com.unity.netcode.gameobjects@1.3.1

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

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

## [1.3.1] - 2023-03-27

### Added

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

### Changed

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

### Fixed

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

CHANGELOG.md

@@ -6,6 +6,156 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
+## [1.3.1] - 2023-03-27
+
+### Added
+
+- Added detection and graceful handling of corrupt packets for additional safety. (#2419)
+
+### Changed
+
+- The UTP component UI has been updated to be more user-friendly for new users by adding a simple toggle to switch between local-only (127.0.0.1) and remote (0.0.0.0) binding modes, using the toggle "Allow Remote Connections" (#2408)
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.3. (#2450)
+- `NetworkShow()` of `NetworkObject`s are delayed until the end of the frame to ensure consistency of delta-driven variables like `NetworkList`.
+- Dirty `NetworkObject` are reset at end-of-frame and not at serialization time.
+- `NetworkHide()` of an object that was just `NetworkShow()`n produces a warning, as remote clients will _not_ get a spawn/despawn pair.
+- Renamed the NetworkTransform.SetState parameter `shouldGhostsInterpolate` to `teleportDisabled` for better clarity of what that parameter does. (#2228)
+- Network prefabs are now stored in a ScriptableObject that can be shared between NetworkManagers, and have been exposed for public access. By default, a Default Prefabs List is created that contains all NetworkObject prefabs in the project, and new NetworkManagers will default to using that unless that option is turned off in the Netcode for GameObjects settings. Existing NetworkManagers will maintain their existing lists, which can be migrated to the new format via a button in their inspector. (#2322)
+
+### Fixed
+
+- Fixed issue where changes to a layer's weight would not synchronize unless a state transition was occurring.(#2399)
+- Fixed issue where `NetworkManager.LocalClientId` was returning the `NetworkTransport.ServerClientId` as opposed to the `NetworkManager.m_LocalClientId`. (#2398)
+- Fixed issue where a dynamically spawned `NetworkObject` parented under an in-scene placed `NetworkObject` would have its `InScenePlaced` value changed to `true`. This would result in a soft synchronization error for late joining clients. (#2396)
+- Fixed a UTP test that was failing when you install Unity Transport package 2.0.0 or newer. (#2347)
+- Fixed issue where `NetcodeSettingsProvider` would throw an exception in Unity 2020.3.x versions. (#2345)
+- Fixed server side issue where, depending upon component ordering, some NetworkBehaviour components might not have their OnNetworkDespawn method invoked if the client side disconnected. (#2323)
+- Fixed a case where data corruption could occur when using UnityTransport when reaching a certain level of send throughput. (#2332)
+- Fixed an issue in `UnityTransport` where an exception would be thrown if starting a Relay host/server on WebGL. This exception should only be thrown if using direct connections (where WebGL can't act as a host/server). (#2321)
+- Fixed `NetworkAnimator` issue where it was not checking for `AnimatorStateTtansition.destinationStateMachine` and any possible sub-states defined within it. (#2309)
+- Fixed `NetworkAnimator` issue where the host client was receiving the ClientRpc animation updates when the host was the owner.(#2309)
+- Fixed `NetworkAnimator` issue with using pooled objects and when specific properties are cleaned during despawn and destroy.(#2309)
+- Fixed issue where `NetworkAnimator` was checking for animation changes when the associated `NetworkObject` was not spawned.(#2309)
+- Corrected an issue with the documentation for BufferSerializer (#2401)
+
+## [1.2.0] - 2022-11-21
+
+### Added
+
+- Added protected method `NetworkBehaviour.OnSynchronize` which is invoked during the initial `NetworkObject` synchronization process. This provides users the ability to include custom serialization information that will be applied to the `NetworkBehaviour` prior to the `NetworkObject` being spawned. (#2298)
+- Added support for different versions of the SDK to talk to each other in circumstances where changes permit it. Starting with this version and into future versions, patch versions should be compatible as long as the minor version is the same. (#2290)
+- Added `NetworkObject` auto-add helper and Multiplayer Tools install reminder settings to Project Settings. (#2285)
+- Added `public string DisconnectReason` getter to `NetworkManager` and `string Reason` to `ConnectionApprovalResponse`. Allows connection approval to communicate back a reason. Also added `public void DisconnectClient(ulong clientId, string reason)` allowing setting a disconnection reason, when explicitly disconnecting a client. (#2280)
+
+### Changed
+
+- Changed 3rd-party `XXHash` (32 & 64) implementation with an in-house reimplementation (#2310)
+- When `NetworkConfig.EnsureNetworkVariableLengthSafety` is disabled `NetworkVariable` fields do not write the additional `ushort` size value (_which helps to reduce the total synchronization message size_), but when enabled it still writes the additional `ushort` value. (#2298)
+- Optimized bandwidth usage by encoding most integer fields using variable-length encoding. (#2276)
+
+### Fixed
+- Fixed `IsSpawnedObjectsPendingInDontDestroyOnLoad` is only set to true when loading a scene using `LoadSceneMode.Singleonly`. (#2330)
+- Fixed issue where `NetworkTransform` components nested under a parent with a `NetworkObject` component  (i.e. network prefab) would not have their associated `GameObject`'s transform synchronized. (#2298)
+- Fixed issue where `NetworkObject`s that failed to instantiate could cause the entire synchronization pipeline to be disrupted/halted for a connecting client. (#2298)
+- Fixed issue where in-scene placed `NetworkObject`s nested under a `GameObject` would be added to the orphaned children list causing continual console warning log messages. (#2298)
+- Custom messages are now properly received by the local client when they're sent while running in host mode. (#2296)
+- Fixed issue where the host would receive more than one event completed notification when loading or unloading a scene only when no clients were connected. (#2292)
+- Fixed an issue in `UnityTransport` where an error would be logged if the 'Use Encryption' flag was enabled with a Relay configuration that used a secure protocol. (#2289)
+- Fixed issue where in-scene placed `NetworkObjects` were not honoring the `AutoObjectParentSync` property. (#2281)
+- Fixed the issue where `NetworkManager.OnClientConnectedCallback` was being invoked before in-scene placed `NetworkObject`s had been spawned when starting `NetworkManager` as a host. (#2277)
+- Creating a `FastBufferReader` with `Allocator.None` will not result in extra memory being allocated for the buffer (since it's owned externally in that scenario). (#2265)
+
+### Removed
+
+- Removed the `NetworkObject` auto-add and Multiplayer Tools install reminder settings from the Menu interface. (#2285)
+
+## [1.1.0] - 2022-10-21
+
+### Added
+
+- Added `NetworkManager.IsApproved` flag that is set to `true` a client has been approved.(#2261)
+- `UnityTransport` now provides a way to set the Relay server data directly from the `RelayServerData` structure (provided by the Unity Transport package) throuh its `SetRelayServerData` method. This allows making use of the new APIs in UTP 1.3 that simplify integration of the Relay SDK. (#2235)
+- IPv6 is now supported for direct connections when using `UnityTransport`. (#2232)
+- Added WebSocket support when using UTP 2.0 with `UseWebSockets` property in the `UnityTransport` component of the `NetworkManager` allowing to pick WebSockets for communication. When building for WebGL, this selection happens automatically. (#2201)
+- Added position, rotation, and scale to the `ParentSyncMessage` which provides users the ability to specify the final values on the server-side when `OnNetworkObjectParentChanged` is invoked just before the message is created (when the `Transform` values are applied to the message). (#2146)
+- Added `NetworkObject.TryRemoveParent` method for convenience purposes opposed to having to cast null to either `GameObject` or `NetworkObject`. (#2146)
+
+### Changed
+
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.0. (#2231)
+- The send queues of `UnityTransport` are now dynamically-sized. This means that there shouldn't be any need anymore to tweak the 'Max Send Queue Size' value. In fact, this field is now removed from the inspector and will not be serialized anymore. It is still possible to set it manually using the `MaxSendQueueSize` property, but it is not recommended to do so aside from some specific needs (e.g. limiting the amount of memory used by the send queues in very constrained environments). (#2212)
+- As a consequence of the above change, the `UnityTransport.InitialMaxSendQueueSize` field is now deprecated. There is no default value anymore since send queues are dynamically-sized. (#2212)
+- The debug simulator in `UnityTransport` is now non-deterministic. Its random number generator used to be seeded with a constant value, leading to the same pattern of packet drops, delays, and jitter in every run. (#2196)
+- `NetworkVariable<>` now supports managed `INetworkSerializable` types, as well as other managed types with serialization/deserialization delegates registered to `UserNetworkVariableSerialization<T>.WriteValue` and `UserNetworkVariableSerialization<T>.ReadValue` (#2219)
+- `NetworkVariable<>` and `BufferSerializer<BufferSerializerReader>` now deserialize `INetworkSerializable` types in-place, rather than constructing new ones. (#2219)
+
+### Fixed
+
+- Fixed `NetworkManager.ApprovalTimeout` will not timeout due to slower client synchronization times as it now uses the added `NetworkManager.IsApproved` flag to determined if the client has been approved or not.(#2261)
+- Fixed issue caused when changing ownership of objects hidden to some clients (#2242)
+- Fixed issue where an in-scene placed NetworkObject would not invoke NetworkBehaviour.OnNetworkSpawn if the GameObject was disabled when it was despawned. (#2239)
+- Fixed issue where clients were not rebuilding the `NetworkConfig` hash value for each unique connection request. (#2226)
+- Fixed the issue where player objects were not taking the `DontDestroyWithOwner` property into consideration when a client disconnected. (#2225)
+- Fixed issue where `SceneEventProgress` would not complete if a client late joins while it is still in progress. (#2222)
+- Fixed issue where `SceneEventProgress` would not complete if a client disconnects. (#2222)
+- Fixed issues with detecting if a `SceneEventProgress` has timed out. (#2222)
+- Fixed issue #1924 where `UnityTransport` would fail to restart after a first failure (even if what caused the initial failure was addressed). (#2220)
+- Fixed issue where `NetworkTransform.SetStateServerRpc` and `NetworkTransform.SetStateClientRpc` were not honoring local vs world space settings when applying the position and rotation. (#2203)
+- Fixed ILPP `TypeLoadException` on WebGL on MacOS Editor and potentially other platforms. (#2199)
+- Implicit conversion of NetworkObjectReference to GameObject will now return null instead of throwing an exception if the referenced object could not be found (i.e., was already despawned) (#2158)
+- Fixed warning resulting from a stray NetworkAnimator.meta file (#2153)
+- Fixed Connection Approval Timeout not working client side. (#2164)
+- Fixed issue where the `WorldPositionStays` parenting parameter was not being synchronized with clients. (#2146)
+- Fixed issue where parented in-scene placed `NetworkObject`s would fail for late joining clients. (#2146)
+- Fixed issue where scale was not being synchronized which caused issues with nested parenting and scale when `WorldPositionStays` was true. (#2146)
+- Fixed issue with `NetworkTransform.ApplyTransformToNetworkStateWithInfo` where it was not honoring axis sync settings when `NetworkTransformState.IsTeleportingNextFrame` was true. (#2146)
+- Fixed issue with `NetworkTransform.TryCommitTransformToServer` where it was not honoring the `InLocalSpace` setting. (#2146)
+- Fixed ClientRpcs always reporting in the profiler view as going to all clients, even when limited to a subset of clients by `ClientRpcParams`. (#2144)
+- Fixed RPC codegen failing to choose the correct extension methods for `FastBufferReader` and `FastBufferWriter` when the parameters were a generic type (i.e., List<int>) and extensions for multiple instantiations of that type have been defined (i.e., List<int> and List<string>) (#2142)
+- Fixed the issue where running a server (i.e. not host) the second player would not receive updates (unless a third player joined). (#2127)
+- Fixed issue where late-joining client transition synchronization could fail when more than one transition was occurring.(#2127)
+- Fixed throwing an exception in `OnNetworkUpdate` causing other `OnNetworkUpdate` calls to not be executed. (#1739)
+- Fixed synchronization when Time.timeScale is set to 0. This changes timing update to use unscaled deltatime. Now network updates rate are independent from the local time scale. (#2171)
+- Fixed not sending all NetworkVariables to all clients when a client connects to a server. (#1987)
+- Fixed IsOwner/IsOwnedByServer being wrong on the server after calling RemoveOwnership (#2211)
+
+## [1.0.2] - 2022-09-12
+
+### Fixed
+
+- Fixed issue where `NetworkTransform` was not honoring the InLocalSpace property on the authority side during OnNetworkSpawn. (#2170)
+- Fixed issue where `NetworkTransform` was not ending extrapolation for the previous state causing non-authoritative instances to become out of synch. (#2170)
+- Fixed issue where `NetworkTransform` was not continuing to interpolate for the remainder of the associated tick period. (#2170)
+- Fixed issue during `NetworkTransform.OnNetworkSpawn` for non-authoritative instances where it was initializing interpolators with the replicated network state which now only contains the transform deltas that occurred during a network tick and not the entire transform state. (#2170)
+
+## [1.0.1] - 2022-08-23
+
+### Changed
+
+- Changed version to 1.0.1. (#2131)
+- Updated dependency on `com.unity.transport` to 1.2.0. (#2129)
+- When using `UnityTransport`, _reliable_ payloads are now allowed to exceed the configured 'Max Payload Size'. Unreliable payloads remain bounded by this setting. (#2081)
+- Performance improvements for cases with large number of NetworkObjects, by not iterating over all unchanged NetworkObjects
+
+### Fixed
+
+- Fixed an issue where reading/writing more than 8 bits at a time with BitReader/BitWriter would write/read from the wrong place, returning and incorrect result. (#2130)
+- Fixed issue with the internal `NetworkTransformState.m_Bitset` flag not getting cleared upon the next tick advancement. (#2110)
+- Fixed interpolation issue with `NetworkTransform.Teleport`. (#2110)
+- Fixed issue where the authoritative side was interpolating its transform. (#2110)
+- Fixed Owner-written NetworkVariable infinitely write themselves (#2109)
+- Fixed NetworkList issue that showed when inserting at the very end of a NetworkList (#2099)
+- Fixed issue where a client owner of a `NetworkVariable` with both owner read and write permissions would not update the server side when changed. (#2097)
+- Fixed issue when attempting to spawn a parent `GameObject`, with `NetworkObject` component attached, that has one or more child `GameObject`s, that are inactive in the hierarchy, with `NetworkBehaviour` components it will no longer attempt to spawn the associated `NetworkBehaviour`(s) or invoke ownership changed notifications but will log a warning message. (#2096)
+- Fixed an issue where destroying a NetworkBehaviour would not deregister it from the parent NetworkObject, leading to exceptions when the parent was later destroyed. (#2091)
+- Fixed issue where `NetworkObject.NetworkHide` was despawning and destroying, as opposed to only despawning, in-scene placed `NetworkObject`s. (#2086)
+- Fixed `NetworkAnimator` synchronizing transitions twice due to it detecting the change in animation state once a transition is started by a trigger. (#2084)
+- Fixed issue where `NetworkAnimator` would not synchronize a looping animation for late joining clients if it was at the very end of its loop. (#2076)
+- Fixed issue where `NetworkAnimator` was not removing its subscription from `OnClientConnectedCallback` when despawned during the shutdown sequence. (#2074)
+- Fixed IsServer and IsClient being set to false before object despawn during the shutdown sequence. (#2074)
+- Fixed NetworkList Value event on the server. PreviousValue is now set correctly when a new value is set through property setter. (#2067)
+- Fixed NetworkLists not populating on client. NetworkList now uses the most recent list as opposed to the list at the end of previous frame, when sending full updates to dynamically spawned NetworkObject. The difference in behaviour is required as scene management spawns those objects at a different time in the frame, relative to updates. (#2062)
+
 ## [1.0.0] - 2022-06-27
 
 ### Changed
@@ -69,6 +219,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `ClientNetworkTransform` from the package samples and moved to Boss Room's Utilities package which can be found [here](https://github.com/Unity-Technologies/com.unity.multiplayer.samples.coop/blob/main/Packages/com.unity.multiplayer.samples.coop/Utilities/Net/ClientAuthority/ClientNetworkTransform.cs) (#1912)
 
 ### Fixed
+
 - Fixed issue where `NetworkSceneManager` did not synchronize despawned in-scene placed NetworkObjects. (#1898)
 - Fixed `NetworkTransform` generating false positive rotation delta checks when rolling over between 0 and 360 degrees. (#1890)
 - Fixed client throwing an exception if it has messages in the outbound queue when processing the `NetworkEvent.Disconnect` event and is using UTP. (#1884)
@@ -122,10 +273,12 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ## [1.0.0-pre.6] - 2022-03-02
 
 ### Added
+
 - NetworkAnimator now properly synchrhonizes all animation layers as well as runtime-adjusted weighting between them (#1765)
 - Added first set of tests for NetworkAnimator - parameter syncing, trigger set / reset, override network animator (#1735)
 
 ### Fixed
+
 - Fixed an issue where sometimes the first client to connect to the server could see messages from the server as coming from itself. (#1683)
 - Fixed an issue where clients seemed to be able to send messages to ClientId 1, but these messages would actually still go to the server (id 0) instead of that client. (#1683)
 - Improved clarity of error messaging when a client attempts to send a message to a destination other than the server, which isn't allowed. (#1683)
@@ -177,6 +330,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `FixedQueue`, `StreamExtensions`, `TypeExtensions` (#1398)
 
 ### Fixed
+
 - Fixed in-scene NetworkObjects that are moved into the DDOL scene not getting restored to their original active state (enabled/disabled) after a full scene transition (#1354)
 - Fixed invalid IL code being generated when using `this` instead of `this ref` for the FastBufferReader/FastBufferWriter parameter of an extension method. (#1393)
 - Fixed an issue where if you are running as a server (not host) the LoadEventCompleted and UnloadEventCompleted events would fire early by the NetworkSceneManager (#1379)
@@ -191,6 +345,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Fixed network tick value sometimes being duplicated or skipped. (#1614)
 
 ### Changed
+
 - The SDK no longer limits message size to 64k. (The transport may still impose its own limits, but the SDK no longer does.) (#1384)
 - Updated com.unity.collections to 1.1.0 (#1451)
 - NetworkManager's GameObject is no longer allowed to be nested under one or more GameObject(s).(#1484)

Components/AssemblyInfo.cs

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

Components/Interpolator/BufferedLinearInterpolator.cs

@@ -248,6 +248,8 @@ namespace Unity.Netcode
                 return;
             }
 
+            // Part the of reason for disabling extrapolation is how we add and use measurements over time.
+            // TODO: Add detailed description of this area in Jira ticket
             if (sentTime > m_EndTimeConsumed || m_LifetimeConsumedCount == 0) // treat only if value is newer than the one being interpolated to right now
             {
                 m_LastBufferedItemReceived = new BufferedItem(newMeasurement, sentTime);
@@ -292,7 +294,9 @@ namespace Unity.Netcode
         /// <inheritdoc />
         protected override float InterpolateUnclamped(float start, float end, float time)
         {
-            return Mathf.LerpUnclamped(start, end, time);
+            // Disabling Extrapolation:
+            // TODO: Add Jira Ticket
+            return Mathf.Lerp(start, end, time);
         }
 
         /// <inheritdoc />
@@ -311,13 +315,17 @@ namespace Unity.Netcode
         /// <inheritdoc />
         protected override Quaternion InterpolateUnclamped(Quaternion start, Quaternion end, float time)
         {
-            return Quaternion.SlerpUnclamped(start, end, time);
+            // Disabling Extrapolation:
+            // TODO: Add Jira Ticket
+            return Quaternion.Slerp(start, end, time);
         }
 
         /// <inheritdoc />
         protected override Quaternion Interpolate(Quaternion start, Quaternion end, float time)
         {
-            return Quaternion.SlerpUnclamped(start, end, time);
+            // Disabling Extrapolation:
+            // TODO: Add Jira Ticket
+            return Quaternion.Slerp(start, end, time);
         }
     }
 }

Components/NetworkRigidbody.cs

@@ -9,6 +9,7 @@ namespace Unity.Netcode.Components
     /// </summary>
     [RequireComponent(typeof(Rigidbody))]
     [RequireComponent(typeof(NetworkTransform))]
+    [AddComponentMenu("Netcode/Network Rigidbody")]
     public class NetworkRigidbody : NetworkBehaviour
     {
         /// <summary>

Components/NetworkRigidbody2D.cs

@@ -9,6 +9,7 @@ namespace Unity.Netcode.Components
     /// </summary>
     [RequireComponent(typeof(Rigidbody2D))]
     [RequireComponent(typeof(NetworkTransform))]
+    [AddComponentMenu("Netcode/Network Rigidbody 2D")]
     public class NetworkRigidbody2D : NetworkBehaviour
     {
         private Rigidbody2D m_Rigidbody;

Editor/AssemblyInfo.cs

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

Editor/CodeGen/CodeGenHelpers.cs

@@ -15,6 +15,10 @@ namespace Unity.Netcode.Editor.CodeGen
 {
     internal static class CodeGenHelpers
     {
+        public const string DotnetModuleName = "netstandard.dll";
+        public const string UnityModuleName = "UnityEngine.CoreModule.dll";
+        public const string NetcodeModuleName = "Unity.Netcode.Runtime.dll";
+
         public const string RuntimeAssemblyName = "Unity.Netcode.Runtime";
 
         public static readonly string NetworkBehaviour_FullName = typeof(NetworkBehaviour).FullName;
@@ -119,6 +123,19 @@ namespace Unity.Netcode.Editor.CodeGen
             try
             {
                 var typeDef = typeReference.Resolve();
+                // Note: this won't catch generics correctly.
+                //
+                //     class Foo<T>: IInterface<T> {}
+                //     class Bar: Foo<int> {}
+                //
+                // Bar.HasInterface(IInterface<int>) -> returns false even though it should be true.
+                //
+                // This can be fixed (see GetAllFieldsAndResolveGenerics() in NetworkBehaviourILPP to understand how)
+                // but right now we don't need that to work so it's left alone to reduce complexity
+                if (typeDef.BaseType.HasInterface(interfaceTypeFullName))
+                {
+                    return true;
+                }
                 var typeFaces = typeDef.Interfaces;
                 return typeFaces.Any(iface => iface.InterfaceType.FullName == interfaceTypeFullName);
             }
@@ -380,5 +397,74 @@ namespace Unity.Netcode.Editor.CodeGen
 
             return assemblyDefinition;
         }
+
+        private static void SearchForBaseModulesRecursive(AssemblyDefinition assemblyDefinition, PostProcessorAssemblyResolver assemblyResolver, ref ModuleDefinition unityModule, ref ModuleDefinition netcodeModule, HashSet<string> visited)
+        {
+
+            foreach (var module in assemblyDefinition.Modules)
+            {
+                if (module == null)
+                {
+                    continue;
+                }
+
+                if (unityModule != null && netcodeModule != null)
+                {
+                    return;
+                }
+
+                if (unityModule == null && module.Name == UnityModuleName)
+                {
+                    unityModule = module;
+                    continue;
+                }
+
+                if (netcodeModule == null && module.Name == NetcodeModuleName)
+                {
+                    netcodeModule = module;
+                    continue;
+                }
+            }
+            if (unityModule != null && netcodeModule != null)
+            {
+                return;
+            }
+
+            foreach (var assemblyNameReference in assemblyDefinition.MainModule.AssemblyReferences)
+            {
+                if (assemblyNameReference == null)
+                {
+                    continue;
+                }
+                if (visited.Contains(assemblyNameReference.Name))
+                {
+                    continue;
+                }
+
+                visited.Add(assemblyNameReference.Name);
+
+                var assembly = assemblyResolver.Resolve(assemblyNameReference);
+                if (assembly == null)
+                {
+                    continue;
+                }
+                SearchForBaseModulesRecursive(assembly, assemblyResolver, ref unityModule, ref netcodeModule, visited);
+
+                if (unityModule != null && netcodeModule != null)
+                {
+                    return;
+                }
+            }
+        }
+
+        public static (ModuleDefinition UnityModule, ModuleDefinition NetcodeModule) FindBaseModules(AssemblyDefinition assemblyDefinition, PostProcessorAssemblyResolver assemblyResolver)
+        {
+            ModuleDefinition unityModule = null;
+            ModuleDefinition netcodeModule = null;
+            var visited = new HashSet<string>();
+            SearchForBaseModulesRecursive(assemblyDefinition, assemblyResolver, ref unityModule, ref netcodeModule, visited);
+
+            return (unityModule, netcodeModule);
+        }
     }
 }

Editor/CodeGen/INetworkMessageILPP.cs

@@ -2,7 +2,6 @@ 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;
@@ -17,9 +16,7 @@ namespace Unity.Netcode.Editor.CodeGen
     {
         public override ILPPInterface GetInstance() => this;
 
-        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName;
-            compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName ||
-            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
@@ -33,13 +30,22 @@ namespace Unity.Netcode.Editor.CodeGen
             m_Diagnostics.Clear();
 
             // read
-            var assemblyDefinition = CodeGenHelpers.AssemblyDefinitionFor(compiledAssembly, out var resolver);
+            var assemblyDefinition = CodeGenHelpers.AssemblyDefinitionFor(compiledAssembly, out m_AssemblyResolver);
             if (assemblyDefinition == null)
             {
                 m_Diagnostics.AddError($"Cannot read assembly definition: {compiledAssembly.Name}");
                 return null;
             }
 
+            // modules
+            (_, m_NetcodeModule) = CodeGenHelpers.FindBaseModules(assemblyDefinition, m_AssemblyResolver);
+
+            if (m_NetcodeModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Netcode module: {CodeGenHelpers.NetcodeModuleName}");
+                return null;
+            }
+
             // process
             var mainModule = assemblyDefinition.MainModule;
             if (mainModule != null)
@@ -61,7 +67,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     }
                     catch (Exception e)
                     {
-                        m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                        m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                     }
                 }
                 else
@@ -92,77 +98,136 @@ namespace Unity.Netcode.Editor.CodeGen
             return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
         }
 
+        private ModuleDefinition m_NetcodeModule;
+        private PostProcessorAssemblyResolver m_AssemblyResolver;
 
         private MethodReference m_MessagingSystem_ReceiveMessage_MethodRef;
+        private MethodReference m_MessagingSystem_CreateMessageAndGetVersion_MethodRef;
         private TypeReference m_MessagingSystem_MessageWithHandler_TypeRef;
         private MethodReference m_MessagingSystem_MessageHandler_Constructor_TypeRef;
+        private MethodReference m_MessagingSystem_VersionGetter_Constructor_TypeRef;
         private FieldReference m_ILPPMessageProvider___network_message_types_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_MessageType_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_Handler_FieldRef;
+        private FieldReference m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef;
         private MethodReference m_Type_GetTypeFromHandle_MethodRef;
         private MethodReference m_List_Add_MethodRef;
 
         private const string k_ReceiveMessageName = nameof(MessagingSystem.ReceiveMessage);
+        private const string k_CreateMessageAndGetVersionName = nameof(MessagingSystem.CreateMessageAndGetVersion);
 
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
-            m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(typeof(MessagingSystem.MessageHandler).GetConstructors()[0]);
+            // Different environments seem to have different situations...
+            // Some have these definitions in netstandard.dll...
+            // some seem to have them elsewhere...
+            // Since they're standard .net classes they're not going to cause
+            // the same issues as referencing other assemblies, in theory, since
+            // the definitions should be standard and consistent across platforms
+            // (i.e., there's no #if UNITY_EDITOR in them that could create
+            // invalid IL code)
+            TypeDefinition typeTypeDef = moduleDefinition.ImportReference(typeof(Type)).Resolve();
+            TypeDefinition listTypeDef = moduleDefinition.ImportReference(typeof(List<>)).Resolve();
 
-            var messageWithHandlerType = typeof(MessagingSystem.MessageWithHandler);
+            TypeDefinition messageHandlerTypeDef = null;
-            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerType);
+            TypeDefinition versionGetterTypeDef = null;
-            foreach (var fieldInfo in messageWithHandlerType.GetFields())
+            TypeDefinition messageWithHandlerTypeDef = null;
+            TypeDefinition ilppMessageProviderTypeDef = null;
+            TypeDefinition messagingSystemTypeDef = null;
+            foreach (var netcodeTypeDef in m_NetcodeModule.GetAllTypes())
             {
-                switch (fieldInfo.Name)
+                if (messageHandlerTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.MessageHandler))
+                {
+                    messageHandlerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (versionGetterTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.VersionGetter))
+                {
+                    versionGetterTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (messageWithHandlerTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.MessageWithHandler))
+                {
+                    messageWithHandlerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (ilppMessageProviderTypeDef == null && netcodeTypeDef.Name == nameof(ILPPMessageProvider))
+                {
+                    ilppMessageProviderTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (messagingSystemTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem))
+                {
+                    messagingSystemTypeDef = netcodeTypeDef;
+                    continue;
+                }
+            }
+
+            m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(messageHandlerTypeDef.GetConstructors().First());
+            m_MessagingSystem_VersionGetter_Constructor_TypeRef = moduleDefinition.ImportReference(versionGetterTypeDef.GetConstructors().First());
+
+            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerTypeDef);
+            foreach (var fieldDef in messageWithHandlerTypeDef.Fields)
+            {
+                switch (fieldDef.Name)
                 {
                     case nameof(MessagingSystem.MessageWithHandler.MessageType):
-                        m_MessagingSystem_MessageWithHandler_MessageType_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_MessagingSystem_MessageWithHandler_MessageType_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case nameof(MessagingSystem.MessageWithHandler.Handler):
-                        m_MessagingSystem_MessageWithHandler_Handler_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_MessagingSystem_MessageWithHandler_Handler_FieldRef = moduleDefinition.ImportReference(fieldDef);
+                        break;
+                    case nameof(MessagingSystem.MessageWithHandler.GetVersion):
+                        m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var typeType = typeof(Type);
+            foreach (var methodDef in typeTypeDef.Methods)
-            foreach (var methodInfo in typeType.GetMethods())
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case nameof(Type.GetTypeFromHandle):
-                        m_Type_GetTypeFromHandle_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_Type_GetTypeFromHandle_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
 
-            var ilppMessageProviderType = typeof(ILPPMessageProvider);
+            foreach (var fieldDef in ilppMessageProviderTypeDef.Fields)
-            foreach (var fieldInfo in ilppMessageProviderType.GetFields(BindingFlags.Static | BindingFlags.NonPublic))
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case nameof(ILPPMessageProvider.__network_message_types):
-                        m_ILPPMessageProvider___network_message_types_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_ILPPMessageProvider___network_message_types_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var listType = typeof(List<MessagingSystem.MessageWithHandler>);
+            foreach (var methodDef in listTypeDef.Methods)
-            foreach (var methodInfo in listType.GetMethods())
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
-                    case nameof(List<MessagingSystem.MessageWithHandler>.Add):
+                    case "Add":
-                        m_List_Add_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_List_Add_MethodRef = methodDef;
+                        m_List_Add_MethodRef.DeclaringType = listTypeDef.MakeGenericInstanceType(messageWithHandlerTypeDef);
+                        m_List_Add_MethodRef = moduleDefinition.ImportReference(m_List_Add_MethodRef);
                         break;
                 }
             }
 
-            var messagingSystemType = typeof(MessagingSystem);
+            foreach (var methodDef in messagingSystemTypeDef.Methods)
-            foreach (var methodInfo in messagingSystemType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case k_ReceiveMessageName:
-                        m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodDef);
+                        break;
+                    case k_CreateMessageAndGetVersionName:
+                        m_MessagingSystem_CreateMessageAndGetVersion_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
@@ -189,7 +254,7 @@ namespace Unity.Netcode.Editor.CodeGen
             return staticCtorMethodDef;
         }
 
-        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod)
+        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod, MethodReference versionMethod)
         {
             // MessagingSystem.__network_message_types.Add(new MessagingSystem.MessageWithHandler{MessageType=typeof(type), Handler=type.Receive});
             processor.Body.Variables.Add(new VariableDefinition(m_MessagingSystem_MessageWithHandler_TypeRef));
@@ -205,7 +270,7 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Call, m_Type_GetTypeFromHandle_MethodRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_MessageType_FieldRef));
 
-            // tmp.Handler = type.Receive
+            // tmp.Handler = MessageHandler.ReceveMessage<type>
             instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Ldnull));
 
@@ -213,15 +278,22 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_MessageHandler_Constructor_TypeRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_Handler_FieldRef));
 
+
+            // tmp.GetVersion = MessageHandler.CreateMessageAndGetVersion<type>
+            instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
+            instructions.Add(processor.Create(OpCodes.Ldnull));
+
+            instructions.Add(processor.Create(OpCodes.Ldftn, versionMethod));
+            instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_VersionGetter_Constructor_TypeRef));
+            instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef));
+
             // ILPPMessageProvider.__network_message_types.Add(tmp);
             instructions.Add(processor.Create(OpCodes.Ldloc, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Callvirt, m_List_Add_MethodRef));
         }
 
-        // Creates a static module constructor (which is executed when the module is loaded) that registers all the
+        // Creates a static module constructor (which is executed when the module is loaded) that registers all the message types in the assembly with MessagingSystem.
-        // 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).
-        // 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> networkMessageTypes)
@@ -240,7 +312,9 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         var receiveMethod = new GenericInstanceMethod(m_MessagingSystem_ReceiveMessage_MethodRef);
                         receiveMethod.GenericArguments.Add(type);
-                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod);
+                        var versionMethod = new GenericInstanceMethod(m_MessagingSystem_CreateMessageAndGetVersion_MethodRef);
+                        versionMethod.GenericArguments.Add(type);
+                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod, versionMethod);
                     }
 
                     instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));

Editor/CodeGen/INetworkSerializableILPP.cs

@@ -10,7 +10,6 @@ using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostPr
 
 namespace Unity.Netcode.Editor.CodeGen
 {
-
     internal sealed class INetworkSerializableILPP : ILPPInterface
     {
         public override ILPPInterface GetInstance() => this;
@@ -92,7 +91,7 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
                 catch (Exception e)
                 {
-                    m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                    m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                 }
             }
             else

Editor/CodeGen/NetworkBehaviourILPP.cs

@@ -2,7 +2,6 @@ using System;
 using System.IO;
 using System.Linq;
 using System.Collections.Generic;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
@@ -23,8 +22,7 @@ namespace Unity.Netcode.Editor.CodeGen
 
         public override ILPPInterface GetInstance() => this;
 
-        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
-            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
@@ -35,7 +33,6 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
-
             m_Diagnostics.Clear();
 
             // read
@@ -46,11 +43,27 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
+            // modules
+            (m_UnityModule, m_NetcodeModule) = CodeGenHelpers.FindBaseModules(assemblyDefinition, m_AssemblyResolver);
+
+            if (m_UnityModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Unity module: {CodeGenHelpers.UnityModuleName}");
+                return null;
+            }
+
+            if (m_NetcodeModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Netcode module: {CodeGenHelpers.NetcodeModuleName}");
+                return null;
+            }
+
             // process
             var mainModule = assemblyDefinition.MainModule;
             if (mainModule != null)
             {
                 m_MainModule = mainModule;
+
                 if (ImportReferences(mainModule))
                 {
                     // process `NetworkBehaviour` types
@@ -60,10 +73,12 @@ namespace Unity.Netcode.Editor.CodeGen
                             .Where(t => t.IsSubclassOf(CodeGenHelpers.NetworkBehaviour_FullName))
                             .ToList()
                             .ForEach(b => ProcessNetworkBehaviour(b, compiledAssembly.Defines));
+
+                        CreateNetworkVariableTypeInitializers(assemblyDefinition);
                     }
                     catch (Exception e)
                     {
-                        m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                        m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                     }
                 }
                 else
@@ -92,7 +107,135 @@ namespace Unity.Netcode.Editor.CodeGen
             return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
         }
 
+        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;
+        }
+
+        private bool IsMemcpyableType(TypeReference type)
+        {
+            foreach (var supportedType in BaseSupportedTypes)
+            {
+                if (type.FullName == supportedType.FullName)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private bool IsSpecialCaseType(TypeReference type)
+        {
+            foreach (var supportedType in SpecialCaseTypes)
+            {
+                if (type.FullName == supportedType.FullName)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private void CreateNetworkVariableTypeInitializers(AssemblyDefinition assembly)
+        {
+            foreach (var typeDefinition in assembly.MainModule.Types)
+            {
+                if (typeDefinition.FullName == "<Module>")
+                {
+                    var staticCtorMethodDef = GetOrCreateStaticConstructor(typeDefinition);
+
+                    var processor = staticCtorMethodDef.Body.GetILProcessor();
+
+                    var instructions = new List<Instruction>();
+
+                    foreach (var type in m_WrappedNetworkVariableTypes)
+                    {
+                        if (IsSpecialCaseType(type))
+                        {
+                            continue;
+                        }
+
+                        // If a serializable type isn't found, FallbackSerializer will be used automatically, which will
+                        // call into UserNetworkVariableSerialization, giving the user a chance to define their own serializaiton
+                        // for types that aren't in our official supported types list.
+                        GenericInstanceMethod serializeMethod = null;
+                        GenericInstanceMethod equalityMethod;
+
+                        if (type.IsValueType)
+                        {
+                            if (type.HasInterface(typeof(INetworkSerializeByMemcpy).FullName) || type.Resolve().IsEnum || IsMemcpyableType(type))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef);
+                            }
+                            else if (type.HasInterface(typeof(INetworkSerializable).FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef);
+                            }
+                            else if (type.HasInterface(CodeGenHelpers.IUTF8Bytes_FullName) && type.HasInterface(k_INativeListBool_FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef);
+                            }
+
+                            if (type.HasInterface(typeof(IEquatable<>).FullName + "<" + type.FullName + ">"))
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef);
+                            }
+                            else
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef);
+                            }
+                        }
+                        else
+                        {
+                            if (type.HasInterface(typeof(INetworkSerializable).FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef);
+                            }
+
+                            if (type.HasInterface(typeof(IEquatable<>).FullName + "<" + type.FullName + ">"))
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef);
+                            }
+                            else
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef);
+                            }
+                        }
+
+                        if (serializeMethod != null)
+                        {
+                            serializeMethod.GenericArguments.Add(type);
+                            instructions.Add(processor.Create(OpCodes.Call, m_MainModule.ImportReference(serializeMethod)));
+                        }
+                        equalityMethod.GenericArguments.Add(type);
+                        instructions.Add(processor.Create(OpCodes.Call, m_MainModule.ImportReference(equalityMethod)));
+                    }
+
+                    instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));
+                    break;
+                }
+            }
+        }
+
         private ModuleDefinition m_MainModule;
+        private ModuleDefinition m_UnityModule;
+        private ModuleDefinition m_NetcodeModule;
         private PostProcessorAssemblyResolver m_AssemblyResolver;
 
         private MethodReference m_Debug_LogError_MethodRef;
@@ -123,14 +266,76 @@ namespace Unity.Netcode.Editor.CodeGen
         private FieldReference m_ServerRpcParams_Receive_FieldRef;
         private FieldReference m_ServerRpcParams_Receive_SenderClientId_FieldRef;
         private TypeReference m_ClientRpcParams_TypeRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef;
+
+        private MethodReference m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
 
         private TypeReference m_FastBufferWriter_TypeRef;
-        private Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
+        private readonly Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
-        private List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
+        private readonly List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
 
         private TypeReference m_FastBufferReader_TypeRef;
-        private Dictionary<string, MethodReference> m_FastBufferReader_ReadValue_MethodRefs = new Dictionary<string, MethodReference>();
+        private readonly Dictionary<string, MethodReference> m_FastBufferReader_ReadValue_MethodRefs = new Dictionary<string, MethodReference>();
-        private List<MethodReference> m_FastBufferReader_ExtensionMethodRefs = new List<MethodReference>();
+        private readonly List<MethodReference> m_FastBufferReader_ExtensionMethodRefs = new List<MethodReference>();
+
+        private HashSet<TypeReference> m_WrappedNetworkVariableTypes = new HashSet<TypeReference>();
+
+        internal static readonly Type[] BaseSupportedTypes = new[]
+        {
+            typeof(bool),
+            typeof(byte),
+            typeof(sbyte),
+            typeof(char),
+            typeof(decimal),
+            typeof(double),
+            typeof(float),
+            // the following types have special handling
+            /*typeof(int),
+            typeof(uint),
+            typeof(long),
+            typeof(ulong),
+            typeof(short),
+            typeof(ushort),*/
+            typeof(Vector2),
+            typeof(Vector3),
+            typeof(Vector2Int),
+            typeof(Vector3Int),
+            typeof(Vector4),
+            typeof(Quaternion),
+            typeof(Color),
+            typeof(Color32),
+            typeof(Ray),
+            typeof(Ray2D)
+        };
+        internal static readonly Type[] SpecialCaseTypes = new[]
+        {
+            // the following types have special handling
+            typeof(int),
+            typeof(uint),
+            typeof(long),
+            typeof(ulong),
+            typeof(short),
+            typeof(ushort),
+        };
 
         private const string k_Debug_LogError = nameof(Debug.LogError);
         private const string k_NetworkManager_LocalClientId = nameof(NetworkManager.LocalClientId);
@@ -157,160 +362,257 @@ namespace Unity.Netcode.Editor.CodeGen
         private const string k_ServerRpcParams_Receive = nameof(ServerRpcParams.Receive);
         private const string k_ServerRpcReceiveParams_SenderClientId = nameof(ServerRpcReceiveParams.SenderClientId);
 
+        // CodeGen cannot reference the collections assembly to do a typeof() on it due to a bug that causes that to crash.
+        private const string k_INativeListBool_FullName = "Unity.Collections.INativeList`1<System.Byte>";
+
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
-            var debugType = typeof(Debug);
+            TypeDefinition debugTypeDef = null;
-            foreach (var methodInfo in debugType.GetMethods())
+            foreach (var unityTypeDef in m_UnityModule.GetAllTypes())
             {
-                switch (methodInfo.Name)
+                if (debugTypeDef == null && unityTypeDef.FullName == typeof(Debug).FullName)
+                {
+                    debugTypeDef = unityTypeDef;
+                    continue;
+                }
+            }
+
+            TypeDefinition networkManagerTypeDef = null;
+            TypeDefinition networkBehaviourTypeDef = null;
+            TypeDefinition networkHandlerDelegateTypeDef = null;
+            TypeDefinition rpcParamsTypeDef = null;
+            TypeDefinition serverRpcParamsTypeDef = null;
+            TypeDefinition clientRpcParamsTypeDef = null;
+            TypeDefinition fastBufferWriterTypeDef = null;
+            TypeDefinition fastBufferReaderTypeDef = null;
+            TypeDefinition networkVariableSerializationTypesTypeDef = null;
+            TypeDefinition bytePackerTypeDef = null;
+            TypeDefinition byteUnpackerTypeDef = null;
+            foreach (var netcodeTypeDef in m_NetcodeModule.GetAllTypes())
+            {
+                if (networkManagerTypeDef == null && netcodeTypeDef.Name == nameof(NetworkManager))
+                {
+                    networkManagerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkBehaviourTypeDef == null && netcodeTypeDef.Name == nameof(NetworkBehaviour))
+                {
+                    networkBehaviourTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkHandlerDelegateTypeDef == null && netcodeTypeDef.Name == nameof(NetworkManager.RpcReceiveHandler))
+                {
+                    networkHandlerDelegateTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (rpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(__RpcParams))
+                {
+                    rpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (serverRpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(ServerRpcParams))
+                {
+                    serverRpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (clientRpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(ClientRpcParams))
+                {
+                    clientRpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (fastBufferWriterTypeDef == null && netcodeTypeDef.Name == nameof(FastBufferWriter))
+                {
+                    fastBufferWriterTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (fastBufferReaderTypeDef == null && netcodeTypeDef.Name == nameof(FastBufferReader))
+                {
+                    fastBufferReaderTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkVariableSerializationTypesTypeDef == null && netcodeTypeDef.Name == nameof(NetworkVariableSerializationTypes))
+                {
+                    networkVariableSerializationTypesTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (bytePackerTypeDef == null && netcodeTypeDef.Name == nameof(BytePacker))
+                {
+                    bytePackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (byteUnpackerTypeDef == null && netcodeTypeDef.Name == nameof(ByteUnpacker))
+                {
+                    byteUnpackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+            }
+
+            foreach (var methodDef in debugTypeDef.Methods)
+            {
+                switch (methodDef.Name)
                 {
                     case k_Debug_LogError:
-                        if (methodInfo.GetParameters().Length == 1)
+                        if (methodDef.Parameters.Count == 1)
                         {
-                            m_Debug_LogError_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                            m_Debug_LogError_MethodRef = moduleDefinition.ImportReference(methodDef);
                         }
 
                         break;
                 }
             }
 
-            var networkManagerType = typeof(NetworkManager);
+            m_NetworkManager_TypeRef = moduleDefinition.ImportReference(networkManagerTypeDef);
-            m_NetworkManager_TypeRef = moduleDefinition.ImportReference(networkManagerType);
+            foreach (var propertyDef in networkManagerTypeDef.Properties)
-            foreach (var propertyInfo in networkManagerType.GetProperties())
             {
-                switch (propertyInfo.Name)
+                switch (propertyDef.Name)
                 {
                     case k_NetworkManager_LocalClientId:
-                        m_NetworkManager_getLocalClientId_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getLocalClientId_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsListening:
-                        m_NetworkManager_getIsListening_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsListening_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsHost:
-                        m_NetworkManager_getIsHost_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsHost_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsServer:
-                        m_NetworkManager_getIsServer_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsServer_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsClient:
-                        m_NetworkManager_getIsClient_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsClient_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                 }
             }
 
-            foreach (var fieldInfo in networkManagerType.GetFields(BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var fieldDef in networkManagerTypeDef.Fields)
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_NetworkManager_LogLevel:
-                        m_NetworkManager_LogLevel_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_LogLevel_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case k_NetworkManager_rpc_func_table:
-                        m_NetworkManager_rpc_func_table_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_rpc_func_table_FieldRef = moduleDefinition.ImportReference(fieldDef);
-                        m_NetworkManager_rpc_func_table_Add_MethodRef = moduleDefinition.ImportReference(fieldInfo.FieldType.GetMethod("Add"));
+
+                        m_NetworkManager_rpc_func_table_Add_MethodRef = fieldDef.FieldType.Resolve().Methods.First(m => m.Name == "Add");
+                        m_NetworkManager_rpc_func_table_Add_MethodRef.DeclaringType = fieldDef.FieldType;
+                        m_NetworkManager_rpc_func_table_Add_MethodRef = moduleDefinition.ImportReference(m_NetworkManager_rpc_func_table_Add_MethodRef);
                         break;
                     case k_NetworkManager_rpc_name_table:
-                        m_NetworkManager_rpc_name_table_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_rpc_name_table_FieldRef = moduleDefinition.ImportReference(fieldDef);
-                        m_NetworkManager_rpc_name_table_Add_MethodRef = moduleDefinition.ImportReference(fieldInfo.FieldType.GetMethod("Add"));
+
+                        m_NetworkManager_rpc_name_table_Add_MethodRef = fieldDef.FieldType.Resolve().Methods.First(m => m.Name == "Add");
+                        m_NetworkManager_rpc_name_table_Add_MethodRef.DeclaringType = fieldDef.FieldType;
+                        m_NetworkManager_rpc_name_table_Add_MethodRef = moduleDefinition.ImportReference(m_NetworkManager_rpc_name_table_Add_MethodRef);
                         break;
                 }
             }
 
-            var networkBehaviourType = typeof(NetworkBehaviour);
+            m_NetworkBehaviour_TypeRef = moduleDefinition.ImportReference(networkBehaviourTypeDef);
-            m_NetworkBehaviour_TypeRef = moduleDefinition.ImportReference(networkBehaviourType);
+            foreach (var propertyDef in networkBehaviourTypeDef.Properties)
-            foreach (var propertyInfo in networkBehaviourType.GetProperties())
             {
-                switch (propertyInfo.Name)
+                switch (propertyDef.Name)
                 {
                     case k_NetworkBehaviour_NetworkManager:
-                        m_NetworkBehaviour_getNetworkManager_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkBehaviour_getNetworkManager_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkBehaviour_OwnerClientId:
-                        m_NetworkBehaviour_getOwnerClientId_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkBehaviour_getOwnerClientId_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                 }
             }
 
-            foreach (var methodInfo in networkBehaviourType.GetMethods(BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var methodDef in networkBehaviourTypeDef.Methods)
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case k_NetworkBehaviour_beginSendServerRpc:
-                        m_NetworkBehaviour_beginSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_beginSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_endSendServerRpc:
-                        m_NetworkBehaviour_endSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_endSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_beginSendClientRpc:
-                        m_NetworkBehaviour_beginSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_beginSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_endSendClientRpc:
-                        m_NetworkBehaviour_endSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_endSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
 
-            foreach (var fieldInfo in networkBehaviourType.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var fieldDef in networkBehaviourTypeDef.Fields)
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_NetworkBehaviour_rpc_exec_stage:
-                        m_NetworkBehaviour_rpc_exec_stage_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkBehaviour_rpc_exec_stage_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var networkHandlerDelegateType = typeof(NetworkManager.RpcReceiveHandler);
+            foreach (var ctor in networkHandlerDelegateTypeDef.Resolve().GetConstructors())
-            m_NetworkHandlerDelegateCtor_MethodRef = moduleDefinition.ImportReference(networkHandlerDelegateType.GetConstructor(new[] { typeof(object), typeof(IntPtr) }));
-
-            var rpcParamsType = typeof(__RpcParams);
-            m_RpcParams_TypeRef = moduleDefinition.ImportReference(rpcParamsType);
-            foreach (var fieldInfo in rpcParamsType.GetFields())
             {
-                switch (fieldInfo.Name)
+                if (ctor.HasParameters &&
+                    ctor.Parameters.Count == 2 &&
+                    ctor.Parameters[0].ParameterType.Name == nameof(System.Object) &&
+                    ctor.Parameters[1].ParameterType.Name == nameof(IntPtr))
+                {
+                    m_NetworkHandlerDelegateCtor_MethodRef = moduleDefinition.ImportReference(ctor);
+                    break;
+                }
+            }
+
+            m_RpcParams_TypeRef = moduleDefinition.ImportReference(rpcParamsTypeDef);
+            foreach (var fieldDef in rpcParamsTypeDef.Fields)
+            {
+                switch (fieldDef.Name)
                 {
                     case k_RpcParams_Server:
-                        m_RpcParams_Server_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_RpcParams_Server_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case k_RpcParams_Client:
-                        m_RpcParams_Client_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_RpcParams_Client_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var serverRpcParamsType = typeof(ServerRpcParams);
+            m_ServerRpcParams_TypeRef = moduleDefinition.ImportReference(serverRpcParamsTypeDef);
-            m_ServerRpcParams_TypeRef = moduleDefinition.ImportReference(serverRpcParamsType);
+            foreach (var fieldDef in serverRpcParamsTypeDef.Fields)
-            foreach (var fieldInfo in serverRpcParamsType.GetFields())
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_ServerRpcParams_Receive:
-                        foreach (var recvFieldInfo in fieldInfo.FieldType.GetFields())
+                        foreach (var recvFieldDef in fieldDef.FieldType.Resolve().Fields)
                         {
-                            switch (recvFieldInfo.Name)
+                            switch (recvFieldDef.Name)
                             {
                                 case k_ServerRpcReceiveParams_SenderClientId:
-                                    m_ServerRpcParams_Receive_SenderClientId_FieldRef = moduleDefinition.ImportReference(recvFieldInfo);
+                                    m_ServerRpcParams_Receive_SenderClientId_FieldRef = moduleDefinition.ImportReference(recvFieldDef);
                                     break;
                             }
                         }
 
-                        m_ServerRpcParams_Receive_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_ServerRpcParams_Receive_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var clientRpcParamsType = typeof(ClientRpcParams);
+            m_ClientRpcParams_TypeRef = moduleDefinition.ImportReference(clientRpcParamsTypeDef);
-            m_ClientRpcParams_TypeRef = moduleDefinition.ImportReference(clientRpcParamsType);
+            m_FastBufferWriter_TypeRef = moduleDefinition.ImportReference(fastBufferWriterTypeDef);
+            m_FastBufferReader_TypeRef = moduleDefinition.ImportReference(fastBufferReaderTypeDef);
 
-            var fastBufferWriterType = typeof(FastBufferWriter);
+            // Find all extension methods for FastBufferReader and FastBufferWriter to enable user-implemented methods to be called
-            m_FastBufferWriter_TypeRef = moduleDefinition.ImportReference(fastBufferWriterType);
-
-            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> { m_MainModule.Assembly };
             foreach (var reference in m_MainModule.AssemblyReferences)
             {
@@ -371,9 +673,170 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
+            foreach (var method in networkVariableSerializationTypesTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_UnmanagedByMemcpy):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_UnmanagedINetworkSerializable):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_ManagedINetworkSerializable):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_FixedString):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_ManagedIEquatable):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_UnmanagedIEquatable):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_UnmanagedValueEquals):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_ManagedClassEquals):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef = method;
+                        break;
+                }
+            }
+
+            foreach (var method in bytePackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(BytePacker.WriteValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
+            foreach (var method in byteUnpackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(ByteUnpacker.ReadValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
             return true;
         }
 
+        // This gets all fields from this type as well as any parent types, up to (but not including) the base NetworkBehaviour class
+        // Importantly... this also resolves any generics, so if the base class is Foo<T> and contains a field of NetworkVariable<T>,
+        // and this class is Bar : Foo<int>, it will properly resolve NetworkVariable<T> to NetworkVariable<int>.
+        private void GetAllFieldsAndResolveGenerics(TypeDefinition type, ref List<TypeReference> fieldTypes, Dictionary<string, TypeReference> genericParameters = null)
+        {
+            foreach (var field in type.Fields)
+            {
+                if (field.FieldType.IsGenericInstance)
+                {
+                    var genericType = (GenericInstanceType)field.FieldType;
+                    var newGenericType = new GenericInstanceType(field.FieldType.Resolve());
+                    for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                    {
+                        var argument = genericType.GenericArguments[i];
+
+                        if (genericParameters != null && genericParameters.ContainsKey(argument.Name))
+                        {
+                            newGenericType.GenericArguments.Add(genericParameters[argument.Name]);
+                        }
+                        else
+                        {
+                            newGenericType.GenericArguments.Add(argument);
+                        }
+                    }
+                    fieldTypes.Add(newGenericType);
+                }
+                else
+                {
+                    fieldTypes.Add(field.FieldType);
+                }
+            }
+
+            if (type.BaseType == null || type.BaseType.Name == nameof(NetworkBehaviour))
+            {
+                return;
+            }
+            var genericParams = new Dictionary<string, TypeReference>();
+            var resolved = type.BaseType.Resolve();
+            if (type.BaseType.IsGenericInstance)
+            {
+                var genericType = (GenericInstanceType)type.BaseType;
+                for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                {
+                    genericParams[resolved.GenericParameters[i].Name] = genericType.GenericArguments[i];
+                }
+            }
+            GetAllFieldsAndResolveGenerics(resolved, ref fieldTypes, genericParams);
+        }
+
         private void ProcessNetworkBehaviour(TypeDefinition typeDefinition, string[] assemblyDefines)
         {
             var rpcHandlers = new List<(uint RpcMethodId, MethodDefinition RpcHandler)>();
@@ -416,6 +879,28 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
+            if (!typeDefinition.HasGenericParameters && !typeDefinition.IsGenericInstance)
+            {
+                var fieldTypes = new List<TypeReference>();
+                GetAllFieldsAndResolveGenerics(typeDefinition, ref fieldTypes);
+                foreach (var type in fieldTypes)
+                {
+                    //var type = field.FieldType;
+                    if (type.IsGenericInstance)
+                    {
+                        if (type.Resolve().Name == typeof(NetworkVariable<>).Name || type.Resolve().Name == typeof(NetworkList<>).Name)
+                        {
+                            var genericInstanceType = (GenericInstanceType)type;
+                            var wrappedType = genericInstanceType.GenericArguments[0];
+                            if (!m_WrappedNetworkVariableTypes.Contains(wrappedType))
+                            {
+                                m_WrappedNetworkVariableTypes.Add(wrappedType);
+                            }
+                        }
+                    }
+                }
+            }
+
             if (rpcHandlers.Count > 0 || rpcNames.Count > 0)
             {
                 var staticCtorMethodDef = typeDefinition.GetStaticConstructor();
@@ -656,6 +1141,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetWriteMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
             var foundMethodRef = m_FastBufferWriter_WriteValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);
 
@@ -669,7 +1184,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         if (parameters[1].IsIn)
                         {
-                            if (parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve() &&
+                            if (((ByReferenceType)parameters[1].ParameterType).ElementType.FullName == paramType.FullName &&
                                 ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
@@ -679,8 +1194,7 @@ namespace Unity.Netcode.Editor.CodeGen
                         }
                         else
                         {
-
+                            if (parameters[1].ParameterType.FullName == paramType.FullName &&
-                            if (parameters[1].ParameterType.Resolve() == paramType.Resolve() &&
                                 parameters[1].ParameterType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
@@ -803,6 +1317,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetReadMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
 
             var foundMethodRef = m_FastBufferReader_ReadValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);
@@ -813,7 +1357,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     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.FullName == paramType.FullName &&
                         ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                     {
                         methodRef = method;

Editor/Configuration.meta

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

Editor/Configuration/NetcodeForGameObjectsSettings.cs

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

Editor/Configuration/NetcodeForGameObjectsSettings.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: c2e5a740c1abd4315801e3f26ecf8adb
+guid: 2f9c9b10bc41a0e46ab71324dd0ac6e1
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/Configuration/NetcodeSettingsProvider.cs

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

Editor/Configuration/NetcodeSettingsProvider.cs.meta

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

Editor/Configuration/NetworkPrefabProcessor.cs

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

Editor/Configuration/NetworkPrefabProcessor.cs.meta

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

Editor/Configuration/NetworkPrefabsEditor.cs

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

Editor/Configuration/NetworkPrefabsEditor.cs.meta

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

Editor/HiddenScriptEditor.cs

@@ -0,0 +1,184 @@
+using Unity.Netcode.Components;
+#if UNITY_UNET_PRESENT
+using Unity.Netcode.Transports.UNET;
+#endif
+using Unity.Netcode.Transports.UTP;
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor
+{
+    /// <summary>
+    /// Internal use. Hides the script field for the given component.
+    /// </summary>
+    public class HiddenScriptEditor : UnityEditor.Editor
+    {
+        private static readonly string[] k_HiddenFields = { "m_Script" };
+
+        /// <summary>
+        /// Draws inspector properties without the script field.
+        /// </summary>
+        public override void OnInspectorGUI()
+        {
+            EditorGUI.BeginChangeCheck();
+            serializedObject.UpdateIfRequiredOrScript();
+            DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+            serializedObject.ApplyModifiedProperties();
+            EditorGUI.EndChangeCheck();
+        }
+    }
+#if UNITY_UNET_PRESENT
+    /// <summary>
+    /// Internal use. Hides the script field for UNetTransport.
+    /// </summary>
+    [CustomEditor(typeof(UNetTransport), true)]
+    public class UNetTransportEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+    /// <summary>
+    /// Internal use. Hides the script field for UnityTransport.
+    /// </summary>
+    [CustomEditor(typeof(UnityTransport), true)]
+    public class UnityTransportEditor : HiddenScriptEditor
+    {
+        private static readonly string[] k_HiddenFields = { "m_Script", "ConnectionData" };
+
+        private bool m_AllowIncomingConnections;
+        private bool m_Initialized;
+
+        private UnityTransport m_UnityTransport;
+
+        private SerializedProperty m_ServerAddressProperty;
+        private SerializedProperty m_ServerPortProperty;
+        private SerializedProperty m_OverrideBindIpProperty;
+
+        private const string k_LoopbackIpv4 = "127.0.0.1";
+        private const string k_LoopbackIpv6 = "::1";
+        private const string k_AnyIpv4 = "0.0.0.0";
+        private const string k_AnyIpv6 = "::";
+
+
+        private void Initialize()
+        {
+            if (m_Initialized)
+            {
+                return;
+            }
+            m_Initialized = true;
+            m_UnityTransport = (UnityTransport)target;
+
+            var connectionDataProperty = serializedObject.FindProperty(nameof(UnityTransport.ConnectionData));
+
+            m_ServerAddressProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Address));
+            m_ServerPortProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Port));
+            m_OverrideBindIpProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.ServerListenAddress));
+        }
+
+        /// <summary>
+        /// Draws inspector properties without the script field.
+        /// </summary>
+        public override void OnInspectorGUI()
+        {
+            Initialize();
+            EditorGUI.BeginChangeCheck();
+            serializedObject.UpdateIfRequiredOrScript();
+            DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+            serializedObject.ApplyModifiedProperties();
+            EditorGUI.EndChangeCheck();
+
+            EditorGUILayout.PropertyField(m_ServerAddressProperty);
+            EditorGUILayout.PropertyField(m_ServerPortProperty);
+
+            serializedObject.ApplyModifiedProperties();
+
+            EditorGUILayout.HelpBox("It's recommended to leave remote connections disabled for local testing to avoid exposing ports on your device.", MessageType.Info);
+            bool allowRemoteConnections = m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6 && !string.IsNullOrEmpty(m_UnityTransport.ConnectionData.ServerListenAddress);
+            allowRemoteConnections = EditorGUILayout.Toggle(new GUIContent("Allow Remote Connections?", $"Bind IP: {m_UnityTransport.ConnectionData.ServerListenAddress}"), allowRemoteConnections);
+
+            bool isIpV6 = m_UnityTransport.ConnectionData.IsIpv6;
+
+            if (!allowRemoteConnections)
+            {
+                if (m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6)
+                {
+                    if (isIpV6)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv6;
+                    }
+                    else
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv4;
+                    }
+                    EditorUtility.SetDirty(m_UnityTransport);
+                }
+            }
+
+            using (new EditorGUI.DisabledScope(!allowRemoteConnections))
+            {
+                string overrideIp = m_UnityTransport.ConnectionData.ServerListenAddress;
+                if (overrideIp == k_AnyIpv4 || overrideIp == k_AnyIpv6 || overrideIp == k_LoopbackIpv4 || overrideIp == k_LoopbackIpv6)
+                {
+                    overrideIp = "";
+                }
+
+                overrideIp = EditorGUILayout.TextField("Override Bind IP (optional)", overrideIp);
+                if (allowRemoteConnections)
+                {
+                    if (overrideIp == "")
+                    {
+                        if (isIpV6)
+                        {
+                            overrideIp = k_AnyIpv6;
+                        }
+                        else
+                        {
+                            overrideIp = k_AnyIpv4;
+                        }
+                    }
+
+                    if (m_UnityTransport.ConnectionData.ServerListenAddress != overrideIp)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = overrideIp;
+                        EditorUtility.SetDirty(m_UnityTransport);
+                    }
+                }
+            }
+        }
+    }
+
+#if COM_UNITY_MODULES_ANIMATION
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkAnimator.
+    /// </summary>
+    [CustomEditor(typeof(NetworkAnimator), true)]
+    public class NetworkAnimatorEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+#if COM_UNITY_MODULES_PHYSICS
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkRigidbody.
+    /// </summary>
+    [CustomEditor(typeof(NetworkRigidbody), true)]
+    public class NetworkRigidbodyEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+#if COM_UNITY_MODULES_PHYSICS2D
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkRigidbody2D.
+    /// </summary>
+    [CustomEditor(typeof(NetworkRigidbody2D), true)]
+    public class NetworkRigidbody2DEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+}

Editor/HiddenScriptEditor.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: ebf622cc80e94f488e59caf8b7419f50
+timeCreated: 1661959406

Editor/NetworkBehaviourEditor.cs

@@ -3,9 +3,13 @@ using System.Collections.Generic;
 using System.Reflection;
 using UnityEngine;
 using UnityEditor;
+using Unity.Netcode.Editor.Configuration;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// The <see cref="CustomEditor"/> for <see cref="NetworkBehaviour"/>
+    /// </summary>
     [CustomEditor(typeof(NetworkBehaviour), true)]
     [CanEditMultipleObjects]
     public class NetworkBehaviourEditor : UnityEditor.Editor
@@ -16,6 +20,7 @@ namespace Unity.Netcode.Editor
         private readonly Dictionary<string, object> m_NetworkVariableObjects = new Dictionary<string, object>();
 
         private GUIContent m_NetworkVariableLabelGuiContent;
+        private GUIContent m_NetworkListLabelGuiContent;
 
         private void Init(MonoScript script)
         {
@@ -26,6 +31,7 @@ namespace Unity.Netcode.Editor
             m_NetworkVariableObjects.Clear();
 
             m_NetworkVariableLabelGuiContent = new GUIContent("NetworkVariable", "This variable is a NetworkVariable. It can not be serialized and can only be changed during runtime.");
+            m_NetworkListLabelGuiContent = new GUIContent("NetworkList", "This variable is a NetworkList. It is rendered, but you can't serialize or change it.");
 
             var fields = script.GetClass().GetFields(BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy);
             for (int i = 0; i < fields.Length; i++)
@@ -33,8 +39,15 @@ namespace Unity.Netcode.Editor
                 var ft = fields[i].FieldType;
                 if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkVariable<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
                 {
-                    m_NetworkVariableNames.Add(fields[i].Name);
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
-                    m_NetworkVariableFields.Add(fields[i].Name, fields[i]);
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkVariable {fields[i].Name}");
+                }
+                if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkList<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
+                {
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkList {fields[i].Name}");
                 }
             }
         }
@@ -68,25 +81,48 @@ namespace Unity.Netcode.Editor
             EditorGUILayout.BeginHorizontal();
             if (genericType.IsValueType)
             {
-                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkVariableValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
+                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkContainerValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
                 var genericMethod = method.MakeGenericMethod(genericType);
                 genericMethod.Invoke(this, new[] { (object)index });
             }
             else
             {
                 EditorGUILayout.LabelField("Type not renderable");
-            }
 
                 GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
                 EditorGUILayout.EndHorizontal();
             }
+        }
 
-        private void RenderNetworkVariableValueType<T>(int index) where T : unmanaged
+        private void RenderNetworkContainerValueType<T>(int index) where T : unmanaged, IEquatable<T>
+        {
+            try
             {
                 var networkVariable = (NetworkVariable<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                RenderNetworkVariableValueType(index, networkVariable);
+            }
+            catch (Exception)
+            {
+                try
+                {
+                    var networkList = (NetworkList<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                    RenderNetworkListValueType(index, networkList);
+                }
+                catch (Exception e)
+                {
+                    Debug.Log(e);
+                    throw;
+                }
+            }
+
+            EditorGUILayout.EndHorizontal();
+        }
+
+        private void RenderNetworkVariableValueType<T>(int index, NetworkVariable<T> networkVariable) where T : unmanaged
+        {
             var type = typeof(T);
             object val = networkVariable.Value;
-            string name = m_NetworkVariableNames[index];
+            string variableName = m_NetworkVariableNames[index];
 
             var behaviour = (NetworkBehaviour)target;
 
@@ -95,47 +131,47 @@ namespace Unity.Netcode.Editor
             {
                 if (type == typeof(int))
                 {
-                    val = EditorGUILayout.IntField(name, (int)val);
+                    val = EditorGUILayout.IntField(variableName, (int)val);
                 }
                 else if (type == typeof(uint))
                 {
-                    val = (uint)EditorGUILayout.LongField(name, (long)((uint)val));
+                    val = (uint)EditorGUILayout.LongField(variableName, (long)((uint)val));
                 }
                 else if (type == typeof(short))
                 {
-                    val = (short)EditorGUILayout.IntField(name, (int)((short)val));
+                    val = (short)EditorGUILayout.IntField(variableName, (int)((short)val));
                 }
                 else if (type == typeof(ushort))
                 {
-                    val = (ushort)EditorGUILayout.IntField(name, (int)((ushort)val));
+                    val = (ushort)EditorGUILayout.IntField(variableName, (int)((ushort)val));
                 }
                 else if (type == typeof(sbyte))
                 {
-                    val = (sbyte)EditorGUILayout.IntField(name, (int)((sbyte)val));
+                    val = (sbyte)EditorGUILayout.IntField(variableName, (int)((sbyte)val));
                 }
                 else if (type == typeof(byte))
                 {
-                    val = (byte)EditorGUILayout.IntField(name, (int)((byte)val));
+                    val = (byte)EditorGUILayout.IntField(variableName, (int)((byte)val));
                 }
                 else if (type == typeof(long))
                 {
-                    val = EditorGUILayout.LongField(name, (long)val);
+                    val = EditorGUILayout.LongField(variableName, (long)val);
                 }
                 else if (type == typeof(ulong))
                 {
-                    val = (ulong)EditorGUILayout.LongField(name, (long)((ulong)val));
+                    val = (ulong)EditorGUILayout.LongField(variableName, (long)((ulong)val));
                 }
                 else if (type == typeof(bool))
                 {
-                    val = EditorGUILayout.Toggle(name, (bool)val);
+                    val = EditorGUILayout.Toggle(variableName, (bool)val);
                 }
                 else if (type == typeof(string))
                 {
-                    val = EditorGUILayout.TextField(name, (string)val);
+                    val = EditorGUILayout.TextField(variableName, (string)val);
                 }
                 else if (type.IsEnum)
                 {
-                    val = EditorGUILayout.EnumPopup(name, (Enum)val);
+                    val = EditorGUILayout.EnumPopup(variableName, (Enum)val);
                 }
                 else
                 {
@@ -146,11 +182,31 @@ namespace Unity.Netcode.Editor
             }
             else
             {
-                EditorGUILayout.LabelField(name, EditorStyles.wordWrappedLabel);
+                EditorGUILayout.LabelField(variableName, EditorStyles.wordWrappedLabel);
                 EditorGUILayout.SelectableLabel(val.ToString(), EditorStyles.wordWrappedLabel);
             }
+            GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
         }
 
+        private void RenderNetworkListValueType<T>(int index, NetworkList<T> networkList)
+            where T : unmanaged, IEquatable<T>
+        {
+            string variableName = m_NetworkVariableNames[index];
+
+            string value = "";
+            bool addComma = false;
+            foreach (var v in networkList)
+            {
+                if (addComma)
+                {
+                    value += ", ";
+                }
+                value += v.ToString();
+                addComma = true;
+            }
+            EditorGUILayout.LabelField(variableName, value);
+            GUILayout.Label(m_NetworkListLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkListLabelGuiContent).x));
+        }
 
         /// <inheritdoc/>
         public override void OnInspectorGUI()
@@ -230,8 +286,6 @@ namespace Unity.Netcode.Editor
             CheckForNetworkObject((target as NetworkBehaviour).gameObject);
         }
 
-        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
-
         /// <summary>
         /// Recursively finds the root parent of a <see cref="Transform"/>
         /// </summary>
@@ -263,8 +317,7 @@ namespace Unity.Netcode.Editor
 
             // Now get the root parent transform to the current GameObject (or itself)
             var rootTransform = GetRootParentTransform(gameObject.transform);
-            var networkManager = rootTransform.GetComponent<NetworkManager>();
+            if (!rootTransform.TryGetComponent<NetworkManager>(out var networkManager))
-            if (networkManager == null)
             {
                 networkManager = rootTransform.GetComponentInChildren<NetworkManager>();
             }
@@ -299,8 +352,7 @@ namespace Unity.Netcode.Editor
 
             // 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 (!rootTransform.TryGetComponent<NetworkObject>(out var networkObject))
-            if (networkObject == null)
             {
                 networkObject = rootTransform.GetComponentInChildren<NetworkObject>();
 
@@ -310,7 +362,7 @@ namespace Unity.Netcode.Editor
                     // and the user has already turned "Auto-Add NetworkObject" on when first notified about the requirement
                     // then just send a reminder to the user why the NetworkObject they just deleted seemingly "re-appeared"
                     // again.
-                    if (networkObjectRemoved && EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists) && EditorPrefs.GetBool(AutoAddNetworkObjectIfNoneExists))
+                    if (networkObjectRemoved && NetcodeForGameObjectsEditorSettings.GetAutoAddNetworkObjectSetting())
                     {
                         Debug.LogWarning($"{gameObject.name} still has {nameof(NetworkBehaviour)}s and Auto-Add NetworkObjects is enabled. A NetworkObject is being added back to {gameObject.name}.");
                         Debug.Log($"To reset Auto-Add NetworkObjects: Select the Netcode->General->Reset Auto-Add NetworkObject menu item.");
@@ -319,7 +371,7 @@ namespace Unity.Netcode.Editor
                     // Notify and provide the option to add it one time, always add a NetworkObject, or do nothing and let the user manually add it
                     if (EditorUtility.DisplayDialog($"{nameof(NetworkBehaviour)}s require a {nameof(NetworkObject)}",
                     $"{gameObject.name} does not have a {nameof(NetworkObject)} component.  Would you like to add one now?", "Yes", "No (manually add it)",
-                    DialogOptOutDecisionType.ForThisMachine, AutoAddNetworkObjectIfNoneExists))
+                    DialogOptOutDecisionType.ForThisMachine, NetcodeForGameObjectsEditorSettings.AutoAddNetworkObjectIfNoneExists))
                     {
                         gameObject.AddComponent<NetworkObject>();
                         var activeScene = UnityEngine.SceneManagement.SceneManager.GetActiveScene();
@@ -329,20 +381,5 @@ namespace Unity.Netcode.Editor
                 }
             }
         }
-
-        /// <summary>
-        /// This allows users to reset the Auto-Add NetworkObject preference
-        /// so the next time they add a NetworkBehaviour to a GameObject without
-        /// a NetworkObject it will display the dialog box again and not
-        /// automatically add a NetworkObject.
-        /// </summary>
-        [MenuItem("Netcode/General/Reset Auto-Add NetworkObject", false, 1)]
-        private static void ResetMultiplayerToolsTipStatus()
-        {
-            if (EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists))
-            {
-                EditorPrefs.SetBool(AutoAddNetworkObjectIfNoneExists, false);
-            }
-        }
     }
 }

Editor/NetworkManagerEditor.cs

@@ -1,8 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using UnityEditor;
 using UnityEngine;
-using UnityEditorInternal;
+using Unity.Netcode.Editor.Configuration;
 
 namespace Unity.Netcode.Editor
 {
@@ -14,7 +15,6 @@ namespace Unity.Netcode.Editor
     [CanEditMultipleObjects]
     public class NetworkManagerEditor : UnityEditor.Editor
     {
-        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
         private static GUIStyle s_CenteredWordWrappedLabelStyle;
         private static GUIStyle s_HelpBoxStyle;
 
@@ -40,8 +40,7 @@ namespace Unity.Netcode.Editor
         private SerializedProperty m_NetworkIdRecycleDelayProperty;
         private SerializedProperty m_RpcHashSizeProperty;
         private SerializedProperty m_LoadSceneTimeOutProperty;
-
+        private SerializedProperty m_PrefabsList;
-        private ReorderableList m_NetworkPrefabsList;
 
         private NetworkManager m_NetworkManager;
         private bool m_Initialized;
@@ -106,7 +105,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-
+            m_PrefabsList = m_NetworkConfigProperty
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
 
             ReloadTransports();
         }
@@ -132,76 +133,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-        }
+            m_PrefabsList = m_NetworkConfigProperty
-
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
-        private void OnEnable()
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
-        {
-            m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig)).FindPropertyRelative(nameof(NetworkConfig.NetworkPrefabs)), true, true, true, true);
-            m_NetworkPrefabsList.elementHeightCallback = index =>
-            {
-                var networkOverrideInt = 0;
-                if (m_NetworkPrefabsList.count > 0)
-                {
-                    var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                    var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                    networkOverrideInt = networkOverrideProp.enumValueIndex;
-                }
-
-                return 8 + (networkOverrideInt == 0 ? EditorGUIUtility.singleLineHeight : (EditorGUIUtility.singleLineHeight * 2) + 5);
-            };
-            m_NetworkPrefabsList.drawElementCallback = (rect, index, isActive, isFocused) =>
-            {
-                rect.y += 5;
-
-                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                var networkPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Prefab));
-                var networkSourceHashProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourceHashToOverride));
-                var networkSourcePrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourcePrefabToOverride));
-                var networkTargetPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.OverridingTargetPrefab));
-                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                var networkOverrideInt = networkOverrideProp.enumValueIndex;
-                var networkOverrideEnum = (NetworkPrefabOverride)networkOverrideInt;
-                EditorGUI.LabelField(new Rect(rect.x + rect.width - 70, rect.y, 60, EditorGUIUtility.singleLineHeight), "Override");
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    if (EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), false))
-                    {
-                        networkOverrideProp.enumValueIndex = (int)NetworkPrefabOverride.Prefab;
-                    }
-                }
-                else
-                {
-                    if (!EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), true))
-                    {
-                        networkOverrideProp.enumValueIndex = 0;
-                        networkOverrideEnum = NetworkPrefabOverride.None;
-                    }
-                }
-
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width - 80, EditorGUIUtility.singleLineHeight), networkPrefabProp, GUIContent.none);
-                }
-                else
-                {
-                    networkOverrideProp.enumValueIndex = GUI.Toolbar(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), networkOverrideInt - 1, new[] { "Prefab", "Hash" }) + 1;
-
-                    if (networkOverrideEnum == NetworkPrefabOverride.Prefab)
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourcePrefabProp, GUIContent.none);
-                    }
-                    else
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourceHashProp, GUIContent.none);
-                    }
-
-                    rect.y += EditorGUIUtility.singleLineHeight + 5;
-
-                    EditorGUI.LabelField(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), "Overriding Prefab");
-                    EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 110, EditorGUIUtility.singleLineHeight), networkTargetPrefabProp, GUIContent.none);
-                }
-            };
-            m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
         }
 
         /// <inheritdoc/>
@@ -214,18 +148,6 @@ namespace Unity.Netcode.Editor
             DrawInstallMultiplayerToolsTip();
 #endif
 
-            {
-                var iterator = serializedObject.GetIterator();
-
-                for (bool enterChildren = true; iterator.NextVisible(enterChildren); enterChildren = false)
-                {
-                    using (new EditorGUI.DisabledScope("m_Script" == iterator.propertyPath))
-                    {
-                        EditorGUILayout.PropertyField(iterator, false);
-                    }
-                }
-            }
-
             if (!m_NetworkManager.IsServer && !m_NetworkManager.IsClient)
             {
                 serializedObject.Update();
@@ -236,7 +158,62 @@ namespace Unity.Netcode.Editor
                 EditorGUILayout.PropertyField(m_PlayerPrefabProperty);
                 EditorGUILayout.Space();
 
-                m_NetworkPrefabsList.DoLayoutList();
+                if (m_NetworkManager.NetworkConfig.HasOldPrefabList())
+                {
+                    EditorGUILayout.HelpBox("Network Prefabs serialized in old format. Migrate to new format to edit the list.", MessageType.Info);
+                    if (GUILayout.Button(new GUIContent("Migrate Prefab List", "Converts the old format Network Prefab list to a new Scriptable Object")))
+                    {
+                        // Default directory
+                        var directory = "Assets/";
+                        var assetPath = AssetDatabase.GetAssetPath(m_NetworkManager);
+                        if (assetPath == "")
+                        {
+                            assetPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(m_NetworkManager);
+                        }
+
+                        if (assetPath != "")
+                        {
+                            directory = Path.GetDirectoryName(assetPath);
+                        }
+                        else
+                        {
+#if UNITY_2021_1_OR_NEWER
+                            var prefabStage = UnityEditor.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#else
+                            var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#endif
+                            if (prefabStage != null)
+                            {
+                                var prefabPath = prefabStage.assetPath;
+                                if (!string.IsNullOrEmpty(prefabPath))
+                                {
+                                    directory = Path.GetDirectoryName(prefabPath);
+                                }
+                            }
+                            if (m_NetworkManager.gameObject.scene != null)
+                            {
+                                var scenePath = m_NetworkManager.gameObject.scene.path;
+                                if (!string.IsNullOrEmpty(scenePath))
+                                {
+                                    directory = Path.GetDirectoryName(scenePath);
+                                }
+                            }
+                        }
+                        var networkPrefabs = m_NetworkManager.NetworkConfig.MigrateOldNetworkPrefabsToNetworkPrefabsList();
+                        string path = Path.Combine(directory, $"NetworkPrefabs-{m_NetworkManager.GetInstanceID()}.asset");
+                        Debug.Log("Saving migrated Network Prefabs List to " + path);
+                        AssetDatabase.CreateAsset(networkPrefabs, path);
+                        EditorUtility.SetDirty(m_NetworkManager);
+                    }
+                }
+                else
+                {
+                    if (m_NetworkManager.NetworkConfig.Prefabs.NetworkPrefabsLists.Count == 0)
+                    {
+                        EditorGUILayout.HelpBox("You have no prefab list selected. You will have to add your prefabs manually at runtime for netcode to work.", MessageType.Warning);
+                    }
+                    EditorGUILayout.PropertyField(m_PrefabsList);
+                }
                 EditorGUILayout.Space();
 
                 EditorGUILayout.LabelField("General", EditorStyles.boldLabel);
@@ -371,7 +348,7 @@ namespace Unity.Netcode.Editor
             const string targetUrl = "https://docs-multiplayer.unity3d.com/netcode/current/tools/install-tools";
             const string infoIconName = "console.infoicon";
 
-            if (PlayerPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 0) != 0)
+            if (NetcodeForGameObjectsEditorSettings.GetNetcodeInstallMultiplayerToolTips() != 0)
             {
                 return;
             }
@@ -417,7 +394,7 @@ namespace Unity.Netcode.Editor
                 GUILayout.FlexibleSpace();
                 if (GUILayout.Button(dismissButtonText, dismissButtonStyle, GUILayout.ExpandWidth(false)))
                 {
-                    PlayerPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 1);
+                    NetcodeForGameObjectsEditorSettings.SetNetcodeInstallMultiplayerToolTips(1);
                 }
                 EditorGUIUtility.AddCursorRect(GUILayoutUtility.GetLastRect(), MouseCursor.Link);
                 GUILayout.FlexibleSpace();

Editor/NetworkManagerHelper.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Linq;
+using Unity.Netcode.Editor.Configuration;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 using UnityEditor;
@@ -32,6 +33,24 @@ namespace Unity.Netcode.Editor
 
             EditorApplication.playModeStateChanged += EditorApplication_playModeStateChanged;
             EditorApplication.hierarchyChanged += EditorApplication_hierarchyChanged;
+
+            // Initialize default values for new NetworkManagers
+            //
+            // When the default prefab list is enabled, this will default
+            // new NetworkManagers to using it.
+            //
+            // This will get run when new NetworkManagers are added, and
+            // when the user presses the "reset" button on a NetworkManager
+            // in the inspector.
+            NetworkManager.OnNetworkManagerReset = manager =>
+            {
+                var settings = NetcodeForGameObjectsProjectSettings.instance;
+                if (settings.GenerateDefaultNetworkPrefabs)
+                {
+                    manager.NetworkConfig = new NetworkConfig();
+                    manager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out _, true) };
+                }
+            };
         }
 
         private static void EditorApplication_playModeStateChanged(PlayModeStateChange playModeStateChange)
@@ -64,8 +83,12 @@ namespace Unity.Netcode.Editor
         {
             var scenesList = EditorBuildSettings.scenes.ToList();
             var activeScene = SceneManager.GetActiveScene();
-            var isSceneInBuildSettings = scenesList.Where((c) => c.path == activeScene.path).Count() == 1;
+            var isSceneInBuildSettings = scenesList.Count((c) => c.path == activeScene.path) == 1;
+#if UNITY_2023_1_OR_NEWER
+            var networkManager = Object.FindFirstObjectByType<NetworkManager>();
+#else
             var networkManager = Object.FindObjectOfType<NetworkManager>();
+#endif
             if (!isSceneInBuildSettings && networkManager != null)
             {
                 if (networkManager.NetworkConfig != null && networkManager.NetworkConfig.EnableSceneManagement)
@@ -109,9 +132,8 @@ namespace Unity.Netcode.Editor
         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 (!networkManager.gameObject.TryGetComponent<NetworkObject>(out var networkObject))
             {
                 // if none is found, check to see if any children have a NetworkObject
                 networkObject = networkManager.gameObject.GetComponentInChildren<NetworkObject>();

Editor/NetworkObjectEditor.cs

@@ -15,6 +15,8 @@ namespace Unity.Netcode.Editor
         private NetworkObject m_NetworkObject;
         private bool m_ShowObservers;
 
+        private static readonly string[] k_HiddenFields = { "m_Script" };
+
         private void Initialize()
         {
             if (m_Initialized)
@@ -95,7 +97,11 @@ namespace Unity.Netcode.Editor
             }
             else
             {
-                base.OnInspectorGUI();
+                EditorGUI.BeginChangeCheck();
+                serializedObject.UpdateIfRequiredOrScript();
+                DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+                serializedObject.ApplyModifiedProperties();
+                EditorGUI.EndChangeCheck();
 
                 var guiEnabled = GUI.enabled;
                 GUI.enabled = false;

Editor/com.unity.netcode.editor.asmdef

@@ -13,6 +13,26 @@
             "name": "com.unity.multiplayer.tools",
             "expression": "",
             "define": "MULTIPLAYER_TOOLS"
+        },
+        {
+            "name": "Unity",
+            "expression": "(0,2022.2.0a5)",
+            "define": "UNITY_UNET_PRESENT"
+        },
+        {
+            "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"
         }
     ]
 }

README.md

@@ -9,7 +9,7 @@ Netcode for GameObjects is a Unity package that provides networking capabilities
 
 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.
 
-You can also jump right into our [Hello World](https://docs-multiplayer.unity3d.com/netcode/current/tutorials/helloworld/helloworldintro) guide for a taste of how to use the framework for basic networked tasks.
+You can also jump right into our [Hello World](https://docs-multiplayer.unity3d.com/netcode/current/tutorials/helloworld) guide for a taste of how to use the framework for basic networked tasks.
 
 ### Community and Feedback
 

Runtime/AssemblyInfo.cs

@@ -1,14 +1,25 @@
 using System.Runtime.CompilerServices;
 
 #if UNITY_EDITOR
-[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
-#endif
+#endif // UNITY_EDITOR
-[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#if MULTIPLAYER_TOOLS
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+[assembly: InternalsVisibleTo("Unity.Multiplayer.Tools.Adapters.Ngo1WithUtp2")]
+#endif // MULTIPLAYER_TOOLS
+#if COM_UNITY_NETCODE_ADAPTER_UTP
+[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+#endif // COM_UNITY_NETCODE_ADAPTER_UTP
+
+#if UNITY_INCLUDE_TESTS
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.TestHelpers.Runtime")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#if MULTIPLAYER_TOOLS
+[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#endif // MULTIPLAYER_TOOLS
+#endif // UNITY_INCLUDE_TESTS

Runtime/Configuration/NetworkConfig.cs

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

Runtime/Configuration/NetworkPrefab.cs

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

Runtime/Configuration/NetworkPrefabs.cs

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

Runtime/Configuration/NetworkPrefabs.cs.meta

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

Runtime/Configuration/NetworkPrefabsList.cs

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

Runtime/Configuration/NetworkPrefabsList.cs.meta

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

Runtime/Core/NetworkBehaviour.cs

@@ -21,6 +21,7 @@ namespace Unity.Netcode
             Client = 2
         }
 
+
         // NetworkBehaviourILPP will override this in derived classes to return the name of the concrete type
         internal virtual string __getTypeName() => nameof(NetworkBehaviour);
 
@@ -235,16 +236,44 @@ namespace Unity.Netcode
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
             {
-                foreach (var client in NetworkManager.ConnectedClients)
+                if (clientRpcParams.Send.TargetClientIds != null)
+                {
+                    foreach (var targetClientId in clientRpcParams.Send.TargetClientIds)
                     {
                         NetworkManager.NetworkMetrics.TrackRpcSent(
-                        client.Key,
+                            targetClientId,
                             NetworkObject,
                             rpcMethodName,
                             __getTypeName(),
                             rpcWriteSize);
                     }
                 }
+                else if (clientRpcParams.Send.TargetClientIdsNativeArray != null)
+                {
+                    foreach (var targetClientId in clientRpcParams.Send.TargetClientIdsNativeArray)
+                    {
+                        NetworkManager.NetworkMetrics.TrackRpcSent(
+                            targetClientId,
+                            NetworkObject,
+                            rpcMethodName,
+                            __getTypeName(),
+                            rpcWriteSize);
+                    }
+                }
+                else
+                {
+                    var observerEnumerator = NetworkObject.Observers.GetEnumerator();
+                    while (observerEnumerator.MoveNext())
+                    {
+                        NetworkManager.NetworkMetrics.TrackRpcSent(
+                            observerEnumerator.Current,
+                            NetworkObject,
+                            rpcMethodName,
+                            __getTypeName(),
+                            rpcWriteSize);
+                    }
+                }
+            }
 #endif
         }
 
@@ -258,7 +287,18 @@ namespace Unity.Netcode
         /// Gets the NetworkManager that owns this NetworkBehaviour instance
         ///   See note around `NetworkObject` for how there is a chicken / egg problem when we are not initialized
         /// </summary>
-        public NetworkManager NetworkManager => NetworkObject.NetworkManager;
+        public NetworkManager NetworkManager
+        {
+            get
+            {
+                if (NetworkObject?.NetworkManager != null)
+                {
+                    return NetworkObject?.NetworkManager;
+                }
+
+                return NetworkManager.Singleton;
+            }
+        }
 
         /// <summary>
         /// If a NetworkObject is assigned, it will return whether or not this NetworkObject
@@ -274,18 +314,18 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets if we are executing as server
         /// </summary>
-        protected bool IsServer { get; private set; }
+        public bool IsServer { get; private set; }
 
         /// <summary>
         /// Gets if we are executing as client
         /// </summary>
-        protected bool IsClient { get; private set; }
+        public bool IsClient { get; private set; }
 
 
         /// <summary>
         /// Gets if we are executing as Host, I.E Server and Client
         /// </summary>
-        protected bool IsHost { get; private set; }
+        public bool IsHost { get; private set; }
 
         /// <summary>
         /// Gets Whether or not the object has a owner
@@ -307,31 +347,38 @@ namespace Unity.Netcode
                 m_NetworkObject.NetworkManager.IsServer;
         }
 
-        /// <summary>
-        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         ///  TODO: this needs an overhaul.  It's expensive, it's ja little naive in how it looks for networkObject in
         ///   its parent and worst, it creates a puzzle if you are a NetworkBehaviour wanting to see if you're live or not
         ///   (e.g. editor code).  All you want to do is find out if NetworkManager is null, but to do that you
         ///   need NetworkObject, but if you try and grab NetworkObject and NetworkManager isn't up you'll get
         ///   the warning below.  This is why IsBehaviourEditable had to be created.  Matt was going to re-do
         ///   how NetworkObject works but it was close to the release and too risky to change
-        ///
+        /// <summary>
+        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         /// </summary>
         public NetworkObject NetworkObject
         {
             get
+            {
+                try
                 {
                     if (m_NetworkObject == null)
                     {
                         m_NetworkObject = GetComponentInParent<NetworkObject>();
                     }
+                }
+                catch (Exception)
+                {
+                    return null;
+                }
 
                 // ShutdownInProgress check:
                 // This prevents an edge case scenario where the NetworkManager is shutting down but user code
                 // 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))
+                // We must check IsSpawned, otherwise a warning will be logged under certain valid conditions (see OnDestroy)
+                if (IsSpawned && m_NetworkObject == null && (NetworkManager.Singleton == null || !NetworkManager.Singleton.ShutdownInProgress))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -435,15 +482,42 @@ namespace Unity.Netcode
             IsSpawned = true;
             InitializeVariables();
             UpdateNetworkProperties();
+        }
+
+        internal void VisibleOnNetworkSpawn()
+        {
+            try
+            {
                 OnNetworkSpawn();
             }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
+
+            InitializeVariables();
+            if (IsServer)
+            {
+                // Since we just spawned the object and since user code might have modified their NetworkVariable, esp.
+                // NetworkList, we need to mark the object as free of updates.
+                // This should happen for all objects on the machine triggering the spawn.
+                PostNetworkVariableWrite(true);
+            }
+        }
 
         internal void InternalOnNetworkDespawn()
         {
             IsSpawned = false;
             UpdateNetworkProperties();
+            try
+            {
                 OnNetworkDespawn();
             }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
+        }
 
         /// <summary>
         /// Gets called when the local client gains ownership of this object
@@ -496,11 +570,11 @@ namespace Unity.Netcode
             if (list == null)
             {
                 list = new List<FieldInfo>();
-                list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance));
+                list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly));
             }
             else
             {
-                list.AddRange(type.GetFields(BindingFlags.NonPublic | BindingFlags.Instance));
+                list.AddRange(type.GetFields(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly));
             }
 
             if (type.BaseType != null && type.BaseType != typeof(NetworkBehaviour))
@@ -575,7 +649,18 @@ namespace Unity.Netcode
             NetworkVariableIndexesToResetSet.Clear();
         }
 
-        internal void PostNetworkVariableWrite()
+        internal void PostNetworkVariableWrite(bool forced = false)
+        {
+            if (forced)
+            {
+                // Mark every variable as no longer dirty. We just spawned the object and whatever the game code did
+                // during OnNetworkSpawn has been sent and needs to be cleared
+                for (int i = 0; i < NetworkVariableFields.Count; i++)
+                {
+                    NetworkVariableFields[i].ResetDirty();
+                }
+            }
+            else
             {
                 // mark any variables we wrote as no longer dirty
                 for (int i = 0; i < NetworkVariableIndexesToReset.Count; i++)
@@ -584,7 +669,10 @@ namespace Unity.Netcode
                 }
             }
 
-        internal void VariableUpdate(ulong targetClientId)
+            MarkVariablesDirty(false);
+        }
+
+        internal void PreVariableUpdate()
         {
             if (!m_VarInit)
             {
@@ -592,6 +680,10 @@ namespace Unity.Netcode
             }
 
             PreNetworkVariableWrite();
+        }
+
+        internal void VariableUpdate(ulong targetClientId)
+        {
             NetworkVariableUpdate(targetClientId, NetworkBehaviourId);
         }
 
@@ -638,7 +730,7 @@ namespace Unity.Netcode
                         var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, MessagingSystem.FRAGMENTED_MESSAGE_MAX_SIZE);
                         using (tmpWriter)
                         {
-                            message.Serialize(tmpWriter);
+                            message.Serialize(tmpWriter, message.Version);
                         }
                     }
                     else
@@ -663,14 +755,22 @@ namespace Unity.Netcode
             return false;
         }
 
-        internal void MarkVariablesDirty()
+        internal void MarkVariablesDirty(bool dirty)
         {
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                NetworkVariableFields[j].SetDirty(true);
+                NetworkVariableFields[j].SetDirty(dirty);
             }
         }
 
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
         internal void WriteNetworkVariableData(FastBufferWriter writer, ulong targetClientId)
         {
             if (NetworkVariableFields.Count == 0)
@@ -680,11 +780,17 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                bool canClientRead = NetworkVariableFields[j].CanClientRead(targetClientId);
 
-                if (canClientRead)
+                if (NetworkVariableFields[j].CanClientRead(targetClientId))
+                {
+                    if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
                         var writePos = writer.Position;
+                        // Note: This value can't be packed because we don't know how large it will be in advance
+                        // we reserve space for it, then write the data, then come back and fill in the space
+                        // to pack here, we'd have to write data to a temporary buffer and copy it in - which
+                        // isn't worth possibly saving one byte if and only if the data is less than 63 bytes long...
+                        // The way we do packing, any value > 63 in a ushort will use the full 2 bytes to represent.
                         writer.WriteValueSafe((ushort)0);
                         var startPos = writer.Position;
                         NetworkVariableFields[j].WriteField(writer);
@@ -694,13 +800,27 @@ namespace Unity.Netcode
                         writer.Seek(startPos + size);
                     }
                     else
+                    {
+                        NetworkVariableFields[j].WriteField(writer);
+                    }
+                }
+                else // Only if EnsureNetworkVariableLengthSafety, otherwise just skip
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     writer.WriteValueSafe((ushort)0);
                 }
             }
         }
 
-        internal void SetNetworkVariableData(FastBufferReader reader)
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
+        internal void SetNetworkVariableData(FastBufferReader reader, ulong clientId)
         {
             if (NetworkVariableFields.Count == 0)
             {
@@ -709,13 +829,23 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                reader.ReadValueSafe(out ushort varSize);
+                var varSize = (ushort)0;
+                var readStartPos = 0;
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
+                {
+                    reader.ReadValueSafe(out varSize);
                     if (varSize == 0)
                     {
                         continue;
                     }
+                    readStartPos = reader.Position;
+                }
+                else // If the client cannot read this field, then skip it
+                if (!NetworkVariableFields[j].CanClientRead(clientId))
+                {
+                    continue;
+                }
 
-                var readStartPos = reader.Position;
                 NetworkVariableFields[j].ReadField(reader);
 
                 if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
@@ -752,6 +882,138 @@ namespace Unity.Netcode
             return NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(networkId, out NetworkObject networkObject) ? networkObject : null;
         }
 
+        /// <summary>
+        /// Override this method if your derived NetworkBehaviour requires custom synchronization data.
+        /// Note: Use of this method is only for the initial client synchronization of NetworkBehaviours
+        /// and will increase the payload size for client synchronization and dynamically spawned
+        /// <see cref="NetworkObject"/>s.
+        /// </summary>
+        /// <remarks>
+        /// When serializing (writing) this will be invoked during the client synchronization period and
+        /// when spawning new NetworkObjects.
+        /// When deserializing (reading), this will be invoked prior to the NetworkBehaviour's associated
+        /// NetworkObject being spawned.
+        /// </remarks>
+        /// <param name="serializer">The serializer to use to read and write the data.</param>
+        /// <typeparam name="T">
+        /// Either BufferSerializerReader or BufferSerializerWriter, depending whether the serializer
+        /// is in read mode or write mode.
+        /// </typeparam>
+        protected virtual void OnSynchronize<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+
+        }
+
+        /// <summary>
+        /// Internal method that determines if a NetworkBehaviour has additional synchronization data to
+        /// be synchronized when first instantiated prior to its associated NetworkObject being spawned.
+        /// </summary>
+        /// <remarks>
+        /// This includes try-catch blocks to recover from exceptions that might occur and continue to
+        /// synchronize any remaining NetworkBehaviours.
+        /// </remarks>
+        /// <returns>true if it wrote synchronization data and false if it did not</returns>
+        internal bool Synchronize<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+            if (serializer.IsWriter)
+            {
+                // Get the writer to handle seeking and determining how many bytes were written
+                var writer = serializer.GetFastBufferWriter();
+                // Save our position before we attempt to write anything so we can seek back to it (i.e. error occurs)
+                var positionBeforeWrite = writer.Position;
+                writer.WriteValueSafe(NetworkBehaviourId);
+
+                // Save our position where we will write the final size being written so we can skip over it in the
+                // event an exception occurs when deserializing.
+                var sizePosition = writer.Position;
+                writer.WriteValueSafe((ushort)0);
+
+                // Save our position before synchronizing to determine how much was written
+                var positionBeforeSynchronize = writer.Position;
+                var threwException = false;
+                try
+                {
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    threwException = true;
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization serialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                }
+                var finalPosition = writer.Position;
+
+                // If we wrote nothing then skip writing anything for this NetworkBehaviour
+                if (finalPosition == positionBeforeSynchronize || threwException)
+                {
+                    writer.Seek(positionBeforeWrite);
+                    return false;
+                }
+                else
+                {
+                    // Write the number of bytes serialized to handle exceptions on the deserialization side
+                    var bytesWritten = finalPosition - positionBeforeSynchronize;
+                    writer.Seek(sizePosition);
+                    writer.WriteValueSafe((ushort)bytesWritten);
+                    writer.Seek(finalPosition);
+                }
+                return true;
+            }
+            else
+            {
+                var reader = serializer.GetFastBufferReader();
+                // We will always read the expected byte count
+                reader.ReadValueSafe(out ushort expectedBytesToRead);
+
+                // Save our position before we begin synchronization deserialization
+                var positionBeforeSynchronize = reader.Position;
+                var synchronizationError = false;
+                try
+                {
+                    // Invoke synchronization
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization deserialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                    synchronizationError = true;
+                }
+
+                var totalBytesRead = reader.Position - positionBeforeSynchronize;
+                if (totalBytesRead != expectedBytesToRead)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} read {totalBytesRead} bytes but was expected to read {expectedBytesToRead} bytes during synchronization deserialization! This {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                    }
+                    synchronizationError = true;
+                }
+
+                // Skip over the entry if deserialization fails
+                if (synchronizationError)
+                {
+                    var skipToPosition = positionBeforeSynchronize + expectedBytesToRead;
+                    reader.Seek(skipToPosition);
+                    return false;
+                }
+                return true;
+            }
+        }
+
+
         /// <summary>
         /// Invoked when the <see cref="GameObject"/> the <see cref="NetworkBehaviour"/> is attached to.
         /// NOTE:  If you override this, you will want to always invoke this base class version of this
@@ -759,6 +1021,14 @@ namespace Unity.Netcode
         /// </summary>
         public virtual void OnDestroy()
         {
+            if (NetworkObject != null && NetworkObject.IsSpawned && IsSpawned)
+            {
+                // If the associated NetworkObject is still spawned then this
+                // NetworkBehaviour will be removed from the NetworkObject's
+                // ChildNetworkBehaviours list.
+                NetworkObject.OnNetworkBehaviourDestroyed(this);
+            }
+
             // this seems odd to do here, but in fact especially in tests we can find ourselves
             //  here without having called InitializedVariables, which causes problems if any
             //  of those variables use native containers (e.g. NetworkList) as they won't be
@@ -770,6 +1040,7 @@ namespace Unity.Netcode
                 InitializeVariables();
             }
 
+
             for (int i = 0; i < NetworkVariableFields.Count; i++)
             {
                 NetworkVariableFields[i].Dispose();

Runtime/Core/NetworkBehaviourUpdater.cs

@@ -8,12 +8,17 @@ namespace Unity.Netcode
     /// </summary>
     public class NetworkBehaviourUpdater
     {
-        private HashSet<NetworkObject> m_Touched = new HashSet<NetworkObject>();
+        private HashSet<NetworkObject> m_DirtyNetworkObjects = new HashSet<NetworkObject>();
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
         private ProfilerMarker m_NetworkBehaviourUpdate = new ProfilerMarker($"{nameof(NetworkBehaviour)}.{nameof(NetworkBehaviourUpdate)}");
 #endif
 
+        internal void AddForUpdate(NetworkObject networkObject)
+        {
+            m_DirtyNetworkObjects.Add(networkObject);
+        }
+
         internal void NetworkBehaviourUpdate(NetworkManager networkManager)
         {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
@@ -21,59 +26,75 @@ namespace Unity.Netcode
 #endif
             try
             {
+                // NetworkObject references can become null, when hidden or despawned. Once NUll, there is no point
+                // trying to process them, even if they were previously marked as dirty.
+                m_DirtyNetworkObjects.RemoveWhere((sobj) => sobj == null);
+
                 if (networkManager.IsServer)
                 {
-                    m_Touched.Clear();
+                    foreach (var dirtyObj in m_DirtyNetworkObjects)
+                    {
+                        for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
+                        {
+                            dirtyObj.ChildNetworkBehaviours[k].PreVariableUpdate();
+                        }
+
                         for (int i = 0; i < networkManager.ConnectedClientsList.Count; i++)
                         {
                             var client = networkManager.ConnectedClientsList[i];
-                        var spawnedObjs = networkManager.SpawnManager.SpawnedObjectsList;
+
-                        m_Touched.UnionWith(spawnedObjs);
+                            if (dirtyObj.IsNetworkVisibleTo(client.ClientId))
-                        foreach (var sobj in spawnedObjs)
-                        {
-                            if (sobj.IsNetworkVisibleTo(client.ClientId))
                             {
                                 // Sync just the variables for just the objects this client sees
-                                for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                                for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
                                 {
-                                    sobj.ChildNetworkBehaviours[k].VariableUpdate(client.ClientId);
+                                    dirtyObj.ChildNetworkBehaviours[k].VariableUpdate(client.ClientId);
                                 }
                             }
                         }
                     }
-
-                    // Now, reset all the no-longer-dirty variables
-                    foreach (var sobj in m_Touched)
-                    {
-                        for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
-                        {
-                            sobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                        }
-                    }
                 }
                 else
                 {
                     // when client updates the server, it tells it about all its objects
-                    foreach (var sobj in networkManager.SpawnManager.SpawnedObjectsList)
+                    foreach (var sobj in m_DirtyNetworkObjects)
                     {
                         if (sobj.IsOwner)
                         {
+                            for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                            {
+                                sobj.ChildNetworkBehaviours[k].PreVariableUpdate();
+                            }
                             for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
                             {
                                 sobj.ChildNetworkBehaviours[k].VariableUpdate(NetworkManager.ServerClientId);
                             }
                         }
                     }
+                }
 
+                foreach (var dirtyObj in m_DirtyNetworkObjects)
+                {
+                    for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
+                    {
+                        var behaviour = dirtyObj.ChildNetworkBehaviours[k];
+                        for (int i = 0; i < behaviour.NetworkVariableFields.Count; i++)
+                        {
+                            if (behaviour.NetworkVariableFields[i].IsDirty() &&
+                                !behaviour.NetworkVariableIndexesToResetSet.Contains(i))
+                            {
+                                behaviour.NetworkVariableIndexesToResetSet.Add(i);
+                                behaviour.NetworkVariableIndexesToReset.Add(i);
+                            }
+                        }
+                    }
+                }
                 // Now, reset all the no-longer-dirty variables
-                    foreach (var sobj in networkManager.SpawnManager.SpawnedObjectsList)
+                foreach (var dirtyobj in m_DirtyNetworkObjects)
                 {
-                        for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                    dirtyobj.PostNetworkVariableWrite();
-                        {
-                            sobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                        }
-                    }
                 }
+                m_DirtyNetworkObjects.Clear();
             }
             finally
             {

Runtime/Hashing/XXHash.cs

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

Runtime/Hashing/XXHash.cs.meta

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

Runtime/Hashing/XXHash.meta

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

Runtime/Hashing/XXHash/LICENSE

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

Runtime/Hashing/XXHash/LICENSE.meta

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

Runtime/Hashing/XXHash/XXHash.cs

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

Runtime/Messaging/BatchHeader.cs

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

Runtime/Messaging/CustomMessageManager.cs

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

Runtime/Messaging/DisconnectReasonMessage.cs

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

Runtime/Messaging/DisconnectReasonMessage.cs.meta

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

Runtime/Messaging/INetworkMessage.cs

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

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

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

Runtime/Messaging/Messages/ConnectionApprovedMessage.cs

@@ -1,10 +1,12 @@
-using System;
 using System.Collections.Generic;
+using Unity.Collections;
 
 namespace Unity.Netcode
 {
     internal struct ConnectionApprovedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong OwnerClientId;
         public int NetworkTick;
 
@@ -13,14 +15,26 @@ namespace Unity.Netcode
 
         private FastBufferReader m_ReceivedSceneObjectData;
 
-        public void Serialize(FastBufferWriter writer)
+        public NativeArray<MessageVersionData> MessageVersions;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            if (!writer.TryBeginWrite(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            BytePacker.WriteValueBitPacked(writer, MessageVersions.Length);
+            foreach (var messageVersion in MessageVersions)
             {
-                throw new OverflowException($"Not enough space in the write buffer to serialize {nameof(ConnectionApprovedMessage)}");
+                messageVersion.Serialize(writer);
             }
-            writer.WriteValue(OwnerClientId);
+            // ============================================================
-            writer.WriteValue(NetworkTick);
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            BytePacker.WriteValueBitPacked(writer, OwnerClientId);
+            BytePacker.WriteValueBitPacked(writer, NetworkTick);
 
             uint sceneObjectCount = 0;
             if (SpawnedObjectsList != null)
@@ -39,17 +53,19 @@ namespace Unity.Netcode
                         ++sceneObjectCount;
                     }
                 }
+
                 writer.Seek(pos);
-                writer.WriteValue(sceneObjectCount);
+                // Can't pack this value because its space is reserved, so it needs to always use all the reserved space.
+                writer.WriteValueSafe(sceneObjectCount);
                 writer.Seek(writer.Length);
             }
             else
             {
-                writer.WriteValue(sceneObjectCount);
+                writer.WriteValueSafe(sceneObjectCount);
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -57,13 +73,36 @@ namespace Unity.Netcode
                 return false;
             }
 
-            if (!reader.TryBeginRead(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            ByteUnpacker.ReadValueBitPacked(reader, out int length);
+            var messageHashesInOrder = new NativeArray<uint>(length, Allocator.Temp);
+            for (var i = 0; i < length; ++i)
             {
-                throw new OverflowException($"Not enough space in the buffer to read {nameof(ConnectionApprovedMessage)}");
+                var messageVersion = new MessageVersionData();
-            }
+                messageVersion.Deserialize(reader);
+                networkManager.MessagingSystem.SetVersion(context.SenderId, messageVersion.Hash, messageVersion.Version);
+                messageHashesInOrder[i] = messageVersion.Hash;
 
-            reader.ReadValue(out OwnerClientId);
+                // Update the received version since this message will always be passed version 0, due to the map not
-            reader.ReadValue(out NetworkTick);
+                // being initialized until just now.
+                var messageType = networkManager.MessagingSystem.GetMessageForHash(messageVersion.Hash);
+                if (messageType == typeof(ConnectionApprovedMessage))
+                {
+                    receivedMessageVersion = messageVersion.Version;
+                }
+            }
+            networkManager.MessagingSystem.SetServerMessageOrder(messageHashesInOrder);
+            messageHashesInOrder.Dispose();
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkTick);
             m_ReceivedSceneObjectData = reader;
             return true;
         }
@@ -79,12 +118,13 @@ namespace Unity.Netcode
             networkManager.NetworkTickSystem.Reset(networkManager.NetworkTimeSystem.LocalTime, networkManager.NetworkTimeSystem.ServerTime);
 
             networkManager.LocalClient = new NetworkClient() { ClientId = networkManager.LocalClientId };
+            networkManager.IsApproved = true;
 
             // Only if scene management is disabled do we handle NetworkObject synchronization at this point
             if (!networkManager.NetworkConfig.EnableSceneManagement)
             {
                 networkManager.SpawnManager.DestroySceneObjects();
-                m_ReceivedSceneObjectData.ReadValue(out uint sceneObjectCount);
+                m_ReceivedSceneObjectData.ReadValueSafe(out uint sceneObjectCount);
 
                 // Deserializing NetworkVariable data is deferred from Receive() to Handle to avoid needing
                 // to create a list to hold the data. This is a breach of convention for performance reasons.

Runtime/Messaging/Messages/ConnectionRequestMessage.cs

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

Runtime/Messaging/Messages/CreateObjectMessage.cs

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

Runtime/Messaging/Messages/DestroyObjectMessage.cs

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

Runtime/Messaging/Messages/MessageMetadata.cs

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

Runtime/Messaging/Messages/MessageMetadata.cs.meta

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

Runtime/Messaging/Messages/NamedMessage.cs

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

Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

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

Runtime/Messaging/Messages/ParentSyncMessage.cs

@@ -1,32 +1,65 @@
+using UnityEngine;
+
 namespace Unity.Netcode
 {
     internal struct ParentSyncMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
 
-        public bool IsReparented;
+        private byte m_BitField;
+
+        public bool WorldPositionStays
+        {
+            get => ByteUtility.GetBit(m_BitField, 0);
+            set => ByteUtility.SetBit(ref m_BitField, 0, value);
+        }
 
         //If(Metadata.IsReparented)
-        public bool IsLatestParentSet;
+        public bool IsLatestParentSet
+        {
+            get => ByteUtility.GetBit(m_BitField, 1);
+            set => ByteUtility.SetBit(ref m_BitField, 1, value);
+        }
 
         //If(IsLatestParentSet)
         public ulong? LatestParent;
 
-        public void Serialize(FastBufferWriter writer)
+        // Is set when the parent should be removed (similar to IsReparented functionality but only for removing the parent)
+        public bool RemoveParent
         {
-            writer.WriteValueSafe(NetworkObjectId);
+            get => ByteUtility.GetBit(m_BitField, 2);
-            writer.WriteValueSafe(IsReparented);
+            set => ByteUtility.SetBit(ref m_BitField, 2, value);
-            if (IsReparented)
+        }
+
+        // These additional properties are used to synchronize clients with the current position,
+        // rotation, and scale after parenting/de-parenting (world/local space relative). This
+        // allows users to control the final child's transform values without having to have a
+        // NetworkTransform component on the child. (i.e. picking something up)
+        public Vector3 Position;
+        public Quaternion Rotation;
+        public Vector3 Scale;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
+        {
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            writer.WriteValueSafe(m_BitField);
+            if (!RemoveParent)
             {
-                writer.WriteValueSafe(IsLatestParentSet);
                 if (IsLatestParentSet)
                 {
-                    writer.WriteValueSafe((ulong)LatestParent);
+                    BytePacker.WriteValueBitPacked(writer, LatestParent.Value);
-                }
                 }
             }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            // Whether parenting or removing a parent, we always update the position, rotation, and scale
+            writer.WriteValueSafe(Position);
+            writer.WriteValueSafe(Rotation);
+            writer.WriteValueSafe(Scale);
+        }
+
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -34,24 +67,27 @@ namespace Unity.Netcode
                 return false;
             }
 
-            reader.ReadValueSafe(out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
-            reader.ReadValueSafe(out IsReparented);
+            reader.ReadValueSafe(out m_BitField);
-            if (IsReparented)
+            if (!RemoveParent)
             {
-                reader.ReadValueSafe(out IsLatestParentSet);
                 if (IsLatestParentSet)
                 {
-                    reader.ReadValueSafe(out ulong latestParent);
+                    ByteUnpacker.ReadValueBitPacked(reader, out ulong latestParent);
                     LatestParent = latestParent;
                 }
             }
 
+            // Whether parenting or removing a parent, we always update the position, rotation, and scale
+            reader.ReadValueSafe(out Position);
+            reader.ReadValueSafe(out Rotation);
+            reader.ReadValueSafe(out Scale);
+
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
             {
                 networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);
                 return false;
             }
-
             return true;
         }
 
@@ -59,8 +95,22 @@ namespace Unity.Netcode
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
-            networkObject.SetNetworkParenting(IsReparented, LatestParent);
+            networkObject.SetNetworkParenting(LatestParent, WorldPositionStays);
-            networkObject.ApplyNetworkParenting();
+            networkObject.ApplyNetworkParenting(RemoveParent);
+
+            // We set all of the transform values after parenting as they are
+            // the values of the server-side post-parenting transform values
+            if (!WorldPositionStays)
+            {
+                networkObject.transform.localPosition = Position;
+                networkObject.transform.localRotation = Rotation;
+            }
+            else
+            {
+                networkObject.transform.position = Position;
+                networkObject.transform.rotation = Rotation;
+            }
+            networkObject.transform.localScale = Scale;
         }
     }
 }

Runtime/Messaging/Messages/RpcMessages.cs

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

Runtime/Messaging/Messages/SceneEventMessage.cs

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

Runtime/Messaging/Messages/ServerLogMessage.cs

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

Runtime/Messaging/Messages/TimeSyncMessage.cs

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

Runtime/Messaging/Messages/UnnamedMessage.cs

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

Runtime/Messaging/MessagingSystem.cs

@@ -2,12 +2,18 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
+using System.Text;
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using UnityEngine;
 
 namespace Unity.Netcode
 {
+    internal class HandlerNotRegisteredException : SystemException
+    {
+        public HandlerNotRegisteredException() { }
+        public HandlerNotRegisteredException(string issue) : base(issue) { }
+    }
 
     internal class InvalidMessageStructureException : SystemException
     {
@@ -36,20 +42,27 @@ namespace Unity.Netcode
             {
                 Writer = new FastBufferWriter(writerSize, writerAllocator, maxWriterSize);
                 NetworkDelivery = delivery;
-                BatchHeader = default;
+                BatchHeader = new BatchHeader { Magic = BatchHeader.MagicValue };
             }
         }
 
         internal delegate void MessageHandler(FastBufferReader reader, ref NetworkContext context, MessagingSystem system);
+        internal delegate int VersionGetter();
 
         private NativeList<ReceiveQueueItem> m_IncomingMessageQueue = new NativeList<ReceiveQueueItem>(16, Allocator.Persistent);
 
-        private MessageHandler[] m_MessageHandlers = new MessageHandler[255];
+        // These array will grow as we need more message handlers. 4 is just a starting size.
-        private Type[] m_ReverseTypeMap = new Type[255];
+        private MessageHandler[] m_MessageHandlers = new MessageHandler[4];
+        private Type[] m_ReverseTypeMap = new Type[4];
 
         private Dictionary<Type, uint> m_MessageTypes = new Dictionary<Type, uint>();
         private Dictionary<ulong, NativeList<SendQueueItem>> m_SendQueues = new Dictionary<ulong, NativeList<SendQueueItem>>();
 
+        // This is m_PerClientMessageVersion[clientId][messageType] = version
+        private Dictionary<ulong, Dictionary<Type, int>> m_PerClientMessageVersions = new Dictionary<ulong, Dictionary<Type, int>>();
+        private Dictionary<uint, Type> m_MessagesByHash = new Dictionary<uint, Type>();
+        private Dictionary<Type, int> m_LocalVersions = new Dictionary<Type, int>();
+
         private List<INetworkHooks> m_Hooks = new List<INetworkHooks>();
 
         private uint m_HighMessageType;
@@ -59,6 +72,7 @@ namespace Unity.Netcode
 
         internal Type[] MessageTypes => m_ReverseTypeMap;
         internal MessageHandler[] MessageHandlers => m_MessageHandlers;
+
         internal uint MessageHandlerCount => m_HighMessageType;
 
         internal uint GetMessageType(Type t)
@@ -67,12 +81,40 @@ namespace Unity.Netcode
         }
 
         public const int NON_FRAGMENTED_MESSAGE_MAX_SIZE = 1300;
-        public const int FRAGMENTED_MESSAGE_MAX_SIZE = BytePacker.BitPackedIntMax;
+        public const int FRAGMENTED_MESSAGE_MAX_SIZE = int.MaxValue;
 
         internal struct MessageWithHandler
         {
             public Type MessageType;
             public MessageHandler Handler;
+            public VersionGetter GetVersion;
+        }
+
+        internal List<MessageWithHandler> PrioritizeMessageOrder(List<MessageWithHandler> allowedTypes)
+        {
+            var prioritizedTypes = new List<MessageWithHandler>();
+
+            // first pass puts the priority message in the first indices
+            // Those are the messages that must be delivered in order to allow re-ordering the others later
+            foreach (var t in allowedTypes)
+            {
+                if (t.MessageType.FullName == typeof(ConnectionRequestMessage).FullName ||
+                    t.MessageType.FullName == typeof(ConnectionApprovedMessage).FullName)
+                {
+                    prioritizedTypes.Add(t);
+                }
+            }
+
+            foreach (var t in allowedTypes)
+            {
+                if (t.MessageType.FullName != typeof(ConnectionRequestMessage).FullName &&
+                    t.MessageType.FullName != typeof(ConnectionApprovedMessage).FullName)
+                {
+                    prioritizedTypes.Add(t);
+                }
+            }
+
+            return prioritizedTypes;
         }
 
         public MessagingSystem(IMessageSender messageSender, object owner, IMessageProvider provider = null)
@@ -89,6 +131,7 @@ namespace Unity.Netcode
                 var allowedTypes = provider.GetMessages();
 
                 allowedTypes.Sort((a, b) => string.CompareOrdinal(a.MessageType.FullName, b.MessageType.FullName));
+                allowedTypes = PrioritizeMessageOrder(allowedTypes);
                 foreach (var type in allowedTypes)
                 {
                     RegisterMessageType(type);
@@ -143,9 +186,34 @@ namespace Unity.Netcode
 
         private void RegisterMessageType(MessageWithHandler messageWithHandler)
         {
+            // if we are out of space, perform amortized linear growth
+            if (m_HighMessageType == m_MessageHandlers.Length)
+            {
+                Array.Resize(ref m_MessageHandlers, 2 * m_MessageHandlers.Length);
+                Array.Resize(ref m_ReverseTypeMap, 2 * m_ReverseTypeMap.Length);
+            }
+
             m_MessageHandlers[m_HighMessageType] = messageWithHandler.Handler;
             m_ReverseTypeMap[m_HighMessageType] = messageWithHandler.MessageType;
+            m_MessagesByHash[XXHash.Hash32(messageWithHandler.MessageType.FullName)] = messageWithHandler.MessageType;
             m_MessageTypes[messageWithHandler.MessageType] = m_HighMessageType++;
+            m_LocalVersions[messageWithHandler.MessageType] = messageWithHandler.GetVersion();
+        }
+
+        public int GetLocalVersion(Type messageType)
+        {
+            return m_LocalVersions[messageType];
+        }
+
+        internal static string ByteArrayToString(byte[] ba, int offset, int count)
+        {
+            var hex = new StringBuilder(ba.Length * 2);
+            for (int i = offset; i < offset + count; ++i)
+            {
+                hex.AppendFormat("{0:x2} ", ba[i]);
+            }
+
+            return hex.ToString();
         }
 
         internal void HandleIncomingData(ulong clientId, ArraySegment<byte> data, float receiveTime)
@@ -158,18 +226,38 @@ namespace Unity.Netcode
                         new FastBufferReader(nativeData + data.Offset, Allocator.None, data.Count);
                     if (!batchReader.TryBeginRead(sizeof(BatchHeader)))
                     {
-                        NetworkLog.LogWarning("Received a packet too small to contain a BatchHeader. Ignoring it.");
+                        NetworkLog.LogError("Received a packet too small to contain a BatchHeader. Ignoring it.");
                         return;
                     }
 
                     batchReader.ReadValue(out BatchHeader batchHeader);
 
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    if (batchHeader.Magic != BatchHeader.MagicValue)
                     {
-                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        NetworkLog.LogError($"Received a packet with an invalid Magic Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
                     }
 
-                    for (var messageIdx = 0; messageIdx < batchHeader.BatchSize; ++messageIdx)
+                    if (batchHeader.BatchSize != data.Count)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Batch Size Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Expected Size: {batchHeader.BatchSize}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    var hash = XXHash.Hash64(batchReader.GetUnsafePtrAtCurrentPosition(), batchReader.Length - batchReader.Position);
+
+                    if (hash != batchHeader.BatchHash)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Hash Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Received Hash: {batchHeader.BatchHash}, Calculated Hash: {hash}, Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    {
+                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
+                    }
+
+                    for (var messageIdx = 0; messageIdx < batchHeader.BatchCount; ++messageIdx)
                     {
 
                         var messageHeader = new MessageHeader();
@@ -181,7 +269,7 @@ namespace Unity.Netcode
                         }
                         catch (OverflowException)
                         {
-                            NetworkLog.LogWarning("Received a batch that didn't have enough data for all of its batches, ending early!");
+                            NetworkLog.LogError("Received a batch that didn't have enough data for all of its batches, ending early!");
                             throw;
                         }
 
@@ -189,7 +277,7 @@ namespace Unity.Netcode
 
                         if (!batchReader.TryBeginRead((int)messageHeader.MessageSize))
                         {
-                            NetworkLog.LogWarning("Received a message that claimed a size larger than the packet, ending early!");
+                            NetworkLog.LogError("Received a message that claimed a size larger than the packet, ending early!");
                             return;
                         }
                         m_IncomingMessageQueue.Add(new ReceiveQueueItem
@@ -207,7 +295,7 @@ namespace Unity.Netcode
                     }
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
                     }
                 }
             }
@@ -226,6 +314,55 @@ namespace Unity.Netcode
             return true;
         }
 
+        internal Type GetMessageForHash(uint messageHash)
+        {
+            if (!m_MessagesByHash.ContainsKey(messageHash))
+            {
+                return null;
+            }
+            return m_MessagesByHash[messageHash];
+        }
+
+        internal void SetVersion(ulong clientId, uint messageHash, int version)
+        {
+            if (!m_MessagesByHash.ContainsKey(messageHash))
+            {
+                return;
+            }
+            var messageType = m_MessagesByHash[messageHash];
+
+            if (!m_PerClientMessageVersions.ContainsKey(clientId))
+            {
+                m_PerClientMessageVersions[clientId] = new Dictionary<Type, int>();
+            }
+
+            m_PerClientMessageVersions[clientId][messageType] = version;
+        }
+
+        internal void SetServerMessageOrder(NativeArray<uint> messagesInIdOrder)
+        {
+            var oldHandlers = m_MessageHandlers;
+            var oldTypes = m_MessageTypes;
+            m_ReverseTypeMap = new Type[messagesInIdOrder.Length];
+            m_MessageHandlers = new MessageHandler[messagesInIdOrder.Length];
+            m_MessageTypes = new Dictionary<Type, uint>();
+
+            for (var i = 0; i < messagesInIdOrder.Length; ++i)
+            {
+                if (!m_MessagesByHash.ContainsKey(messagesInIdOrder[i]))
+                {
+                    continue;
+                }
+                var messageType = m_MessagesByHash[messagesInIdOrder[i]];
+                var oldId = oldTypes[messageType];
+                var handler = oldHandlers[oldId];
+                var newId = (uint)i;
+                m_MessageTypes[messageType] = newId;
+                m_MessageHandlers[newId] = handler;
+                m_ReverseTypeMap[newId] = messageType;
+            }
+        }
+
         public void HandleMessage(in MessageHeader header, FastBufferReader reader, ulong senderId, float timestamp, int serializedHeaderSize)
         {
             if (header.MessageType >= m_HighMessageType)
@@ -258,6 +395,16 @@ namespace Unity.Netcode
 
             var handler = m_MessageHandlers[header.MessageType];
             using (reader)
+            {
+                // This will also log an exception is if the server knows about a message type the client doesn't know
+                // about. In this case the handler will be null. It is still an issue the user must deal with: If the
+                // two connecting builds know about different messages, the server should not send a message to a client
+                // that doesn't know about it
+                if (handler == null)
+                {
+                    Debug.LogException(new HandlerNotRegisteredException(header.MessageType.ToString()));
+                }
+                else
                 {
                     // No user-land message handler exceptions should escape the receive loop.
                     // If an exception is throw, the message is ignored.
@@ -273,6 +420,7 @@ namespace Unity.Netcode
                         Debug.LogException(e);
                     }
                 }
+            }
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
             {
                 m_Hooks[hookIdx].OnAfterReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<MessageHeader>());
@@ -314,7 +462,7 @@ namespace Unity.Netcode
             m_SendQueues.Remove(clientId);
         }
 
-        private unsafe void CleanupDisconnectedClient(ulong clientId)
+        private void CleanupDisconnectedClient(ulong clientId)
         {
             var queue = m_SendQueues[clientId];
             for (var i = 0; i < queue.Length; ++i)
@@ -325,10 +473,67 @@ namespace Unity.Netcode
             queue.Dispose();
         }
 
+        internal void CleanupDisconnectedClients()
+        {
+            var removeList = new NativeList<ulong>(Allocator.Temp);
+            foreach (var clientId in m_PerClientMessageVersions.Keys)
+            {
+                if (!m_SendQueues.ContainsKey(clientId))
+                {
+                    removeList.Add(clientId);
+                }
+            }
+
+            foreach (var clientId in removeList)
+            {
+                m_PerClientMessageVersions.Remove(clientId);
+            }
+        }
+
+        public static int CreateMessageAndGetVersion<T>() where T : INetworkMessage, new()
+        {
+            return new T().Version;
+        }
+
+        internal int GetMessageVersion(Type type, ulong clientId, bool forReceive = false)
+        {
+            if (!m_PerClientMessageVersions.TryGetValue(clientId, out var versionMap))
+            {
+                if (forReceive)
+                {
+                    Debug.LogWarning($"Trying to receive {type.Name} from client {clientId} which is not in a connected state.");
+
+                }
+                else
+                {
+                    Debug.LogWarning($"Trying to send {type.Name} to client {clientId} which is not in a connected state.");
+                }
+                return -1;
+            }
+            if (!versionMap.TryGetValue(type, out var messageVersion))
+            {
+                return -1;
+            }
+
+            return messageVersion;
+        }
+
         public static void ReceiveMessage<T>(FastBufferReader reader, ref NetworkContext context, MessagingSystem system) where T : INetworkMessage, new()
         {
             var message = new T();
-            if (message.Deserialize(reader, ref context))
+            var messageVersion = 0;
+            // Special cases because these are the messages that carry the version info - thus the version info isn't
+            // populated yet when we get these. The first part of these messages always has to be the version data
+            // and can't change.
+            if (typeof(T) != typeof(ConnectionRequestMessage) && typeof(T) != typeof(ConnectionApprovedMessage) && typeof(T) != typeof(DisconnectReasonMessage))
+            {
+                messageVersion = system.GetMessageVersion(typeof(T), context.SenderId, true);
+                if (messageVersion < 0)
+                {
+                    return;
+                }
+            }
+            if (message.Deserialize(reader, ref context, messageVersion))
             {
                 for (var hookIdx = 0; hookIdx < system.m_Hooks.Count; ++hookIdx)
                 {
@@ -366,16 +571,47 @@ namespace Unity.Netcode
                 return 0;
             }
 
+            var largestSerializedSize = 0;
+            var sentMessageVersions = new NativeHashSet<int>(clientIds.Count, Allocator.Temp);
+            for (var i = 0; i < clientIds.Count; ++i)
+            {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+                }
+
+                if (sentMessageVersions.Contains(messageVersion))
+                {
+                    continue;
+                }
+
+                sentMessageVersions.Add(messageVersion);
+
                 var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FRAGMENTED_MESSAGE_MAX_SIZE : NON_FRAGMENTED_MESSAGE_MAX_SIZE;
 
                 using var tmpSerializer = new FastBufferWriter(NON_FRAGMENTED_MESSAGE_MAX_SIZE - FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp, maxSize - FastBufferWriter.GetWriteSize<MessageHeader>());
 
-            message.Serialize(tmpSerializer);
+                message.Serialize(tmpSerializer, messageVersion);
 
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds);
+                var size = SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds, messageVersion);
+                largestSerializedSize = size > largestSerializedSize ? size : largestSerializedSize;
             }
 
-        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds)
+            sentMessageVersions.Dispose();
+
+            return largestSerializedSize;
+        }
+
+        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds, int messageVersionFilter)
             where TMessageType : INetworkMessage
         {
             using var headerSerializer = new FastBufferWriter(FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp);
@@ -390,6 +626,25 @@ namespace Unity.Netcode
 
             for (var i = 0; i < clientIds.Count; ++i)
             {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+
+                    if (messageVersion != messageVersionFilter)
+                    {
+                        continue;
+                    }
+                }
+
                 var clientId = clientIds[i];
 
                 if (!CanSend(clientId, typeof(TMessageType), delivery))
@@ -427,7 +682,7 @@ namespace Unity.Netcode
 
                 writeQueueItem.Writer.WriteBytes(headerSerializer.GetUnsafePtr(), headerSerializer.Length);
                 writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
-                writeQueueItem.BatchHeader.BatchSize++;
+                writeQueueItem.BatchHeader.BatchCount++;
                 for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                 {
                     m_Hooks[hookIdx].OnAfterSendMessage(clientId, ref message, delivery, tmpSerializer.Length + headerSerializer.Length);
@@ -440,8 +695,22 @@ namespace Unity.Netcode
         internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, ulong clientId)
             where TMessageType : INetworkMessage
         {
+            var messageVersion = 0;
+            // Special case because this is the message that carries the version info - thus the version info isn't
+            // populated yet when we get this. The first part of this message always has to be the version data
+            // and can't change.
+            if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+            {
+                messageVersion = GetMessageVersion(typeof(TMessageType), clientId);
+                if (messageVersion < 0)
+                {
+                    // Client doesn't know this message exists, don't send it at all.
+                    return 0;
+                }
+            }
+
             ulong* clientIds = stackalloc ulong[] { clientId };
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
+            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1), messageVersion);
         }
 
         private struct PointerListWrapper<T> : IReadOnlyList<T>
@@ -508,7 +777,7 @@ namespace Unity.Netcode
                 for (var i = 0; i < sendQueueItem.Length; ++i)
                 {
                     ref var queueItem = ref sendQueueItem.ElementAt(i);
-                    if (queueItem.BatchHeader.BatchSize == 0)
+                    if (queueItem.BatchHeader.BatchCount == 0)
                     {
                         queueItem.Writer.Dispose();
                         continue;
@@ -516,23 +785,28 @@ namespace Unity.Netcode
 
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                     }
 
                     queueItem.Writer.Seek(0);
 #if UNITY_EDITOR || DEVELOPMENT_BUILD
                     // Skipping the Verify and sneaking the write mark in because we know it's fine.
-                    queueItem.Writer.Handle->AllowedWriteMark = 2;
+                    queueItem.Writer.Handle->AllowedWriteMark = sizeof(BatchHeader);
 #endif
+                    queueItem.BatchHeader.BatchHash = XXHash.Hash64(queueItem.Writer.GetUnsafePtr() + sizeof(BatchHeader), queueItem.Writer.Length - sizeof(BatchHeader));
+
+                    queueItem.BatchHeader.BatchSize = queueItem.Writer.Length;
+
                     queueItem.Writer.WriteValue(queueItem.BatchHeader);
 
+
                     try
                     {
                         m_MessageSender.Send(clientId, queueItem.NetworkDelivery, queueItem.Writer);
 
                         for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                         {
-                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                         }
                     }
                     finally

Runtime/Metrics/NetworkMetrics.cs

@@ -5,17 +5,14 @@ using Unity.Multiplayer.Tools;
 using Unity.Multiplayer.Tools.MetricTypes;
 using Unity.Multiplayer.Tools.NetStats;
 using Unity.Profiling;
-using UnityEngine;
 
 namespace Unity.Netcode
 {
     internal class NetworkMetrics : INetworkMetrics
     {
-        const ulong k_MaxMetricsPerFrame = 1000L;
+        private const ulong k_MaxMetricsPerFrame = 1000L;
-
+        private static Dictionary<uint, string> s_SceneEventTypeNames;
-        static Dictionary<uint, string> s_SceneEventTypeNames;
+        private static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
-
-        static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
 
         static NetworkMetrics()
         {

Runtime/Metrics/NetworkObjectProvider.cs

@@ -4,7 +4,7 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
-    class NetworkObjectProvider : INetworkObjectProvider
+    internal class NetworkObjectProvider : INetworkObjectProvider
     {
         private readonly NetworkManager m_NetworkManager;
 

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -11,7 +12,6 @@ namespace Unity.Netcode
     public class NetworkList<T> : NetworkVariableBase where T : unmanaged, IEquatable<T>
     {
         private NativeList<T> m_List = new NativeList<T>(64, Allocator.Persistent);
-        private NativeList<T> m_ListAtLastReset = new NativeList<T>(64, Allocator.Persistent);
         private NativeList<NetworkListEvent<T>> m_DirtyEvents = new NativeList<NetworkListEvent<T>>(64, Allocator.Persistent);
 
         /// <summary>
@@ -38,12 +38,16 @@ namespace Unity.Netcode
             NetworkVariableReadPermission readPerm = DefaultReadPerm,
             NetworkVariableWritePermission writePerm = DefaultWritePerm)
             : base(readPerm, writePerm)
+        {
+            // allow null IEnumerable<T> to mean "no values"
+            if (values != null)
             {
                 foreach (var value in values)
                 {
                     m_List.Add(value);
                 }
             }
+        }
 
         /// <inheritdoc />
         public override void ResetDirty()
@@ -52,7 +56,6 @@ namespace Unity.Netcode
             if (m_DirtyEvents.Length > 0)
             {
                 m_DirtyEvents.Clear();
-                m_ListAtLastReset.CopyFrom(m_List);
             }
         }
 
@@ -63,6 +66,18 @@ namespace Unity.Netcode
             return base.IsDirty() || m_DirtyEvents.Length > 0;
         }
 
+        internal void MarkNetworkObjectDirty()
+        {
+            if (m_NetworkBehaviour == null)
+            {
+                Debug.LogWarning($"NetworkList is written to, but doesn't know its NetworkBehaviour yet. " +
+                                 "Are you modifying a NetworkList before the NetworkObject is spawned?");
+                return;
+            }
+
+            m_NetworkBehaviour.NetworkManager.MarkNetworkObjectDirty(m_NetworkBehaviour.NetworkObject);
+        }
+
         /// <inheritdoc />
         public override void WriteDelta(FastBufferWriter writer)
         {
@@ -122,10 +137,10 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void WriteField(FastBufferWriter writer)
         {
-            writer.WriteValueSafe((ushort)m_ListAtLastReset.Length);
+            writer.WriteValueSafe((ushort)m_List.Length);
-            for (int i = 0; i < m_ListAtLastReset.Length; i++)
+            for (int i = 0; i < m_List.Length; i++)
             {
-                NetworkVariableSerialization<T>.Write(writer, ref m_ListAtLastReset.ElementAt(i));
+                NetworkVariableSerialization<T>.Write(writer, ref m_List.ElementAt(i));
             }
         }
 
@@ -136,7 +151,8 @@ namespace Unity.Netcode
             reader.ReadValueSafe(out ushort count);
             for (int i = 0; i < count; i++)
             {
-                NetworkVariableSerialization<T>.Read(reader, out T value);
+                var value = new T();
+                NetworkVariableSerialization<T>.Read(reader, ref value);
                 m_List.Add(value);
             }
         }
@@ -152,7 +168,8 @@ namespace Unity.Netcode
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             m_List.Add(value);
 
                             if (OnListChanged != null)
@@ -173,15 +190,25 @@ namespace Unity.Netcode
                                     Index = m_List.Length - 1,
                                     Value = m_List[m_List.Length - 1]
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Insert:
                         {
                             reader.ReadValueSafe(out int index);
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
+
+                            if (index < m_List.Length)
+                            {
                                 m_List.InsertRangeWithBeginEnd(index, index + 1);
                                 m_List[index] = value;
+                            }
+                            else
+                            {
+                                m_List.Add(value);
+                            }
 
                             if (OnListChanged != null)
                             {
@@ -201,12 +228,14 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = m_List[index]
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             int index = m_List.IndexOf(value);
                             if (index == -1)
                             {
@@ -233,6 +262,7 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -260,13 +290,15 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Value:
                         {
                             reader.ReadValueSafe(out int index);
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             if (index >= m_List.Length)
                             {
                                 throw new Exception("Shouldn't be here, index is higher than list length");
@@ -295,6 +327,7 @@ namespace Unity.Netcode
                                     Value = value,
                                     PreviousValue = previousValue
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -317,6 +350,7 @@ namespace Unity.Netcode
                                 {
                                     Type = eventType
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -339,6 +373,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void Add(T item)
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.Add(item);
 
             var listEvent = new NetworkListEvent<T>()
@@ -354,6 +394,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void Clear()
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.Clear();
 
             var listEvent = new NetworkListEvent<T>()
@@ -367,14 +413,20 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public bool Contains(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             return index != -1;
         }
 
         /// <inheritdoc />
         public bool Remove(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
+            int index = m_List.IndexOf(item);
             if (index == -1)
             {
                 return false;
@@ -402,9 +454,22 @@ namespace Unity.Netcode
 
         /// <inheritdoc />
         public void Insert(int index, T item)
+        {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
+            if (index < m_List.Length)
             {
                 m_List.InsertRangeWithBeginEnd(index, index + 1);
                 m_List[index] = item;
+            }
+            else
+            {
+                m_List.Add(item);
+            }
 
             var listEvent = new NetworkListEvent<T>()
             {
@@ -419,6 +484,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void RemoveAt(int index)
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.RemoveAt(index);
 
             var listEvent = new NetworkListEvent<T>()
@@ -436,13 +507,21 @@ namespace Unity.Netcode
             get => m_List[index];
             set
             {
+                // check write permissions
+                if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+                {
+                    throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+                }
+
+                var previousValue = m_List[index];
                 m_List[index] = value;
 
                 var listEvent = new NetworkListEvent<T>()
                 {
                     Type = NetworkListEvent<T>.EventType.Value,
                     Index = index,
-                    Value = value
+                    Value = value,
+                    PreviousValue = previousValue
                 };
 
                 HandleAddListEvent(listEvent);
@@ -452,6 +531,7 @@ namespace Unity.Netcode
         private void HandleAddListEvent(NetworkListEvent<T> listEvent)
         {
             m_DirtyEvents.Add(listEvent);
+            MarkNetworkObjectDirty();
             OnListChanged?.Invoke(listEvent);
         }
 
@@ -475,7 +555,6 @@ namespace Unity.Netcode
         public override void Dispose()
         {
             m_List.Dispose();
-            m_ListAtLastReset.Dispose();
             m_DirtyEvents.Dispose();
         }
     }

Runtime/NetworkVariable/NetworkVariable.cs

@@ -1,7 +1,5 @@
 using UnityEngine;
 using System;
-using System.Runtime.CompilerServices;
-using Unity.Collections.LowLevel.Unsafe;
 
 namespace Unity.Netcode
 {
@@ -10,7 +8,7 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">the unmanaged type for <see cref="NetworkVariable{T}"/> </typeparam>
     [Serializable]
-    public class NetworkVariable<T> : NetworkVariableBase where T : unmanaged
+    public class NetworkVariable<T> : NetworkVariableBase
     {
         /// <summary>
         /// Delegate type for value changed event
@@ -52,7 +50,7 @@ namespace Unity.Netcode
             set
             {
                 // Compare bitwise
-                if (ValueEquals(ref m_InternalValue, ref value))
+                if (NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref value))
                 {
                     return;
                 }
@@ -66,20 +64,6 @@ namespace Unity.Netcode
             }
         }
 
-        // Compares two values of the same unmanaged type by underlying memory
-        // Ignoring any overridden 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;
-        }
-
         /// <summary>
         /// Sets the <see cref="Value"/>, marks the <see cref="NetworkVariable{T}"/> dirty, and invokes the <see cref="OnValueChanged"/> callback
         /// if there are subscribers to that event.
@@ -87,7 +71,7 @@ namespace Unity.Netcode
         /// <param name="value">the new value of type `T` to be set/></param>
         private protected void Set(T value)
         {
-            m_IsDirty = true;
+            SetDirty(true);
             T previousValue = m_InternalValue;
             m_InternalValue = value;
             OnValueChanged?.Invoke(previousValue, m_InternalValue);
@@ -115,11 +99,11 @@ namespace Unity.Netcode
             // would be stored in different fields
 
             T previousValue = m_InternalValue;
-            NetworkVariableSerialization<T>.Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
 
             if (keepDirtyDelta)
             {
-                m_IsDirty = true;
+                SetDirty(true);
             }
 
             OnValueChanged?.Invoke(previousValue, m_InternalValue);
@@ -128,7 +112,7 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void ReadField(FastBufferReader reader)
         {
-            NetworkVariableSerialization<T>.Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
         }
 
         /// <inheritdoc />

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -1,4 +1,5 @@
 using System;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -17,6 +18,11 @@ namespace Unity.Netcode
         /// </summary>
         private protected NetworkBehaviour m_NetworkBehaviour;
 
+        public NetworkBehaviour GetBehaviour()
+        {
+            return m_NetworkBehaviour;
+        }
+
         /// <summary>
         /// Initializes the NetworkVariable
         /// </summary>
@@ -54,7 +60,7 @@ namespace Unity.Netcode
         /// The <see cref="m_IsDirty"/> property is used to determine if the
         /// value of the `NetworkVariable` has changed.
         /// </summary>
-        private protected bool m_IsDirty;
+        private bool m_IsDirty;
 
         /// <summary>
         /// Gets or sets the name of the network variable's instance
@@ -79,6 +85,17 @@ namespace Unity.Netcode
         public virtual void SetDirty(bool isDirty)
         {
             m_IsDirty = isDirty;
+
+            if (m_IsDirty)
+            {
+                if (m_NetworkBehaviour == null)
+                {
+                    Debug.LogWarning($"NetworkVariable is written to, but doesn't know its NetworkBehaviour yet. " +
+                                     "Are you modifying a NetworkVariable before the NetworkObject is spawned?");
+                    return;
+                }
+                m_NetworkBehaviour.NetworkManager.MarkNetworkObjectDirty(m_NetworkBehaviour.NetworkObject);
+            }
         }
 
         /// <summary>
@@ -111,7 +128,7 @@ namespace Unity.Netcode
                 case NetworkVariableReadPermission.Everyone:
                     return true;
                 case NetworkVariableReadPermission.Owner:
-                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId;
+                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId || NetworkManager.ServerClientId == clientId;
             }
         }
 

Runtime/NetworkVariable/NetworkVariableSerialization.cs

@@ -1,6 +1,7 @@
 using System;
-using System.Collections.Generic;
 using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+using UnityEditor;
 using UnityEngine;
 
 namespace Unity.Netcode
@@ -18,7 +19,97 @@ namespace Unity.Netcode
         // Taking T as an in parameter like we do in other places would require making a copy
         // of it to pass it as a ref parameter.
         public void Write(FastBufferWriter writer, ref T value);
-        public void Read(FastBufferReader reader, out T value);
+        public void Read(FastBufferReader reader, ref T value);
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class ShortSerializer : INetworkVariableSerializer<short>
+    {
+        public void Write(FastBufferWriter writer, ref short value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref short value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class UshortSerializer : INetworkVariableSerializer<ushort>
+    {
+        public void Write(FastBufferWriter writer, ref ushort value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ushort value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class IntSerializer : INetworkVariableSerializer<int>
+    {
+        public void Write(FastBufferWriter writer, ref int value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref int value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class UintSerializer : INetworkVariableSerializer<uint>
+    {
+        public void Write(FastBufferWriter writer, ref uint value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref uint value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class LongSerializer : INetworkVariableSerializer<long>
+    {
+        public void Write(FastBufferWriter writer, ref long value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref long value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class UlongSerializer : INetworkVariableSerializer<ulong>
+    {
+        public void Write(FastBufferWriter writer, ref ulong value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ulong value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
     }
 
     /// <summary>
@@ -35,79 +126,80 @@ namespace Unity.Netcode
         {
             writer.WriteUnmanagedSafe(value);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
             reader.ReadUnmanagedSafe(out value);
         }
     }
 
     /// <summary>
-    /// Serializer for FixedStrings, which does the same thing FastBufferWriter/FastBufferReader do,
+    /// Serializer for FixedStrings
-    /// but is implemented to get the data it needs using open instance delegates that are passed in
-    /// via reflection. This prevents needing T to meet any interface requirements (which isn't achievable
-    /// without incurring GC allocs on every call to Write or Read - reflection + Open Instance Delegates
-    /// circumvent that.)
-    ///
-    /// Tests show that calling these delegates doesn't cause any GC allocations even though they're
-    /// obtained via reflection and Delegate.CreateDelegate() and called on types that, at compile time,
-    /// aren't known to actually contain those methods.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    internal class FixedStringSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged
+    internal class FixedStringSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INativeList<byte>, IUTF8Bytes
     {
-        internal delegate int GetLengthDelegate(ref T value);
+        public void Write(FastBufferWriter writer, ref T value)
-        internal delegate void SetLengthDelegate(ref T value, int length);
-        internal unsafe delegate byte* GetUnsafePtrDelegate(ref T value);
-
-        internal GetLengthDelegate GetLength;
-        internal SetLengthDelegate SetLength;
-        internal GetUnsafePtrDelegate GetUnsafePtr;
-
-        public unsafe void Write(FastBufferWriter writer, ref T value)
         {
-            int length = GetLength(ref value);
+            writer.WriteValueSafe(value);
-            byte* data = GetUnsafePtr(ref value);
-            writer.WriteUnmanagedSafe(length);
-            writer.WriteBytesSafe(data, length);
         }
-        public unsafe void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
-            value = new T();
+            reader.ReadValueSafeInPlace(ref value);
-            reader.ReadValueSafe(out int length);
-            SetLength(ref value, length);
-            reader.ReadBytesSafe(GetUnsafePtr(ref value), length);
         }
     }
 
     /// <summary>
-    /// Serializer for INetworkSerializable types, which does the same thing
+    /// Serializer for unmanaged INetworkSerializable types
-    /// FastBufferWriter/FastBufferReader do, but is implemented to call the NetworkSerialize() method
-    /// via open instance delegates passed in via reflection. This prevents needing T to meet any interface
-    /// requirements (which isn't achievable without incurring GC allocs on every call to Write or Read -
-    /// reflection + Open Instance Delegates circumvent that.)
-    ///
-    /// Tests show that calling these delegates doesn't cause any GC allocations even though they're
-    /// obtained via reflection and Delegate.CreateDelegate() and called on types that, at compile time,
-    /// aren't known to actually contain those methods.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    internal class NetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged
+    internal class UnmanagedNetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INetworkSerializable
     {
-        internal delegate void WriteValueDelegate(ref T value, BufferSerializer<BufferSerializerWriter> serializer);
-        internal delegate void ReadValueDelegate(ref T value, BufferSerializer<BufferSerializerReader> serializer);
-
-        internal WriteValueDelegate WriteValue;
-        internal ReadValueDelegate ReadValue;
         public void Write(FastBufferWriter writer, ref T value)
         {
             var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
-            WriteValue(ref value, bufferSerializer);
+            value.NetworkSerialize(bufferSerializer);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+            value.NetworkSerialize(bufferSerializer);
+
+        }
+    }
+
+    /// <summary>
+    /// Serializer for managed INetworkSerializable types, which differs from the unmanaged implementation in that it
+    /// has to be null-aware
+    /// <typeparam name="T"></typeparam>
+    internal class ManagedNetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : class, INetworkSerializable, new()
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
+            bool isNull = (value == null);
+            bufferSerializer.SerializeValue(ref isNull);
+            if (!isNull)
+            {
+                value.NetworkSerialize(bufferSerializer);
+            }
+        }
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+            bool isNull = false;
+            bufferSerializer.SerializeValue(ref isNull);
+            if (isNull)
+            {
+                value = null;
+            }
+            else
+            {
+                if (value == null)
                 {
                     value = new T();
-            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+                }
-            ReadValue(ref value, bufferSerializer);
+                value.NetworkSerialize(bufferSerializer);
+            }
         }
     }
 
@@ -164,7 +256,7 @@ namespace Unity.Netcode
             }
             UserNetworkVariableSerialization<T>.WriteValue(writer, value);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
             if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null)
             {
@@ -174,34 +266,115 @@ namespace Unity.Netcode
         }
     }
 
-    internal static class NetworkVariableSerializationTypes
+    /// <summary>
+    /// This class contains initialization functions for various different types used in NetworkVariables.
+    /// Generally speaking, these methods are called by a module initializer created by codegen (NetworkBehaviourILPP)
+    /// and do not need to be called manually.
+    ///
+    /// There are two types of initializers: Serializers and EqualityCheckers. Every type must have an EqualityChecker
+    /// registered to it in order to be used in NetworkVariable; however, not all types need a Serializer. Types without
+    /// a serializer registered will fall back to using the delegates in <see cref="UserNetworkVariableSerialization{T}"/>.
+    /// If no such delegate has been registered, a type without a serializer will throw an exception on the first attempt
+    /// to serialize or deserialize it. (Again, however, codegen handles this automatically and this registration doesn't
+    /// typically need to be performed manually.)
+    /// </summary>
+    public static class NetworkVariableSerializationTypes
     {
-        internal static readonly HashSet<Type> BaseSupportedTypes = new HashSet<Type>
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
+#if UNITY_EDITOR
+        [InitializeOnLoadMethod]
+#endif
+        internal static void InitializeIntegerSerialization()
         {
-            typeof(bool),
+            NetworkVariableSerialization<short>.Serializer = new ShortSerializer();
-            typeof(byte),
+            NetworkVariableSerialization<short>.AreEqual = NetworkVariableSerialization<short>.ValueEquals;
-            typeof(sbyte),
+            NetworkVariableSerialization<ushort>.Serializer = new UshortSerializer();
-            typeof(char),
+            NetworkVariableSerialization<ushort>.AreEqual = NetworkVariableSerialization<ushort>.ValueEquals;
-            typeof(decimal),
+            NetworkVariableSerialization<int>.Serializer = new IntSerializer();
-            typeof(double),
+            NetworkVariableSerialization<int>.AreEqual = NetworkVariableSerialization<int>.ValueEquals;
-            typeof(float),
+            NetworkVariableSerialization<uint>.Serializer = new UintSerializer();
-            typeof(int),
+            NetworkVariableSerialization<uint>.AreEqual = NetworkVariableSerialization<uint>.ValueEquals;
-            typeof(uint),
+            NetworkVariableSerialization<long>.Serializer = new LongSerializer();
-            typeof(long),
+            NetworkVariableSerialization<long>.AreEqual = NetworkVariableSerialization<long>.ValueEquals;
-            typeof(ulong),
+            NetworkVariableSerialization<ulong>.Serializer = new UlongSerializer();
-            typeof(short),
+            NetworkVariableSerialization<ulong>.AreEqual = NetworkVariableSerialization<ulong>.ValueEquals;
-            typeof(ushort),
+        }
-            typeof(Vector2),
+
-            typeof(Vector3),
+        /// <summary>
-            typeof(Vector2Int),
+        /// Registeres an unmanaged type that will be serialized by a direct memcpy into a buffer
-            typeof(Vector3Int),
+        /// </summary>
-            typeof(Vector4),
+        /// <typeparam name="T"></typeparam>
-            typeof(Quaternion),
+        public static void InitializeSerializer_UnmanagedByMemcpy<T>() where T : unmanaged
-            typeof(Color),
+        {
-            typeof(Color32),
+            NetworkVariableSerialization<T>.Serializer = new UnmanagedTypeSerializer<T>();
-            typeof(Ray),
+        }
-            typeof(Ray2D)
+
-        };
+        /// <summary>
+        /// Registers an unmanaged type that implements INetworkSerializable and will be serialized through a call to
+        /// NetworkSerialize
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_UnmanagedINetworkSerializable<T>() where T : unmanaged, INetworkSerializable
+        {
+            NetworkVariableSerialization<T>.Serializer = new UnmanagedNetworkSerializableSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a managed type that implements INetworkSerializable and will be serialized through a call to
+        /// NetworkSerialize
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_ManagedINetworkSerializable<T>() where T : class, INetworkSerializable, new()
+        {
+            NetworkVariableSerialization<T>.Serializer = new ManagedNetworkSerializableSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a FixedString type that will be serialized through FastBufferReader/FastBufferWriter's FixedString
+        /// serializers
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_FixedString<T>() where T : unmanaged, INativeList<byte>, IUTF8Bytes
+        {
+            NetworkVariableSerialization<T>.Serializer = new FixedStringSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a managed type that will be checked for equality using T.Equals()
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_ManagedIEquatable<T>() where T : class, IEquatable<T>
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.EqualityEqualsObject;
+        }
+
+        /// <summary>
+        /// Registers an unmanaged type that will be checked for equality using T.Equals()
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_UnmanagedIEquatable<T>() where T : unmanaged, IEquatable<T>
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.EqualityEquals;
+        }
+
+        /// <summary>
+        /// Registers an unmanaged type that will be checked for equality using memcmp and only considered
+        /// equal if they are bitwise equivalent in memory
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_UnmanagedValueEquals<T>() where T : unmanaged
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.ValueEquals;
+        }
+
+        /// <summary>
+        /// Registers a managed type that will be checked for equality using the == operator
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_ManagedClassEquals<T>() where T : class
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.ClassEquals;
+        }
     }
 
     /// <summary>
@@ -212,56 +385,59 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">The type the associated NetworkVariable is templated on</typeparam>
     [Serializable]
-    public static class NetworkVariableSerialization<T> where T : unmanaged
+    public static class NetworkVariableSerialization<T>
     {
-        private static INetworkVariableSerializer<T> s_Serializer = GetSerializer();
+        internal static INetworkVariableSerializer<T> Serializer = new FallbackSerializer<T>();
 
-        private static INetworkVariableSerializer<T> GetSerializer()
+        internal delegate bool EqualsDelegate(ref T a, ref T b);
+        internal static EqualsDelegate AreEqual;
+
+        // Compares two values of the same unmanaged type by underlying memory
+        // Ignoring any overridden value checks
+        // Size is fixed
+        internal static unsafe bool ValueEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : unmanaged
         {
-            if (NetworkVariableSerializationTypes.BaseSupportedTypes.Contains(typeof(T)))
+            // get unmanaged pointers
-            {
+            var aptr = UnsafeUtility.AddressOf(ref a);
-                return new UnmanagedTypeSerializer<T>();
+            var bptr = UnsafeUtility.AddressOf(ref b);
-            }
+
-            if (typeof(INetworkSerializeByMemcpy).IsAssignableFrom(typeof(T)))
+            // compare addresses
-            {
+            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(TValueType)) == 0;
-                return new UnmanagedTypeSerializer<T>();
-            }
-            if (typeof(Enum).IsAssignableFrom(typeof(T)))
-            {
-                return new UnmanagedTypeSerializer<T>();
         }
 
-            if (typeof(INetworkSerializable).IsAssignableFrom(typeof(T)))
+        internal static bool EqualityEqualsObject<TValueType>(ref TValueType a, ref TValueType b) where TValueType : class, IEquatable<TValueType>
         {
-                // Obtains "Open Instance Delegates" for the type's NetworkSerialize() methods -
+            if (a == null)
-                // one for an instance of the generic method taking BufferSerializerWriter as T,
+            {
-                // one for an instance of the generic method taking BufferSerializerReader as T
+                return b == null;
-                var writeMethod = (NetworkSerializableSerializer<T>.WriteValueDelegate)Delegate.CreateDelegate(typeof(NetworkSerializableSerializer<T>.WriteValueDelegate), null, typeof(T).GetMethod(nameof(INetworkSerializable.NetworkSerialize)).MakeGenericMethod(typeof(BufferSerializerWriter)));
-                var readMethod = (NetworkSerializableSerializer<T>.ReadValueDelegate)Delegate.CreateDelegate(typeof(NetworkSerializableSerializer<T>.ReadValueDelegate), null, typeof(T).GetMethod(nameof(INetworkSerializable.NetworkSerialize)).MakeGenericMethod(typeof(BufferSerializerReader)));
-                return new NetworkSerializableSerializer<T> { WriteValue = writeMethod, ReadValue = readMethod };
             }
 
-            if (typeof(IUTF8Bytes).IsAssignableFrom(typeof(T)) && typeof(INativeList<byte>).IsAssignableFrom(typeof(T)))
+            if (b == null)
             {
-                // Get "OpenInstanceDelegates" for the Length property (get and set, which are prefixed
+                return false;
-                // with "get_" and "set_" under the hood and emitted as methods) and GetUnsafePtr()
-                var getLength = (FixedStringSerializer<T>.GetLengthDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.GetLengthDelegate), null, typeof(T).GetMethod("get_" + nameof(INativeList<byte>.Length)));
-                var setLength = (FixedStringSerializer<T>.SetLengthDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.SetLengthDelegate), null, typeof(T).GetMethod("set_" + nameof(INativeList<byte>.Length)));
-                var getUnsafePtr = (FixedStringSerializer<T>.GetUnsafePtrDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.GetUnsafePtrDelegate), null, typeof(T).GetMethod(nameof(IUTF8Bytes.GetUnsafePtr)));
-                return new FixedStringSerializer<T> { GetLength = getLength, SetLength = setLength, GetUnsafePtr = getUnsafePtr };
             }
 
-            return new FallbackSerializer<T>();
+            return a.Equals(b);
+        }
+
+        internal static bool EqualityEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : unmanaged, IEquatable<TValueType>
+        {
+            return a.Equals(b);
+        }
+
+        internal static bool ClassEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : class
+        {
+            return a == b;
         }
 
         internal static void Write(FastBufferWriter writer, ref T value)
         {
-            s_Serializer.Write(writer, ref value);
+            Serializer.Write(writer, ref value);
         }
 
-        internal static void Read(FastBufferReader reader, out T value)
+        internal static void Read(FastBufferReader reader, ref T value)
         {
-            s_Serializer.Read(reader, out value);
+            Serializer.Read(reader, ref value);
         }
     }
 }

Runtime/SceneManagement/ISceneManagerHandler.cs

@@ -1,4 +1,3 @@
-using System;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
@@ -10,25 +9,8 @@ namespace Unity.Netcode
     /// </summary>
     internal interface ISceneManagerHandler
     {
-        // Generic action to call when a scene is finished loading/unloading
+        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventProgress sceneEventProgress);
-        struct SceneEventAction
-        {
-            internal uint SceneEventId;
-            internal Action<uint> EventAction;
-            /// <summary>
-            /// Used server-side for integration testing in order to
-            /// invoke the SceneEventProgress once done loading
-            /// </summary>
-            internal Action Completed;
-            internal void Invoke()
-            {
-                Completed?.Invoke();
-                EventAction.Invoke(SceneEventId);
-            }
-        }
 
-        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventAction sceneEventAction);
+        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventProgress sceneEventProgress);
-
-        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventAction sceneEventAction);
     }
 }

Runtime/SceneManagement/NetworkSceneManager.cs

@@ -338,17 +338,17 @@ namespace Unity.Netcode
         /// </summary>
         private class DefaultSceneManagerHandler : ISceneManagerHandler
         {
-            public AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, ISceneManagerHandler.SceneEventAction sceneEventAction)
+            public AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventProgress sceneEventProgress)
             {
                 var operation = SceneManager.LoadSceneAsync(sceneName, loadSceneMode);
-                operation.completed += new Action<AsyncOperation>(asyncOp2 => { sceneEventAction.Invoke(); });
+                sceneEventProgress.SetAsyncOperation(operation);
                 return operation;
             }
 
-            public AsyncOperation UnloadSceneAsync(Scene scene, ISceneManagerHandler.SceneEventAction sceneEventAction)
+            public AsyncOperation UnloadSceneAsync(Scene scene, SceneEventProgress sceneEventProgress)
             {
                 var operation = SceneManager.UnloadSceneAsync(scene);
-                operation.completed += new Action<AsyncOperation>(asyncOp2 => { sceneEventAction.Invoke(); });
+                sceneEventProgress.SetAsyncOperation(operation);
                 return operation;
             }
         }
@@ -862,16 +862,6 @@ namespace Unity.Netcode
 
             SceneEventProgressTracking.Add(sceneEventProgress.Guid, sceneEventProgress);
 
-            if (!isUnloading)
-            {
-                // The Condition: While a scene is asynchronously loaded in single loading scene mode, if any new NetworkObjects are spawned
-                // they need to be moved into the do not destroy temporary scene
-                // When it is set: Just before starting the asynchronous loading call
-                // When it is unset: After the scene has loaded, the PopulateScenePlacedObjects is called, and all NetworkObjects in the do
-                // not destroy temporary scene are moved into the active scene
-                IsSpawnedObjectsPendingInDontDestroyOnLoad = true;
-            }
-
             m_IsSceneEventActive = true;
 
             // Set our callback delegate handler for completion
@@ -887,12 +877,14 @@ namespace Unity.Netcode
         private bool OnSceneEventProgressCompleted(SceneEventProgress sceneEventProgress)
         {
             var sceneEventData = BeginSceneEvent();
+            var clientsThatCompleted = sceneEventProgress.GetClientsWithStatus(true);
+            var clientsThatTimedOut = sceneEventProgress.GetClientsWithStatus(false);
             sceneEventData.SceneEventProgressId = sceneEventProgress.Guid;
             sceneEventData.SceneHash = sceneEventProgress.SceneHash;
             sceneEventData.SceneEventType = sceneEventProgress.SceneEventType;
-            sceneEventData.ClientsCompleted = sceneEventProgress.DoneClients;
+            sceneEventData.ClientsCompleted = clientsThatCompleted;
             sceneEventData.LoadSceneMode = sceneEventProgress.LoadSceneMode;
-            sceneEventData.ClientsTimedOut = sceneEventProgress.ClientsThatStartedSceneEvent.Except(sceneEventProgress.DoneClients).ToList();
+            sceneEventData.ClientsTimedOut = clientsThatTimedOut;
 
             var message = new SceneEventMessage
             {
@@ -913,8 +905,8 @@ namespace Unity.Netcode
                 SceneName = SceneNameFromHash(sceneEventProgress.SceneHash),
                 ClientId = NetworkManager.ServerClientId,
                 LoadSceneMode = sceneEventProgress.LoadSceneMode,
-                ClientsThatCompleted = sceneEventProgress.DoneClients,
+                ClientsThatCompleted = clientsThatCompleted,
-                ClientsThatTimedOut = m_NetworkManager.ConnectedClients.Keys.Except(sceneEventProgress.DoneClients).ToList(),
+                ClientsThatTimedOut = clientsThatTimedOut,
             });
 
             if (sceneEventData.SceneEventType == SceneEventType.LoadEventCompleted)
@@ -969,18 +961,9 @@ namespace Unity.Netcode
             sceneEventProgress.SceneEventType = SceneEventType.UnloadEventCompleted;
 
             ScenesLoaded.Remove(scene.handle);
-            var sceneEventAction = new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventData.SceneEventId, EventAction = OnSceneUnloaded };
+            sceneEventProgress.SceneEventId = sceneEventData.SceneEventId;
-            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(scene, sceneEventAction);
+            sceneEventProgress.OnSceneEventCompleted = OnSceneUnloaded;
-
+            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(scene, sceneEventProgress);
-            // If integration testing, IntegrationTestSceneHandler returns null
-            if (sceneUnload == null)
-            {
-                sceneEventProgress.SetSceneLoadOperation(sceneEventAction);
-            }
-            else
-            {
-                sceneEventProgress.SetSceneLoadOperation(sceneUnload);
-            }
 
             // Notify local server that a scene is going to be unloaded
             OnSceneEvent?.Invoke(new SceneEvent()
@@ -1024,9 +1007,10 @@ namespace Unity.Netcode
                     $"because the client scene handle {sceneHandle} was not found in ScenesLoaded!");
             }
             m_IsSceneEventActive = true;
-
+            var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
-            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(ScenesLoaded[sceneHandle],
+            sceneEventProgress.SceneEventId = sceneEventData.SceneEventId;
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventData.SceneEventId, EventAction = OnSceneUnloaded });
+            sceneEventProgress.OnSceneEventCompleted = OnSceneUnloaded;
+            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(ScenesLoaded[sceneHandle], sceneEventProgress);
 
             ScenesLoaded.Remove(sceneHandle);
 
@@ -1070,7 +1054,7 @@ namespace Unity.Netcode
                 //Only if we are a host do we want register having loaded for the associated SceneEventProgress
                 if (SceneEventProgressTracking.ContainsKey(sceneEventData.SceneEventProgressId) && m_NetworkManager.IsHost)
                 {
-                    SceneEventProgressTracking[sceneEventData.SceneEventProgressId].AddClientAsDone(NetworkManager.ServerClientId);
+                    SceneEventProgressTracking[sceneEventData.SceneEventProgressId].ClientFinishedSceneEvent(NetworkManager.ServerClientId);
                 }
             }
 
@@ -1119,8 +1103,10 @@ namespace Unity.Netcode
                 // Validate the scene as well as ignore the DDOL (which will have a negative buildIndex)
                 if (currentActiveScene.name != keyHandleEntry.Value.name && keyHandleEntry.Value.buildIndex >= 0)
                 {
-                    var sceneUnload = SceneManagerHandler.UnloadSceneAsync(keyHandleEntry.Value,
+                    var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
-                        new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = EmptySceneUnloadedOperation });
+                    sceneEventProgress.SceneEventId = sceneEventId;
+                    sceneEventProgress.OnSceneEventCompleted = EmptySceneUnloadedOperation;
+                    var sceneUnload = SceneManagerHandler.UnloadSceneAsync(keyHandleEntry.Value, sceneEventProgress);
                     SceneUnloadEventHandler.RegisterScene(this, keyHandleEntry.Value, LoadSceneMode.Additive, sceneUnload);
                 }
             }
@@ -1166,6 +1152,13 @@ namespace Unity.Netcode
 
             if (sceneEventData.LoadSceneMode == LoadSceneMode.Single)
             {
+                // The Condition: While a scene is asynchronously loaded in single loading scene mode, if any new NetworkObjects are spawned
+                // they need to be moved into the do not destroy temporary scene
+                // When it is set: Just before starting the asynchronous loading call
+                // When it is unset: After the scene has loaded, the PopulateScenePlacedObjects is called, and all NetworkObjects in the do
+                // not destroy temporary scene are moved into the active scene
+                IsSpawnedObjectsPendingInDontDestroyOnLoad = true;
+
                 // Destroy current scene objects before switching.
                 m_NetworkManager.SpawnManager.ServerDestroySpawnedSceneObjects();
 
@@ -1180,18 +1173,9 @@ namespace Unity.Netcode
             }
 
             // Now start loading the scene
-            var sceneEventAction = new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = OnSceneLoaded };
+            sceneEventProgress.SceneEventId = sceneEventId;
-            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode, sceneEventAction);
+            sceneEventProgress.OnSceneEventCompleted = OnSceneLoaded;
-            // If integration testing, IntegrationTestSceneHandler returns null
+            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode, sceneEventProgress);
-            if (sceneLoad == null)
-            {
-                sceneEventProgress.SetSceneLoadOperation(sceneEventAction);
-            }
-            else
-            {
-                sceneEventProgress.SetSceneLoadOperation(sceneLoad);
-            }
-
             // Notify the local server that a scene loading event has begun
             OnSceneEvent?.Invoke(new SceneEvent()
             {
@@ -1355,9 +1339,10 @@ namespace Unity.Netcode
                 SceneUnloadEventHandler.RegisterScene(this, SceneManager.GetActiveScene(), LoadSceneMode.Single);
 
             }
-
+            var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
-            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, sceneEventData.LoadSceneMode,
+            sceneEventProgress.SceneEventId = sceneEventId;
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = OnSceneLoaded });
+            sceneEventProgress.OnSceneEventCompleted = OnSceneLoaded;
+            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, sceneEventData.LoadSceneMode, sceneEventProgress);
 
             OnSceneEvent?.Invoke(new SceneEvent()
             {
@@ -1453,6 +1438,9 @@ namespace Unity.Netcode
                 }
             }
 
+            // Add any despawned when spawned in-scene placed NetworkObjects to the scene event data
+            sceneEventData.AddDespawnedInSceneNetworkObjects();
+
             // Set the server's scene's handle so the client can build a look up table
             sceneEventData.SceneHandle = scene.handle;
 
@@ -1488,7 +1476,7 @@ namespace Unity.Netcode
             //Second, only if we are a host do we want register having loaded for the associated SceneEventProgress
             if (SceneEventProgressTracking.ContainsKey(sceneEventData.SceneEventProgressId) && m_NetworkManager.IsHost)
             {
-                SceneEventProgressTracking[sceneEventData.SceneEventProgressId].AddClientAsDone(NetworkManager.ServerClientId);
+                SceneEventProgressTracking[sceneEventData.SceneEventProgressId].ClientFinishedSceneEvent(NetworkManager.ServerClientId);
             }
             EndSceneEvent(sceneEventId);
         }
@@ -1662,8 +1650,10 @@ namespace Unity.Netcode
             if (!shouldPassThrough)
             {
                 // If not, then load the scene
-                sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode,
+                var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = ClientLoadedSynchronization });
+                sceneEventProgress.SceneEventId = sceneEventId;
+                sceneEventProgress.OnSceneEventCompleted = ClientLoadedSynchronization;
+                sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode, sceneEventProgress);
 
                 // Notify local client that a scene load has begun
                 OnSceneEvent?.Invoke(new SceneEvent()
@@ -1880,7 +1870,7 @@ namespace Unity.Netcode
 
                         if (SceneEventProgressTracking.ContainsKey(sceneEventData.SceneEventProgressId))
                         {
-                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].AddClientAsDone(clientId);
+                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].ClientFinishedSceneEvent(clientId);
                         }
                         EndSceneEvent(sceneEventId);
                         break;
@@ -1889,7 +1879,7 @@ namespace Unity.Netcode
                     {
                         if (SceneEventProgressTracking.ContainsKey(sceneEventData.SceneEventProgressId))
                         {
-                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].AddClientAsDone(clientId);
+                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].ClientFinishedSceneEvent(clientId);
                         }
                         // Notify the local server that the client has finished unloading a scene
                         OnSceneEvent?.Invoke(new SceneEvent()
@@ -2025,7 +2015,11 @@ namespace Unity.Netcode
                 ScenePlacedObjects.Clear();
             }
 
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             // Just add every NetworkObject found that isn't already in the list
             // With additive scenes, we can have multiple in-scene placed NetworkObjects with the same GlobalObjectIdHash value

Runtime/SceneManagement/SceneEventData.cs

@@ -243,13 +243,38 @@ namespace Unity.Netcode
                     m_NetworkObjectsSync.Add(sobj);
                 }
             }
+
+            // Sort by parents before children
+            m_NetworkObjectsSync.Sort(SortParentedNetworkObjects);
+
+            // Sort by INetworkPrefabInstanceHandler implementation before the
+            // NetworkObjects spawned by the implementation
             m_NetworkObjectsSync.Sort(SortNetworkObjects);
+
+            // This is useful to know what NetworkObjects a client is going to be synchronized with
+            // as well as the order in which they will be deserialized
+            if (m_NetworkManager.LogLevel == LogLevel.Developer)
+            {
+                var messageBuilder = new System.Text.StringBuilder(0xFFFF);
+                messageBuilder.Append("[Server-Side Client-Synchronization] NetworkObject serialization order:");
+                foreach (var networkObject in m_NetworkObjectsSync)
+                {
+                    messageBuilder.Append($"{networkObject.name}");
+                }
+                NetworkLog.LogInfo(messageBuilder.ToString());
+            }
         }
 
         internal void AddDespawnedInSceneNetworkObjects()
         {
             m_DespawnedInSceneObjectsSync.Clear();
-            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.NetworkManager == m_NetworkManager);
+            // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) => c.NetworkManager == m_NetworkManager);
+#else
+            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) => c.NetworkManager == m_NetworkManager);
+
+#endif
             foreach (var sobj in inSceneNetworkObjects)
             {
                 if (sobj.IsSceneObject.HasValue && sobj.IsSceneObject.Value && !sobj.IsSpawned)
@@ -323,6 +348,32 @@ namespace Unity.Netcode
             return 0;
         }
 
+        /// <summary>
+        /// Sorts the synchronization order of the NetworkObjects to be serialized
+        /// by parents before children.
+        /// </summary>
+        /// <remarks>
+        /// This only handles late joining players. Spawning and nesting several children
+        /// dynamically is still handled by the orphaned child list when deserialized out of
+        /// hierarchical order (i.e. Spawn parent and child dynamically, parent message is
+        /// dropped and re-sent but child object is received and processed)
+        /// </remarks>
+        private int SortParentedNetworkObjects(NetworkObject first, NetworkObject second)
+        {
+            // If the first has a parent, move the first down
+            if (first.transform.parent != null)
+            {
+                return 1;
+            }
+            else // If the second has a parent and the first does not, then move the first up
+            if (second.transform.parent != null)
+            {
+                return -1;
+            }
+            return 0;
+        }
+
+
         /// <summary>
         /// Client and Server Side:
         /// Serializes data based on the SceneEvent type (<see cref="SceneEventType"/>)
@@ -334,7 +385,7 @@ namespace Unity.Netcode
             writer.WriteValueSafe(SceneEventType);
 
             // Write the scene loading mode
-            writer.WriteValueSafe(LoadSceneMode);
+            writer.WriteValueSafe((byte)LoadSceneMode);
 
             // Write the scene event progress Guid
             if (SceneEventType != SceneEventType.Synchronize)
@@ -398,27 +449,26 @@ namespace Unity.Netcode
             int totalBytes = 0;
 
             // Write the number of NetworkObjects we are serializing
-            BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync.Count());
+            writer.WriteValueSafe(m_NetworkObjectsSync.Count);
+
             // Serialize all NetworkObjects that are spawned
-            for (var i = 0; i < m_NetworkObjectsSync.Count(); ++i)
+            for (var i = 0; i < m_NetworkObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
                 var sceneObject = m_NetworkObjectsSync[i].GetMessageSceneObject(TargetClientId);
-                BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync[i].GetSceneOriginHandle());
                 sceneObject.Serialize(writer);
                 var noStop = writer.Position;
                 totalBytes += (int)(noStop - noStart);
             }
 
             // Write the number of despawned in-scene placed NetworkObjects
-            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count());
+            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count);
             // Write the scene handle and GlobalObjectIdHash value
-            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count(); ++i)
+            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
-                var sceneObject = m_DespawnedInSceneObjectsSync[i].GetMessageSceneObject(TargetClientId);
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
                 var noStop = writer.Position;
                 totalBytes += (int)(noStop - noStart);
             }
@@ -452,8 +502,6 @@ namespace Unity.Netcode
                 {
                     if (keyValuePairBySceneHandle.Value.Observers.Contains(TargetClientId))
                     {
-                        // Write our server relative scene handle for the NetworkObject being serialized
-                        writer.WriteValueSafe(keyValuePairBySceneHandle.Key);
                         // Serialize the NetworkObject
                         var sceneObject = keyValuePairBySceneHandle.Value.GetMessageSceneObject(TargetClientId);
                         sceneObject.Serialize(writer);
@@ -462,6 +510,15 @@ namespace Unity.Netcode
                 }
             }
 
+            // Write the number of despawned in-scene placed NetworkObjects
+            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count);
+            // Write the scene handle and GlobalObjectIdHash value
+            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
+            {
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
+            }
+
             var tailPosition = writer.Position;
             // Reposition to our count position to the head before we wrote our object count
             writer.Seek(headPosition);
@@ -479,7 +536,8 @@ namespace Unity.Netcode
         internal void Deserialize(FastBufferReader reader)
         {
             reader.ReadValueSafe(out SceneEventType);
-            reader.ReadValueSafe(out LoadSceneMode);
+            reader.ReadValueSafe(out byte loadSceneMode);
+            LoadSceneMode = (LoadSceneMode)loadSceneMode;
 
             if (SceneEventType != SceneEventType.Synchronize)
             {
@@ -570,15 +628,19 @@ namespace Unity.Netcode
 
                 for (ushort i = 0; i < newObjectsCount; i++)
                 {
-                    InternalBuffer.ReadValueSafe(out int sceneHandle);
-                    // Set our relative scene to the NetworkObject
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneHandle);
-
-                    // Deserialize the NetworkObject
                     var sceneObject = new NetworkObject.SceneObject();
                     sceneObject.Deserialize(InternalBuffer);
+
+                    if (sceneObject.IsSceneObject)
+                    {
+                        // Set our relative scene to the NetworkObject
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
+
                     NetworkObject.AddSceneObject(sceneObject, InternalBuffer, m_NetworkManager);
                 }
+                // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
+                DeserializeDespawnedInScenePlacedNetworkObjects();
             }
             finally
             {
@@ -600,7 +662,11 @@ namespace Unity.Netcode
 
             if (networkObjectsToRemove.Length > 0)
             {
+#if UNITY_2023_1_OR_NEWER
+                var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsSortMode.InstanceID);
+#else
                 var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
                 var networkObjectIdToNetworkObject = new Dictionary<ulong, NetworkObject>();
                 foreach (var networkObject in networkObjects)
                 {
@@ -702,38 +768,11 @@ namespace Unity.Netcode
         }
 
         /// <summary>
-        /// Client Side:
+        /// For synchronizing any despawned in-scene placed NetworkObjects that were
-        /// During the processing of a server sent Event_Sync, this method will be called for each scene once
+        /// despawned by the server during synchronization or scene loading
-        /// it is finished loading.  The client will also build a list of NetworkObjects that it spawned during
-        /// this process which will be used as part of the Event_Sync_Complete response.
         /// </summary>
-        /// <param name="networkManager"></param>
+        private void DeserializeDespawnedInScenePlacedNetworkObjects()
-        internal void SynchronizeSceneNetworkObjects(NetworkManager networkManager)
         {
-            try
-            {
-                // Process all spawned NetworkObjects for this network session
-                ByteUnpacker.ReadValuePacked(InternalBuffer, out int newObjectsCount);
-
-
-                for (int i = 0; i < newObjectsCount; i++)
-                {
-                    // We want to make sure for each NetworkObject we have the appropriate scene selected as the scene that is
-                    // currently being synchronized.  This assures in-scene placed NetworkObjects will use the right NetworkObject
-                    // from the list of populated <see cref="NetworkSceneManager.ScenePlacedObjects"/>
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out int handle);
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(handle);
-
-                    var sceneObject = new NetworkObject.SceneObject();
-                    sceneObject.Deserialize(InternalBuffer);
-
-                    var spawnedNetworkObject = NetworkObject.AddSceneObject(sceneObject, InternalBuffer, networkManager);
-                    if (!m_NetworkObjectsSync.Contains(spawnedNetworkObject))
-                    {
-                        m_NetworkObjectsSync.Add(spawnedNetworkObject);
-                    }
-                }
-
             // Process all de-spawned in-scene NetworkObjects for this network session
             m_DespawnedInSceneObjects.Clear();
             InternalBuffer.ReadValueSafe(out int despawnedObjectsCount);
@@ -742,8 +781,8 @@ namespace Unity.Netcode
             for (int i = 0; i < despawnedObjectsCount; i++)
             {
                 // We just need to get the scene
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out int networkSceneHandle);
+                InternalBuffer.ReadValueSafe(out int networkSceneHandle);
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out uint globalObjectIdHash);
+                InternalBuffer.ReadValueSafe(out uint globalObjectIdHash);
                 var sceneRelativeNetworkObjects = new Dictionary<uint, NetworkObject>();
                 if (!sceneCache.ContainsKey(networkSceneHandle))
                 {
@@ -753,13 +792,24 @@ namespace Unity.Netcode
                         if (m_NetworkManager.SceneManager.ScenesLoaded.ContainsKey(localSceneHandle))
                         {
                             var objectRelativeScene = m_NetworkManager.SceneManager.ScenesLoaded[localSceneHandle];
-                                var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) =>
+
+                            // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) =>
                             c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#else
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) =>
+                            c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#endif
+
 
                             foreach (var inSceneObject in inSceneNetworkObjects)
+                            {
+                                if (!sceneRelativeNetworkObjects.ContainsKey(inSceneObject.GlobalObjectIdHash))
                                 {
                                     sceneRelativeNetworkObjects.Add(inSceneObject.GlobalObjectIdHash, inSceneObject);
                                 }
+                            }
                             // Add this to a cache so we don't have to run this potentially multiple times (nothing will spawn or despawn during this time
                             sceneCache.Add(networkSceneHandle, sceneRelativeNetworkObjects);
                         }
@@ -793,7 +843,6 @@ namespace Unity.Netcode
                     {
                         m_NetworkManager.SceneManager.ScenePlacedObjects[globalObjectIdHash].Add(sceneRelativeNetworkObjects[globalObjectIdHash].GetSceneOriginHandle(), sceneRelativeNetworkObjects[globalObjectIdHash]);
                     }
-
                 }
                 else
                 {
@@ -801,6 +850,46 @@ namespace Unity.Netcode
                 }
             }
         }
+
+        /// <summary>
+        /// Client Side:
+        /// During the processing of a server sent Event_Sync, this method will be called for each scene once
+        /// it is finished loading.  The client will also build a list of NetworkObjects that it spawned during
+        /// this process which will be used as part of the Event_Sync_Complete response.
+        /// </summary>
+        /// <param name="networkManager"></param>
+        internal void SynchronizeSceneNetworkObjects(NetworkManager networkManager)
+        {
+            try
+            {
+                // Process all spawned NetworkObjects for this network session
+                InternalBuffer.ReadValueSafe(out int newObjectsCount);
+                for (int i = 0; i < newObjectsCount; i++)
+                {
+                    var sceneObject = new NetworkObject.SceneObject();
+                    sceneObject.Deserialize(InternalBuffer);
+
+                    // If the sceneObject is in-scene placed, then set the scene being synchronized
+                    if (sceneObject.IsSceneObject)
+                    {
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
+                    var spawnedNetworkObject = NetworkObject.AddSceneObject(sceneObject, InternalBuffer, networkManager);
+
+                    // If we failed to deserialize the NetowrkObject then don't add null to the list
+                    if (spawnedNetworkObject != null)
+                    {
+                        if (!m_NetworkObjectsSync.Contains(spawnedNetworkObject))
+                        {
+                            m_NetworkObjectsSync.Add(spawnedNetworkObject);
+                        }
+                    }
+                }
+
+                // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
+                DeserializeDespawnedInScenePlacedNetworkObjects();
+
+            }
             finally
             {
                 InternalBuffer.Dispose();

Runtime/SceneManagement/SceneEventProgress.cs

@@ -58,12 +58,13 @@ namespace Unity.Netcode
         /// <summary>
         /// List of clientIds of those clients that is done loading the scene.
         /// </summary>
-        internal List<ulong> DoneClients { get; } = new List<ulong>();
+        internal Dictionary<ulong, bool> ClientsProcessingSceneEvent { get; } = new Dictionary<ulong, bool>();
+        internal List<ulong> ClientsThatDisconnected = new List<ulong>();
 
         /// <summary>
-        /// The local time when the scene event was "roughly started"
+        /// This is when the current scene event will have timed out
         /// </summary>
-        internal float TimeAtInitiation { get; }
+        internal float WhenSceneEventHasTimedOut;
 
         /// <summary>
         /// Delegate type for when the switch scene progress is completed. Either by all clients done loading the scene or by time out.
@@ -75,17 +76,15 @@ namespace Unity.Netcode
         /// </summary>
         internal OnCompletedDelegate OnComplete;
 
-        /// <summary>
+        internal Action<uint> OnSceneEventCompleted;
-        /// Is this scene switch progresses completed, all clients are done loading the scene or a timeout has occurred.
-        /// </summary>
-        internal bool IsCompleted { get; private set; }
-
-        internal bool TimedOut { get; private set; }
 
         /// <summary>
-        /// If all clients are done loading the scene, at the moment of completed.
+        /// This will make sure that we only have timed out if we never completed
         /// </summary>
-        internal bool AreAllClientsDoneLoading { get; private set; }
+        internal bool HasTimedOut()
+        {
+            return WhenSceneEventHasTimedOut <= Time.realtimeSinceStartup;
+        }
 
         /// <summary>
         /// The hash value generated from the full scene path
@@ -93,9 +92,10 @@ namespace Unity.Netcode
         internal uint SceneHash { get; set; }
 
         internal Guid Guid { get; } = Guid.NewGuid();
+        internal uint SceneEventId;
 
         private Coroutine m_TimeOutCoroutine;
-        private AsyncOperation m_SceneLoadOperation;
+        private AsyncOperation m_AsyncOperation;
 
         private NetworkManager m_NetworkManager { get; }
 
@@ -105,21 +105,85 @@ namespace Unity.Netcode
 
         internal LoadSceneMode LoadSceneMode;
 
-        internal List<ulong> ClientsThatStartedSceneEvent;
+        internal List<ulong> GetClientsWithStatus(bool completedSceneEvent)
+        {
+            var clients = new List<ulong>();
+            if (completedSceneEvent)
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that completed if the AsyncOperation is done.
+                if (m_NetworkManager.IsHost && m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
+
+                // Add all clients that completed the scene event
+                foreach (var clientStatus in ClientsProcessingSceneEvent)
+                {
+                    if (clientStatus.Value == completedSceneEvent)
+                    {
+                        clients.Add(clientStatus.Key);
+                    }
+                }
+            }
+            else
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that did not complete if the AsyncOperation is
+                // not done.
+                if (m_NetworkManager.IsHost && !m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
+
+                // If we are getting the list of clients that have not completed the
+                // scene event, then add any clients that disconnected during this
+                // scene event.
+                clients.AddRange(ClientsThatDisconnected);
+            }
+            return clients;
+        }
 
         internal SceneEventProgress(NetworkManager networkManager, SceneEventProgressStatus status = SceneEventProgressStatus.Started)
         {
             if (status == SceneEventProgressStatus.Started)
             {
-                // Track the clients that were connected when we started this event
-                ClientsThatStartedSceneEvent = new List<ulong>(networkManager.ConnectedClientsIds);
                 m_NetworkManager = networkManager;
+
+                if (networkManager.IsServer)
+                {
+                    m_NetworkManager.OnClientDisconnectCallback += OnClientDisconnectCallback;
+                    // Track the clients that were connected when we started this event
+                    foreach (var connectedClientId in networkManager.ConnectedClientsIds)
+                    {
+                        // Ignore the host client
+                        if (NetworkManager.ServerClientId == connectedClientId)
+                        {
+                            continue;
+                        }
+                        ClientsProcessingSceneEvent.Add(connectedClientId, false);
+                    }
+
+                    WhenSceneEventHasTimedOut = Time.realtimeSinceStartup + networkManager.NetworkConfig.LoadSceneTimeOut;
                     m_TimeOutCoroutine = m_NetworkManager.StartCoroutine(TimeOutSceneEventProgress());
-                TimeAtInitiation = Time.realtimeSinceStartup;
+                }
             }
             Status = status;
         }
 
+        /// <summary>
+        /// Remove the client from the clients processing the current scene event
+        /// Add this client to the clients that disconnected list
+        /// </summary>
+        private void OnClientDisconnectCallback(ulong clientId)
+        {
+            if (ClientsProcessingSceneEvent.ContainsKey(clientId))
+            {
+                ClientsThatDisconnected.Add(clientId);
+                ClientsProcessingSceneEvent.Remove(clientId);
+            }
+        }
+
         /// <summary>
         /// Coroutine that checks to see if the scene event is complete every network tick period.
         /// This will handle completing the scene event when one or more client(s) disconnect(s)
@@ -129,79 +193,107 @@ namespace Unity.Netcode
         internal IEnumerator TimeOutSceneEventProgress()
         {
             var waitForNetworkTick = new WaitForSeconds(1.0f / m_NetworkManager.NetworkConfig.TickRate);
-            while (!TimedOut && !IsCompleted)
+            while (!HasTimedOut())
             {
                 yield return waitForNetworkTick;
 
-                CheckCompletion();
+                TryFinishingSceneEventProgress();
-                if (!IsCompleted)
-                {
-                    TimedOut = TimeAtInitiation - Time.realtimeSinceStartup >= m_NetworkManager.NetworkConfig.LoadSceneTimeOut;
             }
         }
-        }
-
-        internal void AddClientAsDone(ulong clientId)
-        {
-            DoneClients.Add(clientId);
-            CheckCompletion();
-        }
-
-        internal void RemoveClientAsDone(ulong clientId)
-        {
-            DoneClients.Remove(clientId);
-            CheckCompletion();
-        }
-
-        internal void SetSceneLoadOperation(AsyncOperation sceneLoadOperation)
-        {
-            m_SceneLoadOperation = sceneLoadOperation;
-            m_SceneLoadOperation.completed += operation => CheckCompletion();
-        }
 
         /// <summary>
-        /// Called only on the server-side during integration test (NetcodeIntegrationTest specific)
+        /// Sets the client's scene event progress to finished/true
-        /// scene loading and unloading.
-        ///
-        /// Note: During integration testing we must queue all scene loading and unloading requests for
-        /// both the server and all clients so they can be processed in a FIFO/linear fashion to avoid
-        /// conflicts when the  <see cref="SceneManager.sceneLoaded"/> and <see cref="SceneManager.sceneUnloaded"/>
-        /// events are triggered. The Completed action simulates the <see cref="AsyncOperation.completed"/> event.
-        /// (See: Unity.Netcode.TestHelpers.Runtime.IntegrationTestSceneHandler)
         /// </summary>
-        internal void SetSceneLoadOperation(ISceneManagerHandler.SceneEventAction sceneEventAction)
+        internal void ClientFinishedSceneEvent(ulong clientId)
         {
-            sceneEventAction.Completed = SetComplete;
+            if (ClientsProcessingSceneEvent.ContainsKey(clientId))
+            {
+                ClientsProcessingSceneEvent[clientId] = true;
+                TryFinishingSceneEventProgress();
+            }
         }
 
         /// <summary>
-        /// Finalizes the SceneEventProgress
+        /// Determines if the scene event has finished for both
+        /// client(s) and server.
         /// </summary>
-        internal void SetComplete()
+        /// <remarks>
+        /// The server checks if all known clients processing this scene event
+        /// have finished and then it returns its local AsyncOperation status.
+        /// Clients finish when their AsyncOperation finishes.
+        /// </remarks>
+        private bool HasFinished()
         {
-            IsCompleted = true;
+            // If the network session is terminated/terminating then finish tracking
-            AreAllClientsDoneLoading = true;
+            // this scene event
+            if (!IsNetworkSessionActive())
+            {
+                return true;
+            }
 
-            // If OnComplete is not registered or it is and returns true then remove this from the progress tracking
+            // Clients skip over this
-            if (OnComplete == null || (OnComplete != null && OnComplete.Invoke(this)))
+            foreach (var clientStatus in ClientsProcessingSceneEvent)
             {
+                if (!clientStatus.Value)
+                {
+                    return false;
+                }
+            }
+
+            // Return the local scene event's AsyncOperation status
+            // Note: Integration tests process scene loading through a queue
+            // and the AsyncOperation could not be assigned for several
+            // network tick periods. Return false if that is the case.
+            return m_AsyncOperation == null ? false : m_AsyncOperation.isDone;
+        }
+
+        /// <summary>
+        /// Sets the AsyncOperation for the scene load/unload event
+        /// </summary>
+        internal void SetAsyncOperation(AsyncOperation asyncOperation)
+        {
+            m_AsyncOperation = asyncOperation;
+            m_AsyncOperation.completed += new Action<AsyncOperation>(asyncOp2 =>
+            {
+                // Don't invoke the callback if the network session is disconnected
+                // during a SceneEventProgress
+                if (IsNetworkSessionActive())
+                {
+                    OnSceneEventCompleted?.Invoke(SceneEventId);
+                }
+
+                // Go ahead and try finishing even if the network session is terminated/terminating
+                // as we might need to stop the coroutine
+                TryFinishingSceneEventProgress();
+            });
+        }
+
+
+        internal bool IsNetworkSessionActive()
+        {
+            return m_NetworkManager != null && m_NetworkManager.IsListening && !m_NetworkManager.ShutdownInProgress;
+        }
+
+        /// <summary>
+        /// Will try to finish the current scene event in progress as long as
+        /// all conditions are met.
+        /// </summary>
+        internal void TryFinishingSceneEventProgress()
+        {
+            if (HasFinished() || HasTimedOut())
+            {
+                // Don't attempt to finalize this scene event if we are no longer listening or a shutdown is in progress
+                if (IsNetworkSessionActive())
+                {
+                    OnComplete?.Invoke(this);
                     m_NetworkManager.SceneManager.SceneEventProgressTracking.Remove(Guid);
+                    m_NetworkManager.OnClientDisconnectCallback -= OnClientDisconnectCallback;
                 }
+
+                if (m_TimeOutCoroutine != null)
+                {
                     m_NetworkManager.StopCoroutine(m_TimeOutCoroutine);
                 }
-
-        internal void CheckCompletion()
-        {
-            try
-            {
-                if ((!IsCompleted && DoneClients.Count == m_NetworkManager.ConnectedClientsList.Count && (m_SceneLoadOperation == null || m_SceneLoadOperation.isDone)) || (!IsCompleted && TimedOut))
-                {
-                    SetComplete();
-                }
-            }
-            catch (Exception ex)
-            {
-                Debug.LogException(ex);
             }
         }
     }

Runtime/Serialization/BitReader.cs

@@ -21,6 +21,8 @@ namespace Unity.Netcode
 
         private const int k_BitsPerByte = 8;
 
+        private int BytePosition => m_BitPosition >> 3;
+
         /// <summary>
         /// Whether or not the current BitPosition is evenly divisible by 8. I.e. whether or not the BitPosition is at a byte boundary.
         /// </summary>
@@ -98,11 +100,6 @@ namespace Unity.Netcode
                 throw new ArgumentOutOfRangeException(nameof(bitCount), "Cannot read more than 64 bits from a 64-bit value!");
             }
 
-            if (bitCount < 0)
-            {
-                throw new ArgumentOutOfRangeException(nameof(bitCount), "Cannot read fewer than 0 bits!");
-            }
-
             int checkPos = (int)(m_BitPosition + bitCount);
             if (checkPos > m_AllowedBitwiseReadMark)
             {
@@ -165,7 +162,7 @@ namespace Unity.Netcode
 #endif
 
             int offset = m_BitPosition & 7;
-            int pos = m_BitPosition >> 3;
+            int pos = BytePosition;
             bit = (m_BufferPointer[pos] & (1 << offset)) != 0;
             ++m_BitPosition;
         }
@@ -175,7 +172,7 @@ namespace Unity.Netcode
         {
             var val = new T();
             byte* ptr = ((byte*)&val) + offsetBytes;
-            byte* bufferPointer = m_BufferPointer + m_Position;
+            byte* bufferPointer = m_BufferPointer + BytePosition;
             UnsafeUtility.MemCpy(ptr, bufferPointer, bytesToRead);
 
             m_BitPosition += bytesToRead * k_BitsPerByte;

Runtime/Serialization/BitWriter.cs

@@ -29,6 +29,8 @@ namespace Unity.Netcode
             get => (m_BitPosition & 7) == 0;
         }
 
+        private int BytePosition => m_BitPosition >> 3;
+
         internal unsafe BitWriter(FastBufferWriter writer)
         {
             m_Writer = writer;
@@ -181,7 +183,7 @@ namespace Unity.Netcode
 #endif
 
             int offset = m_BitPosition & 7;
-            int pos = m_BitPosition >> 3;
+            int pos = BytePosition;
             ++m_BitPosition;
             m_BufferPointer[pos] = (byte)(bit ? (m_BufferPointer[pos] & ~(1 << offset)) | (1 << offset) : (m_BufferPointer[pos] & ~(1 << offset)));
         }
@@ -190,7 +192,7 @@ namespace Unity.Netcode
         private unsafe void WritePartialValue<T>(T value, int bytesToWrite, int offsetBytes = 0) where T : unmanaged
         {
             byte* ptr = ((byte*)&value) + offsetBytes;
-            byte* bufferPointer = m_BufferPointer + m_Position;
+            byte* bufferPointer = m_BufferPointer + BytePosition;
             UnsafeUtility.MemCpy(bufferPointer, ptr, bytesToWrite);
 
             m_BitPosition += bytesToWrite * k_BitsPerByte;

Runtime/Serialization/BufferSerializer.cs

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

Runtime/Serialization/BufferSerializerReader.cs

@@ -34,7 +34,7 @@ namespace Unity.Netcode
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Reader.ReadValueSafe(out value);
         public void SerializeValue<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValueSafe(out value);
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValueSafe(out value);
-        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadValue(out value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadNetworkSerializableInPlace(ref value);
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadValue(out value);
 
         public void SerializeValue<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)

Runtime/Serialization/BytePacker.cs

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

Runtime/Serialization/ByteUnpacker.cs

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

Runtime/Serialization/ByteUtility.cs

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

Runtime/Serialization/ByteUtility.cs.meta

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

Runtime/Serialization/FastBufferReader.cs

@@ -65,7 +65,7 @@ namespace Unity.Netcode
             ReaderHandle* readerHandle = null;
             if (copyAllocator == Allocator.None)
             {
-                readerHandle = (ReaderHandle*)UnsafeUtility.Malloc(sizeof(ReaderHandle) + length, UnsafeUtility.AlignOf<byte>(), internalAllocator);
+                readerHandle = (ReaderHandle*)UnsafeUtility.Malloc(sizeof(ReaderHandle), UnsafeUtility.AlignOf<byte>(), internalAllocator);
                 readerHandle->BufferPointer = buffer;
                 readerHandle->Position = offset;
             }
@@ -461,6 +461,19 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Read an INetworkSerializable in-place, without constructing a new one
+        /// Note that this will NOT check for null before calling NetworkSerialize
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="value">INetworkSerializable instance</param>
+        /// <exception cref="NotImplementedException"></exception>
+        public void ReadNetworkSerializableInPlace<T>(ref T value) where T : INetworkSerializable
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(this));
+            value.NetworkSerialize(bufferSerializer);
+        }
+
         /// <summary>
         /// Reads a string
         /// NOTE: ALLOCATES
@@ -1310,5 +1323,24 @@ namespace Unity.Netcode
             value.Length = length;
             ReadBytesSafe(value.GetUnsafePtr(), length);
         }
+
+
+        /// <summary>
+        /// Read a FixedString value.
+        ///
+        /// "Safe" version - automatically performs bounds checking. Less efficient than bounds checking
+        /// for multiple reads at once by calling TryBeginRead.
+        /// </summary>
+        /// <param name="value">the value to read</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution based on generic constraints</param>
+        /// <typeparam name="T">The type being serialized</typeparam>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public unsafe void ReadValueSafeInPlace<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes
+        {
+            ReadUnmanagedSafe(out int length);
+            value.Length = length;
+            ReadBytesSafe(value.GetUnsafePtr(), length);
+        }
     }
 }

Runtime/Serialization/NetworkObjectReference.cs

@@ -139,7 +139,16 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="networkObjectRef">The <see cref="NetworkObjectReference"/> to convert from.</param>
         /// <returns>This returns the <see cref="GameObject"/> that the <see cref="NetworkObject"/> is attached to and is referenced by the <see cref="NetworkObjectReference"/> passed in as a parameter</returns>
-        public static implicit operator GameObject(NetworkObjectReference networkObjectRef) => Resolve(networkObjectRef).gameObject;
+        public static implicit operator GameObject(NetworkObjectReference networkObjectRef)
+        {
+            var networkObject = Resolve(networkObjectRef);
+            if (networkObject != null)
+            {
+                return networkObject.gameObject;
+            }
+
+            return null;
+        }
 
         /// <summary>
         /// Implicitly convert <see cref="GameObject"/> to <see cref="NetworkObject"/>.

Runtime/Spawning/NetworkPrefabHandler.cs

@@ -119,8 +119,7 @@ namespace Unity.Netcode
                         // Now we register all
                         foreach (var gameObject in networkPrefabOverrides)
                         {
-                            var targetNetworkObject = gameObject.GetComponent<NetworkObject>();
+                            if (gameObject.TryGetComponent<NetworkObject>(out var targetNetworkObject))
-                            if (targetNetworkObject != null)
                             {
                                 if (!m_PrefabInstanceToPrefabAsset.ContainsKey(targetNetworkObject.GlobalObjectIdHash))
                                 {

Runtime/Spawning/NetworkSpawnManager.cs

@@ -213,11 +213,11 @@ namespace Unity.Netcode
                 return;
             }
 
+            networkObject.OwnerClientId = NetworkManager.ServerClientId;
+
             // 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,
@@ -270,6 +270,9 @@ namespace Unity.Netcode
 
             networkObject.OwnerClientId = clientId;
 
+            networkObject.MarkVariablesDirty(true);
+            NetworkManager.BehaviourUpdater.AddForUpdate(networkObject);
+
             // Server adds entries for all client ownership
             UpdateOwnershipTable(networkObject, networkObject.OwnerClientId);
 
@@ -278,23 +281,26 @@ namespace Unity.Netcode
                 NetworkObjectId = networkObject.NetworkObjectId,
                 OwnerClientId = networkObject.OwnerClientId
             };
-            var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, NetworkManager.ConnectedClientsIds);
 
             foreach (var client in NetworkManager.ConnectedClients)
             {
+                if (networkObject.IsNetworkVisibleTo(client.Value.ClientId))
+                {
+                    var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableSequenced, client.Value.ClientId);
                     NetworkManager.NetworkMetrics.TrackOwnershipChangeSent(client.Key, networkObject, size);
                 }
             }
+        }
 
         internal bool HasPrefab(NetworkObject.SceneObject sceneObject)
         {
-            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.Header.IsSceneObject)
+            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.IsSceneObject)
             {
-                if (NetworkManager.PrefabHandler.ContainsHandler(sceneObject.Header.Hash))
+                if (NetworkManager.PrefabHandler.ContainsHandler(sceneObject.Hash))
                 {
                     return true;
                 }
-                if (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks.TryGetValue(sceneObject.Header.Hash, out var networkPrefab))
+                if (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.TryGetValue(sceneObject.Hash, out var networkPrefab))
                 {
                     switch (networkPrefab.Override)
                     {
@@ -309,69 +315,54 @@ namespace Unity.Netcode
 
                 return false;
             }
-            var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(sceneObject.Header.Hash, sceneObject.NetworkSceneHandle);
+            var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(sceneObject.Hash, sceneObject.NetworkSceneHandle);
             return networkObject != null;
         }
 
         /// <summary>
-        /// Should only run on the client
+        /// Creates a local NetowrkObject to be spawned.
         /// </summary>
-        internal NetworkObject CreateLocalNetworkObject(bool isSceneObject, uint globalObjectIdHash, ulong ownerClientId, ulong? parentNetworkId, int? networkSceneHandle, Vector3? position, Quaternion? rotation, bool isReparented = false)
+        /// <remarks>
+        /// For most cases this is client-side only, with the exception of when the server
+        /// is spawning a player.
+        /// </remarks>
+        internal NetworkObject CreateLocalNetworkObject(NetworkObject.SceneObject sceneObject)
         {
-            NetworkObject parentNetworkObject = null;
+            NetworkObject networkObject = null;
+            var globalObjectIdHash = sceneObject.Hash;
+            var position = sceneObject.HasTransform ? sceneObject.Transform.Position : default;
+            var rotation = sceneObject.HasTransform ? sceneObject.Transform.Rotation : default;
+            var scale = sceneObject.HasTransform ? sceneObject.Transform.Scale : default;
+            var parentNetworkId = sceneObject.HasParent ? sceneObject.ParentObjectId : default;
+            var worldPositionStays = (!sceneObject.HasParent) || sceneObject.WorldPositionStays;
+            var isSpawnedByPrefabHandler = false;
 
-            if (parentNetworkId != null && !isReparented)
+            // If scene management is disabled or the NetworkObject was dynamically spawned
-            {
+            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !sceneObject.IsSceneObject)
-                if (SpawnedObjects.TryGetValue(parentNetworkId.Value, out NetworkObject networkObject))
-                {
-                    parentNetworkObject = networkObject;
-                }
-                else
-                {
-                    if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
-                    {
-                        NetworkLog.LogWarning("Cannot find parent. Parent objects always have to be spawned and replicated BEFORE the child");
-                    }
-                }
-            }
-
-            if (!NetworkManager.NetworkConfig.EnableSceneManagement || !isSceneObject)
             {
                 // If the prefab hash has a registered INetworkPrefabInstanceHandler derived class
                 if (NetworkManager.PrefabHandler.ContainsHandler(globalObjectIdHash))
                 {
                     // Let the handler spawn the NetworkObject
-                    var networkObject = NetworkManager.PrefabHandler.HandleNetworkPrefabSpawn(globalObjectIdHash, ownerClientId, position.GetValueOrDefault(Vector3.zero), rotation.GetValueOrDefault(Quaternion.identity));
+                    networkObject = NetworkManager.PrefabHandler.HandleNetworkPrefabSpawn(globalObjectIdHash, sceneObject.OwnerClientId, position, rotation);
-
                     networkObject.NetworkManagerOwner = NetworkManager;
-
+                    isSpawnedByPrefabHandler = true;
-                    if (parentNetworkObject != null)
-                    {
-                        networkObject.transform.SetParent(parentNetworkObject.transform, true);
-                    }
-
-                    if (NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
-                    {
-                        UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
-                    }
-
-                    return networkObject;
                 }
                 else
                 {
                     // See if there is a valid registered NetworkPrefabOverrideLink associated with the provided prefabHash
                     GameObject networkPrefabReference = null;
-                    if (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
+                    if (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks.ContainsKey(globalObjectIdHash))
                     {
-                        switch (NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Override)
+                        switch (NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].Override)
                         {
                             default:
                             case NetworkPrefabOverride.None:
-                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].Prefab;
+                                networkPrefabReference = NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].Prefab;
                                 break;
                             case NetworkPrefabOverride.Hash:
                             case NetworkPrefabOverride.Prefab:
-                                networkPrefabReference = NetworkManager.NetworkConfig.NetworkPrefabOverrideLinks[globalObjectIdHash].OverridingTargetPrefab;
+                                networkPrefabReference = NetworkManager.NetworkConfig.Prefabs.NetworkPrefabOverrideLinks[globalObjectIdHash].OverridingTargetPrefab;
                                 break;
                         }
                     }
@@ -383,31 +374,18 @@ namespace Unity.Netcode
                         {
                             NetworkLog.LogError($"Failed to create object locally. [{nameof(globalObjectIdHash)}={globalObjectIdHash}]. {nameof(NetworkPrefab)} could not be found. Is the prefab registered with {nameof(NetworkManager)}?");
                         }
-
-                        return null;
-                    }
-
-                    // Otherwise, instantiate an instance of the NetworkPrefab linked to the prefabHash
-                    var networkObject = ((position == null && rotation == null) ? UnityEngine.Object.Instantiate(networkPrefabReference) : UnityEngine.Object.Instantiate(networkPrefabReference, position.GetValueOrDefault(Vector3.zero), rotation.GetValueOrDefault(Quaternion.identity))).GetComponent<NetworkObject>();
-
-                    networkObject.NetworkManagerOwner = NetworkManager;
-
-                    if (parentNetworkObject != null)
-                    {
-                        networkObject.transform.SetParent(parentNetworkObject.transform, true);
-                    }
-
-                    if (NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
-                    {
-                        UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
-                    }
-
-                    return networkObject;
-                }
                     }
                     else
                     {
-                var networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(globalObjectIdHash, networkSceneHandle);
+                        // Create prefab instance
+                        networkObject = UnityEngine.Object.Instantiate(networkPrefabReference).GetComponent<NetworkObject>();
+                        networkObject.NetworkManagerOwner = NetworkManager;
+                    }
+                }
+            }
+            else // Get the in-scene placed NetworkObject
+            {
+                networkObject = NetworkManager.SceneManager.GetSceneRelativeInSceneNetworkObject(globalObjectIdHash, sceneObject.NetworkSceneHandle);
 
                 if (networkObject == null)
                 {
@@ -415,19 +393,91 @@ namespace Unity.Netcode
                     {
                         NetworkLog.LogError($"{nameof(NetworkPrefab)} hash was not found! In-Scene placed {nameof(NetworkObject)} soft synchronization failure for Hash: {globalObjectIdHash}!");
                     }
-
-                    return null;
                 }
 
-                if (parentNetworkObject != null)
+                // Since this NetworkObject is an in-scene placed NetworkObject, if it is disabled then enable it so
+                // NetworkBehaviours will have their OnNetworkSpawn method invoked
+                if (networkObject != null && !networkObject.gameObject.activeInHierarchy)
                 {
-                    networkObject.transform.SetParent(parentNetworkObject.transform, true);
+                    networkObject.gameObject.SetActive(true);
+                }
             }
 
-                return networkObject;
+            if (networkObject != null)
+            {
+                // SPECIAL CASE FOR IN-SCENE PLACED:  (only when the parent has a NetworkObject)
+                // This is a special case scenario where a late joining client has joined and loaded one or
+                // more scenes that contain nested in-scene placed NetworkObject children yet the server's
+                // synchronization information does not indicate the NetworkObject in question has a parent.
+                // Under this scenario, we want to remove the parent before spawning and setting the transform values.
+                if (sceneObject.IsSceneObject && !sceneObject.HasParent && networkObject.transform.parent != null)
+                {
+                    // if the in-scene placed NetworkObject has a parent NetworkObject but the synchronization information does not
+                    // include parenting, then we need to force the removal of that parent
+                    if (networkObject.transform.parent.GetComponent<NetworkObject>() != null)
+                    {
+                        // remove the parent
+                        networkObject.ApplyNetworkParenting(true, true);
                     }
                 }
 
+                // Set the transform unless we were spawned by a prefab handler
+                // Note: prefab handlers are provided the position and rotation
+                // but it is up to the user to set those values
+                if (sceneObject.HasTransform && !isSpawnedByPrefabHandler)
+                {
+                    // If world position stays is true or we have auto object parent synchronization disabled
+                    // then we want to apply the position and rotation values world space relative
+                    if (worldPositionStays || !networkObject.AutoObjectParentSync)
+                    {
+                        networkObject.transform.position = position;
+                        networkObject.transform.rotation = rotation;
+                    }
+                    else
+                    {
+                        networkObject.transform.localPosition = position;
+                        networkObject.transform.localRotation = rotation;
+                    }
+
+                    // SPECIAL CASE:
+                    // Since players are created uniquely we don't apply scale because
+                    // the ConnectionApprovalResponse does not currently provide the
+                    // ability to specify scale. So, we just use the default scale of
+                    // the network prefab used to represent the player.
+                    // Note: not doing this would set the player's scale to zero since
+                    // that is the default value of Vector3.
+                    if (!sceneObject.IsPlayerObject)
+                    {
+                        // Since scale is always applied to local space scale, we do the transform
+                        // space logic during serialization such that it works out whether AutoObjectParentSync
+                        // is enabled or not (see NetworkObject.SceneObject)
+                        networkObject.transform.localScale = scale;
+                    }
+                }
+
+                if (sceneObject.HasParent)
+                {
+                    // Go ahead and set network parenting properties, if the latest parent is not set then pass in null
+                    // (we always want to set worldPositionStays)
+                    ulong? parentId = null;
+                    if (sceneObject.IsLatestParentSet)
+                    {
+                        parentId = parentNetworkId;
+                    }
+                    networkObject.SetNetworkParenting(parentId, worldPositionStays);
+                }
+
+
+                // Dynamically spawned NetworkObjects that occur during a LoadSceneMode.Single load scene event are migrated into the DDOL
+                // until the scene is loaded. They are then migrated back into the newly loaded and currently active scene.
+                if (!sceneObject.IsSceneObject && NetworkSceneManager.IsSpawnedObjectsPendingInDontDestroyOnLoad)
+                {
+                    UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
+                }
+            }
+            return networkObject;
+        }
+
         // Ran on both server and client
         internal void SpawnNetworkObjectLocally(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
         {
@@ -454,8 +504,7 @@ namespace Unity.Netcode
         }
 
         // Ran on both server and client
-        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, in NetworkObject.SceneObject sceneObject,
+        internal void SpawnNetworkObjectLocally(NetworkObject networkObject, in NetworkObject.SceneObject sceneObject, bool destroyWithScene)
-            FastBufferReader variableData, bool destroyWithScene)
         {
             if (networkObject == null)
             {
@@ -467,9 +516,7 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is already spawned");
             }
 
-            networkObject.SetNetworkVariableData(variableData);
+            SpawnNetworkObjectLocallyCommon(networkObject, sceneObject.NetworkObjectId, sceneObject.IsSceneObject, sceneObject.IsPlayerObject, sceneObject.OwnerClientId, destroyWithScene);
-
-            SpawnNetworkObjectLocallyCommon(networkObject, sceneObject.Header.NetworkObjectId, sceneObject.Header.IsSceneObject, sceneObject.Header.IsPlayerObject, sceneObject.Header.OwnerClientId, destroyWithScene);
         }
 
         private void SpawnNetworkObjectLocallyCommon(NetworkObject networkObject, ulong networkId, bool sceneObject, bool playerObject, ulong ownerClientId, bool destroyWithScene)
@@ -545,7 +592,6 @@ namespace Unity.Netcode
                 }
             }
 
-            networkObject.SetCachedParent(networkObject.transform.parent);
             networkObject.ApplyNetworkParenting();
             NetworkObject.CheckOrphanChildren();
 
@@ -557,6 +603,11 @@ namespace Unity.Netcode
             var children = networkObject.GetComponentsInChildren<NetworkObject>();
             foreach (var childObject in children)
             {
+                // Do not propagate the in-scene object setting if a child was dynamically spawned.
+                if (childObject.IsSceneObject.HasValue && !childObject.IsSceneObject.Value)
+                {
+                    continue;
+                }
                 childObject.IsSceneObject = sceneObject;
             }
         }
@@ -575,8 +626,6 @@ namespace Unity.Netcode
             };
             var size = NetworkManager.SendMessage(ref message, NetworkDelivery.ReliableFragmentedSequenced, clientId);
             NetworkManager.NetworkMetrics.TrackObjectSpawnSent(clientId, networkObject, size);
-
-            networkObject.MarkVariablesDirty();
         }
 
         internal ulong? GetSpawnParentId(NetworkObject networkObject)
@@ -614,7 +663,11 @@ namespace Unity.Netcode
         // Makes scene objects ready to be reused
         internal void ServerResetShudownStateForSceneObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID).Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.IsSceneObject != null && c.IsSceneObject == true);
+#endif
             foreach (var sobj in networkObjects)
             {
                 sobj.IsSpawned = false;
@@ -645,7 +698,11 @@ namespace Unity.Netcode
 
         internal void DespawnAndDestroyNetworkObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             for (int i = 0; i < networkObjects.Length; i++)
             {
@@ -675,7 +732,11 @@ namespace Unity.Netcode
 
         internal void DestroySceneObjects()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
 
             for (int i = 0; i < networkObjects.Length; i++)
             {
@@ -702,7 +763,11 @@ namespace Unity.Netcode
 
         internal void ServerSpawnSceneObjectsOnStartSweep()
         {
+#if UNITY_2023_1_OR_NEWER
+            var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(FindObjectsSortMode.InstanceID);
+#else
             var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
             var networkObjectsToSpawn = new List<NetworkObject>();
 
             for (int i = 0; i < networkObjects.Length; i++)
@@ -745,15 +810,26 @@ namespace Unity.Netcode
             }
 
             // If we are shutting down the NetworkManager, then ignore resetting the parent
-            if (!NetworkManager.ShutdownInProgress)
+            // and only attempt to remove the child's parent on the server-side
+            if (!NetworkManager.ShutdownInProgress && NetworkManager.IsServer)
             {
                 // Move child NetworkObjects to the root when parent NetworkObject is destroyed
                 foreach (var spawnedNetObj in SpawnedObjectsList)
                 {
-                    var (isReparented, latestParent) = spawnedNetObj.GetNetworkParenting();
+                    var latestParent = spawnedNetObj.GetNetworkParenting();
-                    if (isReparented && latestParent == networkObject.NetworkObjectId)
+                    if (latestParent.HasValue && latestParent.Value == networkObject.NetworkObjectId)
                     {
-                        spawnedNetObj.gameObject.transform.parent = null;
+                        // Try to remove the parent using the cached WorldPositioNStays value
+                        // Note: WorldPositionStays will still default to true if this was an
+                        // in-scene placed NetworkObject and parenting was predefined in the
+                        // scene via the editor.
+                        if (!spawnedNetObj.TryRemoveParentCachedWorldPositionStays())
+                        {
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                            {
+                                NetworkLog.LogError($"{nameof(NetworkObject)} #{spawnedNetObj.NetworkObjectId} could not be moved to the root when its parent {nameof(NetworkObject)} #{networkObject.NetworkObjectId} was being destroyed");
+                            }
+                        }
 
                         if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                         {

Runtime/Timing/NetworkTime.cs

@@ -25,7 +25,7 @@ namespace Unity.Netcode
         public double TickOffset => m_CachedTickOffset;
 
         /// <summary>
-        /// Gets the current time. This is a non fixed time value and similar to <see cref="Time.time"/>
+        /// Gets the current time. This is a non fixed time value and similar to <see cref="Time.time"/>.
         /// </summary>
         public double Time => m_TimeSec;
 
@@ -35,13 +35,13 @@ namespace Unity.Netcode
         public float TimeAsFloat => (float)m_TimeSec;
 
         /// <summary>
-        /// Gets he current fixed network time. This is the time value of the last network tick. Similar to <see cref="Time.fixedTime"/>
+        /// Gets he current fixed network time. This is the time value of the last network tick. Similar to <see cref="Time.fixedUnscaledTime"/>.
         /// </summary>
         public double FixedTime => m_CachedTick * m_TickInterval;
 
         /// <summary>
         /// Gets the fixed delta time. This value is based on the <see cref="TickRate"/> and stays constant.
-        /// Similar to <see cref="Time.fixedDeltaTime"/> There is no equivalent to <see cref="Time.deltaTime"/>
+        /// Similar to <see cref="Time.fixedUnscaledTime"/> There is no equivalent to <see cref="Time.deltaTime"/>.
         /// </summary>
         public float FixedDeltaTime => (float)m_TickInterval;
 

Runtime/Timing/NetworkTimeSystem.cs

@@ -76,7 +76,7 @@ namespace Unity.Netcode
         }
 
         /// <summary>
-        /// Advances the time system by a certain amount of time. Should be called once per frame with Time.deltaTime or similar.
+        /// Advances the time system by a certain amount of time. Should be called once per frame with Time.unscaledDeltaTime or similar.
         /// </summary>
         /// <param name="deltaTimeSec">The amount of time to advance. The delta time which passed since Advance was last called.</param>
         /// <returns></returns>

Runtime/Transports/UNET/UNetTransport.cs

@@ -7,6 +7,7 @@ using UnityEngine.Networking;
 
 namespace Unity.Netcode.Transports.UNET
 {
+    [AddComponentMenu("Netcode/UNet Transport")]
     public class UNetTransport : NetworkTransport
     {
         public enum SendMode

Runtime/Transports/UTP/BatchedReceiveQueue.cs

@@ -1,5 +1,9 @@
 using System;
 using Unity.Networking.Transport;
+#if UTP_TRANSPORT_2_0_ABOVE
+using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+#endif
 
 namespace Unity.Netcode.Transports.UTP
 {
@@ -25,7 +29,11 @@ namespace Unity.Netcode.Transports.UTP
             {
                 fixed (byte* dataPtr = m_Data)
                 {
+#if UTP_TRANSPORT_2_0_ABOVE
+                    reader.ReadBytesUnsafe(dataPtr, reader.Length);
+#else
                     reader.ReadBytes(dataPtr, reader.Length);
+#endif
                 }
             }
 
@@ -62,7 +70,11 @@ namespace Unity.Netcode.Transports.UTP
             {
                 fixed (byte* dataPtr = m_Data)
                 {
+#if UTP_TRANSPORT_2_0_ABOVE
+                    reader.ReadBytesUnsafe(dataPtr + m_Offset + m_Length, reader.Length);
+#else
                     reader.ReadBytes(dataPtr + m_Offset + m_Length, reader.Length);
+#endif
                 }
             }
 

Runtime/Transports/UTP/BatchedSendQueue.cs

@@ -8,22 +8,30 @@ 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
+    /// messages, call <see cref="FillWriterWithMessages"/> or <see cref="FillWriterWithBytes"/>
-    /// <see cref="NetworkDriver.BeginSend"/>. This will fill the writer with as many messages as
+    /// with the <see cref="DataStreamWriter"/> obtained from <see cref="NetworkDriver.BeginSend"/>.
-    /// possible. If the send is successful, call <see cref="Consume"/> to remove the data from the
+    /// This will fill the writer with as many messages/bytes as possible. If the send is
-    /// queue.
+    /// 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;
+        // Note that we're using NativeList basically like a growable NativeArray, where the length
+        // of the list is the capacity of our array. (We can't use the capacity of the list as our
+        // queue capacity because NativeList may elect to set it higher than what we'd set it to
+        // with SetCapacity, which breaks the logic of our code.)
+        private NativeList<byte> m_Data;
         private NativeArray<int> m_HeadTailIndices;
+        private int m_MaximumCapacity;
+        private int m_MinimumCapacity;
 
         /// <summary>Overhead that is added to each message in the queue.</summary>
         public const int PerMessageOverhead = sizeof(int);
 
+        internal const int MinimumMinimumCapacity = 4096;
+
         // Indices into m_HeadTailIndicies.
         private const int k_HeadInternalIndex = 0;
         private const int k_TailInternalIndex = 1;
@@ -43,18 +51,33 @@ namespace Unity.Netcode.Transports.UTP
         }
 
         public int Length => TailIndex - HeadIndex;
-
+        public int Capacity => m_Data.Length;
         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);
+            // Make sure the maximum capacity will be even.
+            m_MaximumCapacity = capacity + (capacity & 1);
+
+            // We pick the minimum capacity such that if we keep doubling it, we'll eventually hit
+            // the maximum capacity exactly. The alternative would be to use capacities that are
+            // powers of 2, but this can lead to over-allocating quite a bit of memory (especially
+            // since we expect maximum capacities to be in the megabytes range). The approach taken
+            // here avoids this issue, at the cost of not having allocations of nice round sizes.
+            m_MinimumCapacity = m_MaximumCapacity;
+            while (m_MinimumCapacity / 2 >= MinimumMinimumCapacity)
+            {
+                m_MinimumCapacity /= 2;
+            }
+
+            m_Data = new NativeList<byte>(m_MinimumCapacity, Allocator.Persistent);
             m_HeadTailIndices = new NativeArray<int>(2, Allocator.Persistent);
 
+            m_Data.ResizeUninitialized(m_MinimumCapacity);
+
             HeadIndex = 0;
             TailIndex = 0;
         }
@@ -68,18 +91,28 @@ namespace Unity.Netcode.Transports.UTP
             }
         }
 
+        /// <summary>Write a raw buffer to a DataStreamWriter.</summary>
+        private unsafe void WriteBytes(ref DataStreamWriter writer, byte* data, int length)
+        {
+#if UTP_TRANSPORT_2_0_ABOVE
+            writer.WriteBytesUnsafe(data, length);
+#else
+            writer.WriteBytes(data, length);
+#endif
+        }
+
         /// <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);
+                var writer = new DataStreamWriter((byte*)m_Data.GetUnsafePtr() + TailIndex, Capacity - TailIndex);
 
                 writer.WriteInt(data.Count);
 
                 fixed (byte* dataPtr = data.Array)
                 {
-                    writer.WriteBytes(dataPtr + data.Offset, data.Count);
+                    WriteBytes(ref writer, dataPtr + data.Offset, data.Count);
                 }
             }
 
@@ -100,16 +133,16 @@ namespace Unity.Netcode.Transports.UTP
             }
 
             // Check if there's enough room after the current tail index.
-            if (m_Data.Length - TailIndex >= sizeof(int) + message.Count)
+            if (Capacity - 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.
+            // Move the data at the beginning of of m_Data. Either it will leave enough space for
-            if (m_Data.Length - TailIndex + HeadIndex >= sizeof(int) + message.Count)
+            // the message, or we'll grow m_Data and will want the data at the beginning anyway.
+            if (HeadIndex > 0 && Length > 0)
             {
-                // Move the data back at the beginning of m_Data.
                 unsafe
                 {
                     UnsafeUtility.MemMove(m_Data.GetUnsafePtr(), (byte*)m_Data.GetUnsafePtr() + HeadIndex, Length);
@@ -117,14 +150,40 @@ namespace Unity.Netcode.Transports.UTP
 
                 TailIndex = Length;
                 HeadIndex = 0;
+            }
 
+            // If there's enough space left at the end for the message, now is a good time to trim
+            // the capacity of m_Data if it got very large. We define "very large" here as having
+            // more than 75% of m_Data unused after adding the new message.
+            if (Capacity - TailIndex >= sizeof(int) + message.Count)
+            {
                 AppendDataAtTail(message);
+
+                while (TailIndex < Capacity / 4 && Capacity > m_MinimumCapacity)
+                {
+                    m_Data.ResizeUninitialized(Capacity / 2);
+                }
+
                 return true;
             }
 
+            // If we get here we need to grow m_Data until the data fits (or it's too large).
+            while (Capacity - TailIndex < sizeof(int) + message.Count)
+            {
+                // Can't grow m_Data anymore. Message simply won't fit.
+                if (Capacity * 2 > m_MaximumCapacity)
+                {
                     return false;
                 }
 
+                m_Data.ResizeUninitialized(Capacity * 2);
+            }
+
+            // If we get here we know there's now enough room for the message.
+            AppendDataAtTail(message);
+            return true;
+        }
+
         /// <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.
@@ -149,12 +208,12 @@ namespace Unity.Netcode.Transports.UTP
 
             unsafe
             {
-                var reader = new DataStreamReader((byte*)m_Data.GetUnsafePtr() + HeadIndex, Length);
+                var reader = new DataStreamReader(m_Data.AsArray());
 
                 var writerAvailable = writer.Capacity;
-                var readerOffset = 0;
+                var readerOffset = HeadIndex;
 
-                while (readerOffset < Length)
+                while (readerOffset < TailIndex)
                 {
                     reader.SeekSet(readerOffset);
                     var messageLength = reader.ReadInt();
@@ -167,8 +226,8 @@ namespace Unity.Netcode.Transports.UTP
                     {
                         writer.WriteInt(messageLength);
 
-                        var messageOffset = HeadIndex + reader.GetBytesRead();
+                        var messageOffset = reader.GetBytesRead();
-                        writer.WriteBytes((byte*)m_Data.GetUnsafePtr() + messageOffset, messageLength);
+                        WriteBytes(ref writer, (byte*)m_Data.GetUnsafePtr() + messageOffset, messageLength);
 
                         writerAvailable -= sizeof(int) + messageLength;
                         readerOffset += sizeof(int) + messageLength;
@@ -205,7 +264,7 @@ namespace Unity.Netcode.Transports.UTP
 
             unsafe
             {
-                writer.WriteBytes((byte*)m_Data.GetUnsafePtr() + HeadIndex, copyLength);
+                WriteBytes(ref writer, (byte*)m_Data.GetUnsafePtr() + HeadIndex, copyLength);
             }
 
             return copyLength;
@@ -219,10 +278,14 @@ namespace Unity.Netcode.Transports.UTP
         /// <param name="size">Number of bytes to consume from the queue.</param>
         public void Consume(int size)
         {
+            // Adjust the head/tail indices such that we consume the given size.
             if (size >= Length)
             {
                 HeadIndex = 0;
                 TailIndex = 0;
+
+                // This is a no-op if m_Data is already at minimum capacity.
+                m_Data.ResizeUninitialized(m_MinimumCapacity);
             }
             else
             {

Runtime/Transports/UTP/NetworkMetricsPipelineStage.cs

@@ -4,25 +4,24 @@ using AOT;
 using Unity.Burst;
 using Unity.Collections.LowLevel.Unsafe;
 using Unity.Networking.Transport;
-using UnityEngine;
 
 namespace Unity.Netcode.Transports.UTP
 {
     [BurstCompile]
     internal unsafe struct NetworkMetricsPipelineStage : INetworkPipelineStage
     {
-        static TransportFunctionPointer<NetworkPipelineStage.ReceiveDelegate> ReceiveFunction = new TransportFunctionPointer<NetworkPipelineStage.ReceiveDelegate>(Receive);
+        private static TransportFunctionPointer<NetworkPipelineStage.ReceiveDelegate> s_ReceiveFunction = new TransportFunctionPointer<NetworkPipelineStage.ReceiveDelegate>(Receive);
-        static TransportFunctionPointer<NetworkPipelineStage.SendDelegate> SendFunction = new TransportFunctionPointer<NetworkPipelineStage.SendDelegate>(Send);
+        private static TransportFunctionPointer<NetworkPipelineStage.SendDelegate> s_SendFunction = new TransportFunctionPointer<NetworkPipelineStage.SendDelegate>(Send);
-        static TransportFunctionPointer<NetworkPipelineStage.InitializeConnectionDelegate> InitializeConnectionFunction = new TransportFunctionPointer<NetworkPipelineStage.InitializeConnectionDelegate>(InitializeConnection);
+        private static TransportFunctionPointer<NetworkPipelineStage.InitializeConnectionDelegate> s_InitializeConnectionFunction = new TransportFunctionPointer<NetworkPipelineStage.InitializeConnectionDelegate>(InitializeConnection);
 
         public NetworkPipelineStage StaticInitialize(byte* staticInstanceBuffer,
             int staticInstanceBufferLength,
             NetworkSettings settings)
         {
             return new NetworkPipelineStage(
-                ReceiveFunction,
+                s_ReceiveFunction,
-                SendFunction,
+                s_SendFunction,
-                InitializeConnectionFunction,
+                s_InitializeConnectionFunction,
                 ReceiveCapacity: 0,
                 SendCapacity: 0,
                 HeaderCapacity: 0,

Runtime/Transports/UTP/SecretsLoaderHelper.cs

@@ -0,0 +1,188 @@
+using System;
+using System.IO;
+using UnityEngine;
+
+namespace Unity.Netcode.Transports.UTP
+{
+    /// <summary>
+    /// Component to add to a NetworkManager if you want the certificates to be loaded from files.
+    /// Mostly helpful to ease development and testing, especially with self-signed certificates
+    ///
+    /// Shipping code should make the calls to
+    /// - SetServerSecrets
+    /// - SetClientSecrets
+    /// directly, instead of relying on this.
+    /// </summary>
+    public class SecretsLoaderHelper : MonoBehaviour
+    {
+        internal struct ServerSecrets
+        {
+            public string ServerPrivate;
+            public string ServerCertificate;
+        };
+
+        internal struct ClientSecrets
+        {
+            public string ServerCommonName;
+            public string ClientCertificate;
+        };
+
+        private void Awake()
+        {
+            var serverSecrets = new ServerSecrets();
+
+            try
+            {
+                serverSecrets.ServerCertificate = ServerCertificate;
+            }
+            catch (Exception exception)
+            {
+                Debug.Log(exception);
+            }
+
+            try
+            {
+                serverSecrets.ServerPrivate = ServerPrivate;
+            }
+            catch (Exception exception)
+            {
+                Debug.Log(exception);
+            }
+
+            var clientSecrets = new ClientSecrets();
+            try
+            {
+                clientSecrets.ClientCertificate = ClientCA;
+            }
+            catch (Exception exception)
+            {
+                Debug.Log(exception);
+            }
+
+            try
+            {
+                clientSecrets.ServerCommonName = ServerCommonName;
+            }
+            catch (Exception exception)
+            {
+                Debug.Log(exception);
+            }
+
+            var unityTransportComponent = GetComponent<UnityTransport>();
+
+            if (unityTransportComponent == null)
+            {
+                Debug.LogError($"You need to select the UnityTransport protocol, in the NetworkManager, in order for the SecretsLoaderHelper component to be useful.");
+                return;
+            }
+
+            unityTransportComponent.SetServerSecrets(serverSecrets.ServerCertificate, serverSecrets.ServerPrivate);
+            unityTransportComponent.SetClientSecrets(clientSecrets.ServerCommonName, clientSecrets.ClientCertificate);
+        }
+
+        [Tooltip("Hostname")]
+        [SerializeField]
+        private string m_ServerCommonName = "localhost";
+
+        /// <summary>Common name of the server (typically its hostname).</summary>
+        public string ServerCommonName
+        {
+            get => m_ServerCommonName;
+            set => m_ServerCommonName = value;
+        }
+
+        [Tooltip("Client CA filepath. Useful with self-signed certificates")]
+        [SerializeField]
+        private string m_ClientCAFilePath = ""; // "Assets/Secure/myGameClientCA.pem"
+
+        /// <summary>Client CA filepath. Useful with self-signed certificates</summary>
+        public string ClientCAFilePath
+        {
+            get => m_ClientCAFilePath;
+            set => m_ClientCAFilePath = value;
+        }
+
+        [Tooltip("Client CA Override. Only useful for development with self-signed certificates. Certificate content, for platforms that lack file access (WebGL)")]
+        [SerializeField]
+        private string m_ClientCAOverride = "";
+
+        /// <summary>
+        /// Client CA Override. Only useful for development with self-signed certificates.
+        /// Certificate content, for platforms that lack file access (WebGL)
+        /// </summary>
+        public string ClientCAOverride
+        {
+            get => m_ClientCAOverride;
+            set => m_ClientCAOverride = value;
+        }
+
+        [Tooltip("Server Certificate filepath")]
+        [SerializeField]
+        private string m_ServerCertificateFilePath = ""; // "Assets/Secure/myGameServerCertificate.pem"
+
+        /// <summary>Server Certificate filepath</summary>
+        public string ServerCertificateFilePath
+        {
+            get => m_ServerCertificateFilePath;
+            set => m_ServerCertificateFilePath = value;
+        }
+
+        [Tooltip("Server Private Key filepath")]
+        [SerializeField]
+        private string m_ServerPrivateFilePath = ""; // "Assets/Secure/myGameServerPrivate.pem"
+
+        /// <summary>Server Private Key filepath</summary>
+        public string ServerPrivateFilePath
+        {
+            get => m_ServerPrivateFilePath;
+            set => m_ServerPrivate = value;
+        }
+
+        private string m_ClientCA;
+
+        /// <summary>CA certificate used by the client.</summary>
+        public string ClientCA
+        {
+            get
+            {
+                if (m_ClientCAOverride != "")
+                {
+                    return m_ClientCAOverride;
+                }
+                return ReadFile(m_ClientCAFilePath, "Client Certificate");
+            }
+            set => m_ClientCA = value;
+        }
+
+        private string m_ServerCertificate;
+
+        /// <summary>Certificate used by the server.</summary>
+        public string ServerCertificate
+        {
+            get => ReadFile(m_ServerCertificateFilePath, "Server Certificate");
+            set => m_ServerCertificate = value;
+        }
+
+        private string m_ServerPrivate;
+
+        /// <summary>Private key used by the server.</summary>
+        public string ServerPrivate
+        {
+            get => ReadFile(m_ServerPrivateFilePath, "Server Key");
+            set => m_ServerPrivate = value;
+        }
+
+        private static string ReadFile(string path, string label)
+        {
+            if (path == null || path == "")
+            {
+                return "";
+            }
+
+            var reader = new StreamReader(path);
+            string fileContent = reader.ReadToEnd();
+            Debug.Log((fileContent.Length > 1) ? ("Successfully loaded " + fileContent.Length + " byte(s) from " + label) : ("Could not read " + label + " file"));
+            return fileContent;
+        }
+    }
+}

Runtime/Transports/UTP/SecretsLoaderHelper.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: dc1e7a8dc597cf24c95e4acf92c0edf5
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Transports/UTP/UnityTransport.cs

@@ -1,13 +1,29 @@
+// NetSim Implementation compilation boilerplate
+// All references to UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED should be defined in the same way,
+// as any discrepancies are likely to result in build failures
+#if UNITY_EDITOR || (DEVELOPMENT_BUILD && !UNITY_MP_TOOLS_NETSIM_DISABLED_IN_DEVELOP) || (!DEVELOPMENT_BUILD && UNITY_MP_TOOLS_NETSIM_ENABLED_IN_RELEASE)
+#define UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED
+#endif
+
 using System;
 using System.Collections.Generic;
 using UnityEngine;
 using NetcodeNetworkEvent = Unity.Netcode.NetworkEvent;
 using TransportNetworkEvent = Unity.Networking.Transport.NetworkEvent;
+using Unity.Burst;
 using Unity.Collections.LowLevel.Unsafe;
 using Unity.Collections;
+using Unity.Jobs;
 using Unity.Networking.Transport;
 using Unity.Networking.Transport.Relay;
 using Unity.Networking.Transport.Utilities;
+#if UTP_TRANSPORT_2_0_ABOVE
+using Unity.Networking.Transport.TLS;
+#endif
+
+#if !UTP_TRANSPORT_2_0_ABOVE
+using NetworkEndpoint = Unity.Networking.Transport.NetworkEndPoint;
+#endif
 
 namespace Unity.Netcode.Transports.UTP
 {
@@ -37,50 +53,48 @@ namespace Unity.Netcode.Transports.UTP
     /// </summary>
     public static class ErrorUtilities
     {
-        private const string k_NetworkSuccess = "Success";
+        private static readonly FixedString128Bytes k_NetworkSuccess = "Success";
-        private const string k_NetworkIdMismatch = "NetworkId is invalid, likely caused by stale connection {0}.";
+        private static readonly FixedString128Bytes k_NetworkIdMismatch = "Invalid connection ID {0}.";
-        private const string k_NetworkVersionMismatch = "NetworkVersion is invalid, likely caused by stale connection {0}.";
+        private static readonly FixedString128Bytes k_NetworkVersionMismatch = "Connection ID is invalid. Likely caused by sending on stale connection {0}.";
-        private const string k_NetworkStateMismatch = "Sending data while connecting on connection {0} is not allowed.";
+        private static readonly FixedString128Bytes k_NetworkStateMismatch = "Connection state is invalid. Likely caused by sending on connection {0} which is stale or still connecting.";
-        private const string k_NetworkPacketOverflow = "Unable to allocate packet due to buffer overflow.";
+        private static readonly FixedString128Bytes k_NetworkPacketOverflow = "Packet is too large to be allocated by the transport.";
-        private const string k_NetworkSendQueueFull = "Currently unable to queue packet as there is too many in-flight packets. This could be because the send queue size ('Max Send Queue Size') is too small.";
+        private static readonly FixedString128Bytes k_NetworkSendQueueFull = "Unable to queue packet in the transport. Likely caused by send queue size ('Max Send Queue Size') being too small.";
-        private const string k_NetworkHeaderInvalid = "Invalid Unity Transport Protocol header.";
-        private const string k_NetworkDriverParallelForErr = "The parallel network driver needs to process a single unique connection per job, processing a single connection multiple times in a parallel for is not supported.";
-        private const string k_NetworkSendHandleInvalid = "Invalid NetworkInterface Send Handle. Likely caused by pipeline send data corruption.";
-        private const string k_NetworkArgumentMismatch = "Invalid NetworkEndpoint Arguments.";
 
         /// <summary>
-        /// Convert error code to human readable error message.
+        /// Convert a UTP error code to human-readable error message.
         /// </summary>
-        /// <param name="error">Status code of the error</param>
+        /// <param name="error">UTP error code.</param>
-        /// <param name="connectionId">Subject connection ID of the error</param>
+        /// <param name="connectionId">ID of the connection on which the error occurred.</param>
-        /// <returns>Human readable error message.</returns>
+        /// <returns>Human-readable error message.</returns>
         public static string ErrorToString(Networking.Transport.Error.StatusCode error, ulong connectionId)
         {
-            switch (error)
+            return ErrorToString((int)error, connectionId);
+        }
+
+        internal static string ErrorToString(int error, ulong connectionId)
+        {
+            return ErrorToFixedString(error, connectionId).ToString();
+        }
+
+        internal static FixedString128Bytes ErrorToFixedString(int error, ulong connectionId)
+        {
+            switch ((Networking.Transport.Error.StatusCode)error)
             {
                 case Networking.Transport.Error.StatusCode.Success:
                     return k_NetworkSuccess;
                 case Networking.Transport.Error.StatusCode.NetworkIdMismatch:
-                    return string.Format(k_NetworkIdMismatch, connectionId);
+                    return FixedString.Format(k_NetworkIdMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkVersionMismatch:
-                    return string.Format(k_NetworkVersionMismatch, connectionId);
+                    return FixedString.Format(k_NetworkVersionMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkStateMismatch:
-                    return string.Format(k_NetworkStateMismatch, connectionId);
+                    return FixedString.Format(k_NetworkStateMismatch, connectionId);
                 case Networking.Transport.Error.StatusCode.NetworkPacketOverflow:
                     return k_NetworkPacketOverflow;
                 case Networking.Transport.Error.StatusCode.NetworkSendQueueFull:
                     return k_NetworkSendQueueFull;
-                case Networking.Transport.Error.StatusCode.NetworkHeaderInvalid:
+                default:
-                    return k_NetworkHeaderInvalid;
+                    return FixedString.Format("Unknown error code {0}.", error);
-                case Networking.Transport.Error.StatusCode.NetworkDriverParallelForErr:
-                    return k_NetworkDriverParallelForErr;
-                case Networking.Transport.Error.StatusCode.NetworkSendHandleInvalid:
-                    return k_NetworkSendHandleInvalid;
-                case Networking.Transport.Error.StatusCode.NetworkArgumentMismatch:
-                    return k_NetworkArgumentMismatch;
             }
-
-            return $"Unknown ErrorCode {Enum.GetName(typeof(Networking.Transport.Error.StatusCode), error)}";
         }
     }
 
@@ -88,6 +102,7 @@ namespace Unity.Netcode.Transports.UTP
     /// The Netcode for GameObjects NetworkTransport for UnityTransport.
     /// Note: This is highly recommended to use over UNet.
     /// </summary>
+    [AddComponentMenu("Netcode/Unity Transport")]
     public partial class UnityTransport : NetworkTransport, INetworkStreamDriverConstructor
     {
         /// <summary>
@@ -125,8 +140,13 @@ namespace Unity.Netcode.Transports.UTP
         /// <summary>
         /// The default maximum send queue size
         /// </summary>
+        [Obsolete("MaxSendQueueSize is now determined dynamically (can still be set programmatically using the MaxSendQueueSize property). This initial value is not used anymore.", false)]
         public const int InitialMaxSendQueueSize = 16 * InitialMaxPayloadSize;
 
+        // Maximum reliable throughput, assuming the full reliable window can be sent on every
+        // frame at 60 FPS. This will be a large over-estimation in any realistic scenario.
+        private const int k_MaxReliableThroughput = (NetworkParameterConstants.MTU * 64 * 60) / 1000; // bytes per millisecond
+
         private static ConnectionAddressData s_DefaultConnectionAddressData = new ConnectionAddressData { Address = "127.0.0.1", Port = 7777, ServerListenAddress = string.Empty };
 
 #pragma warning disable IDE1006 // Naming Styles
@@ -146,6 +166,30 @@ namespace Unity.Netcode.Transports.UTP
         [SerializeField]
         private ProtocolType m_ProtocolType;
 
+#if UTP_TRANSPORT_2_0_ABOVE
+        [Tooltip("Per default the client/server will communicate over UDP. Set to true to communicate with WebSocket.")]
+        [SerializeField]
+        private bool m_UseWebSockets = false;
+
+        public bool UseWebSockets
+        {
+            get => m_UseWebSockets;
+            set => m_UseWebSockets = value;
+        }
+
+        /// <summary>
+        /// Per default the client/server communication will not be encrypted. Select true to enable DTLS for UDP and TLS for Websocket.
+        /// </summary>
+        [Tooltip("Per default the client/server communication will not be encrypted. Select true to enable DTLS for UDP and TLS for Websocket.")]
+        [SerializeField]
+        private bool m_UseEncryption = false;
+        public bool UseEncryption
+        {
+            get => m_UseEncryption;
+            set => m_UseEncryption = value;
+        }
+#endif
+
         [Tooltip("The maximum amount of packets that can be in the internal send/receive queues. Basically this is how many packets can be sent/received in a single update/frame.")]
         [SerializeField]
         private int m_MaxPacketQueueSize = InitialMaxPacketQueueSize;
@@ -158,26 +202,28 @@ namespace Unity.Netcode.Transports.UTP
             set => m_MaxPacketQueueSize = value;
         }
 
-        [Tooltip("The maximum size of a payload that can be handled by the transport.")]
+        [Tooltip("The maximum size of an unreliable payload that can be handled by the transport.")]
         [SerializeField]
         private int m_MaxPayloadSize = InitialMaxPayloadSize;
 
-        /// <summary>The maximum size of a payload that can be handled by the transport.</summary>
+        /// <summary>The maximum size of an unreliable payload that can be handled by the transport.</summary>
         public int MaxPayloadSize
         {
             get => m_MaxPayloadSize;
             set => m_MaxPayloadSize = value;
         }
 
-        [Tooltip("The maximum size in bytes of the transport send queue. The send queue accumulates messages for batching and stores messages when other internal send queues are full. If you routinely observe an error about too many in-flight packets, try increasing this.")]
+        private int m_MaxSendQueueSize = 0;
-        [SerializeField]
-        private int m_MaxSendQueueSize = InitialMaxSendQueueSize;
 
         /// <summary>The maximum size in bytes of the transport send queue.</summary>
         /// <remarks>
         /// The send queue accumulates messages for batching and stores messages when other internal
-        /// send queues are full. If you routinely observe an error about too many in-flight packets,
+        /// send queues are full. Note that there should not be any need to set this value manually
-        /// try increasing this.
+        /// since the send queue size is dynamically sized based on need.
+        ///
+        /// This value should only be set if you have particular requirements (e.g. if you want to
+        /// limit the memory usage of the send queues). Note however that setting this value too low
+        /// can easily lead to disconnections under heavy traffic.
         /// </remarks>
         public int MaxSendQueueSize
         {
@@ -257,18 +303,23 @@ namespace Unity.Netcode.Transports.UTP
             public ushort Port;
 
             /// <summary>
-            /// IP address the server will listen on. If not provided, will use 'Address'.
+            /// IP address the server will listen on. If not provided, will use localhost.
             /// </summary>
-            [Tooltip("IP address the server will listen on. If not provided, will use 'Address'.")]
+            [Tooltip("IP address the server will listen on. If not provided, will use localhost.")]
             [SerializeField]
             public string ServerListenAddress;
 
-            private static NetworkEndPoint ParseNetworkEndpoint(string ip, ushort port)
+            private static NetworkEndpoint ParseNetworkEndpoint(string ip, ushort port, bool silent = false)
             {
-                if (!NetworkEndPoint.TryParse(ip, port, out var endpoint))
+                NetworkEndpoint endpoint = default;
+
+                if (!NetworkEndpoint.TryParse(ip, port, out endpoint, NetworkFamily.Ipv4) &&
+                    !NetworkEndpoint.TryParse(ip, port, out endpoint, NetworkFamily.Ipv6))
+                {
+                    if (!silent)
                     {
                         Debug.LogError($"Invalid network endpoint: {ip}:{port}.");
-                    return default;
+                    }
                 }
 
                 return endpoint;
@@ -277,14 +328,39 @@ namespace Unity.Netcode.Transports.UTP
             /// <summary>
             /// Endpoint (IP address and port) clients will connect to.
             /// </summary>
-            public NetworkEndPoint ServerEndPoint => ParseNetworkEndpoint(Address, Port);
+            public NetworkEndpoint ServerEndPoint => ParseNetworkEndpoint(Address, Port);
 
             /// <summary>
             /// Endpoint (IP address and port) server will listen/bind on.
             /// </summary>
-            public NetworkEndPoint ListenEndPoint => ParseNetworkEndpoint((ServerListenAddress == string.Empty) ? Address : ServerListenAddress, Port);
+            public NetworkEndpoint ListenEndPoint
+            {
+                get
+                {
+                    if (string.IsNullOrEmpty(ServerListenAddress))
+                    {
+                        var ep = NetworkEndpoint.LoopbackIpv4;
+
+                        // If an address was entered and it's IPv6, switch to using ::1 as the
+                        // default listen address. (Otherwise we always assume IPv4.)
+                        if (!string.IsNullOrEmpty(Address) && ServerEndPoint.Family == NetworkFamily.Ipv6)
+                        {
+                            ep = NetworkEndpoint.LoopbackIpv6;
                         }
 
+                        return ep.WithPort(Port);
+                    }
+                    else
+                    {
+                        return ParseNetworkEndpoint(ServerListenAddress, Port);
+                    }
+                }
+            }
+
+            public bool IsIpv6 => !string.IsNullOrEmpty(Address) && ParseNetworkEndpoint(Address, Port, true).Family == NetworkFamily.Ipv6;
+        }
+
+
         /// <summary>
         /// The connection (address) data for this <see cref="UnityTransport"/> instance.
         /// This is where you can change IP Address, Port, or server's listen address.
@@ -326,6 +402,9 @@ namespace Unity.Netcode.Transports.UTP
         /// - packet jitter (variances in latency, see: https://en.wikipedia.org/wiki/Jitter)
         /// - packet drop rate (packet loss)
         /// </summary>
+#if UTP_TRANSPORT_2_0_ABOVE
+        [Obsolete("DebugSimulator is no longer supported and has no effect. Use Network Simulator from the Multiplayer Tools package.", false)]
+#endif
         public SimulatorParameters DebugSimulator = new SimulatorParameters
         {
             PacketDelayMS = 0,
@@ -333,6 +412,8 @@ namespace Unity.Netcode.Transports.UTP
             PacketDropRate = 0
         };
 
+        internal uint? DebugSimulatorRandomSeed { get; set; } = null;
+
         private struct PacketLossCache
         {
             public int PacketsReceived;
@@ -340,6 +421,10 @@ namespace Unity.Netcode.Transports.UTP
             public float PacketLoss;
         };
 
+        internal static event Action<int, NetworkDriver> TransportInitialized;
+        internal static event Action<int> TransportDisposed;
+        internal NetworkDriver NetworkDriver => m_Driver;
+
         private PacketLossCache m_PacketLossCache = new PacketLossCache();
 
         private State m_State = State.Disconnected;
@@ -383,6 +468,8 @@ namespace Unity.Netcode.Transports.UTP
                 out m_UnreliableFragmentedPipeline,
                 out m_UnreliableSequencedFragmentedPipeline,
                 out m_ReliableSequencedPipeline);
+
+            TransportInitialized?.Invoke(GetInstanceID(), NetworkDriver);
         }
 
         private void DisposeInternals()
@@ -400,6 +487,8 @@ namespace Unity.Netcode.Transports.UTP
             }
 
             m_SendQueue.Clear();
+
+            TransportDisposed?.Invoke(GetInstanceID());
         }
 
         private NetworkPipeline SelectSendPipeline(NetworkDelivery delivery)
@@ -425,7 +514,7 @@ namespace Unity.Netcode.Transports.UTP
 
         private bool ClientBindAndConnect()
         {
-            var serverEndpoint = default(NetworkEndPoint);
+            var serverEndpoint = default(NetworkEndpoint);
 
             if (m_ProtocolType == ProtocolType.RelayUnityTransport)
             {
@@ -438,6 +527,7 @@ namespace Unity.Netcode.Transports.UTP
                 }
 
                 m_NetworkSettings.WithRelayParameters(ref m_RelayServerData, m_HeartbeatTimeoutMS);
+                serverEndpoint = m_RelayServerData.Endpoint;
             }
             else
             {
@@ -446,7 +536,8 @@ namespace Unity.Netcode.Transports.UTP
 
             InitDriver();
 
-            int result = m_Driver.Bind(NetworkEndPoint.AnyIpv4);
+            var bindEndpoint = serverEndpoint.Family == NetworkFamily.Ipv6 ? NetworkEndpoint.AnyIpv6 : NetworkEndpoint.AnyIpv4;
+            int result = m_Driver.Bind(bindEndpoint);
             if (result != 0)
             {
                 Debug.LogError("Client failed to bind");
@@ -459,21 +550,21 @@ namespace Unity.Netcode.Transports.UTP
             return true;
         }
 
-        private bool ServerBindAndListen(NetworkEndPoint endPoint)
+        private bool ServerBindAndListen(NetworkEndpoint endPoint)
         {
             InitDriver();
 
             int result = m_Driver.Bind(endPoint);
             if (result != 0)
             {
-                Debug.LogError("Server failed to bind");
+                Debug.LogError("Server failed to bind. This is usually caused by another process being bound to the same port.");
                 return false;
             }
 
             result = m_Driver.Listen();
             if (result != 0)
             {
-                Debug.LogError("Server failed to listen");
+                Debug.LogError("Server failed to listen.");
                 return false;
             }
 
@@ -481,51 +572,13 @@ namespace Unity.Netcode.Transports.UTP
             return true;
         }
 
-        private static RelayAllocationId ConvertFromAllocationIdBytes(byte[] allocationIdBytes)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = allocationIdBytes)
-                {
-                    return RelayAllocationId.FromBytePointer(ptr, allocationIdBytes.Length);
-                }
-            }
-        }
-
-        private static RelayHMACKey ConvertFromHMAC(byte[] hmac)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = hmac)
-                {
-                    return RelayHMACKey.FromBytePointer(ptr, RelayHMACKey.k_Length);
-                }
-            }
-        }
-
-        private static RelayConnectionData ConvertConnectionData(byte[] connectionData)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = connectionData)
-                {
-                    return RelayConnectionData.FromBytePointer(ptr, RelayConnectionData.k_Length);
-                }
-            }
-        }
-
-        internal void SetMaxPayloadSize(int maxPayloadSize)
-        {
-            m_MaxPayloadSize = maxPayloadSize;
-        }
-
         private void SetProtocol(ProtocolType inProtocol)
         {
             m_ProtocolType = inProtocol;
         }
 
         /// <summary>Set the relay server data for the server.</summary>
-        /// <param name="ipv4Address">IP address of the relay server.</param>
+        /// <param name="ipv4Address">IP address or hostname of the relay server.</param>
         /// <param name="port">UDP port of the relay server.</param>
         /// <param name="allocationIdBytes">Allocation ID as a byte array.</param>
         /// <param name="keyBytes">Allocation key as a byte array.</param>
@@ -534,39 +587,21 @@ namespace Unity.Netcode.Transports.UTP
         /// <param name="isSecure">Whether the connection is secure (uses DTLS).</param>
         public void SetRelayServerData(string ipv4Address, ushort port, byte[] allocationIdBytes, byte[] keyBytes, byte[] connectionDataBytes, byte[] hostConnectionDataBytes = null, bool isSecure = false)
         {
-            RelayConnectionData hostConnectionData;
+            var hostConnectionData = hostConnectionDataBytes ?? connectionDataBytes;
-
+            m_RelayServerData = new RelayServerData(ipv4Address, port, allocationIdBytes, connectionDataBytes, hostConnectionData, keyBytes, isSecure);
-            if (!NetworkEndPoint.TryParse(ipv4Address, port, out var serverEndpoint))
+            SetProtocol(ProtocolType.RelayUnityTransport);
-            {
-                Debug.LogError($"Invalid address {ipv4Address}:{port}");
-
-                // We set this to default to cause other checks to fail to state you need to call this
-                // function again.
-                m_RelayServerData = default;
-                return;
         }
 
-            var allocationId = ConvertFromAllocationIdBytes(allocationIdBytes);
+        /// <summary>Set the relay server data (using the lower-level Unity Transport data structure).</summary>
-            var key = ConvertFromHMAC(keyBytes);
+        /// <param name="serverData">Data for the Relay server to use.</param>
-            var connectionData = ConvertConnectionData(connectionDataBytes);
+        public void SetRelayServerData(RelayServerData serverData)
-
-            if (hostConnectionDataBytes != null)
         {
-                hostConnectionData = ConvertConnectionData(hostConnectionDataBytes);
+            m_RelayServerData = serverData;
-            }
-            else
-            {
-                hostConnectionData = connectionData;
-            }
-
-            m_RelayServerData = new RelayServerData(ref serverEndpoint, 0, ref allocationId, ref connectionData, ref hostConnectionData, ref key, isSecure);
-            m_RelayServerData.ComputeNewNonce();
-
             SetProtocol(ProtocolType.RelayUnityTransport);
         }
 
         /// <summary>Set the relay server data for the host.</summary>
-        /// <param name="ipAddress">IP address of the relay server.</param>
+        /// <param name="ipAddress">IP address or hostname of the relay server.</param>
         /// <param name="port">UDP port of the relay server.</param>
         /// <param name="allocationId">Allocation ID as a byte array.</param>
         /// <param name="key">Allocation key as a byte array.</param>
@@ -578,7 +613,7 @@ namespace Unity.Netcode.Transports.UTP
         }
 
         /// <summary>Set the relay server data for the host.</summary>
-        /// <param name="ipAddress">IP address of the relay server.</param>
+        /// <param name="ipAddress">IP address or hostname of the relay server.</param>
         /// <param name="port">UDP port of the relay server.</param>
         /// <param name="allocationId">Allocation ID as a byte array.</param>
         /// <param name="key">Allocation key as a byte array.</param>
@@ -593,7 +628,7 @@ namespace Unity.Netcode.Transports.UTP
         /// <summary>
         /// Sets IP and Port information. This will be ignored if using the Unity Relay and you should call <see cref="SetRelayServerData"/>
         /// </summary>
-        /// <param name="ipv4Address">The remote IP address</param>
+        /// <param name="ipv4Address">The remote IP address (despite the name, can be an IPv6 address)</param>
         /// <param name="port">The remote port</param>
         /// <param name="listenAddress">The local listen address</param>
         public void SetConnectionData(string ipv4Address, ushort port, string listenAddress = null)
@@ -602,7 +637,7 @@ namespace Unity.Netcode.Transports.UTP
             {
                 Address = ipv4Address,
                 Port = port,
-                ServerListenAddress = listenAddress ?? string.Empty
+                ServerListenAddress = listenAddress ?? ipv4Address
             };
 
             SetProtocol(ProtocolType.UnityTransport);
@@ -613,7 +648,7 @@ namespace Unity.Netcode.Transports.UTP
         /// </summary>
         /// <param name="endPoint">The remote end point</param>
         /// <param name="listenEndPoint">The local listen endpoint</param>
-        public void SetConnectionData(NetworkEndPoint endPoint, NetworkEndPoint listenEndPoint = default)
+        public void SetConnectionData(NetworkEndpoint endPoint, NetworkEndpoint listenEndPoint = default)
         {
             string serverAddress = endPoint.Address.Split(':')[0];
 
@@ -634,6 +669,9 @@ namespace Unity.Netcode.Transports.UTP
         /// <param name="packetDelay">Packet delay in milliseconds.</param>
         /// <param name="packetJitter">Packet jitter in milliseconds.</param>
         /// <param name="dropRate">Packet drop percentage.</param>
+#if UTP_TRANSPORT_2_0_ABOVE
+        [Obsolete("SetDebugSimulatorParameters is no longer supported and has no effect. Use Network Simulator from the Multiplayer Tools package.", false)]
+#endif
         public void SetDebugSimulatorParameters(int packetDelay, int packetJitter, int dropRate)
         {
             if (m_Driver.IsCreated)
@@ -662,24 +700,30 @@ namespace Unity.Netcode.Transports.UTP
             else
             {
                 m_NetworkSettings.WithRelayParameters(ref m_RelayServerData, m_HeartbeatTimeoutMS);
-                return ServerBindAndListen(NetworkEndPoint.AnyIpv4);
+                return ServerBindAndListen(NetworkEndpoint.AnyIpv4);
             }
         }
 
-        // Send as many batched messages from the queue as possible.
+        [BurstCompile]
-        private void SendBatchedMessages(SendTarget sendTarget, BatchedSendQueue queue)
+        private struct SendBatchedMessagesJob : IJob
         {
-            var clientId = sendTarget.ClientId;
+            public NetworkDriver.Concurrent Driver;
+            public SendTarget Target;
+            public BatchedSendQueue Queue;
+            public NetworkPipeline ReliablePipeline;
+
+            public void Execute()
+            {
+                var clientId = Target.ClientId;
                 var connection = ParseClientId(clientId);
-            var pipeline = sendTarget.NetworkPipeline;
+                var pipeline = Target.NetworkPipeline;
 
-            while (!queue.IsEmpty)
+                while (!Queue.IsEmpty)
                 {
-                var result = m_Driver.BeginSend(pipeline, connection, out var writer);
+                    var result = Driver.BeginSend(pipeline, connection, out var writer);
                     if (result != (int)Networking.Transport.Error.StatusCode.Success)
                     {
-                    Debug.LogError("Error sending the message: " +
+                        Debug.LogError($"Error sending message: {ErrorUtilities.ErrorToFixedString(result, clientId)}");
-                        ErrorUtilities.ErrorToString((Networking.Transport.Error.StatusCode)result, clientId));
                         return;
                     }
 
@@ -689,31 +733,44 @@ namespace Unity.Netcode.Transports.UTP
                     // in the stream (the send queue does that automatically) we are sure they'll be
                     // reassembled properly at the other end. This allows us to lift the limit of ~44KB
                     // on reliable payloads (because of the reliable window size).
-                var written = pipeline == m_ReliableSequencedPipeline ? queue.FillWriterWithBytes(ref writer) : queue.FillWriterWithMessages(ref writer);
+                    var written = pipeline == ReliablePipeline ? Queue.FillWriterWithBytes(ref writer) : Queue.FillWriterWithMessages(ref writer);
 
-                result = m_Driver.EndSend(writer);
+                    result = Driver.EndSend(writer);
                     if (result == written)
                     {
                         // Batched message was sent successfully. Remove it from the queue.
-                    queue.Consume(written);
+                        Queue.Consume(written);
                     }
                     else
                     {
                         // Some error occured. If it's just the UTP queue being full, then don't log
                         // anything since that's okay (the unsent message(s) are still in the queue
-                    // and we'll retry sending the later). Otherwise log the error and remove the
+                        // and we'll retry sending them later). Otherwise log the error and remove the
                         // message from the queue (we don't want to resend it again since we'll likely
                         // just get the same error again).
                         if (result != (int)Networking.Transport.Error.StatusCode.NetworkSendQueueFull)
                         {
-                        Debug.LogError("Error sending the message: " + ErrorUtilities.ErrorToString((Networking.Transport.Error.StatusCode)result, clientId));
+                            Debug.LogError($"Error sending the message: {ErrorUtilities.ErrorToFixedString(result, clientId)}");
-                        queue.Consume(written);
+                            Queue.Consume(written);
                         }
 
                         return;
                     }
                 }
             }
+        }
+
+        // Send as many batched messages from the queue as possible.
+        private void SendBatchedMessages(SendTarget sendTarget, BatchedSendQueue queue)
+        {
+            new SendBatchedMessagesJob
+            {
+                Driver = m_Driver.ToConcurrent(),
+                Target = sendTarget,
+                Queue = queue,
+                ReliablePipeline = m_ReliableSequencedPipeline
+            }.Run();
+        }
 
         private bool AcceptConnection()
         {
@@ -907,7 +964,11 @@ namespace Unity.Netcode.Transports.UTP
         {
             //Don't need to dispose of the buffers, they are filled with data pointers.
             m_Driver.GetPipelineBuffers(pipeline,
+#if UTP_TRANSPORT_2_0_ABOVE
+                NetworkPipelineStageId.Get<NetworkMetricsPipelineStage>(),
+#else
                 NetworkPipelineStageCollection.GetStageId(typeof(NetworkMetricsPipelineStage)),
+#endif
                 networkConnection,
                 out _,
                 out _,
@@ -934,7 +995,11 @@ namespace Unity.Netcode.Transports.UTP
             }
 
             m_Driver.GetPipelineBuffers(m_ReliableSequencedPipeline,
+#if UTP_TRANSPORT_2_0_ABOVE
+                NetworkPipelineStageId.Get<ReliableSequencedPipelineStage>(),
+#else
                 NetworkPipelineStageCollection.GetStageId(typeof(ReliableSequencedPipelineStage)),
+#endif
                 networkConnection,
                 out _,
                 out _,
@@ -956,7 +1021,11 @@ namespace Unity.Netcode.Transports.UTP
             }
 
             m_Driver.GetPipelineBuffers(m_ReliableSequencedPipeline,
+#if UTP_TRANSPORT_2_0_ABOVE
+                NetworkPipelineStageId.Get<ReliableSequencedPipelineStage>(),
+#else
                 NetworkPipelineStageCollection.GetStageId(typeof(ReliableSequencedPipelineStage)),
+#endif
                 networkConnection,
                 out _,
                 out _,
@@ -1112,14 +1181,18 @@ namespace Unity.Netcode.Transports.UTP
 
             m_NetworkSettings = new NetworkSettings(Allocator.Persistent);
 
-#if !UNITY_WEBGL
             // If the user sends a message of exactly m_MaxPayloadSize in length, we need to
             // account for the overhead of its length when we store it in the send queue.
             var fragmentationCapacity = m_MaxPayloadSize + BatchedSendQueue.PerMessageOverhead;
+            m_NetworkSettings.WithFragmentationStageParameters(payloadCapacity: fragmentationCapacity);
 
-            m_NetworkSettings
+            // Bump the reliable window size to its maximum size of 64. Since NGO makes heavy use of
-                .WithFragmentationStageParameters(payloadCapacity: fragmentationCapacity)
+            // reliable delivery, we're better off with the increased window size compared to the
-                .WithBaselibNetworkInterfaceParameters(
+            // extra 4 bytes of header that this costs us.
+            m_NetworkSettings.WithReliableStageParameters(windowSize: 64);
+
+#if !UTP_TRANSPORT_2_0_ABOVE && !UNITY_WEBGL
+            m_NetworkSettings.WithBaselibNetworkInterfaceParameters(
                 receiveQueueCapacity: m_MaxPacketQueueSize,
                 sendQueueCapacity: m_MaxPacketQueueSize);
 #endif
@@ -1148,18 +1221,34 @@ namespace Unity.Netcode.Transports.UTP
         /// <param name="networkDelivery">The delivery type (QoS) to send data with</param>
         public override void Send(ulong clientId, ArraySegment<byte> payload, NetworkDelivery networkDelivery)
         {
-            if (payload.Count > m_MaxPayloadSize)
+            var pipeline = SelectSendPipeline(networkDelivery);
+
+            if (pipeline != m_ReliableSequencedPipeline && payload.Count > m_MaxPayloadSize)
             {
-                Debug.LogError($"Payload of size {payload.Count} larger than configured 'Max Payload Size' ({m_MaxPayloadSize}).");
+                Debug.LogError($"Unreliable payload of size {payload.Count} larger than configured 'Max Payload Size' ({m_MaxPayloadSize}).");
                 return;
             }
 
-            var pipeline = SelectSendPipeline(networkDelivery);
-
             var sendTarget = new SendTarget(clientId, pipeline);
             if (!m_SendQueue.TryGetValue(sendTarget, out var queue))
             {
-                queue = new BatchedSendQueue(Math.Max(m_MaxSendQueueSize, m_MaxPayloadSize));
+                // The maximum size of a send queue is determined according to the disconnection
+                // timeout. The idea being that if the send queue contains enough reliable data that
+                // sending it all out would take longer than the disconnection timeout, then there's
+                // no point storing even more in the queue (it would be like having a ping higher
+                // than the disconnection timeout, which is far into the realm of unplayability).
+                //
+                // The throughput used to determine what consists the maximum send queue size is
+                // the maximum theoritical throughput of the reliable pipeline assuming we only send
+                // on each update at 60 FPS, which turns out to be around 2.688 MB/s.
+                //
+                // Note that we only care about reliable throughput for send queues because that's
+                // the only case where a full send queue causes a connection loss. Full unreliable
+                // send queues are dealt with by flushing it out to the network or simply dropping
+                // new messages if that fails.
+                var maxCapacity = m_MaxSendQueueSize > 0 ? m_MaxSendQueueSize : m_DisconnectTimeoutMS * k_MaxReliableThroughput;
+
+                queue = new BatchedSendQueue(Math.Max(maxCapacity, m_MaxPayloadSize));
                 m_SendQueue.Add(sendTarget, queue);
             }
 
@@ -1173,8 +1262,7 @@ namespace Unity.Netcode.Transports.UTP
 
                     var ngoClientId = NetworkManager?.TransportIdToClientId(clientId) ?? clientId;
                     Debug.LogError($"Couldn't add payload of size {payload.Count} to reliable send queue. " +
-                        $"Closing connection {ngoClientId} as reliability guarantees can't be maintained. " +
+                        $"Closing connection {ngoClientId} as reliability guarantees can't be maintained.");
-                        $"Perhaps 'Max Send Queue Size' ({m_MaxSendQueueSize}) is too small for workload.");
 
                     if (clientId == m_ServerClientId)
                     {
@@ -1223,9 +1311,9 @@ namespace Unity.Netcode.Transports.UTP
             }
 
             var succeeded = ClientBindAndConnect();
-            if (!succeeded)
+            if (!succeeded && m_Driver.IsCreated)
             {
-                Shutdown();
+                m_Driver.Dispose();
             }
             return succeeded;
         }
@@ -1250,16 +1338,16 @@ namespace Unity.Netcode.Transports.UTP
             {
                 case ProtocolType.UnityTransport:
                     succeeded = ServerBindAndListen(ConnectionData.ListenEndPoint);
-                    if (!succeeded)
+                    if (!succeeded && m_Driver.IsCreated)
                     {
-                        Shutdown();
+                        m_Driver.Dispose();
                     }
                     return succeeded;
                 case ProtocolType.RelayUnityTransport:
                     succeeded = StartRelayServer();
-                    if (!succeeded)
+                    if (!succeeded && m_Driver.IsCreated)
                     {
-                        Shutdown();
+                        m_Driver.Dispose();
                     }
                     return succeeded;
                 default:
@@ -1285,10 +1373,10 @@ namespace Unity.Netcode.Transports.UTP
                 SendBatchedMessages(kvp.Key, kvp.Value);
             }
 
-            // The above flush only puts the message in UTP internal buffers, need the flush send
+            // The above flush only puts the message in UTP internal buffers, need an update to
-            // job to execute to actually get things out on the wire. This will also ensure any
+            // actually get the messages on the wire. (Normally a flush send would be sufficient,
-            // disconnect messages are sent out.
+            // but there might be disconnect messages and those require an update call.)
-            m_Driver.ScheduleFlushSend(default).Complete();
+            m_Driver.ScheduleUpdate().Complete();
 
             DisposeInternals();
 
@@ -1298,16 +1386,65 @@ namespace Unity.Netcode.Transports.UTP
             m_ServerClientId = 0;
         }
 
-        private void ConfigureSimulator()
+#if UTP_TRANSPORT_2_0_ABOVE
+        private void ConfigureSimulatorForUtp2()
+        {
+            // As DebugSimulator is deprecated, the 'packetDelayMs', 'packetJitterMs' and 'packetDropPercentage'
+            // parameters are set to the default and are supposed to be changed using Network Simulator tool instead.
+            m_NetworkSettings.WithSimulatorStageParameters(
+                maxPacketCount: 300, // TODO Is there any way to compute a better value?
+                maxPacketSize: NetworkParameterConstants.MTU,
+                packetDelayMs: 0,
+                packetJitterMs: 0,
+                packetDropPercentage: 0,
+                randomSeed: DebugSimulatorRandomSeed ?? (uint)System.Diagnostics.Stopwatch.GetTimestamp()
+                , mode: ApplyMode.AllPackets
+            );
+
+            m_NetworkSettings.WithNetworkSimulatorParameters();
+        }
+#else
+        private void ConfigureSimulatorForUtp1()
         {
             m_NetworkSettings.WithSimulatorStageParameters(
                 maxPacketCount: 300, // TODO Is there any way to compute a better value?
                 maxPacketSize: NetworkParameterConstants.MTU,
                 packetDelayMs: DebugSimulator.PacketDelayMS,
                 packetJitterMs: DebugSimulator.PacketJitterMS,
-                packetDropPercentage: DebugSimulator.PacketDropRate
+                packetDropPercentage: DebugSimulator.PacketDropRate,
+                randomSeed: DebugSimulatorRandomSeed ?? (uint)System.Diagnostics.Stopwatch.GetTimestamp()
             );
         }
+#endif
+
+        private string m_ServerPrivateKey;
+        private string m_ServerCertificate;
+
+        private string m_ServerCommonName;
+        private string m_ClientCaCertificate;
+
+        /// <summary>Set the server parameters for encryption.</summary>
+        /// <param name="serverCertificate">Public certificate for the server (PEM format).</param>
+        /// <param name="serverPrivateKey">Private key for the server (PEM format).</param>
+        public void SetServerSecrets(string serverCertificate, string serverPrivateKey)
+        {
+            m_ServerPrivateKey = serverPrivateKey;
+            m_ServerCertificate = serverCertificate;
+        }
+
+        /// <summary>Set the client parameters for encryption.</summary>
+        /// <remarks>
+        /// If the CA certificate is not provided, validation will be done against the OS/browser
+        /// certificate store. This is what you'd want if using certificates from a known provider.
+        /// For self-signed certificates, the CA certificate needs to be provided.
+        /// </remarks>
+        /// <param name="serverCommonName">Common name of the server (typically hostname).</param>
+        /// <param name="caCertificate">CA certificate used to validate the server's authenticity.</param>
+        public void SetClientSecrets(string serverCommonName, string caCertificate = null)
+        {
+            m_ServerCommonName = serverCommonName;
+            m_ClientCaCertificate = caCertificate;
+        }
 
         /// <summary>
         /// Creates the internal NetworkDriver
@@ -1322,25 +1459,118 @@ namespace Unity.Netcode.Transports.UTP
             out NetworkPipeline unreliableSequencedFragmentedPipeline,
             out NetworkPipeline reliableSequencedPipeline)
         {
-#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7 && !UTP_TRANSPORT_2_0_ABOVE
             NetworkPipelineStageCollection.RegisterPipelineStage(new NetworkMetricsPipelineStage());
 #endif
-            var maxFrameTimeMS = 0;
 
-#if UNITY_EDITOR || DEVELOPMENT_BUILD
+#if UTP_TRANSPORT_2_0_ABOVE && UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED
-            maxFrameTimeMS = 100;
+            ConfigureSimulatorForUtp2();
-            ConfigureSimulator();
+#elif !UTP_TRANSPORT_2_0_ABOVE && (UNITY_EDITOR || DEVELOPMENT_BUILD)
+            ConfigureSimulatorForUtp1();
 #endif
 
             m_NetworkSettings.WithNetworkConfigParameters(
                 maxConnectAttempts: transport.m_MaxConnectAttempts,
                 connectTimeoutMS: transport.m_ConnectTimeoutMS,
                 disconnectTimeoutMS: transport.m_DisconnectTimeoutMS,
-                heartbeatTimeoutMS: transport.m_HeartbeatTimeoutMS,
+#if UTP_TRANSPORT_2_0_ABOVE
-                maxFrameTimeMS: maxFrameTimeMS);
+                sendQueueCapacity: m_MaxPacketQueueSize,
+                receiveQueueCapacity: m_MaxPacketQueueSize,
+#endif
+                heartbeatTimeoutMS: transport.m_HeartbeatTimeoutMS);
 
+#if UNITY_WEBGL && !UNITY_EDITOR
+            if (NetworkManager.IsServer && m_ProtocolType != ProtocolType.RelayUnityTransport)
+            {
+                throw new Exception("WebGL as a server is not supported by Unity Transport, outside the Editor.");
+            }
+#endif
+
+#if UTP_TRANSPORT_2_0_ABOVE
+            if (m_UseEncryption)
+            {
+                if (m_ProtocolType == ProtocolType.RelayUnityTransport)
+                {
+                    if (m_RelayServerData.IsSecure == 0)
+                    {
+                        // log an error because we have mismatched configuration
+                        Debug.LogError("Mismatched security configuration, between Relay and local NetworkManager settings");
+                    }
+
+                    // No need to to anything else if using Relay because UTP will handle the
+                    // configuration of the security parameters on its own.
+                }
+                else
+                {
+                    if (NetworkManager.IsServer)
+                    {
+                        if (string.IsNullOrEmpty(m_ServerCertificate) || string.IsNullOrEmpty(m_ServerPrivateKey))
+                        {
+                            throw new Exception("In order to use encrypted communications, when hosting, you must set the server certificate and key.");
+                        }
+
+                        m_NetworkSettings.WithSecureServerParameters(m_ServerCertificate, m_ServerPrivateKey);
+                    }
+                    else
+                    {
+                        if (string.IsNullOrEmpty(m_ServerCommonName))
+                        {
+                            throw new Exception("In order to use encrypted communications, clients must set the server common name.");
+                        }
+                        else if (string.IsNullOrEmpty(m_ClientCaCertificate))
+                        {
+                            m_NetworkSettings.WithSecureClientParameters(m_ServerCommonName);
+                        }
+                        else
+                        {
+                            m_NetworkSettings.WithSecureClientParameters(m_ClientCaCertificate, m_ServerCommonName);
+                        }
+                    }
+                }
+            }
+#endif
+
+#if UTP_TRANSPORT_2_0_ABOVE
+            if (m_UseWebSockets)
+            {
+                driver = NetworkDriver.Create(new WebSocketNetworkInterface(), m_NetworkSettings);
+            }
+            else
+            {
+#if UNITY_WEBGL
+                Debug.LogWarning($"WebSockets were used even though they're not selected in NetworkManager. You should check {nameof(UseWebSockets)}', on the Unity Transport component, to silence this warning.");
+                driver = NetworkDriver.Create(new WebSocketNetworkInterface(), m_NetworkSettings);
+#else
+                driver = NetworkDriver.Create(new UDPNetworkInterface(), m_NetworkSettings);
+#endif
+            }
+#else
             driver = NetworkDriver.Create(m_NetworkSettings);
+#endif
 
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7 && UTP_TRANSPORT_2_0_ABOVE
+            driver.RegisterPipelineStage(new NetworkMetricsPipelineStage());
+#endif
+
+#if !UTP_TRANSPORT_2_0_ABOVE
+            SetupPipelinesForUtp1(driver,
+                out unreliableFragmentedPipeline,
+                out unreliableSequencedFragmentedPipeline,
+                out reliableSequencedPipeline);
+#else
+            SetupPipelinesForUtp2(driver,
+                out unreliableFragmentedPipeline,
+                out unreliableSequencedFragmentedPipeline,
+                out reliableSequencedPipeline);
+#endif
+        }
+
+#if !UTP_TRANSPORT_2_0_ABOVE
+        private void SetupPipelinesForUtp1(NetworkDriver driver,
+            out NetworkPipeline unreliableFragmentedPipeline,
+            out NetworkPipeline unreliableSequencedFragmentedPipeline,
+            out NetworkPipeline reliableSequencedPipeline)
+        {
 #if UNITY_EDITOR || DEVELOPMENT_BUILD
             if (DebugSimulator.PacketDelayMS > 0 || DebugSimulator.PacketDropRate > 0)
             {
@@ -1394,7 +1624,45 @@ namespace Unity.Netcode.Transports.UTP
                 );
             }
         }
+#else
+        private void SetupPipelinesForUtp2(NetworkDriver driver,
+            out NetworkPipeline unreliableFragmentedPipeline,
+            out NetworkPipeline unreliableSequencedFragmentedPipeline,
+            out NetworkPipeline reliableSequencedPipeline)
+        {
 
+            unreliableFragmentedPipeline = driver.CreatePipeline(
+                typeof(FragmentationPipelineStage)
+#if UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED
+                , typeof(SimulatorPipelineStage)
+#endif
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+                , typeof(NetworkMetricsPipelineStage)
+#endif
+            );
+
+            unreliableSequencedFragmentedPipeline = driver.CreatePipeline(
+                typeof(FragmentationPipelineStage),
+                typeof(UnreliableSequencedPipelineStage)
+#if UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED
+                , typeof(SimulatorPipelineStage)
+#endif
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+                , typeof(NetworkMetricsPipelineStage)
+#endif
+            );
+
+            reliableSequencedPipeline = driver.CreatePipeline(
+                typeof(ReliableSequencedPipelineStage)
+#if UNITY_MP_TOOLS_NETSIM_IMPLEMENTATION_ENABLED
+                , typeof(SimulatorPipelineStage)
+#endif
+#if MULTIPLAYER_TOOLS_1_0_0_PRE_7
+                , typeof(NetworkMetricsPipelineStage)
+#endif
+            );
+        }
+#endif
         // -------------- Utility Types -------------------------------------------------------------------------------
 
 

Runtime/com.unity.netcode.runtime.asmdef

@@ -30,6 +30,11 @@
             "name": "com.unity.multiplayer.tools",
             "expression": "1.0.0-pre.7",
             "define": "MULTIPLAYER_TOOLS_1_0_0_PRE_7"
+        },
+        {
+            "name": "com.unity.transport",
+            "expression": "2.0.0-exp",
+            "define": "UTP_TRANSPORT_2_0_ABOVE"
         }
     ]
 }

TestHelpers/Runtime/AssemblyInfo.cs

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