com.unity.netcode.gameobjects@1.0.0-pre.7

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).

## [1.0.0-pre.7] - 2022-04-01

### Added

- Added editor only check prior to entering into play mode if the currently open and active scene is in the build list and if not displays a dialog box asking the user if they would like to automatically add it prior to entering into play mode. (#1828)
- Added `UnityTransport` implementation and `com.unity.transport` package dependency (#1823)
- Added `NetworkVariableWritePermission` to `NetworkVariableBase` and implemented `Owner` client writable netvars. (#1762)
- `UnityTransport` settings can now be set programmatically. (#1845)
- `FastBufferWriter` and Reader IsInitialized property. (#1859)

### Changed

- Updated `UnityTransport` dependency on `com.unity.transport` to 1.0.0 (#1849)

### Removed

- Removed `SnapshotSystem` (#1852)
- Removed `com.unity.modules.animation`, `com.unity.modules.physics` and `com.unity.modules.physics2d` dependencies from the package (#1812)
- Removed `com.unity.collections` dependency from the package (#1849)

### Fixed
- Fixed in-scene placed NetworkObjects not being found/ignored after a client disconnects and then reconnects. (#1850)
- Fixed issue where `UnityTransport` send queues were not flushed when calling `DisconnectLocalClient` or `DisconnectRemoteClient`. (#1847)
- Fixed NetworkBehaviour dependency verification check for an existing NetworkObject not searching from root parent transform relative GameObject. (#1841)
- Fixed issue where entries were not being removed from the NetworkSpawnManager.OwnershipToObjectsTable. (#1838)
- Fixed ClientRpcs would always send to all connected clients by default as opposed to only sending to the NetworkObject's Observers list by default. (#1836)
- Fixed clarity for NetworkSceneManager client side notification when it receives a scene hash value that does not exist in its local hash table. (#1828)
- Fixed client throws a key not found exception when it times out using UNet or UTP. (#1821)
- Fixed network variable updates are no longer limited to 32,768 bytes when NetworkConfig.EnsureNetworkVariableLengthSafety is enabled. The limits are now determined by what the transport can send in a message. (#1811)
- Fixed in-scene NetworkObjects get destroyed if a client fails to connect and shuts down the NetworkManager. (#1809)
- Fixed user never being notified in the editor that a NetworkBehaviour requires a NetworkObject to function properly. (#1808)
- Fixed PlayerObjects and dynamically spawned NetworkObjects not being added to the NetworkClient's OwnedObjects (#1801)
- Fixed issue where NetworkManager would continue starting even if the NetworkTransport selected failed. (#1780)
- Fixed issue when spawning new player if an already existing player exists it does not remove IsPlayer from the previous player (#1779)
- Fixed lack of notification that NetworkManager and NetworkObject cannot be added to the same GameObject with in-editor notifications (#1777)
- Fixed parenting warning printing for false positives (#1855)

CHANGELOG.md

@@ -6,7 +6,137 @@ 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).
 
-## [1.0.0-pre.2] - 2020-12-20
+## [1.0.0-pre.7] - 2022-04-01
+
+### Added
+
+- Added editor only check prior to entering into play mode if the currently open and active scene is in the build list and if not displays a dialog box asking the user if they would like to automatically add it prior to entering into play mode. (#1828)
+- Added `UnityTransport` implementation and `com.unity.transport` package dependency (#1823)
+- Added `NetworkVariableWritePermission` to `NetworkVariableBase` and implemented `Owner` client writable netvars. (#1762)
+- `UnityTransport` settings can now be set programmatically. (#1845)
+- `FastBufferWriter` and Reader IsInitialized property. (#1859)
+
+### Changed
+
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.0.0 (#1849)
+
+### Removed
+
+- Removed `SnapshotSystem` (#1852)
+- Removed `com.unity.modules.animation`, `com.unity.modules.physics` and `com.unity.modules.physics2d` dependencies from the package (#1812)
+- Removed `com.unity.collections` dependency from the package (#1849)
+
+### Fixed
+- Fixed in-scene placed NetworkObjects not being found/ignored after a client disconnects and then reconnects. (#1850)
+- Fixed issue where `UnityTransport` send queues were not flushed when calling `DisconnectLocalClient` or `DisconnectRemoteClient`. (#1847)
+- Fixed NetworkBehaviour dependency verification check for an existing NetworkObject not searching from root parent transform relative GameObject. (#1841)
+- Fixed issue where entries were not being removed from the NetworkSpawnManager.OwnershipToObjectsTable. (#1838)
+- Fixed ClientRpcs would always send to all connected clients by default as opposed to only sending to the NetworkObject's Observers list by default. (#1836)
+- Fixed clarity for NetworkSceneManager client side notification when it receives a scene hash value that does not exist in its local hash table. (#1828)
+- Fixed client throws a key not found exception when it times out using UNet or UTP. (#1821)
+- Fixed network variable updates are no longer limited to 32,768 bytes when NetworkConfig.EnsureNetworkVariableLengthSafety is enabled. The limits are now determined by what the transport can send in a message. (#1811)
+- Fixed in-scene NetworkObjects get destroyed if a client fails to connect and shuts down the NetworkManager. (#1809)
+- Fixed user never being notified in the editor that a NetworkBehaviour requires a NetworkObject to function properly. (#1808)
+- Fixed PlayerObjects and dynamically spawned NetworkObjects not being added to the NetworkClient's OwnedObjects (#1801)
+- Fixed issue where NetworkManager would continue starting even if the NetworkTransport selected failed. (#1780)
+- Fixed issue when spawning new player if an already existing player exists it does not remove IsPlayer from the previous player (#1779)
+- Fixed lack of notification that NetworkManager and NetworkObject cannot be added to the same GameObject with in-editor notifications (#1777)
+- Fixed parenting warning printing for false positives (#1855)
+
+## [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)
+
+### Changed
+
+### 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)
+- Disallowed async keyword in RPCs (#1681)
+- Fixed an issue where Alpha release versions of Unity (version 2022.2.0a5 and later) will not compile due to the UNet Transport no longer existing (#1678)
+- Fixed messages larger than 64k being written with incorrectly truncated message size in header (#1686) (credit: @kaen)
+- Fixed overloading RPC methods causing collisions and failing on IL2CPP targets. (#1694)
+- Fixed spawn flow to propagate `IsSceneObject` down to children NetworkObjects, decouple implicit relationship between object spawning & `IsSceneObject` flag (#1685)
+- Fixed error when serializing ConnectionApprovalMessage with scene management disabled when one or more objects is hidden via the CheckObjectVisibility delegate (#1720)
+- Fixed CheckObjectVisibility delegate not being properly invoked for connecting clients when Scene Management is enabled. (#1680)
+- Fixed NetworkList to properly call INetworkSerializable's NetworkSerialize() method (#1682)
+- Fixed NetworkVariables containing more than 1300 bytes of data (such as large NetworkLists) no longer cause an OverflowException (the limit on data size is now whatever limit the chosen transport imposes on fragmented NetworkDelivery mechanisms) (#1725)
+- Fixed ServerRpcParams and ClientRpcParams must be the last parameter of an RPC in order to function properly. Added a compile-time check to ensure this is the case and trigger an error if they're placed elsewhere (#1721)
+- Fixed FastBufferReader being created with a length of 1 if provided an input of length 0 (#1724)
+- Fixed The NetworkConfig's checksum hash includes the NetworkTick so that clients with a different tickrate than the server are identified and not allowed to connect (#1728)
+- Fixed OwnedObjects not being properly modified when using ChangeOwnership (#1731)
+- Improved performance in NetworkAnimator (#1735)
+- Removed the "always sync" network animator (aka "autosend") parameters (#1746)
+- Fixed in-scene placed NetworkObjects not respawning after shutting down the NetworkManager and then starting it back up again (#1769)
+
+## [1.0.0-pre.5] - 2022-01-26
+
+### Added
+
+- Added `PreviousValue` in `NetworkListEvent`, when `Value` has changed (#1528)
+
+### Changed
+
+- NetworkManager's GameObject is no longer allowed to be nested under one or more GameObject(s).(#1484)
+- NetworkManager DontDestroy property was removed and now NetworkManager always is migrated into the DontDestroyOnLoad scene. (#1484)'
+
+### Fixed
+
+- Fixed network tick value sometimes being duplicated or skipped. (#1614)
+- Fixed The ClientNetworkTransform sample script to allow for owner changes at runtime. (#1606)
+- Fixed When the LogLevel is set to developer NetworkBehaviour generates warning messages when it should not (#1631)
+- Fixed NetworkTransport Initialize now can receive the associated NetworkManager instance to avoid using NetworkManager.Singleton in transport layer (#1677)
+- Fixed a bug where NetworkList.Contains value was inverted (#1363)
+
+## [1.0.0-pre.4] - 2021-01-04
+
+### Added
+
+- Added `com.unity.modules.physics` and `com.unity.modules.physics2d` package dependencies (#1565)
+
+### Removed
+
+- Removed `com.unity.modules.ai` package dependency (#1565)
+- 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)
+- Fixed a runtime error when sending an array of an INetworkSerializable type that's implemented as a struct (#1402)
+- NetworkConfig will no longer throw an OverflowException in GetConfig() when ForceSamePrefabs is enabled and the number of prefabs causes the config blob size to exceed 1300 bytes. (#1385)
+- Fixed NetworkVariable not calling NetworkSerialize on INetworkSerializable types (#1383)
+- Fixed NullReferenceException on ImportReferences call in NetworkBehaviourILPP (#1434)
+- Fixed NetworkObjects not being despawned before they are destroyed during shutdown for client, host, and server instances. (#1390)
+- Fixed KeyNotFound exception when removing ownership of a newly spawned NetworkObject that is already owned by the server. (#1500)
+- Fixed NetworkManager.LocalClient not being set when starting as a host. (#1511)
+- Fixed a few memory leak cases when shutting down NetworkManager during Incoming Message Queue processing. (#1323)
+- 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)
+- NetworkManager DontDestroy property was removed and now NetworkManager always is migrated into the DontDestroyOnLoad scene. (#1484)
+
+## [1.0.0-pre.3] - 2021-10-22
+
+### Added
+
+- ResetTrigger function to NetworkAnimator (#1327)
+
+### Fixed 
+
+- Overflow exception when syncing Animator state. (#1327)
+- Added `try`/`catch` around RPC calls, preventing exception from causing further RPC calls to fail (#1329)
+- Fixed an issue where ServerClientId and LocalClientId could have the same value, causing potential confusion, and also fixed an issue with the UNet where the server could be identified with two different values, one of which might be the same as LocalClientId, and the other of which would not.(#1368)
+- IL2CPP would not properly compile (#1359)
+
+## [1.0.0-pre.2] - 2021-10-19
+
 
 ### Added
 
@@ -16,7 +146,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 - Updated label for `1.0.0-pre.1` changelog section
 
-## [1.0.0-pre.1] - 2020-12-20
+## [1.0.0-pre.1] - 2021-10-19
 
 ### Added
 

Components/Interpolator/BufferedLinearInterpolator.cs

@@ -69,6 +69,13 @@ namespace Unity.Netcode
 
         private bool InvalidState => m_Buffer.Count == 0 && m_LifetimeConsumedCount == 0;
 
+        public void Clear()
+        {
+            m_Buffer.Clear();
+            m_EndTimeConsumed = 0.0d;
+            m_StartTimeConsumed = 0.0d;
+        }
+
         public void ResetTo(T targetValue, double serverTime)
         {
             m_LifetimeConsumedCount = 1;
@@ -179,7 +186,14 @@ namespace Unity.Netcode
 
                     if (t < 0.0f)
                     {
-                        throw new OverflowException($"t = {t} but must be >= 0. range {range}, RenderTime {renderTime}, Start time {m_StartTimeConsumed}, end time {m_EndTimeConsumed}");
+                        // There is no mechanism to guarantee renderTime to not be before m_StartTimeConsumed
+                        // This clamps t to a minimum of 0 and fixes issues with longer frames and pauses
+
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"renderTime was before m_StartTimeConsumed. This should never happen. {nameof(renderTime)} is {renderTime}, {nameof(m_StartTimeConsumed)} is {m_StartTimeConsumed}");
+                        }
+                        t = 0.0f;
                     }
 
                     if (t > 3.0f) // max extrapolation
@@ -211,6 +225,8 @@ namespace Unity.Netcode
                 {
                     m_LastBufferedItemReceived = new BufferedItem(newMeasurement, sentTime);
                     ResetTo(newMeasurement, sentTime);
+                    // Next line keeps renderTime above m_StartTimeConsumed. Fixes pause/unpause issues
+                    m_Buffer.Add(m_LastBufferedItemReceived);
                 }
 
                 return;

Components/NetworkAnimator.cs

@@ -1,3 +1,4 @@
+#if COM_UNITY_MODULES_ANIMATION
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using UnityEngine;
@@ -5,7 +6,7 @@ using UnityEngine;
 namespace Unity.Netcode.Components
 {
     /// <summary>
-    /// A prototype component for syncing animations
+    /// NetworkAnimator enables remote synchronization of <see cref="UnityEngine.Animator"/> state for on network objects.
     /// </summary>
     [AddComponentMenu("Netcode/" + nameof(NetworkAnimator))]
     [RequireComponent(typeof(Animator))]
@@ -13,24 +14,19 @@ namespace Unity.Netcode.Components
     {
         internal struct AnimationMessage : INetworkSerializable
         {
-            public int StateHash;      // if non-zero, then Play() this animation, skipping transitions
+            // state hash per layer.  if non-zero, then Play() this animation, skipping transitions
+            public int StateHash;
             public float NormalizedTime;
+            public int Layer;
+            public float Weight;
             public byte[] Parameters;
 
             public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
             {
                 serializer.SerializeValue(ref StateHash);
                 serializer.SerializeValue(ref NormalizedTime);
-                serializer.SerializeValue(ref Parameters);
-            }
-        }
-
-        internal struct AnimationParametersMessage : INetworkSerializable
-        {
-            public byte[] Parameters;
-
-            public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
-            {
+                serializer.SerializeValue(ref Layer);
+                serializer.SerializeValue(ref Weight);
                 serializer.SerializeValue(ref Parameters);
             }
         }
@@ -38,17 +34,16 @@ namespace Unity.Netcode.Components
         internal struct AnimationTriggerMessage : INetworkSerializable
         {
             public int Hash;
+            public bool Reset;
 
             public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
             {
                 serializer.SerializeValue(ref Hash);
-
+                serializer.SerializeValue(ref Reset);
             }
         }
 
         [SerializeField] private Animator m_Animator;
-        [SerializeField] private uint m_ParameterSendBits;
-        [SerializeField] private float m_SendRate = 0.1f;
 
         public Animator Animator
         {
@@ -56,43 +51,17 @@ namespace Unity.Netcode.Components
             set
             {
                 m_Animator = value;
-                ResetParameterOptions();
             }
         }
 
-        /* 
-         * AutoSend is the ability to select which parameters linked to this animator 
-         * get replicated on a regular basis regardless of a state change. The thinking
-         * behind this is that many of the parameters people use are usually booleans 
-         * which result in a state change and thus would cause a full sync of state. 
-         * Thus if you really care about a parameter syncing then you need to be explict
-         * by selecting it in the inspector when an NetworkAnimator is selected.
-         */
-        public void SetParameterAutoSend(int index, bool value)
-        {
-            if (value)
-            {
-                m_ParameterSendBits |= (uint)(1 << index);
-            }
-            else
-            {
-                m_ParameterSendBits &= (uint)(~(1 << index));
-            }
-        }
-
-        public bool GetParameterAutoSend(int index)
-        {
-            return (m_ParameterSendBits & (uint)(1 << index)) != 0;
-        }
+        private bool m_SendMessagesAllowed = false;
 
         // Animators only support up to 32 params
         public static int K_MaxAnimationParams = 32;
 
-        private int m_TransitionHash;
-        private double m_NextSendTime = 0.0f;
-
-        private int m_AnimationHash;
-        public int AnimationHash { get => m_AnimationHash; }
+        private int[] m_TransitionHash;
+        private int[] m_AnimationHash;
+        private float[] m_LayerWeights;
 
         private unsafe struct AnimatorParamCache
         {
@@ -101,11 +70,11 @@ namespace Unity.Netcode.Components
             public fixed byte Value[4]; // this is a max size of 4 bytes
         }
 
-        // 128bytes per Animator 
+        // 128 bytes per Animator
         private FastBufferWriter m_ParameterWriter = new FastBufferWriter(K_MaxAnimationParams * sizeof(float), Allocator.Persistent);
         private NativeArray<AnimatorParamCache> m_CachedAnimatorParameters;
 
-        // We cache these values because UnsafeUtility.EnumToInt use direct IL that allows a nonboxing conversion
+        // We cache these values because UnsafeUtility.EnumToInt uses direct IL that allows a non-boxing conversion
         private struct AnimationParamEnumWrapper
         {
             public static readonly int AnimatorControllerParameterInt;
@@ -120,25 +89,6 @@ namespace Unity.Netcode.Components
             }
         }
 
-        internal void ResetParameterOptions()
-        {
-
-            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
-            {
-                NetworkLog.LogInfoServer("ResetParameterOptions");
-            }
-
-            m_ParameterSendBits = 0;
-        }
-
-        private bool sendMessagesAllowed
-        {
-            get
-            {
-                return IsServer && NetworkObject.IsSpawned;
-            }
-        }
-
         public override void OnDestroy()
         {
             if (m_CachedAnimatorParameters.IsCreated)
@@ -151,25 +101,36 @@ namespace Unity.Netcode.Components
 
         public override void OnNetworkSpawn()
         {
+            if (IsServer)
+            {
+                m_SendMessagesAllowed = true;
+                int layers = m_Animator.layerCount;
+
+                m_TransitionHash = new int[layers];
+                m_AnimationHash = new int[layers];
+                m_LayerWeights = new float[layers];
+            }
+
             var parameters = m_Animator.parameters;
             m_CachedAnimatorParameters = new NativeArray<AnimatorParamCache>(parameters.Length, Allocator.Persistent);
 
-            m_AnimationHash = -1;
-
             for (var i = 0; i < parameters.Length; i++)
             {
                 var parameter = parameters[i];
 
                 if (m_Animator.IsParameterControlledByCurve(parameter.nameHash))
                 {
-                    //we are ignoring parameters that are controlled by animation curves - syncing the layer states indirectly syncs the values that are driven by the animation curves
+                    // we are ignoring parameters that are controlled by animation curves - syncing the layer
+                    //  states indirectly syncs the values that are driven by the animation curves
                     continue;
                 }
 
-                var cacheParam = new AnimatorParamCache();
+                var cacheParam = new AnimatorParamCache
+                {
+                    Type = UnsafeUtility.EnumToInt(parameter.type),
+                    Hash = parameter.nameHash
+                };
 
-                cacheParam.Type = UnsafeUtility.EnumToInt(parameter.type);
-                cacheParam.Hash = parameter.nameHash;
                 unsafe
                 {
                     switch (parameter.type)
@@ -197,109 +158,100 @@ namespace Unity.Netcode.Components
             }
         }
 
+        public override void OnNetworkDespawn()
+        {
+            m_SendMessagesAllowed = false;
+        }
+
         private void FixedUpdate()
         {
-            if (!sendMessagesAllowed)
+            if (!m_SendMessagesAllowed || !m_Animator || !m_Animator.enabled)
             {
                 return;
             }
 
-            int stateHash;
-            float normalizedTime;
-            if (!CheckAnimStateChanged(out stateHash, out normalizedTime))
+            for (int layer = 0; layer < m_Animator.layerCount; layer++)
             {
-                // We only want to check and send if we don't have any other state to since
-                // as we will sync all params as part of the state sync
-                CheckAndSend();
-
-                return;
-            }
-
-            var animMsg = new AnimationMessage();
-            animMsg.StateHash = stateHash;
-            animMsg.NormalizedTime = normalizedTime;
-
-            m_ParameterWriter.Seek(0);
-            m_ParameterWriter.Truncate();
-
-            WriteParameters(m_ParameterWriter, false);
-            animMsg.Parameters = m_ParameterWriter.ToArray();
-
-            SendAnimStateClientRpc(animMsg);
-        }
-
-        private void CheckAndSend()
-        {
-            var networkTime = NetworkManager.ServerTime.Time;
-            if (sendMessagesAllowed && m_SendRate != 0 && m_NextSendTime < networkTime)
-            {
-                m_NextSendTime = networkTime + m_SendRate;
-
-                m_ParameterWriter.Seek(0);
-                m_ParameterWriter.Truncate();
-
-                if (WriteParameters(m_ParameterWriter, true))
-                {
-                    // we then sync the params we care about
-                    var animMsg = new AnimationParametersMessage()
-                    {
-                        Parameters = m_ParameterWriter.ToArray()
-                    };
-
-                    SendParamsClientRpc(animMsg);
-                }
-            }
-        }
-
-        private bool CheckAnimStateChanged(out int stateHash, out float normalizedTime)
-        {
-            stateHash = 0;
-            normalizedTime = 0;
-
-            if (m_Animator.IsInTransition(0))
-            {
-                AnimatorTransitionInfo tt = m_Animator.GetAnimatorTransitionInfo(0);
-                if (tt.fullPathHash != m_TransitionHash)
-                {
-                    // first time in this transition
-                    m_TransitionHash = tt.fullPathHash;
-                    m_AnimationHash = 0;
-                    return true;
-                }
-                return false;
-            }
-
-            AnimatorStateInfo st = m_Animator.GetCurrentAnimatorStateInfo(0);
-            if (st.fullPathHash != m_AnimationHash)
-            {
-                // first time in this animation state
-                if (m_AnimationHash != 0)
-                {
-                    // came from another animation directly - from Play()
-                    stateHash = st.fullPathHash;
-                    normalizedTime = st.normalizedTime;
-                }
-                m_TransitionHash = 0;
-                m_AnimationHash = st.fullPathHash;
-                return true;
-            }
-            return false;
-        }
-
-        private unsafe bool WriteParameters(FastBufferWriter writer, bool autoSend)
-        {
-            if (m_CachedAnimatorParameters == null)
-            {
-                return false;
-            }
-
-            for (int i = 0; i < m_CachedAnimatorParameters.Length; i++)
-            {
-                if (autoSend && !GetParameterAutoSend(i))
+                int stateHash;
+                float normalizedTime;
+                if (!CheckAnimStateChanged(out stateHash, out normalizedTime, layer))
                 {
                     continue;
                 }
 
+                var animMsg = new AnimationMessage
+                {
+                    StateHash = stateHash,
+                    NormalizedTime = normalizedTime,
+                    Layer = layer,
+                    Weight = m_LayerWeights[layer]
+                };
+
+                m_ParameterWriter.Seek(0);
+                m_ParameterWriter.Truncate();
+
+                WriteParameters(m_ParameterWriter);
+                animMsg.Parameters = m_ParameterWriter.ToArray();
+
+                SendAnimStateClientRpc(animMsg);
+            }
+        }
+
+        private bool CheckAnimStateChanged(out int stateHash, out float normalizedTime, int layer)
+        {
+            bool shouldUpdate = false;
+            stateHash = 0;
+            normalizedTime = 0;
+
+            float layerWeightNow = m_Animator.GetLayerWeight(layer);
+
+            if (!Mathf.Approximately(layerWeightNow, m_LayerWeights[layer]))
+            {
+                m_LayerWeights[layer] = layerWeightNow;
+                shouldUpdate = true;
+            }
+            if (m_Animator.IsInTransition(layer))
+            {
+                AnimatorTransitionInfo tt = m_Animator.GetAnimatorTransitionInfo(layer);
+                if (tt.fullPathHash != m_TransitionHash[layer])
+                {
+                    // first time in this transition for this layer
+                    m_TransitionHash[layer] = tt.fullPathHash;
+                    m_AnimationHash[layer] = 0;
+                    shouldUpdate = true;
+                }
+            }
+            else
+            {
+                AnimatorStateInfo st = m_Animator.GetCurrentAnimatorStateInfo(layer);
+                if (st.fullPathHash != m_AnimationHash[layer])
+                {
+                    // first time in this animation state
+                    if (m_AnimationHash[layer] != 0)
+                    {
+                        // came from another animation directly - from Play()
+                        stateHash = st.fullPathHash;
+                        normalizedTime = st.normalizedTime;
+                    }
+                    m_TransitionHash[layer] = 0;
+                    m_AnimationHash[layer] = st.fullPathHash;
+                    shouldUpdate = true;
+                }
+            }
+
+            return shouldUpdate;
+        }
+
+        /* $AS TODO: Right now we are not checking for changed values this is because
+        the read side of this function doesn't have similar logic which would cause
+        an overflow read because it doesn't know if the value is there or not. So
+        there needs to be logic to track which indexes changed in order for there
+        to be proper value change checking. Will revist in 1.1.0.
+        */
+        private unsafe void WriteParameters(FastBufferWriter writer)
+        {
+            for (int i = 0; i < m_CachedAnimatorParameters.Length; i++)
+            {
                 ref var cacheValue = ref UnsafeUtility.ArrayElementAsRef<AnimatorParamCache>(m_CachedAnimatorParameters.GetUnsafePtr(), i);
                 var hash = cacheValue.Hash;
 
@@ -308,12 +260,8 @@ namespace Unity.Netcode.Components
                     var valueInt = m_Animator.GetInteger(hash);
                     fixed (void* value = cacheValue.Value)
                     {
-                        var oldValue = UnsafeUtility.AsRef<int>(value);
-                        if (valueInt != oldValue)
-                        {
-                            UnsafeUtility.WriteArrayElement(value, 0, valueInt);
-                            BytePacker.WriteValuePacked(writer, (uint)valueInt);
-                        }
+                        UnsafeUtility.WriteArrayElement(value, 0, valueInt);
+                        BytePacker.WriteValuePacked(writer, (uint)valueInt);
                     }
                 }
                 else if (cacheValue.Type == AnimationParamEnumWrapper.AnimatorControllerParameterBool)
@@ -321,12 +269,8 @@ namespace Unity.Netcode.Components
                     var valueBool = m_Animator.GetBool(hash);
                     fixed (void* value = cacheValue.Value)
                     {
-                        var oldValue = UnsafeUtility.AsRef<bool>(value);
-                        if (valueBool != oldValue)
-                        {
-                            UnsafeUtility.WriteArrayElement(value, 0, valueBool);
-                            writer.WriteValueSafe(valueBool);
-                        }
+                        UnsafeUtility.WriteArrayElement(value, 0, valueBool);
+                        writer.WriteValueSafe(valueBool);
                     }
                 }
                 else if (cacheValue.Type == AnimationParamEnumWrapper.AnimatorControllerParameterFloat)
@@ -334,34 +278,18 @@ namespace Unity.Netcode.Components
                     var valueFloat = m_Animator.GetFloat(hash);
                     fixed (void* value = cacheValue.Value)
                     {
-                        var oldValue = UnsafeUtility.AsRef<float>(value);
-                        if (valueFloat != oldValue)
-                        {
-                            UnsafeUtility.WriteArrayElement(value, 0, valueFloat);
 
-                            writer.WriteValueSafe(valueFloat);
-                        }
+                        UnsafeUtility.WriteArrayElement(value, 0, valueFloat);
+                        writer.WriteValueSafe(valueFloat);
                     }
                 }
             }
-
-            // If we do not write any values to the writer then we should not send any data
-            return writer.Length > 0;
         }
 
-        private unsafe void ReadParameters(FastBufferReader reader, bool autoSend)
+        private unsafe void ReadParameters(FastBufferReader reader)
         {
-            if (m_CachedAnimatorParameters == null)
-            {
-                return;
-            }
-
             for (int i = 0; i < m_CachedAnimatorParameters.Length; i++)
             {
-                if (autoSend && !GetParameterAutoSend(i))
-                {
-                    continue;
-                }
                 ref var cacheValue = ref UnsafeUtility.ArrayElementAsRef<AnimatorParamCache>(m_CachedAnimatorParameters.GetUnsafePtr(), i);
                 var hash = cacheValue.Hash;
 
@@ -395,28 +323,20 @@ namespace Unity.Netcode.Components
             }
         }
 
-        [ClientRpc]
-        private unsafe void SendParamsClientRpc(AnimationParametersMessage animSnapshot, ClientRpcParams clientRpcParams = default)
-        {
-            if (animSnapshot.Parameters != null)
-            {
-                // We use a fixed value here to avoid the copy of data from the byte buffer since we own the data
-                fixed (byte* parameters = animSnapshot.Parameters)
-                {
-                    var reader = new FastBufferReader(parameters, Allocator.None, animSnapshot.Parameters.Length);
-                    ReadParameters(reader, true);
-                }
-            }
-        }
-
+        /// <summary>
+        /// Internally-called RPC client receiving function to update some animation parameters on a client when
+        ///   the server wants to update them
+        /// </summary>
+        /// <param name="animSnapshot">the payload containing the parameters to apply</param>
+        /// <param name="clientRpcParams">unused</param>
         [ClientRpc]
         private unsafe void SendAnimStateClientRpc(AnimationMessage animSnapshot, ClientRpcParams clientRpcParams = default)
         {
             if (animSnapshot.StateHash != 0)
             {
-                m_AnimationHash = animSnapshot.StateHash;
-                m_Animator.Play(animSnapshot.StateHash, 0, animSnapshot.NormalizedTime);
+                m_Animator.Play(animSnapshot.StateHash, animSnapshot.Layer, animSnapshot.NormalizedTime);
             }
+            m_Animator.SetLayerWeight(animSnapshot.Layer, animSnapshot.Weight);
 
             if (animSnapshot.Parameters != null && animSnapshot.Parameters.Length != 0)
             {
@@ -424,31 +344,88 @@ namespace Unity.Netcode.Components
                 fixed (byte* parameters = animSnapshot.Parameters)
                 {
                     var reader = new FastBufferReader(parameters, Allocator.None, animSnapshot.Parameters.Length);
-                    ReadParameters(reader, false);
+                    ReadParameters(reader);
                 }
             }
         }
 
+        /// <summary>
+        /// Internally-called RPC client receiving function to update a trigger when the server wants to forward
+        ///   a trigger for a client to play / reset
+        /// </summary>
+        /// <param name="animSnapshot">the payload containing the trigger data to apply</param>
+        /// <param name="clientRpcParams">unused</param>
         [ClientRpc]
         private void SendAnimTriggerClientRpc(AnimationTriggerMessage animSnapshot, ClientRpcParams clientRpcParams = default)
         {
-            m_Animator.SetTrigger(animSnapshot.Hash);
+            if (animSnapshot.Reset)
+            {
+                m_Animator.ResetTrigger(animSnapshot.Hash);
+            }
+            else
+            {
+                m_Animator.SetTrigger(animSnapshot.Hash);
+            }
         }
 
+        /// <summary>
+        /// Sets the trigger for the associated animation
+        ///  Note, triggers are special vs other kinds of parameters.  For all the other parameters we watch for changes
+        ///  in FixedUpdate and users can just set them normally off of Animator. But because triggers are transitory
+        ///  and likely to come and go between FixedUpdate calls, we require users to set them here to guarantee us to
+        ///  catch it...then we forward it to the Animator component
+        /// </summary>
+        /// <param name="triggerName">The string name of the trigger to activate</param>
         public void SetTrigger(string triggerName)
         {
             SetTrigger(Animator.StringToHash(triggerName));
         }
 
-        public void SetTrigger(int hash)
+        /// <inheritdoc cref="SetTrigger(string)" />
+        /// <param name="hash">The hash for the trigger to activate</param>
+        /// <param name="reset">If true, resets the trigger</param>
+        public void SetTrigger(int hash, bool reset = false)
         {
             var animMsg = new AnimationTriggerMessage();
             animMsg.Hash = hash;
+            animMsg.Reset = reset;
 
             if (IsServer)
             {
+                //  trigger the animation locally on the server...
+                if (reset)
+                {
+                    m_Animator.ResetTrigger(hash);
+                }
+                else
+                {
+                    m_Animator.SetTrigger(hash);
+                }
+
+                // ...then tell all the clients to do the same
                 SendAnimTriggerClientRpc(animMsg);
             }
+            else
+            {
+                Debug.LogWarning("Trying to call NetworkAnimator.SetTrigger on a client...ignoring");
+            }
+        }
+
+        /// <summary>
+        /// Resets the trigger for the associated animation.  See <see cref="SetTrigger(string)">SetTrigger</see> for more on how triggers are special
+        /// </summary>
+        /// <param name="triggerName">The string name of the trigger to reset</param>
+        public void ResetTrigger(string triggerName)
+        {
+            ResetTrigger(Animator.StringToHash(triggerName));
+        }
+
+        /// <inheritdoc cref="ResetTrigger(string)" path="summary" />
+        /// <param name="hash">The hash for the trigger to activate</param>
+        public void ResetTrigger(int hash)
+        {
+            SetTrigger(hash, true);
         }
     }
 }
+#endif // COM_UNITY_MODULES_ANIMATION

Components/NetworkRigidbody.cs

@@ -1,3 +1,4 @@
+#if COM_UNITY_MODULES_PHYSICS
 using UnityEngine;
 
 namespace Unity.Netcode.Components
@@ -78,3 +79,4 @@ namespace Unity.Netcode.Components
         }
     }
 }
+#endif // COM_UNITY_MODULES_PHYSICS

Components/NetworkRigidbody2D.cs

@@ -1,3 +1,4 @@
+#if COM_UNITY_MODULES_PHYSICS2D
 using UnityEngine;
 
 namespace Unity.Netcode.Components
@@ -32,7 +33,7 @@ namespace Unity.Netcode.Components
 
         private void FixedUpdate()
         {
-            if (NetworkManager.IsListening)
+            if (IsSpawned)
             {
                 if (HasAuthority != m_IsAuthority)
                 {
@@ -74,8 +75,8 @@ namespace Unity.Netcode.Components
         /// <inheritdoc />
         public override void OnNetworkDespawn()
         {
-            m_IsAuthority = false;
             UpdateRigidbodyKinematicMode();
         }
     }
 }
+#endif // COM_UNITY_MODULES_PHYSICS2D

Components/NetworkTransform.cs

@@ -260,8 +260,10 @@ namespace Unity.Netcode.Components
         /// </summary>
         [Tooltip("Sets whether this transform should sync in local space or in world space")]
         public bool InLocalSpace = false;
+        private bool m_LastInterpolateLocal = false; // was the last frame local
 
         public bool Interpolate = true;
+        private bool m_LastInterpolate = true; // was the last frame interpolated
 
         /// <summary>
         /// Used to determine who can write to this transform. Server only for this transform.
@@ -270,7 +272,7 @@ namespace Unity.Netcode.Components
         /// If using different values, please use RPCs to write to the server. Netcode doesn't support client side network variable writing
         /// </summary>
         // This is public to make sure that users don't depend on this IsClient && IsOwner check in their code. If this logic changes in the future, we can make it invisible here
-        public bool CanCommitToTransform;
+        public bool CanCommitToTransform { get; protected set; }
         protected bool m_CachedIsServer;
         protected NetworkManager m_CachedNetworkManager;
 
@@ -367,7 +369,11 @@ namespace Unity.Netcode.Components
         private void CommitLocallyAndReplicate(NetworkTransformState networkState)
         {
             m_ReplicatedNetworkState.Value = networkState;
-            AddInterpolatedState(networkState);
+
+            if (Interpolate)
+            {
+                AddInterpolatedState(networkState);
+            }
         }
 
         private void ResetInterpolatedStateToCurrentAuthoritativeState()
@@ -532,7 +538,12 @@ namespace Unity.Netcode.Components
             // again, we should be using quats here
             if (SyncRotAngleX || SyncRotAngleY || SyncRotAngleZ)
             {
-                var eulerAngles = m_RotationInterpolator.GetInterpolatedValue().eulerAngles;
+                var eulerAngles = new Vector3();
+                if (Interpolate)
+                {
+                    eulerAngles = m_RotationInterpolator.GetInterpolatedValue().eulerAngles;
+                }
+
                 if (SyncRotAngleX)
                 {
                     interpolatedRotAngles.x = networkState.IsTeleportingNextFrame || !Interpolate ? networkState.Rotation.x : eulerAngles.x;
@@ -603,10 +614,46 @@ namespace Unity.Netcode.Components
             }
         }
 
-        private void AddInterpolatedState(NetworkTransformState newState)
+        private void AddInterpolatedState(NetworkTransformState newState, bool reset = false)
         {
             var sentTime = newState.SentTime;
 
+            if (reset)
+            {
+                if (newState.HasPositionX)
+                {
+                    m_PositionXInterpolator.ResetTo(newState.PositionX, sentTime);
+                }
+
+                if (newState.HasPositionY)
+                {
+                    m_PositionYInterpolator.ResetTo(newState.PositionY, sentTime);
+                }
+
+                if (newState.HasPositionZ)
+                {
+                    m_PositionZInterpolator.ResetTo(newState.PositionZ, sentTime);
+                }
+
+                m_RotationInterpolator.ResetTo(Quaternion.Euler(newState.Rotation), sentTime);
+
+                if (newState.HasScaleX)
+                {
+                    m_ScaleXInterpolator.ResetTo(newState.ScaleX, sentTime);
+                }
+
+                if (newState.HasScaleY)
+                {
+                    m_ScaleYInterpolator.ResetTo(newState.ScaleY, sentTime);
+                }
+
+                if (newState.HasScaleZ)
+                {
+                    m_ScaleZInterpolator.ResetTo(newState.ScaleZ, sentTime);
+                }
+
+                return;
+            }
             if (newState.HasPositionX)
             {
                 m_PositionXInterpolator.AddMeasurement(newState.PositionX, sentTime);
@@ -644,7 +691,6 @@ namespace Unity.Netcode.Components
         {
             if (!NetworkObject.IsSpawned)
             {
-                // todo MTT-849 should never happen but yet it does! maybe revisit/dig after NetVar updates and snapshot system lands?
                 return;
             }
 
@@ -656,7 +702,11 @@ namespace Unity.Netcode.Components
 
             Debug.DrawLine(newState.Position, newState.Position + Vector3.up + Vector3.left, Color.green, 10, false);
 
-            AddInterpolatedState(newState);
+            if (Interpolate)
+            {
+                AddInterpolatedState(newState, (newState.InLocalSpace != m_LastInterpolateLocal));
+            }
+            m_LastInterpolateLocal = newState.InLocalSpace;
 
             if (m_CachedNetworkManager.LogLevel == LogLevel.Developer)
             {
@@ -734,7 +784,7 @@ namespace Unity.Netcode.Components
             {
                 m_ReplicatedNetworkState.SetDirty(true);
             }
-            else
+            else if (m_Transform != null)
             {
                 ApplyInterpolatedNetworkStateToTransform(m_ReplicatedNetworkState.Value, m_Transform);
             }
@@ -807,11 +857,22 @@ namespace Unity.Netcode.Components
         // conditional to users only making transform update changes in FixedUpdate.
         protected virtual void Update()
         {
-            if (!NetworkObject.IsSpawned)
+            if (!IsSpawned)
             {
                 return;
             }
 
+            if (!Interpolate && m_LastInterpolate)
+            {
+                // if we just stopped interpolating, let's clear the interpolators
+                foreach (var interpolator in m_AllFloatInterpolators)
+                {
+                    interpolator.Clear();
+                }
+            }
+
+            m_LastInterpolate = Interpolate;
+
             if (CanCommitToTransform)
             {
                 if (m_CachedIsServer)
@@ -831,12 +892,15 @@ namespace Unity.Netcode.Components
                 var cachedServerTime = serverTime.Time;
                 var cachedRenderTime = serverTime.TimeTicksAgo(1).Time;
 
-                foreach (var interpolator in m_AllFloatInterpolators)
+                if (Interpolate)
                 {
-                    interpolator.Update(cachedDeltaTime, cachedRenderTime, cachedServerTime);
-                }
+                    foreach (var interpolator in m_AllFloatInterpolators)
+                    {
+                        interpolator.Update(cachedDeltaTime, cachedRenderTime, cachedServerTime);
+                    }
 
-                m_RotationInterpolator.Update(cachedDeltaTime, cachedRenderTime, cachedServerTime);
+                    m_RotationInterpolator.Update(cachedDeltaTime, cachedRenderTime, cachedServerTime);
+                }
 
                 if (!CanCommitToTransform)
                 {

Components/com.unity.netcode.components.asmdef

@@ -5,13 +5,22 @@
         "Unity.Netcode.Runtime",
         "Unity.Collections"
     ],
-    "includePlatforms": [],
-    "excludePlatforms": [],
     "allowUnsafeCode": true,
-    "overrideReferences": false,
-    "precompiledReferences": [],
-    "autoReferenced": true,
-    "defineConstraints": [],
-    "versionDefines": [],
-    "noEngineReferences": false
+    "versionDefines": [
+        {
+            "name": "com.unity.modules.animation",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_ANIMATION"
+        },
+        {
+            "name": "com.unity.modules.physics",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_PHYSICS"
+        },
+        {
+            "name": "com.unity.modules.physics2d",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_PHYSICS2D"
+        }
+    ]
 }

Editor/CodeGen/CodeGenHelpers.cs

@@ -22,6 +22,10 @@ namespace Unity.Netcode.Editor.CodeGen
         public static readonly string ClientRpcAttribute_FullName = typeof(ClientRpcAttribute).FullName;
         public static readonly string ServerRpcParams_FullName = typeof(ServerRpcParams).FullName;
         public static readonly string ClientRpcParams_FullName = typeof(ClientRpcParams).FullName;
+        public static readonly string ClientRpcSendParams_FullName = typeof(ClientRpcSendParams).FullName;
+        public static readonly string ClientRpcReceiveParams_FullName = typeof(ClientRpcReceiveParams).FullName;
+        public static readonly string ServerRpcSendParams_FullName = typeof(ServerRpcSendParams).FullName;
+        public static readonly string ServerRpcReceiveParams_FullName = typeof(ServerRpcReceiveParams).FullName;
         public static readonly string INetworkSerializable_FullName = typeof(INetworkSerializable).FullName;
         public static readonly string UnityColor_FullName = typeof(Color).FullName;
         public static readonly string UnityColor32_FullName = typeof(Color32).FullName;
@@ -264,6 +268,28 @@ namespace Unity.Netcode.Editor.CodeGen
             });
         }
 
+        public static void AddWarning(this List<DiagnosticMessage> diagnostics, string message)
+        {
+            diagnostics.AddWarning((SequencePoint)null, message);
+        }
+
+        public static void AddWarning(this List<DiagnosticMessage> diagnostics, MethodDefinition methodDefinition, string message)
+        {
+            diagnostics.AddWarning(methodDefinition.DebugInformation.SequencePoints.FirstOrDefault(), message);
+        }
+
+        public static void AddWarning(this List<DiagnosticMessage> diagnostics, SequencePoint sequencePoint, string message)
+        {
+            diagnostics.Add(new DiagnosticMessage
+            {
+                DiagnosticType = DiagnosticType.Warning,
+                File = sequencePoint?.Document.Url.Replace($"{Environment.CurrentDirectory}{Path.DirectorySeparatorChar}", ""),
+                Line = sequencePoint?.StartLine ?? 0,
+                Column = sequencePoint?.StartColumn ?? 0,
+                MessageData = $" - {message}"
+            });
+        }
+
         public static void RemoveRecursiveReferences(this ModuleDefinition moduleDefinition)
         {
             // Weird behavior from Cecil: When importing a reference to a specific implementation of a generic

Editor/CodeGen/INetworkMessageILPP.cs

@@ -13,7 +13,6 @@ using MethodAttributes = Mono.Cecil.MethodAttributes;
 
 namespace Unity.Netcode.Editor.CodeGen
 {
-
     internal sealed class INetworkMessageILPP : ILPPInterface
     {
         public override ILPPInterface GetInstance() => this;
@@ -31,7 +30,6 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
-
             m_Diagnostics.Clear();
 
             // read
@@ -95,27 +93,23 @@ namespace Unity.Netcode.Editor.CodeGen
         }
 
 
-        private TypeReference m_FastBufferReader_TypeRef;
-        private TypeReference m_NetworkContext_TypeRef;
+        private MethodReference m_MessagingSystem_ReceiveMessage_MethodRef;
         private TypeReference m_MessagingSystem_MessageWithHandler_TypeRef;
         private MethodReference m_MessagingSystem_MessageHandler_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 MethodReference m_Type_GetTypeFromHandle_MethodRef;
-
         private MethodReference m_List_Add_MethodRef;
 
+        private const string k_ReceiveMessageName = nameof(MessagingSystem.ReceiveMessage);
+
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
-            m_FastBufferReader_TypeRef = moduleDefinition.ImportReference(typeof(FastBufferReader));
-            m_NetworkContext_TypeRef = moduleDefinition.ImportReference(typeof(NetworkContext));
-            m_MessagingSystem_MessageHandler_Constructor_TypeRef =
-                moduleDefinition.ImportReference(typeof(MessagingSystem.MessageHandler).GetConstructors()[0]);
+            m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(typeof(MessagingSystem.MessageHandler).GetConstructors()[0]);
 
             var messageWithHandlerType = typeof(MessagingSystem.MessageWithHandler);
-            m_MessagingSystem_MessageWithHandler_TypeRef =
-                moduleDefinition.ImportReference(messageWithHandlerType);
+            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerType);
             foreach (var fieldInfo in messageWithHandlerType.GetFields())
             {
                 switch (fieldInfo.Name)
@@ -162,38 +156,18 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
-
-            return true;
-        }
-
-        private MethodReference GetNetworkMessageRecieveHandler(TypeDefinition typeDefinition)
-        {
-            SequencePoint typeSequence = null;
-            foreach (var method in typeDefinition.Methods)
+            var messagingSystemType = typeof(MessagingSystem);
+            foreach (var methodInfo in messagingSystemType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
             {
-                var resolved = method.Resolve();
-                var methodSequence = resolved.DebugInformation.SequencePoints.FirstOrDefault();
-                if (typeSequence == null || methodSequence.StartLine < typeSequence.StartLine)
+                switch (methodInfo.Name)
                 {
-                    typeSequence = methodSequence;
-                }
-
-                if (resolved.IsStatic && resolved.IsPublic && resolved.Name == "Receive" && resolved.Parameters.Count == 2
-                    && !resolved.Parameters[0].IsIn
-                    && !resolved.Parameters[0].ParameterType.IsByReference
-                    && resolved.Parameters[0].ParameterType.Resolve() ==
-                        m_FastBufferReader_TypeRef.Resolve()
-                    && resolved.Parameters[1].IsIn
-                    && resolved.Parameters[1].ParameterType.IsByReference
-                    && resolved.Parameters[1].ParameterType.GetElementType().Resolve() == m_NetworkContext_TypeRef.Resolve()
-                    && resolved.ReturnType == resolved.Module.TypeSystem.Void)
-                {
-                    return method;
+                    case k_ReceiveMessageName:
+                        m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        break;
                 }
             }
 
-            m_Diagnostics.AddError(typeSequence, $"Class {typeDefinition.FullName} does not implement required method: `public static void Receive(FastBufferReader, in NetworkContext)`");
-            return null;
+            return true;
         }
 
         private MethodDefinition GetOrCreateStaticConstructor(TypeDefinition typeDefinition)
@@ -264,11 +238,8 @@ namespace Unity.Netcode.Editor.CodeGen
 
                     foreach (var type in networkMessageTypes)
                     {
-                        var receiveMethod = GetNetworkMessageRecieveHandler(type);
-                        if (receiveMethod == null)
-                        {
-                            continue;
-                        }
+                        var receiveMethod = new GenericInstanceMethod(m_MessagingSystem_ReceiveMessage_MethodRef);
+                        receiveMethod.GenericArguments.Add(type);
                         CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod);
                     }
 

Editor/CodeGen/INetworkSerializableILPP.cs

@@ -0,0 +1,167 @@
+using System;
+using System.IO;
+using System.Linq;
+using System.Collections.Generic;
+using System.Reflection;
+using Mono.Cecil;
+using Mono.Cecil.Cil;
+using Mono.Cecil.Rocks;
+using Unity.CompilationPipeline.Common.Diagnostics;
+using Unity.CompilationPipeline.Common.ILPostProcessing;
+using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostProcessor;
+using MethodAttributes = Mono.Cecil.MethodAttributes;
+
+namespace Unity.Netcode.Editor.CodeGen
+{
+
+    internal sealed class INetworkSerializableILPP : ILPPInterface
+    {
+        public override ILPPInterface GetInstance() => this;
+
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+            compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName ||
+            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
+
+        private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
+
+        public override ILPostProcessResult Process(ICompiledAssembly compiledAssembly)
+        {
+            if (!WillProcess(compiledAssembly))
+            {
+                return null;
+            }
+
+
+            m_Diagnostics.Clear();
+
+            // read
+            var assemblyDefinition = CodeGenHelpers.AssemblyDefinitionFor(compiledAssembly, out var resolver);
+            if (assemblyDefinition == null)
+            {
+                m_Diagnostics.AddError($"Cannot read assembly definition: {compiledAssembly.Name}");
+                return null;
+            }
+
+            // process
+            var mainModule = assemblyDefinition.MainModule;
+            if (mainModule != null)
+            {
+                try
+                {
+                    if (ImportReferences(mainModule))
+                    {
+                        var types = mainModule.GetTypes()
+                            .Where(t => t.Resolve().HasInterface(CodeGenHelpers.INetworkSerializable_FullName) && !t.Resolve().IsAbstract && t.Resolve().IsValueType)
+                            .ToList();
+                        // process `INetworkMessage` types
+                        if (types.Count == 0)
+                        {
+                            return null;
+                        }
+
+                        CreateModuleInitializer(assemblyDefinition, types);
+                    }
+                    else
+                    {
+                        m_Diagnostics.AddError($"Cannot import references into main module: {mainModule.Name}");
+                    }
+                }
+                catch (Exception e)
+                {
+                    m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                }
+            }
+            else
+            {
+                m_Diagnostics.AddError($"Cannot get main module from assembly definition: {compiledAssembly.Name}");
+            }
+
+            mainModule.RemoveRecursiveReferences();
+
+            // write
+            var pe = new MemoryStream();
+            var pdb = new MemoryStream();
+
+            var writerParameters = new WriterParameters
+            {
+                SymbolWriterProvider = new PortablePdbWriterProvider(),
+                SymbolStream = pdb,
+                WriteSymbols = true
+            };
+
+            assemblyDefinition.Write(pe, writerParameters);
+
+            return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
+        }
+
+        private MethodReference m_InitializeDelegates_MethodRef;
+
+        private const string k_InitializeMethodName = nameof(NetworkVariableHelper.InitializeDelegates);
+
+        private bool ImportReferences(ModuleDefinition moduleDefinition)
+        {
+
+            var helperType = typeof(NetworkVariableHelper);
+            foreach (var methodInfo in helperType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
+            {
+                switch (methodInfo.Name)
+                {
+                    case k_InitializeMethodName:
+                        m_InitializeDelegates_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        break;
+                }
+            }
+            return true;
+        }
+
+        private MethodDefinition GetOrCreateStaticConstructor(TypeDefinition typeDefinition)
+        {
+            var staticCtorMethodDef = typeDefinition.GetStaticConstructor();
+            if (staticCtorMethodDef == null)
+            {
+                staticCtorMethodDef = new MethodDefinition(
+                    ".cctor", // Static Constructor (constant-constructor)
+                    MethodAttributes.HideBySig |
+                    MethodAttributes.SpecialName |
+                    MethodAttributes.RTSpecialName |
+                    MethodAttributes.Static,
+                    typeDefinition.Module.TypeSystem.Void);
+                staticCtorMethodDef.Body.Instructions.Add(Instruction.Create(OpCodes.Ret));
+                typeDefinition.Methods.Add(staticCtorMethodDef);
+            }
+
+            return staticCtorMethodDef;
+        }
+
+        // Creates a static module constructor (which is executed when the module is loaded) that registers all the
+        // message types in the assembly with MessagingSystem.
+        // This is the same behavior as annotating a static method with [ModuleInitializer] in standardized
+        // C# (that attribute doesn't exist in Unity, but the static module constructor still works)
+        // https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.moduleinitializerattribute?view=net-5.0
+        // https://web.archive.org/web/20100212140402/http://blogs.msdn.com/junfeng/archive/2005/11/19/494914.aspx
+        private void CreateModuleInitializer(AssemblyDefinition assembly, List<TypeDefinition> networkSerializableTypes)
+        {
+            foreach (var typeDefinition in assembly.MainModule.Types)
+            {
+                if (typeDefinition.FullName == "<Module>")
+                {
+                    var staticCtorMethodDef = GetOrCreateStaticConstructor(typeDefinition);
+
+                    var processor = staticCtorMethodDef.Body.GetILProcessor();
+
+                    var instructions = new List<Instruction>();
+
+                    foreach (var type in networkSerializableTypes)
+                    {
+                        var method = new GenericInstanceMethod(m_InitializeDelegates_MethodRef);
+                        method.GenericArguments.Add(type);
+                        instructions.Add(processor.Create(OpCodes.Call, method));
+                    }
+
+                    instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));
+                    break;
+                }
+            }
+        }
+    }
+}

Editor/CodeGen/INetworkSerializableILPP.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 64a0c1e708fa46a389d64e7b4708e6c7
+timeCreated: 1635535237

Editor/CodeGen/NetworkBehaviourILPP.cs

@@ -7,7 +7,6 @@ using System.Runtime.CompilerServices;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 using Mono.Cecil.Rocks;
-using Unity.Collections;
 using Unity.CompilationPipeline.Common.Diagnostics;
 using Unity.CompilationPipeline.Common.ILPostProcessing;
 using UnityEngine;
@@ -17,7 +16,6 @@ using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostPr
 
 namespace Unity.Netcode.Editor.CodeGen
 {
-
     internal sealed class NetworkBehaviourILPP : ILPPInterface
     {
         private const string k_ReadValueMethodName = nameof(FastBufferReader.ReadValueSafe);
@@ -25,7 +23,8 @@ namespace Unity.Netcode.Editor.CodeGen
 
         public override ILPPInterface GetInstance() => this;
 
-        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
@@ -109,8 +108,10 @@ namespace Unity.Netcode.Editor.CodeGen
         private FieldReference m_NetworkManager_rpc_name_table_FieldRef;
         private MethodReference m_NetworkManager_rpc_name_table_Add_MethodRef;
         private TypeReference m_NetworkBehaviour_TypeRef;
-        private MethodReference m_NetworkBehaviour_SendServerRpc_MethodRef;
-        private MethodReference m_NetworkBehaviour_SendClientRpc_MethodRef;
+        private MethodReference m_NetworkBehaviour_beginSendServerRpc_MethodRef;
+        private MethodReference m_NetworkBehaviour_endSendServerRpc_MethodRef;
+        private MethodReference m_NetworkBehaviour_beginSendClientRpc_MethodRef;
+        private MethodReference m_NetworkBehaviour_endSendClientRpc_MethodRef;
         private FieldReference m_NetworkBehaviour_rpc_exec_stage_FieldRef;
         private MethodReference m_NetworkBehaviour_getNetworkManager_MethodRef;
         private MethodReference m_NetworkBehaviour_getOwnerClientId_MethodRef;
@@ -124,8 +125,6 @@ namespace Unity.Netcode.Editor.CodeGen
         private TypeReference m_ClientRpcParams_TypeRef;
 
         private TypeReference m_FastBufferWriter_TypeRef;
-        private MethodReference m_FastBufferWriter_Constructor;
-        private MethodReference m_FastBufferWriter_Dispose;
         private Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
         private List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
 
@@ -144,8 +143,10 @@ namespace Unity.Netcode.Editor.CodeGen
         private const string k_NetworkManager_rpc_name_table = nameof(NetworkManager.__rpc_name_table);
 
         private const string k_NetworkBehaviour_rpc_exec_stage = nameof(NetworkBehaviour.__rpc_exec_stage);
-        private const string k_NetworkBehaviour_SendServerRpc = nameof(NetworkBehaviour.__sendServerRpc);
-        private const string k_NetworkBehaviour_SendClientRpc = nameof(NetworkBehaviour.__sendClientRpc);
+        private const string k_NetworkBehaviour_beginSendServerRpc = nameof(NetworkBehaviour.__beginSendServerRpc);
+        private const string k_NetworkBehaviour_endSendServerRpc = nameof(NetworkBehaviour.__endSendServerRpc);
+        private const string k_NetworkBehaviour_beginSendClientRpc = nameof(NetworkBehaviour.__beginSendClientRpc);
+        private const string k_NetworkBehaviour_endSendClientRpc = nameof(NetworkBehaviour.__endSendClientRpc);
         private const string k_NetworkBehaviour_NetworkManager = nameof(NetworkBehaviour.NetworkManager);
         private const string k_NetworkBehaviour_OwnerClientId = nameof(NetworkBehaviour.OwnerClientId);
 
@@ -234,11 +235,17 @@ namespace Unity.Netcode.Editor.CodeGen
             {
                 switch (methodInfo.Name)
                 {
-                    case k_NetworkBehaviour_SendServerRpc:
-                        m_NetworkBehaviour_SendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                    case k_NetworkBehaviour_beginSendServerRpc:
+                        m_NetworkBehaviour_beginSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
                         break;
-                    case k_NetworkBehaviour_SendClientRpc:
-                        m_NetworkBehaviour_SendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                    case k_NetworkBehaviour_endSendServerRpc:
+                        m_NetworkBehaviour_endSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        break;
+                    case k_NetworkBehaviour_beginSendClientRpc:
+                        m_NetworkBehaviour_beginSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        break;
+                    case k_NetworkBehaviour_endSendClientRpc:
+                        m_NetworkBehaviour_endSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
                         break;
                 }
             }
@@ -299,24 +306,22 @@ namespace Unity.Netcode.Editor.CodeGen
             var fastBufferWriterType = typeof(FastBufferWriter);
             m_FastBufferWriter_TypeRef = moduleDefinition.ImportReference(fastBufferWriterType);
 
-            m_FastBufferWriter_Constructor = moduleDefinition.ImportReference(
-                fastBufferWriterType.GetConstructor(new[] { typeof(int), typeof(Allocator), typeof(int) }));
-            m_FastBufferWriter_Dispose = moduleDefinition.ImportReference(fastBufferWriterType.GetMethod("Dispose"));
-
             var fastBufferReaderType = typeof(FastBufferReader);
             m_FastBufferReader_TypeRef = moduleDefinition.ImportReference(fastBufferReaderType);
 
             // Find all extension methods for FastBufferReader and FastBufferWriter to enable user-implemented
             // methods to be called.
-            var assemblies = new List<AssemblyDefinition>();
-            assemblies.Add(m_MainModule.Assembly);
+            var assemblies = new List<AssemblyDefinition> { m_MainModule.Assembly };
             foreach (var reference in m_MainModule.AssemblyReferences)
             {
-                assemblies.Add(m_AssemblyResolver.Resolve(reference));
+                var assembly = m_AssemblyResolver.Resolve(reference);
+                if (assembly != null)
+                {
+                    assemblies.Add(assembly);
+                }
             }
 
-            var extensionConstructor =
-                moduleDefinition.ImportReference(typeof(ExtensionAttribute).GetConstructor(new Type[] { }));
+            var extensionConstructor = moduleDefinition.ImportReference(typeof(ExtensionAttribute).GetConstructor(new Type[] { }));
             foreach (var assembly in assemblies)
             {
                 foreach (var module in assembly.Modules)
@@ -328,6 +333,7 @@ namespace Unity.Netcode.Editor.CodeGen
                         {
                             continue;
                         }
+
                         foreach (var method in type.Methods)
                         {
                             if (!method.IsStatic)
@@ -352,13 +358,11 @@ namespace Unity.Netcode.Editor.CodeGen
 
                             var parameters = method.Parameters;
 
-                            if (parameters.Count == 2
-                                && parameters[0].ParameterType.Resolve() == m_FastBufferWriter_TypeRef.MakeByReferenceType().Resolve())
+                            if (parameters.Count == 2 && parameters[0].ParameterType.Resolve() == m_FastBufferWriter_TypeRef.MakeByReferenceType().Resolve())
                             {
                                 m_FastBufferWriter_ExtensionMethodRefs.Add(m_MainModule.ImportReference(method));
                             }
-                            else if (parameters.Count == 2
-                                && parameters[0].ParameterType.Resolve() == m_FastBufferReader_TypeRef.MakeByReferenceType().Resolve())
+                            else if (parameters.Count == 2 && parameters[0].ParameterType.Resolve() == m_FastBufferReader_TypeRef.MakeByReferenceType().Resolve())
                             {
                                 m_FastBufferReader_ExtensionMethodRefs.Add(m_MainModule.ImportReference(method));
                             }
@@ -391,9 +395,20 @@ namespace Unity.Netcode.Editor.CodeGen
                     continue;
                 }
 
+                if (methodDefinition.HasCustomAttributes)
+                {
+                    foreach (var attribute in methodDefinition.CustomAttributes)
+                    {
+                        if (attribute.AttributeType.Name == nameof(AsyncStateMachineAttribute))
+                        {
+                            m_Diagnostics.AddError(methodDefinition, $"{methodDefinition.FullName}: RPCs cannot be 'async'");
+                        }
+                    }
+                }
+
                 InjectWriteAndCallBlocks(methodDefinition, rpcAttribute, rpcMethodId);
 
-                rpcHandlers.Add((rpcMethodId, GenerateStaticHandler(methodDefinition, rpcAttribute)));
+                rpcHandlers.Add((rpcMethodId, GenerateStaticHandler(methodDefinition, rpcAttribute, rpcMethodId)));
 
                 if (isEditorOrDevelopment)
                 {
@@ -473,7 +488,6 @@ namespace Unity.Netcode.Editor.CodeGen
         private CustomAttribute CheckAndGetRpcAttribute(MethodDefinition methodDefinition)
         {
             CustomAttribute rpcAttribute = null;
-            bool isServerRpc = false;
             foreach (var customAttribute in methodDefinition.CustomAttributes)
             {
                 var customAttributeType_FullName = customAttribute.AttributeType.FullName;
@@ -517,7 +531,6 @@ namespace Unity.Netcode.Editor.CodeGen
 
                     if (isValid)
                     {
-                        isServerRpc = customAttributeType_FullName == CodeGenHelpers.ServerRpcAttribute_FullName;
                         rpcAttribute = customAttribute;
                     }
                 }
@@ -565,31 +578,36 @@ namespace Unity.Netcode.Editor.CodeGen
                         checkType = paramType.GetElementType().Resolve();
                     }
 
-                    if (
-                        (parameters[0].ParameterType.Resolve() == checkType
-                        || (parameters[0].ParameterType.Resolve() == checkType.MakeByReferenceType().Resolve() && parameters[0].IsIn)))
+                    if ((parameters[0].ParameterType.Resolve() == checkType ||
+                        (parameters[0].ParameterType.Resolve() == checkType.MakeByReferenceType().Resolve() && parameters[0].IsIn)))
                     {
                         return method;
                     }
+
                     if (method.HasGenericParameters && method.GenericParameters.Count == 1)
                     {
                         if (method.GenericParameters[0].HasConstraints)
                         {
+                            var meetsConstraints = true;
                             foreach (var constraint in method.GenericParameters[0].Constraints)
                             {
                                 var resolvedConstraint = constraint.Resolve();
 
-                                if (
-                                    (resolvedConstraint.IsInterface &&
-                                     checkType.HasInterface(resolvedConstraint.FullName))
-                                    || (resolvedConstraint.IsClass &&
-                                        checkType.Resolve().IsSubclassOf(resolvedConstraint.FullName)))
+                                if ((resolvedConstraint.IsInterface && !checkType.HasInterface(resolvedConstraint.FullName)) ||
+                                    (resolvedConstraint.IsClass && !checkType.Resolve().IsSubclassOf(resolvedConstraint.FullName)) ||
+                                    (resolvedConstraint.Name == "ValueType" && !checkType.IsValueType))
                                 {
-                                    var instanceMethod = new GenericInstanceMethod(method);
-                                    instanceMethod.GenericArguments.Add(checkType);
-                                    return instanceMethod;
+                                    meetsConstraints = false;
+                                    break;
                                 }
                             }
+
+                            if (meetsConstraints)
+                            {
+                                var instanceMethod = new GenericInstanceMethod(method);
+                                instanceMethod.GenericArguments.Add(checkType);
+                                return instanceMethod;
+                            }
                         }
                     }
                 }
@@ -613,8 +631,8 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         if (parameters[1].IsIn)
                         {
-                            if (parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve()
-                                && ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
+                            if (parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve() &&
+                                ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
                                 m_FastBufferWriter_WriteValue_MethodRefs[assemblyQualifiedName] = methodRef;
@@ -624,8 +642,8 @@ namespace Unity.Netcode.Editor.CodeGen
                         else
                         {
 
-                            if (parameters[1].ParameterType.Resolve() == paramType.Resolve()
-                                && parameters[1].ParameterType.IsArray == paramType.IsArray)
+                            if (parameters[1].ParameterType.Resolve() == paramType.Resolve() &&
+                                parameters[1].ParameterType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
                                 m_FastBufferWriter_WriteValue_MethodRefs[assemblyQualifiedName] = methodRef;
@@ -696,11 +714,8 @@ namespace Unity.Netcode.Editor.CodeGen
                             {
                                 var resolvedConstraint = constraint.Resolve();
 
-                                if (
-                                    (resolvedConstraint.IsInterface &&
-                                     checkType.HasInterface(resolvedConstraint.FullName))
-                                    || (resolvedConstraint.IsClass &&
-                                        checkType.Resolve().IsSubclassOf(resolvedConstraint.FullName)))
+                                if ((resolvedConstraint.IsInterface && checkType.HasInterface(resolvedConstraint.FullName)) ||
+                                    (resolvedConstraint.IsClass && checkType.Resolve().IsSubclassOf(resolvedConstraint.FullName)))
                                 {
                                     var instanceMethod = new GenericInstanceMethod(method);
                                     instanceMethod.GenericArguments.Add(checkType);
@@ -725,11 +740,10 @@ namespace Unity.Netcode.Editor.CodeGen
                 foreach (var method in m_FastBufferReader_ExtensionMethodRefs)
                 {
                     var parameters = method.Resolve().Parameters;
-                    if (
-                        method.Name == k_ReadValueMethodName
-                        && parameters[1].IsOut
-                        && parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve()
-                        && ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
+                    if (method.Name == k_ReadValueMethodName &&
+                        parameters[1].IsOut &&
+                        parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve() &&
+                        ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                     {
                         methodRef = method;
                         m_FastBufferReader_ReadValue_MethodRefs[assemblyQualifiedName] = methodRef;
@@ -761,8 +775,8 @@ namespace Unity.Netcode.Editor.CodeGen
             var instructions = new List<Instruction>();
             var processor = methodDefinition.Body.GetILProcessor();
             var isServerRpc = rpcAttribute.AttributeType.FullName == CodeGenHelpers.ServerRpcAttribute_FullName;
-            var requireOwnership = true; // default value MUST be = `ServerRpcAttribute.RequireOwnership`
-            var rpcDelivery = RpcDelivery.Reliable; // default value MUST be = `RpcAttribute.Delivery`
+            var requireOwnership = true; // default value MUST be == `ServerRpcAttribute.RequireOwnership`
+            var rpcDelivery = RpcDelivery.Reliable; // default value MUST be == `RpcAttribute.Delivery`
             foreach (var attrField in rpcAttribute.Fields)
             {
                 switch (attrField.Name)
@@ -786,9 +800,9 @@ namespace Unity.Netcode.Editor.CodeGen
             // NetworkManager networkManager;
             methodDefinition.Body.Variables.Add(new VariableDefinition(m_NetworkManager_TypeRef));
             int netManLocIdx = methodDefinition.Body.Variables.Count - 1;
-            // NetworkSerializer serializer;
+            // FastBufferWriter bufferWriter;
             methodDefinition.Body.Variables.Add(new VariableDefinition(m_FastBufferWriter_TypeRef));
-            int serializerLocIdx = methodDefinition.Body.Variables.Count - 1;
+            int bufWriterLocIdx = methodDefinition.Body.Variables.Count - 1;
 
             // XXXRpcParams
             if (!hasRpcParams)
@@ -843,6 +857,8 @@ namespace Unity.Netcode.Editor.CodeGen
 
                 instructions.Add(beginInstr);
 
+                // var bufferWriter = __beginSendServerRpc(rpcMethodId, serverRpcParams, rpcDelivery) -> ServerRpc
+                // var bufferWriter = __beginSendClientRpc(rpcMethodId, clientRpcParams, rpcDelivery) -> ClientRpc
                 if (isServerRpc)
                 {
                     // ServerRpc
@@ -856,8 +872,7 @@ namespace Unity.Netcode.Editor.CodeGen
                         instructions.Add(processor.Create(OpCodes.Ldarg_0));
                         instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_getOwnerClientId_MethodRef));
                         instructions.Add(processor.Create(OpCodes.Ldloc, netManLocIdx));
-                        instructions.Add(
-                            processor.Create(OpCodes.Callvirt, m_NetworkManager_getLocalClientId_MethodRef));
+                        instructions.Add(processor.Create(OpCodes.Callvirt, m_NetworkManager_getLocalClientId_MethodRef));
                         instructions.Add(processor.Create(OpCodes.Ceq));
                         instructions.Add(processor.Create(OpCodes.Ldc_I4, 0));
                         instructions.Add(processor.Create(OpCodes.Ceq));
@@ -875,8 +890,7 @@ namespace Unity.Netcode.Editor.CodeGen
                         instructions.Add(processor.Create(OpCodes.Brfalse, logNextInstr));
 
                         // Debug.LogError(...);
-                        instructions.Add(processor.Create(OpCodes.Ldstr,
-                            "Only the owner can invoke a ServerRpc that requires ownership!"));
+                        instructions.Add(processor.Create(OpCodes.Ldstr, "Only the owner can invoke a ServerRpc that requires ownership!"));
                         instructions.Add(processor.Create(OpCodes.Call, m_Debug_LogError_MethodRef));
 
                         instructions.Add(logNextInstr);
@@ -884,31 +898,86 @@ namespace Unity.Netcode.Editor.CodeGen
                         instructions.Add(roReturnInstr);
                         instructions.Add(roLastInstr);
                     }
+
+                    // var bufferWriter = __beginSendServerRpc(rpcMethodId, serverRpcParams, rpcDelivery);
+                    instructions.Add(processor.Create(OpCodes.Ldarg_0));
+
+                    // rpcMethodId
+                    instructions.Add(processor.Create(OpCodes.Ldc_I4, unchecked((int)rpcMethodId)));
+
+                    // rpcParams
+                    instructions.Add(hasRpcParams ? processor.Create(OpCodes.Ldarg, paramCount) : processor.Create(OpCodes.Ldloc, rpcParamsIdx));
+
+                    // rpcDelivery
+                    instructions.Add(processor.Create(OpCodes.Ldc_I4, (int)rpcDelivery));
+
+                    // __beginSendServerRpc
+                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_beginSendServerRpc_MethodRef));
+                    instructions.Add(processor.Create(OpCodes.Stloc, bufWriterLocIdx));
                 }
+                else
+                {
+                    // ClientRpc
 
-                // var writer = new FastBufferWriter(1285, Allocator.Temp, 63985);
-                instructions.Add(processor.Create(OpCodes.Ldloca, serializerLocIdx));
-                instructions.Add(processor.Create(OpCodes.Ldc_I4, 1300 - sizeof(byte) - sizeof(ulong) - sizeof(uint) - sizeof(ushort)));
-                instructions.Add(processor.Create(OpCodes.Ldc_I4_2));
-                instructions.Add(processor.Create(OpCodes.Ldc_I4, 64000 - sizeof(byte) - sizeof(ulong) - sizeof(uint) - sizeof(ushort)));
-                instructions.Add(processor.Create(OpCodes.Call, m_FastBufferWriter_Constructor));
+                    // var bufferWriter = __beginSendClientRpc(rpcMethodId, clientRpcParams, rpcDelivery);
+                    instructions.Add(processor.Create(OpCodes.Ldarg_0));
 
-                var firstInstruction = processor.Create(OpCodes.Nop);
-                instructions.Add(firstInstruction);
+                    // rpcMethodId
+                    instructions.Add(processor.Create(OpCodes.Ldc_I4, unchecked((int)rpcMethodId)));
+
+                    // rpcParams
+                    instructions.Add(hasRpcParams ? processor.Create(OpCodes.Ldarg, paramCount) : processor.Create(OpCodes.Ldloc, rpcParamsIdx));
+
+                    // rpcDelivery
+                    instructions.Add(processor.Create(OpCodes.Ldc_I4, (int)rpcDelivery));
+
+                    // __beginSendClientRpc
+                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_beginSendClientRpc_MethodRef));
+                    instructions.Add(processor.Create(OpCodes.Stloc, bufWriterLocIdx));
+                }
 
                 // write method parameters into stream
                 for (int paramIndex = 0; paramIndex < paramCount; ++paramIndex)
                 {
                     var paramDef = methodDefinition.Parameters[paramIndex];
                     var paramType = paramDef.ParameterType;
-                    // ServerRpcParams
-                    if (paramType.FullName == CodeGenHelpers.ServerRpcParams_FullName && isServerRpc && paramIndex == paramCount - 1)
+                    if (paramType.FullName == CodeGenHelpers.ClientRpcSendParams_FullName ||
+                        paramType.FullName == CodeGenHelpers.ClientRpcReceiveParams_FullName)
                     {
+                        m_Diagnostics.AddError($"Rpcs may not accept {paramType.FullName} as a parameter. Use {nameof(ClientRpcParams)} instead.");
+                        continue;
+                    }
+
+                    if (paramType.FullName == CodeGenHelpers.ServerRpcSendParams_FullName ||
+                        paramType.FullName == CodeGenHelpers.ServerRpcReceiveParams_FullName)
+                    {
+                        m_Diagnostics.AddError($"Rpcs may not accept {paramType.FullName} as a parameter. Use {nameof(ServerRpcParams)} instead.");
+                        continue;
+                    }
+                    // ServerRpcParams
+                    if (paramType.FullName == CodeGenHelpers.ServerRpcParams_FullName)
+                    {
+                        if (paramIndex != paramCount - 1)
+                        {
+                            m_Diagnostics.AddError(methodDefinition, $"{nameof(ServerRpcParams)} must be the last parameter in a ServerRpc.");
+                        }
+                        if (!isServerRpc)
+                        {
+                            m_Diagnostics.AddError($"ClientRpcs may not accept {nameof(ServerRpcParams)} as a parameter.");
+                        }
                         continue;
                     }
                     // ClientRpcParams
-                    if (paramType.FullName == CodeGenHelpers.ClientRpcParams_FullName && !isServerRpc && paramIndex == paramCount - 1)
+                    if (paramType.FullName == CodeGenHelpers.ClientRpcParams_FullName)
                     {
+                        if (paramIndex != paramCount - 1)
+                        {
+                            m_Diagnostics.AddError(methodDefinition, $"{nameof(ClientRpcParams)} must be the last parameter in a ClientRpc.");
+                        }
+                        if (isServerRpc)
+                        {
+                            m_Diagnostics.AddError($"ServerRpcs may not accept {nameof(ClientRpcParams)} as a parameter.");
+                        }
                         continue;
                     }
 
@@ -931,8 +1000,8 @@ namespace Unity.Netcode.Editor.CodeGen
                         instructions.Add(processor.Create(OpCodes.Cgt_Un));
                         instructions.Add(processor.Create(OpCodes.Stloc, isSetLocalIndex));
 
-                        // writer.WriteValueSafe(isSet);
-                        instructions.Add(processor.Create(OpCodes.Ldloca, serializerLocIdx));
+                        // bufferWriter.WriteValueSafe(isSet);
+                        instructions.Add(processor.Create(OpCodes.Ldloca, bufWriterLocIdx));
                         instructions.Add(processor.Create(OpCodes.Ldloca, isSetLocalIndex));
                         instructions.Add(processor.Create(OpCodes.Call, boolMethodRef));
 
@@ -945,22 +1014,28 @@ namespace Unity.Netcode.Editor.CodeGen
                     var foundMethodRef = GetWriteMethodForParameter(paramType, out var methodRef);
                     if (foundMethodRef)
                     {
-                        // writer.WriteNetworkSerializable(param) for INetworkSerializable, OR
-                        // writer.WriteNetworkSerializable(param, -1, 0) for INetworkSerializable arrays, OR
-                        // writer.WriteValueSafe(param) for value types, OR
-                        // writer.WriteValueSafe(param, -1, 0) for arrays of value types, OR
-                        // writer.WriteValueSafe(param, false) for strings
-                        instructions.Add(processor.Create(OpCodes.Ldloca, serializerLocIdx));
+                        // bufferWriter.WriteNetworkSerializable(param) for INetworkSerializable, OR
+                        // bufferWriter.WriteNetworkSerializable(param, -1, 0) for INetworkSerializable arrays, OR
+                        // bufferWriter.WriteValueSafe(param) for value types, OR
+                        // bufferWriter.WriteValueSafe(param, -1, 0) for arrays of value types, OR
+                        // bufferWriter.WriteValueSafe(param, false) for strings
                         var method = methodRef.Resolve();
                         var checkParameter = method.Parameters[0];
                         var isExtensionMethod = false;
-                        if (checkParameter.ParameterType.Resolve() ==
-                            m_FastBufferWriter_TypeRef.MakeByReferenceType().Resolve())
+                        if (methodRef.Resolve().DeclaringType != m_FastBufferWriter_TypeRef.Resolve())
                         {
                             isExtensionMethod = true;
                             checkParameter = method.Parameters[1];
                         }
-                        if (checkParameter.IsIn)
+                        if (!isExtensionMethod || method.Parameters[0].ParameterType.IsByReference)
+                        {
+                            instructions.Add(processor.Create(OpCodes.Ldloca, bufWriterLocIdx));
+                        }
+                        else
+                        {
+                            instructions.Add(processor.Create(OpCodes.Ldloc, bufWriterLocIdx));
+                        }
+                        if (checkParameter.IsIn || checkParameter.IsOut || checkParameter.ParameterType.IsByReference)
                         {
                             instructions.Add(processor.Create(OpCodes.Ldarga, paramIndex + 1));
                         }
@@ -969,16 +1044,14 @@ namespace Unity.Netcode.Editor.CodeGen
                             instructions.Add(processor.Create(OpCodes.Ldarg, paramIndex + 1));
                         }
                         // Special handling for WriteValue() on arrays and strings since they have additional arguments.
-                        if (paramType.IsArray
-                            && ((!isExtensionMethod && methodRef.Parameters.Count == 3)
-                                || (isExtensionMethod && methodRef.Parameters.Count == 4)))
+                        if (paramType.IsArray && ((!isExtensionMethod && methodRef.Parameters.Count == 3) ||
+                            (isExtensionMethod && methodRef.Parameters.Count == 4)))
                         {
                             instructions.Add(processor.Create(OpCodes.Ldc_I4_M1));
                             instructions.Add(processor.Create(OpCodes.Ldc_I4_0));
                         }
-                        else if (paramType == typeSystem.String
-                             && ((!isExtensionMethod && methodRef.Parameters.Count == 2)
-                                 || (isExtensionMethod && methodRef.Parameters.Count == 3)))
+                        else if (paramType == typeSystem.String && ((!isExtensionMethod && methodRef.Parameters.Count == 2) ||
+                            (isExtensionMethod && methodRef.Parameters.Count == 3)))
                         {
                             instructions.Add(processor.Create(OpCodes.Ldc_I4_0));
                         }
@@ -998,20 +1071,20 @@ namespace Unity.Netcode.Editor.CodeGen
 
                 instructions.Add(endInstr);
 
-                // __sendServerRpc(ref serializer, rpcMethodId, serverRpcParams, rpcDelivery) -> ServerRpc
-                // __sendClientRpc(ref serializer, rpcMethodId, clientRpcParams, rpcDelivery) -> ClientRpc
+                // __endSendServerRpc(ref bufferWriter, rpcMethodId, serverRpcParams, rpcDelivery) -> ServerRpc
+                // __endSendClientRpc(ref bufferWriter, rpcMethodId, clientRpcParams, rpcDelivery) -> ClientRpc
                 if (isServerRpc)
                 {
                     // ServerRpc
-                    // __sendServerRpc(ref serializer, rpcMethodId, serverRpcParams, rpcDelivery);
+
+                    // __endSendServerRpc(ref bufferWriter, rpcMethodId, serverRpcParams, rpcDelivery);
                     instructions.Add(processor.Create(OpCodes.Ldarg_0));
 
-                    // serializer
-                    instructions.Add(processor.Create(OpCodes.Ldloc, serializerLocIdx));
+                    // bufferWriter
+                    instructions.Add(processor.Create(OpCodes.Ldloca, bufWriterLocIdx));
 
                     // rpcMethodId
                     instructions.Add(processor.Create(OpCodes.Ldc_I4, unchecked((int)rpcMethodId)));
-
                     if (hasRpcParams)
                     {
                         // rpcParams
@@ -1022,25 +1095,24 @@ namespace Unity.Netcode.Editor.CodeGen
                         // default
                         instructions.Add(processor.Create(OpCodes.Ldloc, rpcParamsIdx));
                     }
-
                     // rpcDelivery
                     instructions.Add(processor.Create(OpCodes.Ldc_I4, (int)rpcDelivery));
 
-                    // EndSendServerRpc
-                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_SendServerRpc_MethodRef));
+                    // __endSendServerRpc
+                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_endSendServerRpc_MethodRef));
                 }
                 else
                 {
                     // ClientRpc
-                    // __sendClientRpc(ref serializer, rpcMethodId, clientRpcParams, rpcDelivery);
+
+                    // __endSendClientRpc(ref bufferWriter, rpcMethodId, clientRpcParams, rpcDelivery);
                     instructions.Add(processor.Create(OpCodes.Ldarg_0));
 
-                    // serializer
-                    instructions.Add(processor.Create(OpCodes.Ldloc, serializerLocIdx));
+                    // bufferWriter
+                    instructions.Add(processor.Create(OpCodes.Ldloca, bufWriterLocIdx));
 
                     // rpcMethodId
                     instructions.Add(processor.Create(OpCodes.Ldc_I4, unchecked((int)rpcMethodId)));
-
                     if (hasRpcParams)
                     {
                         // rpcParams
@@ -1051,36 +1123,11 @@ namespace Unity.Netcode.Editor.CodeGen
                         // default
                         instructions.Add(processor.Create(OpCodes.Ldloc, rpcParamsIdx));
                     }
-
                     // rpcDelivery
                     instructions.Add(processor.Create(OpCodes.Ldc_I4, (int)rpcDelivery));
 
-                    // EndSendClientRpc
-                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_SendClientRpc_MethodRef));
-                }
-
-                {
-                    // TODO: Figure out why try/catch here cause the try block not to execute at all.
-                    // End try block
-                    //instructions.Add(processor.Create(OpCodes.Leave, lastInstr));
-
-                    // writer.Dispose();
-                    var handlerFirst = processor.Create(OpCodes.Ldloca, serializerLocIdx);
-                    instructions.Add(handlerFirst);
-                    instructions.Add(processor.Create(OpCodes.Call, m_FastBufferWriter_Dispose));
-
-                    // End finally block
-                    //instructions.Add(processor.Create(OpCodes.Endfinally));
-
-                    // try { ... serialization code ... } finally { writer.Dispose(); }
-                    /*var handler = new ExceptionHandler(ExceptionHandlerType.Finally)
-                    {
-                        TryStart = firstInstruction,
-                        TryEnd = handlerFirst,
-                        HandlerStart = handlerFirst,
-                        HandlerEnd = lastInstr
-                    };
-                    processor.Body.ExceptionHandlers.Add(handler);*/
+                    // __endSendClientRpc
+                    instructions.Add(processor.Create(OpCodes.Call, m_NetworkBehaviour_endSendClientRpc_MethodRef));
                 }
 
                 instructions.Add(lastInstr);
@@ -1115,20 +1162,21 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.ForEach(instruction => processor.Body.Instructions.Insert(0, instruction));
         }
 
-        private MethodDefinition GenerateStaticHandler(MethodDefinition methodDefinition, CustomAttribute rpcAttribute)
+        private MethodDefinition GenerateStaticHandler(MethodDefinition methodDefinition, CustomAttribute rpcAttribute, uint rpcMethodId)
         {
             var typeSystem = methodDefinition.Module.TypeSystem;
-            var nhandler = new MethodDefinition(
-                $"{methodDefinition.Name}__nhandler",
+            var rpcHandler = new MethodDefinition(
+                $"__rpc_handler_{rpcMethodId}",
                 MethodAttributes.Private | MethodAttributes.Static | MethodAttributes.HideBySig,
                 methodDefinition.Module.TypeSystem.Void);
-            nhandler.Parameters.Add(new ParameterDefinition("target", ParameterAttributes.None, m_NetworkBehaviour_TypeRef));
-            nhandler.Parameters.Add(new ParameterDefinition("reader", ParameterAttributes.None, m_FastBufferReader_TypeRef));
-            nhandler.Parameters.Add(new ParameterDefinition("rpcParams", ParameterAttributes.None, m_RpcParams_TypeRef));
+            rpcHandler.Parameters.Add(new ParameterDefinition("target", ParameterAttributes.None, m_NetworkBehaviour_TypeRef));
+            rpcHandler.Parameters.Add(new ParameterDefinition("reader", ParameterAttributes.None, m_FastBufferReader_TypeRef));
+            rpcHandler.Parameters.Add(new ParameterDefinition("rpcParams", ParameterAttributes.None, m_RpcParams_TypeRef));
+
+            var processor = rpcHandler.Body.GetILProcessor();
 
-            var processor = nhandler.Body.GetILProcessor();
             var isServerRpc = rpcAttribute.AttributeType.FullName == CodeGenHelpers.ServerRpcAttribute_FullName;
-            var requireOwnership = true; // default value MUST be = `ServerRpcAttribute.RequireOwnership`
+            var requireOwnership = true; // default value MUST be == `ServerRpcAttribute.RequireOwnership`
             foreach (var attrField in rpcAttribute.Fields)
             {
                 switch (attrField.Name)
@@ -1139,10 +1187,10 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
-            nhandler.Body.InitLocals = true;
+            rpcHandler.Body.InitLocals = true;
             // NetworkManager networkManager;
-            nhandler.Body.Variables.Add(new VariableDefinition(m_NetworkManager_TypeRef));
-            int netManLocIdx = nhandler.Body.Variables.Count - 1;
+            rpcHandler.Body.Variables.Add(new VariableDefinition(m_NetworkManager_TypeRef));
+            int netManLocIdx = rpcHandler.Body.Variables.Count - 1;
 
             {
                 var returnInstr = processor.Create(OpCodes.Ret);
@@ -1211,8 +1259,8 @@ namespace Unity.Netcode.Editor.CodeGen
                 var paramType = paramDef.ParameterType;
 
                 // local variable
-                nhandler.Body.Variables.Add(new VariableDefinition(paramType));
-                int localIndex = nhandler.Body.Variables.Count - 1;
+                rpcHandler.Body.Variables.Add(new VariableDefinition(paramType));
+                int localIndex = rpcHandler.Body.Variables.Count - 1;
                 paramLocalMap[paramIndex] = localIndex;
 
                 // ServerRpcParams, ClientRpcParams
@@ -1246,8 +1294,8 @@ namespace Unity.Netcode.Editor.CodeGen
                     }
 
                     // reader.ReadValueSafe(out bool isSet)
-                    nhandler.Body.Variables.Add(new VariableDefinition(typeSystem.Boolean));
-                    int isSetLocalIndex = nhandler.Body.Variables.Count - 1;
+                    rpcHandler.Body.Variables.Add(new VariableDefinition(typeSystem.Boolean));
+                    int isSetLocalIndex = rpcHandler.Body.Variables.Count - 1;
                     processor.Emit(OpCodes.Ldarga, 1);
                     processor.Emit(OpCodes.Ldloca, isSetLocalIndex);
                     processor.Emit(OpCodes.Call, boolMethodRef);
@@ -1266,7 +1314,18 @@ namespace Unity.Netcode.Editor.CodeGen
                 if (foundMethodRef)
                 {
                     // reader.ReadValueSafe(out localVar);
-                    processor.Emit(OpCodes.Ldarga, 1);
+
+                    var checkParameter = methodRef.Resolve().Parameters[0];
+
+                    var isExtensionMethod = methodRef.Resolve().DeclaringType != m_FastBufferReader_TypeRef.Resolve();
+                    if (!isExtensionMethod || checkParameter.ParameterType.IsByReference)
+                    {
+                        processor.Emit(OpCodes.Ldarga, 1);
+                    }
+                    else
+                    {
+                        processor.Emit(OpCodes.Ldarg, 1);
+                    }
                     processor.Emit(OpCodes.Ldloca, localIndex);
                     if (paramType == typeSystem.String)
                     {
@@ -1304,7 +1363,7 @@ namespace Unity.Netcode.Editor.CodeGen
             processor.Emit(OpCodes.Stfld, m_NetworkBehaviour_rpc_exec_stage_FieldRef);
 
             processor.Emit(OpCodes.Ret);
-            return nhandler;
+            return rpcHandler;
         }
     }
 }

Editor/CodeGen/RuntimeAccessModifiersILPP.cs

@@ -52,6 +52,9 @@ namespace Unity.Netcode.Editor.CodeGen
                         case nameof(NetworkBehaviour):
                             ProcessNetworkBehaviour(typeDefinition);
                             break;
+                        case nameof(NetworkVariableHelper):
+                            ProcessNetworkVariableHelper(typeDefinition);
+                            break;
                         case nameof(__RpcParams):
                             typeDefinition.IsPublic = true;
                             break;
@@ -100,6 +103,17 @@ namespace Unity.Netcode.Editor.CodeGen
             }
         }
 
+        private void ProcessNetworkVariableHelper(TypeDefinition typeDefinition)
+        {
+            foreach (var methodDefinition in typeDefinition.Methods)
+            {
+                if (methodDefinition.Name == nameof(NetworkVariableHelper.InitializeDelegates))
+                {
+                    methodDefinition.IsPublic = true;
+                }
+            }
+        }
+
         private void ProcessNetworkBehaviour(TypeDefinition typeDefinition)
         {
             foreach (var nestedType in typeDefinition.NestedTypes)
@@ -120,8 +134,10 @@ namespace Unity.Netcode.Editor.CodeGen
 
             foreach (var methodDefinition in typeDefinition.Methods)
             {
-                if (methodDefinition.Name == nameof(NetworkBehaviour.__sendServerRpc)
-                    || methodDefinition.Name == nameof(NetworkBehaviour.__sendClientRpc))
+                if (methodDefinition.Name == nameof(NetworkBehaviour.__beginSendServerRpc) ||
+                    methodDefinition.Name == nameof(NetworkBehaviour.__endSendServerRpc) ||
+                    methodDefinition.Name == nameof(NetworkBehaviour.__beginSendClientRpc) ||
+                    methodDefinition.Name == nameof(NetworkBehaviour.__endSendClientRpc))
                 {
                     methodDefinition.IsFamily = true;
                 }

Editor/DontShowInTransportDropdownAttribute.cs

@@ -1,8 +0,0 @@
-using System;
-
-namespace Unity.Netcode.Editor
-{
-    public class DontShowInTransportDropdownAttribute : Attribute
-    {
-    }
-}

Editor/DontShowInTransportDropdownAttribute.cs.meta

@@ -1,3 +0,0 @@
-fileFormatVersion: 2
-guid: 5f097067d4254dc7ad018d7ad90df7c3
-timeCreated: 1620386886

Editor/NetworkAnimatorEditor.cs

@@ -1,103 +0,0 @@
-using System;
-using Unity.Netcode.Components;
-using UnityEditor;
-using UnityEditor.Animations;
-using UnityEngine;
-
-namespace Unity.Netcode.Editor
-{
-    public static class TextUtility
-    {
-        public static GUIContent TextContent(string name, string tooltip)
-        {
-            var newContent = new GUIContent(name);
-            newContent.tooltip = tooltip;
-            return newContent;
-        }
-
-        public static GUIContent TextContent(string name)
-        {
-            return new GUIContent(name);
-        }
-    }
-
-    [CustomEditor(typeof(NetworkAnimator), true)]
-    [CanEditMultipleObjects]
-    public class NetworkAnimatorEditor : UnityEditor.Editor
-    {
-        private NetworkAnimator m_AnimSync;
-        [NonSerialized] private bool m_Initialized;
-        private SerializedProperty m_AnimatorProperty;
-        private GUIContent m_AnimatorLabel;
-
-        private void Init()
-        {
-            if (m_Initialized)
-            {
-                return;
-            }
-
-            m_Initialized = true;
-            m_AnimSync = target as NetworkAnimator;
-
-            m_AnimatorProperty = serializedObject.FindProperty("m_Animator");
-            m_AnimatorLabel = TextUtility.TextContent("Animator", "The Animator component to synchronize.");
-        }
-
-        public override void OnInspectorGUI()
-        {
-            Init();
-            serializedObject.Update();
-            DrawControls();
-            serializedObject.ApplyModifiedProperties();
-        }
-
-        private void DrawControls()
-        {
-            EditorGUI.BeginChangeCheck();
-            EditorGUILayout.PropertyField(m_AnimatorProperty, m_AnimatorLabel);
-            if (EditorGUI.EndChangeCheck())
-            {
-                m_AnimSync.ResetParameterOptions();
-            }
-
-            if (m_AnimSync.Animator == null)
-            {
-                return;
-            }
-
-            var controller = m_AnimSync.Animator.runtimeAnimatorController as AnimatorController;
-            if (controller != null)
-            {
-                var showWarning = false;
-                EditorGUI.indentLevel += 1;
-                int i = 0;
-
-                foreach (var p in controller.parameters)
-                {
-                    if (i >= NetworkAnimator.K_MaxAnimationParams)
-                    {
-                        showWarning = true;
-                        break;
-                    }
-
-                    bool oldSend = m_AnimSync.GetParameterAutoSend(i);
-                    bool send = EditorGUILayout.Toggle(p.name, oldSend);
-                    if (send != oldSend)
-                    {
-                        m_AnimSync.SetParameterAutoSend(i, send);
-                        EditorUtility.SetDirty(target);
-                    }
-                    i += 1;
-                }
-
-                if (showWarning)
-                {
-                    EditorGUILayout.HelpBox($"NetworkAnimator can only select between the first {NetworkAnimator.K_MaxAnimationParams} parameters in a mecanim controller", MessageType.Warning);
-                }
-
-                EditorGUI.indentLevel -= 1;
-            }
-        }
-    }
-}

Editor/NetworkBehaviourEditor.cs

@@ -211,5 +211,91 @@ namespace Unity.Netcode.Editor
             serializedObject.ApplyModifiedProperties();
             EditorGUI.EndChangeCheck();
         }
+
+        /// <summary>
+        /// Invoked once when a NetworkBehaviour component is
+        /// displayed in the inspector view.
+        /// </summary>
+        private void OnEnable()
+        {
+            // When we first add a NetworkBehaviour this editor will be enabled
+            // so we go ahead and check for an already existing NetworkObject here
+            CheckForNetworkObject((target as NetworkBehaviour).gameObject);
+        }
+
+        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
+
+        public static Transform GetRootParentTransform(Transform transform)
+        {
+            if (transform.parent == null || transform.parent == transform)
+            {
+                return transform;
+            }
+            return GetRootParentTransform(transform.parent);
+        }
+
+        /// <summary>
+        /// Used to determine if a GameObject has one or more NetworkBehaviours but
+        /// does not already have a NetworkObject component.  If not it will notify
+        /// the user that NetworkBehaviours require a NetworkObject.
+        /// </summary>
+        public static void CheckForNetworkObject(GameObject gameObject, bool networkObjectRemoved = false)
+        {
+            // If there are no NetworkBehaviours or no gameObject, then exit early
+            if (gameObject == null || (gameObject.GetComponent<NetworkBehaviour>() == null && gameObject.GetComponentInChildren<NetworkBehaviour>() == null))
+            {
+                return;
+            }
+
+            // Now get the root parent transform to the current GameObject (or itself)
+            var rootTransform = GetRootParentTransform(gameObject.transform);
+
+            // Otherwise, check to see if there is any NetworkObject from the root GameObject down to all children.
+            // If not, notify the user that NetworkBehaviours require that the relative GameObject has a NetworkObject component.
+            var networkObject = rootTransform.GetComponent<NetworkObject>();
+            if (networkObject == null)
+            {
+                networkObject = rootTransform.GetComponentInChildren<NetworkObject>();
+
+                if (networkObject == null)
+                {
+                    // If we are removing a NetworkObject but there is still one or more NetworkBehaviour components
+                    // 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))
+                    {
+                        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.");
+                    }
+
+                    // 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))
+                    {
+                        gameObject.AddComponent<NetworkObject>();
+                        var activeScene = UnityEngine.SceneManagement.SceneManager.GetActiveScene();
+                        UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(activeScene);
+                        UnityEditor.SceneManagement.EditorSceneManager.SaveScene(activeScene);
+                    }
+                }
+            }
+        }
+
+        /// <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

@@ -15,7 +15,6 @@ namespace Unity.Netcode.Editor
         private static GUIStyle s_HelpBoxStyle;
 
         // Properties
-        private SerializedProperty m_DontDestroyOnLoadProperty;
         private SerializedProperty m_RunInBackgroundProperty;
         private SerializedProperty m_LogLevelProperty;
 
@@ -58,7 +57,7 @@ namespace Unity.Netcode.Editor
 
                 foreach (var type in types)
                 {
-                    if (type.IsSubclassOf(typeof(NetworkTransport)) && type.GetCustomAttributes(typeof(DontShowInTransportDropdownAttribute), true).Length == 0)
+                    if (type.IsSubclassOf(typeof(NetworkTransport)) && !type.IsSubclassOf(typeof(TestingNetworkTransport)) && type != typeof(TestingNetworkTransport))
                     {
                         m_TransportTypes.Add(type);
                     }
@@ -85,7 +84,6 @@ namespace Unity.Netcode.Editor
             m_NetworkManager = (NetworkManager)target;
 
             // Base properties
-            m_DontDestroyOnLoadProperty = serializedObject.FindProperty(nameof(NetworkManager.DontDestroy));
             m_RunInBackgroundProperty = serializedObject.FindProperty(nameof(NetworkManager.RunInBackground));
             m_LogLevelProperty = serializedObject.FindProperty(nameof(NetworkManager.LogLevel));
             m_NetworkConfigProperty = serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig));
@@ -112,7 +110,6 @@ namespace Unity.Netcode.Editor
         private void CheckNullProperties()
         {
             // Base properties
-            m_DontDestroyOnLoadProperty = serializedObject.FindProperty(nameof(NetworkManager.DontDestroy));
             m_RunInBackgroundProperty = serializedObject.FindProperty(nameof(NetworkManager.RunInBackground));
             m_LogLevelProperty = serializedObject.FindProperty(nameof(NetworkManager.LogLevel));
             m_NetworkConfigProperty = serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig));
@@ -138,9 +135,13 @@ namespace Unity.Netcode.Editor
             m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig)).FindPropertyRelative(nameof(NetworkConfig.NetworkPrefabs)), true, true, true, true);
             m_NetworkPrefabsList.elementHeightCallback = index =>
             {
-                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                var networkOverrideInt = networkOverrideProp.enumValueIndex;
+                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);
             };
@@ -223,7 +224,6 @@ namespace Unity.Netcode.Editor
             if (!m_NetworkManager.IsServer && !m_NetworkManager.IsClient)
             {
                 serializedObject.Update();
-                EditorGUILayout.PropertyField(m_DontDestroyOnLoadProperty);
                 EditorGUILayout.PropertyField(m_RunInBackgroundProperty);
                 EditorGUILayout.PropertyField(m_LogLevelProperty);
                 EditorGUILayout.Space();
@@ -363,7 +363,7 @@ namespace Unity.Netcode.Editor
             const string getToolsText = "Access additional tools for multiplayer development by installing the Multiplayer Tools package in the Package Manager.";
             const string openDocsButtonText = "Open Docs";
             const string dismissButtonText = "Dismiss";
-            const string targetUrl = "https://docs-multiplayer.unity3d.com/docs/tutorials/goldenpath_series/goldenpath_foundation_module";
+            const string targetUrl = "https://docs-multiplayer.unity3d.com/docs/tools/install-tools";
             const string infoIconName = "console.infoicon";
 
             if (PlayerPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 0) != 0)

Editor/NetworkManagerHelper.cs

@@ -0,0 +1,195 @@
+using System.Collections.Generic;
+using System.Linq;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+using UnityEditor;
+
+namespace Unity.Netcode.Editor
+{
+#if UNITY_EDITOR
+    /// <summary>
+    /// Specialized editor specific NetworkManager code
+    /// </summary>
+    public class NetworkManagerHelper : NetworkManager.INetworkManagerHelper
+    {
+        internal static NetworkManagerHelper Singleton;
+
+        // This is primarily to handle IntegrationTest scenarios where more than 1 NetworkManager could exist
+        private static Dictionary<NetworkManager, Transform> s_LastKnownNetworkManagerParents = new Dictionary<NetworkManager, Transform>();
+
+        /// <summary>
+        /// Initializes the singleton instance and registers for:
+        /// Hierarchy changed notification: to notify the user when they nest a NetworkManager
+        /// Play mode state change notification: to capture when entering or exiting play mode (currently only exiting)
+        /// </summary>
+        [InitializeOnLoadMethod]
+        private static void InitializeOnload()
+        {
+            Singleton = new NetworkManagerHelper();
+            NetworkManager.NetworkManagerHelper = Singleton;
+            EditorApplication.playModeStateChanged -= EditorApplication_playModeStateChanged;
+            EditorApplication.hierarchyChanged -= EditorApplication_hierarchyChanged;
+
+            EditorApplication.playModeStateChanged += EditorApplication_playModeStateChanged;
+            EditorApplication.hierarchyChanged += EditorApplication_hierarchyChanged;
+        }
+
+        private static void EditorApplication_playModeStateChanged(PlayModeStateChange playModeStateChange)
+        {
+            switch (playModeStateChange)
+            {
+                case PlayModeStateChange.ExitingEditMode:
+                    {
+                        s_LastKnownNetworkManagerParents.Clear();
+                        ScenesInBuildActiveSceneCheck();
+                        break;
+                    }
+            }
+        }
+
+        /// <summary>
+        /// Detects if a user is trying to enter into play mode when both conditions are true:
+        /// - the currently active and open scene is not added to the scenes in build list
+        /// - an instance of a NetworkManager with scene management enabled can be found
+        /// If both conditions are met then the user is presented with a dialog box that
+        /// provides the user with the option to add the scene to the scenes in build list
+        /// before entering into play mode or the user can continue under those conditions.
+        ///
+        /// ** When scene management is enabled the user should treat all scenes that need to
+        /// be synchronized using network scene management as if they were preparing for a build.
+        /// Any scene that needs to be loaded at run time has to be included in the scenes in
+        /// build list. **
+        /// </summary>
+        private static void ScenesInBuildActiveSceneCheck()
+        {
+            var scenesList = EditorBuildSettings.scenes.ToList();
+            var activeScene = SceneManager.GetActiveScene();
+            var isSceneInBuildSettings = scenesList.Where((c) => c.path == activeScene.path).Count() == 1;
+            var networkManager = Object.FindObjectOfType<NetworkManager>();
+            if (!isSceneInBuildSettings && networkManager != null)
+            {
+                if (networkManager.NetworkConfig != null && networkManager.NetworkConfig.EnableSceneManagement)
+                {
+                    if (EditorUtility.DisplayDialog("Add Scene to Scenes in Build", $"The current scene was not found in the scenes" +
+                        $" in build and a {nameof(NetworkManager)} instance was found with scene management enabled! Clients will not be able " +
+                        $"to synchronize to this scene unless it is added to the scenes in build list.\n\nWould you like to add it now?",
+                        "Yes", "No - Continue"))
+                    {
+                        scenesList.Add(new EditorBuildSettingsScene(activeScene.path, true));
+                        EditorBuildSettings.scenes = scenesList.ToArray();
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Invoked only when the hierarchy changes
+        /// </summary>
+        private static void EditorApplication_hierarchyChanged()
+        {
+            var allNetworkManagers = Resources.FindObjectsOfTypeAll<NetworkManager>();
+            foreach (var networkManager in allNetworkManagers)
+            {
+                if (!networkManager.NetworkManagerCheckForParent())
+                {
+                    Singleton.CheckAndNotifyUserNetworkObjectRemoved(networkManager);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Handles notifying users that they cannot add a NetworkObject component
+        /// to a GameObject that also has a NetworkManager component. The NetworkObject
+        /// will always be removed.
+        /// GameObject + NetworkObject then NetworkManager = NetworkObject removed
+        /// GameObject + NetworkManager then NetworkObject = NetworkObject removed
+        /// Note: Since this is always invoked after <see cref="NetworkManagerCheckForParent"/>
+        /// we do not need to check for parent when searching for a NetworkObject component
+        /// </summary>
+        public void CheckAndNotifyUserNetworkObjectRemoved(NetworkManager networkManager, bool editorTest = false)
+        {
+            // Check for any NetworkObject at the same gameObject relative layer
+            var networkObject = networkManager.gameObject.GetComponent<NetworkObject>();
+
+            if (networkObject == null)
+            {
+                // if none is found, check to see if any children have a NetworkObject
+                networkObject = networkManager.gameObject.GetComponentInChildren<NetworkObject>();
+                if (networkObject == null)
+                {
+                    return;
+                }
+            }
+
+            if (!EditorApplication.isUpdating)
+            {
+                Object.DestroyImmediate(networkObject);
+
+                if (!EditorApplication.isPlaying && !editorTest)
+                {
+                    EditorUtility.DisplayDialog($"Removing {nameof(NetworkObject)}", NetworkManagerAndNetworkObjectNotAllowedMessage(), "OK");
+                }
+                else
+                {
+                    Debug.LogError(NetworkManagerAndNetworkObjectNotAllowedMessage());
+                }
+            }
+        }
+
+        public string NetworkManagerAndNetworkObjectNotAllowedMessage()
+        {
+            return $"A {nameof(GameObject)} cannot have both a {nameof(NetworkManager)} and {nameof(NetworkObject)} assigned to it or any children under it.";
+        }
+
+        /// <summary>
+        /// Handles notifying the user, via display dialog window, that they have nested a NetworkManager.
+        /// When in edit mode it provides the option to automatically fix the issue
+        /// When in play mode it just notifies the user when entering play mode as well as when the user
+        /// tries to start a network session while a NetworkManager is still nested.
+        /// </summary>
+        public bool NotifyUserOfNestedNetworkManager(NetworkManager networkManager, bool ignoreNetworkManagerCache = false, bool editorTest = false)
+        {
+            var gameObject = networkManager.gameObject;
+            var transform = networkManager.transform;
+            var isParented = transform.root != transform;
+
+            var message = NetworkManager.GenerateNestedNetworkManagerMessage(transform);
+            if (s_LastKnownNetworkManagerParents.ContainsKey(networkManager) && !ignoreNetworkManagerCache)
+            {
+                // If we have already notified the user, then don't notify them again
+                if (s_LastKnownNetworkManagerParents[networkManager] == transform.root)
+                {
+                    return isParented;
+                }
+                else // If we are no longer a child, then we can remove ourself from this list
+                if (transform.root == gameObject.transform)
+                {
+                    s_LastKnownNetworkManagerParents.Remove(networkManager);
+                }
+            }
+            if (!EditorApplication.isUpdating && isParented)
+            {
+                if (!EditorApplication.isPlaying && !editorTest)
+                {
+                    message += $"Click 'Auto-Fix' to automatically remove it from {transform.root.gameObject.name} or 'Manual-Fix' to fix it yourself in the hierarchy view.";
+                    if (EditorUtility.DisplayDialog("Invalid Nested NetworkManager", message, "Auto-Fix", "Manual-Fix"))
+                    {
+                        transform.parent = null;
+                        isParented = false;
+                    }
+                }
+                else
+                {
+                    Debug.LogError(message);
+                }
+
+                if (!s_LastKnownNetworkManagerParents.ContainsKey(networkManager) && isParented)
+                {
+                    s_LastKnownNetworkManagerParents.Add(networkManager, networkManager.transform.root);
+                }
+            }
+            return isParented;
+        }
+    }
+#endif
+}

Editor/NetworkManagerHelper.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: 69c3c1c5a885d4aed99ee2e1fa40f763
+guid: b26b53dc28ae1b5488bbbecc3e499bbc
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/NetworkObjectEditor.cs

@@ -100,5 +100,32 @@ namespace Unity.Netcode.Editor
                 GUI.enabled = guiEnabled;
             }
         }
+
+        // Saved for use in OnDestroy
+        private GameObject m_GameObject;
+
+        /// <summary>
+        /// Invoked once when a NetworkObject component is
+        /// displayed in the inspector view.
+        /// </summary>
+        private void OnEnable()
+        {
+            // We set the GameObject upon being enabled because when the
+            // NetworkObject component is removed (i.e. when OnDestroy is invoked)
+            // it is no longer valid/available.
+            m_GameObject = (target as NetworkObject).gameObject;
+        }
+
+        /// <summary>
+        /// Invoked once when a NetworkObject component is
+        /// no longer displayed in the inspector view.
+        /// </summary>
+        private void OnDestroy()
+        {
+            // Since this is also invoked when a NetworkObject component is removed
+            // from a GameObject, we go ahead and check for a NetworkObject when
+            // this custom editor is destroyed.
+            NetworkBehaviourEditor.CheckForNetworkObject(m_GameObject, true);
+        }
     }
 }

Editor/NetworkTransformEditor.cs

@@ -4,7 +4,7 @@ using Unity.Netcode.Components;
 
 namespace Unity.Netcode.Editor
 {
-    [CustomEditor(typeof(NetworkTransform))]
+    [CustomEditor(typeof(NetworkTransform), true)]
     public class NetworkTransformEditor : UnityEditor.Editor
     {
         private SerializedProperty m_SyncPositionXProperty;
@@ -112,6 +112,7 @@ namespace Unity.Netcode.Editor
             EditorGUILayout.PropertyField(m_InLocalSpaceProperty);
             EditorGUILayout.PropertyField(m_InterpolateProperty);
 
+#if COM_UNITY_MODULES_PHYSICS
             // if rigidbody is present but network rigidbody is not present
             var go = ((NetworkTransform)target).gameObject;
             if (go.TryGetComponent<Rigidbody>(out _) && go.TryGetComponent<NetworkRigidbody>(out _) == false)
@@ -119,12 +120,15 @@ namespace Unity.Netcode.Editor
                 EditorGUILayout.HelpBox("This GameObject contains a Rigidbody but no NetworkRigidbody.\n" +
                     "Add a NetworkRigidbody component to improve Rigidbody synchronization.", MessageType.Warning);
             }
+#endif // COM_UNITY_MODULES_PHYSICS
 
+#if COM_UNITY_MODULES_PHYSICS2D
             if (go.TryGetComponent<Rigidbody2D>(out _) && go.TryGetComponent<NetworkRigidbody2D>(out _) == false)
             {
                 EditorGUILayout.HelpBox("This GameObject contains a Rigidbody2D but no NetworkRigidbody2D.\n" +
                     "Add a NetworkRigidbody2D component to improve Rigidbody2D synchronization.", MessageType.Warning);
             }
+#endif // COM_UNITY_MODULES_PHYSICS2D
 
             serializedObject.ApplyModifiedProperties();
         }

Editor/PackageChecker.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: f2ef964afcae91248b2298b479ed1b53
+guid: a325130169714440ba1b4878082e8956
 folderAsset: yes
 DefaultImporter:
   externalObjects: {}

Editor/PackageChecker/UTPAdapterChecker.cs

@@ -0,0 +1,53 @@
+#if COM_UNITY_NETCODE_ADAPTER_UTP
+using System.Linq;
+using UnityEngine;
+using UnityEditor;
+using UnityEditor.PackageManager;
+using UnityEditor.PackageManager.Requests;
+
+namespace Unity.Netcode.Editor.PackageChecker
+{
+    [InitializeOnLoad]
+    internal class UTPAdapterChecker
+    {
+        private const string k_UTPAdapterPackageName = "com.unity.netcode.adapter.utp";
+
+        private static ListRequest s_ListRequest = null;
+
+        static UTPAdapterChecker()
+        {
+            if (s_ListRequest == null)
+            {
+                s_ListRequest = Client.List();
+                EditorApplication.update += EditorUpdate;
+            }
+        }
+
+        private static void EditorUpdate()
+        {
+            if (!s_ListRequest.IsCompleted)
+            {
+                return;
+            }
+
+            EditorApplication.update -= EditorUpdate;
+
+            if (s_ListRequest.Status == StatusCode.Success)
+            {
+                if (s_ListRequest.Result.Any(p => p.name == k_UTPAdapterPackageName))
+                {
+                    Debug.Log($"({nameof(UTPAdapterChecker)}) Found UTP Adapter package, it is no longer needed, `UnityTransport` is now directly integrated into the SDK therefore removing it from the project.");
+                    Client.Remove(k_UTPAdapterPackageName);
+                }
+            }
+            else
+            {
+                var error = s_ListRequest.Error;
+                Debug.LogError($"({nameof(UTPAdapterChecker)}) Cannot check the list of packages -> error #{error.errorCode}: {error.message}");
+            }
+
+            s_ListRequest = null;
+        }
+    }
+}
+#endif // COM_UNITY_NETCODE_ADAPTER_UTP

Editor/PackageChecker/UTPAdapterChecker.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: a8514b4eca0c7044d9b92faf9407ec93
+guid: df5ed97df956b4aad91a221ba59fa304
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/PackageChecker/com.unity.netcode.editor.packagechecker.asmdef

@@ -0,0 +1,14 @@
+{
+    "name": "Unity.Netcode.Editor.PackageChecker",
+    "rootNamespace": "Unity.Netcode.Editor.PackageChecker",
+    "includePlatforms": [
+        "Editor"
+    ],
+    "versionDefines": [
+        {
+            "name": "com.unity.netcode.adapter.utp",
+            "expression": "",
+            "define": "COM_UNITY_NETCODE_ADAPTER_UTP"
+        }
+    ]
+}

Editor/PackageChecker/com.unity.netcode.editor.packagechecker.asmdef.meta

@@ -0,0 +1,7 @@
+fileFormatVersion: 2
+guid: de64d7f9ca85d4bf59c8c24738bc1057
+AssemblyDefinitionImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/com.unity.netcode.editor.asmdef

@@ -8,18 +8,11 @@
     "includePlatforms": [
         "Editor"
     ],
-    "excludePlatforms": [],
-    "allowUnsafeCode": false,
-    "overrideReferences": false,
-    "precompiledReferences": [],
-    "autoReferenced": true,
-    "defineConstraints": [],
     "versionDefines": [
         {
             "name": "com.unity.multiplayer.tools",
             "expression": "",
             "define": "MULTIPLAYER_TOOLS"
         }
-    ],
-    "noEngineReferences": false
+    ]
 }

README.md

@@ -1,7 +1,9 @@
+# Netcode for GameObjects
+
 [![Forums](https://img.shields.io/badge/unity--forums-multiplayer-blue)](https://forum.unity.com/forums/multiplayer.26/) [![Discord](https://img.shields.io/discord/449263083769036810.svg?label=discord&logo=discord&color=informational)](https://discord.gg/FM8SE9E)
 [![Website](https://img.shields.io/badge/docs-website-informational.svg)](https://docs-multiplayer.unity3d.com/) [![Api](https://img.shields.io/badge/docs-api-informational.svg)](https://docs-multiplayer.unity3d.com/docs/mlapi-api/introduction)
 
-Netcode for GameObjects provides networking capabilities to GameObject & MonoBehaviour Unity workflows. The framework is interoperable with many low-level transports, including the official [Unity Transport Package](https://docs.unity3d.com/Packages/com.unity.transport@1.0/manual/index.html).
+Netcode for GameObjects provides networking capabilities to GameObject & MonoBehaviour Unity workflows. The framework is interoperable with many low-level transports, including the official [Unity Transport Package](https://docs-multiplayer.unity3d.com/transport/1.0.0/introduction).
 
 ### Getting Started
 Visit the [Multiplayer Docs Site](https://docs-multiplayer.unity3d.com/) for package & API documentation, as well as information about several samples which leverage the Netcode for GameObjects package.

Runtime/AssemblyInfo.cs

@@ -5,8 +5,9 @@ using System.Runtime.CompilerServices;
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
 [assembly: InternalsVisibleTo("TestProject.EditorTests")]
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
-[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
 #endif
+[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
-
+[assembly: InternalsVisibleTo("Unity.Netcode.TestHelpers.Runtime")]
+[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]

Runtime/Collections/FixedQueue.cs

@@ -1,77 +0,0 @@
-using System;
-
-namespace Unity.Netcode
-{
-    /// <summary>
-    /// Queue with a fixed size
-    /// </summary>
-    /// <typeparam name="T">The type of the queue</typeparam>
-    public sealed class FixedQueue<T>
-    {
-        private readonly T[] m_Queue;
-        private int m_QueueCount = 0;
-        private int m_QueueStart;
-
-        /// <summary>
-        /// The amount of enqueued objects
-        /// </summary>
-        public int Count => m_QueueCount;
-
-        /// <summary>
-        /// Gets the element at a given virtual index
-        /// </summary>
-        /// <param name="index">The virtual index to get the item from</param>
-        /// <returns>The element at the virtual index</returns>
-        public T this[int index] => m_Queue[(m_QueueStart + index) % m_Queue.Length];
-
-        /// <summary>
-        /// Creates a new FixedQueue with a given size
-        /// </summary>
-        /// <param name="maxSize">The size of the queue</param>
-        public FixedQueue(int maxSize)
-        {
-            m_Queue = new T[maxSize];
-            m_QueueStart = 0;
-        }
-
-        /// <summary>
-        /// Enqueues an object
-        /// </summary>
-        /// <param name="t"></param>
-        /// <returns></returns>
-        public bool Enqueue(T t)
-        {
-            m_Queue[(m_QueueStart + m_QueueCount) % m_Queue.Length] = t;
-            if (++m_QueueCount > m_Queue.Length)
-            {
-                --m_QueueCount;
-                return true;
-            }
-
-            return false;
-        }
-
-        /// <summary>
-        /// Dequeues an object
-        /// </summary>
-        /// <returns></returns>
-        public T Dequeue()
-        {
-            if (--m_QueueCount == -1)
-            {
-                throw new IndexOutOfRangeException("Cannot dequeue empty queue!");
-            }
-
-            T res = m_Queue[m_QueueStart];
-            m_QueueStart = (m_QueueStart + 1) % m_Queue.Length;
-            return res;
-        }
-
-        /// <summary>
-        /// Gets the element at a given virtual index
-        /// </summary>
-        /// <param name="index">The virtual index to get the item from</param>
-        /// <returns>The element at the virtual index</returns>
-        public T ElementAt(int index) => m_Queue[(m_QueueStart + index) % m_Queue.Length];
-    }
-}

Runtime/Configuration/NetworkConfig.cs

@@ -138,19 +138,6 @@ namespace Unity.Netcode
         /// </summary>
         public bool EnableNetworkLogs = true;
 
-        /// <summary>
-        /// Whether or not to enable Snapshot System for variable updates. Not supported in this version.
-        /// </summary>
-        public bool UseSnapshotDelta { get; } = false;
-        /// <summary>
-        /// Whether or not to enable Snapshot System for spawn and despawn commands. Not supported in this version.
-        /// </summary>
-        public bool UseSnapshotSpawn { get; } = false;
-        /// <summary>
-        /// When Snapshot System spawn is enabled: max size of Snapshot Messages. Meant to fit MTU.
-        /// </summary>
-        public int SnapshotMaxSpawnUsage { get; } = 1200;
-
         public const int RttAverageSamples = 5; // number of RTT to keep an average of (plus one)
         public const int RttWindowSize = 64; // number of slots to use for RTT computations (max number of in-flight packets)
         /// <summary>
@@ -224,7 +211,7 @@ namespace Unity.Netcode
                 return m_ConfigHash.Value;
             }
 
-            var writer = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp);
+            var writer = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, int.MaxValue);
             using (writer)
             {
                 writer.WriteValueSafe(ProtocolVersion);
@@ -239,6 +226,8 @@ namespace Unity.Netcode
                         writer.WriteValueSafe(sortedEntry.Key);
                     }
                 }
+
+                writer.WriteValueSafe(TickRate);
                 writer.WriteValueSafe(ConnectionApproval);
                 writer.WriteValueSafe(ForceSamePrefabs);
                 writer.WriteValueSafe(EnableSceneManagement);

Runtime/Configuration/NetworkConstants.cs

@@ -5,6 +5,6 @@ namespace Unity.Netcode
     /// </summary>
     internal static class NetworkConstants
     {
-        internal const string PROTOCOL_VERSION = "14.0.0";
+        internal const string PROTOCOL_VERSION = "15.0.0";
     }
 }

Runtime/Connection/NetworkClient.cs

@@ -20,6 +20,17 @@ namespace Unity.Netcode
         /// <summary>
         /// The NetworkObject's owned by this Client
         /// </summary>
-        public readonly List<NetworkObject> OwnedObjects = new List<NetworkObject>();
+        public List<NetworkObject> OwnedObjects
+        {
+            get
+            {
+                if (PlayerObject != null && PlayerObject.NetworkManager != null && PlayerObject.NetworkManager.IsListening)
+                {
+                    return PlayerObject.NetworkManager.SpawnManager.GetClientOwnedObjects(ClientId);
+                }
+
+                return new List<NetworkObject>();
+            }
+        }
     }
 }

Runtime/Core/IndexAllocator.cs

@@ -1,388 +0,0 @@
-using UnityEngine;
-
-namespace Unity.Netcode
-{
-    internal struct IndexAllocatorEntry
-    {
-        internal int Pos; // Position where the memory of this slot is
-        internal int Length; // Length of the memory allocated to this slot
-        internal int Next; // Next and Prev define the order of the slots in the buffer
-        internal int Prev;
-        internal bool Free;  // Whether this is a free slot
-    }
-
-    internal class IndexAllocator
-    {
-        private const int k_NotSet = -1;
-        private readonly int m_MaxSlot; // Maximum number of sections (free or not) in the buffer
-        private readonly int m_BufferSize; // Size of the buffer we allocated into
-        private int m_LastSlot = 0; // Last allocated slot
-        private IndexAllocatorEntry[] m_Slots; // Array of slots
-        private int[] m_IndexToSlot; // Mapping from the client's index to the slot index
-
-        internal IndexAllocator(int bufferSize, int maxSlot)
-        {
-            m_MaxSlot = maxSlot;
-            m_BufferSize = bufferSize;
-            m_Slots = new IndexAllocatorEntry[m_MaxSlot];
-            m_IndexToSlot = new int[m_MaxSlot];
-            Reset();
-        }
-
-        /// <summary>
-        /// Reset this IndexAllocator to an empty one, with the same sized buffer and slots
-        /// </summary>
-        internal void Reset()
-        {
-            // todo: could be made faster, for example by having a last index
-            // and not needing valid stuff past it
-            for (int i = 0; i < m_MaxSlot; i++)
-            {
-                m_Slots[i].Free = true;
-                m_Slots[i].Next = i + 1;
-                m_Slots[i].Prev = i - 1;
-                m_Slots[i].Pos = m_BufferSize;
-                m_Slots[i].Length = 0;
-
-                m_IndexToSlot[i] = k_NotSet;
-            }
-
-            m_Slots[0].Pos = 0;
-            m_Slots[0].Length = m_BufferSize;
-            m_Slots[0].Prev = k_NotSet;
-            m_Slots[m_MaxSlot - 1].Next = k_NotSet;
-        }
-
-        /// <summary>
-        /// Returns the amount of memory used
-        /// </summary>
-        /// <returns>
-        /// Returns the amount of memory used, starting at 0, ending after the last used slot
-        /// </returns>
-        internal int Range
-        {
-            get
-            {
-                // when the whole buffer is free, m_LastSlot points to an empty slot
-                if (m_Slots[m_LastSlot].Free)
-                {
-                    return 0;
-                }
-                // otherwise return the end of the last slot used
-                return m_Slots[m_LastSlot].Pos + m_Slots[m_LastSlot].Length;
-            }
-        }
-
-        /// <summary>
-        /// Allocate a slot with "size" position, for index "index"
-        /// </summary>
-        /// <param name="index">The client index to identify this. Used in Deallocate to identify which slot</param>
-        /// <param name="size">The size required. </param>
-        /// <param name="pos">Returns the position to use in the buffer </param>
-        /// <returns>
-        /// true if successful, false is there isn't enough memory available or no slots are large enough
-        /// </returns>
-        internal bool Allocate(int index, int size, out int pos)
-        {
-            pos = 0;
-            // size must be positive, index must be within range
-            if (size < 0 || index < 0 || index >= m_MaxSlot)
-            {
-                return false;
-            }
-
-            // refuse allocation if the index is already in use
-            if (m_IndexToSlot[index] != k_NotSet)
-            {
-                return false;
-            }
-
-            // todo: this is the slowest part
-            // improvement 1: list of free blocks (minor)
-            // improvement 2: heap of free blocks
-            for (int i = 0; i < m_MaxSlot; i++)
-            {
-                if (m_Slots[i].Free && m_Slots[i].Length >= size)
-                {
-                    m_IndexToSlot[index] = i;
-
-                    int leftOver = m_Slots[i].Length - size;
-                    int next = m_Slots[i].Next;
-                    if (m_Slots[next].Free)
-                    {
-                        m_Slots[next].Pos -= leftOver;
-                        m_Slots[next].Length += leftOver;
-                    }
-                    else
-                    {
-                        int add = MoveSlotAfter(i);
-
-                        m_Slots[add].Pos = m_Slots[i].Pos + size;
-                        m_Slots[add].Length = m_Slots[i].Length - size;
-                    }
-
-                    m_Slots[i].Free = false;
-                    m_Slots[i].Length = size;
-
-                    pos = m_Slots[i].Pos;
-
-                    // if we allocate past the current range, we are the last slot
-                    if (m_Slots[i].Pos + m_Slots[i].Length > Range)
-                    {
-                        m_LastSlot = i;
-                    }
-
-                    return true;
-                }
-            }
-
-            return false;
-        }
-
-        /// <summary>
-        /// Deallocate a slot
-        /// </summary>
-        /// <param name="index">The client index to identify this. Same index used in Allocate </param>
-        /// <returns>
-        /// true if successful, false is there isn't an allocated slot at this index
-        /// </returns>
-        internal bool Deallocate(int index)
-        {
-            // size must be positive, index must be within range
-            if (index < 0 || index >= m_MaxSlot)
-            {
-                return false;
-            }
-
-            int slot = m_IndexToSlot[index];
-
-            if (slot == k_NotSet)
-            {
-                return false;
-            }
-
-            if (m_Slots[slot].Free)
-            {
-                return false;
-            }
-
-            m_Slots[slot].Free = true;
-
-            int prev = m_Slots[slot].Prev;
-            int next = m_Slots[slot].Next;
-
-            // if previous slot was free, merge and grow
-            if (prev != k_NotSet && m_Slots[prev].Free)
-            {
-                m_Slots[prev].Length += m_Slots[slot].Length;
-                m_Slots[slot].Length = 0;
-
-                // if the slot we're merging was the last one, the last one is now the one we merged with
-                if (slot == m_LastSlot)
-                {
-                    m_LastSlot = prev;
-                }
-
-                // todo: verify what this does on full or nearly full cases
-                MoveSlotToEnd(slot);
-                slot = prev;
-            }
-
-            next = m_Slots[slot].Next;
-
-            // merge with next slot if it is free
-            if (next != k_NotSet && m_Slots[next].Free)
-            {
-                m_Slots[slot].Length += m_Slots[next].Length;
-                m_Slots[next].Length = 0;
-                MoveSlotToEnd(next);
-            }
-
-            // if we just deallocate the last one, we need to move last back
-            if (slot == m_LastSlot)
-            {
-                m_LastSlot = m_Slots[m_LastSlot].Prev;
-                // if there's nothing allocated anymore, use 0
-                if (m_LastSlot == k_NotSet)
-                {
-                    m_LastSlot = 0;
-                }
-            }
-
-            // mark the index as available
-            m_IndexToSlot[index] = k_NotSet;
-
-            return true;
-        }
-
-        // Take a slot at the end and link it to go just after "slot".
-        // Used when allocating part of a slot and we need an entry for the rest
-        // Returns the slot that was picked
-        private int MoveSlotAfter(int slot)
-        {
-            int ret = m_Slots[m_MaxSlot - 1].Prev;
-            int p0 = m_Slots[ret].Prev;
-
-            m_Slots[p0].Next = m_MaxSlot - 1;
-            m_Slots[m_MaxSlot - 1].Prev = p0;
-
-            int p1 = m_Slots[slot].Next;
-            m_Slots[slot].Next = ret;
-            m_Slots[p1].Prev = ret;
-
-            m_Slots[ret].Prev = slot;
-            m_Slots[ret].Next = p1;
-
-            return ret;
-        }
-
-        // Move the slot "slot" to the end of the list.
-        // Used when merging two slots, that gives us an extra entry at the end
-        private void MoveSlotToEnd(int slot)
-        {
-            // if we're already there
-            if (m_Slots[slot].Next == k_NotSet)
-            {
-                return;
-            }
-
-            int prev = m_Slots[slot].Prev;
-            int next = m_Slots[slot].Next;
-
-            m_Slots[prev].Next = next;
-            if (next != k_NotSet)
-            {
-                m_Slots[next].Prev = prev;
-            }
-
-            int p0 = m_Slots[m_MaxSlot - 1].Prev;
-
-            m_Slots[p0].Next = slot;
-            m_Slots[slot].Next = m_MaxSlot - 1;
-
-            m_Slots[m_MaxSlot - 1].Prev = slot;
-            m_Slots[slot].Prev = p0;
-
-            m_Slots[slot].Pos = m_BufferSize;
-        }
-
-        // runs a bunch of consistency check on the Allocator
-        internal bool Verify()
-        {
-            int pos = k_NotSet;
-            int count = 0;
-            int total = 0;
-            int endPos = 0;
-
-            do
-            {
-                int prev = pos;
-                if (pos != k_NotSet)
-                {
-                    pos = m_Slots[pos].Next;
-                    if (pos == k_NotSet)
-                    {
-                        break;
-                    }
-                }
-                else
-                {
-                    pos = 0;
-                }
-
-                if (m_Slots[pos].Prev != prev)
-                {
-                    // the previous is not correct
-                    return false;
-                }
-
-                if (m_Slots[pos].Length < 0)
-                {
-                    // Length should be positive
-                    return false;
-                }
-
-                if (prev != k_NotSet && m_Slots[prev].Free && m_Slots[pos].Free && m_Slots[pos].Length > 0)
-                {
-                    // should not have two consecutive free slots
-                    return false;
-                }
-
-                if (m_Slots[pos].Pos != total)
-                {
-                    // slots should all line up nicely
-                    return false;
-                }
-
-                if (!m_Slots[pos].Free)
-                {
-                    endPos = m_Slots[pos].Pos + m_Slots[pos].Length;
-                }
-
-                total += m_Slots[pos].Length;
-                count++;
-
-            } while (pos != k_NotSet);
-
-            if (count != m_MaxSlot)
-            {
-                // some slots were lost
-                return false;
-            }
-
-            if (total != m_BufferSize)
-            {
-                // total buffer should be accounted for
-                return false;
-            }
-
-            if (endPos != Range)
-            {
-                // end position should match reported end position
-                return false;
-            }
-
-            return true;
-        }
-
-        // Debug display the allocator structure
-        internal void DebugDisplay()
-        {
-            string logMessage = "IndexAllocator structure\n";
-
-            bool[] seen = new bool[m_MaxSlot];
-
-            int pos = 0;
-            int count = 0;
-            bool prevEmpty = false;
-            do
-            {
-                seen[pos] = true;
-                count++;
-                if (m_Slots[pos].Length == 0 && prevEmpty)
-                {
-                    // don't display repetitive empty slots
-                }
-                else
-                {
-                    logMessage += string.Format("{0}:{1}, {2} ({3}) \n", m_Slots[pos].Pos, m_Slots[pos].Length,
-                        m_Slots[pos].Free ? "Free" : "Used", pos);
-                    if (m_Slots[pos].Length == 0)
-                    {
-                        prevEmpty = true;
-                    }
-                    else
-                    {
-                        prevEmpty = false;
-                    }
-                }
-
-                pos = m_Slots[pos].Next;
-            } while (pos != k_NotSet && !seen[pos]);
-
-            logMessage += string.Format("{0} Total entries\n", count);
-
-            Debug.Log(logMessage);
-        }
-    }
-}

Runtime/Core/NetworkBehaviour.cs

@@ -15,41 +15,56 @@ namespace Unity.Netcode
 #pragma warning disable IDE1006 // disable naming rule violation check
         // RuntimeAccessModifiersILPP will make this `protected`
         internal enum __RpcExecStage
-#pragma warning restore IDE1006 // restore naming rule violation check
         {
             None = 0,
             Server = 1,
             Client = 2
         }
 
-#pragma warning disable IDE1006 // disable naming rule violation check
         // NetworkBehaviourILPP will override this in derived classes to return the name of the concrete type
         internal virtual string __getTypeName() => nameof(NetworkBehaviour);
-#pragma warning restore IDE1006 // restore naming rule violation check
 
-#pragma warning disable 414 // disable assigned but its value is never used
-#pragma warning disable IDE1006 // disable naming rule violation check
         [NonSerialized]
         // RuntimeAccessModifiersILPP will make this `protected`
         internal __RpcExecStage __rpc_exec_stage = __RpcExecStage.None;
-#pragma warning restore 414 // restore assigned but its value is never used
 #pragma warning restore IDE1006 // restore naming rule violation check
 
-#pragma warning disable 414 // disable assigned but its value is never used
+        private const int k_RpcMessageDefaultSize = 1024; // 1k
+        private const int k_RpcMessageMaximumSize = 1024 * 64; // 64k
+
 #pragma warning disable IDE1006 // disable naming rule violation check
         // RuntimeAccessModifiersILPP will make this `protected`
-        internal void __sendServerRpc(FastBufferWriter writer, uint rpcMethodId, ServerRpcParams rpcParams, RpcDelivery delivery)
-#pragma warning restore 414 // restore assigned but its value is never used
+        internal FastBufferWriter __beginSendServerRpc(uint rpcMethodId, ServerRpcParams serverRpcParams, RpcDelivery rpcDelivery)
 #pragma warning restore IDE1006 // restore naming rule violation check
         {
-            NetworkDelivery networkDelivery = NetworkDelivery.Reliable;
-            switch (delivery)
+            return new FastBufferWriter(k_RpcMessageDefaultSize, Allocator.Temp, k_RpcMessageMaximumSize);
+        }
+
+#pragma warning disable IDE1006 // disable naming rule violation check
+        // RuntimeAccessModifiersILPP will make this `protected`
+        internal void __endSendServerRpc(ref FastBufferWriter bufferWriter, uint rpcMethodId, ServerRpcParams serverRpcParams, RpcDelivery rpcDelivery)
+#pragma warning restore IDE1006 // restore naming rule violation check
+        {
+            var serverRpcMessage = new ServerRpcMessage
             {
+                Metadata = new RpcMetadata
+                {
+                    NetworkObjectId = NetworkObjectId,
+                    NetworkBehaviourId = NetworkBehaviourId,
+                    NetworkRpcMethodId = rpcMethodId,
+                },
+                WriteBuffer = bufferWriter
+            };
+
+            NetworkDelivery networkDelivery;
+            switch (rpcDelivery)
+            {
+                default:
                 case RpcDelivery.Reliable:
                     networkDelivery = NetworkDelivery.ReliableFragmentedSequenced;
                     break;
                 case RpcDelivery.Unreliable:
-                    if (writer.Length > MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE - sizeof(RpcMessage.RpcType) - sizeof(ulong) - sizeof(uint) - sizeof(ushort))
+                    if (bufferWriter.Length > MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE)
                     {
                         throw new OverflowException("RPC parameters are too large for unreliable delivery.");
                     }
@@ -57,41 +72,33 @@ namespace Unity.Netcode
                     break;
             }
 
-            var message = new RpcMessage
-            {
-                Header = new RpcMessage.HeaderData
-                {
-                    Type = RpcMessage.RpcType.Server,
-                    NetworkObjectId = NetworkObjectId,
-                    NetworkBehaviourId = NetworkBehaviourId,
-                    NetworkMethodId = rpcMethodId
-                },
-                RpcData = writer
-            };
-
-            var rpcMessageSize = 0;
+            var rpcWriteSize = 0;
 
             // If we are a server/host then we just no op and send to ourself
             if (IsHost || IsServer)
             {
-                using var tempBuffer = new FastBufferReader(writer, Allocator.Temp);
+                using var tempBuffer = new FastBufferReader(bufferWriter, Allocator.Temp);
                 var context = new NetworkContext
                 {
                     SenderId = NetworkManager.ServerClientId,
                     Timestamp = Time.realtimeSinceStartup,
                     SystemOwner = NetworkManager,
                     // header information isn't valid since it's not a real message.
-                    // Passing false to canDefer prevents it being accessed.
-                    Header = new MessageHeader()
+                    // RpcMessage doesn't access this stuff so it's just left empty.
+                    Header = new MessageHeader(),
+                    SerializedHeaderSize = 0,
+                    MessageSize = 0
                 };
-                message.Handle(tempBuffer, context, NetworkManager, NetworkManager.ServerClientId, false);
-                rpcMessageSize = tempBuffer.Length;
+                serverRpcMessage.ReadBuffer = tempBuffer;
+                serverRpcMessage.Handle(ref context);
+                rpcWriteSize = tempBuffer.Length;
             }
             else
             {
-                rpcMessageSize = NetworkManager.SendMessage(message, networkDelivery, NetworkManager.ServerClientId);
+                rpcWriteSize = NetworkManager.SendMessage(ref serverRpcMessage, networkDelivery, NetworkManager.ServerClientId);
             }
 
+            bufferWriter.Dispose();
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
@@ -101,26 +108,44 @@ namespace Unity.Netcode
                     NetworkObject,
                     rpcMethodName,
                     __getTypeName(),
-                    rpcMessageSize);
+                    rpcWriteSize);
             }
 #endif
         }
 
-#pragma warning disable 414 // disable assigned but its value is never used
 #pragma warning disable IDE1006 // disable naming rule violation check
         // RuntimeAccessModifiersILPP will make this `protected`
-        internal unsafe void __sendClientRpc(FastBufferWriter writer, uint rpcMethodId, ClientRpcParams rpcParams, RpcDelivery delivery)
-#pragma warning disable 414 // disable assigned but its value is never used
-#pragma warning disable IDE1006 // disable naming rule violation check
+        internal FastBufferWriter __beginSendClientRpc(uint rpcMethodId, ClientRpcParams clientRpcParams, RpcDelivery rpcDelivery)
+#pragma warning restore IDE1006 // restore naming rule violation check
         {
-            NetworkDelivery networkDelivery = NetworkDelivery.Reliable;
-            switch (delivery)
+            return new FastBufferWriter(k_RpcMessageDefaultSize, Allocator.Temp, k_RpcMessageMaximumSize);
+        }
+
+#pragma warning disable IDE1006 // disable naming rule violation check
+        // RuntimeAccessModifiersILPP will make this `protected`
+        internal void __endSendClientRpc(ref FastBufferWriter bufferWriter, uint rpcMethodId, ClientRpcParams clientRpcParams, RpcDelivery rpcDelivery)
+#pragma warning restore IDE1006 // restore naming rule violation check
+        {
+            var clientRpcMessage = new ClientRpcMessage
             {
+                Metadata = new RpcMetadata
+                {
+                    NetworkObjectId = NetworkObjectId,
+                    NetworkBehaviourId = NetworkBehaviourId,
+                    NetworkRpcMethodId = rpcMethodId,
+                },
+                WriteBuffer = bufferWriter
+            };
+
+            NetworkDelivery networkDelivery;
+            switch (rpcDelivery)
+            {
+                default:
                 case RpcDelivery.Reliable:
                     networkDelivery = NetworkDelivery.ReliableFragmentedSequenced;
                     break;
                 case RpcDelivery.Unreliable:
-                    if (writer.Length > MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE - sizeof(RpcMessage.RpcType) - sizeof(ulong) - sizeof(uint) - sizeof(ushort))
+                    if (bufferWriter.Length > MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE)
                     {
                         throw new OverflowException("RPC parameters are too large for unreliable delivery.");
                     }
@@ -128,72 +153,85 @@ namespace Unity.Netcode
                     break;
             }
 
-            var message = new RpcMessage
-            {
-                Header = new RpcMessage.HeaderData
-                {
-                    Type = RpcMessage.RpcType.Client,
-                    NetworkObjectId = NetworkObjectId,
-                    NetworkBehaviourId = NetworkBehaviourId,
-                    NetworkMethodId = rpcMethodId
-                },
-                RpcData = writer
-            };
-            int messageSize;
+            var rpcWriteSize = 0;
 
             // We check to see if we need to shortcut for the case where we are the host/server and we can send a clientRPC
             // to ourself. Sadly we have to figure that out from the list of clientIds :(
             bool shouldSendToHost = false;
-
-            if (rpcParams.Send.TargetClientIds != null)
+            if (clientRpcParams.Send.TargetClientIds != null)
             {
-                foreach (var clientId in rpcParams.Send.TargetClientIds)
+                foreach (var targetClientId in clientRpcParams.Send.TargetClientIds)
                 {
-                    if (clientId == NetworkManager.ServerClientId)
+                    if (targetClientId == NetworkManager.ServerClientId)
                     {
                         shouldSendToHost = true;
                         break;
                     }
+
+                    // Check to make sure we are sending to only observers, if not log an error.
+                    if (NetworkManager.LogLevel >= LogLevel.Error && !NetworkObject.Observers.Contains(targetClientId))
+                    {
+                        NetworkLog.LogError(GenerateObserverErrorMessage(clientRpcParams, targetClientId));
+                    }
                 }
 
-                messageSize = NetworkManager.SendMessage(message, networkDelivery, in rpcParams.Send.TargetClientIds);
+                rpcWriteSize = NetworkManager.SendMessage(ref clientRpcMessage, networkDelivery, in clientRpcParams.Send.TargetClientIds);
             }
-            else if (rpcParams.Send.TargetClientIdsNativeArray != null)
+            else if (clientRpcParams.Send.TargetClientIdsNativeArray != null)
             {
-                foreach (var clientId in rpcParams.Send.TargetClientIdsNativeArray)
+                foreach (var targetClientId in clientRpcParams.Send.TargetClientIdsNativeArray)
                 {
-                    if (clientId == NetworkManager.ServerClientId)
+                    if (targetClientId == NetworkManager.ServerClientId)
                     {
                         shouldSendToHost = true;
                         break;
                     }
+
+                    // Check to make sure we are sending to only observers, if not log an error.
+                    if (NetworkManager.LogLevel >= LogLevel.Error && !NetworkObject.Observers.Contains(targetClientId))
+                    {
+                        NetworkLog.LogError(GenerateObserverErrorMessage(clientRpcParams, targetClientId));
+                    }
                 }
 
-                messageSize = NetworkManager.SendMessage(message, networkDelivery, rpcParams.Send.TargetClientIdsNativeArray.Value);
+                rpcWriteSize = NetworkManager.SendMessage(ref clientRpcMessage, networkDelivery, clientRpcParams.Send.TargetClientIdsNativeArray.Value);
             }
             else
             {
-                shouldSendToHost = IsHost;
-                messageSize = NetworkManager.SendMessage(message, networkDelivery, NetworkManager.ConnectedClientsIds);
+                var observerEnumerator = NetworkObject.Observers.GetEnumerator();
+                while (observerEnumerator.MoveNext())
+                {
+                    // Skip over the host
+                    if (IsHost && observerEnumerator.Current == NetworkManager.LocalClientId)
+                    {
+                        shouldSendToHost = true;
+                        continue;
+                    }
+                    rpcWriteSize = NetworkManager.MessagingSystem.SendMessage(ref clientRpcMessage, networkDelivery, observerEnumerator.Current);
+                }
             }
 
             // If we are a server/host then we just no op and send to ourself
             if (shouldSendToHost)
             {
-                using var tempBuffer = new FastBufferReader(writer, Allocator.Temp);
+                using var tempBuffer = new FastBufferReader(bufferWriter, Allocator.Temp);
                 var context = new NetworkContext
                 {
                     SenderId = NetworkManager.ServerClientId,
                     Timestamp = Time.realtimeSinceStartup,
                     SystemOwner = NetworkManager,
                     // header information isn't valid since it's not a real message.
-                    // Passing false to canDefer prevents it being accessed.
-                    Header = new MessageHeader()
+                    // RpcMessage doesn't access this stuff so it's just left empty.
+                    Header = new MessageHeader(),
+                    SerializedHeaderSize = 0,
+                    MessageSize = 0
                 };
-                message.Handle(tempBuffer, context, NetworkManager, NetworkManager.ServerClientId, false);
-                messageSize = tempBuffer.Length;
+                clientRpcMessage.ReadBuffer = tempBuffer;
+                clientRpcMessage.Handle(ref context);
             }
 
+            bufferWriter.Dispose();
+
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
             {
@@ -204,12 +242,18 @@ namespace Unity.Netcode
                         NetworkObject,
                         rpcMethodName,
                         __getTypeName(),
-                        messageSize);
+                        rpcWriteSize);
                 }
             }
 #endif
         }
 
+        internal string GenerateObserverErrorMessage(ClientRpcParams clientRpcParams, ulong targetClientId)
+        {
+            var containerNameHoldingId = clientRpcParams.Send.TargetClientIds != null ? nameof(ClientRpcParams.Send.TargetClientIds) : nameof(ClientRpcParams.Send.TargetClientIdsNativeArray);
+            return $"Sending ClientRpc to non-observer! {containerNameHoldingId} contains clientId {targetClientId} that is not an observer!";
+        }
+
         /// <summary>
         /// 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
@@ -217,50 +261,50 @@ namespace Unity.Netcode
         public NetworkManager NetworkManager => NetworkObject.NetworkManager;
 
         /// <summary>
-        /// Gets if the object is the the personal clients player object
+        /// If a NetworkObject is assigned, it will return whether or not this NetworkObject
+        /// is the local player object.  If no NetworkObject is assigned it will always return false.
         /// </summary>
-        public bool IsLocalPlayer => NetworkObject.IsLocalPlayer;
+        public bool IsLocalPlayer { get; private set; }
 
         /// <summary>
         /// Gets if the object is owned by the local player or if the object is the local player object
         /// </summary>
-        public bool IsOwner => NetworkObject.IsOwner;
+        public bool IsOwner { get; internal set; }
 
         /// <summary>
         /// Gets if we are executing as server
         /// </summary>
-        protected bool IsServer => IsRunning && NetworkManager.IsServer;
+        protected bool IsServer { get; private set; }
 
         /// <summary>
         /// Gets if we are executing as client
         /// </summary>
-        protected bool IsClient => IsRunning && NetworkManager.IsClient;
+        protected bool IsClient { get; private set; }
+
 
         /// <summary>
         /// Gets if we are executing as Host, I.E Server and Client
         /// </summary>
-        protected bool IsHost => IsRunning && NetworkManager.IsHost;
-
-        private bool IsRunning => NetworkManager && NetworkManager.IsListening;
+        protected bool IsHost { get; private set; }
 
         /// <summary>
         /// Gets Whether or not the object has a owner
         /// </summary>
-        public bool IsOwnedByServer => NetworkObject.IsOwnedByServer;
+        public bool IsOwnedByServer { get; internal set; }
 
         /// <summary>
         /// Used to determine if it is safe to access NetworkObject and NetworkManager from within a NetworkBehaviour component
         /// Primarily useful when checking NetworkObject/NetworkManager properties within FixedUpate
         /// </summary>
-        public bool IsSpawned => HasNetworkObject ? NetworkObject.IsSpawned : false;
+        public bool IsSpawned { get; internal set; }
 
         internal bool IsBehaviourEditable()
         {
             // Only server can MODIFY. So allow modification if network is either not running or we are server
             return !m_NetworkObject ||
-                   (m_NetworkObject.NetworkManager == null ||
-                    !m_NetworkObject.NetworkManager.IsListening ||
-                    m_NetworkObject.NetworkManager.IsServer);
+                m_NetworkObject.NetworkManager == null ||
+                m_NetworkObject.NetworkManager.IsListening == false ||
+                m_NetworkObject.NetworkManager.IsServer;
         }
 
         /// <summary>
@@ -282,9 +326,17 @@ namespace Unity.Netcode
                     m_NetworkObject = GetComponentInParent<NetworkObject>();
                 }
 
-                if (m_NetworkObject == null && NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                // ShutdownInProgress check:
+                // This prevents an edge case scenario where the NetworkManager is shutting down but user code
+                // in Update and/or in FixedUpdate could still be checking NetworkBehaviour.NetworkObject directly (i.e. does it exist?)
+                // or NetworkBehaviour.IsSpawned (i.e. to early exit if not spawned) which, in turn, could generate several Warning messages
+                // per spawned NetworkObject.  Checking for ShutdownInProgress prevents these unnecessary LogWarning messages.
+                if (m_NetworkObject == null && (NetworkManager.Singleton == null || !NetworkManager.Singleton.ShutdownInProgress))
                 {
-                    NetworkLog.LogWarning($"Could not get {nameof(NetworkObject)} for the {nameof(NetworkBehaviour)}. Are you missing a {nameof(NetworkObject)} component?");
+                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"Could not get {nameof(NetworkObject)} for the {nameof(NetworkBehaviour)}. Are you missing a {nameof(NetworkObject)} component?");
+                    }
                 }
 
                 return m_NetworkObject;
@@ -301,12 +353,12 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets the NetworkId of the NetworkObject that owns this NetworkBehaviour
         /// </summary>
-        public ulong NetworkObjectId => NetworkObject.NetworkObjectId;
+        public ulong NetworkObjectId { get; internal set; }
 
         /// <summary>
         /// Gets NetworkId for this NetworkBehaviour from the owner NetworkObject
         /// </summary>
-        public ushort NetworkBehaviourId => NetworkObject.GetNetworkBehaviourOrderIndex(this);
+        public ushort NetworkBehaviourId { get; internal set; }
 
         /// <summary>
         /// Internally caches the Id of this behaviour in a NetworkObject. Makes look-up faster
@@ -326,7 +378,47 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets the ClientId that owns the NetworkObject
         /// </summary>
-        public ulong OwnerClientId => NetworkObject.OwnerClientId;
+        public ulong OwnerClientId { get; internal set; }
+
+        /// <summary>
+        /// Updates properties with network session related
+        /// dependencies such as a NetworkObject's spawned
+        /// state or NetworkManager's session state.
+        /// </summary>
+        internal void UpdateNetworkProperties()
+        {
+            // Set NetworkObject dependent properties
+            if (NetworkObject != null)
+            {
+                // Set identification related properties
+                NetworkObjectId = NetworkObject.NetworkObjectId;
+                IsLocalPlayer = NetworkObject.IsLocalPlayer;
+
+                // This is "OK" because GetNetworkBehaviourOrderIndex uses the order of
+                // NetworkObject.ChildNetworkBehaviours which is set once when first
+                // accessed.
+                NetworkBehaviourId = NetworkObject.GetNetworkBehaviourOrderIndex(this);
+
+                // Set ownership related properties
+                IsOwnedByServer = NetworkObject.IsOwnedByServer;
+                IsOwner = NetworkObject.IsOwner;
+                OwnerClientId = NetworkObject.OwnerClientId;
+
+                // Set NetworkManager dependent properties
+                if (NetworkManager != null)
+                {
+                    IsHost = NetworkManager.IsListening && NetworkManager.IsHost;
+                    IsClient = NetworkManager.IsListening && NetworkManager.IsClient;
+                    IsServer = NetworkManager.IsListening && NetworkManager.IsServer;
+                }
+            }
+            else // Shouldn't happen, but if so then set the properties to their default value;
+            {
+                OwnerClientId = NetworkObjectId = default;
+                IsOwnedByServer = IsOwner = IsHost = IsClient = IsServer = default;
+                NetworkBehaviourId = default;
+            }
+        }
 
         /// <summary>
         /// Gets called when the <see cref="NetworkObject"/> gets spawned, message handlers are ready to be registered and the network is setup.
@@ -340,12 +432,17 @@ namespace Unity.Netcode
 
         internal void InternalOnNetworkSpawn()
         {
+            IsSpawned = true;
             InitializeVariables();
+            UpdateNetworkProperties();
+            OnNetworkSpawn();
         }
 
         internal void InternalOnNetworkDespawn()
         {
-
+            IsSpawned = false;
+            UpdateNetworkProperties();
+            OnNetworkDespawn();
         }
 
         /// <summary>
@@ -353,11 +450,23 @@ namespace Unity.Netcode
         /// </summary>
         public virtual void OnGainedOwnership() { }
 
+        internal void InternalOnGainedOwnership()
+        {
+            UpdateNetworkProperties();
+            OnGainedOwnership();
+        }
+
         /// <summary>
         /// Gets called when we loose ownership of this object
         /// </summary>
         public virtual void OnLostOwnership() { }
 
+        internal void InternalOnLostOwnership()
+        {
+            UpdateNetworkProperties();
+            OnLostOwnership();
+        }
+
         /// <summary>
         /// Gets called when the parent NetworkObject of this NetworkBehaviour's NetworkObject has changed
         /// </summary>
@@ -410,20 +519,17 @@ namespace Unity.Netcode
 
             m_VarInit = true;
 
-            FieldInfo[] sortedFields = GetFieldInfoForType(GetType());
-
+            var sortedFields = GetFieldInfoForType(GetType());
             for (int i = 0; i < sortedFields.Length; i++)
             {
-                Type fieldType = sortedFields[i].FieldType;
-
+                var fieldType = sortedFields[i].FieldType;
                 if (fieldType.IsSubclassOf(typeof(NetworkVariableBase)))
                 {
                     var instance = (NetworkVariableBase)sortedFields[i].GetValue(this);
 
                     if (instance == null)
                     {
-                        instance = (NetworkVariableBase)Activator.CreateInstance(fieldType, true);
-                        sortedFields[i].SetValue(this, instance);
+                        throw new Exception($"{GetType().FullName}.{sortedFields[i].Name} cannot be null. All {nameof(NetworkVariableBase)} instances must be initialized.");
                     }
 
                     instance.Initialize(this);
@@ -477,7 +583,7 @@ namespace Unity.Netcode
             }
         }
 
-        internal void VariableUpdate(ulong clientId)
+        internal void VariableUpdate(ulong targetClientId)
         {
             if (!m_VarInit)
             {
@@ -485,67 +591,58 @@ namespace Unity.Netcode
             }
 
             PreNetworkVariableWrite();
-            NetworkVariableUpdate(clientId, NetworkBehaviourId);
+            NetworkVariableUpdate(targetClientId, NetworkBehaviourId);
         }
 
         internal readonly List<int> NetworkVariableIndexesToReset = new List<int>();
         internal readonly HashSet<int> NetworkVariableIndexesToResetSet = new HashSet<int>();
 
-        private void NetworkVariableUpdate(ulong clientId, int behaviourIndex)
+        private void NetworkVariableUpdate(ulong targetClientId, int behaviourIndex)
         {
             if (!CouldHaveDirtyNetworkVariables())
             {
                 return;
             }
 
-            if (NetworkManager.NetworkConfig.UseSnapshotDelta)
+            for (int j = 0; j < m_DeliveryMappedNetworkVariableIndices.Count; j++)
             {
+                var shouldSend = false;
                 for (int k = 0; k < NetworkVariableFields.Count; k++)
                 {
-                    NetworkManager.SnapshotSystem.Store(NetworkObjectId, behaviourIndex, k, NetworkVariableFields[k]);
-                }
-            }
-
-            if (!NetworkManager.NetworkConfig.UseSnapshotDelta)
-            {
-                for (int j = 0; j < m_DeliveryMappedNetworkVariableIndices.Count; j++)
-                {
-                    var shouldSend = false;
-                    for (int k = 0; k < NetworkVariableFields.Count; k++)
+                    var networkVariable = NetworkVariableFields[k];
+                    if (networkVariable.IsDirty() && networkVariable.CanClientRead(targetClientId))
                     {
-                        if (NetworkVariableFields[k].ShouldWrite(clientId, IsServer))
+                        shouldSend = true;
+                        break;
+                    }
+                }
+
+                if (shouldSend)
+                {
+                    var message = new NetworkVariableDeltaMessage
+                    {
+                        NetworkObjectId = NetworkObjectId,
+                        NetworkBehaviourIndex = NetworkObject.GetNetworkBehaviourOrderIndex(this),
+                        NetworkBehaviour = this,
+                        TargetClientId = targetClientId,
+                        DeliveryMappedNetworkVariableIndex = m_DeliveryMappedNetworkVariableIndices[j]
+                    };
+                    // TODO: Serialization is where the IsDirty flag gets changed.
+                    // Messages don't get sent from the server to itself, so if we're host and sending to ourselves,
+                    // we still have to actually serialize the message even though we're not sending it, otherwise
+                    // the dirty flag doesn't change properly. These two pieces should be decoupled at some point
+                    // so we don't have to do this serialization work if we're not going to use the result.
+                    if (IsServer && targetClientId == NetworkManager.ServerClientId)
+                    {
+                        var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, MessagingSystem.FRAGMENTED_MESSAGE_MAX_SIZE);
+                        using (tmpWriter)
                         {
-                            shouldSend = true;
+                            message.Serialize(tmpWriter);
                         }
                     }
-
-                    if (shouldSend)
+                    else
                     {
-                        var message = new NetworkVariableDeltaMessage
-                        {
-                            NetworkObjectId = NetworkObjectId,
-                            NetworkBehaviourIndex = NetworkObject.GetNetworkBehaviourOrderIndex(this),
-                            NetworkBehaviour = this,
-                            ClientId = clientId,
-                            DeliveryMappedNetworkVariableIndex = m_DeliveryMappedNetworkVariableIndices[j]
-                        };
-                        // TODO: Serialization is where the IsDirty flag gets changed.
-                        // Messages don't get sent from the server to itself, so if we're host and sending to ourselves,
-                        // we still have to actually serialize the message even though we're not sending it, otherwise
-                        // the dirty flag doesn't change properly. These two pieces should be decoupled at some point
-                        // so we don't have to do this serialization work if we're not going to use the result.
-                        if (IsServer && clientId == NetworkManager.ServerClientId)
-                        {
-                            var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp);
-                            using (tmpWriter)
-                            {
-                                message.Serialize(tmpWriter);
-                            }
-                        }
-                        else
-                        {
-                            NetworkManager.SendMessage(message, m_DeliveryTypesForNetworkVariableGroups[j], clientId);
-                        }
+                        NetworkManager.SendMessage(ref message, m_DeliveryTypesForNetworkVariableGroups[j], targetClientId);
                     }
                 }
             }
@@ -573,7 +670,7 @@ namespace Unity.Netcode
             }
         }
 
-        internal void WriteNetworkVariableData(FastBufferWriter writer, ulong clientId)
+        internal void WriteNetworkVariableData(FastBufferWriter writer, ulong targetClientId)
         {
             if (NetworkVariableFields.Count == 0)
             {
@@ -582,7 +679,7 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                bool canClientRead = NetworkVariableFields[j].CanClientRead(clientId);
+                bool canClientRead = NetworkVariableFields[j].CanClientRead(targetClientId);
 
                 if (canClientRead)
                 {

Runtime/Core/NetworkBehaviourUpdater.cs

@@ -57,7 +57,7 @@ namespace Unity.Netcode
                         {
                             for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
                             {
-                                sobj.ChildNetworkBehaviours[k].VariableUpdate(networkManager.ServerClientId);
+                                sobj.ChildNetworkBehaviours[k].VariableUpdate(NetworkManager.ServerClientId);
                             }
                         }
                     }

Runtime/Core/NetworkManager.cs

@@ -12,6 +12,7 @@ using Unity.Multiplayer.Tools;
 #endif
 using Unity.Profiling;
 using UnityEngine.SceneManagement;
+using System.Runtime.CompilerServices;
 using Debug = UnityEngine.Debug;
 
 namespace Unity.Netcode
@@ -45,7 +46,7 @@ namespace Unity.Netcode
         private static ProfilerMarker s_TransportDisconnect = new ProfilerMarker($"{nameof(NetworkManager)}.TransportDisconnect");
 #endif
 
-        private const double k_TimeSyncFrequency = 1.0d; // sync every second, TODO will be removed once timesync is done via snapshots
+        private const double k_TimeSyncFrequency = 1.0d; // sync every second
         private const float k_DefaultBufferSizeSec = 0.05f; // todo talk with UX/Product, find good default value for this
 
         internal static string PrefabDebugHelper(NetworkPrefab networkPrefab)
@@ -53,7 +54,6 @@ namespace Unity.Netcode
             return $"{nameof(NetworkPrefab)} \"{networkPrefab.Prefab.gameObject.name}\"";
         }
 
-        internal SnapshotSystem SnapshotSystem { get; private set; }
         internal NetworkBehaviourUpdater BehaviourUpdater { get; private set; }
 
         internal MessagingSystem MessagingSystem { get; private set; }
@@ -73,6 +73,9 @@ namespace Unity.Netcode
             }
         }
 
+        private bool m_ShuttingDown;
+        private bool m_StopProcessingMessages;
+
         private class NetworkManagerHooks : INetworkHooks
         {
             private NetworkManager m_NetworkManager;
@@ -82,11 +85,11 @@ namespace Unity.Netcode
                 m_NetworkManager = manager;
             }
 
-            public void OnBeforeSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery)
+            public void OnBeforeSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery) where T : INetworkMessage
             {
             }
 
-            public void OnAfterSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery, int messageSizeBytes)
+            public void OnAfterSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery, int messageSizeBytes) where T : INetworkMessage
             {
             }
 
@@ -116,25 +119,31 @@ namespace Unity.Netcode
 
             public bool OnVerifyCanSend(ulong destinationId, Type messageType, NetworkDelivery delivery)
             {
-                return true;
+                return !m_NetworkManager.m_StopProcessingMessages;
             }
 
             public bool OnVerifyCanReceive(ulong senderId, Type messageType)
             {
                 if (m_NetworkManager.PendingClients.TryGetValue(senderId, out PendingClient client) &&
-                       (client.ConnectionState == PendingClient.State.PendingApproval ||
-                        (client.ConnectionState == PendingClient.State.PendingConnection &&
-                         messageType != typeof(ConnectionRequestMessage))))
+                    (client.ConnectionState == PendingClient.State.PendingApproval || (client.ConnectionState == PendingClient.State.PendingConnection && messageType != typeof(ConnectionRequestMessage))))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
-                        NetworkLog.LogWarning($"Message received from {nameof(senderId)}={senderId.ToString()} before it has been accepted");
+                        NetworkLog.LogWarning($"Message received from {nameof(senderId)}={senderId} before it has been accepted");
                     }
 
                     return false;
                 }
 
-                return true;
+                return !m_NetworkManager.m_StopProcessingMessages;
+            }
+
+            public void OnBeforeHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+            {
+            }
+
+            public void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+            {
             }
         }
 
@@ -149,14 +158,9 @@ namespace Unity.Netcode
 
             public void Send(ulong clientId, NetworkDelivery delivery, FastBufferWriter batchData)
             {
+                var sendBuffer = batchData.ToTempByteArray();
 
-                var length = batchData.Length;
-                //TODO: Transport needs to have a way to send it data without copying and allocating here.
-                var bytes = batchData.ToArray();
-                var sendBuffer = new ArraySegment<byte>(bytes, 0, length);
-
-                m_NetworkManager.NetworkConfig.NetworkTransport.Send(clientId, sendBuffer, delivery);
-
+                m_NetworkManager.NetworkConfig.NetworkTransport.Send(m_NetworkManager.ClientIdToTransportId(clientId), sendBuffer, delivery);
             }
         }
 
@@ -199,11 +203,6 @@ namespace Unity.Netcode
 
         public NetworkTime ServerTime => NetworkTickSystem?.ServerTime ?? default;
 
-        /// <summary>
-        /// Gets or sets if the NetworkManager should be marked as DontDestroyOnLoad
-        /// </summary>
-        [HideInInspector] public bool DontDestroy = true;
-
         /// <summary>
         /// Gets or sets if the application should be set to run in background
         /// </summary>
@@ -228,12 +227,12 @@ namespace Unity.Netcode
 
         public NetworkSceneManager SceneManager { get; private set; }
 
+        public const ulong ServerClientId = 0;
+
         /// <summary>
         /// Gets the networkId of the server
         /// </summary>
-        public ulong ServerClientId => NetworkConfig.NetworkTransport?.ServerClientId ??
-                                       throw new NullReferenceException(
-                                           $"The transport in the active {nameof(NetworkConfig)} is null");
+        private ulong m_ServerTransportId => NetworkConfig.NetworkTransport?.ServerClientId ?? throw new NullReferenceException($"The transport in the active {nameof(NetworkConfig)} is null");
 
         /// <summary>
         /// Returns ServerClientId if IsServer or LocalClientId if not
@@ -248,6 +247,10 @@ namespace Unity.Netcode
 
         private Dictionary<ulong, NetworkClient> m_ConnectedClients = new Dictionary<ulong, NetworkClient>();
 
+        private ulong m_NextClientId = 1;
+        private Dictionary<ulong, ulong> m_ClientIdToTransportIdMap = new Dictionary<ulong, ulong>();
+        private Dictionary<ulong, ulong> m_TransportIdToClientIdMap = new Dictionary<ulong, ulong>();
+
         private List<NetworkClient> m_ConnectedClientsList = new List<NetworkClient>();
 
         private List<ulong> m_ConnectedClientIds = new List<ulong>();
@@ -332,6 +335,9 @@ namespace Unity.Netcode
         /// </summary>
         public bool IsConnectedClient { get; internal set; }
 
+
+        public bool ShutdownInProgress { get { return m_ShuttingDown; } }
+
         /// <summary>
         /// The callback to invoke once a client connects. This callback is only ran on the server and on the local client that connects.
         /// </summary>
@@ -344,8 +350,6 @@ namespace Unity.Netcode
         /// </summary>
         public event Action<ulong> OnClientDisconnectCallback = null;
 
-        internal void InvokeOnClientDisconnectCallback(ulong clientId) => OnClientDisconnectCallback?.Invoke(clientId);
-
         /// <summary>
         /// The callback to invoke once the server is ready
         /// </summary>
@@ -359,16 +363,14 @@ namespace Unity.Netcode
         /// <param name="approved">Whether or not the client was approved</param>
         /// <param name="position">The position to spawn the client at. If null, the prefab position is used.</param>
         /// <param name="rotation">The rotation to spawn the client with. If null, the prefab position is used.</param>
-        public delegate void ConnectionApprovedDelegate(bool createPlayerObject, uint? playerPrefabHash, bool approved,
-            Vector3? position, Quaternion? rotation);
+        public delegate void ConnectionApprovedDelegate(bool createPlayerObject, uint? playerPrefabHash, bool approved, Vector3? position, Quaternion? rotation);
 
         /// <summary>
         /// The callback to invoke during connection approval
         /// </summary>
         public event Action<byte[], ulong, ConnectionApprovedDelegate> ConnectionApprovalCallback = null;
 
-        internal void InvokeConnectionApproval(byte[] payload, ulong clientId, ConnectionApprovedDelegate action) =>
-            ConnectionApprovalCallback?.Invoke(payload, clientId, action);
+        internal void InvokeConnectionApproval(byte[] payload, ulong clientId, ConnectionApprovedDelegate action) => ConnectionApprovalCallback?.Invoke(payload, clientId, action);
 
         /// <summary>
         /// The current NetworkConfig
@@ -485,6 +487,13 @@ namespace Unity.Netcode
 
         private void Initialize(bool server)
         {
+            // Don't allow the user to start a network session if the NetworkManager is
+            // still parented under another GameObject
+            if (NetworkManagerCheckForParent(true))
+            {
+                return;
+            }
+
             if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
             {
                 NetworkLog.LogInfo(nameof(Initialize));
@@ -548,14 +557,7 @@ namespace Unity.Netcode
                 return;
             }
 
-            //This 'if' should never enter
-            if (SnapshotSystem != null)
-            {
-                SnapshotSystem.Dispose();
-                SnapshotSystem = null;
-            }
-
-            SnapshotSystem = new SnapshotSystem(this);
+            NetworkConfig.NetworkTransport.NetworkMetrics = NetworkMetrics;
 
             if (server)
             {
@@ -576,6 +578,7 @@ namespace Unity.Netcode
 
             // Always clear our prefab override links before building
             NetworkConfig.NetworkPrefabOverrideLinks.Clear();
+            NetworkConfig.OverrideToNetworkPrefab.Clear();
 
             // Build the NetworkPrefabOverrideLinks dictionary
             for (int i = 0; i < NetworkConfig.NetworkPrefabs.Count; i++)
@@ -772,7 +775,7 @@ namespace Unity.Netcode
 
             NetworkConfig.NetworkTransport.OnTransportEvent += HandleRawTransportPoll;
 
-            NetworkConfig.NetworkTransport.Initialize();
+            NetworkConfig.NetworkTransport.Initialize(this);
         }
 
         /// <summary>
@@ -782,44 +785,35 @@ namespace Unity.Netcode
         {
             if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
             {
-                NetworkLog.LogInfo("StartServer()");
+                NetworkLog.LogInfo(nameof(StartServer));
             }
 
-            if (IsServer || IsClient)
+            if (!CanStart(StartType.Server))
             {
-                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                {
-                    NetworkLog.LogWarning("Cannot start server while an instance is already running");
-                }
-
                 return false;
             }
 
-            if (NetworkConfig.ConnectionApproval)
-            {
-                if (ConnectionApprovalCallback == null)
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                    {
-                        NetworkLog.LogWarning(
-                            "No ConnectionApproval callback defined. Connection approval will timeout");
-                    }
-                }
-            }
-
             Initialize(true);
 
-            var result = NetworkConfig.NetworkTransport.StartServer();
+            // If we failed to start then shutdown and notify user that the transport failed to start
+            if (NetworkConfig.NetworkTransport.StartServer())
+            {
+                IsServer = true;
+                IsClient = false;
+                IsListening = true;
 
-            IsServer = true;
-            IsClient = false;
-            IsListening = true;
+                SpawnManager.ServerSpawnSceneObjectsOnStartSweep();
 
-            SpawnManager.ServerSpawnSceneObjectsOnStartSweep();
+                OnServerStarted?.Invoke();
+                return true;
+            }
+            else
+            {
+                Debug.LogError($"Server is shutting down due to network transport start failure of {NetworkConfig.NetworkTransport.GetType().Name}!");
+                Shutdown();
+            }
 
-            OnServerStarted?.Invoke();
-
-            return result;
+            return false;
         }
 
         /// <summary>
@@ -832,26 +826,26 @@ namespace Unity.Netcode
                 NetworkLog.LogInfo(nameof(StartClient));
             }
 
-            if (IsServer || IsClient)
+            if (!CanStart(StartType.Client))
             {
-                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                {
-                    NetworkLog.LogWarning("Cannot start client while an instance is already running");
-                }
-
                 return false;
             }
 
             Initialize(false);
             MessagingSystem.ClientConnected(ServerClientId);
 
-            var result = NetworkConfig.NetworkTransport.StartClient();
+            if (!NetworkConfig.NetworkTransport.StartClient())
+            {
+                Debug.LogError($"Client is shutting down due to network transport start failure of {NetworkConfig.NetworkTransport.GetType().Name}!");
+                Shutdown();
+                return false;
+            }
 
             IsServer = false;
             IsClient = true;
             IsListening = true;
 
-            return result;
+            return true;
         }
 
         /// <summary>
@@ -864,31 +858,21 @@ namespace Unity.Netcode
                 NetworkLog.LogInfo(nameof(StartHost));
             }
 
-            if (IsServer || IsClient)
+            if (!CanStart(StartType.Host))
             {
-                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                {
-                    NetworkLog.LogWarning("Cannot start host while an instance is already running");
-                }
-
                 return false;
             }
 
-            if (NetworkConfig.ConnectionApproval)
-            {
-                if (ConnectionApprovalCallback == null)
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                    {
-                        NetworkLog.LogWarning(
-                            "No ConnectionApproval callback defined. Connection approval will timeout");
-                    }
-                }
-            }
-
             Initialize(true);
 
-            var result = NetworkConfig.NetworkTransport.StartServer();
+            // If we failed to start then shutdown and notify user that the transport failed to start
+            if (!NetworkConfig.NetworkTransport.StartServer())
+            {
+                Debug.LogError($"Server is shutting down due to network transport start failure of {NetworkConfig.NetworkTransport.GetType().Name}!");
+                Shutdown();
+                return false;
+            }
+
             MessagingSystem.ClientConnected(ServerClientId);
             LocalClientId = ServerClientId;
             NetworkMetrics.SetConnectionId(LocalClientId);
@@ -924,7 +908,53 @@ namespace Unity.Netcode
 
             OnServerStarted?.Invoke();
 
-            return result;
+            return true;
+        }
+
+        private enum StartType
+        {
+            Server,
+            Host,
+            Client
+        }
+
+        private bool CanStart(StartType type)
+        {
+            if (IsListening)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                {
+                    NetworkLog.LogWarning("Cannot start " + type + " while an instance is already running");
+                }
+
+                return false;
+            }
+
+            if (NetworkConfig.ConnectionApproval)
+            {
+                if (ConnectionApprovalCallback == null)
+                {
+                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning(
+                            "No ConnectionApproval callback defined. Connection approval will timeout");
+                    }
+                }
+            }
+
+            if (ConnectionApprovalCallback != null)
+            {
+                if (!NetworkConfig.ConnectionApproval)
+                {
+                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning(
+                            "A ConnectionApproval callback is defined but ConnectionApproval is disabled. In order to use ConnectionApproval it has to be explicitly enabled ");
+                    }
+                }
+            }
+
+            return true;
         }
 
         public void SetSingleton()
@@ -936,11 +966,6 @@ namespace Unity.Netcode
 
         private void OnEnable()
         {
-            if (DontDestroy)
-            {
-                DontDestroyOnLoad(gameObject);
-            }
-
             if (RunInBackground)
             {
                 Application.runInBackground = true;
@@ -950,6 +975,11 @@ namespace Unity.Netcode
             {
                 SetSingleton();
             }
+
+            if (!NetworkManagerCheckForParent())
+            {
+                DontDestroyOnLoad(gameObject);
+            }
         }
 
         private void Awake()
@@ -957,6 +987,49 @@ namespace Unity.Netcode
             UnityEngine.SceneManagement.SceneManager.sceneUnloaded += OnSceneUnloaded;
         }
 
+        /// <summary>
+        /// Handle runtime detection for parenting the NetworkManager's GameObject under another GameObject
+        /// </summary>
+        private void OnTransformParentChanged()
+        {
+            NetworkManagerCheckForParent();
+        }
+
+        /// <summary>
+        /// Determines if the NetworkManager's GameObject is parented under another GameObject and
+        /// notifies the user that this is not allowed for the NetworkManager.
+        /// </summary>
+        internal bool NetworkManagerCheckForParent(bool ignoreNetworkManagerCache = false)
+        {
+#if UNITY_EDITOR
+            var isParented = NetworkManagerHelper.NotifyUserOfNestedNetworkManager(this, ignoreNetworkManagerCache);
+#else
+            var isParented = transform.root != transform;
+            if (isParented)
+            {
+                throw new Exception(GenerateNestedNetworkManagerMessage(transform));
+            }
+#endif
+            return isParented;
+        }
+
+        static internal string GenerateNestedNetworkManagerMessage(Transform transform)
+        {
+            return $"{transform.name} is nested under {transform.root.name}. NetworkManager cannot be nested.\n";
+        }
+
+#if UNITY_EDITOR
+        static internal INetworkManagerHelper NetworkManagerHelper;
+        /// <summary>
+        /// Interface for NetworkManagerHelper
+        /// </summary>
+        internal interface INetworkManagerHelper
+        {
+            bool NotifyUserOfNestedNetworkManager(NetworkManager networkManager, bool ignoreNetworkManagerCache = false, bool editorTest = false);
+            void CheckAndNotifyUserNetworkObjectRemoved(NetworkManager networkManager, bool editorTest = false);
+        }
+#endif
+
         // Ensures that the NetworkManager is cleaned up before OnDestroy is run on NetworkObjects and NetworkBehaviours when unloading a scene with a NetworkManager
         private void OnSceneUnloaded(Scene scene)
         {
@@ -975,7 +1048,7 @@ namespace Unity.Netcode
         // Note that this gets also called manually by OnSceneUnloaded and OnApplicationQuit
         private void OnDestroy()
         {
-            Shutdown();
+            ShutdownInternal();
 
             UnityEngine.SceneManagement.SceneManager.sceneUnloaded -= OnSceneUnloaded;
 
@@ -985,17 +1058,40 @@ namespace Unity.Netcode
             }
         }
 
+        private void DisconnectRemoteClient(ulong clientId)
+        {
+            var transportId = ClientIdToTransportId(clientId);
+            NetworkConfig.NetworkTransport.DisconnectRemoteClient(transportId);
+        }
+
         /// <summary>
         /// Globally shuts down the library.
         /// Disconnects clients if connected and stops server if running.
         /// </summary>
-        public void Shutdown()
+        /// <param name="discardMessageQueue">
+        /// If false, any messages that are currently in the incoming queue will be handled,
+        /// and any messages in the outgoing queue will be sent, before the shutdown is processed.
+        /// If true, NetworkManager will shut down immediately, and any unprocessed or unsent messages
+        /// will be discarded.
+        /// </param>
+        public void Shutdown(bool discardMessageQueue = false)
         {
             if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
             {
                 NetworkLog.LogInfo(nameof(Shutdown));
             }
 
+            m_ShuttingDown = true;
+            m_StopProcessingMessages = discardMessageQueue;
+        }
+
+        internal void ShutdownInternal()
+        {
+            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
+            {
+                NetworkLog.LogInfo(nameof(ShutdownInternal));
+            }
+
             if (IsServer)
             {
                 // make sure all messages are flushed before transport disconnect clients
@@ -1019,7 +1115,7 @@ namespace Unity.Netcode
                             continue;
                         }
 
-                        NetworkConfig.NetworkTransport.DisconnectRemoteClient(pair.Key);
+                        DisconnectRemoteClient(pair.Key);
                     }
                 }
 
@@ -1033,7 +1129,7 @@ namespace Unity.Netcode
                             continue;
                         }
 
-                        NetworkConfig.NetworkTransport.DisconnectRemoteClient(pair.Key);
+                        DisconnectRemoteClient(pair.Key);
                     }
                 }
             }
@@ -1050,12 +1146,6 @@ namespace Unity.Netcode
 
             this.UnregisterAllNetworkUpdates();
 
-            if (SnapshotSystem != null)
-            {
-                SnapshotSystem.Dispose();
-                SnapshotSystem = null;
-            }
-
             if (NetworkTickSystem != null)
             {
                 NetworkTickSystem.Tick -= OnNetworkManagerTick;
@@ -1068,11 +1158,15 @@ namespace Unity.Netcode
                 MessagingSystem = null;
             }
 
-            NetworkConfig.NetworkTransport.OnTransportEvent -= HandleRawTransportPoll;
+            if (NetworkConfig?.NetworkTransport != null)
+            {
+                NetworkConfig.NetworkTransport.OnTransportEvent -= HandleRawTransportPoll;
+            }
 
             if (SpawnManager != null)
             {
-                SpawnManager.DestroyNonSceneObjects();
+                SpawnManager.CleanupAllTriggers();
+                SpawnManager.DespawnAndDestroyNetworkObjects();
                 SpawnManager.ServerResetShudownStateForSceneObjects();
 
                 SpawnManager = null;
@@ -1103,7 +1197,12 @@ namespace Unity.Netcode
                 NetworkConfig?.NetworkTransport?.Shutdown();
             }
 
+            m_ClientIdToTransportIdMap.Clear();
+            m_TransportIdToClientIdMap.Clear();
+
             IsListening = false;
+            m_ShuttingDown = false;
+            m_StopProcessingMessages = false;
         }
 
         // INetworkUpdateSystem
@@ -1157,6 +1256,11 @@ namespace Unity.Netcode
                 return;
             }
 
+            if (m_ShuttingDown && m_StopProcessingMessages)
+            {
+                return;
+            }
+
             // Only update RTT here, server time is updated by time sync messages
             var reset = NetworkTimeSystem.Advance(Time.deltaTime);
             if (reset)
@@ -1173,16 +1277,28 @@ namespace Unity.Netcode
 
         private void OnNetworkPostLateUpdate()
         {
-            MessagingSystem.ProcessSendQueues();
-            NetworkMetrics.DispatchFrame();
+
+            if (!m_ShuttingDown || !m_StopProcessingMessages)
+            {
+                MessagingSystem.ProcessSendQueues();
+                NetworkMetrics.UpdateNetworkObjectsCount(SpawnManager.SpawnedObjects.Count);
+                NetworkMetrics.UpdateConnectionsCount((IsServer) ? ConnectedClients.Count : 1);
+                NetworkMetrics.DispatchFrame();
+
+                NetworkObject.VerifyParentingStatus();
+            }
             SpawnManager.CleanupStaleTriggers();
+
+            if (m_ShuttingDown)
+            {
+                ShutdownInternal();
+            }
         }
 
         /// <summary>
         /// This function runs once whenever the local tick is incremented and is responsible for the following (in order):
         /// - collect commands/inputs and send them to the server (TBD)
         /// - call NetworkFixedUpdate on all NetworkBehaviours in prediction/client authority mode
-        /// - create a snapshot from resulting state
         /// </summary>
         private void OnNetworkManagerTick()
         {
@@ -1204,7 +1320,7 @@ namespace Unity.Netcode
                 ShouldSendConnectionData = NetworkConfig.ConnectionApproval,
                 ConnectionData = NetworkConfig.ConnectionData
             };
-            SendMessage(message, NetworkDelivery.ReliableSequenced, ServerClientId);
+            SendMessage(ref message, NetworkDelivery.ReliableSequenced, ServerClientId);
         }
 
         private IEnumerator ApprovalTimeout(ulong clientId)
@@ -1229,14 +1345,43 @@ namespace Unity.Netcode
             }
         }
 
+        internal ulong TransportIdToClientId(ulong transportId)
+        {
+            return transportId == m_ServerTransportId ? ServerClientId : m_TransportIdToClientIdMap[transportId];
+        }
+
+        internal ulong ClientIdToTransportId(ulong clientId)
+        {
+            return clientId == ServerClientId ? m_ServerTransportId : m_ClientIdToTransportIdMap[clientId];
+        }
+
         private void HandleRawTransportPoll(NetworkEvent networkEvent, ulong clientId, ArraySegment<byte> payload, float receiveTime)
         {
+            var transportId = clientId;
             switch (networkEvent)
             {
                 case NetworkEvent.Connect:
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
                     s_TransportConnect.Begin();
 #endif
+
+                    // Assumptions:
+                    // - When server receives a connection, it *must be* a client
+                    // - When client receives one, it *must be* the server
+                    // Client's can't connect to or talk to other clients.
+                    // Server is a sentinel so only one exists, if we are server, we can't be
+                    // connecting to it.
+                    if (IsServer)
+                    {
+                        clientId = m_NextClientId++;
+                    }
+                    else
+                    {
+                        clientId = ServerClientId;
+                    }
+                    m_ClientIdToTransportIdMap[clientId] = transportId;
+                    m_TransportIdToClientIdMap[transportId] = clientId;
+
                     MessagingSystem.ClientConnected(clientId);
                     if (IsServer)
                     {
@@ -1275,6 +1420,8 @@ namespace Unity.Netcode
                             NetworkLog.LogInfo($"Incoming Data From {clientId}: {payload.Count} bytes");
                         }
 
+                        clientId = TransportIdToClientId(clientId);
+
                         HandleIncomingData(clientId, payload, receiveTime);
                         break;
                     }
@@ -1282,12 +1429,15 @@ namespace Unity.Netcode
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
                     s_TransportDisconnect.Begin();
 #endif
+                    clientId = TransportIdCleanUp(clientId, transportId);
 
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                     {
                         NetworkLog.LogInfo($"Disconnect Event From {clientId}");
                     }
 
+                    OnClientDisconnectCallback?.Invoke(clientId);
+
                     if (IsServer)
                     {
                         OnClientDisconnectFromServer(clientId);
@@ -1296,9 +1446,6 @@ namespace Unity.Netcode
                     {
                         Shutdown();
                     }
-
-                    OnClientDisconnectCallback?.Invoke(clientId);
-
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
                     s_TransportDisconnect.End();
 #endif
@@ -1306,7 +1453,32 @@ namespace Unity.Netcode
             }
         }
 
-        internal unsafe int SendMessage<TMessageType, TClientIdListType>(in TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
+        /// <summary>
+        /// Handles cleaning up the transport id/client id tables after
+        /// receiving a disconnect event from transport
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private ulong TransportIdCleanUp(ulong clientId, ulong transportId)
+        {
+            // This check is for clients that attempted to connect but failed.
+            // When this happens, the client will not have an entry within the
+            // m_TransportIdToClientIdMap or m_ClientIdToTransportIdMap lookup
+            // tables so we exit early and just return 0 to be used for the
+            // disconnect event.
+            if (!IsServer && !m_TransportIdToClientIdMap.ContainsKey(clientId))
+            {
+                return 0;
+            }
+
+            clientId = TransportIdToClientId(clientId);
+
+            m_TransportIdToClientIdMap.Remove(transportId);
+            m_ClientIdToTransportIdMap.Remove(clientId);
+
+            return clientId;
+        }
+
+        internal unsafe int SendMessage<TMessageType, TClientIdListType>(ref TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
             where TMessageType : INetworkMessage
             where TClientIdListType : IReadOnlyList<ulong>
         {
@@ -1329,12 +1501,18 @@ namespace Unity.Netcode
                 {
                     return 0;
                 }
-                return MessagingSystem.SendMessage(message, delivery, nonServerIds, newIdx);
+                return MessagingSystem.SendMessage(ref message, delivery, nonServerIds, newIdx);
             }
-            return MessagingSystem.SendMessage(message, delivery, clientIds);
+            // else
+            if (clientIds.Count != 1 || clientIds[0] != ServerClientId)
+            {
+                throw new ArgumentException($"Clients may only send messages to {nameof(ServerClientId)}");
+            }
+
+            return MessagingSystem.SendMessage(ref message, delivery, clientIds);
         }
 
-        internal unsafe int SendMessage<T>(in T message, NetworkDelivery delivery,
+        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery,
             ulong* clientIds, int numClientIds)
             where T : INetworkMessage
         {
@@ -1357,19 +1535,24 @@ namespace Unity.Netcode
                 {
                     return 0;
                 }
-                return MessagingSystem.SendMessage(message, delivery, nonServerIds, newIdx);
+                return MessagingSystem.SendMessage(ref message, delivery, nonServerIds, newIdx);
+            }
+            // else
+            if (numClientIds != 1 || clientIds[0] != ServerClientId)
+            {
+                throw new ArgumentException($"Clients may only send messages to {nameof(ServerClientId)}");
             }
 
-            return MessagingSystem.SendMessage(message, delivery, clientIds, numClientIds);
+            return MessagingSystem.SendMessage(ref message, delivery, clientIds, numClientIds);
         }
 
-        internal unsafe int SendMessage<T>(in T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
+        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
             where T : INetworkMessage
         {
-            return SendMessage(message, delivery, (ulong*)clientIds.GetUnsafePtr(), clientIds.Length);
+            return SendMessage(ref message, delivery, (ulong*)clientIds.GetUnsafePtr(), clientIds.Length);
         }
 
-        internal int SendMessage<T>(in T message, NetworkDelivery delivery, ulong clientId)
+        internal int SendMessage<T>(ref T message, NetworkDelivery delivery, ulong clientId)
             where T : INetworkMessage
         {
             // Prevent server sending to itself
@@ -1377,7 +1560,18 @@ namespace Unity.Netcode
             {
                 return 0;
             }
-            return MessagingSystem.SendMessage(message, delivery, clientId);
+
+            if (!IsServer && clientId != ServerClientId)
+            {
+                throw new ArgumentException($"Clients may only send messages to {nameof(ServerClientId)}");
+            }
+            return MessagingSystem.SendMessage(ref message, delivery, clientId);
+        }
+
+        internal int SendPreSerializedMessage<T>(in FastBufferWriter writer, int maxSize, ref T message, NetworkDelivery delivery, ulong clientId)
+            where T : INetworkMessage
+        {
+            return MessagingSystem.SendPreSerializedMessage(writer, maxSize, ref message, delivery, clientId);
         }
 
         internal void HandleIncomingData(ulong clientId, ArraySegment<byte> payload, float receiveTime)
@@ -1401,12 +1595,11 @@ namespace Unity.Netcode
         {
             if (!IsServer)
             {
-                throw new NotServerException("Only server can disconnect remote clients. Use StopClient instead.");
+                throw new NotServerException($"Only server can disconnect remote clients. Please use `{nameof(Shutdown)}()` instead.");
             }
 
             OnClientDisconnectFromServer(clientId);
-
-            NetworkConfig.NetworkTransport.DisconnectRemoteClient(clientId);
+            DisconnectRemoteClient(clientId);
         }
 
         private void OnClientDisconnectFromServer(ulong clientId)
@@ -1430,32 +1623,45 @@ namespace Unity.Netcode
                         }
                     }
 
-                    for (int i = networkClient.OwnedObjects.Count - 1; i >= 0; i--)
+                    // Get the NetworkObjects owned by the disconnected client
+                    var clientOwnedObjects = SpawnManager.GetClientOwnedObjects(clientId);
+                    if (clientOwnedObjects == null)
                     {
-                        var ownedObject = networkClient.OwnedObjects[i];
-                        if (ownedObject != null)
+                        // This could happen if a client is never assigned a player object and is disconnected
+                        // Only log this in verbose/developer mode
+                        if (LogLevel == LogLevel.Developer)
                         {
-                            if (!ownedObject.DontDestroyWithOwner)
+                            NetworkLog.LogWarning($"ClientID {clientId} disconnected with (0) zero owned objects!  Was a player prefab not assigned?");
+                        }
+                    }
+                    else
+                    {
+                        // Handle changing ownership and prefab handlers
+                        for (int i = clientOwnedObjects.Count - 1; i >= 0; i--)
+                        {
+                            var ownedObject = clientOwnedObjects[i];
+                            if (ownedObject != null)
                             {
-                                if (PrefabHandler.ContainsHandler(ConnectedClients[clientId].OwnedObjects[i]
-                                    .GlobalObjectIdHash))
+                                if (!ownedObject.DontDestroyWithOwner)
                                 {
-                                    PrefabHandler.HandleNetworkPrefabDestroy(ConnectedClients[clientId].OwnedObjects[i]);
+                                    if (PrefabHandler.ContainsHandler(clientOwnedObjects[i].GlobalObjectIdHash))
+                                    {
+                                        PrefabHandler.HandleNetworkPrefabDestroy(clientOwnedObjects[i]);
+                                    }
+                                    else
+                                    {
+                                        Destroy(ownedObject.gameObject);
+                                    }
                                 }
                                 else
                                 {
-                                    Destroy(ownedObject.gameObject);
+                                    ownedObject.RemoveOwnership();
                                 }
                             }
-                            else
-                            {
-                                ownedObject.RemoveOwnership();
-                            }
                         }
                     }
 
                     // TODO: Could(should?) be replaced with more memory per client, by storing the visibility
-
                     foreach (var sobj in SpawnManager.SpawnedObjectsList)
                     {
                         sobj.Observers.Remove(clientId);
@@ -1499,7 +1705,7 @@ namespace Unity.Netcode
             {
                 Tick = NetworkTickSystem.ServerTime.Tick
             };
-            SendMessage(message, NetworkDelivery.Unreliable, ConnectedClientsIds);
+            SendMessage(ref message, NetworkDelivery.Unreliable, ConnectedClientsIds);
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             s_SyncTime.End();
 #endif
@@ -1546,12 +1752,11 @@ namespace Unity.Netcode
                     {
                         if (SpawnManager.SpawnedObjectsList.Count != 0)
                         {
-                            message.SceneObjectCount = SpawnManager.SpawnedObjectsList.Count;
                             message.SpawnedObjectsList = SpawnManager.SpawnedObjectsList;
                         }
                     }
 
-                    SendMessage(message, NetworkDelivery.ReliableFragmentedSequenced, ownerClientId);
+                    SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, ownerClientId);
 
                     // If scene management is enabled, then let NetworkSceneManager handle the initial scene and NetworkObject synchronization
                     if (!NetworkConfig.EnableSceneManagement)
@@ -1565,6 +1770,7 @@ namespace Unity.Netcode
                 }
                 else // Server just adds itself as an observer to all spawned NetworkObjects
                 {
+                    LocalClient = client;
                     SpawnManager.UpdateObservedNetworkObjects(ownerClientId);
                     InvokeOnClientConnectedCallback(ownerClientId);
                 }
@@ -1580,7 +1786,7 @@ namespace Unity.Netcode
             else
             {
                 PendingClients.Remove(ownerClientId);
-                NetworkConfig.NetworkTransport.DisconnectRemoteClient(ownerClientId);
+                DisconnectRemoteClient(ownerClientId);
             }
         }
 
@@ -1603,14 +1809,14 @@ namespace Unity.Netcode
 
                 var message = new CreateObjectMessage
                 {
-                    ObjectInfo = ConnectedClients[clientId].PlayerObject.GetMessageSceneObject(clientPair.Key, false)
+                    ObjectInfo = ConnectedClients[clientId].PlayerObject.GetMessageSceneObject(clientPair.Key)
                 };
                 message.ObjectInfo.Header.Hash = playerPrefabHash;
                 message.ObjectInfo.Header.IsSceneObject = false;
                 message.ObjectInfo.Header.HasParent = false;
                 message.ObjectInfo.Header.IsPlayerObject = true;
                 message.ObjectInfo.Header.OwnerClientId = clientId;
-                var size = SendMessage(message, NetworkDelivery.ReliableFragmentedSequenced, clientPair.Key);
+                var size = SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, clientPair.Key);
                 NetworkMetrics.TrackObjectSpawnSent(clientPair.Key, ConnectedClients[clientId].PlayerObject, size);
             }
         }

Runtime/Core/NetworkObject.cs

@@ -39,7 +39,7 @@ namespace Unity.Netcode
             var globalObjectIdString = UnityEditor.GlobalObjectId.GetGlobalObjectIdSlow(this).ToString();
             GlobalObjectIdHash = XXHash.Hash32(globalObjectIdString);
         }
-#endif
+#endif // UNITY_EDITOR
 
         /// <summary>
         /// Gets the NetworkManager that owns this NetworkObject instance
@@ -54,8 +54,6 @@ namespace Unity.Netcode
         /// </summary>
         internal NetworkManager NetworkManagerOwner;
 
-        private ulong m_NetworkObjectId;
-
         /// <summary>
         /// Gets the unique Id of this object that is synced across the network
         /// </summary>
@@ -64,33 +62,7 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets the ClientId of the owner of this NetworkObject
         /// </summary>
-        public ulong OwnerClientId
-        {
-            get
-            {
-                if (OwnerClientIdInternal == null)
-                {
-                    return NetworkManager != null ? NetworkManager.ServerClientId : 0;
-                }
-                else
-                {
-                    return OwnerClientIdInternal.Value;
-                }
-            }
-            internal set
-            {
-                if (NetworkManager != null && value == NetworkManager.ServerClientId)
-                {
-                    OwnerClientIdInternal = null;
-                }
-                else
-                {
-                    OwnerClientIdInternal = value;
-                }
-            }
-        }
-
-        internal ulong? OwnerClientIdInternal = null;
+        public ulong OwnerClientId { get; internal set; }
 
         /// <summary>
         /// If true, the object will always be replicated as root on clients and the parent will be ignored.
@@ -234,11 +206,6 @@ namespace Unity.Netcode
                 throw new VisibilityChangeException("The object is already visible");
             }
 
-            if (NetworkManager.NetworkConfig.UseSnapshotSpawn)
-            {
-                SnapshotSpawn(clientId);
-            }
-
             Observers.Add(clientId);
 
             NetworkManager.SpawnManager.SendSpawnCallForObject(clientId, this);
@@ -314,23 +281,15 @@ namespace Unity.Netcode
                 throw new VisibilityChangeException("Cannot hide an object from the server");
             }
 
-
             Observers.Remove(clientId);
 
-            if (NetworkManager.NetworkConfig.UseSnapshotSpawn)
+            var message = new DestroyObjectMessage
             {
-                SnapshotDespawn(clientId);
-            }
-            else
-            {
-                var message = new DestroyObjectMessage
-                {
-                    NetworkObjectId = NetworkObjectId
-                };
-                // Send destroy call
-                var size = NetworkManager.SendMessage(message, NetworkDelivery.ReliableSequenced, clientId);
-                NetworkManager.NetworkMetrics.TrackObjectDestroySent(clientId, this, size);
-            }
+                NetworkObjectId = NetworkObjectId
+            };
+            // Send destroy call
+            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, clientId);
+            NetworkManager.NetworkMetrics.TrackObjectDestroySent(clientId, this, size);
         }
 
         /// <summary>
@@ -345,14 +304,14 @@ namespace Unity.Netcode
                 throw new ArgumentNullException("At least one " + nameof(NetworkObject) + " has to be provided");
             }
 
-            NetworkManager networkManager = networkObjects[0].NetworkManager;
+            var networkManager = networkObjects[0].NetworkManager;
 
             if (!networkManager.IsServer)
             {
                 throw new NotServerException("Only server can change visibility");
             }
 
-            if (clientId == networkManager.ServerClientId)
+            if (clientId == NetworkManager.ServerClientId)
             {
                 throw new VisibilityChangeException("Cannot hide an object from the server");
             }
@@ -384,84 +343,21 @@ namespace Unity.Netcode
 
         private void OnDestroy()
         {
-            if (NetworkManager != null && NetworkManager.IsListening && NetworkManager.IsServer == false && IsSpawned
-                && (IsSceneObject == null || (IsSceneObject != null && IsSceneObject.Value != true)))
+            if (NetworkManager != null && NetworkManager.IsListening && NetworkManager.IsServer == false && IsSpawned &&
+                (IsSceneObject == null || (IsSceneObject != null && IsSceneObject.Value != true)))
             {
                 throw new NotServerException($"Destroy a spawned {nameof(NetworkObject)} on a non-host client is not valid. Call {nameof(Destroy)} or {nameof(Despawn)} on the server/host instead.");
             }
 
-            if (NetworkManager != null && NetworkManager.SpawnManager != null && NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
+            if (NetworkManager != null && NetworkManager.SpawnManager != null &&
+                NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
             {
                 NetworkManager.SpawnManager.OnDespawnObject(networkObject, false);
             }
         }
 
-        private SnapshotDespawnCommand GetDespawnCommand()
-        {
-            var command = new SnapshotDespawnCommand();
-            command.NetworkObjectId = NetworkObjectId;
-
-            return command;
-        }
-
-        private SnapshotSpawnCommand GetSpawnCommand()
-        {
-            var command = new SnapshotSpawnCommand();
-            command.NetworkObjectId = NetworkObjectId;
-            command.OwnerClientId = OwnerClientId;
-            command.IsPlayerObject = IsPlayerObject;
-            command.IsSceneObject = (IsSceneObject == null) || IsSceneObject.Value;
-
-            ulong? parent = NetworkManager.SpawnManager.GetSpawnParentId(this);
-            if (parent != null)
-            {
-                command.ParentNetworkId = parent.Value;
-            }
-            else
-            {
-                // write own network id, when no parents. todo: optimize this.
-                command.ParentNetworkId = command.NetworkObjectId;
-            }
-
-            command.GlobalObjectIdHash = HostCheckForGlobalObjectIdHashOverride();
-            // todo: check if (IncludeTransformWhenSpawning == null || IncludeTransformWhenSpawning(clientId)) for any clientId
-            command.ObjectPosition = transform.position;
-            command.ObjectRotation = transform.rotation;
-            command.ObjectScale = transform.localScale;
-
-            return command;
-        }
-
-        private void SnapshotSpawn()
-        {
-            var command = GetSpawnCommand();
-            NetworkManager.SnapshotSystem.Spawn(command);
-        }
-
-        private void SnapshotSpawn(ulong clientId)
-        {
-            var command = GetSpawnCommand();
-            command.TargetClientIds = new List<ulong>();
-            command.TargetClientIds.Add(clientId);
-            NetworkManager.SnapshotSystem.Spawn(command);
-        }
-
-        internal void SnapshotDespawn()
-        {
-            var command = GetDespawnCommand();
-            NetworkManager.SnapshotSystem.Despawn(command);
-        }
-
-        internal void SnapshotDespawn(ulong clientId)
-        {
-            var command = GetDespawnCommand();
-            command.TargetClientIds = new List<ulong>();
-            command.TargetClientIds.Add(clientId);
-            NetworkManager.SnapshotSystem.Despawn(command);
-        }
-
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private void SpawnInternal(bool destroyWithScene, ulong? ownerClientId, bool playerObject)
+        private void SpawnInternal(bool destroyWithScene, ulong ownerClientId, bool playerObject)
         {
             if (!NetworkManager.IsListening)
             {
@@ -475,12 +371,6 @@ namespace Unity.Netcode
 
             NetworkManager.SpawnManager.SpawnNetworkObjectLocally(this, NetworkManager.SpawnManager.GetNetworkObjectId(), false, playerObject, ownerClientId, destroyWithScene);
 
-            if (NetworkManager.NetworkConfig.UseSnapshotSpawn)
-            {
-                SnapshotSpawn();
-            }
-
-            ulong ownerId = ownerClientId != null ? ownerClientId.Value : NetworkManager.ServerClientId;
             for (int i = 0; i < NetworkManager.ConnectedClientsList.Count; i++)
             {
                 if (Observers.Contains(NetworkManager.ConnectedClientsList[i].ClientId))
@@ -496,7 +386,7 @@ namespace Unity.Netcode
         /// <param name="destroyWithScene">Should the object be destroyed when the scene is changed</param>
         public void Spawn(bool destroyWithScene = false)
         {
-            SpawnInternal(destroyWithScene, null, false);
+            SpawnInternal(destroyWithScene, NetworkManager.ServerClientId, false);
         }
 
         /// <summary>
@@ -547,17 +437,29 @@ namespace Unity.Netcode
 
         internal void InvokeBehaviourOnLostOwnership()
         {
+            // Server already handles this earlier, hosts should ignore, all clients should update
+            if (!NetworkManager.IsServer)
+            {
+                NetworkManager.SpawnManager.UpdateOwnershipTable(this, OwnerClientId, true);
+            }
+
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
-                ChildNetworkBehaviours[i].OnLostOwnership();
+                ChildNetworkBehaviours[i].InternalOnLostOwnership();
             }
         }
 
         internal void InvokeBehaviourOnGainedOwnership()
         {
+            // Server already handles this earlier, hosts should ignore and only client owners should update
+            if (!NetworkManager.IsServer && NetworkManager.LocalClientId == OwnerClientId)
+            {
+                NetworkManager.SpawnManager.UpdateOwnershipTable(this, OwnerClientId);
+            }
+
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
-                ChildNetworkBehaviours[i].OnGainedOwnership();
+                ChildNetworkBehaviours[i].InternalOnGainedOwnership();
             }
         }
 
@@ -714,7 +616,7 @@ namespace Unity.Netcode
                     }
                 }
 
-                NetworkManager.SendMessage(message, NetworkDelivery.ReliableSequenced, clientIds, idx);
+                NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, clientIds, idx);
             }
         }
 
@@ -756,13 +658,7 @@ namespace Unity.Netcode
 
             if (!NetworkManager.SpawnManager.SpawnedObjects.ContainsKey(m_LatestParent.Value))
             {
-                if (OrphanChildren.Add(this))
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                    {
-                        NetworkLog.LogWarning($"{nameof(NetworkObject)} ({name}) cannot find its parent, added to {nameof(OrphanChildren)} set");
-                    }
-                }
+                OrphanChildren.Add(this);
                 return false;
             }
 
@@ -793,19 +689,21 @@ namespace Unity.Netcode
 
         internal void InvokeBehaviourNetworkSpawn()
         {
+            NetworkManager.SpawnManager.UpdateOwnershipTable(this, OwnerClientId);
+
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
                 ChildNetworkBehaviours[i].InternalOnNetworkSpawn();
-                ChildNetworkBehaviours[i].OnNetworkSpawn();
             }
         }
 
         internal void InvokeBehaviourNetworkDespawn()
         {
+            NetworkManager.SpawnManager.UpdateOwnershipTable(this, OwnerClientId, true);
+
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
                 ChildNetworkBehaviours[i].InternalOnNetworkDespawn();
-                ChildNetworkBehaviours[i].OnNetworkDespawn();
             }
         }
 
@@ -834,13 +732,13 @@ namespace Unity.Netcode
             }
         }
 
-        internal void WriteNetworkVariableData(FastBufferWriter writer, ulong clientId)
+        internal void WriteNetworkVariableData(FastBufferWriter writer, ulong targetClientId)
         {
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
             {
                 var behavior = ChildNetworkBehaviours[i];
                 behavior.InitializeVariables();
-                behavior.WriteNetworkVariableData(writer, clientId);
+                behavior.WriteNetworkVariableData(writer, targetClientId);
             }
         }
 
@@ -853,6 +751,27 @@ namespace Unity.Netcode
             }
         }
 
+        // NGO currently guarantees that the client will receive spawn data for all objects in one network tick.
+        //  Children may arrive before their parents; when they do they are stored in OrphanedChildren and then
+        //  resolved when their parents arrived.  Because we don't send a partial list of spawns (yet), something
+        //  has gone wrong if by the end of an update we still have unresolved orphans
+        //
+
+        // if and when we have different systems for where it is expected that orphans survive across ticks,
+        //   then this warning will remind us that we need to revamp the system because then we can no longer simply
+        //   spawn the orphan without its parent (at least, not when its transform is set to local coords mode)
+        //   - because then you’ll have children popping at the wrong location not having their parent’s global position to root them
+        //   - and then they’ll pop to the correct location after they get the parent, and that would be not good
+        internal static void VerifyParentingStatus()
+        {
+            if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+            {
+                if (OrphanChildren.Count > 0)
+                {
+                    NetworkLog.LogWarning($"{nameof(NetworkObject)} ({OrphanChildren.Count}) children not resolved to parents by the end of frame");
+                }
+            }
+        }
         internal void SetNetworkVariableData(FastBufferReader reader)
         {
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
@@ -918,7 +837,6 @@ namespace Unity.Netcode
                 public bool IsSceneObject;
                 public bool HasTransform;
                 public bool IsReparented;
-                public bool HasNetworkVariables;
             }
 
             public HeaderData Header;
@@ -979,10 +897,7 @@ namespace Unity.Netcode
                     }
                 }
 
-                if (Header.HasNetworkVariables)
-                {
-                    OwnerObject.WriteNetworkVariableData(writer, TargetClientId);
-                }
+                OwnerObject.WriteNetworkVariableData(writer, TargetClientId);
             }
 
             public unsafe void Deserialize(FastBufferReader reader)
@@ -1022,7 +937,7 @@ namespace Unity.Netcode
             }
         }
 
-        internal SceneObject GetMessageSceneObject(ulong targetClientId, bool includeNetworkVariableData = true)
+        internal SceneObject GetMessageSceneObject(ulong targetClientId)
         {
             var obj = new SceneObject
             {
@@ -1033,7 +948,6 @@ namespace Unity.Netcode
                     OwnerClientId = OwnerClientId,
                     IsSceneObject = IsSceneObject ?? true,
                     Hash = HostCheckForGlobalObjectIdHashOverride(),
-                    HasNetworkVariables = includeNetworkVariableData
                 },
                 OwnerObject = this,
                 TargetClientId = targetClientId
@@ -1142,8 +1056,7 @@ namespace Unity.Netcode
                     var globalObjectIdHash = NetworkManager.PrefabHandler.GetSourceGlobalObjectIdHash(GlobalObjectIdHash);
                     return globalObjectIdHash == 0 ? GlobalObjectIdHash : globalObjectIdHash;
                 }
-                else
-                if (NetworkManager.NetworkConfig.OverrideToNetworkPrefab.ContainsKey(GlobalObjectIdHash))
+                else if (NetworkManager.NetworkConfig.OverrideToNetworkPrefab.ContainsKey(GlobalObjectIdHash))
                 {
                     return NetworkManager.NetworkConfig.OverrideToNetworkPrefab[GlobalObjectIdHash];
                 }

Runtime/Core/SnapshotRTT.cs

@@ -1,93 +0,0 @@
-using System;
-
-namespace Unity.Netcode
-{
-    internal class ConnectionRtt
-    {
-        private double[] m_RttSendTimes; // times at which packet were sent for RTT computations
-        private int[] m_SendSequence; // tick, or other key, at which packets were sent (to allow matching)
-        private double[] m_MeasuredLatencies; // measured latencies (ring buffer)
-        private int m_LatenciesBegin = 0; // ring buffer begin
-        private int m_LatenciesEnd = 0; // ring buffer end
-
-        /// <summary>
-        /// Round-trip-time data
-        /// </summary>
-        public struct Rtt
-        {
-            public double BestSec; // best RTT
-            public double AverageSec; // average RTT
-            public double WorstSec; // worst RTT
-            public double LastSec; // latest ack'ed RTT
-            public int SampleCount; // number of contributing samples
-        }
-
-        public ConnectionRtt()
-        {
-            m_RttSendTimes = new double[NetworkConfig.RttWindowSize];
-            m_SendSequence = new int[NetworkConfig.RttWindowSize];
-            m_MeasuredLatencies = new double[NetworkConfig.RttWindowSize];
-        }
-
-        /// <summary>
-        /// Returns the Round-trip-time computation for this client
-        /// </summary>
-        public Rtt GetRtt()
-        {
-            var ret = new Rtt();
-            var index = m_LatenciesBegin;
-            double total = 0.0;
-            ret.BestSec = m_MeasuredLatencies[m_LatenciesBegin];
-            ret.WorstSec = m_MeasuredLatencies[m_LatenciesBegin];
-
-            while (index != m_LatenciesEnd)
-            {
-                total += m_MeasuredLatencies[index];
-                ret.SampleCount++;
-                ret.BestSec = Math.Min(ret.BestSec, m_MeasuredLatencies[index]);
-                ret.WorstSec = Math.Max(ret.WorstSec, m_MeasuredLatencies[index]);
-                index = (index + 1) % NetworkConfig.RttAverageSamples;
-            }
-
-            if (ret.SampleCount != 0)
-            {
-                ret.AverageSec = total / ret.SampleCount;
-                // the latest RTT is one before m_LatenciesEnd
-                ret.LastSec = m_MeasuredLatencies[(m_LatenciesEnd + (NetworkConfig.RttWindowSize - 1)) % NetworkConfig.RttWindowSize];
-            }
-            else
-            {
-                ret.AverageSec = 0;
-                ret.BestSec = 0;
-                ret.WorstSec = 0;
-                ret.SampleCount = 0;
-                ret.LastSec = 0;
-            }
-
-            return ret;
-        }
-
-        internal void NotifySend(int sequence, double timeSec)
-        {
-            m_RttSendTimes[sequence % NetworkConfig.RttWindowSize] = timeSec;
-            m_SendSequence[sequence % NetworkConfig.RttWindowSize] = sequence;
-        }
-
-        internal void NotifyAck(int sequence, double timeSec)
-        {
-            // if the same slot was not used by a later send
-            if (m_SendSequence[sequence % NetworkConfig.RttWindowSize] == sequence)
-            {
-                double latency = timeSec - m_RttSendTimes[sequence % NetworkConfig.RttWindowSize];
-
-                m_MeasuredLatencies[m_LatenciesEnd] = latency;
-                m_LatenciesEnd = (m_LatenciesEnd + 1) % NetworkConfig.RttAverageSamples;
-
-                if (m_LatenciesEnd == m_LatenciesBegin)
-                {
-                    m_LatenciesBegin = (m_LatenciesBegin + 1) % NetworkConfig.RttAverageSamples;
-                }
-            }
-        }
-    }
-}

Runtime/Core/SnapshotSystem.cs.meta

@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: c275febadb27c4d18b41218e3353b84b
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Logging/NetworkLog.cs

@@ -14,9 +14,9 @@ namespace Unity.Netcode
         public static LogLevel CurrentLogLevel => NetworkManager.Singleton == null ? LogLevel.Normal : NetworkManager.Singleton.LogLevel;
 
         // internal logging
-        internal static void LogInfo(string message) => Debug.Log($"[Netcode] {message}");
-        internal static void LogWarning(string message) => Debug.LogWarning($"[Netcode] {message}");
-        internal static void LogError(string message) => Debug.LogError($"[Netcode] {message}");
+        public static void LogInfo(string message) => Debug.Log($"[Netcode] {message}");
+        public static void LogWarning(string message) => Debug.LogWarning($"[Netcode] {message}");
+        public static void LogError(string message) => Debug.LogError($"[Netcode] {message}");
 
         /// <summary>
         /// Logs an info log locally and on the server if possible.
@@ -62,10 +62,9 @@ namespace Unity.Netcode
                     LogType = logType,
                     Message = message
                 };
-                var size = NetworkManager.Singleton.SendMessage(networkMessage, NetworkDelivery.ReliableFragmentedSequenced,
-                    NetworkManager.Singleton.ServerClientId);
+                var size = NetworkManager.Singleton.SendMessage(ref networkMessage, NetworkDelivery.ReliableFragmentedSequenced, NetworkManager.ServerClientId);
 
-                NetworkManager.Singleton.NetworkMetrics.TrackServerLogSent(NetworkManager.Singleton.ServerClientId, (uint)logType, size);
+                NetworkManager.Singleton.NetworkMetrics.TrackServerLogSent(NetworkManager.ServerClientId, (uint)logType, size);
             }
         }
 

Runtime/Messaging/CustomMessageManager.cs

@@ -28,7 +28,7 @@ namespace Unity.Netcode
         /// </summary>
         public event UnnamedMessageDelegate OnUnnamedMessage;
 
-        internal void InvokeUnnamedMessage(ulong clientId, FastBufferReader reader)
+        internal void InvokeUnnamedMessage(ulong clientId, FastBufferReader reader, int serializedHeaderSize)
         {
             if (OnUnnamedMessage != null)
             {
@@ -40,7 +40,7 @@ namespace Unity.Netcode
                     ((UnnamedMessageDelegate)handler).Invoke(clientId, reader);
                 }
             }
-            m_NetworkManager.NetworkMetrics.TrackUnnamedMessageReceived(clientId, reader.Length);
+            m_NetworkManager.NetworkMetrics.TrackUnnamedMessageReceived(clientId, reader.Length + serializedHeaderSize);
         }
 
         /// <summary>
@@ -53,7 +53,6 @@ namespace Unity.Netcode
             SendUnnamedMessage(m_NetworkManager.ConnectedClientsIds, messageBuffer, networkDelivery);
         }
 
-
         /// <summary>
         /// Sends unnamed message to a list of clients
         /// </summary>
@@ -74,9 +73,9 @@ namespace Unity.Netcode
 
             var message = new UnnamedMessage
             {
-                Data = messageBuffer
+                SendData = messageBuffer
             };
-            var size = m_NetworkManager.SendMessage(message, networkDelivery, clientIds);
+            var size = m_NetworkManager.SendMessage(ref message, networkDelivery, clientIds);
 
             // Size is zero if we were only sending the message to ourself in which case it isn't sent.
             if (size != 0)
@@ -95,9 +94,9 @@ namespace Unity.Netcode
         {
             var message = new UnnamedMessage
             {
-                Data = messageBuffer
+                SendData = messageBuffer
             };
-            var size = m_NetworkManager.SendMessage(message, networkDelivery, clientId);
+            var size = m_NetworkManager.SendMessage(ref message, networkDelivery, clientId);
             // Size is zero if we were only sending the message to ourself in which case it isn't sent.
             if (size != 0)
             {
@@ -116,9 +115,9 @@ namespace Unity.Netcode
         private Dictionary<ulong, string> m_MessageHandlerNameLookup32 = new Dictionary<ulong, string>();
         private Dictionary<ulong, string> m_MessageHandlerNameLookup64 = new Dictionary<ulong, string>();
 
-        internal void InvokeNamedMessage(ulong hash, ulong sender, FastBufferReader reader)
+        internal void InvokeNamedMessage(ulong hash, ulong sender, FastBufferReader reader, int serializedHeaderSize)
         {
-            var bytesCount = reader.Length;
+            var bytesCount = reader.Length + serializedHeaderSize;
 
             if (m_NetworkManager == null)
             {
@@ -224,9 +223,9 @@ namespace Unity.Netcode
             var message = new NamedMessage
             {
                 Hash = hash,
-                Data = messageStream
+                SendData = messageStream,
             };
-            var size = m_NetworkManager.SendMessage(message, networkDelivery, clientId);
+            var size = m_NetworkManager.SendMessage(ref message, networkDelivery, clientId);
 
             // Size is zero if we were only sending the message to ourself in which case it isn't sent.
             if (size != 0)
@@ -267,9 +266,9 @@ namespace Unity.Netcode
             var message = new NamedMessage
             {
                 Hash = hash,
-                Data = messageStream
+                SendData = messageStream
             };
-            var size = m_NetworkManager.SendMessage(message, networkDelivery, clientIds);
+            var size = m_NetworkManager.SendMessage(ref message, networkDelivery, clientIds);
 
             // Size is zero if we were only sending the message to ourself in which case it isn't sent.
             if (size != 0)

Runtime/Messaging/INetworkHooks.cs

@@ -13,18 +13,18 @@ namespace Unity.Netcode
         /// Called before an individual message is sent.
         /// </summary>
         /// <param name="clientId">The destination clientId</param>
-        /// <param name="messageType">The type of the message being sent</param>
+        /// <param name="message">The message being sent</param>
         /// <param name="delivery"></param>
-        void OnBeforeSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery);
+        void OnBeforeSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery) where T : INetworkMessage;
 
         /// <summary>
         /// Called after an individual message is sent.
         /// </summary>
         /// <param name="clientId">The destination clientId</param>
-        /// <param name="messageType">The type of the message being sent</param>
+        /// <param name="message">The message being sent</param>
         /// <param name="delivery"></param>
         /// <param name="messageSizeBytes">Number of bytes in the message, not including the message header</param>
-        void OnAfterSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery, int messageSizeBytes);
+        void OnAfterSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery, int messageSizeBytes) where T : INetworkMessage;
 
         /// <summary>
         /// Called before an individual message is received.
@@ -93,5 +93,23 @@ namespace Unity.Netcode
         /// <param name="messageType">The type of the message</param>
         /// <returns></returns>
         bool OnVerifyCanReceive(ulong senderId, Type messageType);
+
+        /// <summary>
+        /// Called after a message is serialized, but before it's handled.
+        /// Differs from OnBeforeReceiveMessage in that the actual message object is passed and can be inspected.
+        /// </summary>
+        /// <param name="message">The message object</param>
+        /// <param name="context">The network context the message is being ahandled in</param>
+        /// <typeparam name="T"></typeparam>
+        void OnBeforeHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage;
+
+        /// <summary>
+        /// Called after a message is serialized and handled.
+        /// Differs from OnAfterReceiveMessage in that the actual message object is passed and can be inspected.
+        /// </summary>
+        /// <param name="message">The message object</param>
+        /// <param name="context">The network context the message is being ahandled in</param>
+        /// <typeparam name="T"></typeparam>
+        void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage;
     }
 }

Runtime/Messaging/INetworkMessage.cs

@@ -15,7 +15,7 @@ namespace Unity.Netcode
     /// static message handler for receiving messages of the following name and signature:
     ///
     /// <code>
-    /// public static void Receive(FastBufferReader reader, in NetworkContext context)
+    /// public static void Receive(FastBufferReader reader, ref NetworkContext context)
     /// </code>
     ///
     /// It is the responsibility of the Serialize and Receive methods to ensure there is enough buffer space
@@ -40,10 +40,8 @@ namespace Unity.Netcode
     /// </summary>
     internal interface INetworkMessage
     {
-        /// <summary>
-        /// Used to serialize the message.
-        /// </summary>
-        /// <param name="writer"></param>
         void Serialize(FastBufferWriter writer);
+        bool Deserialize(FastBufferReader reader, ref NetworkContext context);
+        void Handle(ref NetworkContext context);
     }
 }

Runtime/Messaging/MessageHeader.cs

@@ -11,11 +11,12 @@ namespace Unity.Netcode
         /// unchanged - if new messages are added or messages are removed, MessageType assignments may be
         /// calculated differently.
         /// </summary>
-        public byte MessageType;
+        public uint MessageType;
 
         /// <summary>
         /// The total size of the message, NOT including the header.
+        /// Stored as a uint to avoid zig-zag encoding, but capped at int.MaxValue.
         /// </summary>
-        public ushort MessageSize;
+        public uint MessageSize;
     }
 }

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -10,40 +10,53 @@ namespace Unity.Netcode
             writer.WriteValueSafe(this);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
-            reader.ReadValueSafe(out ChangeOwnershipMessage message);
-            message.Handle(reader, context, context.SenderId, networkManager, reader.Length);
+            reader.ReadValueSafe(out this);
+            if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
+            {
+                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, ref context);
+                return false;
+            }
+
+            return true;
         }
 
-        public void Handle(FastBufferReader reader, in NetworkContext context, ulong senderId, NetworkManager networkManager, int messageSize)
+        public void Handle(ref NetworkContext context)
         {
-            if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
-            {
-                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, context);
-                return;
-            }
-
-            if (networkObject.OwnerClientId == networkManager.LocalClientId)
-            {
-                //We are current owner.
-                networkObject.InvokeBehaviourOnLostOwnership();
-            }
+            var networkManager = (NetworkManager)context.SystemOwner;
+            var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
+            var originalOwner = networkObject.OwnerClientId;
 
             networkObject.OwnerClientId = OwnerClientId;
 
+            // We are current owner.
+            if (originalOwner == networkManager.LocalClientId)
+            {
+                networkObject.InvokeBehaviourOnLostOwnership();
+            }
+
+            // We are new owner.
             if (OwnerClientId == networkManager.LocalClientId)
             {
-                //We are new owner.
                 networkObject.InvokeBehaviourOnGainedOwnership();
             }
 
-            networkManager.NetworkMetrics.TrackOwnershipChangeReceived(senderId, networkObject, messageSize);
+            // For all other clients that are neither the former or current owner, update the behaviours' properties
+            if (OwnerClientId != networkManager.LocalClientId && originalOwner != networkManager.LocalClientId)
+            {
+                for (int i = 0; i < networkObject.ChildNetworkBehaviours.Count; i++)
+                {
+                    networkObject.ChildNetworkBehaviours[i].UpdateNetworkProperties();
+                }
+            }
+
+            networkManager.NetworkMetrics.TrackOwnershipChangeReceived(context.SenderId, networkObject, context.MessageSize);
         }
     }
 }

Runtime/Messaging/Messages/ConnectionApprovedMessage.cs

@@ -7,24 +7,27 @@ namespace Unity.Netcode
     {
         public ulong OwnerClientId;
         public int NetworkTick;
-        public int SceneObjectCount;
 
         // Not serialized, held as references to serialize NetworkVariable data
         public HashSet<NetworkObject> SpawnedObjectsList;
 
+        private FastBufferReader m_ReceivedSceneObjectData;
+
         public void Serialize(FastBufferWriter writer)
         {
             if (!writer.TryBeginWrite(sizeof(ulong) + sizeof(int) + sizeof(int)))
             {
-                throw new OverflowException(
-                    $"Not enough space in the write buffer to serialize {nameof(ConnectionApprovedMessage)}");
+                throw new OverflowException($"Not enough space in the write buffer to serialize {nameof(ConnectionApprovedMessage)}");
             }
             writer.WriteValue(OwnerClientId);
             writer.WriteValue(NetworkTick);
-            writer.WriteValue(SceneObjectCount);
 
-            if (SceneObjectCount != 0)
+            uint sceneObjectCount = 0;
+            if (SpawnedObjectsList != null)
             {
+                var pos = writer.Position;
+                writer.Seek(writer.Position + FastBufferWriter.GetWriteSize(sceneObjectCount));
+
                 // Serialize NetworkVariable data
                 foreach (var sobj in SpawnedObjectsList)
                 {
@@ -33,34 +36,41 @@ namespace Unity.Netcode
                         sobj.Observers.Add(OwnerClientId);
                         var sceneObject = sobj.GetMessageSceneObject(OwnerClientId);
                         sceneObject.Serialize(writer);
+                        ++sceneObjectCount;
                     }
                 }
+                writer.Seek(pos);
+                writer.WriteValue(sceneObjectCount);
+                writer.Seek(writer.Length);
+            }
+            else
+            {
+                writer.WriteValue(sceneObjectCount);
             }
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
 
             if (!reader.TryBeginRead(sizeof(ulong) + sizeof(int) + sizeof(int)))
             {
-                throw new OverflowException(
-                    $"Not enough space in the buffer to read {nameof(ConnectionApprovedMessage)}");
+                throw new OverflowException($"Not enough space in the buffer to read {nameof(ConnectionApprovedMessage)}");
             }
 
-            var message = new ConnectionApprovedMessage();
-            reader.ReadValue(out message.OwnerClientId);
-            reader.ReadValue(out message.NetworkTick);
-            reader.ReadValue(out message.SceneObjectCount);
-            message.Handle(reader, context.SenderId, networkManager);
+            reader.ReadValue(out OwnerClientId);
+            reader.ReadValue(out NetworkTick);
+            m_ReceivedSceneObjectData = reader;
+            return true;
         }
 
-        public void Handle(FastBufferReader reader, ulong clientId, NetworkManager networkManager)
+        public void Handle(ref NetworkContext context)
         {
+            var networkManager = (NetworkManager)context.SystemOwner;
             networkManager.LocalClientId = OwnerClientId;
             networkManager.NetworkMetrics.SetConnectionId(networkManager.LocalClientId);
 
@@ -74,20 +84,21 @@ namespace Unity.Netcode
             if (!networkManager.NetworkConfig.EnableSceneManagement)
             {
                 networkManager.SpawnManager.DestroySceneObjects();
+                m_ReceivedSceneObjectData.ReadValue(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.
-                for (ushort i = 0; i < SceneObjectCount; i++)
+                for (ushort i = 0; i < sceneObjectCount; i++)
                 {
                     var sceneObject = new NetworkObject.SceneObject();
-                    sceneObject.Deserialize(reader);
-                    NetworkObject.AddSceneObject(sceneObject, reader, networkManager);
+                    sceneObject.Deserialize(m_ReceivedSceneObjectData);
+                    NetworkObject.AddSceneObject(sceneObject, m_ReceivedSceneObjectData, networkManager);
                 }
 
                 // Mark the client being connected
                 networkManager.IsConnectedClient = true;
                 // When scene management is disabled we notify after everything is synchronized
-                networkManager.InvokeOnClientConnectedCallback(clientId);
+                networkManager.InvokeOnClientConnectedCallback(context.SenderId);
             }
         }
     }

Runtime/Messaging/Messages/ConnectionRequestMessage.cs

@@ -21,19 +21,17 @@ namespace Unity.Netcode
             }
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsServer)
             {
-                return;
+                return false;
             }
 
-            var message = new ConnectionRequestMessage();
             if (networkManager.NetworkConfig.ConnectionApproval)
             {
-                if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(message.ConfigHash) +
-                                         FastBufferWriter.GetWriteSize<int>()))
+                if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(ConfigHash) + FastBufferWriter.GetWriteSize<int>()))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -41,11 +39,12 @@ namespace Unity.Netcode
                     }
 
                     networkManager.DisconnectClient(context.SenderId);
-                    return;
+                    return false;
                 }
-                reader.ReadValue(out message.ConfigHash);
 
-                if (!networkManager.NetworkConfig.CompareConfig(message.ConfigHash))
+                reader.ReadValue(out ConfigHash);
+
+                if (!networkManager.NetworkConfig.CompareConfig(ConfigHash))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -53,14 +52,14 @@ namespace Unity.Netcode
                     }
 
                     networkManager.DisconnectClient(context.SenderId);
-                    return;
+                    return false;
                 }
 
-                reader.ReadValueSafe(out message.ConnectionData);
+                reader.ReadValueSafe(out ConnectionData);
             }
             else
             {
-                if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(message.ConfigHash)))
+                if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(ConfigHash)))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -68,11 +67,11 @@ namespace Unity.Netcode
                     }
 
                     networkManager.DisconnectClient(context.SenderId);
-                    return;
+                    return false;
                 }
-                reader.ReadValue(out message.ConfigHash);
+                reader.ReadValue(out ConfigHash);
 
-                if (!networkManager.NetworkConfig.CompareConfig(message.ConfigHash))
+                if (!networkManager.NetworkConfig.CompareConfig(ConfigHash))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -80,14 +79,18 @@ namespace Unity.Netcode
                     }
 
                     networkManager.DisconnectClient(context.SenderId);
-                    return;
+                    return false;
                 }
             }
-            message.Handle(networkManager, context.SenderId);
+
+            return true;
         }
 
-        public void Handle(NetworkManager networkManager, ulong senderId)
+        public void Handle(ref NetworkContext context)
         {
+            var networkManager = (NetworkManager)context.SystemOwner;
+            var senderId = context.SenderId;
+
             if (networkManager.PendingClients.TryGetValue(senderId, out PendingClient client))
             {
                 // Set to pending approval to prevent future connection requests from being approved
@@ -102,8 +105,7 @@ namespace Unity.Netcode
                     (createPlayerObject, playerPrefabHash, approved, position, rotation) =>
                     {
                         var localCreatePlayerObject = createPlayerObject;
-                        networkManager.HandleApproval(senderId, localCreatePlayerObject, playerPrefabHash, approved,
-                            position, rotation);
+                        networkManager.HandleApproval(senderId, localCreatePlayerObject, playerPrefabHash, approved, position, rotation);
                     });
             }
             else

Runtime/Messaging/Messages/CreateObjectMessage.cs

@@ -3,28 +3,33 @@ namespace Unity.Netcode
     internal struct CreateObjectMessage : INetworkMessage
     {
         public NetworkObject.SceneObject ObjectInfo;
+        private FastBufferReader m_ReceivedNetworkVariableData;
 
         public void Serialize(FastBufferWriter writer)
         {
             ObjectInfo.Serialize(writer);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
-            var message = new CreateObjectMessage();
-            message.ObjectInfo.Deserialize(reader);
-            message.Handle(context.SenderId, reader, networkManager);
+
+            ObjectInfo.Deserialize(reader);
+            m_ReceivedNetworkVariableData = reader;
+
+            return true;
         }
 
-        public void Handle(ulong senderId, FastBufferReader reader, NetworkManager networkManager)
+        public void Handle(ref NetworkContext context)
         {
-            var networkObject = NetworkObject.AddSceneObject(ObjectInfo, reader, networkManager);
-            networkManager.NetworkMetrics.TrackObjectSpawnReceived(senderId, networkObject, reader.Length);
+            var networkManager = (NetworkManager)context.SystemOwner;
+            var networkObject = NetworkObject.AddSceneObject(ObjectInfo, m_ReceivedNetworkVariableData, networkManager);
+
+            networkManager.NetworkMetrics.TrackObjectSpawnReceived(context.SenderId, networkObject, context.MessageSize);
         }
     }
 }

Runtime/Messaging/Messages/DestroyObjectMessage.cs

@@ -9,32 +9,27 @@ namespace Unity.Netcode
             writer.WriteValueSafe(this);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
-            reader.ReadValueSafe(out DestroyObjectMessage message);
-            message.Handle(context.SenderId, networkManager, reader.Length);
+            reader.ReadValueSafe(out this);
+            return true;
         }
 
-        public void Handle(ulong senderId, NetworkManager networkManager, int messageSize)
+        public void Handle(ref NetworkContext context)
         {
+            var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
             {
                 // This is the same check and log message that happens inside OnDespawnObject, but we have to do it here
-                // while we still have access to the network ID, otherwise the log message will be less useful.
-                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                {
-                    NetworkLog.LogWarning($"Trying to destroy {nameof(NetworkObject)} #{NetworkObjectId} but it does not exist in {nameof(NetworkSpawnManager.SpawnedObjects)} anymore!");
-                }
-
                 return;
             }
 
-            networkManager.NetworkMetrics.TrackObjectDestroyReceived(senderId, networkObject, messageSize);
+            networkManager.NetworkMetrics.TrackObjectDestroyReceived(context.SenderId, networkObject, context.MessageSize);
             networkManager.SpawnManager.OnDespawnObject(networkObject, true);
         }
     }

Runtime/Messaging/Messages/NamedMessage.cs

@@ -3,20 +3,26 @@ namespace Unity.Netcode
     internal struct NamedMessage : INetworkMessage
     {
         public ulong Hash;
-        public FastBufferWriter Data;
+        public FastBufferWriter SendData;
+
+        private FastBufferReader m_ReceiveData;
 
         public unsafe void Serialize(FastBufferWriter writer)
         {
             writer.WriteValueSafe(Hash);
-            writer.WriteBytesSafe(Data.GetUnsafePtr(), Data.Length);
+            writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
-            var message = new NamedMessage();
-            reader.ReadValueSafe(out message.Hash);
+            reader.ReadValueSafe(out Hash);
+            m_ReceiveData = reader;
+            return true;
+        }
 
-            ((NetworkManager)context.SystemOwner).CustomMessagingManager.InvokeNamedMessage(message.Hash, context.SenderId, reader);
+        public void Handle(ref NetworkContext context)
+        {
+            ((NetworkManager)context.SystemOwner).CustomMessagingManager.InvokeNamedMessage(Hash, context.SenderId, m_ReceiveData, context.SerializedHeaderSize);
         }
     }
 }

Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

@@ -16,27 +16,29 @@ namespace Unity.Netcode
         public ushort NetworkBehaviourIndex;
 
         public HashSet<int> DeliveryMappedNetworkVariableIndex;
-        public ulong ClientId;
+        public ulong TargetClientId;
         public NetworkBehaviour NetworkBehaviour;
 
+        private FastBufferReader m_ReceivedNetworkVariableData;
+
         public void Serialize(FastBufferWriter writer)
         {
-            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(NetworkObjectId) +
-                                      FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
+            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
             {
-                throw new OverflowException(
-                    $"Not enough space in the buffer to write {nameof(NetworkVariableDeltaMessage)}");
+                throw new OverflowException($"Not enough space in the buffer to write {nameof(NetworkVariableDeltaMessage)}");
             }
+
             writer.WriteValue(NetworkObjectId);
             writer.WriteValue(NetworkBehaviourIndex);
-            for (int k = 0; k < NetworkBehaviour.NetworkVariableFields.Count; k++)
+
+            for (int i = 0; i < NetworkBehaviour.NetworkVariableFields.Count; i++)
             {
-                if (!DeliveryMappedNetworkVariableIndex.Contains(k))
+                if (!DeliveryMappedNetworkVariableIndex.Contains(i))
                 {
                     // This var does not belong to the currently iterating delivery group.
                     if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
-                        writer.WriteValueSafe((short)0);
+                        writer.WriteValueSafe((ushort)0);
                     }
                     else
                     {
@@ -46,15 +48,17 @@ namespace Unity.Netcode
                     continue;
                 }
 
-                //   if I'm dirty AND a client, write (server always has all permissions)
-                //   if I'm dirty AND the server AND the client can read me, send.
-                bool shouldWrite = NetworkBehaviour.NetworkVariableFields[k].ShouldWrite(ClientId, NetworkBehaviour.NetworkManager.IsServer);
+                var startingSize = writer.Length;
+                var networkVariable = NetworkBehaviour.NetworkVariableFields[i];
+                var shouldWrite = networkVariable.IsDirty() &&
+                    networkVariable.CanClientRead(TargetClientId) &&
+                    (NetworkBehaviour.NetworkManager.IsServer || networkVariable.CanClientWrite(NetworkBehaviour.NetworkManager.LocalClientId));
 
                 if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     if (!shouldWrite)
                     {
-                        writer.WriteValueSafe((ushort)0);
+                        BytePacker.WriteValueBitPacked(writer, 0);
                     }
                 }
                 else
@@ -66,56 +70,62 @@ namespace Unity.Netcode
                 {
                     if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
-                        var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, short.MaxValue);
-                        NetworkBehaviour.NetworkVariableFields[k].WriteDelta(tmpWriter);
+                        var tempWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, MessagingSystem.FRAGMENTED_MESSAGE_MAX_SIZE);
+                        NetworkBehaviour.NetworkVariableFields[i].WriteDelta(tempWriter);
+                        BytePacker.WriteValueBitPacked(writer, tempWriter.Length);
 
-                        writer.WriteValueSafe((ushort)tmpWriter.Length);
-                        tmpWriter.CopyTo(writer);
+                        if (!writer.TryBeginWrite(tempWriter.Length))
+                        {
+                            throw new OverflowException($"Not enough space in the buffer to write {nameof(NetworkVariableDeltaMessage)}");
+                        }
+
+                        tempWriter.CopyTo(writer);
                     }
                     else
                     {
-                        NetworkBehaviour.NetworkVariableFields[k].WriteDelta(writer);
+                        networkVariable.WriteDelta(writer);
                     }
 
-                    if (!NetworkBehaviour.NetworkVariableIndexesToResetSet.Contains(k))
+                    if (!NetworkBehaviour.NetworkVariableIndexesToResetSet.Contains(i))
                     {
-                        NetworkBehaviour.NetworkVariableIndexesToResetSet.Add(k);
-                        NetworkBehaviour.NetworkVariableIndexesToReset.Add(k);
+                        NetworkBehaviour.NetworkVariableIndexesToResetSet.Add(i);
+                        NetworkBehaviour.NetworkVariableIndexesToReset.Add(i);
                     }
 
                     NetworkBehaviour.NetworkManager.NetworkMetrics.TrackNetworkVariableDeltaSent(
-                        ClientId,
+                        TargetClientId,
                         NetworkBehaviour.NetworkObject,
-                        NetworkBehaviour.NetworkVariableFields[k].Name,
+                        networkVariable.Name,
                         NetworkBehaviour.__getTypeName(),
-                        writer.Length);
+                        writer.Length - startingSize);
                 }
             }
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        {
+            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(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;
+
+            return true;
+        }
+
+        public void Handle(ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
 
-            var message = new NetworkVariableDeltaMessage();
-            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(message.NetworkObjectId) +
-                                      FastBufferWriter.GetWriteSize(message.NetworkBehaviourIndex)))
-            {
-                throw new OverflowException(
-                    $"Not enough data in the buffer to read {nameof(NetworkVariableDeltaMessage)}");
-            }
-            reader.ReadValue(out message.NetworkObjectId);
-            reader.ReadValue(out message.NetworkBehaviourIndex);
-            message.Handle(context.SenderId, reader, context, networkManager);
-        }
-
-        public void Handle(ulong senderId, FastBufferReader reader, in NetworkContext context, NetworkManager networkManager)
-        {
             if (networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out NetworkObject networkObject))
             {
-                NetworkBehaviour behaviour = networkObject.GetNetworkBehaviourAtOrderIndex(NetworkBehaviourIndex);
+                var networkBehaviour = networkObject.GetNetworkBehaviourAtOrderIndex(NetworkBehaviourIndex);
 
-                if (behaviour == null)
+                if (networkBehaviour == null)
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -124,13 +134,12 @@ namespace Unity.Netcode
                 }
                 else
                 {
-                    for (int i = 0; i < behaviour.NetworkVariableFields.Count; i++)
+                    for (int i = 0; i < networkBehaviour.NetworkVariableFields.Count; i++)
                     {
-                        ushort varSize = 0;
-
+                        int varSize = 0;
                         if (networkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                         {
-                            reader.ReadValueSafe(out varSize);
+                            ByteUnpacker.ReadValueBitPacked(m_ReceivedNetworkVariableData, out varSize);
 
                             if (varSize == 0)
                             {
@@ -139,25 +148,27 @@ namespace Unity.Netcode
                         }
                         else
                         {
-                            reader.ReadValueSafe(out bool deltaExists);
+                            m_ReceivedNetworkVariableData.ReadValueSafe(out bool deltaExists);
                             if (!deltaExists)
                             {
                                 continue;
                             }
                         }
 
-                        if (networkManager.IsServer)
+                        var networkVariable = networkBehaviour.NetworkVariableFields[i];
+
+                        if (networkManager.IsServer && !networkVariable.CanClientWrite(context.SenderId))
                         {
                             // we are choosing not to fire an exception here, because otherwise a malicious client could use this to crash the server
                             if (networkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                             {
-                                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                                if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                                 {
-                                    NetworkLog.LogWarning($"Client wrote to {typeof(NetworkVariable<>).Name} without permission. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(behaviour)} - VariableIndex: {i}");
-                                    NetworkLog.LogError($"[{behaviour.NetworkVariableFields[i].GetType().Name}]");
+                                    NetworkLog.LogWarning($"Client wrote to {typeof(NetworkVariable<>).Name} without permission. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(networkBehaviour)} - VariableIndex: {i}");
+                                    NetworkLog.LogError($"[{networkVariable.GetType().Name}]");
                                 }
 
-                                reader.Seek(reader.Position + varSize);
+                                m_ReceivedNetworkVariableData.Seek(m_ReceivedNetworkVariableData.Position + varSize);
                                 continue;
                             }
 
@@ -168,47 +179,45 @@ namespace Unity.Netcode
                             //A dummy read COULD be added to the interface for this situation, but it's just being too nice.
                             //This is after all a developer fault. A critical error should be fine.
                             // - TwoTen
-                            if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Developer)
                             {
-                                NetworkLog.LogError($"Client wrote to {typeof(NetworkVariable<>).Name} without permission. No more variables can be read. This is critical. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(behaviour)} - VariableIndex: {i}");
-                                NetworkLog.LogError($"[{behaviour.NetworkVariableFields[i].GetType().Name}]");
+                                NetworkLog.LogError($"Client wrote to {typeof(NetworkVariable<>).Name} without permission. No more variables can be read. This is critical. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(networkBehaviour)} - VariableIndex: {i}");
+                                NetworkLog.LogError($"[{networkVariable.GetType().Name}]");
                             }
 
                             return;
                         }
-                        int readStartPos = reader.Position;
+                        int readStartPos = m_ReceivedNetworkVariableData.Position;
 
-                        behaviour.NetworkVariableFields[i].ReadDelta(reader, networkManager.IsServer);
+                        networkVariable.ReadDelta(m_ReceivedNetworkVariableData, networkManager.IsServer);
 
                         networkManager.NetworkMetrics.TrackNetworkVariableDeltaReceived(
-                            senderId,
+                            context.SenderId,
                             networkObject,
-                            behaviour.NetworkVariableFields[i].Name,
-                            behaviour.__getTypeName(),
-                            reader.Length);
+                            networkVariable.Name,
+                            networkBehaviour.__getTypeName(),
+                            context.MessageSize);
 
 
                         if (networkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                         {
-                            if (reader.Position > (readStartPos + varSize))
+                            if (m_ReceivedNetworkVariableData.Position > (readStartPos + varSize))
                             {
                                 if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                                 {
-                                    NetworkLog.LogWarning(
-                                        $"Var delta read too far. {reader.Position - (readStartPos + varSize)} bytes. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(behaviour)} - VariableIndex: {i}");
+                                    NetworkLog.LogWarning($"Var delta read too far. {m_ReceivedNetworkVariableData.Position - (readStartPos + varSize)} bytes. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(networkBehaviour)} - VariableIndex: {i}");
                                 }
 
-                                reader.Seek(readStartPos + varSize);
+                                m_ReceivedNetworkVariableData.Seek(readStartPos + varSize);
                             }
-                            else if (reader.Position < (readStartPos + varSize))
+                            else if (m_ReceivedNetworkVariableData.Position < (readStartPos + varSize))
                             {
                                 if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                                 {
-                                    NetworkLog.LogWarning(
-                                        $"Var delta read too little. {(readStartPos + varSize) - reader.Position} bytes. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(behaviour)} - VariableIndex: {i}");
+                                    NetworkLog.LogWarning($"Var delta read too little. {readStartPos + varSize - m_ReceivedNetworkVariableData.Position} bytes. => {nameof(NetworkObjectId)}: {NetworkObjectId} - {nameof(NetworkObject.GetNetworkBehaviourOrderIndex)}(): {networkObject.GetNetworkBehaviourOrderIndex(networkBehaviour)} - VariableIndex: {i}");
                                 }
 
-                                reader.Seek(readStartPos + varSize);
+                                m_ReceivedNetworkVariableData.Seek(readStartPos + varSize);
                             }
                         }
                     }
@@ -216,7 +225,7 @@ namespace Unity.Netcode
             }
             else
             {
-                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, context);
+                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, m_ReceivedNetworkVariableData, ref context);
             }
         }
     }

Runtime/Messaging/Messages/ParentSyncMessage.cs

@@ -26,42 +26,41 @@ namespace Unity.Netcode
             }
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
 
-            var message = new ParentSyncMessage();
-            reader.ReadValueSafe(out message.NetworkObjectId);
-            reader.ReadValueSafe(out message.IsReparented);
-            if (message.IsReparented)
+            reader.ReadValueSafe(out NetworkObjectId);
+            reader.ReadValueSafe(out IsReparented);
+            if (IsReparented)
             {
-                reader.ReadValueSafe(out message.IsLatestParentSet);
-                if (message.IsLatestParentSet)
+                reader.ReadValueSafe(out IsLatestParentSet);
+                if (IsLatestParentSet)
                 {
                     reader.ReadValueSafe(out ulong latestParent);
-                    message.LatestParent = latestParent;
+                    LatestParent = latestParent;
                 }
             }
 
-            message.Handle(reader, context, networkManager);
+            if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
+            {
+                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, ref context);
+                return false;
+            }
+
+            return true;
         }
 
-        public void Handle(FastBufferReader reader, in NetworkContext context, NetworkManager networkManager)
+        public void Handle(ref NetworkContext context)
         {
-            if (networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
-            {
-                var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
-                networkObject.SetNetworkParenting(IsReparented, LatestParent);
-                networkObject.ApplyNetworkParenting();
-            }
-            else
-            {
-                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, context);
-            }
+            var networkManager = (NetworkManager)context.SystemOwner;
+            var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
+            networkObject.SetNetworkParenting(IsReparented, LatestParent);
+            networkObject.ApplyNetworkParenting();
         }
     }
 }

Runtime/Messaging/Messages/RpcMessage.cs

@@ -1,109 +0,0 @@
-using System;
-
-namespace Unity.Netcode
-{
-    internal struct RpcMessage : INetworkMessage
-    {
-        public enum RpcType : byte
-        {
-            Server,
-            Client
-        }
-
-        public struct HeaderData
-        {
-            public RpcType Type;
-            public ulong NetworkObjectId;
-            public ushort NetworkBehaviourId;
-            public uint NetworkMethodId;
-        }
-
-        public HeaderData Header;
-        public FastBufferWriter RpcData;
-
-
-        public unsafe void Serialize(FastBufferWriter writer)
-        {
-            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(Header) + RpcData.Length))
-            {
-                throw new OverflowException("Not enough space in the buffer to store RPC data.");
-            }
-            writer.WriteValue(Header);
-            writer.WriteBytes(RpcData.GetUnsafePtr(), RpcData.Length);
-        }
-
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
-        {
-            var message = new RpcMessage();
-            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(message.Header)))
-            {
-                throw new OverflowException("Not enough space in the buffer to read RPC data.");
-            }
-            reader.ReadValue(out message.Header);
-            message.Handle(reader, context, (NetworkManager)context.SystemOwner, context.SenderId, true);
-        }
-
-        public void Handle(FastBufferReader reader, in NetworkContext context, NetworkManager networkManager, ulong senderId, bool canDefer)
-        {
-            if (NetworkManager.__rpc_func_table.ContainsKey(Header.NetworkMethodId))
-            {
-                if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(Header.NetworkObjectId))
-                {
-                    if (canDefer)
-                    {
-                        networkManager.SpawnManager.TriggerOnSpawn(Header.NetworkObjectId, reader, context);
-                    }
-                    else
-                    {
-                        NetworkLog.LogError($"Tried to invoke an RPC on a non-existent {nameof(NetworkObject)} with {nameof(canDefer)}=false");
-                    }
-                    return;
-                }
-
-                var networkObject = networkManager.SpawnManager.SpawnedObjects[Header.NetworkObjectId];
-
-                var networkBehaviour = networkObject.GetNetworkBehaviourAtOrderIndex(Header.NetworkBehaviourId);
-                if (networkBehaviour == null)
-                {
-                    return;
-                }
-
-                var rpcParams = new __RpcParams();
-                switch (Header.Type)
-                {
-                    case RpcType.Server:
-                        rpcParams.Server = new ServerRpcParams
-                        {
-                            Receive = new ServerRpcReceiveParams
-                            {
-                                SenderClientId = senderId
-                            }
-                        };
-                        break;
-                    case RpcType.Client:
-                        rpcParams.Client = new ClientRpcParams
-                        {
-                            Receive = new ClientRpcReceiveParams
-                            {
-                            }
-                        };
-                        break;
-                }
-
-                NetworkManager.__rpc_func_table[Header.NetworkMethodId](networkBehaviour, reader, rpcParams);
-
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
-                if (NetworkManager.__rpc_name_table.TryGetValue(Header.NetworkMethodId, out var rpcMethodName))
-                {
-                    networkManager.NetworkMetrics.TrackRpcReceived(
-                        senderId,
-                        networkObject,
-                        rpcMethodName,
-                        networkBehaviour.__getTypeName(),
-                        reader.Length);
-                }
-#endif
-            }
-        }
-    }
-}

Runtime/Messaging/Messages/RpcMessages.cs

@@ -0,0 +1,157 @@
+using System;
+using UnityEngine;
+using Unity.Collections;
+
+namespace Unity.Netcode
+{
+    internal static class RpcMessageHelpers
+    {
+        public static unsafe void Serialize(ref FastBufferWriter writer, ref RpcMetadata metadata, ref FastBufferWriter payload)
+        {
+            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize<RpcMetadata>() + payload.Length))
+            {
+                throw new OverflowException("Not enough space in the buffer to store RPC data.");
+            }
+
+            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>();
+            if (!reader.TryBeginRead(metadataSize))
+            {
+                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))
+            {
+                networkManager.SpawnManager.TriggerOnSpawn(metadata.NetworkObjectId, reader, ref context);
+                return false;
+            }
+
+            var networkObject = networkManager.SpawnManager.SpawnedObjects[metadata.NetworkObjectId];
+            var networkBehaviour = networkManager.SpawnManager.SpawnedObjects[metadata.NetworkObjectId].GetNetworkBehaviourAtOrderIndex(metadata.NetworkBehaviourId);
+            if (networkBehaviour == null)
+            {
+                return false;
+            }
+
+            if (!NetworkManager.__rpc_func_table.ContainsKey(metadata.NetworkRpcMethodId))
+            {
+                return false;
+            }
+
+            payload = new FastBufferReader(reader.GetUnsafePtr() + metadataSize, Allocator.None, reader.Length - metadataSize);
+
+#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            if (NetworkManager.__rpc_name_table.TryGetValue(metadata.NetworkRpcMethodId, out var rpcMethodName))
+            {
+                networkManager.NetworkMetrics.TrackRpcReceived(
+                    context.SenderId,
+                    networkObject,
+                    rpcMethodName,
+                    networkBehaviour.__getTypeName(),
+                    reader.Length);
+            }
+#endif
+
+            return true;
+        }
+
+        public static void Handle(ref NetworkContext context, ref RpcMetadata metadata, ref FastBufferReader payload, ref __RpcParams rpcParams)
+        {
+            var networkManager = (NetworkManager)context.SystemOwner;
+            if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(metadata.NetworkObjectId, out var networkObject))
+            {
+                throw new InvalidOperationException($"An RPC called on a {nameof(NetworkObject)} that is not in the spawned objects list. Please make sure the {nameof(NetworkObject)} is spawned before calling RPCs.");
+            }
+            var networkBehaviour = networkObject.GetNetworkBehaviourAtOrderIndex(metadata.NetworkBehaviourId);
+
+            try
+            {
+                NetworkManager.__rpc_func_table[metadata.NetworkRpcMethodId](networkBehaviour, payload, rpcParams);
+            }
+            catch (Exception ex)
+            {
+                Debug.LogException(new Exception("Unhandled RPC exception!", ex));
+            }
+        }
+    }
+
+    internal struct RpcMetadata
+    {
+        public ulong NetworkObjectId;
+        public ushort NetworkBehaviourId;
+        public uint NetworkRpcMethodId;
+    }
+
+    internal struct ServerRpcMessage : INetworkMessage
+    {
+        public RpcMetadata Metadata;
+
+        public FastBufferWriter WriteBuffer;
+        public FastBufferReader ReadBuffer;
+
+        public unsafe void Serialize(FastBufferWriter writer)
+        {
+            RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
+        }
+
+        public unsafe bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        {
+            return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            var rpcParams = new __RpcParams
+            {
+                Server = new ServerRpcParams
+                {
+                    Receive = new ServerRpcReceiveParams
+                    {
+                        SenderClientId = context.SenderId
+                    }
+                }
+            };
+            RpcMessageHelpers.Handle(ref context, ref Metadata, ref ReadBuffer, ref rpcParams);
+        }
+    }
+
+    internal struct ClientRpcMessage : INetworkMessage
+    {
+        public RpcMetadata Metadata;
+
+        public FastBufferWriter WriteBuffer;
+        public FastBufferReader ReadBuffer;
+
+        public void Serialize(FastBufferWriter writer)
+        {
+            RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
+        }
+
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        {
+            return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            var rpcParams = new __RpcParams
+            {
+                Client = new ClientRpcParams
+                {
+                    Receive = new ClientRpcReceiveParams
+                    {
+                    }
+                }
+            };
+            RpcMessageHelpers.Handle(ref context, ref Metadata, ref ReadBuffer, ref rpcParams);
+        }
+    }
+}

Runtime/Messaging/Messages/SceneEventMessage.cs

@@ -6,14 +6,22 @@ namespace Unity.Netcode
     {
         public SceneEventData EventData;
 
+        private FastBufferReader m_ReceivedData;
+
         public void Serialize(FastBufferWriter writer)
         {
             EventData.Serialize(writer);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
-            ((NetworkManager)context.SystemOwner).SceneManager.HandleSceneEvent(context.SenderId, reader);
+            m_ReceivedData = reader;
+            return true;
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            ((NetworkManager)context.SystemOwner).SceneManager.HandleSceneEvent(context.SenderId, m_ReceivedData);
         }
     }
 }

Runtime/Messaging/Messages/ServerLogMessage.cs

@@ -17,21 +17,25 @@ namespace Unity.Netcode
             BytePacker.WriteValuePacked(writer, Message);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (networkManager.IsServer && networkManager.NetworkConfig.EnableNetworkLogs)
             {
-                var message = new ServerLogMessage();
-                reader.ReadValueSafe(out message.LogType);
-                ByteUnpacker.ReadValuePacked(reader, out message.Message);
-                message.Handle(context.SenderId, networkManager, reader.Length);
+                reader.ReadValueSafe(out LogType);
+                ByteUnpacker.ReadValuePacked(reader, out Message);
+                return true;
             }
+
+            return false;
         }
 
-        public void Handle(ulong senderId, NetworkManager networkManager, int messageSize)
+        public void Handle(ref NetworkContext context)
         {
-            networkManager.NetworkMetrics.TrackServerLogReceived(senderId, (uint)LogType, messageSize);
+            var networkManager = (NetworkManager)context.SystemOwner;
+            var senderId = context.SenderId;
+
+            networkManager.NetworkMetrics.TrackServerLogReceived(senderId, (uint)LogType, context.MessageSize);
 
             switch (LogType)
             {

Runtime/Messaging/Messages/SnapshotDataMessage.cs

@@ -1,161 +0,0 @@
-using System;
-using Unity.Collections;
-using Unity.Collections.LowLevel.Unsafe;
-using UnityEngine;
-
-namespace Unity.Netcode
-{
-    internal struct SnapshotDataMessage : INetworkMessage
-    {
-        public int CurrentTick;
-        public ushort Sequence;
-
-        public ushort Range;
-
-        public byte[] SendMainBuffer;
-        public NativeArray<byte> ReceiveMainBuffer;
-
-        public struct AckData
-        {
-            public ushort LastReceivedSequence;
-            public ushort ReceivedSequenceMask;
-        }
-
-        public AckData Ack;
-
-        public struct EntryData
-        {
-            public ulong NetworkObjectId;
-            public ushort BehaviourIndex;
-            public ushort VariableIndex;
-            public int TickWritten;
-            public ushort Position;
-            public ushort Length;
-        }
-
-        public NativeList<EntryData> Entries;
-
-        public struct SpawnData
-        {
-            public ulong NetworkObjectId;
-            public uint Hash;
-            public bool IsSceneObject;
-
-            public bool IsPlayerObject;
-            public ulong OwnerClientId;
-            public ulong ParentNetworkId;
-            public Vector3 Position;
-            public Quaternion Rotation;
-            public Vector3 Scale;
-
-            public int TickWritten;
-        }
-
-        public NativeList<SpawnData> Spawns;
-
-        public struct DespawnData
-        {
-            public ulong NetworkObjectId;
-            public int TickWritten;
-        }
-
-        public NativeList<DespawnData> Despawns;
-
-        public unsafe void Serialize(FastBufferWriter writer)
-        {
-            if (!writer.TryBeginWrite(
-                FastBufferWriter.GetWriteSize(CurrentTick) +
-                FastBufferWriter.GetWriteSize(Sequence) +
-                FastBufferWriter.GetWriteSize(Range) + Range +
-                FastBufferWriter.GetWriteSize(Ack) +
-                FastBufferWriter.GetWriteSize<ushort>() +
-                Entries.Length * sizeof(EntryData) +
-                FastBufferWriter.GetWriteSize<ushort>() +
-                Spawns.Length * sizeof(SpawnData) +
-                FastBufferWriter.GetWriteSize<ushort>() +
-                Despawns.Length * sizeof(DespawnData)
-            ))
-            {
-                Entries.Dispose();
-                Spawns.Dispose();
-                Despawns.Dispose();
-                throw new OverflowException($"Not enough space to serialize {nameof(SnapshotDataMessage)}");
-            }
-            writer.WriteValue(CurrentTick);
-            writer.WriteValue(Sequence);
-
-            writer.WriteValue(Range);
-            writer.WriteBytes(SendMainBuffer, Range);
-            writer.WriteValue(Ack);
-
-            writer.WriteValue((ushort)Entries.Length);
-            writer.WriteBytes((byte*)Entries.GetUnsafePtr(), Entries.Length * sizeof(EntryData));
-
-            writer.WriteValue((ushort)Spawns.Length);
-            writer.WriteBytes((byte*)Spawns.GetUnsafePtr(), Spawns.Length * sizeof(SpawnData));
-
-            writer.WriteValue((ushort)Despawns.Length);
-            writer.WriteBytes((byte*)Despawns.GetUnsafePtr(), Despawns.Length * sizeof(DespawnData));
-
-            Entries.Dispose();
-            Spawns.Dispose();
-            Despawns.Dispose();
-        }
-
-        public static unsafe void Receive(FastBufferReader reader, in NetworkContext context)
-        {
-            var networkManager = (NetworkManager)context.SystemOwner;
-            var message = new SnapshotDataMessage();
-            if (!reader.TryBeginRead(
-                FastBufferWriter.GetWriteSize(message.CurrentTick) +
-                FastBufferWriter.GetWriteSize(message.Sequence) +
-                FastBufferWriter.GetWriteSize(message.Range)
-            ))
-            {
-                throw new OverflowException($"Not enough space to deserialize {nameof(SnapshotDataMessage)}");
-            }
-            reader.ReadValue(out message.CurrentTick);
-            reader.ReadValue(out message.Sequence);
-
-            reader.ReadValue(out message.Range);
-            message.ReceiveMainBuffer = new NativeArray<byte>(message.Range, Allocator.Temp);
-            reader.ReadBytesSafe((byte*)message.ReceiveMainBuffer.GetUnsafePtr(), message.Range);
-            reader.ReadValueSafe(out message.Ack);
-
-            reader.ReadValueSafe(out ushort length);
-            message.Entries = new NativeList<EntryData>(length, Allocator.Temp);
-            message.Entries.Length = length;
-            reader.ReadBytesSafe((byte*)message.Entries.GetUnsafePtr(), message.Entries.Length * sizeof(EntryData));
-
-            reader.ReadValueSafe(out length);
-            message.Spawns = new NativeList<SpawnData>(length, Allocator.Temp);
-            message.Spawns.Length = length;
-            reader.ReadBytesSafe((byte*)message.Spawns.GetUnsafePtr(), message.Spawns.Length * sizeof(SpawnData));
-
-            reader.ReadValueSafe(out length);
-            message.Despawns = new NativeList<DespawnData>(length, Allocator.Temp);
-            message.Despawns.Length = length;
-            reader.ReadBytesSafe((byte*)message.Despawns.GetUnsafePtr(), message.Despawns.Length * sizeof(DespawnData));
-
-            using (message.ReceiveMainBuffer)
-            using (message.Entries)
-            using (message.Spawns)
-            using (message.Despawns)
-            {
-                message.Handle(context.SenderId, networkManager);
-            }
-        }
-
-        public void Handle(ulong senderId, NetworkManager networkManager)
-        {
-            // todo: temporary hack around bug
-            if (!networkManager.IsServer)
-            {
-                senderId = networkManager.ServerClientId;
-            }
-
-            var snapshotSystem = networkManager.SnapshotSystem;
-            snapshotSystem.HandleSnapshot(senderId, this);
-        }
-    }
-}

Runtime/Messaging/Messages/SnapshotDataMessage.cs.meta

@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: 5cf75026c2ab86646aac16b39d7259ad
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Messaging/Messages/TimeSyncMessage.cs

@@ -9,21 +9,22 @@ namespace Unity.Netcode
             writer.WriteValueSafe(this);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
-                return;
+                return false;
             }
-            reader.ReadValueSafe(out TimeSyncMessage message);
-            message.Handle(context.SenderId, networkManager);
+            reader.ReadValueSafe(out this);
+            return true;
         }
 
-        public void Handle(ulong senderId, NetworkManager networkManager)
+        public void Handle(ref NetworkContext context)
         {
+            var networkManager = (NetworkManager)context.SystemOwner;
             var time = new NetworkTime(networkManager.NetworkTickSystem.TickRate, Tick);
-            networkManager.NetworkTimeSystem.Sync(time.Time, networkManager.NetworkConfig.NetworkTransport.GetCurrentRtt(senderId) / 1000d);
+            networkManager.NetworkTimeSystem.Sync(time.Time, networkManager.NetworkConfig.NetworkTransport.GetCurrentRtt(context.SenderId) / 1000d);
         }
     }
 }

Runtime/Messaging/Messages/UnnamedMessage.cs

@@ -2,16 +2,23 @@ namespace Unity.Netcode
 {
     internal struct UnnamedMessage : INetworkMessage
     {
-        public FastBufferWriter Data;
+        public FastBufferWriter SendData;
+        private FastBufferReader m_ReceivedData;
 
         public unsafe void Serialize(FastBufferWriter writer)
         {
-            writer.WriteBytesSafe(Data.GetUnsafePtr(), Data.Length);
+            writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public static void Receive(FastBufferReader reader, in NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
         {
-            ((NetworkManager)context.SystemOwner).CustomMessagingManager.InvokeUnnamedMessage(context.SenderId, reader);
+            m_ReceivedData = reader;
+            return true;
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            ((NetworkManager)context.SystemOwner).CustomMessagingManager.InvokeUnnamedMessage(context.SenderId, m_ReceivedData, context.SerializedHeaderSize);
         }
     }
 }

Runtime/Messaging/MessagingSystem.cs

@@ -23,6 +23,7 @@ namespace Unity.Netcode
             public MessageHeader Header;
             public ulong SenderId;
             public float Timestamp;
+            public int MessageHeaderSerializedSize;
         }
 
         private struct SendQueueItem
@@ -39,34 +40,34 @@ namespace Unity.Netcode
             }
         }
 
-        internal delegate void MessageHandler(FastBufferReader reader, in NetworkContext context);
+        internal delegate void MessageHandler(FastBufferReader reader, ref NetworkContext context, MessagingSystem system);
 
         private NativeList<ReceiveQueueItem> m_IncomingMessageQueue = new NativeList<ReceiveQueueItem>(16, Allocator.Persistent);
 
         private MessageHandler[] m_MessageHandlers = new MessageHandler[255];
         private Type[] m_ReverseTypeMap = new Type[255];
 
-        private Dictionary<Type, byte> m_MessageTypes = new Dictionary<Type, byte>();
+        private Dictionary<Type, uint> m_MessageTypes = new Dictionary<Type, uint>();
         private Dictionary<ulong, NativeList<SendQueueItem>> m_SendQueues = new Dictionary<ulong, NativeList<SendQueueItem>>();
 
         private List<INetworkHooks> m_Hooks = new List<INetworkHooks>();
 
-        private byte m_HighMessageType;
+        private uint m_HighMessageType;
         private object m_Owner;
         private IMessageSender m_MessageSender;
         private bool m_Disposed;
 
         internal Type[] MessageTypes => m_ReverseTypeMap;
         internal MessageHandler[] MessageHandlers => m_MessageHandlers;
-        internal int MessageHandlerCount => m_HighMessageType;
+        internal uint MessageHandlerCount => m_HighMessageType;
 
-        internal byte GetMessageType(Type t)
+        internal uint GetMessageType(Type t)
         {
             return m_MessageTypes[t];
         }
 
         public const int NON_FRAGMENTED_MESSAGE_MAX_SIZE = 1300;
-        public const int FRAGMENTED_MESSAGE_MAX_SIZE = 64000;
+        public const int FRAGMENTED_MESSAGE_MAX_SIZE = BytePacker.BitPackedIntMax;
 
         internal struct MessageWithHandler
         {
@@ -100,7 +101,7 @@ namespace Unity.Netcode
             }
         }
 
-        public void Dispose()
+        public unsafe void Dispose()
         {
             if (m_Disposed)
             {
@@ -113,6 +114,14 @@ namespace Unity.Netcode
             {
                 CleanupDisconnectedClient(kvp.Key);
             }
+
+            for (var queueIndex = 0; queueIndex < m_IncomingMessageQueue.Length; ++queueIndex)
+            {
+                // Avoid copies...
+                ref var item = ref m_IncomingMessageQueue.ElementAt(queueIndex);
+                item.Reader.Dispose();
+            }
+
             m_IncomingMessageQueue.Dispose();
             m_Disposed = true;
         }
@@ -141,7 +150,7 @@ namespace Unity.Netcode
                 fixed (byte* nativeData = data.Array)
                 {
                     var batchReader =
-                        new FastBufferReader(nativeData, Allocator.None, data.Count, data.Offset);
+                        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.");
@@ -157,14 +166,23 @@ namespace Unity.Netcode
 
                     for (var messageIdx = 0; messageIdx < batchHeader.BatchSize; ++messageIdx)
                     {
-                        if (!batchReader.TryBeginRead(sizeof(MessageHeader)))
+
+                        var messageHeader = new MessageHeader();
+                        var position = batchReader.Position;
+                        try
+                        {
+                            ByteUnpacker.ReadValueBitPacked(batchReader, out messageHeader.MessageType);
+                            ByteUnpacker.ReadValueBitPacked(batchReader, out messageHeader.MessageSize);
+                        }
+                        catch (OverflowException)
                         {
                             NetworkLog.LogWarning("Received a batch that didn't have enough data for all of its batches, ending early!");
-                            return;
+                            throw;
                         }
-                        batchReader.ReadValue(out MessageHeader messageHeader);
 
-                        if (!batchReader.TryBeginRead(messageHeader.MessageSize))
+                        var receivedHeaderSize = batchReader.Position - position;
+
+                        if (!batchReader.TryBeginRead((int)messageHeader.MessageSize))
                         {
                             NetworkLog.LogWarning("Received a message that claimed a size larger than the packet, ending early!");
                             return;
@@ -177,9 +195,10 @@ namespace Unity.Netcode
                             // Copy the data for this message into a new FastBufferReader that owns that memory.
                             // We can't guarantee the memory in the ArraySegment stays valid because we don't own it,
                             // so we must move it to memory we do own.
-                            Reader = new FastBufferReader(batchReader.GetUnsafePtrAtCurrentPosition(), Allocator.TempJob, messageHeader.MessageSize)
+                            Reader = new FastBufferReader(batchReader.GetUnsafePtrAtCurrentPosition(), Allocator.TempJob, (int)messageHeader.MessageSize),
+                            MessageHeaderSerializedSize = receivedHeaderSize,
                         });
-                        batchReader.Seek(batchReader.Position + messageHeader.MessageSize);
+                        batchReader.Seek(batchReader.Position + (int)messageHeader.MessageSize);
                     }
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
@@ -202,7 +221,7 @@ namespace Unity.Netcode
             return true;
         }
 
-        public void HandleMessage(in MessageHeader header, FastBufferReader reader, ulong senderId, float timestamp)
+        public void HandleMessage(in MessageHeader header, FastBufferReader reader, ulong senderId, float timestamp, int serializedHeaderSize)
         {
             if (header.MessageType >= m_HighMessageType)
             {
@@ -215,8 +234,11 @@ namespace Unity.Netcode
                 SystemOwner = m_Owner,
                 SenderId = senderId,
                 Timestamp = timestamp,
-                Header = header
+                Header = header,
+                SerializedHeaderSize = serializedHeaderSize,
+                MessageSize = header.MessageSize,
             };
+
             var type = m_ReverseTypeMap[header.MessageType];
             if (!CanReceive(senderId, type))
             {
@@ -226,8 +248,9 @@ namespace Unity.Netcode
 
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
             {
-                m_Hooks[hookIdx].OnBeforeReceiveMessage(senderId, type, reader.Length);
+                m_Hooks[hookIdx].OnBeforeReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<MessageHeader>());
             }
+
             var handler = m_MessageHandlers[header.MessageType];
             using (reader)
             {
@@ -238,7 +261,7 @@ namespace Unity.Netcode
                 // for some dynamic-length value.
                 try
                 {
-                    handler.Invoke(reader, context);
+                    handler.Invoke(reader, ref context, this);
                 }
                 catch (Exception e)
                 {
@@ -247,17 +270,21 @@ namespace Unity.Netcode
             }
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
             {
-                m_Hooks[hookIdx].OnAfterReceiveMessage(senderId, type, reader.Length);
+                m_Hooks[hookIdx].OnAfterReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<MessageHeader>());
             }
         }
 
         internal unsafe void ProcessIncomingMessageQueue()
         {
-            for (var i = 0; i < m_IncomingMessageQueue.Length; ++i)
+            for (var index = 0; index < m_IncomingMessageQueue.Length; ++index)
             {
                 // Avoid copies...
-                ref var item = ref m_IncomingMessageQueue.GetUnsafeList()->ElementAt(i);
-                HandleMessage(item.Header, item.Reader, item.SenderId, item.Timestamp);
+                ref var item = ref m_IncomingMessageQueue.ElementAt(index);
+                HandleMessage(item.Header, item.Reader, item.SenderId, item.Timestamp, item.MessageHeaderSerializedSize);
+                if (m_Disposed)
+                {
+                    return;
+                }
             }
 
             m_IncomingMessageQueue.Clear();
@@ -287,12 +314,31 @@ namespace Unity.Netcode
             var queue = m_SendQueues[clientId];
             for (var i = 0; i < queue.Length; ++i)
             {
-                queue.GetUnsafeList()->ElementAt(i).Writer.Dispose();
+                queue.ElementAt(i).Writer.Dispose();
             }
 
             queue.Dispose();
         }
 
+        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))
+            {
+                for (var hookIdx = 0; hookIdx < system.m_Hooks.Count; ++hookIdx)
+                {
+                    system.m_Hooks[hookIdx].OnBeforeHandleMessage(ref message, ref context);
+                }
+
+                message.Handle(ref context);
+
+                for (var hookIdx = 0; hookIdx < system.m_Hooks.Count; ++hookIdx)
+                {
+                    system.m_Hooks[hookIdx].OnAfterHandleMessage(ref message, ref context);
+                }
+            }
+        }
+
         private bool CanSend(ulong clientId, Type messageType, NetworkDelivery delivery)
         {
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
@@ -306,69 +352,91 @@ namespace Unity.Netcode
             return true;
         }
 
-        internal unsafe int SendMessage<TMessageType, TClientIdListType>(in TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
+        internal int SendMessage<TMessageType, TClientIdListType>(ref TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
             where TMessageType : INetworkMessage
             where TClientIdListType : IReadOnlyList<ulong>
         {
-            var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FRAGMENTED_MESSAGE_MAX_SIZE : NON_FRAGMENTED_MESSAGE_MAX_SIZE;
-            var tmpSerializer = new FastBufferWriter(NON_FRAGMENTED_MESSAGE_MAX_SIZE - sizeof(MessageHeader), Allocator.Temp, maxSize - sizeof(MessageHeader));
-            using (tmpSerializer)
+            if (clientIds.Count == 0)
             {
-                message.Serialize(tmpSerializer);
+                return 0;
+            }
 
-                for (var i = 0; i < clientIds.Count; ++i)
+            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);
+
+            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds);
+        }
+
+        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds)
+            where TMessageType : INetworkMessage
+        {
+            using var headerSerializer = new FastBufferWriter(FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp);
+
+            var header = new MessageHeader
+            {
+                MessageSize = (uint)tmpSerializer.Length,
+                MessageType = m_MessageTypes[typeof(TMessageType)],
+            };
+            BytePacker.WriteValueBitPacked(headerSerializer, header.MessageType);
+            BytePacker.WriteValueBitPacked(headerSerializer, header.MessageSize);
+
+            for (var i = 0; i < clientIds.Count; ++i)
+            {
+                var clientId = clientIds[i];
+
+                if (!CanSend(clientId, typeof(TMessageType), delivery))
                 {
-                    var clientId = clientIds[i];
+                    continue;
+                }
 
-                    if (!CanSend(clientId, typeof(TMessageType), delivery))
-                    {
-                        continue;
-                    }
+                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                {
+                    m_Hooks[hookIdx].OnBeforeSendMessage(clientId, ref message, delivery);
+                }
 
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
-                    {
-                        m_Hooks[hookIdx].OnBeforeSendMessage(clientId, typeof(TMessageType), delivery);
-                    }
-
-                    var sendQueueItem = m_SendQueues[clientId];
-                    if (sendQueueItem.Length == 0)
+                var sendQueueItem = m_SendQueues[clientId];
+                if (sendQueueItem.Length == 0)
+                {
+                    sendQueueItem.Add(new SendQueueItem(delivery, NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.TempJob,
+                        maxSize));
+                    sendQueueItem.ElementAt(0).Writer.Seek(sizeof(BatchHeader));
+                }
+                else
+                {
+                    ref var lastQueueItem = ref sendQueueItem.ElementAt(sendQueueItem.Length - 1);
+                    if (lastQueueItem.NetworkDelivery != delivery ||
+                        lastQueueItem.Writer.MaxCapacity - lastQueueItem.Writer.Position
+                        < tmpSerializer.Length + headerSerializer.Length)
                     {
                         sendQueueItem.Add(new SendQueueItem(delivery, NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.TempJob,
                             maxSize));
-                        sendQueueItem.GetUnsafeList()->ElementAt(0).Writer.Seek(sizeof(BatchHeader));
-                    }
-                    else
-                    {
-                        ref var lastQueueItem = ref sendQueueItem.GetUnsafeList()->ElementAt(sendQueueItem.Length - 1);
-                        if (lastQueueItem.NetworkDelivery != delivery ||
-                            lastQueueItem.Writer.MaxCapacity - lastQueueItem.Writer.Position
-                            < tmpSerializer.Length + sizeof(MessageHeader))
-                        {
-                            sendQueueItem.Add(new SendQueueItem(delivery, NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.TempJob,
-                                maxSize));
-                            sendQueueItem.GetUnsafeList()->ElementAt(sendQueueItem.Length - 1).Writer.Seek(sizeof(BatchHeader));
-                        }
-                    }
-
-                    ref var writeQueueItem = ref sendQueueItem.GetUnsafeList()->ElementAt(sendQueueItem.Length - 1);
-                    writeQueueItem.Writer.TryBeginWrite(sizeof(MessageHeader) + tmpSerializer.Length);
-                    var header = new MessageHeader
-                    {
-                        MessageSize = (ushort)tmpSerializer.Length,
-                        MessageType = m_MessageTypes[typeof(TMessageType)],
-                    };
-
-                    writeQueueItem.Writer.WriteValue(header);
-                    writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
-                    writeQueueItem.BatchHeader.BatchSize++;
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
-                    {
-                        m_Hooks[hookIdx].OnAfterSendMessage(clientId, typeof(TMessageType), delivery, tmpSerializer.Length + sizeof(MessageHeader));
+                        sendQueueItem.ElementAt(sendQueueItem.Length - 1).Writer.Seek(sizeof(BatchHeader));
                     }
                 }
 
-                return tmpSerializer.Length;
+                ref var writeQueueItem = ref sendQueueItem.ElementAt(sendQueueItem.Length - 1);
+                writeQueueItem.Writer.TryBeginWrite(tmpSerializer.Length + headerSerializer.Length);
+
+                writeQueueItem.Writer.WriteBytes(headerSerializer.GetUnsafePtr(), headerSerializer.Length);
+                writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
+                writeQueueItem.BatchHeader.BatchSize++;
+                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                {
+                    m_Hooks[hookIdx].OnAfterSendMessage(clientId, ref message, delivery, tmpSerializer.Length + headerSerializer.Length);
+                }
             }
+
+            return tmpSerializer.Length + headerSerializer.Length;
+        }
+
+        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, ulong clientId)
+            where TMessageType : INetworkMessage
+        {
+            ulong* clientIds = stackalloc ulong[] { clientId };
+            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
         }
 
         private struct PointerListWrapper<T> : IReadOnlyList<T>
@@ -406,24 +474,24 @@ namespace Unity.Netcode
             }
         }
 
-        internal unsafe int SendMessage<T>(in T message, NetworkDelivery delivery,
+        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery,
             ulong* clientIds, int numClientIds)
             where T : INetworkMessage
         {
-            return SendMessage(message, delivery, new PointerListWrapper<ulong>(clientIds, numClientIds));
+            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>(clientIds, numClientIds));
         }
 
-        internal unsafe int SendMessage<T>(in T message, NetworkDelivery delivery, ulong clientId)
+        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, ulong clientId)
             where T : INetworkMessage
         {
             ulong* clientIds = stackalloc ulong[] { clientId };
-            return SendMessage(message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
+            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
         }
 
-        internal unsafe int SendMessage<T>(in T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
+        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
             where T : INetworkMessage
         {
-            return SendMessage(message, delivery, new PointerListWrapper<ulong>((ulong*)clientIds.GetUnsafePtr(), clientIds.Length));
+            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>((ulong*)clientIds.GetUnsafePtr(), clientIds.Length));
         }
 
         internal unsafe void ProcessSendQueues()
@@ -434,7 +502,7 @@ namespace Unity.Netcode
                 var sendQueueItem = kvp.Value;
                 for (var i = 0; i < sendQueueItem.Length; ++i)
                 {
-                    ref var queueItem = ref sendQueueItem.GetUnsafeList()->ElementAt(i);
+                    ref var queueItem = ref sendQueueItem.ElementAt(i);
                     if (queueItem.BatchHeader.BatchSize == 0)
                     {
                         queueItem.Writer.Dispose();
@@ -456,16 +524,16 @@ namespace Unity.Netcode
                     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);
+                        }
                     }
                     finally
                     {
                         queueItem.Writer.Dispose();
                     }
-
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
-                    {
-                        m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
-                    }
                 }
                 sendQueueItem.Clear();
             }

Runtime/Messaging/NetworkContext.cs

@@ -25,5 +25,15 @@ namespace Unity.Netcode
         /// The header data that was sent with the message
         /// </summary>
         public MessageHeader Header;
+
+        /// <summary>
+        /// The actual serialized size of the header when packed into the buffer
+        /// </summary>
+        public int SerializedHeaderSize;
+
+        /// <summary>
+        /// The size of the message in the buffer, header excluded
+        /// </summary>
+        public uint MessageSize;
     }
 }

Runtime/Metrics/INetworkMetrics.cs

@@ -83,6 +83,18 @@ namespace Unity.Netcode
 
         void TrackSceneEventReceived(ulong senderClientId, uint sceneEventType, string sceneName, long bytesCount);
 
+        void TrackPacketSent(uint packetCount);
+
+        void TrackPacketReceived(uint packetCount);
+
+        void UpdateRttToServer(int rtt);
+
+        void UpdateNetworkObjectsCount(int count);
+
+        void UpdateConnectionsCount(int count);
+
+        void UpdatePacketLoss(float packetLoss);
+
         void DispatchFrame();
     }
 }

Runtime/Metrics/MetricHooks.cs

@@ -11,14 +11,13 @@ namespace Unity.Netcode
             m_NetworkManager = networkManager;
         }
 
-
-        public void OnBeforeSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery)
+        public void OnBeforeSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery) where T : INetworkMessage
         {
         }
 
-        public void OnAfterSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery, int messageSizeBytes)
+        public void OnAfterSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery, int messageSizeBytes) where T : INetworkMessage
         {
-            m_NetworkManager.NetworkMetrics.TrackNetworkMessageSent(clientId, messageType.Name, messageSizeBytes);
+            m_NetworkManager.NetworkMetrics.TrackNetworkMessageSent(clientId, typeof(T).Name, messageSizeBytes);
         }
 
         public void OnBeforeReceiveMessage(ulong senderId, Type messageType, int messageSizeBytes)
@@ -57,5 +56,15 @@ namespace Unity.Netcode
         {
             return true;
         }
+
+        public void OnBeforeHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+            // TODO: Per-message metrics recording moved here
+        }
+
+        public void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+            // TODO: Per-message metrics recording moved here
+        }
     }
 }

Runtime/Metrics/NetworkMetrics.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using Unity.Multiplayer.Tools;
 using Unity.Multiplayer.Tools.MetricTypes;
 using Unity.Multiplayer.Tools.NetStats;
+using Unity.Profiling;
 using UnityEngine;
 
 namespace Unity.Netcode
@@ -14,6 +15,8 @@ namespace Unity.Netcode
 
         static Dictionary<uint, string> s_SceneEventTypeNames;
 
+        static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
+
         static NetworkMetrics()
         {
             s_SceneEventTypeNames = new Dictionary<uint, string>();
@@ -63,6 +66,30 @@ namespace Unity.Netcode
         private readonly EventMetric<SceneEventMetric> m_SceneEventSentEvent = new EventMetric<SceneEventMetric>(NetworkMetricTypes.SceneEventSent.Id);
         private readonly EventMetric<SceneEventMetric> m_SceneEventReceivedEvent = new EventMetric<SceneEventMetric>(NetworkMetricTypes.SceneEventReceived.Id);
 
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+        private readonly Counter m_PacketSentCounter = new Counter(NetworkMetricTypes.PacketsSent.Id)
+        {
+            ShouldResetOnDispatch = true,
+        };
+        private readonly Counter m_PacketReceivedCounter = new Counter(NetworkMetricTypes.PacketsReceived.Id)
+        {
+            ShouldResetOnDispatch = true,
+        };
+        private readonly Gauge m_RttToServerGauge = new Gauge(NetworkMetricTypes.RttToServer.Id)
+        {
+            ShouldResetOnDispatch = true,
+        };
+        private readonly Gauge m_NetworkObjectsGauge = new Gauge(NetworkMetricTypes.NetworkObjects.Id)
+        {
+            ShouldResetOnDispatch = true,
+        };
+        private readonly Gauge m_ConnectionsGauge = new Gauge(NetworkMetricTypes.ConnectedClients.Id)
+        {
+            ShouldResetOnDispatch = true,
+        };
+        private readonly Gauge m_PacketLossGauge = new Gauge(NetworkMetricTypes.PacketLoss.Id);
+#endif
+
         private ulong m_NumberOfMetricsThisFrame;
 
         public NetworkMetrics()
@@ -79,6 +106,13 @@ namespace Unity.Netcode
                 .WithMetricEvents(m_RpcSentEvent, m_RpcReceivedEvent)
                 .WithMetricEvents(m_ServerLogSentEvent, m_ServerLogReceivedEvent)
                 .WithMetricEvents(m_SceneEventSentEvent, m_SceneEventReceivedEvent)
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+                .WithCounters(m_PacketSentCounter, m_PacketReceivedCounter)
+                .WithGauges(m_RttToServerGauge)
+                .WithGauges(m_NetworkObjectsGauge)
+                .WithGauges(m_ConnectionsGauge)
+                .WithGauges(m_PacketLossGauge)
+#endif
                 .Build();
 
             Dispatcher.RegisterObserver(NetcodeObserver.Observer);
@@ -404,9 +438,85 @@ namespace Unity.Netcode
             IncrementMetricCount();
         }
 
+        public void TrackPacketSent(uint packetCount)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+
+            m_PacketSentCounter.Increment(packetCount);
+            IncrementMetricCount();
+#endif
+        }
+
+        public void TrackPacketReceived(uint packetCount)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+
+            m_PacketReceivedCounter.Increment(packetCount);
+            IncrementMetricCount();
+#endif
+        }
+
+        public void UpdateRttToServer(int rttMilliseconds)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+            var rttSeconds = rttMilliseconds * 1e-3;
+            m_RttToServerGauge.Set(rttSeconds);
+#endif
+        }
+
+        public void UpdateNetworkObjectsCount(int count)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+
+            m_NetworkObjectsGauge.Set(count);
+#endif
+        }
+
+        public void UpdateConnectionsCount(int count)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+
+            m_ConnectionsGauge.Set(count);
+#endif
+        }
+
+        public void UpdatePacketLoss(float packetLoss)
+        {
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+            if (!CanSendMetrics)
+            {
+                return;
+            }
+
+            m_PacketLossGauge.Set(packetLoss);
+#endif
+        }
+
         public void DispatchFrame()
         {
+            s_FrameDispatch.Begin();
             Dispatcher.Dispatch();
+            s_FrameDispatch.End();
             m_NumberOfMetricsThisFrame = 0;
         }
 
@@ -421,7 +531,7 @@ namespace Unity.Netcode
         }
     }
 
-    internal class NetcodeObserver
+        internal class NetcodeObserver
     {
         public static IMetricObserver Observer { get; } = MetricObserverFactory.Construct();
     }

Runtime/Metrics/NullNetworkMetrics.cs

@@ -137,6 +137,30 @@ namespace Unity.Netcode
         {
         }
 
+        public void TrackPacketSent(uint packetCount)
+        {
+        }
+
+        public void TrackPacketReceived(uint packetCount)
+        {
+        }
+
+        public void UpdateRttToServer(int rtt)
+        {
+        }
+
+        public void UpdateNetworkObjectsCount(int count)
+        {
+        }
+
+        public void UpdateConnectionsCount(int count)
+        {
+        }
+
+        public void UpdatePacketLoss(float packetLoss)
+        {
+        }
+
         public void DispatchFrame()
         {
         }

Runtime/Metrics/StreamExtensions.cs

@@ -1,12 +0,0 @@
-using System.IO;
-
-namespace Unity.Netcode
-{
-    public static class StreamExtensions
-    {
-        public static long SafeGetLengthOrDefault(this Stream stream)
-        {
-            return stream.CanSeek ? stream.Length : 0;
-        }
-    }
-}

Runtime/Metrics/StreamExtensions.cs.meta

@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: 61dd9b1558f6d7c46ad323b2c2c03c29
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -24,17 +24,12 @@ namespace Unity.Netcode
         /// </summary>
         public event OnListChangedDelegate OnListChanged;
 
-        /// <summary>
-        /// Creates a NetworkList with the default value and settings
-        /// </summary>
         public NetworkList() { }
 
-        /// <summary>
-        /// Creates a NetworkList with the default value and custom settings
-        /// </summary>
-        /// <param name="readPerm">The read permission to use for the NetworkList</param>
-        /// <param name="values">The initial value to use for the NetworkList</param>
-        public NetworkList(NetworkVariableReadPermission readPerm, IEnumerable<T> values) : base(readPerm)
+        public NetworkList(IEnumerable<T> values = default,
+            NetworkVariableReadPermission readPerm = DefaultReadPerm,
+            NetworkVariableWritePermission writePerm = DefaultWritePerm)
+            : base(readPerm, writePerm)
         {
             foreach (var value in values)
             {
@@ -42,19 +37,6 @@ namespace Unity.Netcode
             }
         }
 
-        /// <summary>
-        /// Creates a NetworkList with a custom value and the default settings
-        /// </summary>
-        /// <param name="values">The initial value to use for the NetworkList</param>
-        public NetworkList(IEnumerable<T> values)
-        {
-            foreach (var value in values)
-            {
-                m_List.Add(value);
-
-            }
-        }
-
         /// <inheritdoc />
         public override void ResetDirty()
         {
@@ -90,18 +72,18 @@ namespace Unity.Netcode
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            writer.WriteValueSafe(m_DirtyEvents[i].Value);
+                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Insert:
                         {
                             writer.WriteValueSafe(m_DirtyEvents[i].Index);
-                            writer.WriteValueSafe(m_DirtyEvents[i].Value);
+                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            writer.WriteValueSafe(m_DirtyEvents[i].Value);
+                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.RemoveAt:
@@ -112,7 +94,7 @@ namespace Unity.Netcode
                     case NetworkListEvent<T>.EventType.Value:
                         {
                             writer.WriteValueSafe(m_DirtyEvents[i].Index);
-                            writer.WriteValueSafe(m_DirtyEvents[i].Value);
+                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Clear:
@@ -130,7 +112,7 @@ namespace Unity.Netcode
             writer.WriteValueSafe((ushort)m_List.Length);
             for (int i = 0; i < m_List.Length; i++)
             {
-                writer.WriteValueSafe(m_List[i]);
+                NetworkVariable<T>.Write(writer, m_List[i]);
             }
         }
 
@@ -141,7 +123,7 @@ namespace Unity.Netcode
             reader.ReadValueSafe(out ushort count);
             for (int i = 0; i < count; i++)
             {
-                reader.ReadValueSafe(out T value);
+                NetworkVariable<T>.Read(reader, out T value);
                 m_List.Add(value);
             }
         }
@@ -157,7 +139,7 @@ namespace Unity.Netcode
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            reader.ReadValueSafe(out T value);
+                            NetworkVariable<T>.Read(reader, out T value);
                             m_List.Add(value);
 
                             if (OnListChanged != null)
@@ -184,7 +166,7 @@ namespace Unity.Netcode
                     case NetworkListEvent<T>.EventType.Insert:
                         {
                             reader.ReadValueSafe(out int index);
-                            reader.ReadValueSafe(out T value);
+                            NetworkVariable<T>.Read(reader, out T value);
                             m_List.InsertRangeWithBeginEnd(index, index + 1);
                             m_List[index] = value;
 
@@ -211,7 +193,7 @@ namespace Unity.Netcode
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            reader.ReadValueSafe(out T value);
+                            NetworkVariable<T>.Read(reader, out T value);
                             int index = m_List.IndexOf(value);
                             if (index == -1)
                             {
@@ -271,19 +253,23 @@ namespace Unity.Netcode
                     case NetworkListEvent<T>.EventType.Value:
                         {
                             reader.ReadValueSafe(out int index);
-                            reader.ReadValueSafe(out T value);
-                            if (index < m_List.Length)
+                            NetworkVariable<T>.Read(reader, out T value);
+                            if (index >= m_List.Length)
                             {
-                                m_List[index] = value;
+                                throw new Exception("Shouldn't be here, index is higher than list length");
                             }
 
+                            var previousValue = m_List[index];
+                            m_List[index] = value;
+
                             if (OnListChanged != null)
                             {
                                 OnListChanged(new NetworkListEvent<T>
                                 {
                                     Type = eventType,
                                     Index = index,
-                                    Value = value
+                                    Value = value,
+                                    PreviousValue = previousValue
                                 });
                             }
 
@@ -293,7 +279,8 @@ namespace Unity.Netcode
                                 {
                                     Type = eventType,
                                     Index = index,
-                                    Value = value
+                                    Value = value,
+                                    PreviousValue = previousValue
                                 });
                             }
                         }
@@ -368,7 +355,7 @@ namespace Unity.Netcode
         public bool Contains(T item)
         {
             int index = NativeArrayExtensions.IndexOf(m_List, item);
-            return index == -1;
+            return index != -1;
         }
 
         /// <inheritdoc />
@@ -528,6 +515,11 @@ namespace Unity.Netcode
         /// </summary>
         public T Value;
 
+        /// <summary>
+        /// The previous value when "Value" has changed, if available.
+        /// </summary>
+        public T PreviousValue;
+
         /// <summary>
         /// the index changed, added or removed if available
         /// </summary>

Runtime/NetworkVariable/NetworkVariable.cs

@@ -1,5 +1,7 @@
 using UnityEngine;
 using System;
+using System.Runtime.CompilerServices;
+using Unity.Collections.LowLevel.Unsafe;
 
 namespace Unity.Netcode
 {
@@ -9,6 +11,53 @@ namespace Unity.Netcode
     [Serializable]
     public class NetworkVariable<T> : NetworkVariableBase where T : unmanaged
     {
+        // Functions that know how to serialize INetworkSerializable
+        internal static void WriteNetworkSerializable<TForMethod>(FastBufferWriter writer, in TForMethod value)
+            where TForMethod : INetworkSerializable, new()
+        {
+            writer.WriteNetworkSerializable(value);
+        }
+        internal static void ReadNetworkSerializable<TForMethod>(FastBufferReader reader, out TForMethod value)
+            where TForMethod : INetworkSerializable, new()
+        {
+            reader.ReadNetworkSerializable(out value);
+        }
+
+        // Functions that serialize other types
+        private static void WriteValue<TForMethod>(FastBufferWriter writer, in TForMethod value)
+            where TForMethod : unmanaged
+        {
+            writer.WriteValueSafe(value);
+        }
+
+        private static void ReadValue<TForMethod>(FastBufferReader reader, out TForMethod value)
+            where TForMethod : unmanaged
+        {
+            reader.ReadValueSafe(out value);
+        }
+
+        internal delegate void WriteDelegate<TForMethod>(FastBufferWriter writer, in TForMethod value);
+
+        internal delegate void ReadDelegate<TForMethod>(FastBufferReader reader, out TForMethod value);
+
+        // These static delegates provide the right implementation for writing and reading a particular network variable type.
+        // For most types, these default to WriteValue() and ReadValue(), which perform simple memcpy operations.
+        //
+        // INetworkSerializableILPP will generate startup code that will set it to WriteNetworkSerializable()
+        // and ReadNetworkSerializable() for INetworkSerializable types, which will call NetworkSerialize().
+        //
+        // In the future we may be able to use this to provide packing implementations for floats and integers to optimize bandwidth usage.
+        //
+        // The reason this is done is to avoid runtime reflection and boxing in NetworkVariable - without this,
+        // NetworkVariable would need to do a `var is INetworkSerializable` check, and then cast to INetworkSerializable,
+        // *both* of which would cause a boxing allocation. Alternatively, NetworkVariable could have been split into
+        // NetworkVariable and NetworkSerializableVariable or something like that, which would have caused a poor
+        // user experience and an API that's easier to get wrong than right. This is a bit ugly on the implementation
+        // side, but it gets the best achievable user experience and performance.
+        internal static WriteDelegate<T> Write = WriteValue;
+        internal static ReadDelegate<T> Read = ReadValue;
+
+
         /// <summary>
         /// Delegate type for value changed event
         /// </summary>
@@ -20,38 +69,11 @@ namespace Unity.Netcode
         /// </summary>
         public OnValueChangedDelegate OnValueChanged;
 
-        /// <summary>
-        /// Creates a NetworkVariable with the default value and custom read permission
-        /// </summary>
-        /// <param name="readPerm">The read permission for the NetworkVariable</param>
 
-        public NetworkVariable()
-        {
-        }
-
-        /// <summary>
-        /// Creates a NetworkVariable with the default value and custom read permission
-        /// </summary>
-        /// <param name="readPerm">The read permission for the NetworkVariable</param>
-        public NetworkVariable(NetworkVariableReadPermission readPerm) : base(readPerm)
-        {
-        }
-
-        /// <summary>
-        /// Creates a NetworkVariable with a custom value and custom settings
-        /// </summary>
-        /// <param name="readPerm">The read permission for the NetworkVariable</param>
-        /// <param name="value">The initial value to use for the NetworkVariable</param>
-        public NetworkVariable(NetworkVariableReadPermission readPerm, T value) : base(readPerm)
-        {
-            m_InternalValue = value;
-        }
-
-        /// <summary>
-        /// Creates a NetworkVariable with a custom value and the default read permission
-        /// </summary>
-        /// <param name="value">The initial value to use for the NetworkVariable</param>
-        public NetworkVariable(T value)
+        public NetworkVariable(T value = default,
+            NetworkVariableReadPermission readPerm = DefaultReadPerm,
+            NetworkVariableWritePermission writePerm = DefaultWritePerm)
+            : base(readPerm, writePerm)
         {
             m_InternalValue = value;
         }
@@ -67,19 +89,36 @@ namespace Unity.Netcode
             get => m_InternalValue;
             set
             {
-                // this could be improved. The Networking Manager is not always initialized here
-                //  Good place to decouple network manager from the network variable
-
-                // Also, note this is not really very water-tight, if you are running as a host
-                //  we cannot tell if a NetworkVariable write is happening inside client-ish code
-                if (m_NetworkBehaviour && (m_NetworkBehaviour.NetworkManager.IsClient && !m_NetworkBehaviour.NetworkManager.IsHost))
+                // Compare bitwise
+                if (ValueEquals(ref m_InternalValue, ref value))
                 {
-                    throw new InvalidOperationException("Client can't write to NetworkVariables");
+                    return;
                 }
+
+                if (m_NetworkBehaviour && !CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+                {
+                    throw new InvalidOperationException("Client is not allowed to write to this NetworkVariable");
+                }
+
                 Set(value);
             }
         }
 
+        // Compares two values of the same unmanaged type by underlying memory
+        // Ignoring any overriden value checks
+        // Size is fixed
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static unsafe bool ValueEquals(ref T a, ref T b)
+        {
+            // get unmanaged pointers
+            var aptr = UnsafeUtility.AddressOf(ref a);
+            var bptr = UnsafeUtility.AddressOf(ref b);
+
+            // compare addresses
+            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(T)) == 0;
+        }
+
+
         private protected void Set(T value)
         {
             m_IsDirty = true;
@@ -97,7 +136,6 @@ namespace Unity.Netcode
             WriteField(writer);
         }
 
-
         /// <summary>
         /// Reads value from the reader and applies it
         /// </summary>
@@ -106,7 +144,7 @@ namespace Unity.Netcode
         public override void ReadDelta(FastBufferReader reader, bool keepDirtyDelta)
         {
             T previousValue = m_InternalValue;
-            reader.ReadValueSafe(out m_InternalValue);
+            Read(reader, out m_InternalValue);
 
             if (keepDirtyDelta)
             {
@@ -119,13 +157,13 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void ReadField(FastBufferReader reader)
         {
-            reader.ReadValueSafe(out m_InternalValue);
+            Read(reader, out m_InternalValue);
         }
 
         /// <inheritdoc />
         public override void WriteField(FastBufferWriter writer)
         {
-            writer.WriteValueSafe(m_InternalValue);
+            Write(writer, m_InternalValue);
         }
     }
 }

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -10,7 +10,7 @@ namespace Unity.Netcode
         /// <summary>
         /// The delivery type (QoS) to send data with
         /// </summary>
-        internal const NetworkDelivery Delivery = NetworkDelivery.ReliableSequenced;
+        internal const NetworkDelivery Delivery = NetworkDelivery.ReliableFragmentedSequenced;
 
         private protected NetworkBehaviour m_NetworkBehaviour;
 
@@ -19,9 +19,15 @@ namespace Unity.Netcode
             m_NetworkBehaviour = networkBehaviour;
         }
 
-        protected NetworkVariableBase(NetworkVariableReadPermission readPermIn = NetworkVariableReadPermission.Everyone)
+        public const NetworkVariableReadPermission DefaultReadPerm = NetworkVariableReadPermission.Everyone;
+        public const NetworkVariableWritePermission DefaultWritePerm = NetworkVariableWritePermission.Server;
+
+        protected NetworkVariableBase(
+            NetworkVariableReadPermission readPerm = DefaultReadPerm,
+            NetworkVariableWritePermission writePerm = DefaultWritePerm)
         {
-            ReadPerm = readPermIn;
+            ReadPerm = readPerm;
+            WritePerm = writePerm;
         }
 
         private protected bool m_IsDirty;
@@ -37,6 +43,8 @@ namespace Unity.Netcode
         /// </summary>
         public readonly NetworkVariableReadPermission ReadPerm;
 
+        public readonly NetworkVariableWritePermission WritePerm;
+
         /// <summary>
         /// Sets whether or not the variable needs to be delta synced
         /// </summary>
@@ -62,26 +70,28 @@ namespace Unity.Netcode
             return m_IsDirty;
         }
 
-        public virtual bool ShouldWrite(ulong clientId, bool isServer)
-        {
-            return IsDirty() && isServer && CanClientRead(clientId);
-        }
-
-        /// <summary>
-        /// Gets Whether or not a specific client can read to the varaible
-        /// </summary>
-        /// <param name="clientId">The clientId of the remote client</param>
-        /// <returns>Whether or not the client can read to the variable</returns>
         public bool CanClientRead(ulong clientId)
         {
             switch (ReadPerm)
             {
+                default:
                 case NetworkVariableReadPermission.Everyone:
                     return true;
-                case NetworkVariableReadPermission.OwnerOnly:
-                    return m_NetworkBehaviour.OwnerClientId == clientId;
+                case NetworkVariableReadPermission.Owner:
+                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId;
+            }
+        }
+
+        public bool CanClientWrite(ulong clientId)
+        {
+            switch (WritePerm)
+            {
+                default:
+                case NetworkVariableWritePermission.Server:
+                    return clientId == NetworkManager.ServerClientId;
+                case NetworkVariableWritePermission.Owner:
+                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId;
             }
-            return true;
         }
 
         /// <summary>
@@ -107,7 +117,6 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="reader">The stream to read the delta from</param>
         /// <param name="keepDirtyDelta">Whether or not the delta should be kept as dirty or consumed</param>
-
         public abstract void ReadDelta(FastBufferReader reader, bool keepDirtyDelta);
 
         public virtual void Dispose()

Runtime/NetworkVariable/NetworkVariableHelper.cs

@@ -0,0 +1,22 @@
+namespace Unity.Netcode
+{
+    public class NetworkVariableHelper
+    {
+        // This is called by ILPP during module initialization for all unmanaged INetworkSerializable types
+        // This sets up NetworkVariable so that it properly calls NetworkSerialize() when wrapping an INetworkSerializable value
+        //
+        // The reason this is done is to avoid runtime reflection and boxing in NetworkVariable - without this,
+        // NetworkVariable would need to do a `var is INetworkSerializable` check, and then cast to INetworkSerializable,
+        // *both* of which would cause a boxing allocation. Alternatively, NetworkVariable could have been split into
+        // NetworkVariable and NetworkSerializableVariable or something like that, which would have caused a poor
+        // user experience and an API that's easier to get wrong than right. This is a bit ugly on the implementation
+        // side, but it gets the best achievable user experience and performance.
+        //
+        // RuntimeAccessModifiersILPP will make this `public`
+        internal static void InitializeDelegates<T>() where T : unmanaged, INetworkSerializable
+        {
+            NetworkVariable<T>.Write = NetworkVariable<T>.WriteNetworkSerializable;
+            NetworkVariable<T>.Read = NetworkVariable<T>.ReadNetworkSerializable;
+        }
+    }
+}

Runtime/NetworkVariable/NetworkVariableHelper.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: bd9e1475e8c8e4a6d935fe2409e3bd26
+guid: e54b65208bd3bbe4eaf62ca0384ae21f
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Runtime/NetworkVariable/NetworkVariablePermission.cs

@@ -1,18 +1,14 @@
 namespace Unity.Netcode
 {
-    /// <summary>
-    /// Permission type
-    /// </summary>
     public enum NetworkVariableReadPermission
     {
-        /// <summary>
-        /// Everyone
-        /// </summary>
         Everyone,
+        Owner,
+    }
 
-        /// <summary>
-        /// Owner-ownly
-        /// </summary>
-        OwnerOnly,
+    public enum NetworkVariableWritePermission
+    {
+        Server,
+        Owner
     }
 }

Runtime/Profiling/ProfilingHooks.cs

@@ -37,14 +37,14 @@ namespace Unity.Netcode
             return marker;
         }
 
-        public void OnBeforeSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery)
+        public void OnBeforeSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery) where T : INetworkMessage
         {
-            GetSenderProfilerMarker(messageType).Begin();
+            GetSenderProfilerMarker(typeof(T)).Begin();
         }
 
-        public void OnAfterSendMessage(ulong clientId, Type messageType, NetworkDelivery delivery, int messageSizeBytes)
+        public void OnAfterSendMessage<T>(ulong clientId, ref T message, NetworkDelivery delivery, int messageSizeBytes) where T : INetworkMessage
         {
-            GetSenderProfilerMarker(messageType).End();
+            GetSenderProfilerMarker(typeof(T)).End();
         }
 
         public void OnBeforeReceiveMessage(ulong senderId, Type messageType, int messageSizeBytes)
@@ -86,5 +86,15 @@ namespace Unity.Netcode
         {
             return true;
         }
+
+        public void OnBeforeHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+            // nop
+        }
+
+        public void OnAfterHandleMessage<T>(ref T message, ref NetworkContext context) where T : INetworkMessage
+        {
+            // nop
+        }
     }
 }

Runtime/Reflection/TypeExtensions.cs

@@ -1,31 +0,0 @@
-using System;
-
-namespace Unity.Netcode
-{
-    internal static class TypeExtensions
-    {
-        internal static bool HasInterface(this Type type, Type interfaceType)
-        {
-            var ifaces = type.GetInterfaces();
-            for (int i = 0; i < ifaces.Length; i++)
-            {
-                if (ifaces[i] == interfaceType)
-                {
-                    return true;
-                }
-            }
-
-            return false;
-        }
-
-        internal static bool IsNullable(this Type type)
-        {
-            if (!type.IsValueType)
-            {
-                return true; // ref-type
-            }
-
-            return Nullable.GetUnderlyingType(type) != null;
-        }
-    }
-}

Runtime/Reflection/TypeExtensions.cs.meta

@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: 3e168a2bc1a1e2642af0369780fb560c
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/SceneManagement/ISceneManagerHandler.cs

@@ -0,0 +1,28 @@
+using System;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Used to override the LoadSceneAsync and UnloadSceneAsync methods called
+    /// within the NetworkSceneManager.
+    /// </summary>
+    internal interface ISceneManagerHandler
+    {
+        // Generic action to call when a scene is finished loading/unloading
+        struct SceneEventAction
+        {
+            internal uint SceneEventId;
+            internal Action<uint> EventAction;
+            internal void Invoke()
+            {
+                EventAction.Invoke(SceneEventId);
+            }
+        }
+
+        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventAction sceneEventAction);
+
+        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventAction sceneEventAction);
+    }
+}

Runtime/SceneManagement/ISceneManagerHandler.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: a32aeecf69a2542469927066f5b88005
+guid: de907a9fb8151e240800dbcc97f8e745
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Runtime/SceneManagement/SceneEventData.cs

@@ -4,88 +4,88 @@ using System.Linq;
 using Unity.Collections;
 using UnityEngine.SceneManagement;
 
-
 namespace Unity.Netcode
 {
     /// <summary>
-    /// The different types of scene events communicated between a server and client.
-    /// Used by <see cref="NetworkSceneManager"/> for <see cref="SceneEventMessage"/> messages
-    /// Note: This is only when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled
-    /// See also: <see cref="SceneEvent"/>
+    /// The different types of scene events communicated between a server and client. <br/>
+    /// Used by <see cref="NetworkSceneManager"/> for <see cref="SceneEventMessage"/> messages.<br/>
+    /// <em>Note: This is only when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled.</em><br/>
+    /// See also: <br/>
+    /// <seealso cref="SceneEvent"/>
     /// </summary>
     public enum SceneEventType : byte
     {
         /// <summary>
-        /// Load a scene
-        /// Invocation: Server Side
-        /// Message Flow: Server to client
-        /// Event Notification: Both server and client are notified a load scene event started
+        /// Load a scene<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to client<br/>
+        /// <b>Event Notification:</b> Both server and client are notified a load scene event started
         /// </summary>
         Load,
         /// <summary>
-        /// Unload a scene
-        /// Invocation: Server Side
-        /// Message Flow: Server to client
-        /// Event Notification: Both server and client are notified an unload scene event started
+        /// Unload a scene<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to client<br/>
+        /// <b>Event Notification:</b> Both server and client are notified an unload scene event started.
         /// </summary>
         Unload,
         /// <summary>
-        /// Synchronize current game session state for approved clients
-        /// Invocation: Server Side
-        /// Message Flow: Server to client
-        /// Event Notification: Server and Client receives a local notification (server receives the ClientId being synchronized)
+        /// Synchronizes current game session state for newly approved clients<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to client<br/>
+        /// <b>Event Notification:</b> Server and Client receives a local notification (<em>server receives the ClientId being synchronized</em>).
         /// </summary>
         Synchronize,
         /// <summary>
-        /// Game session re-synchronization of NetworkObjects that were destroyed during a <see cref="Synchronize"/> event
-        /// Invocation: Server Side
-        /// Message Flow: Server to client
-        /// Event Notification: Both server and client receive a local notification
-        /// Note: This will be removed once snapshot and buffered messages are finalized as it will no longer be needed at that point
+        /// Game session re-synchronization of NetworkObjects that were destroyed during a <see cref="Synchronize"/> event<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to client<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification<br/>
         /// </summary>
         ReSynchronize,
         /// <summary>
-        /// All clients have finished loading a scene
-        /// Invocation: Server Side
-        /// Message Flow: Server to Client
-        /// Event Notification: Both server and client receive a local notification containing the clients that finished
-        /// as well as the clients that timed out (if any).
+        /// All clients have finished loading a scene<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to Client<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification containing the clients that finished
+        /// as well as the clients that timed out(<em>if any</em>).
         /// </summary>
         LoadEventCompleted,
         /// <summary>
-        /// All clients have unloaded a scene
-        /// Invocation: Server Side
-        /// Message Flow: Server to Client
-        /// Event Notification: Both server and client receive a local notification containing the clients that finished
-        /// as well as the clients that timed out (if any).
+        /// All clients have unloaded a scene<br/>
+        /// <b>Invocation:</b> Server Side<br/>
+        /// <b>Message Flow:</b> Server to Client<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification containing the clients that finished
+        /// as well as the clients that timed out(<em>if any</em>).
         /// </summary>
         UnloadEventCompleted,
         /// <summary>
-        /// A client has finished loading a scene
-        /// Invocation: Client Side
-        /// Message Flow: Client to Server
-        /// Event Notification: Both server and client receive a local notification
+        /// A client has finished loading a scene<br/>
+        /// <b>Invocation:</b> Client Side<br/>
+        /// <b>Message Flow:</b> Client to Server<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification.
         /// </summary>
         LoadComplete,
         /// <summary>
-        /// A client has finished unloading a scene
-        /// Invocation: Client Side
-        /// Message Flow: Client to Server
-        /// Event Notification: Both server and client receive a local notification
+        /// A client has finished unloading a scene<br/>
+        /// <b>Invocation:</b> Client Side<br/>
+        /// <b>Message Flow:</b> Client to Server<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification.
         /// </summary>
         UnloadComplete,
         /// <summary>
-        /// A client has finished synchronizing from a <see cref="Synchronize"/> event
-        /// Invocation: Client Side
-        /// Message Flow: Client to Server
-        /// Event Notification: Both server and client receive a local notification
+        /// A client has finished synchronizing from a <see cref="Synchronize"/> event<br/>
+        /// <b>Invocation:</b> Client Side<br/>
+        /// <b>Message Flow:</b> Client to Server<br/>
+        /// <b>Event Notification:</b> Both server and client receive a local notification.
         /// </summary>
         SynchronizeComplete,
     }
 
     /// <summary>
     /// Used by <see cref="NetworkSceneManager"/> for <see cref="SceneEventMessage"/> messages
-    /// Note: This is only when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled
+    /// <em>Note: This is only when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled.</em><br/>
+    /// See also: <seealso cref="SceneEvent"/>
     /// </summary>
     internal class SceneEventData : IDisposable
     {
@@ -98,6 +98,10 @@ namespace Unity.Netcode
         internal uint SceneHash;
         internal int SceneHandle;
 
+        // Used by the client during synchronization
+        internal uint ClientSceneHash;
+        internal int ClientSceneHandle;
+
         /// Only used for <see cref="SceneEventType.Synchronize"/> scene events, this assures permissions when writing
         /// NetworkVariable information.  If that process changes, then we need to update this
         internal ulong TargetClientId;
@@ -228,7 +232,14 @@ namespace Unity.Netcode
 
         internal void AddSpawnedNetworkObjects()
         {
-            m_NetworkObjectsSync = m_NetworkManager.SpawnManager.SpawnedObjectsList.ToList();
+            m_NetworkObjectsSync.Clear();
+            foreach (var sobj in m_NetworkManager.SpawnManager.SpawnedObjectsList)
+            {
+                if (sobj.Observers.Contains(TargetClientId))
+                {
+                    m_NetworkObjectsSync.Add(sobj);
+                }
+            }
             m_NetworkObjectsSync.Sort(SortNetworkObjects);
         }
 
@@ -580,9 +591,6 @@ namespace Unity.Netcode
                         networkObject.IsSpawned = false;
                         if (m_NetworkManager.PrefabHandler.ContainsHandler(networkObject))
                         {
-                            // Since this is the client side and we have missed the delete message, until the Snapshot system is in place for spawn and despawn handling
-                            // we have to remove this from the list of spawned objects manually or when a NetworkObjectId is recycled the client will throw an error
-                            // about the id already being assigned.
                             if (m_NetworkManager.SpawnManager.SpawnedObjects.ContainsKey(networkObjectId))
                             {
                                 m_NetworkManager.SpawnManager.SpawnedObjects.Remove(networkObjectId);

Runtime/SceneManagement/SceneEventProgress.cs

@@ -9,10 +9,10 @@ namespace Unity.Netcode
 {
     /// <summary>
     /// Used by <see cref="NetworkSceneManager"/> to determine if a server invoked scene event has started.
-    /// The returned status is stored in the <see cref="SceneEventProgress.Status"/> property.
-    /// Note: This was formally known as SwitchSceneProgress which contained the <see cref="AsyncOperation"/>.
+    /// The returned status is stored in the <see cref="SceneEventProgress.Status"/> property.<br/>
+    /// <em>Note: This was formally known as SwitchSceneProgress which contained the <see cref="AsyncOperation"/>.
     /// All <see cref="AsyncOperation"/>s are now delivered by the <see cref="NetworkSceneManager.OnSceneEvent"/> event handler
-    /// via the <see cref="SceneEvent"/> parameter.
+    /// via the <see cref="SceneEvent"/> parameter.</em>
     /// </summary>
     public enum SceneEventProgressStatus
     {
@@ -21,31 +21,30 @@ namespace Unity.Netcode
         /// </summary>
         None,
         /// <summary>
-        /// The scene event was successfully started
+        /// The scene event was successfully started.
         /// </summary>
         Started,
         /// <summary>
-        /// Returned if you try to unload a scene that was not yet loaded
+        /// Returned if you try to unload a scene that was not yet loaded.
         /// </summary>
         SceneNotLoaded,
         /// <summary>
-        /// Returned if you try to start a new scene event before a previous one is finished
+        /// Returned if you try to start a new scene event before a previous one is finished.
         /// </summary>
         SceneEventInProgress,
         /// <summary>
         /// Returned if the scene name used with <see cref="NetworkSceneManager.LoadScene(string, LoadSceneMode)"/>
-        /// or <see cref="NetworkSceneManager.UnloadScene(Scene)"/>is invalid
+        /// or <see cref="NetworkSceneManager.UnloadScene(Scene)"/>is invalid.
         /// </summary>
         InvalidSceneName,
         /// <summary>
         /// Server side: Returned if the <see cref="NetworkSceneManager.VerifySceneBeforeLoading"/> delegate handler returns false
-        /// (i.e. scene is considered not valid/safe to load)
+        /// (<em>i.e. scene is considered not valid/safe to load</em>).
         /// </summary>
         SceneFailedVerification,
         /// <summary>
-        /// This is used for internal error notifications.
-        /// If you receive this event then it is most likely due to a bug.
-        /// If you receive this event repeatedly, then please open a GitHub issue with steps to replicate
+        /// This is used for internal error notifications.<br/>
+        /// If you receive this event then it is most likely due to a bug (<em>please open a GitHub issue with steps to replicate</em>).<br/>
         /// </summary>
         InternalNetcodeError,
     }

Runtime/Serialization/BytePacker.cs

@@ -10,7 +10,7 @@ namespace Unity.Netcode
     public static class BytePacker
     {
 #if UNITY_NETCODE_DEBUG_NO_PACKING
-        
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void WriteValuePacked<T>(FastBufferWriter writer, T value) where T: unmanaged => writer.WriteValueSafe(value);
 #else
@@ -277,10 +277,21 @@ namespace Unity.Netcode
 
 
 #if UNITY_NETCODE_DEBUG_NO_PACKING
-        
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void WriteValueBitPacked<T>(FastBufferWriter writer, T value) where T: unmanaged => writer.WriteValueSafe(value);
 #else
+
+        public const ushort BitPackedUshortMax = (1 << 15) - 1;
+        public const short BitPackedShortMax = (1 << 14) - 1;
+        public const short BitPackedShortMin = -(1 << 14);
+        public const uint BitPackedUintMax = (1 << 30) - 1;
+        public const int BitPackedIntMax = (1 << 29) - 1;
+        public const int BitPackedIntMin = -(1 << 29);
+        public const ulong BitPackedULongMax = (1L << 61) - 1;
+        public const long BitPackedLongMax = (1L << 60) - 1;
+        public const long BitPackedLongMin = -(1L << 60);
+
         /// <summary>
         /// Writes a 14-bit signed short to the buffer in a bit-encoded packed format.
         /// The first bit indicates whether the value is 1 byte or 2.
@@ -307,7 +318,7 @@ namespace Unity.Netcode
         public static void WriteValueBitPacked(FastBufferWriter writer, ushort value)
         {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value >= 0b1000_0000_0000_0000)
+            if (value >= BitPackedUshortMax)
             {
                 throw new ArgumentException("BitPacked ushorts must be <= 15 bits");
             }
@@ -356,7 +367,7 @@ namespace Unity.Netcode
         public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
         {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value >= 0b0100_0000_0000_0000_0000_0000_0000_0000)
+            if (value > BitPackedUintMax)
             {
                 throw new ArgumentException("BitPacked uints must be <= 30 bits");
             }
@@ -396,7 +407,7 @@ namespace Unity.Netcode
         public static void WriteValueBitPacked(FastBufferWriter writer, ulong value)
         {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value >= 0b0010_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000_0000)
+            if (value > BitPackedULongMax)
             {
                 throw new ArgumentException("BitPacked ulongs must be <= 61 bits");
             }

Runtime/Serialization/FastBufferReader.cs

@@ -19,7 +19,7 @@ namespace Unity.Netcode
 #endif
         }
 
-        internal readonly unsafe ReaderHandle* Handle;
+        internal unsafe ReaderHandle* Handle;
 
         /// <summary>
         /// Get the current read position
@@ -39,6 +39,11 @@ namespace Unity.Netcode
             get => Handle->Length;
         }
 
+        /// <summary>
+        /// Gets a value indicating whether the reader has been initialized and a handle allocated.
+        /// </summary>
+        public unsafe bool IsInitialized => Handle != null;
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal unsafe void CommitBitwiseReads(int amount)
         {
@@ -76,7 +81,7 @@ namespace Unity.Netcode
 
         /// <summary>
         /// Create a FastBufferReader from a NativeArray.
-        /// 
+        ///
         /// A new buffer will be created using the given allocator and the value will be copied in.
         /// FastBufferReader will then own the data.
         ///
@@ -93,12 +98,12 @@ namespace Unity.Netcode
         /// <param name="offset"></param>
         public unsafe FastBufferReader(NativeArray<byte> buffer, Allocator allocator, int length = -1, int offset = 0)
         {
-            Handle = CreateHandle((byte*)buffer.GetUnsafePtr(), Math.Max(1, length == -1 ? buffer.Length : length), offset, allocator);
+            Handle = CreateHandle((byte*)buffer.GetUnsafePtr(), length == -1 ? buffer.Length : length, offset, allocator);
         }
 
         /// <summary>
         /// Create a FastBufferReader from an ArraySegment.
-        /// 
+        ///
         /// A new buffer will be created using the given allocator and the value will be copied in.
         /// FastBufferReader will then own the data.
         ///
@@ -117,13 +122,13 @@ namespace Unity.Netcode
             }
             fixed (byte* data = buffer.Array)
             {
-                Handle = CreateHandle(data, Math.Max(1, length == -1 ? buffer.Count : length), offset, allocator);
+                Handle = CreateHandle(data, length == -1 ? buffer.Count : length, offset, allocator);
             }
         }
 
         /// <summary>
         /// Create a FastBufferReader from an existing byte array.
-        /// 
+        ///
         /// A new buffer will be created using the given allocator and the value will be copied in.
         /// FastBufferReader will then own the data.
         ///
@@ -142,13 +147,13 @@ namespace Unity.Netcode
             }
             fixed (byte* data = buffer)
             {
-                Handle = CreateHandle(data, Math.Max(1, length == -1 ? buffer.Length : length), offset, allocator);
+                Handle = CreateHandle(data, length == -1 ? buffer.Length : length, offset, allocator);
             }
         }
 
         /// <summary>
         /// Create a FastBufferReader from an existing byte buffer.
-        /// 
+        ///
         /// A new buffer will be created using the given allocator and the value will be copied in.
         /// FastBufferReader will then own the data.
         ///
@@ -165,12 +170,12 @@ namespace Unity.Netcode
         /// <param name="offset">The offset of the buffer to start copying from</param>
         public unsafe FastBufferReader(byte* buffer, Allocator allocator, int length, int offset = 0)
         {
-            Handle = CreateHandle(buffer, Math.Max(1, length), offset, allocator);
+            Handle = CreateHandle(buffer, length, offset, allocator);
         }
 
         /// <summary>
         /// Create a FastBufferReader from a FastBufferWriter.
-        /// 
+        ///
         /// A new buffer will be created using the given allocator and the value will be copied in.
         /// FastBufferReader will then own the data.
         ///
@@ -187,7 +192,7 @@ namespace Unity.Netcode
         /// <param name="offset">The offset of the buffer to start copying from</param>
         public unsafe FastBufferReader(FastBufferWriter writer, Allocator allocator, int length = -1, int offset = 0)
         {
-            Handle = CreateHandle(writer.GetUnsafePtr(), Math.Max(1, length == -1 ? writer.Length : length), offset, allocator);
+            Handle = CreateHandle(writer.GetUnsafePtr(), length == -1 ? writer.Length : length, offset, allocator);
         }
 
         /// <summary>
@@ -196,6 +201,7 @@ namespace Unity.Netcode
         public unsafe void Dispose()
         {
             UnsafeUtility.Free(Handle, Handle->Allocator);
+            Handle = null;
         }
 
         /// <summary>
@@ -250,7 +256,7 @@ namespace Unity.Netcode
         /// When you know you will be reading multiple fields back-to-back and you know the total size,
         /// you can call TryBeginRead() once on the total size, and then follow it with calls to
         /// ReadValue() instead of ReadValueSafe() for faster serialization.
-        /// 
+        ///
         /// Unsafe read operations will throw OverflowException in editor and development builds if you
         /// go past the point you've marked using TryBeginRead(). In release builds, OverflowException will not be thrown
         /// for performance reasons, since the point of using TryBeginRead is to avoid bounds checking in the following
@@ -284,7 +290,7 @@ namespace Unity.Netcode
         /// When you know you will be reading multiple fields back-to-back and you know the total size,
         /// you can call TryBeginRead() once on the total size, and then follow it with calls to
         /// ReadValue() instead of ReadValueSafe() for faster serialization.
-        /// 
+        ///
         /// Unsafe read operations will throw OverflowException in editor and development builds if you
         /// go past the point you've marked using TryBeginRead(). In release builds, OverflowException will not be thrown
         /// for performance reasons, since the point of using TryBeginRead is to avoid bounds checking in the following

Runtime/Serialization/FastBufferWriter.cs

@@ -22,7 +22,9 @@ namespace Unity.Netcode
 #endif
         }
 
-        internal readonly unsafe WriterHandle* Handle;
+        internal unsafe WriterHandle* Handle;
+
+        private static byte[] s_ByteArrayCache = new byte[65535];
 
         /// <summary>
         /// The current write position
@@ -60,6 +62,11 @@ namespace Unity.Netcode
             get => Handle->Position > Handle->Length ? Handle->Position : Handle->Length;
         }
 
+        /// <summary>
+        /// Gets a value indicating whether the writer has been initialized and a handle allocated.
+        /// </summary>
+        public unsafe bool IsInitialized => Handle != null;
+
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal unsafe void CommitBitwiseWrites(int amount)
@@ -78,6 +85,10 @@ namespace Unity.Netcode
         /// <param name="maxSize">Maximum size the buffer can grow to. If less than size, buffer cannot grow.</param>
         public unsafe FastBufferWriter(int size, Allocator allocator, int maxSize = -1)
         {
+            // Allocating both the Handle struct and the buffer in a single allocation - sizeof(WriterHandle) + size
+            // The buffer for the initial allocation is the next block of memory after the handle itself.
+            // If the buffer grows, a new buffer will be allocated and the handle pointer pointed at the new location...
+            // The original buffer won't be deallocated until the writer is destroyed since it's part of the handle allocation.
             Handle = (WriterHandle*)UnsafeUtility.Malloc(sizeof(WriterHandle) + size, UnsafeUtility.AlignOf<WriterHandle>(), allocator);
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             UnsafeUtility.MemSet(Handle, 0, sizeof(WriterHandle) + size);
@@ -105,6 +116,7 @@ namespace Unity.Netcode
                 UnsafeUtility.Free(Handle->BufferPointer, Handle->Allocator);
             }
             UnsafeUtility.Free(Handle, Handle->Allocator);
+            Handle = null;
         }
 
         /// <summary>
@@ -183,7 +195,7 @@ namespace Unity.Netcode
             var newSize = Math.Min(desiredSize, Handle->MaxCapacity);
             byte* newBuffer = (byte*)UnsafeUtility.Malloc(newSize, UnsafeUtility.AlignOf<byte>(), Handle->Allocator);
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            UnsafeUtility.MemSet(newBuffer, 0, sizeof(WriterHandle) + newSize);
+            UnsafeUtility.MemSet(newBuffer, 0, newSize);
 #endif
             UnsafeUtility.MemCpy(newBuffer, Handle->BufferPointer, Length);
             if (Handle->BufferGrew)
@@ -201,7 +213,7 @@ namespace Unity.Netcode
         /// When you know you will be writing multiple fields back-to-back and you know the total size,
         /// you can call TryBeginWrite() once on the total size, and then follow it with calls to
         /// WriteValue() instead of WriteValueSafe() for faster serialization.
-        /// 
+        ///
         /// Unsafe write operations will throw OverflowException in editor and development builds if you
         /// go past the point you've marked using TryBeginWrite(). In release builds, OverflowException will not be thrown
         /// for performance reasons, since the point of using TryBeginWrite is to avoid bounds checking in the following
@@ -247,7 +259,7 @@ namespace Unity.Netcode
         /// When you know you will be writing multiple fields back-to-back and you know the total size,
         /// you can call TryBeginWrite() once on the total size, and then follow it with calls to
         /// WriteValue() instead of WriteValueSafe() for faster serialization.
-        /// 
+        ///
         /// Unsafe write operations will throw OverflowException in editor and development builds if you
         /// go past the point you've marked using TryBeginWrite(). In release builds, OverflowException will not be thrown
         /// for performance reasons, since the point of using TryBeginWrite is to avoid bounds checking in the following
@@ -349,6 +361,29 @@ namespace Unity.Netcode
             return ret;
         }
 
+        /// <summary>
+        /// Uses a static cached array to create an array segment with no allocations.
+        /// This array can only be used until the next time ToTempByteArray() is called on ANY FastBufferWriter,
+        /// as the cached buffer is shared by all of them and will be overwritten.
+        /// As such, this should be used with care.
+        /// </summary>
+        /// <returns></returns>
+        internal unsafe ArraySegment<byte> ToTempByteArray()
+        {
+            var length = Length;
+            if (length > s_ByteArrayCache.Length)
+            {
+                return new ArraySegment<byte>(ToArray(), 0, length);
+            }
+
+            fixed (byte* b = s_ByteArrayCache)
+            {
+                UnsafeUtility.MemCpy(b, Handle->BufferPointer, length);
+            }
+
+            return new ArraySegment<byte>(s_ByteArrayCache, 0, length);
+        }
+
         /// <summary>
         /// Gets a direct pointer to the underlying buffer
         /// </summary>
@@ -399,7 +434,7 @@ namespace Unity.Netcode
         /// <param name="count"></param>
         /// <param name="offset"></param>
         /// <typeparam name="T"></typeparam>
-        public void WriteNetworkSerializable<T>(INetworkSerializable[] array, int count = -1, int offset = 0) where T : INetworkSerializable
+        public void WriteNetworkSerializable<T>(T[] array, int count = -1, int offset = 0) where T : INetworkSerializable
         {
             int sizeInTs = count != -1 ? count : array.Length - offset;
             WriteValueSafe(sizeInTs);

Runtime/Spawning/NetworkSpawnManager.cs

@@ -21,12 +21,129 @@ namespace Unity.Netcode
         /// </summary>
         public readonly HashSet<NetworkObject> SpawnedObjectsList = new HashSet<NetworkObject>();
 
+        /// <summary>
+        /// Use to get all NetworkObjects owned by a client
+        /// Ownership to Objects Table Format:
+        /// [ClientId][NetworkObjectId][NetworkObject]
+        /// Server: Keeps track of all clients' ownership
+        /// Client: Keeps track of only its ownership
+        /// </summary>
+        public readonly Dictionary<ulong, Dictionary<ulong, NetworkObject>> OwnershipToObjectsTable = new Dictionary<ulong, Dictionary<ulong, NetworkObject>>();
+
+        /// <summary>
+        /// Object to Ownership Table:
+        /// [NetworkObjectId][ClientId]
+        /// Used internally to find the client Id that currently owns
+        /// the NetworkObject
+        /// </summary>
+        private Dictionary<ulong, ulong> m_ObjectToOwnershipTable = new Dictionary<ulong, ulong>();
+
+        /// <summary>
+        /// Used to update a NetworkObject's ownership
+        /// </summary>
+        internal void UpdateOwnershipTable(NetworkObject networkObject, ulong newOwner, bool isRemoving = false)
+        {
+            var previousOwner = newOwner;
+
+            // Use internal lookup table to see if the NetworkObject has a previous owner
+            if (m_ObjectToOwnershipTable.ContainsKey(networkObject.NetworkObjectId))
+            {
+                // Keep track of the previous owner's ClientId
+                previousOwner = m_ObjectToOwnershipTable[networkObject.NetworkObjectId];
+
+                // We are either despawning (remove) or changing ownership (assign)
+                if (isRemoving)
+                {
+                    m_ObjectToOwnershipTable.Remove(networkObject.NetworkObjectId);
+                }
+                else
+                {
+                    m_ObjectToOwnershipTable[networkObject.NetworkObjectId] = newOwner;
+                }
+            }
+            else
+            {
+                // Otherwise, just add a new lookup entry
+                m_ObjectToOwnershipTable.Add(networkObject.NetworkObjectId, newOwner);
+            }
+
+            // Check to see if we had a previous owner
+            if (previousOwner != newOwner && OwnershipToObjectsTable.ContainsKey(previousOwner))
+            {
+                // Before updating the previous owner, assure this entry exists
+                if (OwnershipToObjectsTable[previousOwner].ContainsKey(networkObject.NetworkObjectId))
+                {
+                    // Remove the previous owner's entry
+                    OwnershipToObjectsTable[previousOwner].Remove(networkObject.NetworkObjectId);
+
+                    // Server or Host alway invokes the lost ownership notification locally
+                    if (NetworkManager.IsServer)
+                    {
+                        networkObject.InvokeBehaviourOnLostOwnership();
+                    }
+
+                    // If we are removing the entry (i.e. despawning or client lost ownership)
+                    if (isRemoving)
+                    {
+                        return;
+                    }
+                }
+                else
+                {
+                    // Really, as long as UpdateOwnershipTable is invoked when ownership is gained or lost this should never happen
+                    throw new Exception($"Client-ID {previousOwner} had a partial {nameof(m_ObjectToOwnershipTable)} entry! Potentially corrupted {nameof(OwnershipToObjectsTable)}?");
+                }
+            }
+
+            // If the owner doesn't have an entry then create one
+            if (!OwnershipToObjectsTable.ContainsKey(newOwner))
+            {
+                OwnershipToObjectsTable.Add(newOwner, new Dictionary<ulong, NetworkObject>());
+            }
+
+            // Sanity check to make sure we don't already have this entry (we shouldn't)
+            if (!OwnershipToObjectsTable[newOwner].ContainsKey(networkObject.NetworkObjectId))
+            {
+                // Add the new ownership entry
+                OwnershipToObjectsTable[newOwner].Add(networkObject.NetworkObjectId, networkObject);
+
+                // Server or Host always invokes the gained ownership notification locally
+                if (NetworkManager.IsServer)
+                {
+                    networkObject.InvokeBehaviourOnGainedOwnership();
+                }
+            }
+            else if (isRemoving)
+            {
+                OwnershipToObjectsTable[previousOwner].Remove(networkObject.NetworkObjectId);
+            }
+            else if (NetworkManager.LogLevel == LogLevel.Developer)
+            {
+                NetworkLog.LogWarning($"Setting ownership twice? Client-ID {previousOwner} already owns NetworkObject ID {networkObject.NetworkObjectId}!");
+            }
+        }
+
+        /// <summary>
+        /// Returns a list of all NetworkObjects that belong to a client.
+        /// </summary>
+        /// <param name="clientId">the client's id  <see cref="NetworkManager.LocalClientId"/></param>
+        public List<NetworkObject> GetClientOwnedObjects(ulong clientId)
+        {
+            if (!OwnershipToObjectsTable.ContainsKey(clientId))
+            {
+                OwnershipToObjectsTable.Add(clientId, new Dictionary<ulong, NetworkObject>());
+            }
+            return OwnershipToObjectsTable[clientId].Values.ToList();
+        }
+
+
         private struct TriggerData
         {
             public FastBufferReader Reader;
             public MessageHeader Header;
             public ulong SenderId;
             public float Timestamp;
+            public int SerializedHeaderSize;
         }
         private struct TriggerInfo
         {
@@ -95,13 +212,12 @@ namespace Unity.Netcode
         /// <summary>
         /// Defers processing of a message until the moment a specific networkObjectId is spawned.
         /// This is to handle situations where an RPC or other object-specific message arrives before the spawn does,
-        /// either due to it being requested in OnNetworkSpawn before the spawn call has been executed, or with
-        /// snapshot spawns enabled where the spawn is sent unreliably and not until the end of the frame.
+        /// either due to it being requested in OnNetworkSpawn before the spawn call has been executed
         ///
         /// There is a one second maximum lifetime of triggers to avoid memory leaks. After one second has passed
         /// without the requested object ID being spawned, the triggers for it are automatically deleted.
         /// </summary>
-        internal unsafe void TriggerOnSpawn(ulong networkObjectId, FastBufferReader reader, in NetworkContext context)
+        internal unsafe void TriggerOnSpawn(ulong networkObjectId, FastBufferReader reader, ref NetworkContext context)
         {
             if (!m_Triggers.ContainsKey(networkObjectId))
             {
@@ -117,7 +233,8 @@ namespace Unity.Netcode
                 Reader = new FastBufferReader(reader.GetUnsafePtr(), Allocator.Persistent, reader.Length),
                 Header = context.Header,
                 Timestamp = context.Timestamp,
-                SenderId = context.SenderId
+                SenderId = context.SenderId,
+                SerializedHeaderSize = context.SerializedHeaderSize
             });
         }
 
@@ -154,6 +271,24 @@ namespace Unity.Netcode
                 m_Triggers.Remove(staleKeys[i]);
             }
         }
+        /// <summary>
+        /// Cleans up any trigger that's existed for more than a second.
+        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
+        /// </summary>
+        internal void CleanupAllTriggers()
+        {
+            foreach (var kvp in m_Triggers)
+            {
+                foreach (var data in kvp.Value.TriggerData)
+                {
+                    data.Reader.Dispose();
+                }
+
+                kvp.Value.TriggerData.Dispose();
+            }
+
+            m_Triggers.Clear();
+        }
 
         internal void RemoveOwnership(NetworkObject networkObject)
         {
@@ -167,24 +302,24 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is not spawned");
             }
 
-            for (int i = NetworkManager.ConnectedClients[networkObject.OwnerClientId].OwnedObjects.Count - 1;
-                i > -1;
-                i--)
+            // If we made it here then we are the server and if the server is determined to already be the owner
+            // then ignore the RemoveOwnership invocation.
+            if (networkObject.OwnerClientId == NetworkManager.ServerClientId)
             {
-                if (NetworkManager.ConnectedClients[networkObject.OwnerClientId].OwnedObjects[i] == networkObject)
-                {
-                    NetworkManager.ConnectedClients[networkObject.OwnerClientId].OwnedObjects.RemoveAt(i);
-                }
+                return;
             }
 
-            networkObject.OwnerClientIdInternal = null;
+            // Server removes the entry and takes over ownership before notifying
+            UpdateOwnershipTable(networkObject, NetworkManager.ServerClientId, true);
+
+            networkObject.OwnerClientId = NetworkManager.ServerClientId;
 
             var message = new ChangeOwnershipMessage
             {
                 NetworkObjectId = networkObject.NetworkObjectId,
                 OwnerClientId = networkObject.OwnerClientId
             };
-            var size = NetworkManager.SendMessage(message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);
+            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);
 
             foreach (var client in NetworkManager.ConnectedClients)
             {
@@ -207,7 +342,7 @@ namespace Unity.Netcode
                 return NetworkManager.ConnectedClients.TryGetValue(clientId, out networkClient);
             }
 
-            if (clientId == NetworkManager.LocalClient.ClientId)
+            if (NetworkManager.LocalClient != null && clientId == NetworkManager.LocalClient.ClientId)
             {
                 networkClient = NetworkManager.LocalClient;
                 return true;
@@ -229,28 +364,17 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is not spawned");
             }
 
-            if (TryGetNetworkClient(networkObject.OwnerClientId, out NetworkClient networkClient))
-            {
-                for (int i = networkClient.OwnedObjects.Count - 1; i >= 0; i--)
-                {
-                    if (networkClient.OwnedObjects[i] == networkObject)
-                    {
-                        networkClient.OwnedObjects.RemoveAt(i);
-                    }
-                }
-
-                networkClient.OwnedObjects.Add(networkObject);
-            }
-
             networkObject.OwnerClientId = clientId;
 
+            // Server adds entries for all client ownership
+            UpdateOwnershipTable(networkObject, networkObject.OwnerClientId);
 
             var message = new ChangeOwnershipMessage
             {
                 NetworkObjectId = networkObject.NetworkObjectId,
                 OwnerClientId = networkObject.OwnerClientId
             };
-            var size = NetworkManager.SendMessage(message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);
+            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);
 
             foreach (var client in NetworkManager.ConnectedClients)
             {
@@ -374,7 +498,7 @@ namespace Unity.Netcode
         }
 
         // Ran on both server and client
-        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong? ownerClientId, bool destroyWithScene)
+        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
         {
             if (networkObject == null)
             {
@@ -386,6 +510,15 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is already spawned");
             }
 
+            if (!sceneObject)
+            {
+                var networkObjectChildren = networkObject.GetComponentsInChildren<NetworkObject>();
+                if (networkObjectChildren.Length > 1)
+                {
+                    Debug.LogError("Spawning NetworkObjects with nested NetworkObjects is only supported for scene objects. Child NetworkObjects will not be spawned over the network!");
+                }
+            }
+
             SpawnNetworkObjectLocallyCommon(networkObject, networkId, sceneObject, playerObject, ownerClientId, destroyWithScene);
         }
 
@@ -403,15 +536,12 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is already spawned");
             }
 
-            if (sceneObject.Header.HasNetworkVariables)
-            {
-                networkObject.SetNetworkVariableData(variableData);
-            }
+            networkObject.SetNetworkVariableData(variableData);
 
             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)
+        private void SpawnNetworkObjectLocallyCommon(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
         {
             if (SpawnedObjects.ContainsKey(networkId))
             {
@@ -422,38 +552,45 @@ namespace Unity.Netcode
             // this initialization really should be at the bottom of the function
             networkObject.IsSpawned = true;
 
-            // this initialization really should be at the top of this function.  If and when we break the
+            // this initialization really should be at the top of this function. If and when we break the
             //  NetworkVariable dependency on NetworkBehaviour, this otherwise creates problems because
             //  SetNetworkVariableData above calls InitializeVariables, and the 'baked out' data isn't ready there;
-            //  the current design banks on getting the network behaviour set and then only reading from it
-            //  after the below initialization code.  However cowardice compels me to hold off on moving this until
-            //  that commit
+            //  the current design banks on getting the network behaviour set and then only reading from it after the
+            //  below initialization code. However cowardice compels me to hold off on moving this until that commit
             networkObject.IsSceneObject = sceneObject;
             networkObject.NetworkObjectId = networkId;
 
             networkObject.DestroyWithScene = sceneObject || destroyWithScene;
 
-            networkObject.OwnerClientIdInternal = ownerClientId;
+            networkObject.OwnerClientId = ownerClientId;
+
             networkObject.IsPlayerObject = playerObject;
 
             SpawnedObjects.Add(networkObject.NetworkObjectId, networkObject);
             SpawnedObjectsList.Add(networkObject);
 
-            if (ownerClientId != null)
+            if (NetworkManager.IsServer)
             {
-                if (NetworkManager.IsServer)
+                if (playerObject)
                 {
-                    if (playerObject)
+                    // If there was an already existing player object for this player, then mark it as no longer
+                    // a player object.
+                    if (NetworkManager.ConnectedClients[ownerClientId].PlayerObject != null)
                     {
-                        NetworkManager.ConnectedClients[ownerClientId.Value].PlayerObject = networkObject;
-                    }
-                    else
-                    {
-                        NetworkManager.ConnectedClients[ownerClientId.Value].OwnedObjects.Add(networkObject);
+                        NetworkManager.ConnectedClients[ownerClientId].PlayerObject.IsPlayerObject = false;
                     }
+                    NetworkManager.ConnectedClients[ownerClientId].PlayerObject = networkObject;
                 }
-                else if (playerObject && ownerClientId.Value == NetworkManager.LocalClientId)
+            }
+            else if (ownerClientId == NetworkManager.LocalClientId)
+            {
+                if (playerObject)
                 {
+                    // If there was an already existing player object for this player, then mark it as no longer a player object.
+                    if (NetworkManager.LocalClient.PlayerObject != null)
+                    {
+                        NetworkManager.LocalClient.PlayerObject.IsPlayerObject = false;
+                    }
                     NetworkManager.LocalClient.PlayerObject = networkObject;
                 }
             }
@@ -483,35 +620,38 @@ namespace Unity.Netcode
                 foreach (var trigger in triggerInfo.TriggerData)
                 {
                     // Reader will be disposed within HandleMessage
-                    NetworkManager.MessagingSystem.HandleMessage(trigger.Header, trigger.Reader, trigger.SenderId, trigger.Timestamp);
+                    NetworkManager.MessagingSystem.HandleMessage(trigger.Header, trigger.Reader, trigger.SenderId, trigger.Timestamp, trigger.SerializedHeaderSize);
                 }
 
                 triggerInfo.TriggerData.Dispose();
                 m_Triggers.Remove(networkId);
             }
+
+            // propagate the IsSceneObject setting to child NetworkObjects
+            var children = networkObject.GetComponentsInChildren<NetworkObject>();
+            foreach (var childObject in children)
+            {
+                childObject.IsSceneObject = sceneObject;
+            }
         }
 
         internal void SendSpawnCallForObject(ulong clientId, NetworkObject networkObject)
         {
-            if (!NetworkManager.NetworkConfig.UseSnapshotSpawn)
+            //Currently, if this is called and the clientId (destination) is the server's client Id, this case will be checked
+            // within the below Send function.  To avoid unwarranted allocation of a PooledNetworkBuffer placing this check here. [NSS]
+            if (NetworkManager.IsServer && clientId == NetworkManager.ServerClientId)
             {
-                //Currently, if this is called and the clientId (destination) is the server's client Id, this case
-                //will be checked within the below Send function.  To avoid unwarranted allocation of a PooledNetworkBuffer
-                //placing this check here. [NSS]
-                if (NetworkManager.IsServer && clientId == NetworkManager.ServerClientId)
-                {
-                    return;
-                }
-
-                var message = new CreateObjectMessage
-                {
-                    ObjectInfo = networkObject.GetMessageSceneObject(clientId)
-                };
-                var size = NetworkManager.SendMessage(message, NetworkDelivery.ReliableFragmentedSequenced, clientId);
-                NetworkManager.NetworkMetrics.TrackObjectSpawnSent(clientId, networkObject, size);
-
-                networkObject.MarkVariablesDirty();
+                return;
             }
+
+            var message = new CreateObjectMessage
+            {
+                ObjectInfo = networkObject.GetMessageSceneObject(clientId)
+            };
+            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, clientId);
+            NetworkManager.NetworkMetrics.TrackObjectSpawnSent(clientId, networkObject, size);
+
+            networkObject.MarkVariablesDirty();
         }
 
         internal ulong? GetSpawnParentId(NetworkObject networkObject)
@@ -549,14 +689,12 @@ namespace Unity.Netcode
         // Makes scene objects ready to be reused
         internal void ServerResetShudownStateForSceneObjects()
         {
-            foreach (var sobj in SpawnedObjectsList)
+            var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
+            foreach (var sobj in networkObjects)
             {
-                if ((sobj.IsSceneObject != null && sobj.IsSceneObject == true) || sobj.DestroyWithScene)
-                {
-                    sobj.IsSpawned = false;
-                    sobj.DestroyWithScene = false;
-                    sobj.IsSceneObject = null;
-                }
+                sobj.IsSpawned = false;
+                sobj.DestroyWithScene = false;
+                sobj.IsSceneObject = null;
             }
         }
 
@@ -580,7 +718,7 @@ namespace Unity.Netcode
             }
         }
 
-        internal void DestroyNonSceneObjects()
+        internal void DespawnAndDestroyNetworkObjects()
         {
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
 
@@ -588,17 +726,23 @@ namespace Unity.Netcode
             {
                 if (networkObjects[i].NetworkManager == NetworkManager)
                 {
-                    if (networkObjects[i].IsSceneObject != null && networkObjects[i].IsSceneObject.Value == false)
+                    if (NetworkManager.PrefabHandler.ContainsHandler(networkObjects[i]))
                     {
-                        if (NetworkManager.PrefabHandler.ContainsHandler(networkObjects[i]))
-                        {
-                            NetworkManager.PrefabHandler.HandleNetworkPrefabDestroy(networkObjects[i]);
-                            OnDespawnObject(networkObjects[i], false);
-                        }
-                        else
-                        {
-                            UnityEngine.Object.Destroy(networkObjects[i].gameObject);
-                        }
+                        OnDespawnObject(networkObjects[i], false);
+                        // Leave destruction up to the handler
+                        NetworkManager.PrefabHandler.HandleNetworkPrefabDestroy(networkObjects[i]);
+                    }
+                    else if (networkObjects[i].IsSpawned)
+                    {
+                        // If it is an in-scene placed NetworkObject then just despawn
+                        // and let it be destroyed when the scene is unloaded. Otherwise, despawn and destroy it.
+                        var shouldDestroy = !(networkObjects[i].IsSceneObject != null && networkObjects[i].IsSceneObject.Value);
+
+                        OnDespawnObject(networkObjects[i], shouldDestroy);
+                    }
+                    else if (networkObjects[i].IsSceneObject != null && !networkObjects[i].IsSceneObject.Value)
+                    {
+                        UnityEngine.Object.Destroy(networkObjects[i].gameObject);
                     }
                 }
             }
@@ -634,6 +778,7 @@ namespace Unity.Netcode
         internal void ServerSpawnSceneObjectsOnStartSweep()
         {
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+            var networkObjectsToSpawn = new List<NetworkObject>();
 
             for (int i = 0; i < networkObjects.Length; i++)
             {
@@ -641,10 +786,16 @@ namespace Unity.Netcode
                 {
                     if (networkObjects[i].IsSceneObject == null)
                     {
-                        SpawnNetworkObjectLocally(networkObjects[i], GetNetworkObjectId(), true, false, null, true);
+                        networkObjectsToSpawn.Add(networkObjects[i]);
                     }
                 }
             }
+
+
+            foreach (var networkObject in networkObjectsToSpawn)
+            {
+                SpawnNetworkObjectLocally(networkObject, GetNetworkObjectId(), true, false, networkObject.OwnerClientId, true);
+            }
         }
 
         internal void OnDespawnObject(NetworkObject networkObject, bool destroyGameObject)
@@ -668,29 +819,21 @@ namespace Unity.Netcode
                 return;
             }
 
-            // Move child NetworkObjects to the root when parent NetworkObject is destroyed
-            foreach (var spawnedNetObj in SpawnedObjectsList)
+            // If we are shutting down the NetworkManager, then ignore resetting the parent
+            if (!NetworkManager.ShutdownInProgress)
             {
-                var (isReparented, latestParent) = spawnedNetObj.GetNetworkParenting();
-                if (isReparented && latestParent == networkObject.NetworkObjectId)
+                // Move child NetworkObjects to the root when parent NetworkObject is destroyed
+                foreach (var spawnedNetObj in SpawnedObjectsList)
                 {
-                    spawnedNetObj.gameObject.transform.parent = null;
-
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                    var (isReparented, latestParent) = spawnedNetObj.GetNetworkParenting();
+                    if (isReparented && latestParent == networkObject.NetworkObjectId)
                     {
-                        NetworkLog.LogWarning($"{nameof(NetworkObject)} #{spawnedNetObj.NetworkObjectId} moved to the root because its parent {nameof(NetworkObject)} #{networkObject.NetworkObjectId} is destroyed");
-                    }
-                }
-            }
+                        spawnedNetObj.gameObject.transform.parent = null;
 
-            if (!networkObject.IsOwnedByServer && !networkObject.IsPlayerObject && TryGetNetworkClient(networkObject.OwnerClientId, out NetworkClient networkClient))
-            {
-                //Someone owns it.
-                for (int i = networkClient.OwnedObjects.Count - 1; i > -1; i--)
-                {
-                    if (networkClient.OwnedObjects[i].NetworkObjectId == networkObject.NetworkObjectId)
-                    {
-                        networkClient.OwnedObjects.RemoveAt(i);
+                        if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                        {
+                            NetworkLog.LogWarning($"{nameof(NetworkObject)} #{spawnedNetObj.NetworkObjectId} moved to the root because its parent {nameof(NetworkObject)} #{networkObject.NetworkObjectId} is destroyed");
+                        }
                     }
                 }
             }
@@ -708,38 +851,31 @@ namespace Unity.Netcode
                     });
                 }
 
-                if (NetworkManager.NetworkConfig.UseSnapshotSpawn)
+                if (networkObject != null)
                 {
-                    networkObject.SnapshotDespawn();
-                }
-                else
-                {
-                    if (networkObject != null)
+                    // As long as we have any remaining clients, then notify of the object being destroy.
+                    if (NetworkManager.ConnectedClientsList.Count > 0)
                     {
-                        // As long as we have any remaining clients, then notify of the object being destroy.
-                        if (NetworkManager.ConnectedClientsList.Count > 0)
+                        m_TargetClientIds.Clear();
+
+                        // We keep only the client for which the object is visible
+                        // as the other clients have them already despawned
+                        foreach (var clientId in NetworkManager.ConnectedClientsIds)
                         {
-                            m_TargetClientIds.Clear();
-
-                            // We keep only the client for which the object is visible
-                            // as the other clients have them already despawned
-                            foreach (var clientId in NetworkManager.ConnectedClientsIds)
+                            if (networkObject.IsNetworkVisibleTo(clientId))
                             {
-                                if (networkObject.IsNetworkVisibleTo(clientId))
-                                {
-                                    m_TargetClientIds.Add(clientId);
-                                }
+                                m_TargetClientIds.Add(clientId);
                             }
+                        }
 
-                            var message = new DestroyObjectMessage
-                            {
-                                NetworkObjectId = networkObject.NetworkObjectId
-                            };
-                            var size = NetworkManager.SendMessage(message, NetworkDelivery.ReliableSequenced, m_TargetClientIds);
-                            foreach (var targetClientId in m_TargetClientIds)
-                            {
-                                NetworkManager.NetworkMetrics.TrackObjectDestroySent(targetClientId, networkObject, size);
-                            }
+                        var message = new DestroyObjectMessage
+                        {
+                            NetworkObjectId = networkObject.NetworkObjectId
+                        };
+                        var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, m_TargetClientIds);
+                        foreach (var targetClientId in m_TargetClientIds)
+                        {
+                            NetworkManager.NetworkMetrics.TrackObjectDestroySent(targetClientId, networkObject, size);
                         }
                     }
                 }
@@ -774,7 +910,7 @@ namespace Unity.Netcode
         {
             foreach (var sobj in SpawnedObjectsList)
             {
-                if (sobj.CheckObjectVisibility == null || NetworkManager.IsServer)
+                if (sobj.CheckObjectVisibility == null)
                 {
                     if (!sobj.Observers.Contains(clientId))
                     {

Runtime/Timing/NetworkTime.cs

@@ -114,6 +114,11 @@ namespace Unity.Netcode
         {
             double d = m_TimeSec / m_TickInterval;
             m_CachedTick = (int)d;
+            // This check is needed due to double division imprecision of large numbers
+            if ((d - m_CachedTick) >= 0.999999999999)
+            {
+                m_CachedTick++;
+            }
             m_CachedTickOffset = ((d - Math.Truncate(d)) * m_TickInterval);
 
             // This handles negative time, decreases tick by 1 and makes offset positive.

Runtime/Transports/NetworkTransport.cs

@@ -18,6 +18,8 @@ namespace Unity.Netcode
         /// <value><c>true</c> if is supported; otherwise, <c>false</c>.</value>
         public virtual bool IsSupported => true;
 
+        internal INetworkMetrics NetworkMetrics;
+
         /// <summary>
         /// Delegate for transport network events
         /// </summary>
@@ -95,6 +97,14 @@ namespace Unity.Netcode
         /// <summary>
         /// Initializes the transport
         /// </summary>
-        public abstract void Initialize();
+        /// /// <param name="networkManager">optionally pass in NetworkManager</param>
+        public abstract void Initialize(NetworkManager networkManager = null);
     }
+
+#if UNITY_INCLUDE_TESTS
+    public abstract class TestingNetworkTransport : NetworkTransport
+    {
+
+    }
+#endif
 }

Runtime/Transports/UNET/UNetChannel.cs

@@ -1,52 +0,0 @@
-using System;
-#if UNITY_EDITOR
-using UnityEditor;
-#endif
-using UnityEngine;
-using UnityEngine.Networking;
-
-namespace Unity.Netcode.Transports.UNET
-{
-    /// <summary>
-    /// A transport channel used by the netcode
-    /// </summary>
-    [Serializable]
-    public class UNetChannel
-    {
-        /// <summary>
-        /// The name of the channel
-        /// </summary>
-#if UNITY_EDITOR
-        [ReadOnly]
-#endif
-        public byte Id;
-
-        /// <summary>
-        /// The type of channel
-        /// </summary>
-        public QosType Type;
-
-#if UNITY_EDITOR
-        private class ReadOnlyAttribute : PropertyAttribute { }
-
-        [CustomPropertyDrawer(typeof(ReadOnlyAttribute))]
-        private class ReadOnlyDrawer : PropertyDrawer
-        {
-            public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
-            {
-                // Saving previous GUI enabled value
-                var previousGUIState = GUI.enabled;
-
-                // Disabling edit for property
-                GUI.enabled = false;
-
-                // Drawing Property
-                EditorGUI.PropertyField(position, property, label);
-
-                // Setting old GUI enabled value
-                GUI.enabled = previousGUIState;
-            }
-        }
-#endif
-    }
-}

Runtime/Transports/UNET/UNetChannel.cs.meta

@@ -1,11 +0,0 @@
-fileFormatVersion: 2
-guid: e864534da30ef604992c0ed33c75d3c6
-MonoImporter:
-  externalObjects: {}
-  serializedVersion: 2
-  defaultReferences: []
-  executionOrder: 0
-  icon: {instanceID: 0}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Transports/UNET/UNetTransport.cs

@@ -1,3 +1,4 @@
+#if UNITY_UNET_PRESENT
 #pragma warning disable 618 // disable is obsolete
 #pragma warning disable CS1591 // Missing XML comment for publicly visible type or member
 using System;
@@ -41,6 +42,8 @@ namespace Unity.Netcode.Transports.UNET
 
         public override ulong ServerClientId => GetNetcodeClientId(0, 0, true);
 
+        internal NetworkManager NetworkManager;
+
         protected void LateUpdate()
         {
             if (UnityEngine.Networking.NetworkTransport.IsStarted && MessageSendMode == SendMode.Queued)
@@ -48,7 +51,7 @@ namespace Unity.Netcode.Transports.UNET
 #if UNITY_WEBGL
                 Debug.LogError("Cannot use queued sending mode for WebGL");
 #else
-                if (NetworkManager.Singleton.IsServer)
+                if (NetworkManager != null && NetworkManager.IsServer)
                 {
                     foreach (var targetClient in NetworkManager.Singleton.ConnectedClientsList)
                     {
@@ -230,8 +233,10 @@ namespace Unity.Netcode.Transports.UNET
             UnityEngine.Networking.NetworkTransport.Shutdown();
         }
 
-        public override void Initialize()
+        public override void Initialize(NetworkManager networkManager = null)
         {
+            NetworkManager = networkManager;
+
             m_MessageBuffer = new byte[MessageBufferSize];
 
             UnityEngine.Networking.NetworkTransport.Init();
@@ -279,3 +284,4 @@ namespace Unity.Netcode.Transports.UNET
 }
 #pragma warning restore CS1591 // Missing XML comment for publicly visible type or member
 #pragma warning restore 618 // restore is obsolete
+#endif

Runtime/Transports/UTP.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: af81f9951b096ff4cb8e4f8a4106104a
+guid: 81887adf6d9ca40c9b70728b7018b6f5
 folderAsset: yes
 DefaultImporter:
   externalObjects: {}

Runtime/Transports/UTP/BatchedReceiveQueue.cs

@@ -0,0 +1,96 @@
+using System;
+using Unity.Networking.Transport;
+
+namespace Unity.Netcode.Transports.UTP
+{
+    /// <summary>Queue for batched messages received through UTP.</summary>
+    /// <remarks>This is meant as a companion to <see cref="BatchedSendQueue"/>.</remarks>
+    internal class BatchedReceiveQueue
+    {
+        private byte[] m_Data;
+        private int m_Offset;
+        private int m_Length;
+
+        public bool IsEmpty => m_Length <= 0;
+
+        /// <summary>
+        /// Construct a new receive queue from a <see cref="DataStreamReader"/> returned by
+        /// <see cref="NetworkDriver"/> when popping a data event.
+        /// </summary>
+        /// <param name="reader">The <see cref="DataStreamReader"/> to construct from.</param>
+        public BatchedReceiveQueue(DataStreamReader reader)
+        {
+            m_Data = new byte[reader.Length];
+            unsafe
+            {
+                fixed (byte* dataPtr = m_Data)
+                {
+                    reader.ReadBytes(dataPtr, reader.Length);
+                }
+            }
+
+            m_Offset = 0;
+            m_Length = reader.Length;
+        }
+
+        /// <summary>
+        /// Push the entire data from a <see cref="DataStreamReader"/> (as returned by popping an
+        /// event from a <see cref="NetworkDriver">) to the queue.
+        /// </summary>
+        /// <param name="reader">The <see cref="DataStreamReader"/> to push the data of.</param>
+        public void PushReader(DataStreamReader reader)
+        {
+            // Resize the array and copy the existing data to the beginning if there's not enough
+            // room to copy the reader's data at the end of the existing data.
+            var available = m_Data.Length - (m_Offset + m_Length);
+            if (available < reader.Length)
+            {
+                if (m_Length > 0)
+                {
+                    Array.Copy(m_Data, m_Offset, m_Data, 0, m_Length);
+                }
+
+                m_Offset = 0;
+
+                while (m_Data.Length - m_Length < reader.Length)
+                {
+                    Array.Resize(ref m_Data, m_Data.Length * 2);
+                }
+            }
+
+            unsafe
+            {
+                fixed (byte* dataPtr = m_Data)
+                {
+                    reader.ReadBytes(dataPtr + m_Offset + m_Length, reader.Length);
+                }
+            }
+
+            m_Length += reader.Length;
+        }
+
+        /// <summary>Pop the next full message in the queue.</summary>
+        /// <returns>The message, or the default value if no more full messages.</returns>
+        public ArraySegment<byte> PopMessage()
+        {
+            if (m_Length < sizeof(int))
+            {
+                return default;
+            }
+
+            var messageLength = BitConverter.ToInt32(m_Data, m_Offset);
+
+            if (m_Length - sizeof(int) < messageLength)
+            {
+                return default;
+            }
+
+            var data = new ArraySegment<byte>(m_Data, m_Offset + sizeof(int), messageLength);
+
+            m_Offset += sizeof(int) + messageLength;
+            m_Length -= sizeof(int) + messageLength;
+
+            return data;
+        }
+    }
+}

Runtime/Transports/UTP/BatchedReceiveQueue.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e9ead10b891184bd5b8f2650fd66a5b1
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Transports/UTP/BatchedSendQueue.cs

@@ -0,0 +1,233 @@
+using System;
+using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+using Unity.Networking.Transport;
+
+namespace Unity.Netcode.Transports.UTP
+{
+    /// <summary>Queue for batched messages meant to be sent through UTP.</summary>
+    /// <remarks>
+    /// Messages should be pushed on the queue with <see cref="PushMessage"/>. To send batched
+    /// messages, call <see cref="FillWriter"> with the <see cref="DataStreamWriter"/> obtained from
+    /// <see cref="NetworkDriver.BeginSend"/>. This will fill the writer with as many messages as
+    /// possible. If the send is successful, call <see cref="Consume"/> to remove the data from the
+    /// queue.
+    ///
+    /// This is meant as a companion to <see cref="BatchedReceiveQueue"/>, which should be used to
+    /// read messages sent with this queue.
+    /// </remarks>
+    internal struct BatchedSendQueue : IDisposable
+    {
+        private NativeArray<byte> m_Data;
+        private NativeArray<int> m_HeadTailIndices;
+
+        /// <summary>Overhead that is added to each message in the queue.</summary>
+        public const int PerMessageOverhead = sizeof(int);
+
+        // Indices into m_HeadTailIndicies.
+        private const int k_HeadInternalIndex = 0;
+        private const int k_TailInternalIndex = 1;
+
+        /// <summary>Index of the first byte of the oldest data in the queue.</summary>
+        private int HeadIndex
+        {
+            get { return m_HeadTailIndices[k_HeadInternalIndex]; }
+            set { m_HeadTailIndices[k_HeadInternalIndex] = value; }
+        }
+
+        /// <summary>Index one past the last byte of the most recent data in the queue.</summary>
+        private int TailIndex
+        {
+            get { return m_HeadTailIndices[k_TailInternalIndex]; }
+            set { m_HeadTailIndices[k_TailInternalIndex] = value; }
+        }
+
+        public int Length => TailIndex - HeadIndex;
+
+        public bool IsEmpty => HeadIndex == TailIndex;
+
+        public bool IsCreated => m_Data.IsCreated;
+
+        /// <summary>Construct a new empty send queue.</summary>
+        /// <param name="capacity">Maximum capacity of the send queue.</param>
+        public BatchedSendQueue(int capacity)
+        {
+            m_Data = new NativeArray<byte>(capacity, Allocator.Persistent);
+            m_HeadTailIndices = new NativeArray<int>(2, Allocator.Persistent);
+
+            HeadIndex = 0;
+            TailIndex = 0;
+        }
+
+        public void Dispose()
+        {
+            if (IsCreated)
+            {
+                m_Data.Dispose();
+                m_HeadTailIndices.Dispose();
+            }
+        }
+
+        /// <summary>Append data at the tail of the queue. No safety checks.</summary>
+        private void AppendDataAtTail(ArraySegment<byte> data)
+        {
+            unsafe
+            {
+                var writer = new DataStreamWriter((byte*)m_Data.GetUnsafePtr() + TailIndex, m_Data.Length - TailIndex);
+
+                writer.WriteInt(data.Count);
+
+                fixed (byte* dataPtr = data.Array)
+                {
+                    writer.WriteBytes(dataPtr + data.Offset, data.Count);
+                }
+            }
+
+            TailIndex += sizeof(int) + data.Count;
+        }
+
+        /// <summary>Append a new message to the queue.</summary>
+        /// <param name="message">Message to append to the queue.</param>
+        /// <returns>
+        /// Whether the message was appended successfully. The only way it can fail is if there's
+        /// no more room in the queue. On failure, nothing is written to the queue.
+        /// </returns>
+        public bool PushMessage(ArraySegment<byte> message)
+        {
+            if (!IsCreated)
+            {
+                return false;
+            }
+
+            // Check if there's enough room after the current tail index.
+            if (m_Data.Length - TailIndex >= sizeof(int) + message.Count)
+            {
+                AppendDataAtTail(message);
+                return true;
+            }
+
+            // Check if there would be enough room if we moved data at the beginning of m_Data.
+            if (m_Data.Length - TailIndex + HeadIndex >= sizeof(int) + message.Count)
+            {
+                // Move the data back at the beginning of m_Data.
+                unsafe
+                {
+                    UnsafeUtility.MemMove(m_Data.GetUnsafePtr(), (byte*)m_Data.GetUnsafePtr() + HeadIndex, Length);
+                }
+
+                TailIndex = Length;
+                HeadIndex = 0;
+
+                AppendDataAtTail(message);
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Fill as much of a <see cref="DataStreamWriter"/> as possible with data from the head of
+        /// the queue. Only full messages (and their length) are written to the writer.
+        /// </summary>
+        /// <remarks>
+        /// This does NOT actually consume anything from the queue. That is, calling this method
+        /// does not reduce the length of the queue. Callers are expected to call
+        /// <see cref="Consume"/> with the value returned by this method afterwards if the data can
+        /// be safely removed from the queue (e.g. if it was sent successfully).
+        ///
+        /// This method should not be used together with <see cref="FillWriterWithBytes"> since this
+        /// could lead to a corrupted queue.
+        /// </remarks>
+        /// <param name="writer">The <see cref="DataStreamWriter"/> to write to.</param>
+        /// <returns>How many bytes were written to the writer.</returns>
+        public int FillWriterWithMessages(ref DataStreamWriter writer)
+        {
+            if (!IsCreated || Length == 0)
+            {
+                return 0;
+            }
+
+            unsafe
+            {
+                var reader = new DataStreamReader((byte*)m_Data.GetUnsafePtr() + HeadIndex, Length);
+
+                var writerAvailable = writer.Capacity;
+                var readerOffset = 0;
+
+                while (readerOffset < Length)
+                {
+                    reader.SeekSet(readerOffset);
+                    var messageLength = reader.ReadInt();
+
+                    if (writerAvailable < sizeof(int) + messageLength)
+                    {
+                        break;
+                    }
+                    else
+                    {
+                        writer.WriteInt(messageLength);
+
+                        var messageOffset = HeadIndex + reader.GetBytesRead();
+                        writer.WriteBytes((byte*)m_Data.GetUnsafePtr() + messageOffset, messageLength);
+
+                        writerAvailable -= sizeof(int) + messageLength;
+                        readerOffset += sizeof(int) + messageLength;
+                    }
+                }
+
+                return writer.Capacity - writerAvailable;
+            }
+        }
+
+        /// <summary>
+        /// Fill the given <see cref="DataStreamWriter"/> with as many bytes from the queue as
+        /// possible, disregarding message boundaries.
+        /// </summary>
+        ///<remarks>
+        /// This does NOT actually consume anything from the queue. That is, calling this method
+        /// does not reduce the length of the queue. Callers are expected to call
+        /// <see cref="Consume"/> with the value returned by this method afterwards if the data can
+        /// be safely removed from the queue (e.g. if it was sent successfully).
+        ///
+        /// This method should not be used together with <see cref="FillWriterWithMessages"/> since
+        /// this could lead to reading messages from a corrupted queue.
+        /// </remarks>
+        /// <param name="writer">The <see cref="DataStreamWriter"/> to write to.</param>
+        /// <returns>How many bytes were written to the writer.</returns>
+        public int FillWriterWithBytes(ref DataStreamWriter writer)
+        {
+            if (!IsCreated || Length == 0)
+            {
+                return 0;
+            }
+
+            var copyLength = Math.Min(writer.Capacity, Length);
+
+            unsafe
+            {
+                writer.WriteBytes((byte*)m_Data.GetUnsafePtr() + HeadIndex, copyLength);
+            }
+
+            return copyLength;
+        }
+
+        /// <summary>Consume a number of bytes from the head of the queue.</summary>
+        /// <remarks>
+        /// This should only be called with a size that matches the last value returned by
+        /// <see cref="FillWriter"/>. Anything else will result in a corrupted queue.
+        /// </remarks>
+        /// <param name="size">Number of bytes to consume from the queue.</param>
+        public void Consume(int size)
+        {
+            if (size >= Length)
+            {
+                HeadIndex = 0;
+                TailIndex = 0;
+            }
+            else
+            {
+                HeadIndex += size;
+            }
+        }
+    }
+}

Runtime/Transports/UTP/BatchedSendQueue.cs.meta

@@ -0,0 +1,11 @@
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