_TypeRef = moduleDefinition.ImportReference(versionGetterTypeDef.GetConstructors().First());
 
             m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerTypeDef);
             foreach (var fieldDef in messageWithHandlerTypeDef.Fields)
@@ -169,6 +181,9 @@ namespace Unity.Netcode.Editor.CodeGen
                     case nameof(MessagingSystem.MessageWithHandler.Handler):
                         m_MessagingSystem_MessageWithHandler_Handler_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
+                    case nameof(MessagingSystem.MessageWithHandler.GetVersion):
+                        m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef = moduleDefinition.ImportReference(fieldDef);
+                        break;
                 }
             }
 
@@ -211,6 +226,9 @@ namespace Unity.Netcode.Editor.CodeGen
                     case k_ReceiveMessageName:
                         m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
+                    case k_CreateMessageAndGetVersionName:
+                        m_MessagingSystem_CreateMessageAndGetVersion_MethodRef = moduleDefinition.ImportReference(methodDef);
+                        break;
                 }
             }
 
@@ -236,7 +254,7 @@ namespace Unity.Netcode.Editor.CodeGen
             return staticCtorMethodDef;
         }
 
-        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod)
+        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod, MethodReference versionMethod)
         {
             // MessagingSystem.__network_message_types.Add(new MessagingSystem.MessageWithHandler{MessageType=typeof(type), Handler=type.Receive});
             processor.Body.Variables.Add(new VariableDefinition(m_MessagingSystem_MessageWithHandler_TypeRef));
@@ -252,7 +270,7 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Call, m_Type_GetTypeFromHandle_MethodRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_MessageType_FieldRef));
 
-            // tmp.Handler = type.Receive
+            // tmp.Handler = MessageHandler.ReceveMessage<type>
             instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Ldnull));
 
@@ -260,6 +278,15 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_MessageHandler_Constructor_TypeRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_Handler_FieldRef));
 
+
+            // tmp.GetVersion = MessageHandler.CreateMessageAndGetVersion<type>
+            instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
+            instructions.Add(processor.Create(OpCodes.Ldnull));
+
+            instructions.Add(processor.Create(OpCodes.Ldftn, versionMethod));
+            instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_VersionGetter_Constructor_TypeRef));
+            instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef));
+
             // ILPPMessageProvider.__network_message_types.Add(tmp);
             instructions.Add(processor.Create(OpCodes.Ldloc, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Callvirt, m_List_Add_MethodRef));
@@ -285,7 +312,9 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         var receiveMethod = new GenericInstanceMethod(m_MessagingSystem_ReceiveMessage_MethodRef);
                         receiveMethod.GenericArguments.Add(type);
-                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod);
+                        var versionMethod = new GenericInstanceMethod(m_MessagingSystem_CreateMessageAndGetVersion_MethodRef);
+                        versionMethod.GenericArguments.Add(type);
+                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod, versionMethod);
                     }
 
                     instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));

Editor/CodeGen/NetworkBehaviourILPP.cs

@@ -139,6 +139,19 @@ namespace Unity.Netcode.Editor.CodeGen
             return false;
         }
 
+        private bool IsSpecialCaseType(TypeReference type)
+        {
+            foreach (var supportedType in SpecialCaseTypes)
+            {
+                if (type.FullName == supportedType.FullName)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
         private void CreateNetworkVariableTypeInitializers(AssemblyDefinition assembly)
         {
             foreach (var typeDefinition in assembly.MainModule.Types)
@@ -153,6 +166,11 @@ namespace Unity.Netcode.Editor.CodeGen
 
                     foreach (var type in m_WrappedNetworkVariableTypes)
                     {
+                        if (IsSpecialCaseType(type))
+                        {
+                            continue;
+                        }
+
                         // If a serializable type isn't found, FallbackSerializer will be used automatically, which will
                         // call into UserNetworkVariableSerialization, giving the user a chance to define their own serializaiton
                         // for types that aren't in our official supported types list.
@@ -257,6 +275,20 @@ namespace Unity.Netcode.Editor.CodeGen
         private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef;
         private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef;
 
+        private MethodReference m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
+
         private TypeReference m_FastBufferWriter_TypeRef;
         private readonly Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
         private readonly List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
@@ -276,12 +308,13 @@ namespace Unity.Netcode.Editor.CodeGen
             typeof(decimal),
             typeof(double),
             typeof(float),
-            typeof(int),
+            // the following types have special handling
+            /*typeof(int),
             typeof(uint),
             typeof(long),
             typeof(ulong),
             typeof(short),
-            typeof(ushort),
+            typeof(ushort),*/
             typeof(Vector2),
             typeof(Vector3),
             typeof(Vector2Int),
@@ -293,6 +326,16 @@ namespace Unity.Netcode.Editor.CodeGen
             typeof(Ray),
             typeof(Ray2D)
         };
+        internal static readonly Type[] SpecialCaseTypes = new[]
+        {
+            // the following types have special handling
+            typeof(int),
+            typeof(uint),
+            typeof(long),
+            typeof(ulong),
+            typeof(short),
+            typeof(ushort),
+        };
 
         private const string k_Debug_LogError = nameof(Debug.LogError);
         private const string k_NetworkManager_LocalClientId = nameof(NetworkManager.LocalClientId);
@@ -343,6 +386,8 @@ namespace Unity.Netcode.Editor.CodeGen
             TypeDefinition fastBufferWriterTypeDef = null;
             TypeDefinition fastBufferReaderTypeDef = null;
             TypeDefinition networkVariableSerializationTypesTypeDef = null;
+            TypeDefinition bytePackerTypeDef = null;
+            TypeDefinition byteUnpackerTypeDef = null;
             foreach (var netcodeTypeDef in m_NetcodeModule.GetAllTypes())
             {
                 if (networkManagerTypeDef == null && netcodeTypeDef.Name == nameof(NetworkManager))
@@ -398,6 +443,18 @@ namespace Unity.Netcode.Editor.CodeGen
                     networkVariableSerializationTypesTypeDef = netcodeTypeDef;
                     continue;
                 }
+
+                if (bytePackerTypeDef == null && netcodeTypeDef.Name == nameof(BytePacker))
+                {
+                    bytePackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (byteUnpackerTypeDef == null && netcodeTypeDef.Name == nameof(ByteUnpacker))
+                {
+                    byteUnpackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
             }
 
             foreach (var methodDef in debugTypeDef.Methods)
@@ -652,6 +709,82 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
+            foreach (var method in bytePackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(BytePacker.WriteValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
+            foreach (var method in byteUnpackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(ByteUnpacker.ReadValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
             return true;
         }
 
@@ -1008,6 +1141,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetWriteMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
             var foundMethodRef = m_FastBufferWriter_WriteValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);
 
@@ -1154,6 +1317,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetReadMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
 
             var foundMethodRef = m_FastBufferReader_ReadValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);

Editor/Configuration.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: b2f70916f7024c66aa5dfe1e43c151a2
+timeCreated: 1654274400

Editor/Configuration/NetcodeForGameObjectsSettings.cs

@@ -0,0 +1,53 @@
+using UnityEditor;
+using UnityEngine;
+
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal class NetcodeForGameObjectsEditorSettings
+    {
+        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
+        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
+
+        internal static int GetNetcodeInstallMultiplayerToolTips()
+        {
+            if (EditorPrefs.HasKey(InstallMultiplayerToolsTipDismissedPlayerPrefKey))
+            {
+                return EditorPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey);
+            }
+
+            return 0;
+        }
+
+        internal static void SetNetcodeInstallMultiplayerToolTips(int toolTipPrefSetting)
+        {
+            EditorPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, toolTipPrefSetting);
+        }
+
+        internal static bool GetAutoAddNetworkObjectSetting()
+        {
+            if (EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists))
+            {
+                return EditorPrefs.GetBool(AutoAddNetworkObjectIfNoneExists);
+            }
+
+            return false;
+        }
+
+        internal static void SetAutoAddNetworkObjectSetting(bool autoAddSetting)
+        {
+            EditorPrefs.SetBool(AutoAddNetworkObjectIfNoneExists, autoAddSetting);
+        }
+    }
+
+    [FilePath("ProjectSettings/NetcodeForGameObjects.settings", FilePathAttribute.Location.ProjectFolder)]
+    internal class NetcodeForGameObjectsProjectSettings : ScriptableSingleton<NetcodeForGameObjectsProjectSettings>
+    {
+        [SerializeField] public bool GenerateDefaultNetworkPrefabs = true;
+
+        internal void SaveSettings()
+        {
+            Save(true);
+        }
+    }
+}

Editor/Configuration/NetcodeForGameObjectsSettings.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: 3ada9e8fd5bf94b1f9a6a21531c8a3ee
+guid: 2f9c9b10bc41a0e46ab71324dd0ac6e1
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/Configuration/NetcodeSettingsProvider.cs

@@ -0,0 +1,179 @@
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal static class NetcodeSettingsProvider
+    {
+        private const float k_MaxLabelWidth = 450f;
+        private static float s_MaxLabelWidth;
+        private static bool s_ShowEditorSettingFields = true;
+        private static bool s_ShowProjectSettingFields = true;
+
+        [SettingsProvider]
+        public static SettingsProvider CreateNetcodeSettingsProvider()
+        {
+            // First parameter is the path in the Settings window.
+            // Second parameter is the scope of this setting: it only appears in the Settings window for the Project scope.
+            var provider = new SettingsProvider("Project/NetcodeForGameObjects", SettingsScope.Project)
+            {
+                label = "Netcode for GameObjects",
+                keywords = new[] { "netcode", "editor" },
+                guiHandler = OnGuiHandler,
+            };
+
+            return provider;
+        }
+
+
+        internal static NetcodeSettingsLabel NetworkObjectsSectionLabel;
+        internal static NetcodeSettingsToggle AutoAddNetworkObjectToggle;
+        internal static NetcodeSettingsLabel MultiplayerToolsLabel;
+        internal static NetcodeSettingsToggle MultiplayerToolTipStatusToggle;
+
+        /// <summary>
+        /// Creates an instance of the settings UI Elements if they don't already exist.
+        /// </summary>
+        /// <remarks>
+        /// We have to construct any NetcodeGUISettings derived classes here because in
+        /// version 2020.x.x EditorStyles.label does not exist yet (higher versions it does)
+        /// </remarks>
+        private static void CheckForInitialize()
+        {
+            if (NetworkObjectsSectionLabel == null)
+            {
+                NetworkObjectsSectionLabel = new NetcodeSettingsLabel("NetworkObject Helper Settings", 20);
+            }
+
+            if (AutoAddNetworkObjectToggle == null)
+            {
+                AutoAddNetworkObjectToggle = new NetcodeSettingsToggle("Auto-Add NetworkObject Component", "When enabled, NetworkObject components are automatically added to GameObjects when NetworkBehaviour components are added first.", 20);
+            }
+
+            if (MultiplayerToolsLabel == null)
+            {
+                MultiplayerToolsLabel = new NetcodeSettingsLabel("Multiplayer Tools", 20);
+            }
+
+            if (MultiplayerToolTipStatusToggle == null)
+            {
+                MultiplayerToolTipStatusToggle = new NetcodeSettingsToggle("Multiplayer Tools Install Reminder", "When enabled, the NetworkManager will display the notification to install the multiplayer tools package.", 20);
+            }
+        }
+
+        private static void OnGuiHandler(string obj)
+        {
+            // Make sure all NetcodeGUISettings derived classes are instantiated first
+            CheckForInitialize();
+
+            var autoAddNetworkObjectSetting = NetcodeForGameObjectsEditorSettings.GetAutoAddNetworkObjectSetting();
+            var multiplayerToolsTipStatus = NetcodeForGameObjectsEditorSettings.GetNetcodeInstallMultiplayerToolTips() == 0;
+            var settings = NetcodeForGameObjectsProjectSettings.instance;
+            var generateDefaultPrefabs = settings.GenerateDefaultNetworkPrefabs;
+
+            EditorGUI.BeginChangeCheck();
+
+            GUILayout.BeginVertical("Box");
+            s_ShowEditorSettingFields = EditorGUILayout.BeginFoldoutHeaderGroup(s_ShowEditorSettingFields, "Editor Settings");
+
+            if (s_ShowEditorSettingFields)
+            {
+                GUILayout.BeginVertical("Box");
+                NetworkObjectsSectionLabel.DrawLabel();
+                autoAddNetworkObjectSetting = AutoAddNetworkObjectToggle.DrawToggle(autoAddNetworkObjectSetting);
+                GUILayout.EndVertical();
+
+                GUILayout.BeginVertical("Box");
+                MultiplayerToolsLabel.DrawLabel();
+                multiplayerToolsTipStatus = MultiplayerToolTipStatusToggle.DrawToggle(multiplayerToolsTipStatus);
+                GUILayout.EndVertical();
+            }
+            EditorGUILayout.EndFoldoutHeaderGroup();
+            GUILayout.EndVertical();
+
+            GUILayout.BeginVertical("Box");
+            s_ShowProjectSettingFields = EditorGUILayout.BeginFoldoutHeaderGroup(s_ShowProjectSettingFields, "Project Settings");
+            if (s_ShowProjectSettingFields)
+            {
+                GUILayout.BeginVertical("Box");
+                const string generateNetworkPrefabsString = "Generate Default Network Prefabs List";
+
+                if (s_MaxLabelWidth == 0)
+                {
+                    s_MaxLabelWidth = EditorStyles.label.CalcSize(new GUIContent(generateNetworkPrefabsString)).x;
+                    s_MaxLabelWidth = Mathf.Min(k_MaxLabelWidth, s_MaxLabelWidth);
+                }
+
+                EditorGUIUtility.labelWidth = s_MaxLabelWidth;
+
+                GUILayout.Label("Network Prefabs", EditorStyles.boldLabel);
+                generateDefaultPrefabs = EditorGUILayout.Toggle(
+                    new GUIContent(
+                        generateNetworkPrefabsString,
+                        "When enabled, a default NetworkPrefabsList object will be added to your project and kept up " +
+                        "to date with all NetworkObject prefabs."),
+                    generateDefaultPrefabs,
+                    GUILayout.Width(s_MaxLabelWidth + 20));
+                GUILayout.EndVertical();
+            }
+            EditorGUILayout.EndFoldoutHeaderGroup();
+            GUILayout.EndVertical();
+            if (EditorGUI.EndChangeCheck())
+            {
+                NetcodeForGameObjectsEditorSettings.SetAutoAddNetworkObjectSetting(autoAddNetworkObjectSetting);
+                NetcodeForGameObjectsEditorSettings.SetNetcodeInstallMultiplayerToolTips(multiplayerToolsTipStatus ? 0 : 1);
+                settings.GenerateDefaultNetworkPrefabs = generateDefaultPrefabs;
+                settings.SaveSettings();
+            }
+        }
+    }
+
+    internal class NetcodeSettingsLabel : NetcodeGUISettings
+    {
+        private string m_LabelContent;
+
+        public void DrawLabel()
+        {
+            EditorGUIUtility.labelWidth = m_LabelSize;
+            GUILayout.Label(m_LabelContent, EditorStyles.boldLabel, m_LayoutWidth);
+        }
+
+        public NetcodeSettingsLabel(string labelText, float layoutOffset = 0.0f)
+        {
+            m_LabelContent = labelText;
+            AdjustLabelSize(labelText, layoutOffset);
+        }
+    }
+
+    internal class NetcodeSettingsToggle : NetcodeGUISettings
+    {
+        private GUIContent m_ToggleContent;
+
+        public bool DrawToggle(bool currentSetting)
+        {
+            EditorGUIUtility.labelWidth = m_LabelSize;
+            return EditorGUILayout.Toggle(m_ToggleContent, currentSetting, m_LayoutWidth);
+        }
+
+        public NetcodeSettingsToggle(string labelText, string toolTip, float layoutOffset)
+        {
+            AdjustLabelSize(labelText, layoutOffset);
+            m_ToggleContent = new GUIContent(labelText, toolTip);
+        }
+    }
+
+    internal class NetcodeGUISettings
+    {
+        private const float k_MaxLabelWidth = 450f;
+        protected float m_LabelSize { get; private set; }
+
+        protected GUILayoutOption m_LayoutWidth { get; private set; }
+
+        protected void AdjustLabelSize(string labelText, float offset = 0.0f)
+        {
+            m_LabelSize = Mathf.Min(k_MaxLabelWidth, EditorStyles.label.CalcSize(new GUIContent(labelText)).x);
+            m_LayoutWidth = GUILayout.Width(m_LabelSize + offset);
+        }
+    }
+
+}

Editor/Configuration/NetcodeSettingsProvider.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 6b373a89fcbd41444a97ebd1798b326f
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/Configuration/NetworkPrefabProcessor.cs

@@ -0,0 +1,187 @@
+using System.Collections.Generic;
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    /// <summary>
+    /// Updates the default <see cref="NetworkPrefabsList"/> instance when prefabs are updated (created, moved, deleted) in the project.
+    /// </summary>
+    public class NetworkPrefabProcessor : AssetPostprocessor
+    {
+        private static string s_DefaultNetworkPrefabsPath = "Assets/DefaultNetworkPrefabs.asset";
+        public static string DefaultNetworkPrefabsPath
+        {
+            get
+            {
+                return s_DefaultNetworkPrefabsPath;
+            }
+            internal set
+            {
+                s_DefaultNetworkPrefabsPath = value;
+                // Force a recache of the prefab list
+                s_PrefabsList = null;
+            }
+        }
+        private static NetworkPrefabsList s_PrefabsList;
+        private static Dictionary<string, NetworkPrefab> s_PrefabsListPath = new Dictionary<string, NetworkPrefab>();
+
+        private static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths)
+        {
+            var settings = NetcodeForGameObjectsProjectSettings.instance;
+            if (!settings.GenerateDefaultNetworkPrefabs)
+            {
+                return;
+            }
+
+            bool ProcessImportedAssets(string[] importedAssets1)
+            {
+                var dirty = false;
+                foreach (var assetPath in importedAssets1)
+                {
+                    // We only care about GameObjects, skip everything else. Can't use the more targeted
+                    // OnPostProcessPrefabs since that's not called for moves or deletes
+                    if (AssetDatabase.GetMainAssetTypeAtPath(assetPath) != typeof(GameObject))
+                    {
+                        continue;
+                    }
+
+                    var go = AssetDatabase.LoadAssetAtPath<GameObject>(assetPath);
+                    if (go.TryGetComponent<NetworkObject>(out _))
+                    {
+                        // Make sure we are not duplicating an already existing entry
+                        if (s_PrefabsListPath.ContainsKey(assetPath))
+                        {
+                            // Is the imported asset different from the one we already have in the list?
+                            if (s_PrefabsListPath[assetPath].Prefab.GetHashCode() != go.GetHashCode())
+                            {
+                                // If so remove the one in the list and continue on to add the imported one
+                                s_PrefabsList.List.Remove(s_PrefabsListPath[assetPath]);
+                            }
+                            else // If they are identical, then just ignore the import
+                            {
+                                continue;
+                            }
+                        }
+
+                        s_PrefabsList.List.Add(new NetworkPrefab { Prefab = go });
+                        dirty = true;
+                    }
+                }
+
+                return dirty;
+            }
+
+            bool ProcessDeletedAssets(string[] strings)
+            {
+                var dirty = false;
+                var deleted = new List<string>(strings);
+                for (int i = s_PrefabsList.List.Count - 1; i >= 0 && deleted.Count > 0; --i)
+                {
+                    GameObject prefab;
+                    try
+                    {
+                        prefab = s_PrefabsList.List[i].Prefab;
+                    }
+                    catch (MissingReferenceException)
+                    {
+                        s_PrefabsList.List.RemoveAt(i);
+                        continue;
+                    }
+                    if (prefab == null)
+                    {
+                        s_PrefabsList.List.RemoveAt(i);
+                    }
+                    else
+                    {
+                        string noPath = AssetDatabase.GetAssetPath(prefab);
+                        for (int j = strings.Length - 1; j >= 0; --j)
+                        {
+                            if (noPath == strings[j])
+                            {
+                                s_PrefabsList.List.RemoveAt(i);
+                                deleted.RemoveAt(j);
+                                dirty = true;
+                            }
+                        }
+                    }
+                }
+
+                return dirty;
+            }
+
+            if (s_PrefabsList == null)
+            {
+                s_PrefabsList = GetOrCreateNetworkPrefabs(DefaultNetworkPrefabsPath, out var newList, true);
+                // A new list already processed all existing assets, no need to double-process imports & deletes
+                if (newList)
+                {
+                    return;
+                }
+            }
+            // Clear our asset path to prefab table each time
+            s_PrefabsListPath.Clear();
+
+            // Create our asst path to prefab table
+            foreach (var prefabEntry in s_PrefabsList.List)
+            {
+                if (!s_PrefabsListPath.ContainsKey(AssetDatabase.GetAssetPath(prefabEntry.Prefab)))
+                {
+                    s_PrefabsListPath.Add(AssetDatabase.GetAssetPath(prefabEntry.Prefab), prefabEntry);
+                }
+            }
+
+            // Process the imported and deleted assets
+            var markDirty = ProcessImportedAssets(importedAssets);
+            markDirty &= ProcessDeletedAssets(deletedAssets);
+
+            if (markDirty)
+            {
+                EditorUtility.SetDirty(s_PrefabsList);
+            }
+        }
+
+        internal static NetworkPrefabsList GetOrCreateNetworkPrefabs(string path, out bool isNew, bool addAll)
+        {
+            var defaultPrefabs = AssetDatabase.LoadAssetAtPath<NetworkPrefabsList>(path);
+            if (defaultPrefabs == null)
+            {
+                isNew = true;
+                defaultPrefabs = ScriptableObject.CreateInstance<NetworkPrefabsList>();
+                defaultPrefabs.IsDefault = true;
+                AssetDatabase.CreateAsset(defaultPrefabs, path);
+
+                if (addAll)
+                {
+                    // This could be very expensive in large projects... maybe make it manually triggered via a menu?
+                    defaultPrefabs.List = FindAll();
+                }
+                EditorUtility.SetDirty(defaultPrefabs);
+                AssetDatabase.SaveAssetIfDirty(defaultPrefabs);
+                return defaultPrefabs;
+            }
+
+            isNew = false;
+            return defaultPrefabs;
+        }
+
+        private static List<NetworkPrefab> FindAll()
+        {
+            var list = new List<NetworkPrefab>();
+
+            string[] guids = AssetDatabase.FindAssets("t:GameObject");
+            foreach (var guid in guids)
+            {
+                string assetPath = AssetDatabase.GUIDToAssetPath(guid);
+                var go = AssetDatabase.LoadAssetAtPath<GameObject>(assetPath);
+
+                if (go.TryGetComponent(out NetworkObject _))
+                {
+                    list.Add(new NetworkPrefab { Prefab = go });
+                }
+            }
+
+            return list;
+        }
+    }
+}

Editor/Configuration/NetworkPrefabProcessor.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d8b62a05d80cc444f9c74731c01b8e39
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/Configuration/NetworkPrefabsEditor.cs

@@ -0,0 +1,97 @@
+using UnityEditor;
+using UnityEditorInternal;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor
+{
+    [CustomEditor(typeof(NetworkPrefabsList), true)]
+    [CanEditMultipleObjects]
+    public class NetworkPrefabsEditor : UnityEditor.Editor
+    {
+        private ReorderableList m_NetworkPrefabsList;
+        private SerializedProperty m_IsDefaultBool;
+
+        private void OnEnable()
+        {
+            m_IsDefaultBool = serializedObject.FindProperty(nameof(NetworkPrefabsList.IsDefault));
+            m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty("List"), true, true, true, true);
+            m_NetworkPrefabsList.elementHeightCallback = index =>
+            {
+                var networkOverrideInt = 0;
+                if (m_NetworkPrefabsList.count > 0)
+                {
+                    var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
+                    var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
+                    networkOverrideInt = networkOverrideProp.enumValueIndex;
+                }
+
+                return 8 + (networkOverrideInt == 0 ? EditorGUIUtility.singleLineHeight : (EditorGUIUtility.singleLineHeight * 2) + 5);
+            };
+            m_NetworkPrefabsList.drawElementCallback = (rect, index, isActive, isFocused) =>
+            {
+                rect.y += 5;
+
+                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
+                var networkPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Prefab));
+                var networkSourceHashProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourceHashToOverride));
+                var networkSourcePrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourcePrefabToOverride));
+                var networkTargetPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.OverridingTargetPrefab));
+                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
+                var networkOverrideInt = networkOverrideProp.enumValueIndex;
+                var networkOverrideEnum = (NetworkPrefabOverride)networkOverrideInt;
+                EditorGUI.LabelField(new Rect(rect.x + rect.width - 70, rect.y, 60, EditorGUIUtility.singleLineHeight), "Override");
+                if (networkOverrideEnum == NetworkPrefabOverride.None)
+                {
+                    if (EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), false))
+                    {
+                        networkOverrideProp.enumValueIndex = (int)NetworkPrefabOverride.Prefab;
+                    }
+                }
+                else
+                {
+                    if (!EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), true))
+                    {
+                        networkOverrideProp.enumValueIndex = 0;
+                        networkOverrideEnum = NetworkPrefabOverride.None;
+                    }
+                }
+
+                if (networkOverrideEnum == NetworkPrefabOverride.None)
+                {
+                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width - 80, EditorGUIUtility.singleLineHeight), networkPrefabProp, GUIContent.none);
+                }
+                else
+                {
+                    networkOverrideProp.enumValueIndex = GUI.Toolbar(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), networkOverrideInt - 1, new[] { "Prefab", "Hash" }) + 1;
+
+                    if (networkOverrideEnum == NetworkPrefabOverride.Prefab)
+                    {
+                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourcePrefabProp, GUIContent.none);
+                    }
+                    else
+                    {
+                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourceHashProp, GUIContent.none);
+                    }
+
+                    rect.y += EditorGUIUtility.singleLineHeight + 5;
+
+                    EditorGUI.LabelField(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), "Overriding Prefab");
+                    EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 110, EditorGUIUtility.singleLineHeight), networkTargetPrefabProp, GUIContent.none);
+                }
+            };
+            m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
+        }
+
+        public override void OnInspectorGUI()
+        {
+            using (new EditorGUI.DisabledScope(true))
+            {
+                EditorGUILayout.PropertyField(m_IsDefaultBool);
+            }
+
+            m_NetworkPrefabsList.DoLayoutList();
+
+            serializedObject.ApplyModifiedProperties();
+        }
+    }
+}

Editor/Configuration/NetworkPrefabsEditor.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 8d6d0919fa8ff41c9b1d1241256f7364
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/HiddenScriptEditor.cs

@@ -4,6 +4,7 @@ using Unity.Netcode.Transports.UNET;
 #endif
 using Unity.Netcode.Transports.UTP;
 using UnityEditor;
+using UnityEngine;
 
 namespace Unity.Netcode.Editor
 {
@@ -43,7 +44,109 @@ namespace Unity.Netcode.Editor
     [CustomEditor(typeof(UnityTransport), true)]
     public class UnityTransportEditor : HiddenScriptEditor
     {
+        private static readonly string[] k_HiddenFields = { "m_Script", "ConnectionData" };
 
+        private bool m_AllowIncomingConnections;
+        private bool m_Initialized;
+
+        private UnityTransport m_UnityTransport;
+
+        private SerializedProperty m_ServerAddressProperty;
+        private SerializedProperty m_ServerPortProperty;
+        private SerializedProperty m_OverrideBindIpProperty;
+
+        private const string k_LoopbackIpv4 = "127.0.0.1";
+        private const string k_LoopbackIpv6 = "::1";
+        private const string k_AnyIpv4 = "0.0.0.0";
+        private const string k_AnyIpv6 = "::";
+
+
+        private void Initialize()
+        {
+            if (m_Initialized)
+            {
+                return;
+            }
+            m_Initialized = true;
+            m_UnityTransport = (UnityTransport)target;
+
+            var connectionDataProperty = serializedObject.FindProperty(nameof(UnityTransport.ConnectionData));
+
+            m_ServerAddressProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Address));
+            m_ServerPortProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Port));
+            m_OverrideBindIpProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.ServerListenAddress));
+        }
+
+        /// <summary>
+        /// Draws inspector properties without the script field.
+        /// </summary>
+        public override void OnInspectorGUI()
+        {
+            Initialize();
+            EditorGUI.BeginChangeCheck();
+            serializedObject.UpdateIfRequiredOrScript();
+            DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+            serializedObject.ApplyModifiedProperties();
+            EditorGUI.EndChangeCheck();
+
+            EditorGUILayout.PropertyField(m_ServerAddressProperty);
+            EditorGUILayout.PropertyField(m_ServerPortProperty);
+
+            serializedObject.ApplyModifiedProperties();
+
+            EditorGUILayout.HelpBox("It's recommended to leave remote connections disabled for local testing to avoid exposing ports on your device.", MessageType.Info);
+            bool allowRemoteConnections = m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6 && !string.IsNullOrEmpty(m_UnityTransport.ConnectionData.ServerListenAddress);
+            allowRemoteConnections = EditorGUILayout.Toggle(new GUIContent("Allow Remote Connections?", $"Bind IP: {m_UnityTransport.ConnectionData.ServerListenAddress}"), allowRemoteConnections);
+
+            bool isIpV6 = m_UnityTransport.ConnectionData.IsIpv6;
+
+            if (!allowRemoteConnections)
+            {
+                if (m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6)
+                {
+                    if (isIpV6)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv6;
+                    }
+                    else
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv4;
+                    }
+                    EditorUtility.SetDirty(m_UnityTransport);
+                }
+            }
+
+            using (new EditorGUI.DisabledScope(!allowRemoteConnections))
+            {
+                string overrideIp = m_UnityTransport.ConnectionData.ServerListenAddress;
+                if (overrideIp == k_AnyIpv4 || overrideIp == k_AnyIpv6 || overrideIp == k_LoopbackIpv4 || overrideIp == k_LoopbackIpv6)
+                {
+                    overrideIp = "";
+                }
+
+                overrideIp = EditorGUILayout.TextField("Override Bind IP (optional)", overrideIp);
+                if (allowRemoteConnections)
+                {
+                    if (overrideIp == "")
+                    {
+                        if (isIpV6)
+                        {
+                            overrideIp = k_AnyIpv6;
+                        }
+                        else
+                        {
+                            overrideIp = k_AnyIpv4;
+                        }
+                    }
+
+                    if (m_UnityTransport.ConnectionData.ServerListenAddress != overrideIp)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = overrideIp;
+                        EditorUtility.SetDirty(m_UnityTransport);
+                    }
+                }
+            }
+        }
     }
 
 #if COM_UNITY_MODULES_ANIMATION

Editor/NetworkBehaviourEditor.cs

@@ -3,9 +3,13 @@ using System.Collections.Generic;
 using System.Reflection;
 using UnityEngine;
 using UnityEditor;
+using Unity.Netcode.Editor.Configuration;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// The <see cref="CustomEditor"/> for <see cref="NetworkBehaviour"/>
+    /// </summary>
     [CustomEditor(typeof(NetworkBehaviour), true)]
     [CanEditMultipleObjects]
     public class NetworkBehaviourEditor : UnityEditor.Editor
@@ -16,6 +20,7 @@ namespace Unity.Netcode.Editor
         private readonly Dictionary<string, object> m_NetworkVariableObjects = new Dictionary<string, object>();
 
         private GUIContent m_NetworkVariableLabelGuiContent;
+        private GUIContent m_NetworkListLabelGuiContent;
 
         private void Init(MonoScript script)
         {
@@ -26,6 +31,7 @@ namespace Unity.Netcode.Editor
             m_NetworkVariableObjects.Clear();
 
             m_NetworkVariableLabelGuiContent = new GUIContent("NetworkVariable", "This variable is a NetworkVariable. It can not be serialized and can only be changed during runtime.");
+            m_NetworkListLabelGuiContent = new GUIContent("NetworkList", "This variable is a NetworkList. It is rendered, but you can't serialize or change it.");
 
             var fields = script.GetClass().GetFields(BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy);
             for (int i = 0; i < fields.Length; i++)
@@ -33,8 +39,15 @@ namespace Unity.Netcode.Editor
                 var ft = fields[i].FieldType;
                 if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkVariable<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
                 {
-                    m_NetworkVariableNames.Add(fields[i].Name);
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
-                    m_NetworkVariableFields.Add(fields[i].Name, fields[i]);
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkVariable {fields[i].Name}");
+                }
+                if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkList<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
+                {
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkList {fields[i].Name}");
                 }
             }
         }
@@ -68,25 +81,48 @@ namespace Unity.Netcode.Editor
             EditorGUILayout.BeginHorizontal();
             if (genericType.IsValueType)
             {
-                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkVariableValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
+                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkContainerValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
                 var genericMethod = method.MakeGenericMethod(genericType);
                 genericMethod.Invoke(this, new[] { (object)index });
             }
             else
             {
                 EditorGUILayout.LabelField("Type not renderable");
-            }
 
                 GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
                 EditorGUILayout.EndHorizontal();
             }
+        }
 
-        private void RenderNetworkVariableValueType<T>(int index) where T : unmanaged
+        private void RenderNetworkContainerValueType<T>(int index) where T : unmanaged, IEquatable<T>
+        {
+            try
             {
                 var networkVariable = (NetworkVariable<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                RenderNetworkVariableValueType(index, networkVariable);
+            }
+            catch (Exception)
+            {
+                try
+                {
+                    var networkList = (NetworkList<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                    RenderNetworkListValueType(index, networkList);
+                }
+                catch (Exception e)
+                {
+                    Debug.Log(e);
+                    throw;
+                }
+            }
+
+            EditorGUILayout.EndHorizontal();
+        }
+
+        private void RenderNetworkVariableValueType<T>(int index, NetworkVariable<T> networkVariable) where T : unmanaged
+        {
             var type = typeof(T);
             object val = networkVariable.Value;
-            string name = m_NetworkVariableNames[index];
+            string variableName = m_NetworkVariableNames[index];
 
             var behaviour = (NetworkBehaviour)target;
 
@@ -95,47 +131,47 @@ namespace Unity.Netcode.Editor
             {
                 if (type == typeof(int))
                 {
-                    val = EditorGUILayout.IntField(name, (int)val);
+                    val = EditorGUILayout.IntField(variableName, (int)val);
                 }
                 else if (type == typeof(uint))
                 {
-                    val = (uint)EditorGUILayout.LongField(name, (long)((uint)val));
+                    val = (uint)EditorGUILayout.LongField(variableName, (long)((uint)val));
                 }
                 else if (type == typeof(short))
                 {
-                    val = (short)EditorGUILayout.IntField(name, (int)((short)val));
+                    val = (short)EditorGUILayout.IntField(variableName, (int)((short)val));
                 }
                 else if (type == typeof(ushort))
                 {
-                    val = (ushort)EditorGUILayout.IntField(name, (int)((ushort)val));
+                    val = (ushort)EditorGUILayout.IntField(variableName, (int)((ushort)val));
                 }
                 else if (type == typeof(sbyte))
                 {
-                    val = (sbyte)EditorGUILayout.IntField(name, (int)((sbyte)val));
+                    val = (sbyte)EditorGUILayout.IntField(variableName, (int)((sbyte)val));
                 }
                 else if (type == typeof(byte))
                 {
-                    val = (byte)EditorGUILayout.IntField(name, (int)((byte)val));
+                    val = (byte)EditorGUILayout.IntField(variableName, (int)((byte)val));
                 }
                 else if (type == typeof(long))
                 {
-                    val = EditorGUILayout.LongField(name, (long)val);
+                    val = EditorGUILayout.LongField(variableName, (long)val);
                 }
                 else if (type == typeof(ulong))
                 {
-                    val = (ulong)EditorGUILayout.LongField(name, (long)((ulong)val));
+                    val = (ulong)EditorGUILayout.LongField(variableName, (long)((ulong)val));
                 }
                 else if (type == typeof(bool))
                 {
-                    val = EditorGUILayout.Toggle(name, (bool)val);
+                    val = EditorGUILayout.Toggle(variableName, (bool)val);
                 }
                 else if (type == typeof(string))
                 {
-                    val = EditorGUILayout.TextField(name, (string)val);
+                    val = EditorGUILayout.TextField(variableName, (string)val);
                 }
                 else if (type.IsEnum)
                 {
-                    val = EditorGUILayout.EnumPopup(name, (Enum)val);
+                    val = EditorGUILayout.EnumPopup(variableName, (Enum)val);
                 }
                 else
                 {
@@ -146,11 +182,31 @@ namespace Unity.Netcode.Editor
             }
             else
             {
-                EditorGUILayout.LabelField(name, EditorStyles.wordWrappedLabel);
+                EditorGUILayout.LabelField(variableName, EditorStyles.wordWrappedLabel);
                 EditorGUILayout.SelectableLabel(val.ToString(), EditorStyles.wordWrappedLabel);
             }
+            GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
         }
 
+        private void RenderNetworkListValueType<T>(int index, NetworkList<T> networkList)
+            where T : unmanaged, IEquatable<T>
+        {
+            string variableName = m_NetworkVariableNames[index];
+
+            string value = "";
+            bool addComma = false;
+            foreach (var v in networkList)
+            {
+                if (addComma)
+                {
+                    value += ", ";
+                }
+                value += v.ToString();
+                addComma = true;
+            }
+            EditorGUILayout.LabelField(variableName, value);
+            GUILayout.Label(m_NetworkListLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkListLabelGuiContent).x));
+        }
 
         /// <inheritdoc/>
         public override void OnInspectorGUI()
@@ -230,8 +286,6 @@ namespace Unity.Netcode.Editor
             CheckForNetworkObject((target as NetworkBehaviour).gameObject);
         }
 
-        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
-
         /// <summary>
         /// Recursively finds the root parent of a <see cref="Transform"/>
         /// </summary>
@@ -308,7 +362,7 @@ namespace Unity.Netcode.Editor
                     // and the user has already turned "Auto-Add NetworkObject" on when first notified about the requirement
                     // then just send a reminder to the user why the NetworkObject they just deleted seemingly "re-appeared"
                     // again.
-                    if (networkObjectRemoved && EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists) && EditorPrefs.GetBool(AutoAddNetworkObjectIfNoneExists))
+                    if (networkObjectRemoved && NetcodeForGameObjectsEditorSettings.GetAutoAddNetworkObjectSetting())
                     {
                         Debug.LogWarning($"{gameObject.name} still has {nameof(NetworkBehaviour)}s and Auto-Add NetworkObjects is enabled. A NetworkObject is being added back to {gameObject.name}.");
                         Debug.Log($"To reset Auto-Add NetworkObjects: Select the Netcode->General->Reset Auto-Add NetworkObject menu item.");
@@ -317,7 +371,7 @@ namespace Unity.Netcode.Editor
                     // Notify and provide the option to add it one time, always add a NetworkObject, or do nothing and let the user manually add it
                     if (EditorUtility.DisplayDialog($"{nameof(NetworkBehaviour)}s require a {nameof(NetworkObject)}",
                     $"{gameObject.name} does not have a {nameof(NetworkObject)} component.  Would you like to add one now?", "Yes", "No (manually add it)",
-                    DialogOptOutDecisionType.ForThisMachine, AutoAddNetworkObjectIfNoneExists))
+                    DialogOptOutDecisionType.ForThisMachine, NetcodeForGameObjectsEditorSettings.AutoAddNetworkObjectIfNoneExists))
                     {
                         gameObject.AddComponent<NetworkObject>();
                         var activeScene = UnityEngine.SceneManagement.SceneManager.GetActiveScene();
@@ -327,20 +381,5 @@ namespace Unity.Netcode.Editor
                 }
             }
         }
-
-        /// <summary>
-        /// This allows users to reset the Auto-Add NetworkObject preference
-        /// so the next time they add a NetworkBehaviour to a GameObject without
-        /// a NetworkObject it will display the dialog box again and not
-        /// automatically add a NetworkObject.
-        /// </summary>
-        [MenuItem("Netcode/General/Reset Auto-Add NetworkObject", false, 1)]
-        private static void ResetMultiplayerToolsTipStatus()
-        {
-            if (EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists))
-            {
-                EditorPrefs.SetBool(AutoAddNetworkObjectIfNoneExists, false);
-            }
-        }
     }
 }

Editor/NetworkManagerEditor.cs

@@ -1,8 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using UnityEditor;
 using UnityEngine;
-using UnityEditorInternal;
+using Unity.Netcode.Editor.Configuration;
 
 namespace Unity.Netcode.Editor
 {
@@ -14,7 +15,6 @@ namespace Unity.Netcode.Editor
     [CanEditMultipleObjects]
     public class NetworkManagerEditor : UnityEditor.Editor
     {
-        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
         private static GUIStyle s_CenteredWordWrappedLabelStyle;
         private static GUIStyle s_HelpBoxStyle;
 
@@ -40,8 +40,7 @@ namespace Unity.Netcode.Editor
         private SerializedProperty m_NetworkIdRecycleDelayProperty;
         private SerializedProperty m_RpcHashSizeProperty;
         private SerializedProperty m_LoadSceneTimeOutProperty;
-
+        private SerializedProperty m_PrefabsList;
-        private ReorderableList m_NetworkPrefabsList;
 
         private NetworkManager m_NetworkManager;
         private bool m_Initialized;
@@ -106,7 +105,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-
+            m_PrefabsList = m_NetworkConfigProperty
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
 
             ReloadTransports();
         }
@@ -132,76 +133,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-        }
+            m_PrefabsList = m_NetworkConfigProperty
-
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
-        private void OnEnable()
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
-        {
-            m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig)).FindPropertyRelative(nameof(NetworkConfig.NetworkPrefabs)), true, true, true, true);
-            m_NetworkPrefabsList.elementHeightCallback = index =>
-            {
-                var networkOverrideInt = 0;
-                if (m_NetworkPrefabsList.count > 0)
-                {
-                    var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                    var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                    networkOverrideInt = networkOverrideProp.enumValueIndex;
-                }
-
-                return 8 + (networkOverrideInt == 0 ? EditorGUIUtility.singleLineHeight : (EditorGUIUtility.singleLineHeight * 2) + 5);
-            };
-            m_NetworkPrefabsList.drawElementCallback = (rect, index, isActive, isFocused) =>
-            {
-                rect.y += 5;
-
-                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                var networkPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Prefab));
-                var networkSourceHashProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourceHashToOverride));
-                var networkSourcePrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourcePrefabToOverride));
-                var networkTargetPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.OverridingTargetPrefab));
-                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                var networkOverrideInt = networkOverrideProp.enumValueIndex;
-                var networkOverrideEnum = (NetworkPrefabOverride)networkOverrideInt;
-                EditorGUI.LabelField(new Rect(rect.x + rect.width - 70, rect.y, 60, EditorGUIUtility.singleLineHeight), "Override");
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    if (EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), false))
-                    {
-                        networkOverrideProp.enumValueIndex = (int)NetworkPrefabOverride.Prefab;
-                    }
-                }
-                else
-                {
-                    if (!EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), true))
-                    {
-                        networkOverrideProp.enumValueIndex = 0;
-                        networkOverrideEnum = NetworkPrefabOverride.None;
-                    }
-                }
-
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width - 80, EditorGUIUtility.singleLineHeight), networkPrefabProp, GUIContent.none);
-                }
-                else
-                {
-                    networkOverrideProp.enumValueIndex = GUI.Toolbar(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), networkOverrideInt - 1, new[] { "Prefab", "Hash" }) + 1;
-
-                    if (networkOverrideEnum == NetworkPrefabOverride.Prefab)
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourcePrefabProp, GUIContent.none);
-                    }
-                    else
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourceHashProp, GUIContent.none);
-                    }
-
-                    rect.y += EditorGUIUtility.singleLineHeight + 5;
-
-                    EditorGUI.LabelField(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), "Overriding Prefab");
-                    EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 110, EditorGUIUtility.singleLineHeight), networkTargetPrefabProp, GUIContent.none);
-                }
-            };
-            m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
         }
 
         /// <inheritdoc/>
@@ -224,7 +158,62 @@ namespace Unity.Netcode.Editor
                 EditorGUILayout.PropertyField(m_PlayerPrefabProperty);
                 EditorGUILayout.Space();
 
-                m_NetworkPrefabsList.DoLayoutList();
+                if (m_NetworkManager.NetworkConfig.HasOldPrefabList())
+                {
+                    EditorGUILayout.HelpBox("Network Prefabs serialized in old format. Migrate to new format to edit the list.", MessageType.Info);
+                    if (GUILayout.Button(new GUIContent("Migrate Prefab List", "Converts the old format Network Prefab list to a new Scriptable Object")))
+                    {
+                        // Default directory
+                        var directory = "Assets/";
+                        var assetPath = AssetDatabase.GetAssetPath(m_NetworkManager);
+                        if (assetPath == "")
+                        {
+                            assetPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(m_NetworkManager);
+                        }
+
+                        if (assetPath != "")
+                        {
+                            directory = Path.GetDirectoryName(assetPath);
+                        }
+                        else
+                        {
+#if UNITY_2021_1_OR_NEWER
+                            var prefabStage = UnityEditor.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#else
+                            var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#endif
+                            if (prefabStage != null)
+                            {
+                                var prefabPath = prefabStage.assetPath;
+                                if (!string.IsNullOrEmpty(prefabPath))
+                                {
+                                    directory = Path.GetDirectoryName(prefabPath);
+                                }
+                            }
+                            if (m_NetworkManager.gameObject.scene != null)
+                            {
+                                var scenePath = m_NetworkManager.gameObject.scene.path;
+                                if (!string.IsNullOrEmpty(scenePath))
+                                {
+                                    directory = Path.GetDirectoryName(scenePath);
+                                }
+                            }
+                        }
+                        var networkPrefabs = m_NetworkManager.NetworkConfig.MigrateOldNetworkPrefabsToNetworkPrefabsList();
+                        string path = Path.Combine(directory, $"NetworkPrefabs-{m_NetworkManager.GetInstanceID()}.asset");
+                        Debug.Log("Saving migrated Network Prefabs List to " + path);
+                        AssetDatabase.CreateAsset(networkPrefabs, path);
+                        EditorUtility.SetDirty(m_NetworkManager);
+                    }
+                }
+                else
+                {
+                    if (m_NetworkManager.NetworkConfig.Prefabs.NetworkPrefabsLists.Count == 0)
+                    {
+                        EditorGUILayout.HelpBox("You have no prefab list selected. You will have to add your prefabs manually at runtime for netcode to work.", MessageType.Warning);
+                    }
+                    EditorGUILayout.PropertyField(m_PrefabsList);
+                }
                 EditorGUILayout.Space();
 
                 EditorGUILayout.LabelField("General", EditorStyles.boldLabel);
@@ -359,7 +348,7 @@ namespace Unity.Netcode.Editor
             const string targetUrl = "https://docs-multiplayer.unity3d.com/netcode/current/tools/install-tools";
             const string infoIconName = "console.infoicon";
 
-            if (PlayerPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 0) != 0)
+            if (NetcodeForGameObjectsEditorSettings.GetNetcodeInstallMultiplayerToolTips() != 0)
             {
                 return;
             }
@@ -405,7 +394,7 @@ namespace Unity.Netcode.Editor
                 GUILayout.FlexibleSpace();
                 if (GUILayout.Button(dismissButtonText, dismissButtonStyle, GUILayout.ExpandWidth(false)))
                 {
-                    PlayerPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 1);
+                    NetcodeForGameObjectsEditorSettings.SetNetcodeInstallMultiplayerToolTips(1);
                 }
                 EditorGUIUtility.AddCursorRect(GUILayoutUtility.GetLastRect(), MouseCursor.Link);
                 GUILayout.FlexibleSpace();

Editor/NetworkManagerHelper.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using Unity.Netcode.Editor.Configuration;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 using UnityEditor;
@@ -32,6 +33,24 @@ namespace Unity.Netcode.Editor
 
             EditorApplication.playModeStateChanged += EditorApplication_playModeStateChanged;
             EditorApplication.hierarchyChanged += EditorApplication_hierarchyChanged;
+
+            // Initialize default values for new NetworkManagers
+            //
+            // When the default prefab list is enabled, this will default
+            // new NetworkManagers to using it.
+            //
+            // This will get run when new NetworkManagers are added, and
+            // when the user presses the "reset" button on a NetworkManager
+            // in the inspector.
+            NetworkManager.OnNetworkManagerReset = manager =>
+            {
+                var settings = NetcodeForGameObjectsProjectSettings.instance;
+                if (settings.GenerateDefaultNetworkPrefabs)
+                {
+                    manager.NetworkConfig = new NetworkConfig();
+                    manager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out _, true) };
+                }
+            };
         }
 
         private static void EditorApplication_playModeStateChanged(PlayModeStateChange playModeStateChange)
@@ -65,7 +84,11 @@ namespace Unity.Netcode.Editor
             var scenesList = EditorBuildSettings.scenes.ToList();
             var activeScene = SceneManager.GetActiveScene();
             var isSceneInBuildSettings = scenesList.Count((c) => c.path == activeScene.path) == 1;
+#if UNITY_2023_1_OR_NEWER
+            var networkManager = Object.FindFirstObjectByType<NetworkManager>();
+#else
             var networkManager = Object.FindObjectOfType<NetworkManager>();
+#endif
             if (!isSceneInBuildSettings && networkManager != null)
             {
                 if (networkManager.NetworkConfig != null && networkManager.NetworkConfig.EnableSceneManagement)

Runtime/AssemblyInfo.cs

@@ -1,15 +1,25 @@
 using System.Runtime.CompilerServices;
 
 #if UNITY_EDITOR
-[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
-#endif
+#endif // UNITY_EDITOR
-[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#if MULTIPLAYER_TOOLS
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+[assembly: InternalsVisibleTo("Unity.Multiplayer.Tools.Adapters.Ngo1WithUtp2")]
+#endif // MULTIPLAYER_TOOLS
+#if COM_UNITY_NETCODE_ADAPTER_UTP
+[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+#endif // COM_UNITY_NETCODE_ADAPTER_UTP
+
+#if UNITY_INCLUDE_TESTS
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.TestHelpers.Runtime")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
-[assembly: InternalsVisibleTo("Unity.Multiplayer.Tools.Adapters.Ngo1WithUtp2")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#if MULTIPLAYER_TOOLS
+[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#endif // MULTIPLAYER_TOOLS
+#endif // UNITY_INCLUDE_TESTS

Runtime/Configuration/NetworkConfig.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using UnityEngine;
 using System.Linq;
 using Unity.Collections;
+using UnityEngine.Serialization;
 
 namespace Unity.Netcode
 {
@@ -30,20 +31,8 @@ namespace Unity.Netcode
         [Tooltip("When set, NetworkManager will automatically create and spawn the assigned player prefab. This can be overridden by adding it to the NetworkPrefabs list and selecting override.")]
         public GameObject PlayerPrefab;
 
-        /// <summary>
-        /// A list of prefabs that can be dynamically spawned.
-        /// </summary>
         [SerializeField]
-        [Tooltip("The prefabs that can be spawned across the network")]
+        public NetworkPrefabs Prefabs = new NetworkPrefabs();
-        internal List<NetworkPrefab> NetworkPrefabs = new List<NetworkPrefab>();
-
-        /// <summary>
-        /// This dictionary provides a quick way to check and see if a NetworkPrefab has a NetworkPrefab override.
-        /// Generated at runtime and OnValidate
-        /// </summary>
-        internal Dictionary<uint, NetworkPrefab> NetworkPrefabOverrideLinks = new Dictionary<uint, NetworkPrefab>();
-
-        internal Dictionary<uint, uint> OverrideToNetworkPrefab = new Dictionary<uint, uint>();
 
 
         /// <summary>
@@ -239,7 +228,7 @@ namespace Unity.Netcode
 
                 if (ForceSamePrefabs)
                 {
-                    var sortedDictionary = NetworkPrefabOverrideLinks.OrderBy(x => x.Key);
+                    var sortedDictionary = Prefabs.NetworkPrefabOverrideLinks.OrderBy(x => x.Key);
                     foreach (var sortedEntry in sortedDictionary)
 
                     {
@@ -273,6 +262,79 @@ namespace Unity.Netcode
         {
             return hash == GetConfig();
         }
+
+        internal void InitializePrefabs()
+        {
+            if (HasOldPrefabList())
+            {
+                MigrateOldNetworkPrefabsToNetworkPrefabsList();
+            }
+
+            Prefabs.Initialize();
+        }
+
+        #region Legacy Network Prefab List
+
+        [NonSerialized]
+        private bool m_DidWarnOldPrefabList = false;
+
+        private void WarnOldPrefabList()
+        {
+            if (!m_DidWarnOldPrefabList)
+            {
+                Debug.LogWarning("Using Legacy Network Prefab List. Consider Migrating.");
+                m_DidWarnOldPrefabList = true;
+            }
+        }
+
+        /// <summary>
+        /// Returns true if the old List&lt;NetworkPrefab&gt; serialized data is present.
+        /// </summary>
+        /// <remarks>
+        /// Internal use only to help migrate projects. <seealso cref="MigrateOldNetworkPrefabsToNetworkPrefabsList"/></remarks>
+        internal bool HasOldPrefabList()
+        {
+            return OldPrefabList?.Count > 0;
+        }
+
+        /// <summary>
+        /// Migrate the old format List&lt;NetworkPrefab&gt; prefab registration to the new NetworkPrefabsList ScriptableObject.
+        /// </summary>
+        /// <remarks>
+        /// OnAfterDeserialize cannot instantiate new objects (e.g. NetworkPrefabsList SO) since it executes in a thread, so we have to do it later.
+        /// Since NetworkConfig isn't a Unity.Object it doesn't get an Awake callback, so we have to do this in NetworkManager and expose this API.
+        /// </remarks>
+        internal NetworkPrefabsList MigrateOldNetworkPrefabsToNetworkPrefabsList()
+        {
+            if (OldPrefabList == null || OldPrefabList.Count == 0)
+            {
+                return null;
+            }
+
+            if (Prefabs == null)
+            {
+                throw new Exception("Prefabs field is null.");
+            }
+
+            Prefabs.NetworkPrefabsLists.Add(ScriptableObject.CreateInstance<NetworkPrefabsList>());
+
+            if (OldPrefabList?.Count > 0)
+            {
+                // Migrate legacy types/fields
+                foreach (var networkPrefab in OldPrefabList)
+                {
+                    Prefabs.NetworkPrefabsLists[Prefabs.NetworkPrefabsLists.Count - 1].Add(networkPrefab);
+                }
+            }
+
+            OldPrefabList = null;
+            return Prefabs.NetworkPrefabsLists[Prefabs.NetworkPrefabsLists.Count - 1];
+        }
+
+        [FormerlySerializedAs("NetworkPrefabs")]
+        [SerializeField]
+        internal List<NetworkPrefab> OldPrefabList;
+
+        #endregion
     }
 }
-

Runtime/Configuration/NetworkPrefab.cs

@@ -3,10 +3,23 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
-    internal enum NetworkPrefabOverride
+    /// <summary>
+    /// The method of NetworkPrefab override used to identify the source prefab
+    /// </summary>
+    public enum NetworkPrefabOverride
     {
+        /// <summary>
+        /// No oeverride is present
+        /// </summary>
         None,
+        /// <summary>
+        /// Override the prefab when the given SourcePrefabToOverride is requested
+        /// </summary>
         Prefab,
+        /// <summary>
+        /// Override the prefab when the given SourceHashToOverride is requested
+        /// Used in situations where the server assets do not exist in client builds
+        /// </summary>
         Hash
     }
 
@@ -14,10 +27,10 @@ namespace Unity.Netcode
     /// Class that represents a NetworkPrefab
     /// </summary>
     [Serializable]
-    internal class NetworkPrefab
+    public class NetworkPrefab
     {
         /// <summary>
-        /// The override setttings for this NetworkPrefab
+        /// The override settings for this NetworkPrefab
         /// </summary>
         public NetworkPrefabOverride Override;
 
@@ -41,5 +54,168 @@ namespace Unity.Netcode
         /// The prefab to replace (override) the source prefab with
         /// </summary>
         public GameObject OverridingTargetPrefab;
+
+        public bool Equals(NetworkPrefab other)
+        {
+            return Override == other.Override &&
+                   Prefab == other.Prefab &&
+                   SourcePrefabToOverride == other.SourcePrefabToOverride &&
+                   SourceHashToOverride == other.SourceHashToOverride &&
+                   OverridingTargetPrefab == other.OverridingTargetPrefab;
+        }
+
+        public uint SourcePrefabGlobalObjectIdHash
+        {
+            get
+            {
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.None:
+                        if (Prefab != null && Prefab.TryGetComponent(out NetworkObject no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Prefab field isn't set or isn't a Network Object");
+                    case NetworkPrefabOverride.Prefab:
+                        if (SourcePrefabToOverride != null && SourcePrefabToOverride.TryGetComponent(out no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Source Prefab field isn't set or isn't a Network Object");
+                    case NetworkPrefabOverride.Hash:
+                        return SourceHashToOverride;
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                }
+            }
+        }
+
+        public uint TargetPrefabGlobalObjectIdHash
+        {
+            get
+            {
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.None:
+                        return 0;
+                    case NetworkPrefabOverride.Prefab:
+                    case NetworkPrefabOverride.Hash:
+                        if (OverridingTargetPrefab != null && OverridingTargetPrefab.TryGetComponent(out NetworkObject no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Target Prefab field isn't set or isn't a Network Object");
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                }
+            }
+        }
+
+        public bool Validate(int index = -1)
+        {
+            NetworkObject networkObject;
+            if (Override == NetworkPrefabOverride.None)
+            {
+                if (Prefab == null)
+                {
+                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} cannot be null ({nameof(NetworkPrefab)} at index: {index})");
+                    return false;
+                }
+
+                networkObject = Prefab.GetComponent<NetworkObject>();
+                if (networkObject == null)
+                {
+                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                    {
+                        NetworkLog.LogWarning($"{NetworkManager.PrefabDebugHelper(this)} is missing " +
+                                              $"a {nameof(NetworkObject)} component (entry will be ignored).");
+                    }
+                    return false;
+                }
+
+                return true;
+            }
+
+            // Validate source prefab override values first
+            switch (Override)
+            {
+                case NetworkPrefabOverride.Hash:
+                    {
+                        if (SourceHashToOverride == 0)
+                        {
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(SourceHashToOverride)} is zero " +
+                                    "(entry will be ignored).");
+                            }
+                            return false;
+                        }
+
+                        break;
+                    }
+                case NetworkPrefabOverride.Prefab:
+                    {
+                        if (SourcePrefabToOverride == null)
+                        {
+                            // This is a leftover side-effect from NetworkManager's OnValidate. It's a usability
+                            // adjustment to automatically set the "Prefab" field as the source prefab when a user
+                            // swaps from the default Inspector to the override one.
+                            if (Prefab != null)
+                            {
+                                SourcePrefabToOverride = Prefab;
+                            }
+                            else if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(SourcePrefabToOverride)} is null (entry will be ignored).");
+                                return false;
+                            }
+                        }
+
+                        if (!SourcePrefabToOverride.TryGetComponent(out networkObject))
+                        {
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} ({SourcePrefabToOverride.name}) " +
+                                    $"is missing a {nameof(NetworkObject)} component (entry will be ignored).");
+                            }
+                            return false;
+                        }
+
+                        break;
+                    }
+            }
+
+            // Validate target prefab override values next
+            if (OverridingTargetPrefab == null)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                {
+                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(OverridingTargetPrefab)} is null!");
+                }
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.Hash:
+                        {
+                            Debug.LogWarning($"{nameof(NetworkPrefab)} override entry {SourceHashToOverride} will be removed and ignored.");
+                            break;
+                        }
+                    case NetworkPrefabOverride.Prefab:
+                        {
+                            Debug.LogWarning($"{nameof(NetworkPrefab)} override entry ({SourcePrefabToOverride.name}) will be removed and ignored.");
+                            break;
+                        }
+                }
+                return false;
+            }
+            return true;
+        }
+
+        public override string ToString()
+        {
+            return $"{{SourceHash: {SourceHashToOverride}, TargetHash: {TargetPrefabGlobalObjectIdHash}}}";
+        }
     }
 }

Runtime/Configuration/NetworkPrefabs.cs

@@ -0,0 +1,297 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using UnityEngine;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// A class that represents the runtime aspect of network prefabs.
+    /// This class contains processed prefabs from the NetworkPrefabsList, as
+    /// well as additional modifications (additions and removals) made at runtime.
+    /// </summary>
+    [Serializable]
+    public class NetworkPrefabs
+    {
+        /// <summary>
+        /// Edit-time scripted object containing a list of NetworkPrefabs.
+        /// </summary>
+        /// <remarks>
+        /// This field can be null if no prefabs are pre-configured.
+        /// Runtime usages of <see cref="NetworkPrefabs"/> should not depend on this edit-time field for execution.
+        /// </remarks>
+        [SerializeField]
+        public List<NetworkPrefabsList> NetworkPrefabsLists = new List<NetworkPrefabsList>();
+
+        /// <summary>
+        /// This dictionary provides a quick way to check and see if a NetworkPrefab has a NetworkPrefab override.
+        /// Generated at runtime and OnValidate
+        /// </summary>
+        [NonSerialized]
+        public Dictionary<uint, NetworkPrefab> NetworkPrefabOverrideLinks = new Dictionary<uint, NetworkPrefab>();
+
+        [NonSerialized]
+        public Dictionary<uint, uint> OverrideToNetworkPrefab = new Dictionary<uint, uint>();
+
+        public IReadOnlyList<NetworkPrefab> Prefabs => m_Prefabs;
+
+        [NonSerialized]
+        private List<NetworkPrefab> m_Prefabs = new List<NetworkPrefab>();
+
+        private void AddTriggeredByNetworkPrefabList(NetworkPrefab networkPrefab)
+        {
+            if (AddPrefabRegistration(networkPrefab))
+            {
+                m_Prefabs.Add(networkPrefab);
+            }
+        }
+
+        private void RemoveTriggeredByNetworkPrefabList(NetworkPrefab networkPrefab)
+        {
+            m_Prefabs.Remove(networkPrefab);
+        }
+
+        ~NetworkPrefabs()
+        {
+            foreach (var list in NetworkPrefabsLists)
+            {
+                list.OnAdd -= AddTriggeredByNetworkPrefabList;
+                list.OnRemove -= RemoveTriggeredByNetworkPrefabList;
+            }
+        }
+
+        /// <summary>
+        /// Processes the <see cref="NetworkPrefabsList"/> if one is present for use during runtime execution,
+        /// else processes <see cref="Prefabs"/>.
+        /// </summary>
+        public void Initialize(bool warnInvalid = true)
+        {
+            if (NetworkPrefabsLists.Count != 0 && m_Prefabs.Count > 0)
+            {
+                NetworkLog.LogWarning("Runtime Network Prefabs was not empty at initialization time. Network " +
+                    "Prefab registrations made before initialization will be replaced by NetworkPrefabsList.");
+                m_Prefabs.Clear();
+            }
+
+            foreach (var list in NetworkPrefabsLists)
+            {
+                list.OnAdd += AddTriggeredByNetworkPrefabList;
+                list.OnRemove += RemoveTriggeredByNetworkPrefabList;
+            }
+
+            NetworkPrefabOverrideLinks.Clear();
+            OverrideToNetworkPrefab.Clear();
+
+            var prefabs = NetworkPrefabsLists.Count != 0 ? new List<NetworkPrefab>() : m_Prefabs;
+
+            if (NetworkPrefabsLists.Count != 0)
+            {
+                foreach (var list in NetworkPrefabsLists)
+                {
+                    foreach (var networkPrefab in list.PrefabList)
+                    {
+                        prefabs.Add(networkPrefab);
+                    }
+                }
+            }
+
+            m_Prefabs = new List<NetworkPrefab>();
+
+            List<NetworkPrefab> removeList = null;
+            if (warnInvalid)
+            {
+                removeList = new List<NetworkPrefab>();
+            }
+
+            foreach (var networkPrefab in prefabs)
+            {
+                if (AddPrefabRegistration(networkPrefab))
+                {
+                    m_Prefabs.Add(networkPrefab);
+                }
+                else
+                {
+                    removeList?.Add(networkPrefab);
+                }
+            }
+
+            // Clear out anything that is invalid or not used
+            if (removeList?.Count > 0)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                {
+                    var sb = new StringBuilder("Removing invalid prefabs from Network Prefab registration: ");
+                    sb.Append(string.Join(", ", removeList));
+                    NetworkLog.LogWarning(sb.ToString());
+                }
+            }
+        }
+
+        /// <summary>
+        /// Add a new NetworkPrefab instance to the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public bool Add(NetworkPrefab networkPrefab)
+        {
+            if (AddPrefabRegistration(networkPrefab))
+            {
+                m_Prefabs.Add(networkPrefab);
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Remove a NetworkPrefab instance from the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public void Remove(NetworkPrefab prefab)
+        {
+            if (prefab == null)
+            {
+                throw new ArgumentNullException(nameof(prefab));
+            }
+
+            m_Prefabs.Remove(prefab);
+            OverrideToNetworkPrefab.Remove(prefab.TargetPrefabGlobalObjectIdHash);
+            NetworkPrefabOverrideLinks.Remove(prefab.SourcePrefabGlobalObjectIdHash);
+        }
+
+        /// <summary>
+        /// Remove a NetworkPrefab instance with matching <see cref="NetworkPrefab.Prefab"/> from the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public void Remove(GameObject prefab)
+        {
+            if (prefab == null)
+            {
+                throw new ArgumentNullException(nameof(prefab));
+            }
+
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Prefab == prefab)
+                {
+                    Remove(m_Prefabs[i]);
+                    return;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Check if the given GameObject is present as a prefab within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(GameObject prefab)
+        {
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Prefab == prefab)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Check if the given NetworkPrefab is present within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(NetworkPrefab prefab)
+        {
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Equals(prefab))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Configures <see cref="NetworkPrefabOverrideLinks"/> and <see cref="OverrideToNetworkPrefab"/> for the given <see cref="NetworkPrefab"/>
+        /// </summary>
+        private bool AddPrefabRegistration(NetworkPrefab networkPrefab)
+        {
+            if (networkPrefab == null)
+            {
+                return false;
+            }
+            // Safeguard validation check since this method is called from outside of NetworkConfig and we can't control what's passed in.
+            if (!networkPrefab.Validate())
+            {
+                return false;
+            }
+
+            uint source = networkPrefab.SourcePrefabGlobalObjectIdHash;
+            uint target = networkPrefab.TargetPrefabGlobalObjectIdHash;
+
+            // Make sure the prefab isn't already registered.
+            if (NetworkPrefabOverrideLinks.ContainsKey(source))
+            {
+                var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
+
+                // This should never happen, but in the case it somehow does log an error and remove the duplicate entry
+                Debug.LogError($"{nameof(NetworkPrefab)} ({networkObject.name}) has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} source entry value of: {source}!");
+                return false;
+            }
+
+            // If we don't have an override configured, registration is simple!
+            if (networkPrefab.Override == NetworkPrefabOverride.None)
+            {
+                NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                return true;
+            }
+
+            // Make sure we don't have several overrides targeting the same prefab. Apparently we don't support that... shame.
+            if (OverrideToNetworkPrefab.ContainsKey(target))
+            {
+                var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
+
+                // This can happen if a user tries to make several GlobalObjectIdHash values point to the same target
+                Debug.LogError($"{nameof(NetworkPrefab)} (\"{networkObject.name}\") has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} target entry value of: {target}!");
+                return false;
+            }
+
+            switch (networkPrefab.Override)
+            {
+                case NetworkPrefabOverride.Prefab:
+                    {
+                        NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                        OverrideToNetworkPrefab.Add(target, source);
+                    }
+                    break;
+                case NetworkPrefabOverride.Hash:
+                    {
+                        NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                        OverrideToNetworkPrefab.Add(target, source);
+                    }
+                    break;
+            }
+
+            return true;
+        }
+    }
+}

Runtime/Configuration/NetworkPrefabs.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 230fc75f5639e46dc91734aa67d56a3e
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Configuration/NetworkPrefabsList.cs

@@ -0,0 +1,95 @@
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Serialization;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// A ScriptableObject for holding a network prefabs list, which can be
+    /// shared between multiple NetworkManagers.
+    ///
+    /// When NetworkManagers hold references to this list, modifications to the
+    /// list at runtime will be picked up by all NetworkManagers that reference it.
+    /// </summary>
+    [CreateAssetMenu(fileName = "NetworkPrefabsList", menuName = "Netcode/Network Prefabs List")]
+    public class NetworkPrefabsList : ScriptableObject
+    {
+        internal delegate void OnAddDelegate(NetworkPrefab prefab);
+        internal OnAddDelegate OnAdd;
+
+        internal delegate void OnRemoveDelegate(NetworkPrefab prefab);
+        internal OnRemoveDelegate OnRemove;
+
+        [SerializeField]
+        internal bool IsDefault;
+
+        [FormerlySerializedAs("Prefabs")]
+        [SerializeField]
+        internal List<NetworkPrefab> List = new List<NetworkPrefab>();
+
+        /// <summary>
+        /// Read-only view into the prefabs list, enabling iterating and examining the list.
+        /// Actually modifying the list should be done using <see cref="Add"/>
+        /// and <see cref="Remove"/>.
+        /// </summary>
+        public IReadOnlyList<NetworkPrefab> PrefabList => List;
+
+        /// <summary>
+        /// Adds a prefab to the prefab list. Performing this here will apply the operation to all
+        /// <see cref="NetworkManager"/>s that reference this list.
+        /// </summary>
+        /// <param name="prefab"></param>
+        public void Add(NetworkPrefab prefab)
+        {
+            List.Add(prefab);
+            OnAdd?.Invoke(prefab);
+        }
+
+        /// <summary>
+        /// Removes a prefab from the prefab list. Performing this here will apply the operation to all
+        /// <see cref="NetworkManager"/>s that reference this list.
+        /// </summary>
+        /// <param name="prefab"></param>
+        public void Remove(NetworkPrefab prefab)
+        {
+            List.Remove(prefab);
+            OnRemove?.Invoke(prefab);
+        }
+
+        /// <summary>
+        /// Check if the given GameObject is present as a prefab within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(GameObject prefab)
+        {
+            for (int i = 0; i < List.Count; i++)
+            {
+                if (List[i].Prefab == prefab)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Check if the given NetworkPrefab is present within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(NetworkPrefab prefab)
+        {
+            for (int i = 0; i < List.Count; i++)
+            {
+                if (List[i].Equals(prefab))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+    }
+}

Runtime/Configuration/NetworkPrefabsList.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e651dbb3fbac04af2b8f5abf007ddc23
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Core/NetworkBehaviour.cs

@@ -21,6 +21,7 @@ namespace Unity.Netcode
             Client = 2
         }
 
+
         // NetworkBehaviourILPP will override this in derived classes to return the name of the concrete type
         internal virtual string __getTypeName() => nameof(NetworkBehaviour);
 
@@ -286,7 +287,18 @@ namespace Unity.Netcode
         /// Gets the NetworkManager that owns this NetworkBehaviour instance
         ///   See note around `NetworkObject` for how there is a chicken / egg problem when we are not initialized
         /// </summary>
-        public NetworkManager NetworkManager => NetworkObject.NetworkManager;
+        public NetworkManager NetworkManager
+        {
+            get
+            {
+                if (NetworkObject?.NetworkManager != null)
+                {
+                    return NetworkObject?.NetworkManager;
+                }
+
+                return NetworkManager.Singleton;
+            }
+        }
 
         /// <summary>
         /// If a NetworkObject is assigned, it will return whether or not this NetworkObject
@@ -302,18 +314,18 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets if we are executing as server
         /// </summary>
-        protected bool IsServer { get; private set; }
+        public bool IsServer { get; private set; }
 
         /// <summary>
         /// Gets if we are executing as client
         /// </summary>
-        protected bool IsClient { get; private set; }
+        public bool IsClient { get; private set; }
 
 
         /// <summary>
         /// Gets if we are executing as Host, I.E Server and Client
         /// </summary>
-        protected bool IsHost { get; private set; }
+        public bool IsHost { get; private set; }
 
         /// <summary>
         /// Gets Whether or not the object has a owner
@@ -335,24 +347,30 @@ namespace Unity.Netcode
                 m_NetworkObject.NetworkManager.IsServer;
         }
 
-        /// <summary>
-        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         ///  TODO: this needs an overhaul.  It's expensive, it's ja little naive in how it looks for networkObject in
         ///   its parent and worst, it creates a puzzle if you are a NetworkBehaviour wanting to see if you're live or not
         ///   (e.g. editor code).  All you want to do is find out if NetworkManager is null, but to do that you
         ///   need NetworkObject, but if you try and grab NetworkObject and NetworkManager isn't up you'll get
         ///   the warning below.  This is why IsBehaviourEditable had to be created.  Matt was going to re-do
         ///   how NetworkObject works but it was close to the release and too risky to change
-        ///
+        /// <summary>
+        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         /// </summary>
         public NetworkObject NetworkObject
         {
             get
+            {
+                try
                 {
                     if (m_NetworkObject == null)
                     {
                         m_NetworkObject = GetComponentInParent<NetworkObject>();
                     }
+                }
+                catch (Exception)
+                {
+                    return null;
+                }
 
                 // ShutdownInProgress check:
                 // This prevents an edge case scenario where the NetworkManager is shutting down but user code
@@ -552,11 +570,11 @@ namespace Unity.Netcode
             if (list == null)
             {
                 list = new List<FieldInfo>();
-                list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance));
+                list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly));
             }
             else
             {
-                list.AddRange(type.GetFields(BindingFlags.NonPublic | BindingFlags.Instance));
+                list.AddRange(type.GetFields(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly));
             }
 
             if (type.BaseType != null && type.BaseType != typeof(NetworkBehaviour))
@@ -712,7 +730,7 @@ namespace Unity.Netcode
                         var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, MessagingSystem.FRAGMENTED_MESSAGE_MAX_SIZE);
                         using (tmpWriter)
                         {
-                            message.Serialize(tmpWriter);
+                            message.Serialize(tmpWriter, message.Version);
                         }
                     }
                     else
@@ -745,6 +763,14 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
         internal void WriteNetworkVariableData(FastBufferWriter writer, ulong targetClientId)
         {
             if (NetworkVariableFields.Count == 0)
@@ -754,11 +780,17 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                bool canClientRead = NetworkVariableFields[j].CanClientRead(targetClientId);
 
-                if (canClientRead)
+                if (NetworkVariableFields[j].CanClientRead(targetClientId))
+                {
+                    if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
                         var writePos = writer.Position;
+                        // Note: This value can't be packed because we don't know how large it will be in advance
+                        // we reserve space for it, then write the data, then come back and fill in the space
+                        // to pack here, we'd have to write data to a temporary buffer and copy it in - which
+                        // isn't worth possibly saving one byte if and only if the data is less than 63 bytes long...
+                        // The way we do packing, any value > 63 in a ushort will use the full 2 bytes to represent.
                         writer.WriteValueSafe((ushort)0);
                         var startPos = writer.Position;
                         NetworkVariableFields[j].WriteField(writer);
@@ -768,13 +800,27 @@ namespace Unity.Netcode
                         writer.Seek(startPos + size);
                     }
                     else
+                    {
+                        NetworkVariableFields[j].WriteField(writer);
+                    }
+                }
+                else // Only if EnsureNetworkVariableLengthSafety, otherwise just skip
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     writer.WriteValueSafe((ushort)0);
                 }
             }
         }
 
-        internal void SetNetworkVariableData(FastBufferReader reader)
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
+        internal void SetNetworkVariableData(FastBufferReader reader, ulong clientId)
         {
             if (NetworkVariableFields.Count == 0)
             {
@@ -783,13 +829,23 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                reader.ReadValueSafe(out ushort varSize);
+                var varSize = (ushort)0;
+                var readStartPos = 0;
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
+                {
+                    reader.ReadValueSafe(out varSize);
                     if (varSize == 0)
                     {
                         continue;
                     }
+                    readStartPos = reader.Position;
+                }
+                else // If the client cannot read this field, then skip it
+                if (!NetworkVariableFields[j].CanClientRead(clientId))
+                {
+                    continue;
+                }
 
-                var readStartPos = reader.Position;
                 NetworkVariableFields[j].ReadField(reader);
 
                 if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
@@ -826,6 +882,138 @@ namespace Unity.Netcode
             return NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(networkId, out NetworkObject networkObject) ? networkObject : null;
         }
 
+        /// <summary>
+        /// Override this method if your derived NetworkBehaviour requires custom synchronization data.
+        /// Note: Use of this method is only for the initial client synchronization of NetworkBehaviours
+        /// and will increase the payload size for client synchronization and dynamically spawned
+        /// <see cref="NetworkObject"/>s.
+        /// </summary>
+        /// <remarks>
+        /// When serializing (writing) this will be invoked during the client synchronization period and
+        /// when spawning new NetworkObjects.
+        /// When deserializing (reading), this will be invoked prior to the NetworkBehaviour's associated
+        /// NetworkObject being spawned.
+        /// </remarks>
+        /// <param name="serializer">The serializer to use to read and write the data.</param>
+        /// <typeparam name="T">
+        /// Either BufferSerializerReader or BufferSerializerWriter, depending whether the serializer
+        /// is in read mode or write mode.
+        /// </typeparam>
+        protected virtual void OnSynchronize<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+
+        }
+
+        /// <summary>
+        /// Internal method that determines if a NetworkBehaviour has additional synchronization data to
+        /// be synchronized when first instantiated prior to its associated NetworkObject being spawned.
+        /// </summary>
+        /// <remarks>
+        /// This includes try-catch blocks to recover from exceptions that might occur and continue to
+        /// synchronize any remaining NetworkBehaviours.
+        /// </remarks>
+        /// <returns>true if it wrote synchronization data and false if it did not</returns>
+        internal bool Synchronize<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+            if (serializer.IsWriter)
+            {
+                // Get the writer to handle seeking and determining how many bytes were written
+                var writer = serializer.GetFastBufferWriter();
+                // Save our position before we attempt to write anything so we can seek back to it (i.e. error occurs)
+                var positionBeforeWrite = writer.Position;
+                writer.WriteValueSafe(NetworkBehaviourId);
+
+                // Save our position where we will write the final size being written so we can skip over it in the
+                // event an exception occurs when deserializing.
+                var sizePosition = writer.Position;
+                writer.WriteValueSafe((ushort)0);
+
+                // Save our position before synchronizing to determine how much was written
+                var positionBeforeSynchronize = writer.Position;
+                var threwException = false;
+                try
+                {
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    threwException = true;
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization serialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                }
+                var finalPosition = writer.Position;
+
+                // If we wrote nothing then skip writing anything for this NetworkBehaviour
+                if (finalPosition == positionBeforeSynchronize || threwException)
+                {
+                    writer.Seek(positionBeforeWrite);
+                    return false;
+                }
+                else
+                {
+                    // Write the number of bytes serialized to handle exceptions on the deserialization side
+                    var bytesWritten = finalPosition - positionBeforeSynchronize;
+                    writer.Seek(sizePosition);
+                    writer.WriteValueSafe((ushort)bytesWritten);
+                    writer.Seek(finalPosition);
+                }
+                return true;
+            }
+            else
+            {
+                var reader = serializer.GetFastBufferReader();
+                // We will always read the expected byte count
+                reader.ReadValueSafe(out ushort expectedBytesToRead);
+
+                // Save our position before we begin synchronization deserialization
+                var positionBeforeSynchronize = reader.Position;
+                var synchronizationError = false;
+                try
+                {
+                    // Invoke synchronization
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization deserialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                    synchronizationError = true;
+                }
+
+                var totalBytesRead = reader.Position - positionBeforeSynchronize;
+                if (totalBytesRead != expectedBytesToRead)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} read {totalBytesRead} bytes but was expected to read {expectedBytesToRead} bytes during synchronization deserialization! This {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                    }
+                    synchronizationError = true;
+                }
+
+                // Skip over the entry if deserialization fails
+                if (synchronizationError)
+                {
+                    var skipToPosition = positionBeforeSynchronize + expectedBytesToRead;
+                    reader.Seek(skipToPosition);
+                    return false;
+                }
+                return true;
+            }
+        }
+
+
         /// <summary>
         /// Invoked when the <see cref="GameObject"/> the <see cref="NetworkBehaviour"/> is attached to.
         /// NOTE:  If you override this, you will want to always invoke this base class version of this

Runtime/Core/NetworkBehaviourUpdater.cs

@@ -72,6 +72,23 @@ namespace Unity.Netcode
                         }
                     }
                 }
+
+                foreach (var dirtyObj in m_DirtyNetworkObjects)
+                {
+                    for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
+                    {
+                        var behaviour = dirtyObj.ChildNetworkBehaviours[k];
+                        for (int i = 0; i < behaviour.NetworkVariableFields.Count; i++)
+                        {
+                            if (behaviour.NetworkVariableFields[i].IsDirty() &&
+                                !behaviour.NetworkVariableIndexesToResetSet.Contains(i))
+                            {
+                                behaviour.NetworkVariableIndexesToResetSet.Add(i);
+                                behaviour.NetworkVariableIndexesToReset.Add(i);
+                            }
+                        }
+                    }
+                }
                 // Now, reset all the no-longer-dirty variables
                 foreach (var dirtyobj in m_DirtyNetworkObjects)
                 {

Runtime/Core/NetworkManager.cs

@@ -67,6 +67,9 @@ namespace Unity.Netcode
 
         internal Dictionary<ulong, ConnectionApprovalResponse> ClientsToApprove = new Dictionary<ulong, ConnectionApprovalResponse>();
 
+        // Stores the objects that need to be shown at end-of-frame
+        internal Dictionary<ulong, List<NetworkObject>> ObjectsToShowToClient = new Dictionary<ulong, List<NetworkObject>>();
+
         /// <summary>
         /// The <see cref="NetworkPrefabHandler"/> instance created after starting the <see cref="NetworkManager"/>
         /// </summary>
@@ -86,6 +89,12 @@ namespace Unity.Netcode
         private bool m_ShuttingDown;
         private bool m_StopProcessingMessages;
 
+        /// <summary>
+        /// When disconnected from the server, the server may send a reason. If a reason was sent, this property will
+        /// tell client code what the reason was. It should be queried after the OnClientDisconnectCallback is called
+        /// </summary>
+        public string DisconnectReason { get; internal set; }
+
         private class NetworkManagerHooks : INetworkHooks
         {
             private NetworkManager m_NetworkManager;
@@ -134,6 +143,16 @@ namespace Unity.Netcode
 
             public bool OnVerifyCanReceive(ulong senderId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
             {
+                if (m_NetworkManager.IsServer)
+                {
+                    if (messageType == typeof(ConnectionApprovedMessage))
+                    {
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                        {
+                            NetworkLog.LogError($"A {nameof(ConnectionApprovedMessage)} was received from a client on the server side. This should not happen. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Message Size: {messageContent.Length}. Message Content: {MessagingSystem.ByteArrayToString(messageContent.ToArray(), 0, messageContent.Length)}");
+                        }
+                        return false;
+                    }
                     if (m_NetworkManager.PendingClients.TryGetValue(senderId, out PendingClient client) &&
                                      (client.ConnectionState == PendingClient.State.PendingApproval || (client.ConnectionState == PendingClient.State.PendingConnection && messageType != typeof(ConnectionRequestMessage))))
                     {
@@ -145,6 +164,36 @@ namespace Unity.Netcode
                         return false;
                     }
 
+                    if (m_NetworkManager.ConnectedClients.TryGetValue(senderId, out NetworkClient connectedClient) && messageType == typeof(ConnectionRequestMessage))
+                    {
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                        {
+                            NetworkLog.LogError($"A {nameof(ConnectionRequestMessage)} was received from a client when the connection has already been established. This should not happen. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Message Size: {messageContent.Length}. Message Content: {MessagingSystem.ByteArrayToString(messageContent.ToArray(), 0, messageContent.Length)}");
+                        }
+
+                        return false;
+                    }
+                }
+                else
+                {
+                    if (messageType == typeof(ConnectionRequestMessage))
+                    {
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                        {
+                            NetworkLog.LogError($"A {nameof(ConnectionRequestMessage)} was received from the server on the client side. This should not happen. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Message Size: {messageContent.Length}. Message Content: {MessagingSystem.ByteArrayToString(messageContent.ToArray(), 0, messageContent.Length)}");
+                        }
+                        return false;
+                    }
+                    if (m_NetworkManager.IsConnectedClient && messageType == typeof(ConnectionApprovedMessage))
+                    {
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                        {
+                            NetworkLog.LogError($"A {nameof(ConnectionApprovedMessage)} was received from the server when the connection has already been established. This should not happen. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Message Size: {messageContent.Length}. Message Content: {MessagingSystem.ByteArrayToString(messageContent.ToArray(), 0, messageContent.Length)}");
+                        }
+                        return false;
+                    }
+                }
+
                 return !m_NetworkManager.m_StopProcessingMessages;
             }
 
@@ -189,14 +238,14 @@ namespace Unity.Netcode
         {
             if (gameObject.TryGetComponent<NetworkObject>(out var networkObject))
             {
-                if (NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(networkObject.GlobalObjectIdHash))
+                if (NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.ContainsKey(networkObject.GlobalObjectIdHash))
                 {
-                    switch (NetworkConfig.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].Override)
+                    switch (NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].Override)
                     {
                         case NetworkPrefabOverride.Hash:
                         case NetworkPrefabOverride.Prefab:
                             {
-                                return NetworkConfig.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].OverridingTargetPrefab;
+                                return NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[networkObject.GlobalObjectIdHash].OverridingTargetPrefab;
                             }
                     }
                 }
@@ -274,7 +323,7 @@ namespace Unity.Netcode
         /// </summary>
         public ulong LocalClientId
         {
-            get => IsServer ? NetworkConfig.NetworkTransport.ServerClientId : m_LocalClientId;
+            get => m_LocalClientId;
             internal set => m_LocalClientId = value;
         }
 
@@ -443,6 +492,12 @@ namespace Unity.Netcode
             /// If the Approval decision cannot be made immediately, the client code can set Pending to true, keep a reference to the ConnectionApprovalResponse object and write to it later. Client code must exercise care to setting all the members to the value it wants before marking Pending to false, to indicate completion. If the field is set as Pending = true, we'll monitor the object until it gets set to not pending anymore and use the parameters then.
             /// </summary>
             public bool Pending;
+
+            /// <summary>
+            /// Optional reason. If Approved is false, this reason will be sent to the client so they know why they
+            /// were not approved.
+            /// </summary>
+            public string Reason;
         }
 
         /// <summary>
@@ -496,6 +551,19 @@ namespace Unity.Netcode
 
         internal static event Action OnSingletonReady;
 
+#if UNITY_EDITOR
+        internal delegate void ResetNetworkManagerDelegate(NetworkManager manager);
+
+        internal static ResetNetworkManagerDelegate OnNetworkManagerReset;
+#endif
+
+        private void Reset()
+        {
+#if UNITY_EDITOR
+            OnNetworkManagerReset?.Invoke(this);
+#endif
+        }
+
 #if UNITY_EDITOR
         internal void OnValidate()
         {
@@ -521,24 +589,30 @@ namespace Unity.Netcode
             }
 
             // During OnValidate we will always clear out NetworkPrefabOverrideLinks and rebuild it
-            NetworkConfig.NetworkPrefabOverrideLinks.Clear();
+            NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.Clear();
 
+            var prefabs = NetworkConfig.Prefabs.Prefabs;
             // Check network prefabs and assign to dictionary for quick look up
-            for (int i = 0; i < NetworkConfig.NetworkPrefabs.Count; i++)
+            for (int i = 0; i < prefabs.Count; i++)
             {
-                var networkPrefab = NetworkConfig.NetworkPrefabs[i];
+                var networkPrefab = prefabs[i];
                 var networkPrefabGo = networkPrefab?.Prefab;
-                if (networkPrefabGo != null)
+                if (networkPrefabGo == null)
                 {
-                    if (!networkPrefabGo.TryGetComponent<NetworkObject>(out var networkObject))
+                    continue;
+                }
+
+                var networkObject = networkPrefabGo.GetComponent<NetworkObject>();
+                if (networkObject == null)
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
                         NetworkLog.LogError($"Cannot register {PrefabDebugHelper(networkPrefab)}, it does not have a {nameof(NetworkObject)} component at its root");
                     }
+
+                    continue;
                 }
-                    else
+
-                    {
                 {
                     var childNetworkObjects = new List<NetworkObject>();
                     networkPrefabGo.GetComponentsInChildren(true, childNetworkObjects);
@@ -550,46 +624,6 @@ namespace Unity.Netcode
                         }
                     }
                 }
-
-                        // Default to the standard NetworkPrefab.Prefab's NetworkObject first
-                        var globalObjectIdHash = networkObject.GlobalObjectIdHash;
-
-                        // Now check to see if it has an override
-                        switch (networkPrefab.Override)
-                        {
-                            case NetworkPrefabOverride.Prefab:
-                                {
-                                    if (NetworkConfig.NetworkPrefabs[i].SourcePrefabToOverride == null &&
-                                        NetworkConfig.NetworkPrefabs[i].Prefab != null)
-                                    {
-                                        if (networkPrefab.SourcePrefabToOverride == null)
-                                        {
-                                            networkPrefab.SourcePrefabToOverride = networkPrefabGo;
-                                        }
-
-                                        globalObjectIdHash = networkPrefab.SourcePrefabToOverride.GetComponent<NetworkObject>().GlobalObjectIdHash;
-                                    }
-
-                                    break;
-                                }
-                            case NetworkPrefabOverride.Hash:
-                                globalObjectIdHash = networkPrefab.SourceHashToOverride;
-                                break;
-                        }
-
-                        // Add to the NetworkPrefabOverrideLinks or handle a new (blank) entries
-                        if (!NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
-                        {
-                            NetworkConfig.NetworkPrefabOverrideLinks.Add(globalObjectIdHash, networkPrefab);
-                        }
-                        else
-                        {
-                            // Duplicate entries can happen when adding a new entry into a list of existing entries
-                            // Either this is user error or a new entry, either case we replace it with a new, blank, NetworkPrefab under this condition
-                            NetworkConfig.NetworkPrefabs[i] = new NetworkPrefab();
-                        }
-                    }
-                }
             }
         }
 #endif
@@ -628,22 +662,9 @@ namespace Unity.Netcode
             }
 
             var networkPrefab = new NetworkPrefab { Prefab = prefab };
-            NetworkConfig.NetworkPrefabs.Add(networkPrefab);
+            bool added = NetworkConfig.Prefabs.Add(networkPrefab);
-            if (IsListening)
+            if (IsListening && added)
             {
-                var sourcePrefabGlobalObjectIdHash = (uint)0;
-                var targetPrefabGlobalObjectIdHash = (uint)0;
-                if (!ShouldAddPrefab(networkPrefab, out sourcePrefabGlobalObjectIdHash, out targetPrefabGlobalObjectIdHash))
-                {
-                    NetworkConfig.NetworkPrefabs.Remove(networkPrefab);
-                    return;
-                }
-
-                if (!AddPrefabRegistration(networkPrefab, sourcePrefabGlobalObjectIdHash, targetPrefabGlobalObjectIdHash))
-                {
-                    NetworkConfig.NetworkPrefabs.Remove(networkPrefab);
-                    return;
-                }
                 DeferredMessageManager.ProcessTriggers(IDeferredMessageManager.TriggerType.OnAddPrefab, networkObject.GlobalObjectIdHash);
             }
         }
@@ -666,221 +687,14 @@ namespace Unity.Netcode
             }
 
             var globalObjectIdHash = prefab.GetComponent<NetworkObject>().GlobalObjectIdHash;
-            for (var i = 0; i < NetworkConfig.NetworkPrefabs.Count; ++i)
+            NetworkConfig.Prefabs.Remove(prefab);
-            {
-                if (NetworkConfig.NetworkPrefabs[i].Prefab.GetComponent<NetworkObject>().GlobalObjectIdHash == globalObjectIdHash)
-                {
-                    NetworkConfig.NetworkPrefabs.RemoveAt(i);
-                    break;
-                }
-            }
             if (PrefabHandler.ContainsHandler(globalObjectIdHash))
             {
                 PrefabHandler.RemoveHandler(globalObjectIdHash);
             }
-            if (NetworkConfig.NetworkPrefabOverrideLinks.TryGetValue(globalObjectIdHash, out var targetPrefab))
-            {
-                NetworkConfig.NetworkPrefabOverrideLinks.Remove(globalObjectIdHash);
-                var targetHash = targetPrefab.Prefab.GetComponent<NetworkObject>().GlobalObjectIdHash;
-                if (NetworkConfig.OverrideToNetworkPrefab.ContainsKey(targetHash))
-                {
-                    NetworkConfig.OverrideToNetworkPrefab.Remove(targetHash);
-                }
-            }
         }
 
-        private bool ShouldAddPrefab(NetworkPrefab networkPrefab, out uint sourcePrefabGlobalObjectIdHash, out uint targetPrefabGlobalObjectIdHash, int index = -1)
+        internal void Initialize(bool server)
-        {
-            sourcePrefabGlobalObjectIdHash = 0;
-            targetPrefabGlobalObjectIdHash = 0;
-            var networkObject = (NetworkObject)null;
-            if (networkPrefab == null || (networkPrefab.Prefab == null && networkPrefab.Override == NetworkPrefabOverride.None))
-            {
-                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                {
-                    NetworkLog.LogWarning(
-                        $"{nameof(NetworkPrefab)} cannot be null ({nameof(NetworkPrefab)} at index: {index})");
-                }
-                return false;
-            }
-            else if (networkPrefab.Override == NetworkPrefabOverride.None)
-            {
-                if (!networkPrefab.Prefab.TryGetComponent(out networkObject))
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                    {
-                        NetworkLog.LogWarning($"{PrefabDebugHelper(networkPrefab)} is missing " +
-                                              $"a {nameof(NetworkObject)} component (entry will be ignored).");
-                    }
-                    return false;
-                }
-
-                // Otherwise get the GlobalObjectIdHash value
-                sourcePrefabGlobalObjectIdHash = networkObject.GlobalObjectIdHash;
-            }
-            else // Validate Overrides
-            {
-                // Validate source prefab override values first
-                switch (networkPrefab.Override)
-                {
-                    case NetworkPrefabOverride.Hash:
-                        {
-                            if (networkPrefab.SourceHashToOverride == 0)
-                            {
-                                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                                {
-                                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(NetworkPrefab.SourceHashToOverride)} is zero " +
-                                                          "(entry will be ignored).");
-                                }
-                                return false;
-                            }
-                            sourcePrefabGlobalObjectIdHash = networkPrefab.SourceHashToOverride;
-                            break;
-                        }
-                    case NetworkPrefabOverride.Prefab:
-                        {
-                            if (networkPrefab.SourcePrefabToOverride == null)
-                            {
-                                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                                {
-                                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(NetworkPrefab.SourcePrefabToOverride)} is null (entry will be ignored).");
-                                }
-
-                                Debug.LogWarning($"{nameof(NetworkPrefab)} override entry {networkPrefab.SourceHashToOverride} will be removed and ignored.");
-                                return false;
-                            }
-                            else
-                            {
-                                if (!networkPrefab.SourcePrefabToOverride.TryGetComponent(out networkObject))
-                                {
-                                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                                    {
-                                        NetworkLog.LogWarning($"{nameof(NetworkPrefab)} ({networkPrefab.SourcePrefabToOverride.name}) " +
-                                                              $"is missing a {nameof(NetworkObject)} component (entry will be ignored).");
-                                    }
-
-                                    Debug.LogWarning($"{nameof(NetworkPrefab)} override entry (\"{networkPrefab.SourcePrefabToOverride.name}\") will be removed and ignored.");
-                                    return false;
-                                }
-
-                                sourcePrefabGlobalObjectIdHash = networkObject.GlobalObjectIdHash;
-                            }
-                            break;
-                        }
-                }
-
-                // Validate target prefab override values next
-                if (networkPrefab.OverridingTargetPrefab == null)
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
-                    {
-                        NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(NetworkPrefab.OverridingTargetPrefab)} is null!");
-                    }
-                    switch (networkPrefab.Override)
-                    {
-                        case NetworkPrefabOverride.Hash:
-                            {
-                                Debug.LogWarning($"{nameof(NetworkPrefab)} override entry {networkPrefab.SourceHashToOverride} will be removed and ignored.");
-                                break;
-                            }
-                        case NetworkPrefabOverride.Prefab:
-                            {
-                                Debug.LogWarning($"{nameof(NetworkPrefab)} override entry ({networkPrefab.SourcePrefabToOverride.name}) will be removed and ignored.");
-                                break;
-                            }
-                    }
-                    return false;
-                }
-                else
-                {
-                    targetPrefabGlobalObjectIdHash = networkPrefab.OverridingTargetPrefab.GetComponent<NetworkObject>().GlobalObjectIdHash;
-                }
-            }
-            return true;
-        }
-
-        internal bool AddPrefabRegistration(NetworkPrefab networkPrefab, uint sourcePrefabGlobalObjectIdHash, uint targetPrefabGlobalObjectIdHash)
-        {
-            // Assign the appropriate GlobalObjectIdHash to the appropriate NetworkPrefab
-            if (!NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(sourcePrefabGlobalObjectIdHash))
-            {
-                if (networkPrefab.Override == NetworkPrefabOverride.None)
-                {
-                    NetworkConfig.NetworkPrefabOverrideLinks.Add(sourcePrefabGlobalObjectIdHash, networkPrefab);
-                }
-                else
-                {
-                    if (!NetworkConfig.OverrideToNetworkPrefab.ContainsKey(targetPrefabGlobalObjectIdHash))
-                    {
-                        switch (networkPrefab.Override)
-                        {
-                            case NetworkPrefabOverride.Prefab:
-                                {
-                                    NetworkConfig.NetworkPrefabOverrideLinks.Add(sourcePrefabGlobalObjectIdHash, networkPrefab);
-                                    NetworkConfig.OverrideToNetworkPrefab.Add(targetPrefabGlobalObjectIdHash, sourcePrefabGlobalObjectIdHash);
-                                }
-                                break;
-                            case NetworkPrefabOverride.Hash:
-                                {
-                                    NetworkConfig.NetworkPrefabOverrideLinks.Add(sourcePrefabGlobalObjectIdHash, networkPrefab);
-                                    NetworkConfig.OverrideToNetworkPrefab.Add(targetPrefabGlobalObjectIdHash, sourcePrefabGlobalObjectIdHash);
-                                }
-                                break;
-                        }
-                    }
-                    else
-                    {
-                        var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
-                        // This can happen if a user tries to make several GlobalObjectIdHash values point to the same target
-                        Debug.LogError($"{nameof(NetworkPrefab)} (\"{networkObject.name}\") has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} target entry value of: {targetPrefabGlobalObjectIdHash}! Removing entry from list!");
-                        return false;
-                    }
-                }
-            }
-            else
-            {
-                var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
-                // This should never happen, but in the case it somehow does log an error and remove the duplicate entry
-                Debug.LogError($"{nameof(NetworkPrefab)} ({networkObject.name}) has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} source entry value of: {sourcePrefabGlobalObjectIdHash}! Removing entry from list!");
-                return false;
-            }
-            return true;
-        }
-
-        private void InitializePrefabs(int startIdx = 0)
-        {
-            // This is used to remove entries not needed or invalid
-            var removeEmptyPrefabs = new List<int>();
-
-            // Build the NetworkPrefabOverrideLinks dictionary
-            for (int i = startIdx; i < NetworkConfig.NetworkPrefabs.Count; i++)
-            {
-                var sourcePrefabGlobalObjectIdHash = (uint)0;
-                var targetPrefabGlobalObjectIdHash = (uint)0;
-                if (!ShouldAddPrefab(NetworkConfig.NetworkPrefabs[i], out sourcePrefabGlobalObjectIdHash, out targetPrefabGlobalObjectIdHash, i))
-                {
-                    removeEmptyPrefabs.Add(i);
-                    continue;
-                }
-
-                if (!AddPrefabRegistration(NetworkConfig.NetworkPrefabs[i], sourcePrefabGlobalObjectIdHash, targetPrefabGlobalObjectIdHash))
-                {
-                    removeEmptyPrefabs.Add(i);
-                    continue;
-                }
-            }
-
-            // Clear out anything that is invalid or not used (for invalid entries we already logged warnings to the user earlier)
-            // Iterate backwards so indices don't shift as we remove
-            for (int i = removeEmptyPrefabs.Count - 1; i >= 0; i--)
-            {
-                NetworkConfig.NetworkPrefabs.RemoveAt(removeEmptyPrefabs[i]);
-            }
-
-            removeEmptyPrefabs.Clear();
-        }
-
-        private void Initialize(bool server)
         {
             // Don't allow the user to start a network session if the NetworkManager is
             // still parented under another GameObject
@@ -889,6 +703,7 @@ namespace Unity.Netcode
                 return;
             }
 
+            DisconnectReason = string.Empty;
             IsApproved = false;
 
             ComponentFactory.SetDefaults();
@@ -969,11 +784,7 @@ namespace Unity.Netcode
 
             this.RegisterNetworkUpdate(NetworkUpdateStage.PreUpdate);
 
-            // Always clear our prefab override links before building
+            NetworkConfig.InitializePrefabs();
-            NetworkConfig.NetworkPrefabOverrideLinks.Clear();
-            NetworkConfig.OverrideToNetworkPrefab.Clear();
-
-            InitializePrefabs();
 
             // If we have a player prefab, then we need to verify it is in the list of NetworkPrefabOverrideLinks for client side spawning.
             if (NetworkConfig.PlayerPrefab != null)
@@ -981,15 +792,11 @@ namespace Unity.Netcode
                 if (NetworkConfig.PlayerPrefab.TryGetComponent<NetworkObject>(out var playerPrefabNetworkObject))
                 {
                     //In the event there is no NetworkPrefab entry (i.e. no override for default player prefab)
-                    if (!NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(playerPrefabNetworkObject
+                    if (!NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.ContainsKey(playerPrefabNetworkObject
                         .GlobalObjectIdHash))
                     {
                         //Then add a new entry for the player prefab
-                        var playerNetworkPrefab = new NetworkPrefab();
+                        AddNetworkPrefab(NetworkConfig.PlayerPrefab);
-                        playerNetworkPrefab.Prefab = NetworkConfig.PlayerPrefab;
-                        NetworkConfig.NetworkPrefabs.Insert(0, playerNetworkPrefab);
-                        NetworkConfig.NetworkPrefabOverrideLinks.Add(playerPrefabNetworkObject.GlobalObjectIdHash,
-                            playerNetworkPrefab);
                     }
                 }
                 else
@@ -1035,6 +842,7 @@ namespace Unity.Netcode
             IsServer = true;
             IsClient = false;
             IsListening = true;
+            LocalClientId = ServerClientId;
 
             try
             {
@@ -1181,6 +989,11 @@ namespace Unity.Netcode
 
             SpawnManager.ServerSpawnSceneObjectsOnStartSweep();
 
+            // This assures that any in-scene placed NetworkObject is spawned and
+            // any associated NetworkBehaviours' netcode related properties are
+            // set prior to invoking OnClientConnected.
+            InvokeOnClientConnectedCallback(LocalClientId);
+
             OnServerStarted?.Invoke();
 
             return true;
@@ -1264,6 +1077,8 @@ namespace Unity.Netcode
 
         private void Awake()
         {
+            NetworkConfig?.InitializePrefabs();
+
             UnityEngine.SceneManagement.SceneManager.sceneUnloaded += OnSceneUnloaded;
         }
 
@@ -1341,6 +1156,7 @@ namespace Unity.Netcode
         private void DisconnectRemoteClient(ulong clientId)
         {
             var transportId = ClientIdToTransportId(clientId);
+            MessagingSystem.ProcessSendQueues();
             NetworkConfig.NetworkTransport.DisconnectRemoteClient(transportId);
         }
 
@@ -1421,7 +1237,7 @@ namespace Unity.Netcode
                 }
             }
 
-            if (IsClient && IsConnectedClient)
+            if (IsClient && IsListening)
             {
                 // Client only, send disconnect to server
                 NetworkConfig.NetworkTransport.DisconnectLocalClient();
@@ -1579,6 +1395,7 @@ namespace Unity.Netcode
             } while (IsListening && networkEvent != NetworkEvent.Nothing);
 
             MessagingSystem.ProcessIncomingMessageQueue();
+            MessagingSystem.CleanupDisconnectedClients();
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             s_TransportPoll.End();
@@ -1643,6 +1460,17 @@ namespace Unity.Netcode
             // Do NetworkVariable updates
             BehaviourUpdater.NetworkBehaviourUpdate(this);
 
+            // Handle NetworkObjects to show
+            foreach (var client in ObjectsToShowToClient)
+            {
+                ulong clientId = client.Key;
+                foreach (var networkObject in client.Value)
+                {
+                    SpawnManager.SendSpawnCallForObject(clientId, networkObject);
+                }
+            }
+            ObjectsToShowToClient.Clear();
+
             int timeSyncFrequencyTicks = (int)(k_TimeSyncFrequency * NetworkConfig.TickRate);
             if (IsServer && NetworkTickSystem.ServerTime.Tick % timeSyncFrequencyTicks == 0)
             {
@@ -1660,7 +1488,23 @@ namespace Unity.Netcode
                 ShouldSendConnectionData = NetworkConfig.ConnectionApproval,
                 ConnectionData = NetworkConfig.ConnectionData
             };
+
+            message.MessageVersions = new NativeArray<MessageVersionData>(MessagingSystem.MessageHandlers.Length, Allocator.Temp);
+            for (int index = 0; index < MessagingSystem.MessageHandlers.Length; index++)
+            {
+                if (MessagingSystem.MessageTypes[index] != null)
+                {
+                    var type = MessagingSystem.MessageTypes[index];
+                    message.MessageVersions[index] = new MessageVersionData
+                    {
+                        Hash = XXHash.Hash32(type.FullName),
+                        Version = MessagingSystem.GetLocalVersion(type)
+                    };
+                }
+            }
+
             SendMessage(ref message, NetworkDelivery.ReliableSequenced, ServerClientId);
+            message.MessageVersions.Dispose();
         }
 
         private IEnumerator ApprovalTimeout(ulong clientId)
@@ -1821,7 +1665,18 @@ namespace Unity.Netcode
                         NetworkLog.LogInfo($"Disconnect Event From {clientId}");
                     }
 
+                    // Process the incoming message queue so that we get everything from the server disconnecting us
+                    // or, if we are the server, so we got everything from that client.
+                    MessagingSystem.ProcessIncomingMessageQueue();
+
+                    try
+                    {
                         OnClientDisconnectCallback?.Invoke(clientId);
+                    }
+                    catch (Exception exception)
+                    {
+                        Debug.LogException(exception);
+                    }
 
                     if (IsServer)
                     {
@@ -1987,12 +1842,31 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="clientId">The ClientId to disconnect</param>
         public void DisconnectClient(ulong clientId)
+        {
+            DisconnectClient(clientId, null);
+        }
+
+        /// <summary>
+        /// Disconnects the remote client.
+        /// </summary>
+        /// <param name="clientId">The ClientId to disconnect</param>
+        /// <param name="reason">Disconnection reason. If set, client will receive a DisconnectReasonMessage and have the
+        /// reason available in the NetworkManager.DisconnectReason property</param>
+        public void DisconnectClient(ulong clientId, string reason)
         {
             if (!IsServer)
             {
                 throw new NotServerException($"Only server can disconnect remote clients. Please use `{nameof(Shutdown)}()` instead.");
             }
 
+            if (!string.IsNullOrEmpty(reason))
+            {
+                var disconnectReason = new DisconnectReasonMessage();
+                disconnectReason.Reason = reason;
+                SendMessage(ref disconnectReason, NetworkDelivery.Reliable, clientId);
+            }
+            MessagingSystem.ProcessSendQueues();
+
             OnClientDisconnectFromServer(clientId);
             DisconnectRemoteClient(clientId);
         }
@@ -2016,7 +1890,12 @@ namespace Unity.Netcode
                             }
                             else
                             {
-                                Destroy(playerObject.gameObject);
+                                // Call despawn to assure NetworkBehaviour.OnNetworkDespawn is invoked
+                                // on the server-side (when the client side disconnected).
+                                // This prevents the issue (when just destroying the GameObject) where
+                                // any NetworkBehaviour component(s) destroyed before the NetworkObject
+                                // would not have OnNetworkDespawn invoked.
+                                SpawnManager.DespawnObject(playerObject, true);
                             }
                         }
                         else
@@ -2137,14 +2016,11 @@ namespace Unity.Netcode
                     // Generate a SceneObject for the player object to spawn
                     var sceneObject = new NetworkObject.SceneObject
                     {
-                        Header = new NetworkObject.SceneObject.HeaderData
-                        {
-                            IsPlayerObject = true,
                         OwnerClientId = ownerClientId,
+                        IsPlayerObject = true,
                         IsSceneObject = false,
                         HasTransform = true,
                         Hash = playerPrefabHash,
-                        },
                         TargetClientId = ownerClientId,
                         Transform = new NetworkObject.SceneObject.TransformData
                         {
@@ -2184,21 +2060,22 @@ namespace Unity.Netcode
                         }
                     }
 
-                    SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, ownerClientId);
+                    message.MessageVersions = new NativeArray<MessageVersionData>(MessagingSystem.MessageHandlers.Length, Allocator.Temp);
-
                     for (int index = 0; index < MessagingSystem.MessageHandlers.Length; index++)
                     {
                         if (MessagingSystem.MessageTypes[index] != null)
                         {
-                            var orderingMessage = new OrderingMessage
+                            var type = MessagingSystem.MessageTypes[index];
+                            message.MessageVersions[index] = new MessageVersionData
                             {
-                                Order = index,
+                                Hash = XXHash.Hash32(type.FullName),
-                                Hash = XXHash.Hash32(MessagingSystem.MessageTypes[index].FullName)
+                                Version = MessagingSystem.GetLocalVersion(type)
                             };
+                        }
+                    }
 
-                            SendMessage(ref orderingMessage, NetworkDelivery.ReliableFragmentedSequenced, ownerClientId);
+                    SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, ownerClientId);
-                        }
+                    message.MessageVersions.Dispose();
-                    }
 
                     // If scene management is enabled, then let NetworkSceneManager handle the initial scene and NetworkObject synchronization
                     if (!NetworkConfig.EnableSceneManagement)
@@ -2214,7 +2091,6 @@ namespace Unity.Netcode
                 {
                     LocalClient = client;
                     SpawnManager.UpdateObservedNetworkObjects(ownerClientId);
-                    InvokeOnClientConnectedCallback(ownerClientId);
                 }
 
                 if (!response.CreatePlayerObject || (response.PlayerPrefabHash == null && NetworkConfig.PlayerPrefab == null))
@@ -2227,6 +2103,15 @@ namespace Unity.Netcode
             }
             else
             {
+                if (!string.IsNullOrEmpty(response.Reason))
+                {
+                    var disconnectReason = new DisconnectReasonMessage();
+                    disconnectReason.Reason = response.Reason;
+                    SendMessage(ref disconnectReason, NetworkDelivery.Reliable, ownerClientId);
+
+                    MessagingSystem.ProcessSendQueues();
+                }
+
                 PendingClients.Remove(ownerClientId);
                 DisconnectRemoteClient(ownerClientId);
             }
@@ -2253,14 +2138,46 @@ namespace Unity.Netcode
                 {
                     ObjectInfo = ConnectedClients[clientId].PlayerObject.GetMessageSceneObject(clientPair.Key)
                 };
-                message.ObjectInfo.Header.Hash = playerPrefabHash;
+                message.ObjectInfo.Hash = playerPrefabHash;
-                message.ObjectInfo.Header.IsSceneObject = false;
+                message.ObjectInfo.IsSceneObject = false;
-                message.ObjectInfo.Header.HasParent = false;
+                message.ObjectInfo.HasParent = false;
-                message.ObjectInfo.Header.IsPlayerObject = true;
+                message.ObjectInfo.IsPlayerObject = true;
-                message.ObjectInfo.Header.OwnerClientId = clientId;
+                message.ObjectInfo.OwnerClientId = clientId;
                 var size = SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, clientPair.Key);
                 NetworkMetrics.TrackObjectSpawnSent(clientPair.Key, ConnectedClients[clientId].PlayerObject, size);
             }
         }
+
+        internal void MarkObjectForShowingTo(NetworkObject networkObject, ulong clientId)
+        {
+            if (!ObjectsToShowToClient.ContainsKey(clientId))
+            {
+                ObjectsToShowToClient.Add(clientId, new List<NetworkObject>());
+            }
+            ObjectsToShowToClient[clientId].Add(networkObject);
+        }
+
+        // returns whether any matching objects would have become visible and were returned to hidden state
+        internal bool RemoveObjectFromShowingTo(NetworkObject networkObject, ulong clientId)
+        {
+            var ret = false;
+            if (!ObjectsToShowToClient.ContainsKey(clientId))
+            {
+                return false;
+            }
+
+            // probably overkill, but deals with multiple entries
+            while (ObjectsToShowToClient[clientId].Contains(networkObject))
+            {
+                Debug.LogWarning(
+                    "Object was shown and hidden from the same client in the same Network frame. As a result, the client will _not_ receive a NetworkSpawn");
+                ObjectsToShowToClient[clientId].Remove(networkObject);
+                ret = true;
+            }
+
+            networkObject.Observers.Remove(clientId);
+
+            return ret;
+        }
     }
 }

Runtime/Core/NetworkObject.cs

@@ -265,9 +265,8 @@ namespace Unity.Netcode
                 throw new VisibilityChangeException("The object is already visible");
             }
 
+            NetworkManager.MarkObjectForShowingTo(this, clientId);
             Observers.Add(clientId);
-
-            NetworkManager.SpawnManager.SendSpawnCallForObject(clientId, this);
         }
 
 
@@ -351,16 +350,17 @@ namespace Unity.Netcode
                 throw new NotServerException("Only server can change visibility");
             }
 
-            if (!Observers.Contains(clientId))
-            {
-                throw new VisibilityChangeException("The object is already hidden");
-            }
-
             if (clientId == NetworkManager.ServerClientId)
             {
                 throw new VisibilityChangeException("Cannot hide an object from the server");
             }
 
+            if (!NetworkManager.RemoveObjectFromShowingTo(this, clientId))
+            {
+                if (!Observers.Contains(clientId))
+                {
+                    throw new VisibilityChangeException("The object is already hidden");
+                }
                 Observers.Remove(clientId);
 
                 var message = new DestroyObjectMessage
@@ -372,6 +372,7 @@ namespace Unity.Netcode
                 var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, clientId);
                 NetworkManager.NetworkMetrics.TrackObjectDestroySent(clientId, this, size);
             }
+        }
 
         /// <summary>
         /// Hides a list of <see cref="NetworkObject"/>s from the targeted client.
@@ -830,6 +831,9 @@ namespace Unity.Netcode
                 // parent and then re-parents the child under a GameObject with a NetworkObject component attached.
                 if (parentNetworkObject == null)
                 {
+                    // If we are parented under a GameObject, go ahead and mark the world position stays as false
+                    // so clients synchronize their transform in local space. (only for in-scene placed NetworkObjects)
+                    m_CachedWorldPositionStays = false;
                     return true;
                 }
                 else // If the parent still isn't spawned add this to the orphaned children and return false
@@ -841,8 +845,11 @@ namespace Unity.Netcode
                 else
                 {
                     // If we made it this far, go ahead and set the network parenting values
-                    // with the default WorldPoisitonSays value
+                    // with the WorldPoisitonSays value set to false
-                    SetNetworkParenting(parentNetworkObject.NetworkObjectId, true);
+                    // Note: Since in-scene placed NetworkObjects are parented in the scene
+                    // the default "assumption" is that children are parenting local space
+                    // relative.
+                    SetNetworkParenting(parentNetworkObject.NetworkObjectId, false);
 
                     // Set the cached parent
                     m_CachedParent = parentNetworkObject.transform;
@@ -1002,13 +1009,17 @@ namespace Unity.Netcode
                 }
             }
         }
-        internal void SetNetworkVariableData(FastBufferReader reader)
+
+        /// <summary>
+        /// Only invoked during first synchronization of a NetworkObject (late join or newly spawned)
+        /// </summary>
+        internal void SetNetworkVariableData(FastBufferReader reader, ulong clientId)
         {
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
                 var behaviour = ChildNetworkBehaviours[i];
                 behaviour.InitializeVariables();
-                behaviour.SetNetworkVariableData(reader);
+                behaviour.SetNetworkVariableData(reader, clientId);
             }
         }
 
@@ -1045,7 +1056,20 @@ namespace Unity.Netcode
             {
                 if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
                 {
-                    NetworkLog.LogError($"Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
+                    NetworkLog.LogError($"{nameof(NetworkBehaviour)} index {index} was out of bounds for {name}. NetworkBehaviours must be the same, and in the same order, between server and client.");
+                }
+
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
+                {
+                    var currentKnownChildren = new System.Text.StringBuilder();
+                    currentKnownChildren.Append($"Known child {nameof(NetworkBehaviour)}s:");
+                    for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
+                    {
+                        var childNetworkBehaviour = ChildNetworkBehaviours[i];
+                        currentKnownChildren.Append($" [{i}] {childNetworkBehaviour.__getTypeName()}");
+                        currentKnownChildren.Append(i < ChildNetworkBehaviours.Count - 1 ? "," : ".");
+                    }
+                    NetworkLog.LogInfo(currentKnownChildren.ToString());
                 }
 
                 return null;
@@ -1056,19 +1080,43 @@ namespace Unity.Netcode
 
         internal struct SceneObject
         {
-            public struct HeaderData : INetworkSerializeByMemcpy
+            private byte m_BitField;
-            {
+            public uint Hash;
             public ulong NetworkObjectId;
             public ulong OwnerClientId;
-                public uint Hash;
 
-                public bool IsPlayerObject;
+            public bool IsPlayerObject
-                public bool HasParent;
+            {
-                public bool IsSceneObject;
+                get => ByteUtility.GetBit(m_BitField, 0);
-                public bool HasTransform;
+                set => ByteUtility.SetBit(ref m_BitField, 0, value);
+            }
+            public bool HasParent
+            {
+                get => ByteUtility.GetBit(m_BitField, 1);
+                set => ByteUtility.SetBit(ref m_BitField, 1, value);
+            }
+            public bool IsSceneObject
+            {
+                get => ByteUtility.GetBit(m_BitField, 2);
+                set => ByteUtility.SetBit(ref m_BitField, 2, value);
+            }
+            public bool HasTransform
+            {
+                get => ByteUtility.GetBit(m_BitField, 3);
+                set => ByteUtility.SetBit(ref m_BitField, 3, value);
             }
 
-            public HeaderData Header;
+            public bool IsLatestParentSet
+            {
+                get => ByteUtility.GetBit(m_BitField, 4);
+                set => ByteUtility.SetBit(ref m_BitField, 4, value);
+            }
+
+            public bool WorldPositionStays
+            {
+                get => ByteUtility.GetBit(m_BitField, 5);
+                set => ByteUtility.SetBit(ref m_BitField, 5, value);
+            }
 
             //If(Metadata.HasParent)
             public ulong ParentObjectId;
@@ -1084,7 +1132,6 @@ namespace Unity.Netcode
             public TransformData Transform;
 
             //If(Metadata.IsReparented)
-            public bool IsLatestParentSet;
 
             //If(IsLatestParentSet)
             public ulong? LatestParent;
@@ -1094,114 +1141,90 @@ namespace Unity.Netcode
 
             public int NetworkSceneHandle;
 
-            public bool WorldPositionStays;
 
-            public unsafe void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer)
             {
-                var writeSize = sizeof(HeaderData);
+                writer.WriteValueSafe(m_BitField);
-                if (Header.HasParent)
+                writer.WriteValueSafe(Hash);
+                BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+                BytePacker.WriteValueBitPacked(writer, OwnerClientId);
+
+                if (HasParent)
                 {
-                    writeSize += FastBufferWriter.GetWriteSize(ParentObjectId);
+                    BytePacker.WriteValueBitPacked(writer, ParentObjectId);
-                    writeSize += FastBufferWriter.GetWriteSize(WorldPositionStays);
+                    if (IsLatestParentSet)
-                    writeSize += FastBufferWriter.GetWriteSize(IsLatestParentSet);
+                    {
-                    writeSize += IsLatestParentSet ? FastBufferWriter.GetWriteSize<ulong>() : 0;
+                        BytePacker.WriteValueBitPacked(writer, LatestParent.Value);
                     }
-                writeSize += Header.HasTransform ? FastBufferWriter.GetWriteSize<TransformData>() : 0;
+                }
-                writeSize += Header.IsSceneObject ? FastBufferWriter.GetWriteSize<int>() : 0;
+
+                var writeSize = 0;
+                writeSize += HasTransform ? FastBufferWriter.GetWriteSize<TransformData>() : 0;
+                writeSize += IsSceneObject ? FastBufferWriter.GetWriteSize<int>() : 0;
 
                 if (!writer.TryBeginWrite(writeSize))
                 {
                     throw new OverflowException("Could not serialize SceneObject: Out of buffer space.");
                 }
 
-                writer.WriteValue(Header);
+                if (HasTransform)
-
-                if (Header.HasParent)
-                {
-                    writer.WriteValue(ParentObjectId);
-                    writer.WriteValue(WorldPositionStays);
-                    writer.WriteValue(IsLatestParentSet);
-                    if (IsLatestParentSet)
-                    {
-                        writer.WriteValue(LatestParent.Value);
-                    }
-                }
-
-                if (Header.HasTransform)
                 {
                     writer.WriteValue(Transform);
                 }
 
                 // In-Scene NetworkObjects are uniquely identified NetworkPrefabs defined by their
-                // NetworkSceneHandle and GlobalObjectIdHash. Since each loaded scene has a unique
+                // NetworkSceneHandle and GlobalObjectIdHash. Client-side NetworkSceneManagers use
-                // handle, it provides us with a unique and persistent "scene prefab asset" instance.
+                // this to locate their local instance of the in-scene placed NetworkObject instance.
-                // This is only set on in-scene placed NetworkObjects to reduce the over-all packet
+                // Only written for in-scene placed NetworkObjects.
-                // sizes for dynamically spawned NetworkObjects.
+                if (IsSceneObject)
-                if (Header.IsSceneObject)
                 {
                     writer.WriteValue(OwnerObject.GetSceneOriginHandle());
                 }
 
-                OwnerObject.WriteNetworkVariableData(writer, TargetClientId);
+                // Synchronize NetworkVariables and NetworkBehaviours
+                var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
+                OwnerObject.SynchronizeNetworkBehaviours(ref bufferSerializer, TargetClientId);
             }
 
-            public unsafe void Deserialize(FastBufferReader reader)
+            public void Deserialize(FastBufferReader reader)
             {
-                if (!reader.TryBeginRead(sizeof(HeaderData)))
+                reader.ReadValueSafe(out m_BitField);
+                reader.ReadValueSafe(out Hash);
+                ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+                ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
+
+                if (HasParent)
                 {
-                    throw new OverflowException("Could not deserialize SceneObject: Out of buffer space.");
+                    ByteUnpacker.ReadValueBitPacked(reader, out ParentObjectId);
+                    if (IsLatestParentSet)
+                    {
+                        ByteUnpacker.ReadValueBitPacked(reader, out ulong latestParent);
+                        LatestParent = latestParent;
                     }
-                reader.ReadValue(out Header);
+                }
+
                 var readSize = 0;
-                if (Header.HasParent)
+                readSize += HasTransform ? FastBufferWriter.GetWriteSize<TransformData>() : 0;
-                {
+                readSize += IsSceneObject ? FastBufferWriter.GetWriteSize<int>() : 0;
-                    readSize += FastBufferWriter.GetWriteSize(ParentObjectId);
-                    readSize += FastBufferWriter.GetWriteSize(WorldPositionStays);
-                    readSize += FastBufferWriter.GetWriteSize(IsLatestParentSet);
-                    // We need to read at this point in order to get the IsLatestParentSet value
-                    if (!reader.TryBeginRead(readSize))
-                    {
-                        throw new OverflowException("Could not deserialize SceneObject: Out of buffer space.");
-                    }
-
-                    // Read the initial parenting related properties
-                    reader.ReadValue(out ParentObjectId);
-                    reader.ReadValue(out WorldPositionStays);
-                    reader.ReadValue(out IsLatestParentSet);
-
-                    // Now calculate the remaining bytes to read
-                    readSize = 0;
-                    readSize += IsLatestParentSet ? FastBufferWriter.GetWriteSize<ulong>() : 0;
-                }
-
-                readSize += Header.HasTransform ? FastBufferWriter.GetWriteSize<TransformData>() : 0;
-                readSize += Header.IsSceneObject ? FastBufferWriter.GetWriteSize<int>() : 0;
 
                 // Try to begin reading the remaining bytes
                 if (!reader.TryBeginRead(readSize))
                 {
-                    throw new OverflowException("Could not deserialize SceneObject: Out of buffer space.");
+                    throw new OverflowException("Could not deserialize SceneObject: Reading past the end of the buffer");
                 }
 
-                if (IsLatestParentSet)
+                if (HasTransform)
-                {
-                    reader.ReadValueSafe(out ulong latestParent);
-                    LatestParent = latestParent;
-                }
-
-                if (Header.HasTransform)
                 {
                     reader.ReadValue(out Transform);
                 }
 
                 // In-Scene NetworkObjects are uniquely identified NetworkPrefabs defined by their
-                // NetworkSceneHandle and GlobalObjectIdHash. Since each loaded scene has a unique
+                // NetworkSceneHandle and GlobalObjectIdHash. Client-side NetworkSceneManagers use
-                // handle, it provides us with a unique and persistent "scene prefab asset" instance.
+                // this to locate their local instance of the in-scene placed NetworkObject instance.
-                // Client-side NetworkSceneManagers use this to locate their local instance of the
+                // Only read for in-scene placed NetworkObjects
-                // NetworkObject instance.
+                if (IsSceneObject)
-                if (Header.IsSceneObject)
                 {
-                    reader.ReadValueSafe(out NetworkSceneHandle);
+                    reader.ReadValue(out NetworkSceneHandle);
                 }
             }
         }
@@ -1214,18 +1237,87 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Handles synchronizing NetworkVariables and custom synchronization data for NetworkBehaviours.
+        /// </summary>
+        /// <remarks>
+        /// This is where we determine how much data is written after the associated NetworkObject in order to recover
+        /// from a failed instantiated NetworkObject without completely disrupting client synchronization.
+        /// </remarks>
+        internal void SynchronizeNetworkBehaviours<T>(ref BufferSerializer<T> serializer, ulong targetClientId = 0) where T : IReaderWriter
+        {
+            if (serializer.IsWriter)
+            {
+                var writer = serializer.GetFastBufferWriter();
+                var positionBeforeSynchronizing = writer.Position;
+                writer.WriteValueSafe((ushort)0);
+                var sizeToSkipCalculationPosition = writer.Position;
+
+                // Synchronize NetworkVariables
+                WriteNetworkVariableData(writer, targetClientId);
+                // Reserve the NetworkBehaviour synchronization count position
+                var networkBehaviourCountPosition = writer.Position;
+                writer.WriteValueSafe((byte)0);
+
+                // Parse through all NetworkBehaviours and any that return true
+                // had additional synchronization data written.
+                // (See notes for reading/deserialization below)
+                var synchronizationCount = (byte)0;
+                foreach (var childBehaviour in ChildNetworkBehaviours)
+                {
+                    if (childBehaviour.Synchronize(ref serializer))
+                    {
+                        synchronizationCount++;
+                    }
+                }
+
+                var currentPosition = writer.Position;
+                // Write the total number of bytes written for NetworkVariable and NetworkBehaviour
+                // synchronization.
+                writer.Seek(positionBeforeSynchronizing);
+                // We want the size of everything after our size to skip calculation position
+                var size = (ushort)(currentPosition - sizeToSkipCalculationPosition);
+                writer.WriteValueSafe(size);
+                // Write the number of NetworkBehaviours synchronized
+                writer.Seek(networkBehaviourCountPosition);
+                writer.WriteValueSafe(synchronizationCount);
+                // seek back to the position after writing NetworkVariable and NetworkBehaviour
+                // synchronization data.
+                writer.Seek(currentPosition);
+            }
+            else
+            {
+                var reader = serializer.GetFastBufferReader();
+
+                reader.ReadValueSafe(out ushort sizeOfSynchronizationData);
+                var seekToEndOfSynchData = reader.Position + sizeOfSynchronizationData;
+                // Apply the network variable synchronization data
+                SetNetworkVariableData(reader, targetClientId);
+                // Read the number of NetworkBehaviours to synchronize
+                reader.ReadValueSafe(out byte numberSynchronized);
+                var networkBehaviourId = (ushort)0;
+
+                // If a NetworkBehaviour writes synchronization data, it will first
+                // write its NetworkBehaviourId so when deserializing the client-side
+                // can find the right NetworkBehaviour to deserialize the synchronization data.
+                for (int i = 0; i < numberSynchronized; i++)
+                {
+                    serializer.SerializeValue(ref networkBehaviourId);
+                    var networkBehaviour = GetNetworkBehaviourAtOrderIndex(networkBehaviourId);
+                    networkBehaviour.Synchronize(ref serializer);
+                }
+            }
+        }
+
         internal SceneObject GetMessageSceneObject(ulong targetClientId)
         {
             var obj = new SceneObject
             {
-                Header = new SceneObject.HeaderData
-                {
-                    IsPlayerObject = IsPlayerObject,
                 NetworkObjectId = NetworkObjectId,
                 OwnerClientId = OwnerClientId,
+                IsPlayerObject = IsPlayerObject,
                 IsSceneObject = IsSceneObject ?? true,
                 Hash = HostCheckForGlobalObjectIdHashOverride(),
-                },
                 OwnerObject = this,
                 TargetClientId = targetClientId
             };
@@ -1235,11 +1327,18 @@ namespace Unity.Netcode
             if (!AlwaysReplicateAsRoot && transform.parent != null)
             {
                 parentNetworkObject = transform.parent.GetComponent<NetworkObject>();
+                // In-scene placed NetworkObjects parented under GameObjects with no NetworkObject
+                // should set the has parent flag and preserve the world position stays value
+                if (parentNetworkObject == null && obj.IsSceneObject)
+                {
+                    obj.HasParent = true;
+                    obj.WorldPositionStays = m_CachedWorldPositionStays;
+                }
             }
 
             if (parentNetworkObject != null)
             {
-                obj.Header.HasParent = true;
+                obj.HasParent = true;
                 obj.ParentObjectId = parentNetworkObject.NetworkObjectId;
                 obj.WorldPositionStays = m_CachedWorldPositionStays;
                 var latestParent = GetNetworkParenting();
@@ -1253,20 +1352,38 @@ namespace Unity.Netcode
 
             if (IncludeTransformWhenSpawning == null || IncludeTransformWhenSpawning(OwnerClientId))
             {
-                obj.Header.HasTransform = true;
+                obj.HasTransform = true;
+
+                // We start with the default AutoObjectParentSync values to determine which transform space we will
+                // be synchronizing clients with.
+                var syncRotationPositionLocalSpaceRelative = obj.HasParent && !m_CachedWorldPositionStays;
+                var syncScaleLocalSpaceRelative = obj.HasParent && !m_CachedWorldPositionStays;
+
+                // If auto object synchronization is turned off
+                if (!AutoObjectParentSync)
+                {
+                    // We always synchronize position and rotation world space relative
+                    syncRotationPositionLocalSpaceRelative = false;
+                    // Scale is special, it synchronizes local space relative if it has a
+                    // parent since applying the world space scale under a parent with scale
+                    // will result in the improper scale for the child
+                    syncScaleLocalSpaceRelative = obj.HasParent;
+                }
+
+
                 obj.Transform = new SceneObject.TransformData
                 {
                     // If we are parented and we have the m_CachedWorldPositionStays disabled, then use local space
                     // values as opposed world space values.
-                    Position = parentNetworkObject && !m_CachedWorldPositionStays ? transform.localPosition : transform.position,
+                    Position = syncRotationPositionLocalSpaceRelative ? transform.localPosition : transform.position,
-                    Rotation = parentNetworkObject && !m_CachedWorldPositionStays ? transform.localRotation : transform.rotation,
+                    Rotation = syncRotationPositionLocalSpaceRelative ? transform.localRotation : transform.rotation,
 
                     // We only use the lossyScale if the NetworkObject has a parent. Multi-generation nested children scales can
                     // impact the final scale of the child NetworkObject in question. The solution is to use the lossy scale
                     // which can be thought of as "world space scale".
                     // More information:
                     // https://docs.unity3d.com/ScriptReference/Transform-lossyScale.html
-                    Scale = parentNetworkObject && !m_CachedWorldPositionStays ? transform.localScale : transform.lossyScale,
+                    Scale = syncScaleLocalSpaceRelative ? transform.localScale : transform.lossyScale,
                 };
             }
 
@@ -1278,10 +1395,10 @@ namespace Unity.Netcode
         /// when the client is approved or during a scene transition
         /// </summary>
         /// <param name="sceneObject">Deserialized scene object data</param>
-        /// <param name="variableData">reader for the NetworkVariable data</param>
+        /// <param name="reader">FastBufferReader for the NetworkVariable data</param>
         /// <param name="networkManager">NetworkManager instance</param>
         /// <returns>optional to use NetworkObject deserialized</returns>
-        internal static NetworkObject AddSceneObject(in SceneObject sceneObject, FastBufferReader variableData, NetworkManager networkManager)
+        internal static NetworkObject AddSceneObject(in SceneObject sceneObject, FastBufferReader reader, NetworkManager networkManager)
         {
             //Attempt to create a local NetworkObject
             var networkObject = networkManager.SpawnManager.CreateLocalNetworkObject(sceneObject);
@@ -1289,18 +1406,36 @@ namespace Unity.Netcode
             if (networkObject == null)
             {
                 // Log the error that the NetworkObject failed to construct
-                Debug.LogError($"Failed to spawn {nameof(NetworkObject)} for Hash {sceneObject.Header.Hash}.");
+                if (networkManager.LogLevel <= LogLevel.Normal)
+                {
+                    NetworkLog.LogError($"Failed to spawn {nameof(NetworkObject)} for Hash {sceneObject.Hash}.");
+                }
 
-                // If we failed to load this NetworkObject, then skip past the network variable data
+                try
-                variableData.ReadValueSafe(out ushort varSize);
+                {
-                variableData.Seek(variableData.Position + varSize);
+                    // If we failed to load this NetworkObject, then skip past the Network Variable and (if any) synchronization data
+                    reader.ReadValueSafe(out ushort networkBehaviourSynchronizationDataLength);
+                    reader.Seek(reader.Position + networkBehaviourSynchronizationDataLength);
+                }
+                catch (Exception ex)
+                {
+                    Debug.LogException(ex);
+                }
 
                 // We have nothing left to do here.
                 return null;
             }
 
+            // This will get set again when the NetworkObject is spawned locally, but we set it here ahead of spawning
+            // in order to be able to determine which NetworkVariables the client will be allowed to read.
+            networkObject.OwnerClientId = sceneObject.OwnerClientId;
+
+            // Synchronize NetworkBehaviours
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+            networkObject.SynchronizeNetworkBehaviours(ref bufferSerializer, networkManager.LocalClientId);
+
             // Spawn the NetworkObject
-            networkManager.SpawnManager.SpawnNetworkObjectLocally(networkObject, sceneObject, variableData, false);
+            networkManager.SpawnManager.SpawnNetworkObjectLocally(networkObject, sceneObject, false);
 
             return networkObject;
         }
@@ -1320,9 +1455,9 @@ namespace Unity.Netcode
                     var globalObjectIdHash = NetworkManager.PrefabHandler.GetSourceGlobalObjectIdHash(GlobalObjectIdHash);
                     return globalObjectIdHash == 0 ? GlobalObjectIdHash : globalObjectIdHash;
                 }
-                else if (NetworkManager.NetworkConfig.OverrideToNetworkPrefab.ContainsKey(GlobalObjectIdHash))
+                if (NetworkManager.NetworkConfig.Prefabs.OverrideToNetworkPrefab.TryGetValue(GlobalObjectIdHash, out uint hash))
                 {
-                    return NetworkManager.NetworkConfig.OverrideToNetworkPrefab[GlobalObjectIdHash];
+                    return hash;
                 }
             }
 

Runtime/Hashing/XXHash.cs

@@ -0,0 +1,248 @@
+using System;
+using System.Text;
+using System.Runtime.CompilerServices;
+
+namespace Unity.Netcode
+{
+    internal static class XXHash
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe uint Hash32(byte* input, int length, uint seed = 0)
+        {
+            unchecked
+            {
+                const uint prime1 = 2654435761u;
+                const uint prime2 = 2246822519u;
+                const uint prime3 = 3266489917u;
+                const uint prime4 = 0668265263u;
+                const uint prime5 = 0374761393u;
+
+                uint hash = seed + prime5;
+
+                if (length >= 16)
+                {
+                    uint val0 = seed + prime1 + prime2;
+                    uint val1 = seed + prime2;
+                    uint val2 = seed + 0;
+                    uint val3 = seed - prime1;
+
+                    int count = length >> 4;
+                    for (int i = 0; i < count; i++)
+                    {
+                        var pos0 = *(uint*)(input + 0);
+                        var pos1 = *(uint*)(input + 4);
+                        var pos2 = *(uint*)(input + 8);
+                        var pos3 = *(uint*)(input + 12);
+
+                        val0 += pos0 * prime2;
+                        val0 = (val0 << 13) | (val0 >> (32 - 13));
+                        val0 *= prime1;
+
+                        val1 += pos1 * prime2;
+                        val1 = (val1 << 13) | (val1 >> (32 - 13));
+                        val1 *= prime1;
+
+                        val2 += pos2 * prime2;
+                        val2 = (val2 << 13) | (val2 >> (32 - 13));
+                        val2 *= prime1;
+
+                        val3 += pos3 * prime2;
+                        val3 = (val3 << 13) | (val3 >> (32 - 13));
+                        val3 *= prime1;
+
+                        input += 16;
+                    }
+
+                    hash = ((val0 << 01) | (val0 >> (32 - 01))) +
+                           ((val1 << 07) | (val1 >> (32 - 07))) +
+                           ((val2 << 12) | (val2 >> (32 - 12))) +
+                           ((val3 << 18) | (val3 >> (32 - 18)));
+                }
+
+                hash += (uint)length;
+
+                length &= 15;
+                while (length >= 4)
+                {
+                    hash += *(uint*)input * prime3;
+                    hash = ((hash << 17) | (hash >> (32 - 17))) * prime4;
+                    input += 4;
+                    length -= 4;
+                }
+                while (length > 0)
+                {
+                    hash += *input * prime5;
+                    hash = ((hash << 11) | (hash >> (32 - 11))) * prime1;
+                    ++input;
+                    --length;
+                }
+
+                hash ^= hash >> 15;
+                hash *= prime2;
+                hash ^= hash >> 13;
+                hash *= prime3;
+                hash ^= hash >> 16;
+
+                return hash;
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe ulong Hash64(byte* input, int length, uint seed = 0)
+        {
+            unchecked
+            {
+                const ulong prime1 = 11400714785074694791ul;
+                const ulong prime2 = 14029467366897019727ul;
+                const ulong prime3 = 01609587929392839161ul;
+                const ulong prime4 = 09650029242287828579ul;
+                const ulong prime5 = 02870177450012600261ul;
+
+                ulong hash = seed + prime5;
+
+                if (length >= 32)
+                {
+                    ulong val0 = seed + prime1 + prime2;
+                    ulong val1 = seed + prime2;
+                    ulong val2 = seed + 0;
+                    ulong val3 = seed - prime1;
+
+                    int count = length >> 5;
+                    for (int i = 0; i < count; i++)
+                    {
+                        var pos0 = *(ulong*)(input + 0);
+                        var pos1 = *(ulong*)(input + 8);
+                        var pos2 = *(ulong*)(input + 16);
+                        var pos3 = *(ulong*)(input + 24);
+
+                        val0 += pos0 * prime2;
+                        val0 = (val0 << 31) | (val0 >> (64 - 31));
+                        val0 *= prime1;
+
+                        val1 += pos1 * prime2;
+                        val1 = (val1 << 31) | (val1 >> (64 - 31));
+                        val1 *= prime1;
+
+                        val2 += pos2 * prime2;
+                        val2 = (val2 << 31) | (val2 >> (64 - 31));
+                        val2 *= prime1;
+
+                        val3 += pos3 * prime2;
+                        val3 = (val3 << 31) | (val3 >> (64 - 31));
+                        val3 *= prime1;
+
+                        input += 32;
+                    }
+
+                    hash = ((val0 << 01) | (val0 >> (64 - 01))) +
+                           ((val1 << 07) | (val1 >> (64 - 07))) +
+                           ((val2 << 12) | (val2 >> (64 - 12))) +
+                           ((val3 << 18) | (val3 >> (64 - 18)));
+
+                    val0 *= prime2;
+                    val0 = (val0 << 31) | (val0 >> (64 - 31));
+                    val0 *= prime1;
+                    hash ^= val0;
+                    hash = hash * prime1 + prime4;
+
+                    val1 *= prime2;
+                    val1 = (val1 << 31) | (val1 >> (64 - 31));
+                    val1 *= prime1;
+                    hash ^= val1;
+                    hash = hash * prime1 + prime4;
+
+                    val2 *= prime2;
+                    val2 = (val2 << 31) | (val2 >> (64 - 31));
+                    val2 *= prime1;
+                    hash ^= val2;
+                    hash = hash * prime1 + prime4;
+
+                    val3 *= prime2;
+                    val3 = (val3 << 31) | (val3 >> (64 - 31));
+                    val3 *= prime1;
+                    hash ^= val3;
+                    hash = hash * prime1 + prime4;
+                }
+
+                hash += (ulong)length;
+
+                length &= 31;
+                while (length >= 8)
+                {
+                    ulong lane = *(ulong*)input * prime2;
+                    lane = ((lane << 31) | (lane >> (64 - 31))) * prime1;
+                    hash ^= lane;
+                    hash = ((hash << 27) | (hash >> (64 - 27))) * prime1 + prime4;
+                    input += 8;
+                    length -= 8;
+                }
+                if (length >= 4)
+                {
+                    hash ^= *(uint*)input * prime1;
+                    hash = ((hash << 23) | (hash >> (64 - 23))) * prime2 + prime3;
+                    input += 4;
+                    length -= 4;
+                }
+                while (length > 0)
+                {
+                    hash ^= *input * prime5;
+                    hash = ((hash << 11) | (hash >> (64 - 11))) * prime1;
+                    ++input;
+                    --length;
+                }
+
+                hash ^= hash >> 33;
+                hash *= prime2;
+                hash ^= hash >> 29;
+                hash *= prime3;
+                hash ^= hash >> 32;
+
+                return hash;
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this byte[] buffer)
+        {
+            int length = buffer.Length;
+            unsafe
+            {
+                fixed (byte* pointer = buffer)
+                {
+                    return Hash32(pointer, length);
+                }
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this string text) => Hash32(Encoding.UTF8.GetBytes(text));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this Type type) => Hash32(type.FullName);
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32<T>() => Hash32(typeof(T));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this byte[] buffer)
+        {
+            int length = buffer.Length;
+            unsafe
+            {
+                fixed (byte* pointer = buffer)
+                {
+                    return Hash64(pointer, length);
+                }
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this string text) => Hash64(Encoding.UTF8.GetBytes(text));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this Type type) => Hash64(type.FullName);
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64<T>() => Hash64(typeof(T));
+    }
+}

Runtime/Hashing/XXHash.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: b5aa7a49e9e694f148d810d34577546b
+guid: c3077af091aa443acbdea9d3e97727b0
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Runtime/Hashing/XXHash.meta

@@ -1,8 +0,0 @@
-fileFormatVersion: 2
-guid: 2c61e8fe9a68a486fbbc3128d233ded2
-folderAsset: yes
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Hashing/XXHash/LICENSE

@@ -1,21 +0,0 @@
-The MIT License (MIT)
-
-Copyright (c) 2015, 2016 Sedat Kapanoglu
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.

Runtime/Hashing/XXHash/LICENSE.meta

@@ -1,7 +0,0 @@
-fileFormatVersion: 2
-guid: cf89ecbf6f9954c8ea6d0848b1e79d87
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Hashing/XXHash/XXHash.cs

@@ -1,318 +0,0 @@
-// <copyright file="XXHash.cs" company="Sedat Kapanoglu">
-// Copyright (c) 2015-2019 Sedat Kapanoglu
-// MIT License (see LICENSE file for details)
-// </copyright>
-
-// @mfatihmar (Unity): Modified for Unity support
-
-using System.Text;
-using System.Runtime.CompilerServices;
-
-namespace Unity.Netcode
-{
-    /// <summary>
-    /// XXHash implementation.
-    /// </summary>
-    internal static class XXHash
-    {
-        private const ulong k_Prime64v1 = 11400714785074694791ul;
-        private const ulong k_Prime64v2 = 14029467366897019727ul;
-        private const ulong k_Prime64v3 = 1609587929392839161ul;
-        private const ulong k_Prime64v4 = 9650029242287828579ul;
-        private const ulong k_Prime64v5 = 2870177450012600261ul;
-
-        private const uint k_Prime32v1 = 2654435761u;
-        private const uint k_Prime32v2 = 2246822519u;
-        private const uint k_Prime32v3 = 3266489917u;
-        private const uint k_Prime32v4 = 668265263u;
-        private const uint k_Prime32v5 = 374761393u;
-
-        public static uint Hash32(string text) => Hash32(text, Encoding.UTF8);
-        public static uint Hash32(string text, Encoding encoding) => Hash32(encoding.GetBytes(text));
-        public static uint Hash32(byte[] buffer)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = buffer)
-                {
-                    return Hash32(ptr, buffer.Length);
-                }
-            }
-        }
-
-        /// <summary>
-        /// Generate a 32-bit xxHash value.
-        /// </summary>
-        /// <param name="buffer">Input buffer.</param>
-        /// <param name="bufferLength">Input buffer length.</param>
-        /// <param name="seed">Optional seed.</param>
-        /// <returns>32-bit hash value.</returns>
-        public static unsafe uint Hash32(byte* buffer, int bufferLength, uint seed = 0)
-        {
-            const int stripeLength = 16;
-
-            int len = bufferLength;
-            int remainingLen = len;
-            uint acc;
-
-            byte* pInput = buffer;
-            if (len >= stripeLength)
-            {
-                uint acc1 = seed + k_Prime32v1 + k_Prime32v2;
-                uint acc2 = seed + k_Prime32v2;
-                uint acc3 = seed;
-                uint acc4 = seed - k_Prime32v1;
-
-                do
-                {
-                    acc = processStripe32(ref pInput, ref acc1, ref acc2, ref acc3, ref acc4);
-                    remainingLen -= stripeLength;
-                } while (remainingLen >= stripeLength);
-            }
-            else
-            {
-                acc = seed + k_Prime32v5;
-            }
-
-            acc += (uint)len;
-            acc = processRemaining32(pInput, acc, remainingLen);
-
-            return avalanche32(acc);
-        }
-
-        public static ulong Hash64(string text) => Hash64(text, Encoding.UTF8);
-        public static ulong Hash64(string text, Encoding encoding) => Hash64(encoding.GetBytes(text));
-        public static ulong Hash64(byte[] buffer)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = buffer)
-                {
-                    return Hash64(ptr, buffer.Length);
-                }
-            }
-        }
-
-        /// <summary>
-        /// Generate a 64-bit xxHash value.
-        /// </summary>
-        /// <param name="buffer">Input buffer.</param>
-        /// <param name="bufferLength">Input buffer length.</param>
-        /// <param name="seed">Optional seed.</param>
-        /// <returns>Computed 64-bit hash value.</returns>
-        public static unsafe ulong Hash64(byte* buffer, int bufferLength, ulong seed = 0)
-        {
-            const int stripeLength = 32;
-
-            int len = bufferLength;
-            int remainingLen = len;
-            ulong acc;
-
-            byte* pInput = buffer;
-            if (len >= stripeLength)
-            {
-                ulong acc1 = seed + k_Prime64v1 + k_Prime64v2;
-                ulong acc2 = seed + k_Prime64v2;
-                ulong acc3 = seed;
-                ulong acc4 = seed - k_Prime64v1;
-
-                do
-                {
-                    acc = processStripe64(ref pInput, ref acc1, ref acc2, ref acc3, ref acc4);
-                    remainingLen -= stripeLength;
-                } while (remainingLen >= stripeLength);
-            }
-            else
-            {
-                acc = seed + k_Prime64v5;
-            }
-
-            acc += (ulong)len;
-            acc = processRemaining64(pInput, acc, remainingLen);
-
-
-            return avalanche64(acc);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe ulong processStripe64(
-            ref byte* pInput,
-            ref ulong acc1,
-            ref ulong acc2,
-            ref ulong acc3,
-            ref ulong acc4)
-        {
-            processLane64(ref acc1, ref pInput);
-            processLane64(ref acc2, ref pInput);
-            processLane64(ref acc3, ref pInput);
-            processLane64(ref acc4, ref pInput);
-
-            ulong acc = Bits.RotateLeft(acc1, 1)
-                        + Bits.RotateLeft(acc2, 7)
-                        + Bits.RotateLeft(acc3, 12)
-                        + Bits.RotateLeft(acc4, 18);
-
-            mergeAccumulator64(ref acc, acc1);
-            mergeAccumulator64(ref acc, acc2);
-            mergeAccumulator64(ref acc, acc3);
-            mergeAccumulator64(ref acc, acc4);
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe void processLane64(ref ulong accn, ref byte* pInput)
-        {
-            ulong lane = *(ulong*)pInput;
-            accn = round64(accn, lane);
-            pInput += 8;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe ulong processRemaining64(
-            byte* pInput,
-            ulong acc,
-            int remainingLen)
-        {
-            for (ulong lane; remainingLen >= 8; remainingLen -= 8, pInput += 8)
-            {
-                lane = *(ulong*)pInput;
-
-                acc ^= round64(0, lane);
-                acc = Bits.RotateLeft(acc, 27) * k_Prime64v1;
-                acc += k_Prime64v4;
-            }
-
-            for (uint lane32; remainingLen >= 4; remainingLen -= 4, pInput += 4)
-            {
-                lane32 = *(uint*)pInput;
-
-                acc ^= lane32 * k_Prime64v1;
-                acc = Bits.RotateLeft(acc, 23) * k_Prime64v2;
-                acc += k_Prime64v3;
-            }
-
-            for (byte lane8; remainingLen >= 1; remainingLen--, pInput++)
-            {
-                lane8 = *pInput;
-                acc ^= lane8 * k_Prime64v5;
-                acc = Bits.RotateLeft(acc, 11) * k_Prime64v1;
-            }
-
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static ulong avalanche64(ulong acc)
-        {
-            acc ^= acc >> 33;
-            acc *= k_Prime64v2;
-            acc ^= acc >> 29;
-            acc *= k_Prime64v3;
-            acc ^= acc >> 32;
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static ulong round64(ulong accn, ulong lane)
-        {
-            accn += lane * k_Prime64v2;
-            return Bits.RotateLeft(accn, 31) * k_Prime64v1;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static void mergeAccumulator64(ref ulong acc, ulong accn)
-        {
-            acc ^= round64(0, accn);
-            acc *= k_Prime64v1;
-            acc += k_Prime64v4;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe uint processStripe32(
-            ref byte* pInput,
-            ref uint acc1,
-            ref uint acc2,
-            ref uint acc3,
-            ref uint acc4)
-        {
-            processLane32(ref pInput, ref acc1);
-            processLane32(ref pInput, ref acc2);
-            processLane32(ref pInput, ref acc3);
-            processLane32(ref pInput, ref acc4);
-
-            return Bits.RotateLeft(acc1, 1)
-                   + Bits.RotateLeft(acc2, 7)
-                   + Bits.RotateLeft(acc3, 12)
-                   + Bits.RotateLeft(acc4, 18);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe void processLane32(ref byte* pInput, ref uint accn)
-        {
-            uint lane = *(uint*)pInput;
-            accn = round32(accn, lane);
-            pInput += 4;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe uint processRemaining32(
-            byte* pInput,
-            uint acc,
-            int remainingLen)
-        {
-            for (uint lane; remainingLen >= 4; remainingLen -= 4, pInput += 4)
-            {
-                lane = *(uint*)pInput;
-                acc += lane * k_Prime32v3;
-                acc = Bits.RotateLeft(acc, 17) * k_Prime32v4;
-            }
-
-            for (byte lane; remainingLen >= 1; remainingLen--, pInput++)
-            {
-                lane = *pInput;
-                acc += lane * k_Prime32v5;
-                acc = Bits.RotateLeft(acc, 11) * k_Prime32v1;
-            }
-
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static uint round32(uint accn, uint lane)
-        {
-            accn += lane * k_Prime32v2;
-            accn = Bits.RotateLeft(accn, 13);
-            accn *= k_Prime32v1;
-            return accn;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static uint avalanche32(uint acc)
-        {
-            acc ^= acc >> 15;
-            acc *= k_Prime32v2;
-            acc ^= acc >> 13;
-            acc *= k_Prime32v3;
-            acc ^= acc >> 16;
-            return acc;
-        }
-
-        /// <summary>
-        /// Bit operations.
-        /// </summary>
-        private static class Bits
-        {
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            internal static ulong RotateLeft(ulong value, int bits)
-            {
-                return (value << bits) | (value >> (64 - bits));
-            }
-
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            internal static uint RotateLeft(uint value, int bits)
-            {
-                return (value << bits) | (value >> (32 - bits));
-            }
-        }
-    }
-}

Runtime/Messaging/BatchHeader.cs

@@ -5,9 +5,26 @@ namespace Unity.Netcode
     /// </summary>
     internal struct BatchHeader : INetworkSerializeByMemcpy
     {
+        internal const ushort MagicValue = 0x1160;
+        /// <summary>
+        /// A magic number to detect corrupt messages.
+        /// Always set to k_MagicValue
+        /// </summary>
+        public ushort Magic;
+
+        /// <summary>
+        /// Total number of bytes in the batch.
+        /// </summary>
+        public int BatchSize;
+
+        /// <summary>
+        /// Hash of the message to detect corrupt messages.
+        /// </summary>
+        public ulong BatchHash;
+
         /// <summary>
         /// Total number of messages in the batch.
         /// </summary>
-        public ushort BatchSize;
+        public ushort BatchCount;
     }
 }

Runtime/Messaging/CustomMessageManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Unity.Collections;
 
 namespace Unity.Netcode
 {
@@ -68,9 +69,23 @@ namespace Unity.Netcode
 
             if (clientIds == null)
             {
-                throw new ArgumentNullException("You must pass in a valid clientId List");
+                throw new ArgumentNullException(nameof(clientIds), "You must pass in a valid clientId List");
             }
 
+            if (m_NetworkManager.IsHost)
+            {
+                for (var i = 0; i < clientIds.Count; ++i)
+                {
+                    if (clientIds[i] == m_NetworkManager.LocalClientId)
+                    {
+                        InvokeUnnamedMessage(
+                            m_NetworkManager.LocalClientId,
+                            new FastBufferReader(messageBuffer, Allocator.None),
+                            0
+                        );
+                    }
+                }
+            }
             var message = new UnnamedMessage
             {
                 SendData = messageBuffer
@@ -92,6 +107,18 @@ namespace Unity.Netcode
         /// <param name="networkDelivery">The delivery type (QoS) to send data with</param>
         public void SendUnnamedMessage(ulong clientId, FastBufferWriter messageBuffer, NetworkDelivery networkDelivery = NetworkDelivery.ReliableSequenced)
         {
+            if (m_NetworkManager.IsHost)
+            {
+                if (clientId == m_NetworkManager.LocalClientId)
+                {
+                    InvokeUnnamedMessage(
+                        m_NetworkManager.LocalClientId,
+                        new FastBufferReader(messageBuffer, Allocator.None),
+                        0
+                    );
+                    return;
+                }
+            }
             var message = new UnnamedMessage
             {
                 SendData = messageBuffer
@@ -220,6 +247,20 @@ namespace Unity.Netcode
                     hash = XXHash.Hash64(messageName);
                     break;
             }
+            if (m_NetworkManager.IsHost)
+            {
+                if (clientId == m_NetworkManager.LocalClientId)
+                {
+                    InvokeNamedMessage(
+                        hash,
+                        m_NetworkManager.LocalClientId,
+                        new FastBufferReader(messageStream, Allocator.None),
+                        0
+                    );
+
+                    return;
+                }
+            }
 
             var message = new NamedMessage
             {
@@ -251,7 +292,7 @@ namespace Unity.Netcode
 
             if (clientIds == null)
             {
-                throw new ArgumentNullException("You must pass in a valid clientId List");
+                throw new ArgumentNullException(nameof(clientIds), "You must pass in a valid clientId List");
             }
 
             ulong hash = 0;
@@ -264,6 +305,21 @@ namespace Unity.Netcode
                     hash = XXHash.Hash64(messageName);
                     break;
             }
+            if (m_NetworkManager.IsHost)
+            {
+                for (var i = 0; i < clientIds.Count; ++i)
+                {
+                    if (clientIds[i] == m_NetworkManager.LocalClientId)
+                    {
+                        InvokeNamedMessage(
+                            hash,
+                            m_NetworkManager.LocalClientId,
+                            new FastBufferReader(messageStream, Allocator.None),
+                            0
+                        );
+                    }
+                }
+            }
             var message = new NamedMessage
             {
                 Hash = hash,

Runtime/Messaging/DisconnectReasonMessage.cs

@@ -0,0 +1,50 @@
+namespace Unity.Netcode
+{
+    internal struct DisconnectReasonMessage : INetworkMessage
+    {
+        public string Reason;
+
+        public int Version => 0;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
+        {
+            string reasonSent = Reason;
+            if (reasonSent == null)
+            {
+                reasonSent = string.Empty;
+            }
+
+            // Since we don't send a ConnectionApprovedMessage, the version for this message is encded with the message
+            // itself. However, note that we HAVE received a ConnectionRequestMessage, so we DO have a valid targetVersion
+            // on this side of things - we just have to make sure the receiving side knows what version we sent it,
+            // since whoever has the higher version number is responsible for versioning and they may be the one
+            // with the higher version number.
+            BytePacker.WriteValueBitPacked(writer, Version);
+
+            if (writer.TryBeginWrite(FastBufferWriter.GetWriteSize(reasonSent)))
+            {
+                writer.WriteValue(reasonSent);
+            }
+            else
+            {
+                writer.WriteValueSafe(string.Empty);
+                NetworkLog.LogWarning(
+                    "Disconnect reason didn't fit. Disconnected without sending a reason. Consider shortening the reason string.");
+            }
+        }
+
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+        {
+            // Since we don't get a ConnectionApprovedMessage, the version for this message is encded with the message
+            // itself. This will override what we got from MessagingSystem... which will always be 0 here.
+            ByteUnpacker.ReadValueBitPacked(reader, out receivedMessageVersion);
+            reader.ReadValueSafe(out Reason);
+            return true;
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            ((NetworkManager)context.SystemOwner).DisconnectReason = Reason;
+        }
+    };
+}

Runtime/Messaging/DisconnectReasonMessage.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d7742516058394f96999464f3ea32c71
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Messaging/INetworkMessage.cs

@@ -40,8 +40,9 @@ namespace Unity.Netcode
     /// </summary>
     internal interface INetworkMessage
     {
-        void Serialize(FastBufferWriter writer);
+        void Serialize(FastBufferWriter writer, int targetVersion);
-        bool Deserialize(FastBufferReader reader, ref NetworkContext context);
+        bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion);
         void Handle(ref NetworkContext context);
+        int Version { get; }
     }
 }

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -2,22 +2,26 @@ namespace Unity.Netcode
 {
     internal struct ChangeOwnershipMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public ulong OwnerClientId;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, OwnerClientId);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
                 return false;
             }
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
             {
                 networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);

Runtime/Messaging/Messages/ConnectionApprovedMessage.cs

@@ -1,10 +1,12 @@
-using System;
 using System.Collections.Generic;
+using Unity.Collections;
 
 namespace Unity.Netcode
 {
     internal struct ConnectionApprovedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong OwnerClientId;
         public int NetworkTick;
 
@@ -13,14 +15,26 @@ namespace Unity.Netcode
 
         private FastBufferReader m_ReceivedSceneObjectData;
 
-        public void Serialize(FastBufferWriter writer)
+        public NativeArray<MessageVersionData> MessageVersions;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            if (!writer.TryBeginWrite(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            BytePacker.WriteValueBitPacked(writer, MessageVersions.Length);
+            foreach (var messageVersion in MessageVersions)
             {
-                throw new OverflowException($"Not enough space in the write buffer to serialize {nameof(ConnectionApprovedMessage)}");
+                messageVersion.Serialize(writer);
             }
-            writer.WriteValue(OwnerClientId);
+            // ============================================================
-            writer.WriteValue(NetworkTick);
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            BytePacker.WriteValueBitPacked(writer, OwnerClientId);
+            BytePacker.WriteValueBitPacked(writer, NetworkTick);
 
             uint sceneObjectCount = 0;
             if (SpawnedObjectsList != null)
@@ -39,17 +53,19 @@ namespace Unity.Netcode
                         ++sceneObjectCount;
                     }
                 }
+
                 writer.Seek(pos);
-                writer.WriteValue(sceneObjectCount);
+                // Can't pack this value because its space is reserved, so it needs to always use all the reserved space.
+                writer.WriteValueSafe(sceneObjectCount);
                 writer.Seek(writer.Length);
             }
             else
             {
-                writer.WriteValue(sceneObjectCount);
+                writer.WriteValueSafe(sceneObjectCount);
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -57,13 +73,36 @@ namespace Unity.Netcode
                 return false;
             }
 
-            if (!reader.TryBeginRead(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            ByteUnpacker.ReadValueBitPacked(reader, out int length);
+            var messageHashesInOrder = new NativeArray<uint>(length, Allocator.Temp);
+            for (var i = 0; i < length; ++i)
             {
-                throw new OverflowException($"Not enough space in the buffer to read {nameof(ConnectionApprovedMessage)}");
+                var messageVersion = new MessageVersionData();
-            }
+                messageVersion.Deserialize(reader);
+                networkManager.MessagingSystem.SetVersion(context.SenderId, messageVersion.Hash, messageVersion.Version);
+                messageHashesInOrder[i] = messageVersion.Hash;
 
-            reader.ReadValue(out OwnerClientId);
+                // Update the received version since this message will always be passed version 0, due to the map not
-            reader.ReadValue(out NetworkTick);
+                // being initialized until just now.
+                var messageType = networkManager.MessagingSystem.GetMessageForHash(messageVersion.Hash);
+                if (messageType == typeof(ConnectionApprovedMessage))
+                {
+                    receivedMessageVersion = messageVersion.Version;
+                }
+            }
+            networkManager.MessagingSystem.SetServerMessageOrder(messageHashesInOrder);
+            messageHashesInOrder.Dispose();
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkTick);
             m_ReceivedSceneObjectData = reader;
             return true;
         }
@@ -85,7 +124,7 @@ namespace Unity.Netcode
             if (!networkManager.NetworkConfig.EnableSceneManagement)
             {
                 networkManager.SpawnManager.DestroySceneObjects();
-                m_ReceivedSceneObjectData.ReadValue(out uint sceneObjectCount);
+                m_ReceivedSceneObjectData.ReadValueSafe(out uint sceneObjectCount);
 
                 // Deserializing NetworkVariable data is deferred from Receive() to Handle to avoid needing
                 // to create a list to hold the data. This is a breach of convention for performance reasons.

Runtime/Messaging/Messages/ConnectionRequestMessage.cs

@@ -1,15 +1,35 @@
+using Unity.Collections;
+
 namespace Unity.Netcode
 {
     internal struct ConnectionRequestMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong ConfigHash;
 
         public byte[] ConnectionData;
 
         public bool ShouldSendConnectionData;
 
-        public void Serialize(FastBufferWriter writer)
+        public NativeArray<MessageVersionData> MessageVersions;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            BytePacker.WriteValueBitPacked(writer, MessageVersions.Length);
+            foreach (var messageVersion in MessageVersions)
+            {
+                messageVersion.Serialize(writer);
+            }
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
             if (ShouldSendConnectionData)
             {
                 writer.WriteValueSafe(ConfigHash);
@@ -21,7 +41,7 @@ namespace Unity.Netcode
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsServer)
@@ -29,6 +49,30 @@ namespace Unity.Netcode
                 return false;
             }
 
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            ByteUnpacker.ReadValueBitPacked(reader, out int length);
+            for (var i = 0; i < length; ++i)
+            {
+                var messageVersion = new MessageVersionData();
+                messageVersion.Deserialize(reader);
+                networkManager.MessagingSystem.SetVersion(context.SenderId, messageVersion.Hash, messageVersion.Version);
+
+                // Update the received version since this message will always be passed version 0, due to the map not
+                // being initialized until just now.
+                var messageType = networkManager.MessagingSystem.GetMessageForHash(messageVersion.Hash);
+                if (messageType == typeof(ConnectionRequestMessage))
+                {
+                    receivedMessageVersion = messageVersion.Version;
+                }
+            }
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
             if (networkManager.NetworkConfig.ConnectionApproval)
             {
                 if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(ConfigHash) + FastBufferWriter.GetWriteSize<int>()))

Runtime/Messaging/Messages/CreateObjectMessage.cs

@@ -2,15 +2,17 @@ namespace Unity.Netcode
 {
     internal struct CreateObjectMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public NetworkObject.SceneObject ObjectInfo;
         private FastBufferReader m_ReceivedNetworkVariableData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             ObjectInfo.Serialize(writer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -21,7 +23,7 @@ namespace Unity.Netcode
             ObjectInfo.Deserialize(reader);
             if (!networkManager.NetworkConfig.ForceSamePrefabs && !networkManager.SpawnManager.HasPrefab(ObjectInfo))
             {
-                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnAddPrefab, ObjectInfo.Header.Hash, reader, ref context);
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnAddPrefab, ObjectInfo.Hash, reader, ref context);
                 return false;
             }
             m_ReceivedNetworkVariableData = reader;

Runtime/Messaging/Messages/DestroyObjectMessage.cs

@@ -2,15 +2,18 @@ namespace Unity.Netcode
 {
     internal struct DestroyObjectMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public bool DestroyGameObject;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            writer.WriteValueSafe(DestroyGameObject);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -18,7 +21,8 @@ namespace Unity.Netcode
                 return false;
             }
 
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            reader.ReadValueSafe(out DestroyGameObject);
 
             if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
             {

Runtime/Messaging/Messages/MessageMetadata.cs

@@ -0,0 +1,23 @@
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Conveys a version number on a remote node for the given message (identified by its hash)
+    /// </summary>
+    internal struct MessageVersionData
+    {
+        public uint Hash;
+        public int Version;
+
+        public void Serialize(FastBufferWriter writer)
+        {
+            writer.WriteValueSafe(Hash);
+            BytePacker.WriteValueBitPacked(writer, Version);
+        }
+
+        public void Deserialize(FastBufferReader reader)
+        {
+            reader.ReadValueSafe(out Hash);
+            ByteUnpacker.ReadValueBitPacked(reader, out Version);
+        }
+    }
+}

Runtime/Messaging/Messages/MessageMetadata.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 754d727b316b4263a2fa0d4c54fdad52
+timeCreated: 1666895514

Runtime/Messaging/Messages/NamedMessage.cs

@@ -2,18 +2,20 @@ namespace Unity.Netcode
 {
     internal struct NamedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong Hash;
         public FastBufferWriter SendData;
 
         private FastBufferReader m_ReceiveData;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteValueSafe(Hash);
             writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             reader.ReadValueSafe(out Hash);
             m_ReceiveData = reader;

Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

@@ -12,6 +12,8 @@ namespace Unity.Netcode
     /// </summary>
     internal struct NetworkVariableDeltaMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public ushort NetworkBehaviourIndex;
 
@@ -21,15 +23,15 @@ namespace Unity.Netcode
 
         private FastBufferReader m_ReceivedNetworkVariableData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
             {
                 throw new OverflowException($"Not enough space in the buffer to write {nameof(NetworkVariableDeltaMessage)}");
             }
 
-            writer.WriteValue(NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
-            writer.WriteValue(NetworkBehaviourIndex);
+            BytePacker.WriteValueBitPacked(writer, NetworkBehaviourIndex);
 
             for (int i = 0; i < NetworkBehaviour.NetworkVariableFields.Count; i++)
             {
@@ -38,7 +40,7 @@ namespace Unity.Netcode
                     // This var does not belong to the currently iterating delivery group.
                     if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
-                        writer.WriteValueSafe((ushort)0);
+                        BytePacker.WriteValueBitPacked(writer, (ushort)0);
                     }
                     else
                     {
@@ -62,11 +64,21 @@ namespace Unity.Netcode
                     shouldWrite = false;
                 }
 
+                // The object containing the behaviour we're about to process is about to be shown to this client
+                // As a result, the client will get the fully serialized NetworkVariable and would be confused by
+                // an extraneous delta
+                if (NetworkBehaviour.NetworkManager.ObjectsToShowToClient.ContainsKey(TargetClientId) &&
+                    NetworkBehaviour.NetworkManager.ObjectsToShowToClient[TargetClientId]
+                    .Contains(NetworkBehaviour.NetworkObject))
+                {
+                    shouldWrite = false;
+                }
+
                 if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     if (!shouldWrite)
                     {
-                        BytePacker.WriteValueBitPacked(writer, 0);
+                        BytePacker.WriteValueBitPacked(writer, (ushort)0);
                     }
                 }
                 else
@@ -94,12 +106,6 @@ namespace Unity.Netcode
                         networkVariable.WriteDelta(writer);
                     }
 
-                    if (!NetworkBehaviour.NetworkVariableIndexesToResetSet.Contains(i))
-                    {
-                        NetworkBehaviour.NetworkVariableIndexesToResetSet.Add(i);
-                        NetworkBehaviour.NetworkVariableIndexesToReset.Add(i);
-                    }
-
                     NetworkBehaviour.NetworkManager.NetworkMetrics.TrackNetworkVariableDeltaSent(
                         TargetClientId,
                         NetworkBehaviour.NetworkObject,
@@ -110,15 +116,10 @@ namespace Unity.Netcode
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
-            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
-            {
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkBehaviourIndex);
-                throw new OverflowException($"Not enough data in the buffer to read {nameof(NetworkVariableDeltaMessage)}");
-            }
-
-            reader.ReadValue(out NetworkObjectId);
-            reader.ReadValue(out NetworkBehaviourIndex);
 
             m_ReceivedNetworkVariableData = reader;
 

Runtime/Messaging/Messages/OrderingMessage.cs

@@ -1,50 +0,0 @@
-using System;
-
-namespace Unity.Netcode
-{
-    /// <summary>
-    /// Upon connecting, the host sends a series of OrderingMessage to the client so that it can make sure both sides
-    /// have the same message types in the same positions in
-    /// - MessagingSystem.m_MessageHandlers
-    /// - MessagingSystem.m_ReverseTypeMap
-    /// even if one side has extra messages (compilation, version, patch, or platform differences, etc...)
-    ///
-    /// The ConnectionRequestedMessage, ConnectionApprovedMessage and OrderingMessage are prioritized at the beginning
-    /// of the mapping, to guarantee they can be exchanged before the two sides share their ordering
-    /// The sorting used in also stable so that even if MessageType names share hashes, it will work most of the time
-    /// </summary>
-    internal struct OrderingMessage : INetworkMessage
-    {
-        public int Order;
-        public uint Hash;
-
-        public void Serialize(FastBufferWriter writer)
-        {
-            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(Order) + FastBufferWriter.GetWriteSize(Hash)))
-            {
-                throw new OverflowException($"Not enough space in the buffer to write {nameof(OrderingMessage)}");
-            }
-
-            writer.WriteValue(Order);
-            writer.WriteValue(Hash);
-        }
-
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
-        {
-            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(Order) + FastBufferWriter.GetWriteSize(Hash)))
-            {
-                throw new OverflowException($"Not enough data in the buffer to read {nameof(OrderingMessage)}");
-            }
-
-            reader.ReadValue(out Order);
-            reader.ReadValue(out Hash);
-
-            return true;
-        }
-
-        public void Handle(ref NetworkContext context)
-        {
-            ((NetworkManager)context.SystemOwner).MessagingSystem.ReorderMessage(Order, Hash);
-        }
-    }
-}

Runtime/Messaging/Messages/ParentSyncMessage.cs

@@ -4,18 +4,34 @@ namespace Unity.Netcode
 {
     internal struct ParentSyncMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
 
-        public bool WorldPositionStays;
+        private byte m_BitField;
+
+        public bool WorldPositionStays
+        {
+            get => ByteUtility.GetBit(m_BitField, 0);
+            set => ByteUtility.SetBit(ref m_BitField, 0, value);
+        }
 
         //If(Metadata.IsReparented)
-        public bool IsLatestParentSet;
+        public bool IsLatestParentSet
+        {
+            get => ByteUtility.GetBit(m_BitField, 1);
+            set => ByteUtility.SetBit(ref m_BitField, 1, value);
+        }
 
         //If(IsLatestParentSet)
         public ulong? LatestParent;
 
         // Is set when the parent should be removed (similar to IsReparented functionality but only for removing the parent)
-        public bool RemoveParent;
+        public bool RemoveParent
+        {
+            get => ByteUtility.GetBit(m_BitField, 2);
+            set => ByteUtility.SetBit(ref m_BitField, 2, value);
+        }
 
         // These additional properties are used to synchronize clients with the current position,
         // rotation, and scale after parenting/de-parenting (world/local space relative). This
@@ -25,18 +41,15 @@ namespace Unity.Netcode
         public Quaternion Rotation;
         public Vector3 Scale;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            BytePacker.WriteValuePacked(writer, NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
-            writer.WriteValueSafe(RemoveParent);
+            writer.WriteValueSafe(m_BitField);
-            writer.WriteValueSafe(WorldPositionStays);
             if (!RemoveParent)
             {
-                writer.WriteValueSafe(IsLatestParentSet);
-
                 if (IsLatestParentSet)
                 {
-                    BytePacker.WriteValueBitPacked(writer, (ulong)LatestParent);
+                    BytePacker.WriteValueBitPacked(writer, LatestParent.Value);
                 }
             }
 
@@ -46,7 +59,7 @@ namespace Unity.Netcode
             writer.WriteValueSafe(Scale);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -54,13 +67,10 @@ namespace Unity.Netcode
                 return false;
             }
 
-            ByteUnpacker.ReadValuePacked(reader, out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
-            reader.ReadValueSafe(out RemoveParent);
+            reader.ReadValueSafe(out m_BitField);
-            reader.ReadValueSafe(out WorldPositionStays);
             if (!RemoveParent)
             {
-                reader.ReadValueSafe(out IsLatestParentSet);
-
                 if (IsLatestParentSet)
                 {
                     ByteUnpacker.ReadValueBitPacked(reader, out ulong latestParent);

Runtime/Messaging/Messages/RpcMessages.cs

@@ -8,24 +8,17 @@ namespace Unity.Netcode
     {
         public static unsafe void Serialize(ref FastBufferWriter writer, ref RpcMetadata metadata, ref FastBufferWriter payload)
         {
-            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize<RpcMetadata>() + payload.Length))
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkObjectId);
-            {
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkBehaviourId);
-                throw new OverflowException("Not enough space in the buffer to store RPC data.");
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkRpcMethodId);
-            }
+            writer.WriteBytesSafe(payload.GetUnsafePtr(), payload.Length);
-
-            writer.WriteValue(metadata);
-            writer.WriteBytes(payload.GetUnsafePtr(), payload.Length);
         }
 
         public static unsafe bool Deserialize(ref FastBufferReader reader, ref NetworkContext context, ref RpcMetadata metadata, ref FastBufferReader payload)
         {
-            int metadataSize = FastBufferWriter.GetWriteSize<RpcMetadata>();
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkObjectId);
-            if (!reader.TryBeginRead(metadataSize))
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkBehaviourId);
-            {
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkRpcMethodId);
-                throw new InvalidOperationException("Not enough data in the buffer to read RPC meta.");
-            }
-
-            reader.ReadValue(out metadata);
 
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(metadata.NetworkObjectId))
@@ -46,7 +39,7 @@ namespace Unity.Netcode
                 return false;
             }
 
-            payload = new FastBufferReader(reader.GetUnsafePtr() + metadataSize, Allocator.None, reader.Length - metadataSize);
+            payload = new FastBufferReader(reader.GetUnsafePtrAtCurrentPosition(), Allocator.None, reader.Length - reader.Position);
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(metadata.NetworkRpcMethodId, out var rpcMethodName))
@@ -92,17 +85,19 @@ namespace Unity.Netcode
 
     internal struct ServerRpcMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public RpcMetadata Metadata;
 
         public FastBufferWriter WriteBuffer;
         public FastBufferReader ReadBuffer;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
         }
 
-        public unsafe bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public unsafe bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
         }
@@ -125,17 +120,19 @@ namespace Unity.Netcode
 
     internal struct ClientRpcMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public RpcMetadata Metadata;
 
         public FastBufferWriter WriteBuffer;
         public FastBufferReader ReadBuffer;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
         }

Runtime/Messaging/Messages/SceneEventMessage.cs

@@ -4,16 +4,18 @@ namespace Unity.Netcode
     // like most of the other messages when we have some more time and can come back and refactor this.
     internal struct SceneEventMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public SceneEventData EventData;
 
         private FastBufferReader m_ReceivedData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             EventData.Serialize(writer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             m_ReceivedData = reader;
             return true;

Runtime/Messaging/Messages/ServerLogMessage.cs

@@ -2,6 +2,8 @@ namespace Unity.Netcode
 {
     internal struct ServerLogMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public NetworkLog.LogType LogType;
         // It'd be lovely to be able to replace this with FixedString or NativeArray...
         // But it's not really practical. On the sending side, the user is likely to want
@@ -11,13 +13,13 @@ namespace Unity.Netcode
         public string Message;
 
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteValueSafe(LogType);
             BytePacker.WriteValuePacked(writer, Message);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (networkManager.IsServer && networkManager.NetworkConfig.EnableNetworkLogs)

Runtime/Messaging/Messages/TimeSyncMessage.cs

@@ -2,21 +2,23 @@ namespace Unity.Netcode
 {
     internal struct TimeSyncMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public int Tick;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, Tick);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
                 return false;
             }
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out Tick);
             return true;
         }
 

Runtime/Messaging/Messages/UnnamedMessage.cs

@@ -2,15 +2,17 @@ namespace Unity.Netcode
 {
     internal struct UnnamedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public FastBufferWriter SendData;
         private FastBufferReader m_ReceivedData;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             m_ReceivedData = reader;
             return true;

Runtime/Messaging/MessagingSystem.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
+using System.Text;
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using UnityEngine;
@@ -41,11 +42,12 @@ namespace Unity.Netcode
             {
                 Writer = new FastBufferWriter(writerSize, writerAllocator, maxWriterSize);
                 NetworkDelivery = delivery;
-                BatchHeader = default;
+                BatchHeader = new BatchHeader { Magic = BatchHeader.MagicValue };
             }
         }
 
         internal delegate void MessageHandler(FastBufferReader reader, ref NetworkContext context, MessagingSystem system);
+        internal delegate int VersionGetter();
 
         private NativeList<ReceiveQueueItem> m_IncomingMessageQueue = new NativeList<ReceiveQueueItem>(16, Allocator.Persistent);
 
@@ -56,6 +58,11 @@ namespace Unity.Netcode
         private Dictionary<Type, uint> m_MessageTypes = new Dictionary<Type, uint>();
         private Dictionary<ulong, NativeList<SendQueueItem>> m_SendQueues = new Dictionary<ulong, NativeList<SendQueueItem>>();
 
+        // This is m_PerClientMessageVersion[clientId][messageType] = version
+        private Dictionary<ulong, Dictionary<Type, int>> m_PerClientMessageVersions = new Dictionary<ulong, Dictionary<Type, int>>();
+        private Dictionary<uint, Type> m_MessagesByHash = new Dictionary<uint, Type>();
+        private Dictionary<Type, int> m_LocalVersions = new Dictionary<Type, int>();
+
         private List<INetworkHooks> m_Hooks = new List<INetworkHooks>();
 
         private uint m_HighMessageType;
@@ -74,12 +81,13 @@ namespace Unity.Netcode
         }
 
         public const int NON_FRAGMENTED_MESSAGE_MAX_SIZE = 1300;
-        public const int FRAGMENTED_MESSAGE_MAX_SIZE = BytePacker.BitPackedIntMax;
+        public const int FRAGMENTED_MESSAGE_MAX_SIZE = int.MaxValue;
 
         internal struct MessageWithHandler
         {
             public Type MessageType;
             public MessageHandler Handler;
+            public VersionGetter GetVersion;
         }
 
         internal List<MessageWithHandler> PrioritizeMessageOrder(List<MessageWithHandler> allowedTypes)
@@ -90,9 +98,8 @@ namespace Unity.Netcode
             // Those are the messages that must be delivered in order to allow re-ordering the others later
             foreach (var t in allowedTypes)
             {
-                if (t.MessageType.FullName == "Unity.Netcode.ConnectionRequestMessage" ||
+                if (t.MessageType.FullName == typeof(ConnectionRequestMessage).FullName ||
-                    t.MessageType.FullName == "Unity.Netcode.ConnectionApprovedMessage" ||
+                    t.MessageType.FullName == typeof(ConnectionApprovedMessage).FullName)
-                    t.MessageType.FullName == "Unity.Netcode.OrderingMessage")
                 {
                     prioritizedTypes.Add(t);
                 }
@@ -100,9 +107,8 @@ namespace Unity.Netcode
 
             foreach (var t in allowedTypes)
             {
-                if (t.MessageType.FullName != "Unity.Netcode.ConnectionRequestMessage" &&
+                if (t.MessageType.FullName != typeof(ConnectionRequestMessage).FullName &&
-                    t.MessageType.FullName != "Unity.Netcode.ConnectionApprovedMessage" &&
+                    t.MessageType.FullName != typeof(ConnectionApprovedMessage).FullName)
-                    t.MessageType.FullName != "Unity.Netcode.OrderingMessage")
                 {
                     prioritizedTypes.Add(t);
                 }
@@ -189,7 +195,25 @@ namespace Unity.Netcode
 
             m_MessageHandlers[m_HighMessageType] = messageWithHandler.Handler;
             m_ReverseTypeMap[m_HighMessageType] = messageWithHandler.MessageType;
+            m_MessagesByHash[XXHash.Hash32(messageWithHandler.MessageType.FullName)] = messageWithHandler.MessageType;
             m_MessageTypes[messageWithHandler.MessageType] = m_HighMessageType++;
+            m_LocalVersions[messageWithHandler.MessageType] = messageWithHandler.GetVersion();
+        }
+
+        public int GetLocalVersion(Type messageType)
+        {
+            return m_LocalVersions[messageType];
+        }
+
+        internal static string ByteArrayToString(byte[] ba, int offset, int count)
+        {
+            var hex = new StringBuilder(ba.Length * 2);
+            for (int i = offset; i < offset + count; ++i)
+            {
+                hex.AppendFormat("{0:x2} ", ba[i]);
+            }
+
+            return hex.ToString();
         }
 
         internal void HandleIncomingData(ulong clientId, ArraySegment<byte> data, float receiveTime)
@@ -202,18 +226,38 @@ namespace Unity.Netcode
                         new FastBufferReader(nativeData + data.Offset, Allocator.None, data.Count);
                     if (!batchReader.TryBeginRead(sizeof(BatchHeader)))
                     {
-                        NetworkLog.LogWarning("Received a packet too small to contain a BatchHeader. Ignoring it.");
+                        NetworkLog.LogError("Received a packet too small to contain a BatchHeader. Ignoring it.");
                         return;
                     }
 
                     batchReader.ReadValue(out BatchHeader batchHeader);
 
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    if (batchHeader.Magic != BatchHeader.MagicValue)
                     {
-                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        NetworkLog.LogError($"Received a packet with an invalid Magic Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
                     }
 
-                    for (var messageIdx = 0; messageIdx < batchHeader.BatchSize; ++messageIdx)
+                    if (batchHeader.BatchSize != data.Count)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Batch Size Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Expected Size: {batchHeader.BatchSize}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    var hash = XXHash.Hash64(batchReader.GetUnsafePtrAtCurrentPosition(), batchReader.Length - batchReader.Position);
+
+                    if (hash != batchHeader.BatchHash)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Hash Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Received Hash: {batchHeader.BatchHash}, Calculated Hash: {hash}, Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    {
+                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
+                    }
+
+                    for (var messageIdx = 0; messageIdx < batchHeader.BatchCount; ++messageIdx)
                     {
 
                         var messageHeader = new MessageHeader();
@@ -225,7 +269,7 @@ namespace Unity.Netcode
                         }
                         catch (OverflowException)
                         {
-                            NetworkLog.LogWarning("Received a batch that didn't have enough data for all of its batches, ending early!");
+                            NetworkLog.LogError("Received a batch that didn't have enough data for all of its batches, ending early!");
                             throw;
                         }
 
@@ -233,7 +277,7 @@ namespace Unity.Netcode
 
                         if (!batchReader.TryBeginRead((int)messageHeader.MessageSize))
                         {
-                            NetworkLog.LogWarning("Received a message that claimed a size larger than the packet, ending early!");
+                            NetworkLog.LogError("Received a message that claimed a size larger than the packet, ending early!");
                             return;
                         }
                         m_IncomingMessageQueue.Add(new ReceiveQueueItem
@@ -251,7 +295,7 @@ namespace Unity.Netcode
                     }
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
                     }
                 }
             }
@@ -270,68 +314,53 @@ namespace Unity.Netcode
             return true;
         }
 
-        // Moves the handler for the type having hash `targetHash` to the `desiredOrder` position, in the handler list
+        internal Type GetMessageForHash(uint messageHash)
-        // This allows the server to tell the client which id it is using for which message and make sure the right
-        // message is used when deserializing.
-        internal void ReorderMessage(int desiredOrder, uint targetHash)
         {
-            if (desiredOrder < 0)
+            if (!m_MessagesByHash.ContainsKey(messageHash))
             {
-                throw new ArgumentException("ReorderMessage desiredOrder must be positive");
+                return null;
+            }
+            return m_MessagesByHash[messageHash];
         }
 
-            if (desiredOrder < m_ReverseTypeMap.Length &&
+        internal void SetVersion(ulong clientId, uint messageHash, int version)
-                XXHash.Hash32(m_ReverseTypeMap[desiredOrder].FullName) == targetHash)
+        {
+            if (!m_MessagesByHash.ContainsKey(messageHash))
             {
-                // matching positions and hashes. All good.
                 return;
             }
+            var messageType = m_MessagesByHash[messageHash];
 
-            Debug.Log($"Unexpected hash for {desiredOrder}");
+            if (!m_PerClientMessageVersions.ContainsKey(clientId))
-
-            // Since the message at `desiredOrder` is not the expected one,
-            // insert an empty placeholder and move the messages down
-            var typesAsList = new List<Type>(m_ReverseTypeMap);
-
-            typesAsList.Insert(desiredOrder, null);
-            var handlersAsList = new List<MessageHandler>(m_MessageHandlers);
-            handlersAsList.Insert(desiredOrder, null);
-
-            // we added a dummy message, bump the end up
-            m_HighMessageType++;
-
-            // Here, we rely on the server telling us about all messages, in order.
-            // So, we know the handlers before desiredOrder are correct.
-            // We start at desiredOrder to not shift them when we insert.
-            int position = desiredOrder;
-            bool found = false;
-            while (position < typesAsList.Count)
             {
-                if (typesAsList[position] != null &&
+                m_PerClientMessageVersions[clientId] = new Dictionary<Type, int>();
-                    XXHash.Hash32(typesAsList[position].FullName) == targetHash)
-                {
-                    found = true;
-                    break;
             }
 
-                position++;
+            m_PerClientMessageVersions[clientId][messageType] = version;
         }
 
-            if (found)
+        internal void SetServerMessageOrder(NativeArray<uint> messagesInIdOrder)
         {
-                // Copy the handler and type to the right index
+            var oldHandlers = m_MessageHandlers;
+            var oldTypes = m_MessageTypes;
+            m_ReverseTypeMap = new Type[messagesInIdOrder.Length];
+            m_MessageHandlers = new MessageHandler[messagesInIdOrder.Length];
+            m_MessageTypes = new Dictionary<Type, uint>();
 
-                typesAsList[desiredOrder] = typesAsList[position];
+            for (var i = 0; i < messagesInIdOrder.Length; ++i)
-                handlersAsList[desiredOrder] = handlersAsList[position];
+            {
-                typesAsList.RemoveAt(position);
+                if (!m_MessagesByHash.ContainsKey(messagesInIdOrder[i]))
-                handlersAsList.RemoveAt(position);
+                {
-
+                    continue;
-                // we removed a copy after moving a message, reduce the high message index
+                }
-                m_HighMessageType--;
+                var messageType = m_MessagesByHash[messagesInIdOrder[i]];
+                var oldId = oldTypes[messageType];
+                var handler = oldHandlers[oldId];
+                var newId = (uint)i;
+                m_MessageTypes[messageType] = newId;
+                m_MessageHandlers[newId] = handler;
+                m_ReverseTypeMap[newId] = messageType;
             }
-
-            m_ReverseTypeMap = typesAsList.ToArray();
-            m_MessageHandlers = handlersAsList.ToArray();
         }
 
         public void HandleMessage(in MessageHeader header, FastBufferReader reader, ulong senderId, float timestamp, int serializedHeaderSize)
@@ -433,7 +462,7 @@ namespace Unity.Netcode
             m_SendQueues.Remove(clientId);
         }
 
-        private unsafe void CleanupDisconnectedClient(ulong clientId)
+        private void CleanupDisconnectedClient(ulong clientId)
         {
             var queue = m_SendQueues[clientId];
             for (var i = 0; i < queue.Length; ++i)
@@ -444,10 +473,67 @@ namespace Unity.Netcode
             queue.Dispose();
         }
 
+        internal void CleanupDisconnectedClients()
+        {
+            var removeList = new NativeList<ulong>(Allocator.Temp);
+            foreach (var clientId in m_PerClientMessageVersions.Keys)
+            {
+                if (!m_SendQueues.ContainsKey(clientId))
+                {
+                    removeList.Add(clientId);
+                }
+            }
+
+            foreach (var clientId in removeList)
+            {
+                m_PerClientMessageVersions.Remove(clientId);
+            }
+        }
+
+        public static int CreateMessageAndGetVersion<T>() where T : INetworkMessage, new()
+        {
+            return new T().Version;
+        }
+
+        internal int GetMessageVersion(Type type, ulong clientId, bool forReceive = false)
+        {
+            if (!m_PerClientMessageVersions.TryGetValue(clientId, out var versionMap))
+            {
+                if (forReceive)
+                {
+                    Debug.LogWarning($"Trying to receive {type.Name} from client {clientId} which is not in a connected state.");
+
+                }
+                else
+                {
+                    Debug.LogWarning($"Trying to send {type.Name} to client {clientId} which is not in a connected state.");
+                }
+                return -1;
+            }
+            if (!versionMap.TryGetValue(type, out var messageVersion))
+            {
+                return -1;
+            }
+
+            return messageVersion;
+        }
+
         public static void ReceiveMessage<T>(FastBufferReader reader, ref NetworkContext context, MessagingSystem system) where T : INetworkMessage, new()
         {
             var message = new T();
-            if (message.Deserialize(reader, ref context))
+            var messageVersion = 0;
+            // Special cases because these are the messages that carry the version info - thus the version info isn't
+            // populated yet when we get these. The first part of these messages always has to be the version data
+            // and can't change.
+            if (typeof(T) != typeof(ConnectionRequestMessage) && typeof(T) != typeof(ConnectionApprovedMessage) && typeof(T) != typeof(DisconnectReasonMessage))
+            {
+                messageVersion = system.GetMessageVersion(typeof(T), context.SenderId, true);
+                if (messageVersion < 0)
+                {
+                    return;
+                }
+            }
+            if (message.Deserialize(reader, ref context, messageVersion))
             {
                 for (var hookIdx = 0; hookIdx < system.m_Hooks.Count; ++hookIdx)
                 {
@@ -485,16 +571,47 @@ namespace Unity.Netcode
                 return 0;
             }
 
+            var largestSerializedSize = 0;
+            var sentMessageVersions = new NativeHashSet<int>(clientIds.Count, Allocator.Temp);
+            for (var i = 0; i < clientIds.Count; ++i)
+            {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+                }
+
+                if (sentMessageVersions.Contains(messageVersion))
+                {
+                    continue;
+                }
+
+                sentMessageVersions.Add(messageVersion);
+
                 var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FRAGMENTED_MESSAGE_MAX_SIZE : NON_FRAGMENTED_MESSAGE_MAX_SIZE;
 
                 using var tmpSerializer = new FastBufferWriter(NON_FRAGMENTED_MESSAGE_MAX_SIZE - FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp, maxSize - FastBufferWriter.GetWriteSize<MessageHeader>());
 
-            message.Serialize(tmpSerializer);
+                message.Serialize(tmpSerializer, messageVersion);
 
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds);
+                var size = SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds, messageVersion);
+                largestSerializedSize = size > largestSerializedSize ? size : largestSerializedSize;
             }
 
-        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds)
+            sentMessageVersions.Dispose();
+
+            return largestSerializedSize;
+        }
+
+        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds, int messageVersionFilter)
             where TMessageType : INetworkMessage
         {
             using var headerSerializer = new FastBufferWriter(FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp);
@@ -509,6 +626,25 @@ namespace Unity.Netcode
 
             for (var i = 0; i < clientIds.Count; ++i)
             {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+
+                    if (messageVersion != messageVersionFilter)
+                    {
+                        continue;
+                    }
+                }
+
                 var clientId = clientIds[i];
 
                 if (!CanSend(clientId, typeof(TMessageType), delivery))
@@ -546,7 +682,7 @@ namespace Unity.Netcode
 
                 writeQueueItem.Writer.WriteBytes(headerSerializer.GetUnsafePtr(), headerSerializer.Length);
                 writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
-                writeQueueItem.BatchHeader.BatchSize++;
+                writeQueueItem.BatchHeader.BatchCount++;
                 for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                 {
                     m_Hooks[hookIdx].OnAfterSendMessage(clientId, ref message, delivery, tmpSerializer.Length + headerSerializer.Length);
@@ -559,8 +695,22 @@ namespace Unity.Netcode
         internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, ulong clientId)
             where TMessageType : INetworkMessage
         {
+            var messageVersion = 0;
+            // Special case because this is the message that carries the version info - thus the version info isn't
+            // populated yet when we get this. The first part of this message always has to be the version data
+            // and can't change.
+            if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+            {
+                messageVersion = GetMessageVersion(typeof(TMessageType), clientId);
+                if (messageVersion < 0)
+                {
+                    // Client doesn't know this message exists, don't send it at all.
+                    return 0;
+                }
+            }
+
             ulong* clientIds = stackalloc ulong[] { clientId };
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
+            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1), messageVersion);
         }
 
         private struct PointerListWrapper<T> : IReadOnlyList<T>
@@ -627,7 +777,7 @@ namespace Unity.Netcode
                 for (var i = 0; i < sendQueueItem.Length; ++i)
                 {
                     ref var queueItem = ref sendQueueItem.ElementAt(i);
-                    if (queueItem.BatchHeader.BatchSize == 0)
+                    if (queueItem.BatchHeader.BatchCount == 0)
                     {
                         queueItem.Writer.Dispose();
                         continue;
@@ -635,23 +785,28 @@ namespace Unity.Netcode
 
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                     }
 
                     queueItem.Writer.Seek(0);
 #if UNITY_EDITOR || DEVELOPMENT_BUILD
                     // Skipping the Verify and sneaking the write mark in because we know it's fine.
-                    queueItem.Writer.Handle->AllowedWriteMark = 2;
+                    queueItem.Writer.Handle->AllowedWriteMark = sizeof(BatchHeader);
 #endif
+                    queueItem.BatchHeader.BatchHash = XXHash.Hash64(queueItem.Writer.GetUnsafePtr() + sizeof(BatchHeader), queueItem.Writer.Length - sizeof(BatchHeader));
+
+                    queueItem.BatchHeader.BatchSize = queueItem.Writer.Length;
+
                     queueItem.Writer.WriteValue(queueItem.BatchHeader);
 
+
                     try
                     {
                         m_MessageSender.Send(clientId, queueItem.NetworkDelivery, queueItem.Writer);
 
                         for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                         {
-                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                         }
                     }
                     finally

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -413,7 +413,7 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public bool Contains(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             return index != -1;
         }
 
@@ -426,7 +426,7 @@ namespace Unity.Netcode
                 throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
             }
 
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             if (index == -1)
             {
                 return false;

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -18,6 +18,11 @@ namespace Unity.Netcode
         /// </summary>
         private protected NetworkBehaviour m_NetworkBehaviour;
 
+        public NetworkBehaviour GetBehaviour()
+        {
+            return m_NetworkBehaviour;
+        }
+
         /// <summary>
         /// Initializes the NetworkVariable
         /// </summary>

Runtime/NetworkVariable/NetworkVariableSerialization.cs

@@ -1,6 +1,8 @@
 using System;
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
+using UnityEditor;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -20,6 +22,96 @@ namespace Unity.Netcode
         public void Read(FastBufferReader reader, ref T value);
     }
 
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class ShortSerializer : INetworkVariableSerializer<short>
+    {
+        public void Write(FastBufferWriter writer, ref short value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref short value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class UshortSerializer : INetworkVariableSerializer<ushort>
+    {
+        public void Write(FastBufferWriter writer, ref ushort value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ushort value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class IntSerializer : INetworkVariableSerializer<int>
+    {
+        public void Write(FastBufferWriter writer, ref int value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref int value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class UintSerializer : INetworkVariableSerializer<uint>
+    {
+        public void Write(FastBufferWriter writer, ref uint value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref uint value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class LongSerializer : INetworkVariableSerializer<long>
+    {
+        public void Write(FastBufferWriter writer, ref long value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref long value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class UlongSerializer : INetworkVariableSerializer<ulong>
+    {
+        public void Write(FastBufferWriter writer, ref ulong value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ulong value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
     /// <summary>
     /// Basic serializer for unmanaged types.
     /// This covers primitives, built-in unity types, and IForceSerializeByMemcpy
@@ -188,6 +280,26 @@ namespace Unity.Netcode
     /// </summary>
     public static class NetworkVariableSerializationTypes
     {
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
+#if UNITY_EDITOR
+        [InitializeOnLoadMethod]
+#endif
+        internal static void InitializeIntegerSerialization()
+        {
+            NetworkVariableSerialization<short>.Serializer = new ShortSerializer();
+            NetworkVariableSerialization<short>.AreEqual = NetworkVariableSerialization<short>.ValueEquals;
+            NetworkVariableSerialization<ushort>.Serializer = new UshortSerializer();
+            NetworkVariableSerialization<ushort>.AreEqual = NetworkVariableSerialization<ushort>.ValueEquals;
+            NetworkVariableSerialization<int>.Serializer = new IntSerializer();
+            NetworkVariableSerialization<int>.AreEqual = NetworkVariableSerialization<int>.ValueEquals;
+            NetworkVariableSerialization<uint>.Serializer = new UintSerializer();
+            NetworkVariableSerialization<uint>.AreEqual = NetworkVariableSerialization<uint>.ValueEquals;
+            NetworkVariableSerialization<long>.Serializer = new LongSerializer();
+            NetworkVariableSerialization<long>.AreEqual = NetworkVariableSerialization<long>.ValueEquals;
+            NetworkVariableSerialization<ulong>.Serializer = new UlongSerializer();
+            NetworkVariableSerialization<ulong>.AreEqual = NetworkVariableSerialization<ulong>.ValueEquals;
+        }
+
         /// <summary>
         /// Registeres an unmanaged type that will be serialized by a direct memcpy into a buffer
         /// </summary>

Runtime/SceneManagement/NetworkSceneManager.cs

@@ -862,16 +862,6 @@ namespace Unity.Netcode
 
             SceneEventProgressTracking.Add(sceneEventProgress.Guid, sceneEventProgress);
 
-            if (!isUnloading)
-            {
-                // The Condition: While a scene is asynchronously loaded in single loading scene mode, if any new NetworkObjects are spawned
-                // they need to be moved into the do not destroy temporary scene
-                // When it is set: Just before starting the asynchronous loading call
-                // When it is unset: After the scene has loaded, the PopulateScenePlacedObjects is called, and all NetworkObjects in the do
-                // not destroy temporary scene are moved into the active scene
-                IsSpawnedObjectsPendingInDontDestroyOnLoad = true;
-            }
-
             m_IsSceneEventActive = true;
 
             // Set our callback delegate handler for completion
@@ -1162,6 +1152,13 @@ namespace Unity.Netcode
 
             if (sceneEventData.LoadSceneMode == LoadSceneMode.Single)
             {
+                // The Condition: While a scene is asynchronously loaded in single loading scene mode, if any new NetworkObjects are spawned
+                // they need to be moved into the do not destroy temporary scene
+                // When it is set: Just before starting the asynchronous loading call
+                // When it is unset: After the scene has loaded, the PopulateScenePlacedObjects is called, and all NetworkObjects in the do
+                // not destroy temporary scene are moved into the active scene
+                IsSpawnedObjectsPendingInDontDestroyOnLoad = true;
+
                 // Destroy current scene objects before switching.
                 m_NetworkManager.SpawnManager.ServerDestroySpawnedSceneObjects();
 
@@ -2018,7 +2015,11 @@ namespace Unity.Netcode
                 ScenePlacedObjects.Clear();
             }
 
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             // Just add every NetworkObject found that isn't already in the list
             // With additive scenes, we can have multiple in-scene placed NetworkObjects with the same GlobalObjectIdHash value

Runtime/SceneManagement/SceneEventData.cs

@@ -269,7 +269,12 @@ namespace Unity.Netcode
         {
             m_DespawnedInSceneObjectsSync.Clear();
             // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) => c.NetworkManager == m_NetworkManager);
+#else
             var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) => c.NetworkManager == m_NetworkManager);
+
+#endif
             foreach (var sobj in inSceneNetworkObjects)
             {
                 if (sobj.IsSceneObject.HasValue && sobj.IsSceneObject.Value && !sobj.IsSpawned)
@@ -380,7 +385,7 @@ namespace Unity.Netcode
             writer.WriteValueSafe(SceneEventType);
 
             // Write the scene loading mode
-            writer.WriteValueSafe(LoadSceneMode);
+            writer.WriteValueSafe((byte)LoadSceneMode);
 
             // Write the scene event progress Guid
             if (SceneEventType != SceneEventType.Synchronize)
@@ -444,13 +449,13 @@ namespace Unity.Netcode
             int totalBytes = 0;
 
             // Write the number of NetworkObjects we are serializing
-            BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync.Count);
+            writer.WriteValueSafe(m_NetworkObjectsSync.Count);
+
             // Serialize all NetworkObjects that are spawned
             for (var i = 0; i < m_NetworkObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
                 var sceneObject = m_NetworkObjectsSync[i].GetMessageSceneObject(TargetClientId);
-                BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync[i].GetSceneOriginHandle());
                 sceneObject.Serialize(writer);
                 var noStop = writer.Position;
                 totalBytes += (int)(noStop - noStart);
@@ -462,8 +467,8 @@ namespace Unity.Netcode
             for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
                 var noStop = writer.Position;
                 totalBytes += (int)(noStop - noStart);
             }
@@ -497,8 +502,6 @@ namespace Unity.Netcode
                 {
                     if (keyValuePairBySceneHandle.Value.Observers.Contains(TargetClientId))
                     {
-                        // Write our server relative scene handle for the NetworkObject being serialized
-                        writer.WriteValueSafe(keyValuePairBySceneHandle.Key);
                         // Serialize the NetworkObject
                         var sceneObject = keyValuePairBySceneHandle.Value.GetMessageSceneObject(TargetClientId);
                         sceneObject.Serialize(writer);
@@ -512,8 +515,8 @@ namespace Unity.Netcode
             // Write the scene handle and GlobalObjectIdHash value
             for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
             {
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
             }
 
             var tailPosition = writer.Position;
@@ -533,7 +536,8 @@ namespace Unity.Netcode
         internal void Deserialize(FastBufferReader reader)
         {
             reader.ReadValueSafe(out SceneEventType);
-            reader.ReadValueSafe(out LoadSceneMode);
+            reader.ReadValueSafe(out byte loadSceneMode);
+            LoadSceneMode = (LoadSceneMode)loadSceneMode;
 
             if (SceneEventType != SceneEventType.Synchronize)
             {
@@ -624,13 +628,15 @@ namespace Unity.Netcode
 
                 for (ushort i = 0; i < newObjectsCount; i++)
                 {
-                    InternalBuffer.ReadValueSafe(out int sceneHandle);
-                    // Set our relative scene to the NetworkObject
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneHandle);
-
-                    // Deserialize the NetworkObject
                     var sceneObject = new NetworkObject.SceneObject();
                     sceneObject.Deserialize(InternalBuffer);
+
+                    if (sceneObject.IsSceneObject)
+                    {
+                        // Set our relative scene to the NetworkObject
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
+
                     NetworkObject.AddSceneObject(sceneObject, InternalBuffer, m_NetworkManager);
                 }
                 // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
@@ -656,7 +662,11 @@ namespace Unity.Netcode
 
             if (networkObjectsToRemove.Length > 0)
             {
+#if UNITY_2023_1_OR_NEWER
+                var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsSortMode.InstanceID);
+#else
                 var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
                 var networkObjectIdToNetworkObject = new Dictionary<ulong, NetworkObject>();
                 foreach (var networkObject in networkObjects)
                 {
@@ -771,8 +781,8 @@ namespace Unity.Netcode
             for (int i = 0; i < despawnedObjectsCount; i++)
             {
                 // We just need to get the scene
-                ByteUnpacker.ReadValuePacked(InternalBuffer, out int networkSceneHandle);
+                InternalBuffer.ReadValueSafe(out int networkSceneHandle);
-                ByteUnpacker.ReadValuePacked(InternalBuffer, out uint globalObjectIdHash);
+                InternalBuffer.ReadValueSafe(out uint globalObjectIdHash);
                 var sceneRelativeNetworkObjects = new Dictionary<uint, NetworkObject>();
                 if (!sceneCache.ContainsKey(networkSceneHandle))
                 {
@@ -784,8 +794,14 @@ namespace Unity.Netcode
                             var objectRelativeScene = m_NetworkManager.SceneManager.ScenesLoaded[localSceneHandle];
 
                             // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) =>
+                            c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#else
                             var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) =>
                             c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#endif
+
 
                             foreach (var inSceneObject in inSceneNetworkObjects)
                             {
@@ -847,26 +863,28 @@ namespace Unity.Netcode
             try
             {
                 // Process all spawned NetworkObjects for this network session
-                ByteUnpacker.ReadValuePacked(InternalBuffer, out int newObjectsCount);
+                InternalBuffer.ReadValueSafe(out int newObjectsCount);
-
-
                 for (int i = 0; i < newObjectsCount; i++)
                 {
-                    // We want to make sure for each NetworkObject we have the appropriate scene selected as the scene that is
-                    // currently being synchronized.  This assures in-scene placed NetworkObjects will use the right NetworkObject
-                    // from the list of populated <see cref="NetworkSceneManager.ScenePlacedObjects"/>
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out int handle);
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(handle);
-
                     var sceneObject = new NetworkObject.SceneObject();
                     sceneObject.Deserialize(InternalBuffer);
 
+                    // If the sceneObject is in-scene placed, then set the scene being synchronized
+                    if (sceneObject.IsSceneObject)
+                    {
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
                     var spawnedNetworkObject = NetworkObject.AddSceneObject(sceneObject, InternalBuffer, networkManager);
+
+                    // If we failed to deserialize the NetowrkObject then don't add null to the list
+                    if (spawnedNetworkObject != null)
+                    {
                         if (!m_NetworkObjectsSync.Contains(spawnedNetworkObject))
                         {
                             m_NetworkObjectsSync.Add(spawnedNetworkObject);
                         }
                     }
+                }
 
                 // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
                 DeserializeDespawnedInScenePlacedNetworkObjects();

Runtime/SceneManagement/SceneEventProgress.cs

@@ -108,6 +108,16 @@ namespace Unity.Netcode
         internal List<ulong> GetClientsWithStatus(bool completedSceneEvent)
         {
             var clients = new List<ulong>();
+            if (completedSceneEvent)
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that completed if the AsyncOperation is done.
+                if (m_NetworkManager.IsHost && m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
+
+                // Add all clients that completed the scene event
                 foreach (var clientStatus in ClientsProcessingSceneEvent)
                 {
                     if (clientStatus.Value == completedSceneEvent)
@@ -115,12 +125,20 @@ namespace Unity.Netcode
                         clients.Add(clientStatus.Key);
                     }
                 }
+            }
+            else
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that did not complete if the AsyncOperation is
+                // not done.
+                if (m_NetworkManager.IsHost && !m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
 
                 // If we are getting the list of clients that have not completed the
                 // scene event, then add any clients that disconnected during this
                 // scene event.
-            if (!completedSceneEvent)
-            {
                 clients.AddRange(ClientsThatDisconnected);
             }
             return clients;
@@ -138,6 +156,11 @@ namespace Unity.Netcode
                     // Track the clients that were connected when we started this event
                     foreach (var connectedClientId in networkManager.ConnectedClientsIds)
                     {
+                        // Ignore the host client
+                        if (NetworkManager.ServerClientId == connectedClientId)
+                        {
+                            continue;
+                        }
                         ClientsProcessingSceneEvent.Add(connectedClientId, false);
                     }
 
@@ -218,7 +241,10 @@ namespace Unity.Netcode
             }
 
             // Return the local scene event's AsyncOperation status
-            return m_AsyncOperation.isDone;
+            // Note: Integration tests process scene loading through a queue
+            // and the AsyncOperation could not be assigned for several
+            // network tick periods. Return false if that is the case.
+            return m_AsyncOperation == null ? false : m_AsyncOperation.isDone;
         }
 
         /// <summary>

Runtime/Serialization/BufferSerializer.cs

@@ -7,14 +7,10 @@ namespace Unity.Netcode
     /// <summary>
     /// Two-way serializer wrapping FastBufferReader or FastBufferWriter.
     ///
-    /// Implemented as a ref struct for two reasons:
+    /// Implemented as a ref struct to help enforce the requirement that
-    /// 1. The BufferSerializer cannot outlive the FBR/FBW it wraps or using it will cause a crash
+    /// the BufferSerializer cannot outlive the FBR/FBW it wraps or using it will cause a crash
-    /// 2. The BufferSerializer must always be passed by reference and can't be copied
     ///
-    /// Ref structs help enforce both of those rules: they can't ref live the stack context in which they were
+    /// BufferSerializer doesn't wrap FastBufferReader or FastBufferWriter directly because it can't.
-    /// created, and they're always passed by reference no matter what.
-    ///
-    /// BufferSerializer doesn't wrapp FastBufferReader or FastBufferWriter directly because it can't.
     /// ref structs can't implement interfaces, and in order to be able to have two different implementations with
     /// the same interface (which allows us to avoid an "if(IsReader)" on every call), the thing directly wrapping
     /// the struct has to implement an interface. So IReaderWriter exists as the interface,

Runtime/Serialization/BytePacker.cs

@@ -50,7 +50,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteValuePacked(FastBufferWriter writer, float value)
         {
-            WriteUInt32Packed(writer, ToUint(value));
+            WriteValueBitPacked(writer, ToUint(value));
         }
 
         /// <summary>
@@ -61,7 +61,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteValuePacked(FastBufferWriter writer, double value)
         {
-            WriteUInt64Packed(writer, ToUlong(value));
+            WriteValueBitPacked(writer, ToUlong(value));
         }
 
         /// <summary>
@@ -98,7 +98,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, short value) => WriteUInt32Packed(writer, (ushort)Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, short value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned short (UInt16) as a varint to the buffer.
@@ -109,7 +109,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, ushort value) => WriteUInt32Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, ushort value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write a two-byte character as a varint to the buffer.
@@ -120,7 +120,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="c">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, char c) => WriteUInt32Packed(writer, c);
+        public static void WriteValuePacked(FastBufferWriter writer, char c) => WriteValueBitPacked(writer, c);
 
         /// <summary>
         /// Write a signed int (Int32) as a ZigZag encoded varint to the buffer.
@@ -128,7 +128,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, int value) => WriteUInt32Packed(writer, (uint)Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned int (UInt32) to the buffer.
@@ -136,7 +136,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, uint value) => WriteUInt32Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, uint value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned long (UInt64) to the buffer.
@@ -144,7 +144,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, ulong value) => WriteUInt64Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, ulong value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write a signed long (Int64) as a ZigZag encoded varint to the buffer.
@@ -152,7 +152,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, long value) => WriteUInt64Packed(writer, Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Convenience method that writes two packed Vector3 from the ray to the buffer
@@ -282,231 +282,183 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void WriteValueBitPacked<T>(FastBufferWriter writer, T value) where T: unmanaged => writer.WriteValueSafe(value);
 #else
-
         /// <summary>
-        /// Maximum serializable value for a BitPacked ushort (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const ushort BitPackedUshortMax = (1 << 15) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked short
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const short BitPackedShortMax = (1 << 14) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked ushort
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const short BitPackedShortMin = -(1 << 14);
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked uint (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const uint BitPackedUintMax = (1 << 30) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked int
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const int BitPackedIntMax = (1 << 29) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked int
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const int BitPackedIntMin = -(1 << 29);
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked ulong (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const ulong BitPackedULongMax = (1L << 61) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked long
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const long BitPackedLongMax = (1L << 60) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked long
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const long BitPackedLongMin = -(1L << 60);
 
         /// <summary>
-        /// Writes a 14-bit signed short to the buffer in a bit-encoded packed format.
+        /// Writes a 16-bit signed short to the buffer in a bit-encoded packed format.
-        /// The first bit indicates whether the value is 1 byte or 2.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
-        /// The sign bit takes up another bit.
+        /// are still able to be compressed.
-        /// That leaves 14 bits for the value.
+        /// The first two bits indicate whether the value is 1, 2, or 3 bytes.
-        /// A value greater than 2^14-1 or less than -2^14 will throw an exception in editor and development builds.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its two
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
-        /// most significant bits after zig-zag encoding.
+        /// by the original unmodified 16-bit value in the next 2 bytes.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
         public static void WriteValueBitPacked(FastBufferWriter writer, short value) => WriteValueBitPacked(writer, (ushort)Arithmetic.ZigZagEncode(value));
 
         /// <summary>
-        /// Writes a 15-bit unsigned short to the buffer in a bit-encoded packed format.
+        /// Writes a 16-bit unsigned short to the buffer in a bit-encoded packed format.
-        /// The first bit indicates whether the value is 1 byte or 2.
+        /// The first two bits indicate whether the value is 1, 2, or 3 bytes.
-        /// That leaves 15 bits for the value.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
-        /// A value greater than 2^15-1 will throw an exception in editor and development builds.
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its
+        /// by the original unmodified 16-bit value in the next 2 bytes.
-        /// most significant bit.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
         public static void WriteValueBitPacked(FastBufferWriter writer, ushort value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            if (value > (1 << 14) - 1)
-            if (value >= BitPackedUshortMax)
             {
-                throw new ArgumentException("BitPacked ushorts must be <= 15 bits");
+                if (!writer.TryBeginWriteInternal(3))
-            }
-#endif
-
-            if (value <= 0b0111_1111)
-            {
-                if (!writer.TryBeginWriteInternal(1))
                 {
                     throw new OverflowException("Writing past the end of the buffer");
                 }
-                writer.WriteByte((byte)(value << 1));
+                writer.WriteByte(3);
+                writer.WriteValue(value);
                 return;
             }
 
-            if (!writer.TryBeginWriteInternal(2))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteValue((ushort)((value << 1) | 0b1));
-        }
-
-        /// <summary>
-        /// Writes a 29-bit signed int to the buffer in a bit-encoded packed format.
-        /// The first two bits indicate whether the value is 1, 2, 3, or 4 bytes.
-        /// The sign bit takes up another bit.
-        /// That leaves 29 bits for the value.
-        /// A value greater than 2^29-1 or less than -2^29 will throw an exception in editor and development builds.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its three
-        /// most significant bits after zig-zag encoding.
-        /// </summary>
-        /// <param name="writer">The writer to write to</param>
-        /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, (uint)Arithmetic.ZigZagEncode(value));
-
-        /// <summary>
-        /// Writes a 30-bit unsigned int to the buffer in a bit-encoded packed format.
-        /// The first two bits indicate whether the value is 1, 2, 3, or 4 bytes.
-        /// That leaves 30 bits for the value.
-        /// A value greater than 2^30-1 will throw an exception in editor and development builds.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its two
-        /// most significant bits.
-        /// </summary>
-        /// <param name="writer">The writer to write to</param>
-        /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
-        {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value > BitPackedUintMax)
-            {
-                throw new ArgumentException("BitPacked uints must be <= 30 bits");
-            }
-#endif
             value <<= 2;
             var numBytes = BitCounter.GetUsedByteCount(value);
             if (!writer.TryBeginWriteInternal(numBytes))
             {
                 throw new OverflowException("Writing past the end of the buffer");
             }
-            writer.WritePartialValue(value | (uint)(numBytes - 1), numBytes);
+            writer.WritePartialValue(value | (ushort)(numBytes), numBytes);
         }
 
         /// <summary>
-        /// Writes a 60-bit signed long to the buffer in a bit-encoded packed format.
+        /// Writes a 32-bit signed int to the buffer in a bit-encoded packed format.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
-        /// The sign bit takes up another bit.
+        /// are still able to be compressed.
-        /// That leaves 60 bits for the value.
+        /// The first three bits indicate whether the value is 1, 2, 3, 4, or 5 bytes.
-        /// A value greater than 2^60-1 or less than -2^60 will throw an exception in editor and development builds.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its four
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
-        /// most significant bits after zig-zag encoding.
+        /// by the original unmodified 32-bit value in the next 4 bytes.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, Arithmetic.ZigZagEncode(value));
+        public static void WriteValueBitPacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, (uint)Arithmetic.ZigZagEncode(value));
 
         /// <summary>
-        /// Writes a 61-bit unsigned long to the buffer in a bit-encoded packed format.
+        /// Writes a 32-bit unsigned int to the buffer in a bit-encoded packed format.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
+        /// The first three bits indicate whether the value is 1, 2, 3, 4, or 5 bytes.
-        /// That leaves 31 bits for the value.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
-        /// A value greater than 2^61-1 will throw an exception in editor and development builds.
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its three
+        /// by the original unmodified 32-bit value in the next 4 bytes.
-        /// most significant bits.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, ulong value)
+        public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            if (value > (1 << 29) - 1)
-            if (value > BitPackedULongMax)
             {
-                throw new ArgumentException("BitPacked ulongs must be <= 61 bits");
+                if (!writer.TryBeginWriteInternal(5))
+                {
+                    throw new OverflowException("Writing past the end of the buffer");
                 }
-#endif
+                writer.WriteByte(5);
+                writer.WriteValue(value);
+                return;
+            }
+
             value <<= 3;
             var numBytes = BitCounter.GetUsedByteCount(value);
             if (!writer.TryBeginWriteInternal(numBytes))
             {
                 throw new OverflowException("Writing past the end of the buffer");
             }
-            writer.WritePartialValue(value | (uint)(numBytes - 1), numBytes);
+            writer.WritePartialValue(value | (uint)(numBytes), numBytes);
+        }
+
+        /// <summary>
+        /// Writes a 64-bit signed long to the buffer in a bit-encoded packed format.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
+        /// are still able to be compressed.
+        /// The first four bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, 8, or 9 bytes.
+        /// If the value uses 60 bits or less, the remaining 60 bits contain the value.
+        /// For performance, reasons, if the value is 61 bits or more, there will be four 0 bits, followed
+        /// by the original unmodified 64-bit value in the next 8 bytes.
+        /// </summary>
+        /// <param name="writer">The writer to write to</param>
+        /// <param name="value">The value to pack</param>
+        public static void WriteValueBitPacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, Arithmetic.ZigZagEncode(value));
+
+        /// <summary>
+        /// Writes a 64-bit unsigned long to the buffer in a bit-encoded packed format.
+        /// The first four bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, 8, or 9 bytes.
+        /// If the value uses 60 bits or less, the remaining 60 bits contain the value.
+        /// For performance, reasons, if the value is 61 bits or more, there will be four 0 bits, followed
+        /// by the original unmodified 64-bit value in the next 8 bytes.
+        /// </summary>
+        /// <param name="writer">The writer to write to</param>
+        /// <param name="value">The value to pack</param>
+        public static void WriteValueBitPacked(FastBufferWriter writer, ulong value)
+        {
+            if (value > (1L << 60) - 1)
+            {
+                if (!writer.TryBeginWriteInternal(9))
+                {
+                    throw new OverflowException("Writing past the end of the buffer");
+                }
+                writer.WriteByte(9);
+                writer.WriteValue(value);
+                return;
+            }
+
+            value <<= 4;
+            var numBytes = BitCounter.GetUsedByteCount(value);
+            if (!writer.TryBeginWriteInternal(numBytes))
+            {
+                throw new OverflowException("Writing past the end of the buffer");
+            }
+            writer.WritePartialValue(value | (uint)(numBytes), numBytes);
         }
 #endif
-
-        private static void WriteUInt64Packed(FastBufferWriter writer, ulong value)
-        {
-            if (value <= 240)
-            {
-                writer.WriteByteSafe((byte)value);
-                return;
-            }
-            if (value <= 2287)
-            {
-                writer.WriteByteSafe((byte)(((value - 240) >> 8) + 241));
-                writer.WriteByteSafe((byte)(value - 240));
-                return;
-            }
-            var writeBytes = BitCounter.GetUsedByteCount(value);
-
-            if (!writer.TryBeginWriteInternal(writeBytes + 1))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteByte((byte)(247 + writeBytes));
-            writer.WritePartialValue(value, writeBytes);
-        }
-
-        // Looks like the same code as WriteUInt64Packed?
-        // It's actually different because it will call the more efficient 32-bit version
-        // of BytewiseUtility.GetUsedByteCount().
-        private static void WriteUInt32Packed(FastBufferWriter writer, uint value)
-        {
-            if (value <= 240)
-            {
-                writer.WriteByteSafe((byte)value);
-                return;
-            }
-            if (value <= 2287)
-            {
-                writer.WriteByteSafe((byte)(((value - 240) >> 8) + 241));
-                writer.WriteByteSafe((byte)(value - 240));
-                return;
-            }
-            var writeBytes = BitCounter.GetUsedByteCount(value);
-
-            if (!writer.TryBeginWriteInternal(writeBytes + 1))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteByte((byte)(247 + writeBytes));
-            writer.WritePartialValue(value, writeBytes);
-        }
-
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe uint ToUint<T>(T value) where T : unmanaged
         {

Runtime/Serialization/ByteUnpacker.cs

@@ -11,7 +11,6 @@ namespace Unity.Netcode
     /// </summary>
     public static class ByteUnpacker
     {
-
 #if UNITY_NETCODE_DEBUG_NO_PACKING
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -58,7 +57,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out float value)
         {
-            ReadUInt32Packed(reader, out uint asUInt);
+            ReadValueBitPacked(reader, out uint asUInt);
             value = ToSingle(asUInt);
         }
 
@@ -70,7 +69,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out double value)
         {
-            ReadUInt64Packed(reader, out ulong asULong);
+            ReadValueBitPacked(reader, out ulong asULong);
             value = ToDouble(asULong);
         }
 
@@ -109,11 +108,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out short value)
+        public static void ReadValuePacked(FastBufferReader reader, out short value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (short)Arithmetic.ZigZagDecode(readValue);
-        }
 
         /// <summary>
         /// Read an unsigned short (UInt16) as a varint from the stream.
@@ -121,11 +116,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out ushort value)
+        public static void ReadValuePacked(FastBufferReader reader, out ushort value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (ushort)readValue;
-        }
 
         /// <summary>
         /// Read a two-byte character as a varint from the stream.
@@ -135,7 +126,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out char c)
         {
-            ReadUInt32Packed(reader, out uint readValue);
+            ReadValueBitPacked(reader, out ushort readValue);
             c = (char)readValue;
         }
 
@@ -145,11 +136,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out int value)
+        public static void ReadValuePacked(FastBufferReader reader, out int value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (int)Arithmetic.ZigZagDecode(readValue);
-        }
 
         /// <summary>
         /// Read an unsigned int (UInt32) from the stream.
@@ -157,7 +144,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out uint value) => ReadUInt32Packed(reader, out value);
+        public static void ReadValuePacked(FastBufferReader reader, out uint value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read an unsigned long (UInt64) from the stream.
@@ -165,7 +152,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out ulong value) => ReadUInt64Packed(reader, out value);
+        public static void ReadValuePacked(FastBufferReader reader, out ulong value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read a signed long (Int64) as a ZigZag encoded varint from the stream.
@@ -175,8 +162,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out long value)
         {
-            ReadUInt64Packed(reader, out ulong readValue);
+            ReadValueBitPacked(reader, out value);
-            value = Arithmetic.ZigZagDecode(readValue);
         }
 
         /// <summary>
@@ -341,7 +327,9 @@ namespace Unity.Netcode
             ushort returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b1) + 1;
+            // Mask out the first two bits - they contain the total byte count
+            // (1, 2, or 3)
+            int numBytes = (data[0] & 0b11);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -350,17 +338,23 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
+                case 3:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    value = returnValue;
+                    return;
                 default:
                     throw new InvalidOperationException("Could not read bit-packed value: impossible byte count");
             }
 
-            value = (ushort)(returnValue >> 1);
+            value = (ushort)(returnValue >> 2);
         }
 
         /// <summary>
@@ -386,7 +380,8 @@ namespace Unity.Netcode
             uint returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b11) + 1;
+            // Mask out the first three bits - they contain the total byte count (1-5)
+            int numBytes = (data[0] & 0b111);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -395,26 +390,34 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
                     break;
+                case 5:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    ptr[2] = data[3];
+                    ptr[3] = data[4];
+                    value = returnValue;
+                    return;
             }
 
-            value = returnValue >> 2;
+            value = returnValue >> 3;
         }
 
         /// <summary>
@@ -440,7 +443,8 @@ namespace Unity.Netcode
             ulong returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b111) + 1;
+            // Mask out the first four bits - they contain the total byte count (1-9)
+            int numBytes = (data[0] & 0b1111);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -449,109 +453,74 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
                     break;
                 case 5:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
                     break;
                 case 6:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
                     break;
                 case 7:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
-                    *(ptr + 6) = *(data + 6);
+                    ptr[6] = data[6];
                     break;
                 case 8:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
-                    *(ptr + 6) = *(data + 6);
+                    ptr[6] = data[6];
-                    *(ptr + 7) = *(data + 7);
+                    ptr[7] = data[7];
                     break;
+                case 9:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    ptr[2] = data[3];
+                    ptr[3] = data[4];
+                    ptr[4] = data[5];
+                    ptr[5] = data[6];
+                    ptr[6] = data[7];
+                    ptr[7] = data[8];
+                    value = returnValue;
+                    return;
             }
 
-            value = returnValue >> 3;
+            value = returnValue >> 4;
         }
 #endif
-        private static void ReadUInt64Packed(FastBufferReader reader, out ulong value)
-        {
-            reader.ReadByteSafe(out byte firstByte);
-            if (firstByte <= 240)
-            {
-                value = firstByte;
-                return;
-            }
-
-            if (firstByte <= 248)
-            {
-                reader.ReadByteSafe(out byte secondByte);
-                value = 240UL + ((firstByte - 241UL) << 8) + secondByte;
-                return;
-            }
-
-            var numBytes = firstByte - 247;
-            if (!reader.TryBeginReadInternal(numBytes))
-            {
-                throw new OverflowException("Reading past the end of the buffer");
-            }
-            reader.ReadPartialValue(out value, numBytes);
-        }
-
-        private static void ReadUInt32Packed(FastBufferReader reader, out uint value)
-        {
-            reader.ReadByteSafe(out byte firstByte);
-            if (firstByte <= 240)
-            {
-                value = firstByte;
-                return;
-            }
-
-            if (firstByte <= 248)
-            {
-                reader.ReadByteSafe(out byte secondByte);
-                value = 240U + ((firstByte - 241U) << 8) + secondByte;
-                return;
-            }
-
-            var numBytes = firstByte - 247;
-            if (!reader.TryBeginReadInternal(numBytes))
-            {
-                throw new OverflowException("Reading past the end of the buffer");
-            }
-            reader.ReadPartialValue(out value, numBytes);
-        }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe float ToSingle<T>(T value) where T : unmanaged

Runtime/Serialization/ByteUtility.cs

@@ -0,0 +1,58 @@
+using System.Runtime.CompilerServices;
+
+namespace Unity.Netcode
+{
+    internal class ByteUtility
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static unsafe byte ToByte(bool b) => *(byte*)&b;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(byte bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref byte bitField, ushort bitPosition, bool value)
+        {
+            bitField = (byte)((bitField & ~(1 << bitPosition)) | (ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(ushort bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref ushort bitField, ushort bitPosition, bool value)
+        {
+            bitField = (ushort)((bitField & ~(1 << bitPosition)) | (ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(uint bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref uint bitField, ushort bitPosition, bool value)
+        {
+            bitField = (uint)((bitField & ~(1 << bitPosition)) | ((uint)ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(ulong bitField, ushort bitPosition)
+        {
+            return (bitField & (ulong)(1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref ulong bitField, ushort bitPosition, bool value)
+        {
+            bitField = ((bitField & (ulong)~(1 << bitPosition)) | ((ulong)ToByte(value) << bitPosition));
+        }
+    }
+}

Runtime/Serialization/ByteUtility.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 25bb0dd7157c423b8cfe0ecf06e15ae5
+timeCreated: 1666711082

Runtime/Serialization/FastBufferReader.cs

@@ -65,7 +65,7 @@ namespace Unity.Netcode
             ReaderHandle* readerHandle = null;
             if (copyAllocator == Allocator.None)
             {
-                readerHandle = (ReaderHandle*)UnsafeUtility.Malloc(sizeof(ReaderHandle) + length, UnsafeUtility.AlignOf<byte>(), internalAllocator);
+                readerHandle = (ReaderHandle*)UnsafeUtility.Malloc(sizeof(ReaderHandle), UnsafeUtility.AlignOf<byte>(), internalAllocator);
                 readerHandle->BufferPointer = buffer;
                 readerHandle->Position = offset;
             }

Runtime/Spawning/NetworkSpawnManager.cs

@@ -270,6 +270,9 @@ namespace Unity.Netcode
 
             networkObject.OwnerClientId = clientId;
 
+            networkObject.MarkVariablesDirty(true);
+            NetworkManager.BehaviourUpdater.AddForUpdate(networkObject);
+
             // Server adds entries for all client ownership
             UpdateOwnershipTable(networkObject, networkObject.OwnerClientId);
 
@@ -291,13 +294,13 @@ namespace Unity.Netcode
 
         internal bool HasPrefab(NetworkObject.SceneObject sceneObject)
         {
-            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.Header.IsSceneObject)
+            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.IsSceneObject)
             {
-                if (NetworkManager.PrefabHandler.ContainsHandler(sceneObject.Header.Hash))
+                if (NetworkManager.PrefabHandler.ContainsHandler(sceneObject.Hash))
                 {
                     return true;
                 }
-                if (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks.TryGetValue(sceneObject.Header.Hash, out var networkPrefab))
+                if (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.TryGetValue(sceneObject.Hash, out var networkPrefab))
                 {
                     switch (networkPrefab.Override)
                     {
@@ -312,7 +315,7 @@ namespace Unity.Netcode
 
                 return false;
             }
-            var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(sceneObject.Header.Hash, sceneObject.NetworkSceneHandle);
+            var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(sceneObject.Hash, sceneObject.NetworkSceneHandle);
             return networkObject != null;
         }
 
@@ -326,22 +329,22 @@ namespace Unity.Netcode
         internal NetworkObject CreateLocalNetworkObject(NetworkObject.SceneObject sceneObject)
         {
             NetworkObject networkObject = null;
-            var globalObjectIdHash = sceneObject.Header.Hash;
+            var globalObjectIdHash = sceneObject.Hash;
-            var position = sceneObject.Header.HasTransform ? sceneObject.Transform.Position : default;
+            var position = sceneObject.HasTransform ? sceneObject.Transform.Position : default;
-            var rotation = sceneObject.Header.HasTransform ? sceneObject.Transform.Rotation : default;
+            var rotation = sceneObject.HasTransform ? sceneObject.Transform.Rotation : default;
-            var scale = sceneObject.Header.HasTransform ? sceneObject.Transform.Scale : default;
+            var scale = sceneObject.HasTransform ? sceneObject.Transform.Scale : default;
-            var parentNetworkId = sceneObject.Header.HasParent ? sceneObject.ParentObjectId : default;
+            var parentNetworkId = sceneObject.HasParent ? sceneObject.ParentObjectId : default;
-            var worldPositionStays = sceneObject.Header.HasParent ? sceneObject.WorldPositionStays : true;
+            var worldPositionStays = (!sceneObject.HasParent) || sceneObject.WorldPositionStays;
             var isSpawnedByPrefabHandler = false;
 
             // If scene management is disabled or the NetworkObject was dynamically spawned
-            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.Header.IsSceneObject)
+            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.IsSceneObject)
             {
                 // If the prefab hash has a registered INetworkPrefabInstanceHandler derived class
                 if (NetworkManager.PrefabHandler.ContainsHandler(globalObjectIdHash))
                 {
                     // Let the handler spawn the NetworkObject
-                    networkObject = NetworkManager.PrefabHandler.HandleNetworkPrefabSpawn(globalObjectIdHash, sceneObject.Header.OwnerClientId, position, rotation);
+                    networkObject = NetworkManager.PrefabHandler.HandleNetworkPrefabSpawn(globalObjectIdHash, sceneObject.OwnerClientId, position, rotation);
                     networkObject.NetworkManagerOwner = NetworkManager;
                     isSpawnedByPrefabHandler = true;
                 }
@@ -349,17 +352,17 @@ namespace Unity.Netcode
                 {
                     // See if there is a valid registered NetworkPrefabOverrideLink associated with the provided prefabHash
                     GameObject networkPrefabReference = null;
-                    if (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
+                    if (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
                     {
-                        switch (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Override)
+                        switch (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].Override)
                         {
                             default:
                             case NetworkPrefabOverride.None:
-                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Prefab;
+                                networkPrefabReference = NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].Prefab;
                                 break;
                             case NetworkPrefabOverride.Hash:
                             case NetworkPrefabOverride.Prefab:
-                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].OverridingTargetPrefab;
+                                networkPrefabReference = NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].OverridingTargetPrefab;
                                 break;
                         }
                     }
@@ -402,12 +405,12 @@ namespace Unity.Netcode
 
             if (networkObject != null)
             {
-                // SPECIAL CASE:
+                // SPECIAL CASE FOR IN-SCENE PLACED:  (only when the parent has a NetworkObject)
                 // This is a special case scenario where a late joining client has joined and loaded one or
                 // more scenes that contain nested in-scene placed NetworkObject children yet the server's
                 // synchronization information does not indicate the NetworkObject in question has a parent.
                 // Under this scenario, we want to remove the parent before spawning and setting the transform values.
-                if (sceneObject.Header.IsSceneObject && !sceneObject.Header.HasParent && networkObject.transform.parent != null)
+                if (sceneObject.IsSceneObject && !sceneObject.HasParent && networkObject.transform.parent != null)
                 {
                     // if the in-scene placed NetworkObject has a parent NetworkObject but the synchronization information does not
                     // include parenting, then we need to force the removal of that parent
@@ -421,9 +424,11 @@ namespace Unity.Netcode
                 // Set the transform unless we were spawned by a prefab handler
                 // Note: prefab handlers are provided the position and rotation
                 // but it is up to the user to set those values
-                if (sceneObject.Header.HasTransform && !isSpawnedByPrefabHandler)
+                if (sceneObject.HasTransform && !isSpawnedByPrefabHandler)
                 {
-                    if (worldPositionStays)
+                    // If world position stays is true or we have auto object parent synchronization disabled
+                    // then we want to apply the position and rotation values world space relative
+                    if (worldPositionStays || !networkObject.AutoObjectParentSync)
                     {
                         networkObject.transform.position = position;
                         networkObject.transform.rotation = rotation;
@@ -441,22 +446,31 @@ namespace Unity.Netcode
                     // the network prefab used to represent the player.
                     // Note: not doing this would set the player's scale to zero since
                     // that is the default value of Vector3.
-                    if (!sceneObject.Header.IsPlayerObject)
+                    if (!sceneObject.IsPlayerObject)
                     {
+                        // Since scale is always applied to local space scale, we do the transform
+                        // space logic during serialization such that it works out whether AutoObjectParentSync
+                        // is enabled or not (see NetworkObject.SceneObject)
                         networkObject.transform.localScale = scale;
                     }
                 }
 
-                if (sceneObject.Header.HasParent)
+                if (sceneObject.HasParent)
                 {
-                    // Go ahead and set network parenting properties
+                    // Go ahead and set network parenting properties, if the latest parent is not set then pass in null
-                    networkObject.SetNetworkParenting(parentNetworkId, worldPositionStays);
+                    // (we always want to set worldPositionStays)
+                    ulong? parentId = null;
+                    if (sceneObject.IsLatestParentSet)
+                    {
+                        parentId = parentNetworkId;
+                    }
+                    networkObject.SetNetworkParenting(parentId, worldPositionStays);
                 }
 
 
                 // Dynamically spawned NetworkObjects that occur during a LoadSceneMode.Single load scene event are migrated into the DDOL
                 // until the scene is loaded. They are then migrated back into the newly loaded and currently active scene.
-                if (!sceneObject.Header.IsSceneObject && NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
+                if (!sceneObject.IsSceneObject && NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
                 {
                     UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
                 }
@@ -490,8 +504,7 @@ namespace Unity.Netcode
         }
 
         // Ran on both server and client
-        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, in NetworkObject.SceneObject sceneObject,
+        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, in NetworkObject.SceneObject sceneObject, bool destroyWithScene)
-            FastBufferReader variableData, bool destroyWithScene)
         {
             if (networkObject == null)
             {
@@ -503,9 +516,7 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is already spawned");
             }
 
-            networkObject.SetNetworkVariableData(variableData);
+            SpawnNetworkObjectLocallyCommon(networkObject, sceneObject.NetworkObjectId, sceneObject.IsSceneObject, sceneObject.IsPlayerObject, sceneObject.OwnerClientId, destroyWithScene);
-
-            SpawnNetworkObjectLocallyCommon(networkObject, sceneObject.Header.NetworkObjectId, sceneObject.Header.IsSceneObject, sceneObject.Header.IsPlayerObject, sceneObject.Header.OwnerClientId, destroyWithScene);
         }
 
         private void SpawnNetworkObjectLocallyCommon(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
@@ -592,6 +603,11 @@ namespace Unity.Netcode
             var children = networkObject.GetComponentsInChildren<NetworkObject>();
             foreach (var childObject in children)
             {
+                // Do not propagate the in-scene object setting if a child was dynamically spawned.
+                if (childObject.IsSceneObject.HasValue && !childObject.IsSceneObject.Value)
+                {
+                    continue;
+                }
                 childObject.IsSceneObject = sceneObject;
             }
         }
@@ -647,7 +663,11 @@ namespace Unity.Netcode
         // Makes scene objects ready to be reused
         internal void ServerResetShudownStateForSceneObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID).Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
+#endif
             foreach (var sobj in networkObjects)
             {
                 sobj.IsSpawned = false;
@@ -678,7 +698,11 @@ namespace Unity.Netcode
 
         internal void DespawnAndDestroyNetworkObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             for (int i = 0; i < networkObjects.Length; i++)
             {
@@ -708,7 +732,11 @@ namespace Unity.Netcode
 
         internal void DestroySceneObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             for (int i = 0; i < networkObjects.Length; i++)
             {
@@ -735,7 +763,11 @@ namespace Unity.Netcode
 
         internal void ServerSpawnSceneObjectsOnStartSweep()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
             var networkObjectsToSpawn = new List<NetworkObject>();
 
             for (int i = 0; i < networkObjects.Length; i++)

Runtime/Transports/UTP/BatchedSendQueue.cs

@@ -226,7 +226,7 @@ namespace Unity.Netcode.Transports.UTP
                     {
                         writer.WriteInt(messageLength);
 
-                        var messageOffset = HeadIndex + reader.GetBytesRead();
+                        var messageOffset = reader.GetBytesRead();
                         WriteBytes(ref writer, (byte*)m_Data.GetUnsafePtr() + messageOffset, messageLength);
 
                         writerAvailable -= sizeof(int) + messageLength;

Runtime/Transports/UTP/UnityTransport.cs

@@ -10,8 +10,10 @@ using System.Collections.Generic;
 using UnityEngine;
 using NetcodeNetworkEvent = Unity.Netcode.NetworkEvent;
 using TransportNetworkEvent = Unity.Networking.Transport.NetworkEvent;
+using Unity.Burst;
 using Unity.Collections.LowLevel.Unsafe;
 using Unity.Collections;
+using Unity.Jobs;
 using Unity.Networking.Transport;
 using Unity.Networking.Transport.Relay;
 using Unity.Networking.Transport.Utilities;
@@ -51,50 +53,48 @@ namespace Unity.Netcode.Transports.UTP
     /// </summary>
     public static class ErrorUtilities
     {
-        private const string k_NetworkSuccess = "Success";
+        private static readonly FixedString128Bytes k_NetworkSuccess = "Success";
-        private const string k_NetworkIdMismatch = "NetworkId is invalid, likely caused by stale connection {0}.";
+        private static readonly FixedString128Bytes k_NetworkIdMismatch = "Invalid connection ID {0}.";
-        private const string k_NetworkVersionMismatch = "NetworkVersion is invalid, likely caused by stale connection {0}.";
+        private static readonly FixedString128Bytes k_NetworkVersionMismatch = "Connection ID is invalid. Likely caused by sending on stale connection {0}.";
-        private const string k_NetworkStateMismatch = "Sending data while connecting on connection {0} is not allowed.";
+        private static readonly FixedString128Bytes k_NetworkStateMismatch = "Connection state is invalid. Likely caused by sending on connection {0} which is stale or still connecting.";
-        private const string k_NetworkPacketOverflow = "Unable to allocate packet due to buffer overflow.";
+        private static readonly FixedString128Bytes k_NetworkPacketOverflow = "Packet is too large to be allocated by the transport.";
-        private const string k_NetworkSendQueueFull = "Currently unable to queue packet as there is too many in-flight packets. This could be because the send queue size ('Max Send Queue Size') is too small.";
+        private static readonly FixedString128Bytes k_NetworkSendQueueFull = "Unable to queue packet in the transport. Likely caused by send queue size ('Max Send Queue Size') being too small.";
-        private const string k_NetworkHeaderInvalid = "Invalid Unity Transport Protocol header.";
-        private const string k_NetworkDriverParallelForErr = "The parallel network driver needs to process a single unique connection per job, processing a single connection multiple times in a parallel for is not supported.";
-        private const string k_NetworkSendHandleInvalid = "Invalid NetworkInterface Send Handle. Likely caused by pipeline send data corruption.";
-        private const string k_NetworkArgumentMismatch = "Invalid NetworkEndpoint Arguments.";
 
         /// <summary>
-        /// Convert error code to human readable error message.
+        /// Convert a UTP error code to human-readable error message.
         /// </summary>
-        /// <param name="error">Status code of the error</param>
+        /// <param name="error">UTP error code.</param>
-        /// <param name="connectionId">Subject connection ID of the error</param>
+        /// <param name="connectionId">ID of the connection on which the error occurred.</param>
-        /// <returns>Human readable error message.</returns>
+        /// <returns>Human-readable error message.</returns>
         public static string ErrorToString(Networking.Transport.Error.StatusCode error, ulong connectionId)
         {
-            switch (error)
+            return ErrorToString((int)error, connectionId);
+        }
+
+        internal static string ErrorToString(int error, ulong connectionId)
+        {
+            return ErrorToFixedString(error, connectionId).ToString();
+        }
+
+        internal static FixedString128Bytes ErrorToFixedString(int error, ulong connectionId)
+        {
+            switch ((Networking.Transport.Error.StatusCode)error)
             {
                 case Networking.Transport.Error.StatusCode.Success:
                     return k_NetworkSuccess;
                 case Networking.Transport.Error.StatusCode.NetworkIdMismatch:
-                    return string.Format(k_NetworkIdMismatch, connectionId);
+                    return FixedString.Format(k_NetworkIdMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkVersionMismatch:
-                    return string.Format(k_NetworkVersionMismatch, connectionId);
+                    return FixedString.Format(k_NetworkVersionMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkStateMismatch:
-                    return string.Format(k_NetworkStateMismatch, connectionId);
+                    return FixedString.Format(k_NetworkStateMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkPacketOverflow:
                     return k_NetworkPacketOverflow;
                 case Networking.Transport.Error.StatusCode.NetworkSendQueueFull:
                     return k_NetworkSendQueueFull;
-                case Networking.Transport.Error.StatusCode.NetworkHeaderInvalid:
+                default:
-                    return k_NetworkHeaderInvalid;
+                    return FixedString.Format("Unknown error code {0}.", error);
-                case Networking.Transport.Error.StatusCode.NetworkDriverParallelForErr:
-                    return k_NetworkDriverParallelForErr;
-                case Networking.Transport.Error.StatusCode.NetworkSendHandleInvalid:
-                    return k_NetworkSendHandleInvalid;
-                case Networking.Transport.Error.StatusCode.NetworkArgumentMismatch:
-                    return k_NetworkArgumentMismatch;
             }
-
-            return $"Unknown ErrorCode {Enum.GetName(typeof(Networking.Transport.Error.StatusCode), error)}";
         }
     }
 
@@ -145,7 +145,7 @@ namespace Unity.Netcode.Transports.UTP
 
         // Maximum reliable throughput, assuming the full reliable window can be sent on every
         // frame at 60 FPS. This will be a large over-estimation in any realistic scenario.
-        private const int k_MaxReliableThroughput = (NetworkParameterConstants.MTU * 32 * 60) / 1000; // bytes per millisecond
+        private const int k_MaxReliableThroughput = (NetworkParameterConstants.MTU * 64 * 60) / 1000; // bytes per millisecond
 
         private static ConnectionAddressData s_DefaultConnectionAddressData = new ConnectionAddressData { Address = "127.0.0.1", Port = 7777, ServerListenAddress = string.Empty };
 
@@ -303,21 +303,24 @@ namespace Unity.Netcode.Transports.UTP
             public ushort Port;
 
             /// <summary>
-            /// IP address the server will listen on. If not provided, will use 'Address'.
+            /// IP address the server will listen on. If not provided, will use localhost.
             /// </summary>
-            [Tooltip("IP address the server will listen on. If not provided, will use 'Address'.")]
+            [Tooltip("IP address the server will listen on. If not provided, will use localhost.")]
             [SerializeField]
             public string ServerListenAddress;
 
-            private static NetworkEndpoint ParseNetworkEndpoint(string ip, ushort port)
+            private static NetworkEndpoint ParseNetworkEndpoint(string ip, ushort port, bool silent = false)
             {
                 NetworkEndpoint endpoint = default;
 
                 if (!NetworkEndpoint.TryParse(ip, port, out endpoint, NetworkFamily.Ipv4) &&
                     !NetworkEndpoint.TryParse(ip, port, out endpoint, NetworkFamily.Ipv6))
+                {
+                    if (!silent)
                     {
                         Debug.LogError($"Invalid network endpoint: {ip}:{port}.");
                     }
+                }
 
                 return endpoint;
             }
@@ -330,9 +333,34 @@ namespace Unity.Netcode.Transports.UTP
             /// <summary>
             /// Endpoint (IP address and port) server will listen/bind on.
             /// </summary>
-            public NetworkEndpoint ListenEndPoint => ParseNetworkEndpoint((ServerListenAddress?.Length == 0) ? Address : ServerListenAddress, Port);
+            public NetworkEndpoint ListenEndPoint
+            {
+                get
+                {
+                    if (string.IsNullOrEmpty(ServerListenAddress))
+                    {
+                        var ep = NetworkEndpoint.LoopbackIpv4;
+
+                        // If an address was entered and it's IPv6, switch to using ::1 as the
+                        // default listen address. (Otherwise we always assume IPv4.)
+                        if (!string.IsNullOrEmpty(Address) && ServerEndPoint.Family == NetworkFamily.Ipv6)
+                        {
+                            ep = NetworkEndpoint.LoopbackIpv6;
                         }
 
+                        return ep.WithPort(Port);
+                    }
+                    else
+                    {
+                        return ParseNetworkEndpoint(ServerListenAddress, Port);
+                    }
+                }
+            }
+
+            public bool IsIpv6 => !string.IsNullOrEmpty(Address) && ParseNetworkEndpoint(Address, Port, true).Family == NetworkFamily.Ipv6;
+        }
+
+
         /// <summary>
         /// The connection (address) data for this <see cref="UnityTransport"/> instance.
         /// This is where you can change IP Address, Port, or server's listen address.
@@ -529,14 +557,14 @@ namespace Unity.Netcode.Transports.UTP
             int result = m_Driver.Bind(endPoint);
             if (result != 0)
             {
-                Debug.LogError("Server failed to bind");
+                Debug.LogError("Server failed to bind. This is usually caused by another process being bound to the same port.");
                 return false;
             }
 
             result = m_Driver.Listen();
             if (result != 0)
             {
-                Debug.LogError("Server failed to listen");
+                Debug.LogError("Server failed to listen.");
                 return false;
             }
 
@@ -609,7 +637,7 @@ namespace Unity.Netcode.Transports.UTP
             {
                 Address = ipv4Address,
                 Port = port,
-                ServerListenAddress = listenAddress ?? string.Empty
+                ServerListenAddress = listenAddress ?? ipv4Address
             };
 
             SetProtocol(ProtocolType.UnityTransport);
@@ -676,20 +704,26 @@ namespace Unity.Netcode.Transports.UTP
             }
         }
 
-        // Send as many batched messages from the queue as possible.
+        [BurstCompile]
-        private void SendBatchedMessages(SendTarget sendTarget, BatchedSendQueue queue)
+        private struct SendBatchedMessagesJob : IJob
         {
-            var clientId = sendTarget.ClientId;
+            public NetworkDriver.Concurrent Driver;
-            var connection = ParseClientId(clientId);
+            public SendTarget Target;
-            var pipeline = sendTarget.NetworkPipeline;
+            public BatchedSendQueue Queue;
+            public NetworkPipeline ReliablePipeline;
 
-            while (!queue.IsEmpty)
+            public void Execute()
             {
-                var result = m_Driver.BeginSend(pipeline, connection, out var writer);
+                var clientId = Target.ClientId;
+                var connection = ParseClientId(clientId);
+                var pipeline = Target.NetworkPipeline;
+
+                while (!Queue.IsEmpty)
+                {
+                    var result = Driver.BeginSend(pipeline, connection, out var writer);
                     if (result != (int)Networking.Transport.Error.StatusCode.Success)
                     {
-                    Debug.LogError("Error sending the message: " +
+                        Debug.LogError($"Error sending message: {ErrorUtilities.ErrorToFixedString(result, clientId)}");
-                        ErrorUtilities.ErrorToString((Networking.Transport.Error.StatusCode)result, clientId));
                         return;
                     }
 
@@ -699,31 +733,44 @@ namespace Unity.Netcode.Transports.UTP
                     // in the stream (the send queue does that automatically) we are sure they'll be
                     // reassembled properly at the other end. This allows us to lift the limit of ~44KB
                     // on reliable payloads (because of the reliable window size).
-                var written = pipeline == m_ReliableSequencedPipeline ? queue.FillWriterWithBytes(ref writer) : queue.FillWriterWithMessages(ref writer);
+                    var written = pipeline == ReliablePipeline ? Queue.FillWriterWithBytes(ref writer) : Queue.FillWriterWithMessages(ref writer);
 
-                result = m_Driver.EndSend(writer);
+                    result = Driver.EndSend(writer);
                     if (result == written)
                     {
                         // Batched message was sent successfully. Remove it from the queue.
-                    queue.Consume(written);
+                        Queue.Consume(written);
                     }
                     else
                     {
                         // Some error occured. If it's just the UTP queue being full, then don't log
                         // anything since that's okay (the unsent message(s) are still in the queue
-                    // and we'll retry sending the later). Otherwise log the error and remove the
+                        // and we'll retry sending them later). Otherwise log the error and remove the
                         // message from the queue (we don't want to resend it again since we'll likely
                         // just get the same error again).
                         if (result != (int)Networking.Transport.Error.StatusCode.NetworkSendQueueFull)
                         {
-                        Debug.LogError("Error sending the message: " + ErrorUtilities.ErrorToString((Networking.Transport.Error.StatusCode)result, clientId));
+                            Debug.LogError($"Error sending the message: {ErrorUtilities.ErrorToFixedString(result, clientId)}");
-                        queue.Consume(written);
+                            Queue.Consume(written);
                         }
 
                         return;
                     }
                 }
             }
+        }
+
+        // Send as many batched messages from the queue as possible.
+        private void SendBatchedMessages(SendTarget sendTarget, BatchedSendQueue queue)
+        {
+            new SendBatchedMessagesJob
+            {
+                Driver = m_Driver.ToConcurrent(),
+                Target = sendTarget,
+                Queue = queue,
+                ReliablePipeline = m_ReliableSequencedPipeline
+            }.Run();
+        }
 
         private bool AcceptConnection()
         {
@@ -1134,17 +1181,20 @@ namespace Unity.Netcode.Transports.UTP
 
             m_NetworkSettings = new NetworkSettings(Allocator.Persistent);
 
-#if !UNITY_WEBGL
             // If the user sends a message of exactly m_MaxPayloadSize in length, we need to
             // account for the overhead of its length when we store it in the send queue.
             var fragmentationCapacity = m_MaxPayloadSize + BatchedSendQueue.PerMessageOverhead;
-
             m_NetworkSettings.WithFragmentationStageParameters(payloadCapacity: fragmentationCapacity);
-#if !UTP_TRANSPORT_2_0_ABOVE
+
+            // Bump the reliable window size to its maximum size of 64. Since NGO makes heavy use of
+            // reliable delivery, we're better off with the increased window size compared to the
+            // extra 4 bytes of header that this costs us.
+            m_NetworkSettings.WithReliableStageParameters(windowSize: 64);
+
+#if !UTP_TRANSPORT_2_0_ABOVE && !UNITY_WEBGL
             m_NetworkSettings.WithBaselibNetworkInterfaceParameters(
                 receiveQueueCapacity: m_MaxPacketQueueSize,
                 sendQueueCapacity: m_MaxPacketQueueSize);
-#endif
 #endif
         }
 
@@ -1430,7 +1480,7 @@ namespace Unity.Netcode.Transports.UTP
                 heartbeatTimeoutMS: transport.m_HeartbeatTimeoutMS);
 
 #if UNITY_WEBGL && !UNITY_EDITOR
-            if (NetworkManager.IsServer)
+            if (NetworkManager.IsServer && m_ProtocolType != ProtocolType.RelayUnityTransport)
             {
                 throw new Exception("WebGL as a server is not supported by Unity Transport, outside the Editor.");
             }
@@ -1441,7 +1491,7 @@ namespace Unity.Netcode.Transports.UTP
             {
                 if (m_ProtocolType == ProtocolType.RelayUnityTransport)
                 {
-                    if (m_RelayServerData.IsSecure != 0)
+                    if (m_RelayServerData.IsSecure == 0)
                     {
                         // log an error because we have mismatched configuration
                         Debug.LogError("Mismatched security configuration, between Relay and local NetworkManager settings");
@@ -1451,24 +1501,23 @@ namespace Unity.Netcode.Transports.UTP
                     // configuration of the security parameters on its own.
                 }
                 else
-                {
-                    try
                 {
                     if (NetworkManager.IsServer)
                     {
-                            if (m_ServerCertificate.Length == 0 || m_ServerPrivateKey.Length == 0)
+                        if (string.IsNullOrEmpty(m_ServerCertificate) || string.IsNullOrEmpty(m_ServerPrivateKey))
                         {
                             throw new Exception("In order to use encrypted communications, when hosting, you must set the server certificate and key.");
                         }
+
                         m_NetworkSettings.WithSecureServerParameters(m_ServerCertificate, m_ServerPrivateKey);
                     }
                     else
                     {
-                            if (m_ServerCommonName.Length == 0)
+                        if (string.IsNullOrEmpty(m_ServerCommonName))
                         {
                             throw new Exception("In order to use encrypted communications, clients must set the server common name.");
                         }
-                            else if (m_ClientCaCertificate == null)
+                        else if (string.IsNullOrEmpty(m_ClientCaCertificate))
                         {
                             m_NetworkSettings.WithSecureClientParameters(m_ServerCommonName);
                         }
@@ -1478,11 +1527,6 @@ namespace Unity.Netcode.Transports.UTP
                         }
                     }
                 }
-                    catch(Exception e)
-                    {
-                        Debug.LogException(e, this);
-                    }
-                }
             }
 #endif
 

TestHelpers/Runtime/AssemblyInfo.cs

@@ -1,6 +1,12 @@
 using System.Runtime.CompilerServices;
 
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#if UNITY_INCLUDE_TESTS
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
-[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#if MULTIPLAYER_TOOLS
+[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#endif // MULTIPLAYER_TOOLS
+#endif // UNITY_INCLUDE_TESTS

TestHelpers/Runtime/DebugNetworkHooks.cs

@@ -0,0 +1,63 @@
+using System;
+using UnityEngine;
+
+namespace Unity.Netcode.TestHelpers.Runtime
+{
+    internal class DebugNetworkHooks : INetworkHooks
+    {
+        public void OnBeforeSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery) where T : INetworkMessage
+        {
+        }
+
+        public void OnAfterSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery, int messageSizeBytes) where T : INetworkMessage
+        {
+            Debug.Log($"Sending message of type {typeof(T).Name} to {clientId} ({messageSizeBytes} bytes)");
+        }
+
+        public void OnBeforeReceiveMessage(ulong senderId, Type messageType, int messageSizeBytes)
+        {
+            Debug.Log($"Receiving message of type {messageType.Name} from {senderId}");
+        }
+
+        public void OnAfterReceiveMessage(ulong senderId, Type messageType, int messageSizeBytes)
+        {
+        }
+
+        public void OnBeforeSendBatch(ulong clientId, int messageCount, int batchSizeInBytes, NetworkDelivery delivery)
+        {
+            Debug.Log($"==> Sending a batch of {messageCount} messages ({batchSizeInBytes} bytes) to {clientId} ({delivery})");
+        }
+
+        public void OnAfterSendBatch(ulong clientId, int messageCount, int batchSizeInBytes, NetworkDelivery delivery)
+        {
+        }
+
+        public void OnBeforeReceiveBatch(ulong senderId, int messageCount, int batchSizeInBytes)
+        {
+            Debug.Log($"<== Receiving a batch of {messageCount} messages ({batchSizeInBytes} bytes) from {senderId}");
+        }
+
+        public void OnAfterReceiveBatch(ulong senderId, int messageCount, int batchSizeInBytes)
+        {
+        }
+
+        public bool OnVerifyCanSend(ulong destinationId, Type messageType, NetworkDelivery delivery)
+        {
+            return true;
+        }
+
+        public bool OnVerifyCanReceive(ulong senderId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
+        {
+            return true;
+        }
+
+        public void OnBeforeHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+            Debug.Log($"Handling a message of type {typeof(T).Name}");
+        }
+
+        public void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+        }
+    }
+}

TestHelpers/Runtime/DebugNetworkHooks.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: b5f8098e713443eeba116a25de551cf8
+timeCreated: 1666626883

TestHelpers/Runtime/IntegrationTestSceneHandler.cs

@@ -147,7 +147,12 @@ namespace Unity.Netcode.TestHelpers.Runtime
         private static void ProcessInSceneObjects(Scene scene, NetworkManager networkManager)
         {
             // Get all in-scene placed NeworkObjects that were instantiated when this scene loaded
+#if UNITY_2023_1_OR_NEWER
+            var inSceneNetworkObjects = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID).Where((c) => c.IsSceneObject != false && c.GetSceneOriginHandle() == scene.handle);
+#else
             var inSceneNetworkObjects = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsSceneObject != false && c.GetSceneOriginHandle() == scene.handle);
+#endif
+
             foreach (var sobj in inSceneNetworkObjects)
             {
                 if (sobj.NetworkManagerOwner != networkManager)

TestHelpers/Runtime/MessageHooks.cs

@@ -44,7 +44,7 @@ namespace Unity.Netcode.TestHelpers.Runtime
 
         public void OnAfterReceiveMessage(ulong senderId, Type messageType, int messageSizeBytes)
         {
-            if (!CurrentMessageHasTriggerdAHook && IsWaiting && (HandleCheck == null || HandleCheck.Invoke(messageType)))
+            if (!CurrentMessageHasTriggerdAHook && IsWaiting && ReceiptCheck != null && ReceiptCheck.Invoke(messageType))
             {
                 IsWaiting = false;
                 CurrentMessageHasTriggerdAHook = true;
@@ -92,7 +92,7 @@ namespace Unity.Netcode.TestHelpers.Runtime
 
         public void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
         {
-            if (!CurrentMessageHasTriggerdAHook && IsWaiting && (HandleCheck == null || HandleCheck.Invoke(message)))
+            if (!CurrentMessageHasTriggerdAHook && IsWaiting && HandleCheck != null && HandleCheck.Invoke(message))
             {
                 IsWaiting = false;
                 CurrentMessageHasTriggerdAHook = true;

TestHelpers/Runtime/MessageHooksConditional.cs

@@ -39,7 +39,10 @@ namespace Unity.Netcode.TestHelpers.Runtime
 
             if (AllMessagesReceived)
             {
-                return AllMessagesReceived;
+                foreach (var entry in m_MessageHookEntries)
+                {
+                    entry.RemoveHook();
+                }
             }
 
             return AllMessagesReceived;
@@ -110,6 +113,11 @@ namespace Unity.Netcode.TestHelpers.Runtime
             Initialize();
         }
 
+        internal void RemoveHook()
+        {
+            m_NetworkManager.MessagingSystem.Unhook(MessageHooks);
+        }
+
         internal void AssignMessageType(Type type)
         {
             MessageType = type.Name;

TestHelpers/Runtime/NetcodeIntegrationTest.cs

@@ -241,11 +241,20 @@ namespace Unity.Netcode.TestHelpers.Runtime
         {
         }
 
+        /// <summary>
+        /// Invoked immediately after the player prefab GameObject is created
+        /// prior to adding a NetworkObject component
+        /// </summary>
+        protected virtual void OnPlayerPrefabGameObjectCreated()
+        {
+        }
+
         private void CreatePlayerPrefab()
         {
             VerboseDebug($"Entering {nameof(CreatePlayerPrefab)}");
             // Create playerPrefab
             m_PlayerPrefab = new GameObject("Player");
+            OnPlayerPrefabGameObjectCreated();
             NetworkObject networkObject = m_PlayerPrefab.AddComponent<NetworkObject>();
 
             // Make it a prefab
@@ -274,16 +283,6 @@ namespace Unity.Netcode.TestHelpers.Runtime
             CreateServerAndClients(NumberOfClients);
         }
 
-        protected virtual void OnNewClientCreated(NetworkManager networkManager)
-        {
-
-        }
-
-        protected virtual void OnNewClientStartedAndConnected(NetworkManager networkManager)
-        {
-
-        }
-
         private void AddRemoveNetworkManager(NetworkManager networkManager, bool addNetworkManager)
         {
             var clientNetworkManagersList = new List<NetworkManager>(m_ClientNetworkManagers);
@@ -299,6 +298,37 @@ namespace Unity.Netcode.TestHelpers.Runtime
             m_NumberOfClients = clientNetworkManagersList.Count;
         }
 
+        /// <summary>
+        /// CreateAndStartNewClient Only
+        /// Invoked when the newly created client has been created
+        /// </summary>
+        protected virtual void OnNewClientCreated(NetworkManager networkManager)
+        {
+
+        }
+
+        /// <summary>
+        /// CreateAndStartNewClient Only
+        /// Invoked when the newly created client has been created and started
+        /// </summary>
+        protected virtual void OnNewClientStarted(NetworkManager networkManager)
+        {
+        }
+
+        /// <summary>
+        /// CreateAndStartNewClient Only
+        /// Invoked when the newly created client has been created, started, and connected
+        /// to the server-host.
+        /// </summary>
+        protected virtual void OnNewClientStartedAndConnected(NetworkManager networkManager)
+        {
+
+        }
+
+        /// <summary>
+        /// This will create, start, and connect a new client while in the middle of an
+        /// integration test.
+        /// </summary>
         protected IEnumerator CreateAndStartNewClient()
         {
             var networkManager = NetcodeIntegrationTestHelpers.CreateNewClient(m_ClientNetworkManagers.Length);
@@ -309,9 +339,20 @@ namespace Unity.Netcode.TestHelpers.Runtime
             OnNewClientCreated(networkManager);
 
             NetcodeIntegrationTestHelpers.StartOneClient(networkManager);
+
+            if (LogAllMessages)
+            {
+                networkManager.MessagingSystem.Hook(new DebugNetworkHooks());
+            }
+
             AddRemoveNetworkManager(networkManager, true);
+
+            OnNewClientStarted(networkManager);
+
             // Wait for the new client to connect
             yield return WaitForClientsConnectedOrTimeOut();
+
+            OnNewClientStartedAndConnected(networkManager);
             if (s_GlobalTimeoutHelper.TimedOut)
             {
                 AddRemoveNetworkManager(networkManager, false);
@@ -322,6 +363,9 @@ namespace Unity.Netcode.TestHelpers.Runtime
             VerboseDebug($"[{networkManager.name}] Created and connected!");
         }
 
+        /// <summary>
+        /// This will stop a client while in the middle of an integration test
+        /// </summary>
         protected IEnumerator StopOneClient(NetworkManager networkManager, bool destroy = false)
         {
             NetcodeIntegrationTestHelpers.StopOneClient(networkManager, destroy);
@@ -401,8 +445,19 @@ namespace Unity.Netcode.TestHelpers.Runtime
             networkManager.name = $"NetworkManager - Client - {networkManager.LocalClientId}";
             Assert.NotNull(networkManager.LocalClient.PlayerObject, $"{nameof(StartServerAndClients)} detected that client {networkManager.LocalClientId} does not have an assigned player NetworkObject!");
 
+            // Go ahead and create an entry for this new client
+            if (!m_PlayerNetworkObjects.ContainsKey(networkManager.LocalClientId))
+            {
+                m_PlayerNetworkObjects.Add(networkManager.LocalClientId, new Dictionary<ulong, NetworkObject>());
+            }
+
+#if UNITY_2023_1_OR_NEWER
             // Get all player instances for the current client NetworkManager instance
-            var clientPlayerClones = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsPlayerObject && c.OwnerClientId == networkManager.LocalClientId);
+            var clientPlayerClones = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.None).Where((c) => c.IsPlayerObject && c.OwnerClientId == networkManager.LocalClientId).ToList();
+#else
+            // Get all player instances for the current client NetworkManager instance
+            var clientPlayerClones = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsPlayerObject && c.OwnerClientId == networkManager.LocalClientId).ToList();
+#endif
             // Add this player instance to each client player entry
             foreach (var playerNetworkObject in clientPlayerClones)
             {
@@ -416,6 +471,20 @@ namespace Unity.Netcode.TestHelpers.Runtime
                     m_PlayerNetworkObjects[playerNetworkObject.NetworkManager.LocalClientId].Add(networkManager.LocalClientId, playerNetworkObject);
                 }
             }
+#if UNITY_2023_1_OR_NEWER
+            // For late joining clients, add the remaining (if any) cloned versions of each client's player
+            clientPlayerClones = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.None).Where((c) => c.IsPlayerObject && c.NetworkManager == networkManager).ToList();
+#else
+            // For late joining clients, add the remaining (if any) cloned versions of each client's player
+            clientPlayerClones = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsPlayerObject && c.NetworkManager == networkManager).ToList();
+#endif
+            foreach (var playerNetworkObject in clientPlayerClones)
+            {
+                if (!m_PlayerNetworkObjects[networkManager.LocalClientId].ContainsKey(playerNetworkObject.OwnerClientId))
+                {
+                    m_PlayerNetworkObjects[networkManager.LocalClientId].Add(playerNetworkObject.OwnerClientId, playerNetworkObject);
+                }
+            }
         }
 
         protected void ClientNetworkManagerPostStartInit()
@@ -428,7 +497,11 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
             if (m_UseHost)
             {
+#if UNITY_2023_1_OR_NEWER
+                var clientSideServerPlayerClones = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.None).Where((c) => c.IsPlayerObject && c.OwnerClientId == m_ServerNetworkManager.LocalClientId);
+#else
                 var clientSideServerPlayerClones = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsPlayerObject && c.OwnerClientId == m_ServerNetworkManager.LocalClientId);
+#endif
                 foreach (var playerNetworkObject in clientSideServerPlayerClones)
                 {
                     // When the server is not the host this needs to be done
@@ -444,6 +517,8 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
         }
 
+        protected virtual bool LogAllMessages => false;
+
         /// <summary>
         /// This starts the server and clients as long as <see cref="CanStartServerAndClients"/>
         /// returns true.
@@ -462,6 +537,11 @@ namespace Unity.Netcode.TestHelpers.Runtime
                     Assert.Fail("Failed to start instances");
                 }
 
+                if (LogAllMessages)
+                {
+                    EnableMessageLogging();
+                }
+
                 RegisterSceneManagerHandler();
 
                 // Notification that the server and clients have been started
@@ -477,8 +557,13 @@ namespace Unity.Netcode.TestHelpers.Runtime
 
                     if (m_UseHost || m_ServerNetworkManager.IsHost)
                     {
+#if UNITY_2023_1_OR_NEWER
+                        // Add the server player instance to all m_ClientSidePlayerNetworkObjects entries
+                        var serverPlayerClones = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.None).Where((c) => c.IsPlayerObject && c.OwnerClientId == m_ServerNetworkManager.LocalClientId);
+#else
                         // Add the server player instance to all m_ClientSidePlayerNetworkObjects entries
                         var serverPlayerClones = Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsPlayerObject && c.OwnerClientId == m_ServerNetworkManager.LocalClientId);
+#endif
                         foreach (var playerNetworkObject in serverPlayerClones)
                         {
                             if (!m_PlayerNetworkObjects.ContainsKey(playerNetworkObject.NetworkManager.LocalClientId))
@@ -616,6 +701,7 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
 
             VerboseDebug($"Exiting {nameof(TearDown)}");
+            LogWaitForMessages();
             NetcodeLogAssert.Dispose();
         }
 
@@ -668,7 +754,11 @@ namespace Unity.Netcode.TestHelpers.Runtime
         /// </summary>
         protected void DestroySceneNetworkObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = Object.FindObjectsOfType<NetworkObject>();
+#endif
             foreach (var networkObject in networkObjects)
             {
                 // This can sometimes be null depending upon order of operations
@@ -692,6 +782,18 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
         }
 
+        /// <summary>
+        /// For debugging purposes, this will turn on verbose logging of all messages and batches sent and received
+        /// </summary>
+        protected void EnableMessageLogging()
+        {
+            m_ServerNetworkManager.MessagingSystem.Hook(new DebugNetworkHooks());
+            foreach (var client in m_ClientNetworkManagers)
+            {
+                client.MessagingSystem.Hook(new DebugNetworkHooks());
+            }
+        }
+
         /// <summary>
         /// Waits for the function condition to return true or it will time out.
         /// This will operate at the current m_ServerNetworkManager.NetworkConfig.TickRate
@@ -828,18 +930,7 @@ namespace Unity.Netcode.TestHelpers.Runtime
             Assert.IsNotNull(m_ServerNetworkManager, prefabCreateAssertError);
             Assert.IsFalse(m_ServerNetworkManager.IsListening, prefabCreateAssertError);
 
-            var gameObject = new GameObject();
+            return NetcodeIntegrationTestHelpers.CreateNetworkObjectPrefab(baseName, m_ServerNetworkManager, m_ClientNetworkManagers);
-            gameObject.name = baseName;
-            var networkObject = gameObject.AddComponent<NetworkObject>();
-            networkObject.NetworkManagerOwner = m_ServerNetworkManager;
-            NetcodeIntegrationTestHelpers.MakeNetworkObjectTestPrefab(networkObject);
-            var networkPrefab = new NetworkPrefab() { Prefab = gameObject };
-            m_ServerNetworkManager.NetworkConfig.NetworkPrefabs.Add(networkPrefab);
-            foreach (var clientNetworkManager in m_ClientNetworkManagers)
-            {
-                clientNetworkManager.NetworkConfig.NetworkPrefabs.Add(networkPrefab);
-            }
-            return gameObject;
         }
 
         /// <summary>
@@ -967,5 +1058,61 @@ namespace Unity.Netcode.TestHelpers.Runtime
                 var asyncOperation = SceneManager.UnloadSceneAsync(scene);
             }
         }
+
+        private System.Text.StringBuilder m_WaitForLog = new System.Text.StringBuilder();
+
+        private void LogWaitForMessages()
+        {
+            VerboseDebug(m_WaitForLog.ToString());
+            m_WaitForLog.Clear();
+        }
+
+        private IEnumerator WaitForTickAndFrames(NetworkManager networkManager, int tickCount, float targetFrames)
+        {
+            var tickAndFramesConditionMet = false;
+            var frameCount = 0;
+            var waitForFixedUpdate = new WaitForFixedUpdate();
+            m_WaitForLog.Append($"[NetworkManager-{networkManager.LocalClientId}][WaitForTicks-Begin] Waiting for ({tickCount}) network ticks and ({targetFrames}) frames to pass.\n");
+            var tickStart = networkManager.NetworkTickSystem.LocalTime.Tick;
+            while (!tickAndFramesConditionMet)
+            {
+                // Wait until both tick and frame counts have reached their targeted values
+                if ((networkManager.NetworkTickSystem.LocalTime.Tick - tickStart) >= tickCount && frameCount >= targetFrames)
+                {
+                    tickAndFramesConditionMet = true;
+                }
+                else
+                {
+                    yield return waitForFixedUpdate;
+                    frameCount++;
+                    // In the event something is broken with time systems (or the like)
+                    // Exit if we have exceeded 1000 frames
+                    if (frameCount >= 1000.0f)
+                    {
+                        tickAndFramesConditionMet = true;
+                    }
+                }
+            }
+            m_WaitForLog.Append($"[NetworkManager-{networkManager.LocalClientId}][WaitForTicks-End] Waited for ({networkManager.NetworkTickSystem.LocalTime.Tick - tickStart}) network ticks and ({frameCount}) frames to pass.\n");
+            yield break;
+        }
+
+        /// <summary>
+        /// Yields until specified amount of network ticks and the expected number of frames has been passed.
+        /// </summary>
+        protected IEnumerator WaitForTicks(NetworkManager networkManager, int count)
+        {
+            var targetTick = networkManager.NetworkTickSystem.LocalTime.Tick + count;
+
+            // Calculate the expected number of frame updates that should occur during the tick count wait period
+            var frameFrequency = 1.0f / (Application.targetFrameRate >= 60 && Application.targetFrameRate <= 100 ? Application.targetFrameRate : 60.0f);
+            var tickFrequency = 1.0f / networkManager.NetworkConfig.TickRate;
+            var framesPerTick = tickFrequency / frameFrequency;
+
+            // Total number of frames to occur over the specified number of ticks
+            var totalFrameCount = framesPerTick * count;
+            m_WaitForLog.Append($"[NetworkManager-{networkManager.LocalClientId}][WaitForTicks] TickRate ({networkManager.NetworkConfig.TickRate}) | Tick Wait ({count}) | TargetFrameRate ({Application.targetFrameRate}) | Target Frames ({framesPerTick * count})\n");
+            yield return WaitForTickAndFrames(networkManager, count, totalFrameCount);
+        }
     }
 }

TestHelpers/Runtime/NetcodeIntegrationTestHelpers.cs

@@ -182,11 +182,8 @@ namespace Unity.Netcode.TestHelpers.Runtime
             unityTransport.ConnectTimeoutMS = 500;
 
             // Set the NetworkConfig
-            networkManager.NetworkConfig = new NetworkConfig()
+            networkManager.NetworkConfig ??= new NetworkConfig();
-            {
+            networkManager.NetworkConfig.NetworkTransport = unityTransport;
-                // Set transport
-                NetworkTransport = unityTransport
-            };
         }
 
         public static NetworkManager CreateServer()
@@ -486,6 +483,34 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
         }
 
+        public static GameObject CreateNetworkObjectPrefab(string baseName, NetworkManager server, params NetworkManager[] clients)
+        {
+            void AddNetworkPrefab(NetworkConfig config, NetworkPrefab prefab)
+            {
+                config.Prefabs.Add(prefab);
+            }
+
+            var prefabCreateAssertError = $"You can only invoke this method before starting the network manager(s)!";
+            Assert.IsNotNull(server, prefabCreateAssertError);
+            Assert.IsFalse(server.IsListening, prefabCreateAssertError);
+
+            var gameObject = new GameObject();
+            gameObject.name = baseName;
+            var networkObject = gameObject.AddComponent<NetworkObject>();
+            networkObject.NetworkManagerOwner = server;
+            MakeNetworkObjectTestPrefab(networkObject);
+            var networkPrefab = new NetworkPrefab() { Prefab = gameObject };
+
+            // We could refactor this test framework to share a NetworkPrefabList instance, but at this point it's
+            // probably more trouble than it's worth to verify these lists stay in sync across all tests...
+            AddNetworkPrefab(server.NetworkConfig, networkPrefab);
+            foreach (var clientNetworkManager in clients)
+            {
+                AddNetworkPrefab(clientNetworkManager.NetworkConfig, networkPrefab);
+            }
+            return gameObject;
+        }
+
         // We use GameObject instead of SceneObject to be able to keep hierarchy
         public static void MarkAsSceneObjectRoot(GameObject networkObjectRoot, NetworkManager server, NetworkManager[] clients)
         {
@@ -512,15 +537,6 @@ namespace Unity.Netcode.TestHelpers.Runtime
             }
         }
 
-        /// <summary>
-        /// Waits (yields) until specified amount of network ticks has been passed.
-        /// </summary>
-        public static IEnumerator WaitForTicks(NetworkManager networkManager, int count)
-        {
-            var targetTick = networkManager.NetworkTickSystem.LocalTime.Tick + count;
-            yield return new WaitUntil(() => networkManager.NetworkTickSystem.LocalTime.Tick >= targetTick);
-        }
-
         /// <summary>
         /// Waits on the client side to be connected.
         /// </summary>

Tests/Editor/DisconnectMessageTests.cs

@@ -0,0 +1,56 @@
+using NUnit.Framework;
+using Unity.Collections;
+
+namespace Unity.Netcode.EditorTests
+{
+    public class DisconnectMessageTests
+    {
+        [Test]
+        public void EmptyDisconnectReason()
+        {
+            var networkContext = new NetworkContext();
+            var writer = new FastBufferWriter(20, Allocator.Temp, 20);
+            var msg = new DisconnectReasonMessage();
+            msg.Reason = string.Empty;
+            msg.Serialize(writer, msg.Version);
+
+            var fbr = new FastBufferReader(writer, Allocator.Temp);
+            var recvMsg = new DisconnectReasonMessage();
+            recvMsg.Deserialize(fbr, ref networkContext, msg.Version);
+
+            Assert.IsEmpty(recvMsg.Reason);
+        }
+
+        [Test]
+        public void DisconnectReason()
+        {
+            var networkContext = new NetworkContext();
+            var writer = new FastBufferWriter(20, Allocator.Temp, 20);
+            var msg = new DisconnectReasonMessage();
+            msg.Reason = "Foo";
+            msg.Serialize(writer, msg.Version);
+
+            var fbr = new FastBufferReader(writer, Allocator.Temp);
+            var recvMsg = new DisconnectReasonMessage();
+            recvMsg.Deserialize(fbr, ref networkContext, msg.Version);
+
+            Assert.AreEqual("Foo", recvMsg.Reason);
+        }
+
+        [Test]
+        public void DisconnectReasonTooLong()
+        {
+            var networkContext = new NetworkContext();
+            var writer = new FastBufferWriter(20, Allocator.Temp, 20);
+            var msg = new DisconnectReasonMessage();
+            msg.Reason = "ThisStringIsWayLongerThanTwentyBytes";
+            msg.Serialize(writer, msg.Version);
+
+            var fbr = new FastBufferReader(writer, Allocator.Temp);
+            var recvMsg = new DisconnectReasonMessage();
+            recvMsg.Deserialize(fbr, ref networkContext, msg.Version);
+
+            Assert.IsEmpty(recvMsg.Reason);
+        }
+    }
+}

Tests/Editor/DisconnectMessageTests.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 55a1355c62fe14a118253f8bbee7c3cf
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Tests/Editor/Messaging/MessageCorruptionTests.cs

@@ -0,0 +1,203 @@
+using System;
+using System.Collections.Generic;
+using System.Text.RegularExpressions;
+using NUnit.Framework;
+using NUnit.Framework.Internal;
+using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+using UnityEngine;
+using UnityEngine.TestTools;
+
+namespace Unity.Netcode.EditorTests
+{
+    public class MessageCorruptionTests
+    {
+
+        private struct TestMessage : INetworkMessage, INetworkSerializeByMemcpy
+        {
+            public ForceNetworkSerializeByMemcpy<Guid> Value;
+            public static bool Handled;
+            public static bool Deserialized;
+
+            public void Serialize(FastBufferWriter writer, int targetVersion)
+            {
+                writer.WriteValueSafe(Value);
+            }
+
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+            {
+                Deserialized = true;
+                reader.ReadValueSafe(out Value);
+                return true;
+            }
+
+            public void Handle(ref NetworkContext context)
+            {
+                Handled = true;
+            }
+
+            public int Version => 0;
+        }
+
+        private class TestMessageProvider : IMessageProvider
+        {
+            public List<MessagingSystem.MessageWithHandler> GetMessages()
+            {
+                return new List<MessagingSystem.MessageWithHandler>
+                {
+                    new MessagingSystem.MessageWithHandler
+                    {
+                        MessageType = typeof(TestMessage),
+                        Handler = MessagingSystem.ReceiveMessage<TestMessage>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessage>
+                    }
+                };
+            }
+        }
+
+        public enum TypeOfCorruption
+        {
+            OffsetPlus,
+            OffsetMinus,
+            CorruptBytes,
+            Truncated,
+            AdditionalGarbageData,
+        }
+
+        private class TestMessageSender : IMessageSender
+        {
+
+            public TypeOfCorruption Corruption;
+            public List<byte[]> MessageQueue = new List<byte[]>();
+
+            public unsafe void Send(ulong clientId, NetworkDelivery delivery, FastBufferWriter batchData)
+            {
+                switch (Corruption)
+                {
+                    case TypeOfCorruption.OffsetPlus:
+                        {
+                            using var subWriter = new FastBufferWriter(batchData.Length + 1, Allocator.Temp);
+                            subWriter.WriteByteSafe(0);
+                            subWriter.WriteBytesSafe(batchData.GetUnsafePtr(), batchData.Length);
+                            MessageQueue.Add(subWriter.ToArray());
+                            break;
+                        }
+                    case TypeOfCorruption.OffsetMinus:
+                        {
+                            using var subWriter = new FastBufferWriter(batchData.Length - 1, Allocator.Temp);
+                            subWriter.WriteBytesSafe(batchData.GetUnsafePtr() + 1, batchData.Length - 1);
+                            MessageQueue.Add(subWriter.ToArray());
+                            break;
+                        }
+                    case TypeOfCorruption.CorruptBytes:
+                        batchData.Seek(batchData.Length - 2);
+                        var currentByte = batchData.GetUnsafePtr()[0];
+                        batchData.WriteByteSafe((byte)(currentByte == 0 ? 1 : 0));
+                        MessageQueue.Add(batchData.ToArray());
+                        break;
+                    case TypeOfCorruption.Truncated:
+                        batchData.Truncate(batchData.Length - 1);
+                        MessageQueue.Add(batchData.ToArray());
+                        break;
+                    case TypeOfCorruption.AdditionalGarbageData:
+                        batchData.Seek(batchData.Length);
+                        batchData.WriteByteSafe(0);
+                        MessageQueue.Add(batchData.ToArray());
+                        break;
+                }
+            }
+        }
+
+        private MessagingSystem m_MessagingSystem;
+        private TestMessageSender m_MessageSender;
+
+        [SetUp]
+        public void SetUp()
+        {
+            TestMessage.Handled = false;
+            TestMessage.Deserialized = false;
+            m_MessageSender = new TestMessageSender();
+
+            m_MessagingSystem = new MessagingSystem(m_MessageSender, this, new TestMessageProvider());
+
+            m_MessagingSystem.ClientConnected(0);
+            m_MessagingSystem.SetVersion(0, XXHash.Hash32(typeof(TestMessage).FullName), 0);
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            m_MessagingSystem.Dispose();
+        }
+
+        private TestMessage GetMessage()
+        {
+            return new TestMessage
+            {
+                Value = Guid.NewGuid()
+            };
+        }
+
+        [Test]
+        public unsafe void WhenPacketsAreCorrupted_TheyDontGetProcessed([Values] TypeOfCorruption typeOfCorruption)
+        {
+            m_MessageSender.Corruption = typeOfCorruption;
+
+            switch (typeOfCorruption)
+            {
+                case TypeOfCorruption.OffsetMinus:
+                case TypeOfCorruption.OffsetPlus:
+                    LogAssert.Expect(LogType.Error, new Regex("Received a packet with an invalid Magic Value\\."));
+                    break;
+                case TypeOfCorruption.Truncated:
+                case TypeOfCorruption.AdditionalGarbageData:
+                    LogAssert.Expect(LogType.Error, new Regex("Received a packet with an invalid Batch Size Value\\."));
+                    break;
+                case TypeOfCorruption.CorruptBytes:
+                    LogAssert.Expect(LogType.Error, new Regex("Received a packet with an invalid Hash Value\\."));
+                    break;
+            }
+
+            // Dummy batch header
+            var batchHeader = new BatchHeader
+            {
+                BatchCount = 1
+            };
+            var messageHeader = new MessageHeader
+            {
+                MessageSize = (ushort)UnsafeUtility.SizeOf<TestMessage>(),
+                MessageType = m_MessagingSystem.GetMessageType(typeof(TestMessage)),
+            };
+            var message = GetMessage();
+
+            var writer = new FastBufferWriter(1300, Allocator.Temp);
+            using (writer)
+            {
+                writer.TryBeginWrite(FastBufferWriter.GetWriteSize(batchHeader) +
+                                     FastBufferWriter.GetWriteSize(messageHeader) +
+                                     FastBufferWriter.GetWriteSize(message));
+                writer.WriteValue(batchHeader);
+                writer.WriteValue(messageHeader);
+                writer.WriteValue(message);
+
+                // Fill out the rest of the batch header
+                writer.Seek(0);
+                batchHeader = new BatchHeader
+                {
+                    Magic = BatchHeader.MagicValue,
+                    BatchSize = writer.Length,
+                    BatchHash = XXHash.Hash64(writer.GetUnsafePtr() + sizeof(BatchHeader), writer.Length - sizeof(BatchHeader)),
+                    BatchCount = 1
+                };
+                writer.WriteValue(batchHeader);
+                m_MessageSender.Send(0, NetworkDelivery.Reliable, writer);
+
+                var receivedMessage = m_MessageSender.MessageQueue[0];
+                m_MessageSender.MessageQueue.Clear();
+                m_MessagingSystem.HandleIncomingData(0, new ArraySegment<byte>(receivedMessage), 0);
+                Assert.IsFalse(TestMessage.Deserialized);
+                Assert.IsFalse(TestMessage.Handled);
+            }
+        }
+    }
+}

Tests/Editor/Messaging/MessageCorruptionTests.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: d3c01a0b5a0e478ebc5182fe339bde04
+timeCreated: 1676997550

Tests/Editor/Messaging/MessageReceivingTests.cs

@@ -18,12 +18,12 @@ namespace Unity.Netcode.EditorTests
             public static bool Handled;
             public static List<TestMessage> DeserializedValues = new List<TestMessage>();
 
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 writer.WriteValueSafe(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 Deserialized = true;
                 reader.ReadValueSafe(out this);
@@ -35,6 +35,8 @@ namespace Unity.Netcode.EditorTests
                 Handled = true;
                 DeserializedValues.Add(this);
             }
+
+            public int Version => 0;
         }
 
         private class TestMessageProvider : IMessageProvider
@@ -46,7 +48,8 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessage),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessage>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessage>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessage>
                     }
                 };
             }
@@ -62,6 +65,7 @@ namespace Unity.Netcode.EditorTests
             TestMessage.DeserializedValues.Clear();
 
             m_MessagingSystem = new MessagingSystem(new NopMessageSender(), this, new TestMessageProvider());
+            m_MessagingSystem.SetVersion(0, XXHash.Hash32(typeof(TestMessage).FullName), 0);
         }
 
         [TearDown]
@@ -110,11 +114,11 @@ namespace Unity.Netcode.EditorTests
         }
 
         [Test]
-        public void WhenHandlingIncomingData_ReceiveIsNotCalledBeforeProcessingIncomingMessageQueue()
+        public unsafe void WhenHandlingIncomingData_ReceiveIsNotCalledBeforeProcessingIncomingMessageQueue()
         {
             var batchHeader = new BatchHeader
             {
-                BatchSize = 1
+                BatchCount = 1
             };
             var messageHeader = new MessageHeader
             {
@@ -133,6 +137,17 @@ namespace Unity.Netcode.EditorTests
                 writer.WriteValue(messageHeader);
                 writer.WriteValue(message);
 
+                // Fill out the rest of the batch header
+                writer.Seek(0);
+                batchHeader = new BatchHeader
+                {
+                    Magic = BatchHeader.MagicValue,
+                    BatchSize = writer.Length,
+                    BatchHash = XXHash.Hash64(writer.GetUnsafePtr() + sizeof(BatchHeader), writer.Length - sizeof(BatchHeader)),
+                    BatchCount = 1
+                };
+                writer.WriteValue(batchHeader);
+
                 var reader = new FastBufferReader(writer, Allocator.Temp);
                 using (reader)
                 {
@@ -145,11 +160,11 @@ namespace Unity.Netcode.EditorTests
         }
 
         [Test]
-        public void WhenReceivingAMessageAndProcessingMessageQueue_ReceiveMethodIsCalled()
+        public unsafe void WhenReceivingAMessageAndProcessingMessageQueue_ReceiveMethodIsCalled()
         {
             var batchHeader = new BatchHeader
             {
-                BatchSize = 1
+                BatchCount = 1
             };
             var messageHeader = new MessageHeader
             {
@@ -166,6 +181,17 @@ namespace Unity.Netcode.EditorTests
                 BytePacker.WriteValueBitPacked(writer, messageHeader.MessageSize);
                 writer.WriteValueSafe(message);
 
+                // Fill out the rest of the batch header
+                writer.Seek(0);
+                batchHeader = new BatchHeader
+                {
+                    Magic = BatchHeader.MagicValue,
+                    BatchSize = writer.Length,
+                    BatchHash = XXHash.Hash64(writer.GetUnsafePtr() + sizeof(BatchHeader), writer.Length - sizeof(BatchHeader)),
+                    BatchCount = 1
+                };
+                writer.WriteValue(batchHeader);
+
                 var reader = new FastBufferReader(writer, Allocator.Temp);
                 using (reader)
                 {
@@ -180,11 +206,11 @@ namespace Unity.Netcode.EditorTests
         }
 
         [Test]
-        public void WhenReceivingMultipleMessagesAndProcessingMessageQueue_ReceiveMethodIsCalledMultipleTimes()
+        public unsafe void WhenReceivingMultipleMessagesAndProcessingMessageQueue_ReceiveMethodIsCalledMultipleTimes()
         {
             var batchHeader = new BatchHeader
             {
-                BatchSize = 2
+                BatchCount = 2
             };
             var messageHeader = new MessageHeader
             {
@@ -205,6 +231,17 @@ namespace Unity.Netcode.EditorTests
                 BytePacker.WriteValueBitPacked(writer, messageHeader.MessageSize);
                 writer.WriteValueSafe(message2);
 
+                // Fill out the rest of the batch header
+                writer.Seek(0);
+                batchHeader = new BatchHeader
+                {
+                    Magic = BatchHeader.MagicValue,
+                    BatchSize = writer.Length,
+                    BatchHash = XXHash.Hash64(writer.GetUnsafePtr() + sizeof(BatchHeader), writer.Length - sizeof(BatchHeader)),
+                    BatchCount = 2
+                };
+                writer.WriteValue(batchHeader);
+
                 var reader = new FastBufferReader(writer, Allocator.Temp);
                 using (reader)
                 {

Tests/Editor/Messaging/MessageRegistrationTests.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using NUnit.Framework;
 
@@ -11,12 +10,12 @@ namespace Unity.Netcode.EditorTests
             public int A;
             public int B;
             public int C;
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 writer.WriteValue(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -24,6 +23,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
 
         private struct TestMessageTwo : INetworkMessage, INetworkSerializeByMemcpy
@@ -31,12 +32,12 @@ namespace Unity.Netcode.EditorTests
             public int A;
             public int B;
             public int C;
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 writer.WriteValue(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -44,6 +45,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
         private class TestMessageProviderOne : IMessageProvider
         {
@@ -54,12 +57,14 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessageOne),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessageOne>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessageOne>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessageOne>
                     },
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessageTwo),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessageTwo>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessageTwo>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessageTwo>
                     }
                 };
             }
@@ -70,12 +75,12 @@ namespace Unity.Netcode.EditorTests
             public int A;
             public int B;
             public int C;
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 writer.WriteValue(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -83,6 +88,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
         private class TestMessageProviderTwo : IMessageProvider
         {
@@ -93,7 +100,8 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessageThree),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessageThree>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessageThree>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessageThree>
                     }
                 };
             }
@@ -103,12 +111,12 @@ namespace Unity.Netcode.EditorTests
             public int A;
             public int B;
             public int C;
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 writer.WriteValue(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -116,6 +124,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
         private class TestMessageProviderThree : IMessageProvider
         {
@@ -126,7 +136,8 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessageFour),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessageFour>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessageFour>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessageFour>
                     }
                 };
             }
@@ -183,11 +194,11 @@ namespace Unity.Netcode.EditorTests
 
         internal class AAAEarlyLexicographicNetworkMessage : INetworkMessage
         {
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -195,6 +206,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
 
 #pragma warning disable IDE1006
@@ -212,18 +225,19 @@ namespace Unity.Netcode.EditorTests
                 var messageWithHandler = new MessagingSystem.MessageWithHandler();
 
                 messageWithHandler.MessageType = typeof(zzzLateLexicographicNetworkMessage);
+                messageWithHandler.GetVersion = MessagingSystem.CreateMessageAndGetVersion<zzzLateLexicographicNetworkMessage>;
                 listMessages.Add(messageWithHandler);
 
                 messageWithHandler.MessageType = typeof(ConnectionRequestMessage);
+                messageWithHandler.GetVersion = MessagingSystem.CreateMessageAndGetVersion<ConnectionRequestMessage>;
                 listMessages.Add(messageWithHandler);
 
                 messageWithHandler.MessageType = typeof(ConnectionApprovedMessage);
-                listMessages.Add(messageWithHandler);
+                messageWithHandler.GetVersion = MessagingSystem.CreateMessageAndGetVersion<ConnectionApprovedMessage>;
-
-                messageWithHandler.MessageType = typeof(OrderingMessage);
                 listMessages.Add(messageWithHandler);
 
                 messageWithHandler.MessageType = typeof(AAAEarlyLexicographicNetworkMessage);
+                messageWithHandler.GetVersion = MessagingSystem.CreateMessageAndGetVersion<AAAEarlyLexicographicNetworkMessage>;
                 listMessages.Add(messageWithHandler);
 
                 return listMessages;
@@ -237,65 +251,16 @@ namespace Unity.Netcode.EditorTests
             var provider = new OrderingMessageProvider();
             using var messagingSystem = new MessagingSystem(sender, null, provider);
 
-            // the 3 priority messages should appear first, in lexicographic order
+            // the 2 priority messages should appear first, in lexicographic order
             Assert.AreEqual(messagingSystem.MessageTypes[0], typeof(ConnectionApprovedMessage));
             Assert.AreEqual(messagingSystem.MessageTypes[1], typeof(ConnectionRequestMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[2], typeof(OrderingMessage));
 
             // the other should follow after
-            Assert.AreEqual(messagingSystem.MessageTypes[3], typeof(AAAEarlyLexicographicNetworkMessage));
+            Assert.AreEqual(messagingSystem.MessageTypes[2], typeof(AAAEarlyLexicographicNetworkMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[4], typeof(zzzLateLexicographicNetworkMessage));
+            Assert.AreEqual(messagingSystem.MessageTypes[3], typeof(zzzLateLexicographicNetworkMessage));
 
             // there should not be any extras
-            Assert.AreEqual(messagingSystem.MessageHandlerCount, 5);
+            Assert.AreEqual(messagingSystem.MessageHandlerCount, 4);
-
-            // reorder the zzz one to position 3
-            messagingSystem.ReorderMessage(3, XXHash.Hash32(typeof(zzzLateLexicographicNetworkMessage).FullName));
-
-            // the 3 priority messages should still appear first, in lexicographic order
-            Assert.AreEqual(messagingSystem.MessageTypes[0], typeof(ConnectionApprovedMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[1], typeof(ConnectionRequestMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[2], typeof(OrderingMessage));
-
-            // the other should follow after, but reordered
-            Assert.AreEqual(messagingSystem.MessageTypes[3], typeof(zzzLateLexicographicNetworkMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[4], typeof(AAAEarlyLexicographicNetworkMessage));
-
-            // there should still not be any extras
-            Assert.AreEqual(messagingSystem.MessageHandlerCount, 5);
-
-            // verify we get an exception when asking for an invalid position
-            try
-            {
-                messagingSystem.ReorderMessage(-1, XXHash.Hash32(typeof(zzzLateLexicographicNetworkMessage).FullName));
-                Assert.Fail();
-            }
-            catch (ArgumentException)
-            {
-            }
-
-            // reorder the zzz one to position 3, again, to check nothing bad happens
-            messagingSystem.ReorderMessage(3, XXHash.Hash32(typeof(zzzLateLexicographicNetworkMessage).FullName));
-
-            // the two non-priority should not have moved
-            Assert.AreEqual(messagingSystem.MessageTypes[3], typeof(zzzLateLexicographicNetworkMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[4], typeof(AAAEarlyLexicographicNetworkMessage));
-
-            // there should still not be any extras
-            Assert.AreEqual(messagingSystem.MessageHandlerCount, 5);
-
-            // 4242 is a random hash that should not match anything
-            messagingSystem.ReorderMessage(3, 4242);
-
-            // that should result in an extra entry
-            Assert.AreEqual(messagingSystem.MessageHandlerCount, 6);
-
-            // with a null handler
-            Assert.AreEqual(messagingSystem.MessageHandlers[3], null);
-
-            // and it should have bumped the previous messages down
-            Assert.AreEqual(messagingSystem.MessageTypes[4], typeof(zzzLateLexicographicNetworkMessage));
-            Assert.AreEqual(messagingSystem.MessageTypes[5], typeof(AAAEarlyLexicographicNetworkMessage));
         }
     }
 }

Tests/Editor/Messaging/MessageSendingTests.cs

@@ -18,13 +18,13 @@ namespace Unity.Netcode.EditorTests
             public int B;
             public int C;
             public static bool Serialized;
-            public void Serialize(FastBufferWriter writer)
+            public void Serialize(FastBufferWriter writer, int targetVersion)
             {
                 Serialized = true;
                 writer.WriteValueSafe(this);
             }
 
-            public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
             {
                 return true;
             }
@@ -32,6 +32,8 @@ namespace Unity.Netcode.EditorTests
             public void Handle(ref NetworkContext context)
             {
             }
+
+            public int Version => 0;
         }
 
         private class TestMessageSender : IMessageSender
@@ -66,7 +68,8 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessage),
-                        Handler = MessagingSystem.ReceiveMessage<TestMessage>
+                        Handler = MessagingSystem.ReceiveMessage<TestMessage>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessage>
                     }
                 };
                 // Track messages sent
@@ -88,6 +91,7 @@ namespace Unity.Netcode.EditorTests
             m_TestMessageProvider = new TestMessageProvider();
             m_MessagingSystem = new MessagingSystem(m_MessageSender, this, m_TestMessageProvider);
             m_MessagingSystem.ClientConnected(0);
+            m_MessagingSystem.SetVersion(0, XXHash.Hash32(typeof(TestMessage).FullName), 0);
         }
 
         [TearDown]
@@ -151,7 +155,7 @@ namespace Unity.Netcode.EditorTests
         {
             var message = GetMessage();
             var size = UnsafeUtility.SizeOf<TestMessage>() + 2; // MessageHeader packed with this message will be 2 bytes
-            for (var i = 0; i < 1300 / size; ++i)
+            for (var i = 0; i < (1300 - UnsafeUtility.SizeOf<BatchHeader>()) / size; ++i)
             {
                 m_MessagingSystem.SendMessage(ref message, NetworkDelivery.Reliable, m_Clients);
             }
@@ -165,7 +169,7 @@ namespace Unity.Netcode.EditorTests
         {
             var message = GetMessage();
             var size = UnsafeUtility.SizeOf<TestMessage>() + 2; // MessageHeader packed with this message will be 2 bytes
-            for (var i = 0; i < (1300 / size) + 1; ++i)
+            for (var i = 0; i < ((1300 - UnsafeUtility.SizeOf<BatchHeader>()) / size) + 1; ++i)
             {
                 m_MessagingSystem.SendMessage(ref message, NetworkDelivery.Reliable, m_Clients);
             }
@@ -179,7 +183,7 @@ namespace Unity.Netcode.EditorTests
         {
             var message = GetMessage();
             var size = UnsafeUtility.SizeOf<TestMessage>() + 2; // MessageHeader packed with this message will be 2 bytes
-            for (var i = 0; i < (1300 / size) + 1; ++i)
+            for (var i = 0; i < ((1300 - UnsafeUtility.SizeOf<BatchHeader>()) / size) + 1; ++i)
             {
                 m_MessagingSystem.SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, m_Clients);
             }
@@ -225,7 +229,7 @@ namespace Unity.Netcode.EditorTests
             using (reader)
             {
                 reader.ReadValueSafe(out BatchHeader header);
-                Assert.AreEqual(2, header.BatchSize);
+                Assert.AreEqual(2, header.BatchCount);
 
                 MessageHeader messageHeader;
 
@@ -256,7 +260,8 @@ namespace Unity.Netcode.EditorTests
                     new MessagingSystem.MessageWithHandler
                     {
                         MessageType = typeof(TestMessage),
-                        Handler = null
+                        Handler = null,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<TestMessage>
                     }
                 };
             }

Tests/Editor/Messaging/MessageVersioningTests.cs

@@ -0,0 +1,503 @@
+using System;
+using System.Collections.Generic;
+using NUnit.Framework;
+using NUnit.Framework.Internal;
+
+namespace Unity.Netcode.EditorTests
+{
+    public class MessageVersioningTests
+    {
+        public static int SentVersion;
+        public static int ReceivedVersion;
+
+        private const int k_DefaultB = 5;
+        private const int k_DefaultC = 10;
+        private const int k_DefaultD = 15;
+        private const long k_DefaultE = 20;
+
+        private struct VersionedTestMessage_v0 : INetworkMessage, INetworkSerializeByMemcpy
+        {
+            public int A;
+            public int B;
+            public int C;
+            public static bool Serialized;
+            public static bool Deserialized;
+            public static bool Handled;
+            public static List<VersionedTestMessage_v0> DeserializedValues = new List<VersionedTestMessage_v0>();
+
+            public void Serialize(FastBufferWriter writer, int targetVersion)
+            {
+                SentVersion = Version;
+                Serialized = true;
+                writer.WriteValueSafe(A);
+                writer.WriteValueSafe(B);
+                writer.WriteValueSafe(C);
+            }
+
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+            {
+                ReceivedVersion = Version;
+                Deserialized = true;
+                reader.ReadValueSafe(out A);
+                reader.ReadValueSafe(out B);
+                reader.ReadValueSafe(out C);
+                return true;
+            }
+
+            public void Handle(ref NetworkContext context)
+            {
+                Handled = true;
+                DeserializedValues.Add(this);
+            }
+
+            public int Version => 0;
+        }
+
+        private struct VersionedTestMessage_v1 : INetworkMessage, INetworkSerializeByMemcpy
+        {
+            public int A;
+            public int B;
+            public int C;
+            public int D;
+            public static bool Serialized;
+            public static bool Deserialized;
+            public static bool Downgraded;
+            public static bool Upgraded;
+            public static bool Handled;
+            public static List<VersionedTestMessage_v1> DeserializedValues = new List<VersionedTestMessage_v1>();
+
+            public void Serialize(FastBufferWriter writer, int targetVersion)
+            {
+                if (targetVersion < Version)
+                {
+                    Downgraded = true;
+                    var v0 = new VersionedTestMessage_v0 { A = A, B = B, C = C };
+                    v0.Serialize(writer, targetVersion);
+                    return;
+                }
+                SentVersion = Version;
+                Serialized = true;
+                writer.WriteValueSafe(C);
+                writer.WriteValueSafe(D);
+                writer.WriteValueSafe(A);
+                writer.WriteValueSafe(B);
+            }
+
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+            {
+                if (receivedMessageVersion < Version)
+                {
+                    var v0 = new VersionedTestMessage_v0();
+                    v0.Deserialize(reader, ref context, receivedMessageVersion);
+                    A = v0.A;
+                    B = v0.B;
+                    C = v0.C;
+                    D = k_DefaultD;
+                    Upgraded = true;
+                    return true;
+                }
+                ReceivedVersion = Version;
+                Deserialized = true;
+                reader.ReadValueSafe(out C);
+                reader.ReadValueSafe(out D);
+                reader.ReadValueSafe(out A);
+                reader.ReadValueSafe(out B);
+                return true;
+            }
+
+            public void Handle(ref NetworkContext context)
+            {
+                Handled = true;
+                DeserializedValues.Add(this);
+            }
+
+            public int Version => 1;
+        }
+
+        private struct VersionedTestMessage : INetworkMessage, INetworkSerializeByMemcpy
+        {
+            public int A;
+            public float D;
+            public long E;
+            public static bool Serialized;
+            public static bool Deserialized;
+            public static bool Downgraded;
+            public static bool Upgraded;
+            public static bool Handled;
+            public static List<VersionedTestMessage> DeserializedValues = new List<VersionedTestMessage>();
+
+            public void Serialize(FastBufferWriter writer, int targetVersion)
+            {
+                if (targetVersion < Version)
+                {
+                    Downgraded = true;
+                    var v1 = new VersionedTestMessage_v1 { A = A, B = k_DefaultB, C = k_DefaultC, D = (int)D };
+                    v1.Serialize(writer, targetVersion);
+                    return;
+                }
+                SentVersion = Version;
+                Serialized = true;
+                writer.WriteValueSafe(D);
+                writer.WriteValueSafe(A);
+                writer.WriteValueSafe(E);
+            }
+
+            public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+            {
+                if (receivedMessageVersion < Version)
+                {
+                    var v1 = new VersionedTestMessage_v1();
+                    v1.Deserialize(reader, ref context, receivedMessageVersion);
+                    A = v1.A;
+                    D = (float)v1.D;
+                    E = k_DefaultE;
+                    Upgraded = true;
+                    return true;
+                }
+                ReceivedVersion = Version;
+                Deserialized = true;
+                reader.ReadValueSafe(out D);
+                reader.ReadValueSafe(out A);
+                reader.ReadValueSafe(out E);
+                return true;
+            }
+
+            public void Handle(ref NetworkContext context)
+            {
+                Handled = true;
+                DeserializedValues.Add(this);
+            }
+
+            public int Version => 2;
+        }
+
+        private class TestMessageProvider_v0 : IMessageProvider
+        {
+            public List<MessagingSystem.MessageWithHandler> GetMessages()
+            {
+                return new List<MessagingSystem.MessageWithHandler>
+                {
+                    new MessagingSystem.MessageWithHandler
+                    {
+                        MessageType = typeof(VersionedTestMessage_v0),
+                        Handler = MessagingSystem.ReceiveMessage<VersionedTestMessage_v0>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<VersionedTestMessage_v0>
+                    }
+                };
+            }
+        }
+
+        private class TestMessageProvider_v1 : IMessageProvider
+        {
+            public List<MessagingSystem.MessageWithHandler> GetMessages()
+            {
+                return new List<MessagingSystem.MessageWithHandler>
+                {
+                    new MessagingSystem.MessageWithHandler
+                    {
+                        MessageType = typeof(VersionedTestMessage_v1),
+                        Handler = MessagingSystem.ReceiveMessage<VersionedTestMessage_v1>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<VersionedTestMessage_v1>
+                    }
+                };
+            }
+        }
+
+        private class TestMessageProvider_v2 : IMessageProvider
+        {
+            public List<MessagingSystem.MessageWithHandler> GetMessages()
+            {
+                return new List<MessagingSystem.MessageWithHandler>
+                {
+                    new MessagingSystem.MessageWithHandler
+                    {
+                        MessageType = typeof(VersionedTestMessage),
+                        Handler = MessagingSystem.ReceiveMessage<VersionedTestMessage>,
+                        GetVersion = MessagingSystem.CreateMessageAndGetVersion<VersionedTestMessage>
+                    }
+                };
+            }
+        }
+
+        private class TestMessageSender : IMessageSender
+        {
+            public List<byte[]> MessageQueue = new List<byte[]>();
+
+            public void Send(ulong clientId, NetworkDelivery delivery, FastBufferWriter batchData)
+            {
+                MessageQueue.Add(batchData.ToArray());
+            }
+        }
+
+        private MessagingSystem m_MessagingSystem_v0;
+        private MessagingSystem m_MessagingSystem_v1;
+        private MessagingSystem m_MessagingSystem_v2;
+        private TestMessageSender m_MessageSender;
+
+        private void CreateFakeClients(MessagingSystem system, uint hash)
+        {
+            // Create three fake clients for each messaging system
+            // client 0 has version 0, client 1 has version 1, and client 2 has version 2
+            system.ClientConnected(0);
+            system.ClientConnected(1);
+            system.ClientConnected(2);
+            system.SetVersion(0, hash, 0);
+            system.SetVersion(1, hash, 1);
+            system.SetVersion(2, hash, 2);
+        }
+
+        [SetUp]
+        public void SetUp()
+        {
+            VersionedTestMessage_v0.Serialized = false;
+            VersionedTestMessage_v0.Deserialized = false;
+            VersionedTestMessage_v0.Handled = false;
+            VersionedTestMessage_v0.DeserializedValues.Clear();
+            VersionedTestMessage_v1.Serialized = false;
+            VersionedTestMessage_v1.Deserialized = false;
+            VersionedTestMessage_v1.Downgraded = false;
+            VersionedTestMessage_v1.Upgraded = false;
+            VersionedTestMessage_v1.Handled = false;
+            VersionedTestMessage_v1.DeserializedValues.Clear();
+            VersionedTestMessage.Serialized = false;
+            VersionedTestMessage.Deserialized = false;
+            VersionedTestMessage.Downgraded = false;
+            VersionedTestMessage.Upgraded = false;
+            VersionedTestMessage.Handled = false;
+            VersionedTestMessage.DeserializedValues.Clear();
+            m_MessageSender = new TestMessageSender();
+
+            m_MessagingSystem_v0 = new MessagingSystem(m_MessageSender, this, new TestMessageProvider_v0());
+            m_MessagingSystem_v1 = new MessagingSystem(m_MessageSender, this, new TestMessageProvider_v1());
+            m_MessagingSystem_v2 = new MessagingSystem(m_MessageSender, this, new TestMessageProvider_v2());
+
+            CreateFakeClients(m_MessagingSystem_v0, XXHash.Hash32(typeof(VersionedTestMessage_v0).FullName));
+            CreateFakeClients(m_MessagingSystem_v1, XXHash.Hash32(typeof(VersionedTestMessage_v1).FullName));
+            CreateFakeClients(m_MessagingSystem_v2, XXHash.Hash32(typeof(VersionedTestMessage).FullName));
+
+            // Make sure that all three messages got the same IDs...
+            Assert.AreEqual(
+                m_MessagingSystem_v0.GetMessageType(typeof(VersionedTestMessage_v0)),
+                m_MessagingSystem_v1.GetMessageType(typeof(VersionedTestMessage_v1)));
+            Assert.AreEqual(
+                m_MessagingSystem_v0.GetMessageType(typeof(VersionedTestMessage_v0)),
+                m_MessagingSystem_v2.GetMessageType(typeof(VersionedTestMessage)));
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            m_MessagingSystem_v0.Dispose();
+            m_MessagingSystem_v1.Dispose();
+            m_MessagingSystem_v2.Dispose();
+        }
+
+        private VersionedTestMessage_v0 GetMessage_v0()
+        {
+            var random = new Random();
+            return new VersionedTestMessage_v0
+            {
+                A = random.Next(),
+                B = random.Next(),
+                C = random.Next(),
+            };
+        }
+
+        private VersionedTestMessage_v1 GetMessage_v1()
+        {
+            var random = new Random();
+            return new VersionedTestMessage_v1
+            {
+                A = random.Next(),
+                B = random.Next(),
+                C = random.Next(),
+                D = random.Next(),
+            };
+        }
+
+        private VersionedTestMessage GetMessage_v2()
+        {
+            var random = new Random();
+            return new VersionedTestMessage
+            {
+                A = random.Next(),
+                D = (float)(random.NextDouble() * 10000),
+                E = ((long)random.Next() << 32) + random.Next()
+            };
+        }
+
+        public void CheckPostSendExpectations(int sourceLocalVersion, int remoteVersion)
+        {
+            Assert.AreEqual(Math.Min(sourceLocalVersion, remoteVersion) == 0, VersionedTestMessage_v0.Serialized);
+            Assert.AreEqual(Math.Min(sourceLocalVersion, remoteVersion) == 1, VersionedTestMessage_v1.Serialized);
+            Assert.AreEqual(Math.Min(sourceLocalVersion, remoteVersion) == 2, VersionedTestMessage.Serialized);
+            Assert.AreEqual(sourceLocalVersion >= 1 && remoteVersion < 1, VersionedTestMessage_v1.Downgraded);
+            Assert.AreEqual(sourceLocalVersion >= 2 && remoteVersion < 2, VersionedTestMessage.Downgraded);
+
+            Assert.AreEqual(1, m_MessageSender.MessageQueue.Count);
+            Assert.AreEqual(Math.Min(sourceLocalVersion, remoteVersion), SentVersion);
+        }
+
+        public void CheckPostReceiveExpectations(int sourceLocalVersion, int remoteVersion)
+        {
+            Assert.AreEqual(SentVersion == 0, VersionedTestMessage_v0.Deserialized);
+            Assert.AreEqual(SentVersion == 1, VersionedTestMessage_v1.Deserialized);
+            Assert.AreEqual(SentVersion == 2, VersionedTestMessage.Deserialized);
+            Assert.AreEqual(remoteVersion >= 1 && sourceLocalVersion < 1, VersionedTestMessage_v1.Upgraded);
+            Assert.AreEqual(remoteVersion >= 2 && sourceLocalVersion < 2, VersionedTestMessage.Upgraded);
+
+            Assert.AreEqual((remoteVersion == 0 ? 1 : 0), VersionedTestMessage_v0.DeserializedValues.Count);
+            Assert.AreEqual((remoteVersion == 1 ? 1 : 0), VersionedTestMessage_v1.DeserializedValues.Count);
+            Assert.AreEqual((remoteVersion == 2 ? 1 : 0), VersionedTestMessage.DeserializedValues.Count);
+
+            Assert.AreEqual(SentVersion, ReceivedVersion);
+        }
+
+        private void SendMessageWithVersions<T>(T message, int fromVersion, int toVersion) where T : unmanaged, INetworkMessage
+        {
+            MessagingSystem sendSystem;
+            switch (fromVersion)
+            {
+                case 0: sendSystem = m_MessagingSystem_v0; break;
+                case 1: sendSystem = m_MessagingSystem_v1; break;
+                default: sendSystem = m_MessagingSystem_v2; break;
+            }
+            sendSystem.SendMessage(ref message, NetworkDelivery.Reliable, (ulong)toVersion);
+            sendSystem.ProcessSendQueues();
+            CheckPostSendExpectations(fromVersion, toVersion);
+
+            MessagingSystem receiveSystem;
+            switch (toVersion)
+            {
+                case 0: receiveSystem = m_MessagingSystem_v0; break;
+                case 1: receiveSystem = m_MessagingSystem_v1; break;
+                default: receiveSystem = m_MessagingSystem_v2; break;
+            }
+            receiveSystem.HandleIncomingData((ulong)fromVersion, new ArraySegment<byte>(m_MessageSender.MessageQueue[0]), 0.0f);
+            receiveSystem.ProcessIncomingMessageQueue();
+            CheckPostReceiveExpectations(fromVersion, toVersion);
+
+            m_MessageSender.MessageQueue.Clear();
+        }
+
+        [Test]
+        public void WhenSendingV0ToV0_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v0();
+
+            SendMessageWithVersions(message, 0, 0);
+
+            var receivedMessage = VersionedTestMessage_v0.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(message.B, receivedMessage.B);
+            Assert.AreEqual(message.C, receivedMessage.C);
+        }
+
+        [Test]
+        public void WhenSendingV0ToV1_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v0();
+
+            SendMessageWithVersions(message, 0, 1);
+
+            var receivedMessage = VersionedTestMessage_v1.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(message.B, receivedMessage.B);
+            Assert.AreEqual(message.C, receivedMessage.C);
+            Assert.AreEqual(k_DefaultD, receivedMessage.D);
+        }
+
+        [Test]
+        public void WhenSendingV0ToV2_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v0();
+
+            SendMessageWithVersions(message, 0, 2);
+
+            var receivedMessage = VersionedTestMessage.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual((float)k_DefaultD, receivedMessage.D);
+            Assert.AreEqual(k_DefaultE, receivedMessage.E);
+        }
+
+        [Test]
+        public void WhenSendingV1ToV0_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v1();
+
+            SendMessageWithVersions(message, 1, 0);
+
+            var receivedMessage = VersionedTestMessage_v0.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(message.B, receivedMessage.B);
+            Assert.AreEqual(message.C, receivedMessage.C);
+        }
+
+        [Test]
+        public void WhenSendingV1ToV1_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v1();
+
+            SendMessageWithVersions(message, 1, 1);
+
+            var receivedMessage = VersionedTestMessage_v1.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(message.B, receivedMessage.B);
+            Assert.AreEqual(message.C, receivedMessage.C);
+            Assert.AreEqual(message.D, receivedMessage.D);
+        }
+
+        [Test]
+        public void WhenSendingV1ToV2_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v1();
+
+            SendMessageWithVersions(message, 1, 2);
+
+            var receivedMessage = VersionedTestMessage.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual((float)message.D, receivedMessage.D);
+            Assert.AreEqual(k_DefaultE, receivedMessage.E);
+        }
+
+        [Test]
+        public void WhenSendingV2ToV0_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v2();
+
+            SendMessageWithVersions(message, 2, 0);
+
+            var receivedMessage = VersionedTestMessage_v0.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(k_DefaultB, receivedMessage.B);
+            Assert.AreEqual(k_DefaultC, receivedMessage.C);
+        }
+
+        [Test]
+        public void WhenSendingV2ToV1_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v2();
+
+            SendMessageWithVersions(message, 2, 1);
+
+            var receivedMessage = VersionedTestMessage_v1.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(k_DefaultB, receivedMessage.B);
+            Assert.AreEqual(k_DefaultC, receivedMessage.C);
+            Assert.AreEqual((int)message.D, receivedMessage.D);
+        }
+
+        [Test]
+        public void WhenSendingV2ToV2_DataIsReceivedCorrectly()
+        {
+            var message = GetMessage_v2();
+
+            SendMessageWithVersions(message, 2, 2);
+
+            var receivedMessage = VersionedTestMessage.DeserializedValues[0];
+            Assert.AreEqual(message.A, receivedMessage.A);
+            Assert.AreEqual(message.D, receivedMessage.D);
+            Assert.AreEqual(message.E, receivedMessage.E);
+        }
+    }
+}

Tests/Editor/Messaging/MessageVersioningTests.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: eac9a654aacb4faf91128c9ab6024543
+timeCreated: 1667326658

Tests/Editor/NetworkManagerConfigurationTests.cs

@@ -1,6 +1,8 @@
+using System.Collections.Generic;
 using NUnit.Framework;
 using UnityEngine;
 using Unity.Netcode.Editor;
+using Unity.Netcode.Transports.UTP;
 using UnityEditor.SceneManagement;
 using UnityEngine.SceneManagement;
 using UnityEngine.TestTools;
@@ -105,12 +107,188 @@ namespace Unity.Netcode.EditorTests
             networkManager.OnValidate();
 
             // Expect a warning
-            LogAssert.Expect(LogType.Warning, $"[Netcode] {NetworkManager.PrefabDebugHelper(networkManager.NetworkConfig.NetworkPrefabs[0])} has child {nameof(NetworkObject)}(s) but they will not be spawned across the network (unsupported {nameof(NetworkPrefab)} setup)");
+            LogAssert.Expect(LogType.Warning, $"[Netcode] {NetworkManager.PrefabDebugHelper(networkManager.NetworkConfig.Prefabs.Prefabs[0])} has child {nameof(NetworkObject)}(s) but they will not be spawned across the network (unsupported {nameof(NetworkPrefab)} setup)");
 
             // Clean up
             Object.DestroyImmediate(networkManagerObject);
             Object.DestroyImmediate(parent);
 
         }
+
+        [Test]
+        public void WhenNetworkConfigContainsOldPrefabList_TheyMigrateProperlyToTheNewList()
+        {
+            var networkConfig = new NetworkConfig();
+
+            var regularPrefab = new GameObject("Regular Prefab").AddComponent<NetworkObject>();
+            var overriddenPrefab = new GameObject("Overridden Prefab").AddComponent<NetworkObject>();
+            var overridingTargetPrefab = new GameObject("Overriding Target Prefab").AddComponent<NetworkObject>();
+            var sourcePrefabToOverride = new GameObject("Overriding Source Prefab").AddComponent<NetworkObject>();
+
+            regularPrefab.GlobalObjectIdHash = 1;
+            overriddenPrefab.GlobalObjectIdHash = 2;
+            overridingTargetPrefab.GlobalObjectIdHash = 3;
+            sourcePrefabToOverride.GlobalObjectIdHash = 4;
+
+            networkConfig.OldPrefabList = new List<NetworkPrefab>();
+            networkConfig.OldPrefabList.Add(new NetworkPrefab { Prefab = regularPrefab.gameObject });
+            networkConfig.OldPrefabList.Add(new NetworkPrefab { Prefab = overriddenPrefab.gameObject, Override = NetworkPrefabOverride.Prefab, OverridingTargetPrefab = overridingTargetPrefab.gameObject, SourcePrefabToOverride = sourcePrefabToOverride.gameObject, SourceHashToOverride = 123456 });
+
+            networkConfig.InitializePrefabs();
+
+            Assert.IsNull(networkConfig.OldPrefabList);
+            Assert.IsNotNull(networkConfig.Prefabs);
+            Assert.IsNotNull(networkConfig.Prefabs.Prefabs);
+            Assert.AreEqual(2, networkConfig.Prefabs.Prefabs.Count);
+
+            Assert.AreSame(regularPrefab.gameObject, networkConfig.Prefabs.Prefabs[0].Prefab);
+            Assert.AreEqual(NetworkPrefabOverride.None, networkConfig.Prefabs.Prefabs[0].Override);
+            Assert.IsNull(networkConfig.Prefabs.Prefabs[0].SourcePrefabToOverride);
+            Assert.IsNull(networkConfig.Prefabs.Prefabs[0].OverridingTargetPrefab);
+
+            Assert.AreSame(overriddenPrefab.gameObject, networkConfig.Prefabs.Prefabs[1].Prefab);
+            Assert.AreEqual(NetworkPrefabOverride.Prefab, networkConfig.Prefabs.Prefabs[1].Override);
+            Assert.AreEqual(123456, networkConfig.Prefabs.Prefabs[1].SourceHashToOverride);
+            Assert.AreSame(sourcePrefabToOverride.gameObject, networkConfig.Prefabs.Prefabs[1].SourcePrefabToOverride);
+            Assert.AreSame(overridingTargetPrefab.gameObject, networkConfig.Prefabs.Prefabs[1].OverridingTargetPrefab);
+        }
+
+        [Test]
+        public void WhenModifyingPrefabListUsingNetworkManagerAPI_ModificationIsLocal()
+        {
+            // Setup
+            var networkManagerObject = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager = networkManagerObject.AddComponent<NetworkManager>();
+            networkManager.NetworkConfig = new NetworkConfig();
+            networkManager.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var networkManagerObject2 = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager2 = networkManagerObject2.AddComponent<NetworkManager>();
+            networkManager2.NetworkConfig = new NetworkConfig();
+            networkManager2.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var object1 = new GameObject("Object 1").AddComponent<NetworkObject>();
+            var object2 = new GameObject("Object 2").AddComponent<NetworkObject>();
+            var object3 = new GameObject("Object 3").AddComponent<NetworkObject>();
+
+            object1.GlobalObjectIdHash = 1;
+            object2.GlobalObjectIdHash = 2;
+            object3.GlobalObjectIdHash = 3;
+
+            var sharedList = ScriptableObject.CreateInstance<NetworkPrefabsList>();
+            sharedList.List.Add(new NetworkPrefab { Prefab = object1.gameObject });
+
+            networkManager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+            networkManager2.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+
+            networkManager.Initialize(true);
+            networkManager2.Initialize(false);
+
+            networkManager.AddNetworkPrefab(object2.gameObject);
+            networkManager2.AddNetworkPrefab(object3.gameObject);
+
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsFalse(networkManager2.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object3.gameObject));
+            Assert.IsFalse(networkManager.NetworkConfig.Prefabs.Contains(object3.gameObject));
+
+            Assert.IsTrue(sharedList.Contains(object1.gameObject));
+            Assert.IsFalse(sharedList.Contains(object2.gameObject));
+            Assert.IsFalse(sharedList.Contains(object3.gameObject));
+        }
+
+        [Test]
+        public void WhenModifyingPrefabListUsingPrefabsAPI_ModificationIsLocal()
+        {
+            // Setup
+            var networkManagerObject = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager = networkManagerObject.AddComponent<NetworkManager>();
+            networkManager.NetworkConfig = new NetworkConfig();
+            networkManager.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var networkManagerObject2 = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager2 = networkManagerObject2.AddComponent<NetworkManager>();
+            networkManager2.NetworkConfig = new NetworkConfig();
+            networkManager2.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var object1 = new GameObject("Object 1").AddComponent<NetworkObject>();
+            var object2 = new GameObject("Object 2").AddComponent<NetworkObject>();
+            var object3 = new GameObject("Object 3").AddComponent<NetworkObject>();
+
+            object1.GlobalObjectIdHash = 1;
+            object2.GlobalObjectIdHash = 2;
+            object3.GlobalObjectIdHash = 3;
+
+            var sharedList = ScriptableObject.CreateInstance<NetworkPrefabsList>();
+            sharedList.List.Add(new NetworkPrefab { Prefab = object1.gameObject });
+
+            networkManager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+            networkManager2.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+
+            networkManager.Initialize(true);
+            networkManager2.Initialize(false);
+
+            networkManager.NetworkConfig.Prefabs.Add(new NetworkPrefab { Prefab = object2.gameObject });
+            networkManager2.NetworkConfig.Prefabs.Add(new NetworkPrefab { Prefab = object3.gameObject });
+
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsFalse(networkManager2.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object3.gameObject));
+            Assert.IsFalse(networkManager.NetworkConfig.Prefabs.Contains(object3.gameObject));
+
+            Assert.IsTrue(sharedList.Contains(object1.gameObject));
+            Assert.IsFalse(sharedList.Contains(object2.gameObject));
+            Assert.IsFalse(sharedList.Contains(object3.gameObject));
+        }
+
+        [Test]
+        public void WhenModifyingPrefabListUsingPrefabsListAPI_ModificationIsShared()
+        {
+            // Setup
+            var networkManagerObject = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager = networkManagerObject.AddComponent<NetworkManager>();
+            networkManager.NetworkConfig = new NetworkConfig();
+            networkManager.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var networkManagerObject2 = new GameObject(nameof(NestedNetworkObjectPrefabCheck));
+            var networkManager2 = networkManagerObject2.AddComponent<NetworkManager>();
+            networkManager2.NetworkConfig = new NetworkConfig();
+            networkManager2.NetworkConfig.NetworkTransport = networkManager.gameObject.AddComponent<UnityTransport>();
+
+            var object1 = new GameObject("Object 1").AddComponent<NetworkObject>();
+            var object2 = new GameObject("Object 2").AddComponent<NetworkObject>();
+            var object3 = new GameObject("Object 3").AddComponent<NetworkObject>();
+
+            object1.GlobalObjectIdHash = 1;
+            object2.GlobalObjectIdHash = 2;
+            object3.GlobalObjectIdHash = 3;
+
+            var sharedList = ScriptableObject.CreateInstance<NetworkPrefabsList>();
+            sharedList.List.Add(new NetworkPrefab { Prefab = object1.gameObject });
+
+            networkManager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+            networkManager2.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { sharedList };
+
+            networkManager.Initialize(true);
+            networkManager2.Initialize(false);
+
+            networkManager.NetworkConfig.Prefabs.NetworkPrefabsLists[0].Add(new NetworkPrefab { Prefab = object2.gameObject });
+            networkManager2.NetworkConfig.Prefabs.NetworkPrefabsLists[0].Add(new NetworkPrefab { Prefab = object3.gameObject });
+
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object1.gameObject));
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object2.gameObject));
+            Assert.IsTrue(networkManager2.NetworkConfig.Prefabs.Contains(object3.gameObject));
+            Assert.IsTrue(networkManager.NetworkConfig.Prefabs.Contains(object3.gameObject));
+
+            Assert.IsTrue(sharedList.Contains(object1.gameObject));
+            Assert.IsTrue(sharedList.Contains(object2.gameObject));
+            Assert.IsTrue(sharedList.Contains(object3.gameObject));
+        }
     }
 }

Tests/Editor/NetworkObjectTests.cs

@@ -1,3 +1,4 @@
+using System.Text.RegularExpressions;
 using NUnit.Framework;
 using UnityEngine;
 using UnityEngine.TestTools;
@@ -31,19 +32,17 @@ namespace Unity.Netcode.EditorTests
         }
 
         [Test]
-        public void GetBehaviourIndexNone()
+        [TestCase(0)]
+        [TestCase(1)]
+        [TestCase(2)]
+        public void GetBehaviourIndexNone(int index)
         {
             var gameObject = new GameObject(nameof(GetBehaviourIndexNone));
             var networkObject = gameObject.AddComponent<NetworkObject>();
 
-            // TODO: Maybe not hardcode message?
+            LogAssert.Expect(LogType.Error, new Regex(".*out of bounds.*"));
-            LogAssert.Expect(LogType.Error, $"[Netcode] Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
-            LogAssert.Expect(LogType.Error, $"[Netcode] Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
-            LogAssert.Expect(LogType.Error, $"[Netcode] Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
 
-            Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(0), Is.Null);
+            Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex((ushort)index), Is.Null);
-            Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(1), Is.Null);
-            Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(2), Is.Null);
 
             // Cleanup
             Object.DestroyImmediate(gameObject);
@@ -56,13 +55,10 @@ namespace Unity.Netcode.EditorTests
             var networkObject = gameObject.AddComponent<NetworkObject>();
             var networkBehaviour = gameObject.AddComponent<EmptyNetworkBehaviour>();
 
-            // TODO: Maybe not hardcode message?
+            LogAssert.Expect(LogType.Error, new Regex(".*out of bounds.*"));
-            LogAssert.Expect(LogType.Error, $"[Netcode] Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
-            LogAssert.Expect(LogType.Error, $"[Netcode] Behaviour index was out of bounds. Did you mess up the order of your {nameof(NetworkBehaviour)}s?");
 
             Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(0), Is.EqualTo(networkBehaviour));
             Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(1), Is.Null);
-            Assert.That(networkObject.GetNetworkBehaviourAtOrderIndex(2), Is.Null);
 
             // Cleanup
             Object.DestroyImmediate(gameObject);

Tests/Editor/NetworkPrefabProcessorTests.cs

@@ -0,0 +1,90 @@
+using NUnit.Framework;
+using UnityEngine;
+using Unity.Netcode.Editor.Configuration;
+using UnityEditor;
+
+namespace Unity.Netcode.EditorTests
+{
+    public class NetworkPrefabProcessorTests
+    {
+        private NetcodeForGameObjectsProjectSettings m_Settings;
+        private bool m_EditorDefaultPrefabSetting;
+        private string m_EditorDefaultPrefabLocation;
+
+        private GameObject m_Prefab;
+
+        private const string k_PrefabName = "Assets/TestPrefab.prefab";
+        private const string k_DefaultAssetString = "Assets/TestPrefabList.asset";
+
+        [SetUp]
+        public void SetUp()
+        {
+            m_Settings = NetcodeForGameObjectsProjectSettings.instance;
+            m_EditorDefaultPrefabSetting = m_Settings.GenerateDefaultNetworkPrefabs;
+            m_EditorDefaultPrefabLocation = NetworkPrefabProcessor.DefaultNetworkPrefabsPath;
+            NetworkPrefabProcessor.DefaultNetworkPrefabsPath = k_DefaultAssetString;
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            m_Settings.GenerateDefaultNetworkPrefabs = m_EditorDefaultPrefabSetting;
+            NetworkPrefabProcessor.DefaultNetworkPrefabsPath = m_EditorDefaultPrefabLocation;
+            AssetDatabase.DeleteAsset(k_PrefabName);
+            AssetDatabase.DeleteAsset(k_DefaultAssetString);
+        }
+
+        [Test]
+        public void WhenGenerateDefaultNetworkPrefabsIsEnabled_AddingAPrefabUpdatesDefaultPrefabList()
+        {
+            var obj = new GameObject("Object");
+            obj.AddComponent<NetworkObject>();
+            m_Settings.GenerateDefaultNetworkPrefabs = true;
+            m_Prefab = PrefabUtility.SaveAsPrefabAsset(obj, k_PrefabName);
+            Object.DestroyImmediate(obj);
+
+            var prefabList = NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out var isNew, false);
+            Assert.IsFalse(isNew);
+            Assert.IsTrue(prefabList.Contains(m_Prefab));
+        }
+
+        [Test]
+        public void WhenGenerateDefaultNetworkPrefabsIsEnabled_RemovingAPrefabUpdatesDefaultPrefabList()
+        {
+            WhenGenerateDefaultNetworkPrefabsIsEnabled_AddingAPrefabUpdatesDefaultPrefabList();
+
+            AssetDatabase.DeleteAsset(k_PrefabName);
+            var prefabList = NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out var isNew, false);
+            Assert.IsFalse(isNew);
+            Assert.IsFalse(prefabList.Contains(m_Prefab));
+        }
+
+        [Test]
+        public void WhenGenerateDefaultNetworkPrefabsIsNotEnabled_AddingAPrefabDoesNotUpdateDefaultPrefabList()
+        {
+            var obj = new GameObject("Object");
+            obj.AddComponent<NetworkObject>();
+            m_Settings.GenerateDefaultNetworkPrefabs = false;
+            m_Prefab = PrefabUtility.SaveAsPrefabAsset(obj, k_PrefabName);
+            Object.DestroyImmediate(obj);
+
+            var prefabList = NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out var isNew, false);
+            Assert.IsTrue(isNew);
+            Assert.IsFalse(prefabList.Contains(m_Prefab));
+        }
+
+        [Test]
+        public void WhenGenerateDefaultNetworkPrefabsIsNotEnabled_RemovingAPrefabDoesNotUpdateDefaultPrefabList()
+        {
+            // Add it with the list enabled, then disable the list. Removing it
+            // should then be nop.
+            WhenGenerateDefaultNetworkPrefabsIsEnabled_AddingAPrefabUpdatesDefaultPrefabList();
+
+            m_Settings.GenerateDefaultNetworkPrefabs = false;
+            AssetDatabase.DeleteAsset(k_PrefabName);
+            var prefabList = NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out var isNew, false);
+            Assert.IsFalse(isNew);
+            Assert.IsTrue(prefabList.Contains(m_Prefab));
+        }
+    }
+}

Tests/Editor/NetworkPrefabProcessorTests.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 6471efe05b0548ef9d2171e07d4a561b
+timeCreated: 1669140101

Tests/Editor/Serialization/BytePackerTests.cs

@@ -76,116 +76,6 @@ namespace Unity.Netcode.EditorTests
 
         #endregion
 
-        private void CheckUnsignedPackedSize64(FastBufferWriter writer, ulong value)
-        {
-
-            if (value <= 240)
-            {
-                Assert.AreEqual(1, writer.Position);
-            }
-            else if (value <= 2287)
-            {
-                Assert.AreEqual(2, writer.Position);
-            }
-            else
-            {
-                Assert.AreEqual(BitCounter.GetUsedByteCount(value) + 1, writer.Position);
-            }
-        }
-
-        private void CheckUnsignedPackedValue64(FastBufferWriter writer, ulong value)
-        {
-            var reader = new FastBufferReader(writer, Allocator.Temp);
-            using (reader)
-            {
-                ByteUnpacker.ReadValuePacked(reader, out ulong readValue);
-                Assert.AreEqual(readValue, value);
-            }
-        }
-
-        private void CheckUnsignedPackedSize32(FastBufferWriter writer, uint value)
-        {
-
-            if (value <= 240)
-            {
-                Assert.AreEqual(1, writer.Position);
-            }
-            else if (value <= 2287)
-            {
-                Assert.AreEqual(2, writer.Position);
-            }
-            else
-            {
-                Assert.AreEqual(BitCounter.GetUsedByteCount(value) + 1, writer.Position);
-            }
-        }
-
-        private void CheckUnsignedPackedValue32(FastBufferWriter writer, uint value)
-        {
-            var reader = new FastBufferReader(writer, Allocator.Temp);
-            using (reader)
-            {
-                ByteUnpacker.ReadValuePacked(reader, out uint readValue);
-                Assert.AreEqual(readValue, value);
-            }
-        }
-
-        private void CheckSignedPackedSize64(FastBufferWriter writer, long value)
-        {
-            ulong asUlong = Arithmetic.ZigZagEncode(value);
-
-            if (asUlong <= 240)
-            {
-                Assert.AreEqual(1, writer.Position);
-            }
-            else if (asUlong <= 2287)
-            {
-                Assert.AreEqual(2, writer.Position);
-            }
-            else
-            {
-                Assert.AreEqual(BitCounter.GetUsedByteCount(asUlong) + 1, writer.Position);
-            }
-        }
-
-        private void CheckSignedPackedValue64(FastBufferWriter writer, long value)
-        {
-            var reader = new FastBufferReader(writer, Allocator.Temp);
-            using (reader)
-            {
-                ByteUnpacker.ReadValuePacked(reader, out long readValue);
-                Assert.AreEqual(readValue, value);
-            }
-        }
-
-        private void CheckSignedPackedSize32(FastBufferWriter writer, int value)
-        {
-            ulong asUlong = Arithmetic.ZigZagEncode(value);
-
-            if (asUlong <= 240)
-            {
-                Assert.AreEqual(1, writer.Position);
-            }
-            else if (asUlong <= 2287)
-            {
-                Assert.AreEqual(2, writer.Position);
-            }
-            else
-            {
-                Assert.AreEqual(BitCounter.GetUsedByteCount(asUlong) + 1, writer.Position);
-            }
-        }
-
-        private void CheckSignedPackedValue32(FastBufferWriter writer, int value)
-        {
-            var reader = new FastBufferReader(writer, Allocator.Temp);
-            using (reader)
-            {
-                ByteUnpacker.ReadValuePacked(reader, out int readValue);
-                Assert.AreEqual(readValue, value);
-            }
-        }
-
         private unsafe void VerifyBytewiseEquality<T>(T value, T otherValue) where T : unmanaged
         {
             byte* asBytePointer = (byte*)&value;
@@ -229,164 +119,53 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
+        private int GetByteCount64Bits(ulong value)
+        {
 
-        [Test]
+            if (value <= 0b0000_1111)
-        public void TestPacking64BitsUnsigned()
             {
-            var writer = new FastBufferWriter(9, Allocator.Temp);
+                return 1;
-
-            using (writer)
-            {
-                writer.TryBeginWrite(9);
-                ulong value = 0;
-                BytePacker.WriteValuePacked(writer, value);
-                Assert.AreEqual(1, writer.Position);
-
-                for (var i = 0; i < 64; ++i)
-                {
-                    value = 1UL << i;
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, value);
-                    CheckUnsignedPackedSize64(writer, value);
-                    CheckUnsignedPackedValue64(writer, value);
-                    for (var j = 0; j < 8; ++j)
-                    {
-                        value = (1UL << i) | (1UL << j);
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, value);
-                        CheckUnsignedPackedSize64(writer, value);
-                        CheckUnsignedPackedValue64(writer, value);
-                    }
-                }
-            }
             }
 
-        [Test]
+            if (value <= 0b0000_1111_1111_1111)
-        public void TestPacking32BitsUnsigned()
             {
-            var writer = new FastBufferWriter(9, Allocator.Temp);
+                return 2;
-
-            using (writer)
-            {
-                writer.TryBeginWrite(9);
-                uint value = 0;
-                BytePacker.WriteValuePacked(writer, value);
-                Assert.AreEqual(1, writer.Position);
-
-                for (var i = 0; i < 64; ++i)
-                {
-                    value = 1U << i;
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, value);
-                    CheckUnsignedPackedSize32(writer, value);
-                    CheckUnsignedPackedValue32(writer, value);
-                    for (var j = 0; j < 8; ++j)
-                    {
-                        value = (1U << i) | (1U << j);
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, value);
-                        CheckUnsignedPackedSize32(writer, value);
-                        CheckUnsignedPackedValue32(writer, value);
-                    }
-                }
-            }
             }
 
-        [Test]
+            if (value <= 0b0000_1111_1111_1111_1111_1111)
-        public void TestPacking64BitsSigned()
             {
-            var writer = new FastBufferWriter(9, Allocator.Temp);
+                return 3;
-
-            using (writer)
-            {
-                writer.TryBeginWrite(9);
-                long value = 0;
-                BytePacker.WriteValuePacked(writer, value);
-                Assert.AreEqual(1, writer.Position);
-
-                for (var i = 0; i < 64; ++i)
-                {
-                    value = 1L << i;
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, value);
-                    CheckSignedPackedSize64(writer, value);
-                    CheckSignedPackedValue64(writer, value);
-
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, -value);
-                    CheckSignedPackedSize64(writer, -value);
-                    CheckSignedPackedValue64(writer, -value);
-                    for (var j = 0; j < 8; ++j)
-                    {
-                        value = (1L << i) | (1L << j);
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, value);
-                        CheckSignedPackedSize64(writer, value);
-                        CheckSignedPackedValue64(writer, value);
-
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, -value);
-                        CheckSignedPackedSize64(writer, -value);
-                        CheckSignedPackedValue64(writer, -value);
-                    }
-                }
-            }
             }
 
-        [Test]
+            if (value <= 0b0000_1111_1111_1111_1111_1111_1111_1111)
-        public void TestPacking32BitsSigned()
             {
-            var writer = new FastBufferWriter(9, Allocator.Temp);
+                return 4;
-
-            using (writer)
-            {
-                writer.TryBeginWrite(5);
-                int value = 0;
-                BytePacker.WriteValuePacked(writer, value);
-                Assert.AreEqual(1, writer.Position);
-
-                for (var i = 0; i < 64; ++i)
-                {
-                    value = 1 << i;
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, value);
-                    CheckSignedPackedSize32(writer, value);
-                    CheckSignedPackedValue32(writer, value);
-
-                    writer.Seek(0);
-                    writer.Truncate();
-                    BytePacker.WriteValuePacked(writer, -value);
-                    CheckSignedPackedSize32(writer, -value);
-                    CheckSignedPackedValue32(writer, -value);
-                    for (var j = 0; j < 8; ++j)
-                    {
-                        value = (1 << i) | (1 << j);
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, value);
-                        CheckSignedPackedSize32(writer, value);
-                        CheckSignedPackedValue32(writer, value);
-
-                        writer.Seek(0);
-                        writer.Truncate();
-                        BytePacker.WriteValuePacked(writer, -value);
-                        CheckSignedPackedSize32(writer, -value);
-                        CheckSignedPackedValue32(writer, -value);
-                    }
-                }
-            }
             }
 
-        private int GetByteCount61Bits(ulong value)
+            if (value <= 0b0000_1111_1111_1111_1111_1111_1111_1111_1111_1111)
+            {
+                return 5;
+            }
+
+            if (value <= 0b0000_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111)
+            {
+                return 6;
+            }
+
+            if (value <= 0b0000_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111)
+            {
+                return 7;
+            }
+
+            if (value <= 0b0000_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111)
+            {
+                return 8;
+            }
+
+            return 9;
+        }
+
+        private int GetByteCount32Bits(uint value)
         {
 
             if (value <= 0b0001_1111)
@@ -409,57 +188,25 @@ namespace Unity.Netcode.EditorTests
                 return 4;
             }
 
-            if (value <= 0b0001_1111_1111_1111_1111_1111_1111_1111_1111_1111)
-            {
             return 5;
         }
 
-            if (value <= 0b0001_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111)
+        private int GetByteCount16Bits(ushort value)
-            {
-                return 6;
-            }
-
-            if (value <= 0b0001_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111_1111)
-            {
-                return 7;
-            }
-
-            return 8;
-        }
-
-        private int GetByteCount30Bits(uint value)
         {
 
             if (value <= 0b0011_1111)
             {
                 return 1;
             }
-
             if (value <= 0b0011_1111_1111_1111)
             {
                 return 2;
             }
 
-            if (value <= 0b0011_1111_1111_1111_1111_1111)
-            {
             return 3;
         }
 
-            return 4;
+        private ulong Get64BitEncodedValue(FastBufferWriter writer)
-        }
-
-        private int GetByteCount15Bits(ushort value)
-        {
-
-            if (value <= 0b0111_1111)
-            {
-                return 1;
-            }
-
-            return 2;
-        }
-
-        private ulong Get61BitEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -469,7 +216,7 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
-        private long Get60BitSignedEncodedValue(FastBufferWriter writer)
+        private long Get64BitSignedEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -479,7 +226,7 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
-        private uint Get30BitEncodedValue(FastBufferWriter writer)
+        private uint Get32BitEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -489,7 +236,7 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
-        private int Get29BitSignedEncodedValue(FastBufferWriter writer)
+        private int Get32BitSignedEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -499,7 +246,7 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
-        private ushort Get15BitEncodedValue(FastBufferWriter writer)
+        private ushort Get16BitEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -509,7 +256,7 @@ namespace Unity.Netcode.EditorTests
             }
         }
 
-        private short Get14BitSignedEncodedValue(FastBufferWriter writer)
+        private short Get16BitSignedEncodedValue(FastBufferWriter writer)
         {
             var reader = new FastBufferReader(writer, Allocator.Temp);
             using (reader)
@@ -520,7 +267,7 @@ namespace Unity.Netcode.EditorTests
         }
 
         [Test]
-        public void TestBitPacking61BitsUnsigned()
+        public void TestBitPacking64BitsUnsigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -530,18 +277,18 @@ namespace Unity.Netcode.EditorTests
                 ulong value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b111);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b1111);
-                Assert.AreEqual(value, Get61BitEncodedValue(writer));
+                Assert.AreEqual(value, Get64BitEncodedValue(writer));
 
-                for (var i = 0; i < 61; ++i)
+                for (var i = 0; i < 64; ++i)
                 {
                     value = 1UL << i;
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount61Bits(value), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(value), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount61Bits(value) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(value), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get61BitEncodedValue(writer));
+                    Assert.AreEqual(value, Get64BitEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -549,18 +296,16 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount61Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount61Bits(value) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(value), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get61BitEncodedValue(writer));
+                        Assert.AreEqual(value, Get64BitEncodedValue(writer));
                     }
                 }
-
-                Assert.Throws<ArgumentException>(() => { BytePacker.WriteValueBitPacked(writer, 1UL << 61); });
             }
         }
 
         [Test]
-        public void TestBitPacking60BitsSigned()
+        public void TestBitPacking64BitsSigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -570,28 +315,28 @@ namespace Unity.Netcode.EditorTests
                 long value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b111);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b1111);
-                Assert.AreEqual(value, Get60BitSignedEncodedValue(writer));
+                Assert.AreEqual(value, Get64BitSignedEncodedValue(writer));
 
-                for (var i = 0; i < 61; ++i)
+                for (var i = 0; i < 64; ++i)
                 {
                     value = 1U << i;
                     ulong zzvalue = Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount61Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount61Bits(zzvalue) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get60BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get64BitSignedEncodedValue(writer));
 
                     value = -value;
                     zzvalue = Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount61Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount61Bits(zzvalue) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get60BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get64BitSignedEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -600,27 +345,25 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount61Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount61Bits(zzvalue) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get60BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get64BitSignedEncodedValue(writer));
 
                         value = -value;
                         zzvalue = Arithmetic.ZigZagEncode(value);
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount61Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount61Bits(zzvalue) - 1, writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount64Bits(zzvalue), writer.ToArray()[0] & 0b1111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get60BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get64BitSignedEncodedValue(writer));
                     }
                 }
-
-                Assert.Throws<ArgumentException>(() => { BytePacker.WriteValueBitPacked(writer, 1UL << 61); });
             }
         }
 
         [Test]
-        public void TestBitPacking30BitsUnsigned()
+        public void TestBitPacking32BitsUnsigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -630,18 +373,18 @@ namespace Unity.Netcode.EditorTests
                 uint value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b11);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b111);
-                Assert.AreEqual(value, Get30BitEncodedValue(writer));
+                Assert.AreEqual(value, Get32BitEncodedValue(writer));
 
-                for (var i = 0; i < 30; ++i)
+                for (var i = 0; i < 32; ++i)
                 {
                     value = 1U << i;
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount30Bits(value), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(value), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount30Bits(value) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(value), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get30BitEncodedValue(writer));
+                    Assert.AreEqual(value, Get32BitEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -649,18 +392,16 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount30Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount30Bits(value) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(value), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get30BitEncodedValue(writer));
+                        Assert.AreEqual(value, Get32BitEncodedValue(writer));
                     }
                 }
-
-                Assert.Throws<ArgumentException>(() => { BytePacker.WriteValueBitPacked(writer, 1U << 30); });
             }
         }
 
         [Test]
-        public void TestBitPacking29BitsSigned()
+        public void TestBitPacking32BitsSigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -670,28 +411,28 @@ namespace Unity.Netcode.EditorTests
                 int value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b11);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b111);
-                Assert.AreEqual(value, Get30BitEncodedValue(writer));
+                Assert.AreEqual(value, Get32BitEncodedValue(writer));
 
-                for (var i = 0; i < 29; ++i)
+                for (var i = 0; i < 32; ++i)
                 {
                     value = 1 << i;
                     uint zzvalue = (uint)Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount30Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount30Bits(zzvalue) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get29BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get32BitSignedEncodedValue(writer));
 
                     value = -value;
                     zzvalue = (uint)Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount30Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount30Bits(zzvalue) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get29BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get32BitSignedEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -700,25 +441,25 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount30Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount30Bits(zzvalue) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get29BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get32BitSignedEncodedValue(writer));
 
                         value = -value;
                         zzvalue = (uint)Arithmetic.ZigZagEncode(value);
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount30Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount30Bits(zzvalue) - 1, writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount32Bits(zzvalue), writer.ToArray()[0] & 0b111, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get29BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get32BitSignedEncodedValue(writer));
                     }
                 }
             }
         }
 
         [Test]
-        public void TestBitPacking15BitsUnsigned()
+        public void TestBitPacking16BitsUnsigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -728,18 +469,18 @@ namespace Unity.Netcode.EditorTests
                 ushort value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b1);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b11);
-                Assert.AreEqual(value, Get15BitEncodedValue(writer));
+                Assert.AreEqual(value, Get16BitEncodedValue(writer));
 
-                for (var i = 0; i < 15; ++i)
+                for (var i = 0; i < 16; ++i)
                 {
                     value = (ushort)(1U << i);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount15Bits(value), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(value), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount15Bits(value) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(value), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get15BitEncodedValue(writer));
+                    Assert.AreEqual(value, Get16BitEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -747,17 +488,15 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount15Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(value), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount15Bits(value) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(value), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get15BitEncodedValue(writer));
+                        Assert.AreEqual(value, Get16BitEncodedValue(writer));
                     }
                 }
-
-                Assert.Throws<ArgumentException>(() => { BytePacker.WriteValueBitPacked(writer, (ushort)(1U << 15)); });
             }
         }
         [Test]
-        public void TestBitPacking14BitsSigned()
+        public void TestBitPacking16BitsSigned()
         {
             var writer = new FastBufferWriter(9, Allocator.Temp);
 
@@ -767,28 +506,28 @@ namespace Unity.Netcode.EditorTests
                 short value = 0;
                 BytePacker.WriteValueBitPacked(writer, value);
                 Assert.AreEqual(1, writer.Position);
-                Assert.AreEqual(0, writer.ToArray()[0] & 0b1);
+                Assert.AreEqual(1, writer.ToArray()[0] & 0b11);
-                Assert.AreEqual(value, Get15BitEncodedValue(writer));
+                Assert.AreEqual(value, Get16BitEncodedValue(writer));
 
-                for (var i = 0; i < 14; ++i)
+                for (var i = 0; i < 16; ++i)
                 {
                     value = (short)(1 << i);
                     ushort zzvalue = (ushort)Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount15Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount15Bits(zzvalue) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get14BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get16BitSignedEncodedValue(writer));
 
                     value = (short)-value;
                     zzvalue = (ushort)Arithmetic.ZigZagEncode(value);
                     writer.Seek(0);
                     writer.Truncate();
                     BytePacker.WriteValueBitPacked(writer, value);
-                    Assert.AreEqual(GetByteCount15Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.Position, $"Failed on {value} ({i})");
-                    Assert.AreEqual(GetByteCount15Bits(zzvalue) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i})");
+                    Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i})");
-                    Assert.AreEqual(value, Get14BitSignedEncodedValue(writer));
+                    Assert.AreEqual(value, Get16BitSignedEncodedValue(writer));
 
                     for (var j = 0; j < 8; ++j)
                     {
@@ -797,18 +536,18 @@ namespace Unity.Netcode.EditorTests
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount15Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount15Bits(zzvalue) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get14BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get16BitSignedEncodedValue(writer));
 
                         value = (short)-value;
                         zzvalue = (ushort)Arithmetic.ZigZagEncode(value);
                         writer.Seek(0);
                         writer.Truncate();
                         BytePacker.WriteValueBitPacked(writer, value);
-                        Assert.AreEqual(GetByteCount15Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.Position, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(GetByteCount15Bits(zzvalue) - 1, writer.ToArray()[0] & 0b1, $"Failed on {value} ({i}, {j})");
+                        Assert.AreEqual(GetByteCount16Bits(zzvalue), writer.ToArray()[0] & 0b11, $"Failed on {value} ({i}, {j})");
-                        Assert.AreEqual(value, Get14BitSignedEncodedValue(writer));
+                        Assert.AreEqual(value, Get16BitSignedEncodedValue(writer));
                     }
                 }
             }

Tests/Editor/Transports/BatchedSendQueueTests.cs

@@ -229,6 +229,12 @@ namespace Unity.Netcode.EditorTests
             var writer = new DataStreamWriter(data);
             Assert.AreEqual(messageLength, q.FillWriterWithMessages(ref writer));
             AssertIsTestMessage(data);
+
+            q.Consume(messageLength);
+
+            writer = new DataStreamWriter(data);
+            Assert.AreEqual(messageLength, q.FillWriterWithMessages(ref writer));
+            AssertIsTestMessage(data);
         }
 
         [Test]

Tests/Editor/Transports/UnityTransportTests.cs

@@ -115,16 +115,67 @@ namespace Unity.Netcode.EditorTests
             UnityTransport transport = new GameObject().AddComponent<UnityTransport>();
             transport.Initialize();
 
-            transport.SetConnectionData("127.0.0.", 4242);
+            transport.SetConnectionData("127.0.0.", 4242, "127.0.0.");
             Assert.False(transport.StartServer());
 
             LogAssert.Expect(LogType.Error, "Invalid network endpoint: 127.0.0.:4242.");
-            LogAssert.Expect(LogType.Error, "Server failed to bind");
+#if UTP_TRANSPORT_2_0_ABOVE
+            LogAssert.Expect(LogType.Error, "Socket creation failed (error Unity.Baselib.LowLevel.Binding+Baselib_ErrorState: Invalid argument (0x01000003) <argument name stripped>");
+#endif
+            LogAssert.Expect(LogType.Error, "Server failed to bind. This is usually caused by another process being bound to the same port.");
 
-            transport.SetConnectionData("127.0.0.1", 4242);
+            transport.SetConnectionData("127.0.0.1", 4242, "127.0.0.1");
             Assert.True(transport.StartServer());
 
             transport.Shutdown();
         }
+
+        // Check that leaving all addresses empty is valid.
+        [Test]
+        public void UnityTransport_StartServerWithoutAddresses()
+        {
+            UnityTransport transport = new GameObject().AddComponent<UnityTransport>();
+            transport.Initialize();
+
+            transport.SetConnectionData(string.Empty, 4242);
+            Assert.True(transport.StartServer());
+
+            transport.Shutdown();
+        }
+
+#if UTP_TRANSPORT_2_0_ABOVE
+        [Test]
+        public void UnityTransport_EmptySecurityStringsShouldThrow([Values("", null)] string cert, [Values("", null)] string secret)
+        {
+            var supportingGO = new GameObject();
+            try
+            {
+                var networkManager = supportingGO.AddComponent<NetworkManager>(); // NM is required for UTP to work with certificates.
+                networkManager.NetworkConfig = new NetworkConfig();
+                UnityTransport transport = supportingGO.AddComponent<UnityTransport>();
+                networkManager.NetworkConfig.NetworkTransport = transport;
+                transport.Initialize();
+                transport.SetServerSecrets(serverCertificate: cert, serverPrivateKey: secret);
+
+                // Use encryption, but don't set certificate and check for exception
+                transport.UseEncryption = true;
+                Assert.Throws<System.Exception>(() =>
+                {
+                    networkManager.StartServer();
+                });
+                // Make sure StartServer failed
+                Assert.False(transport.NetworkDriver.IsCreated);
+                Assert.False(networkManager.IsServer);
+                Assert.False(networkManager.IsListening);
+            }
+            finally
+            {
+                if (supportingGO != null)
+                {
+                    Object.DestroyImmediate(supportingGO);
+                }
+            }
+        }
+#endif
     }
 }

Tests/Editor/UI.meta

@@ -1,3 +0,0 @@
-fileFormatVersion: 2
-guid: f672293e0efc41a6a7e930fd7ff14436
-timeCreated: 1631650280

Tests/Editor/UI/UITestHelpers.cs

@@ -1,15 +0,0 @@
-using Unity.Netcode.Editor;
-using UnityEditor;
-using UnityEngine;
-
-namespace Unity.Netcode.EditorTests
-{
-    internal static class UITestHelpers
-    {
-        [MenuItem("Netcode/UI/Reset Multiplayer Tools Tip Status")]
-        private static void ResetMultiplayerToolsTipStatus()
-        {
-            PlayerPrefs.DeleteKey(NetworkManagerEditor.InstallMultiplayerToolsTipDismissedPlayerPrefKey);
-        }
-    }
-}