com.unity.netcode.gameobjects@1.2.0

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).

## [1.2.0] - 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 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)

CHANGELOG.md

@@ -6,7 +6,198 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
-## [1.0.0-pre.7] - 2022-04-01
+## [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 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
+
+- Changed version to 1.0.0. (#2046)
+
+## [1.0.0-pre.10] - 2022-06-21
+
+### Added
+
+- Added a new `OnTransportFailure` callback to `NetworkManager`. This callback is invoked when the manager's `NetworkTransport` encounters an unrecoverable error. Transport failures also cause the `NetworkManager` to shut down. Currently, this is only used by `UnityTransport` to signal a timeout of its connection to the Unity Relay servers. (#1994)
+- Added `NetworkEvent.TransportFailure`, which can be used by implementations of `NetworkTransport` to signal to `NetworkManager` that an unrecoverable error was encountered. (#1994)
+- Added test to ensure a warning occurs when nesting NetworkObjects in a NetworkPrefab (#1969)
+- Added `NetworkManager.RemoveNetworkPrefab(...)` to remove a prefab from the prefabs list (#1950)
+
+### Changed
+
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.1.0. (#2025)
+- (API Breaking) `ConnectionApprovalCallback` is no longer an `event` and will not allow more than 1 handler registered at a time. Also, `ConnectionApprovalCallback` is now an `Action<>` taking a `ConnectionApprovalRequest` and a `ConnectionApprovalResponse` that the client code must fill (#1972) (#2002)
+
+### Removed
+
+### Fixed
+- Fixed issue where dynamically spawned `NetworkObject`s could throw an exception if the scene of origin handle was zero (0) and the `NetworkObject` was already spawned. (#2017)
+- Fixed issue where `NetworkObject.Observers` was not being cleared when despawned. (#2009)
+- Fixed `NetworkAnimator` could not run in the server authoritative mode. (#2003)
+- Fixed issue where late joining clients would get a soft synchronization error if any in-scene placed NetworkObjects were parented under another `NetworkObject`. (#1985)
+- Fixed issue where `NetworkBehaviourReference` would throw a type cast exception if using `NetworkBehaviourReference.TryGet` and the component type was not found. (#1984)
+- Fixed `NetworkSceneManager` was not sending scene event notifications for the currently active scene and any additively loaded scenes when loading a new scene in `LoadSceneMode.Single` mode. (#1975)
+- Fixed issue where one or more clients disconnecting during a scene event would cause `LoadEventCompleted` or `UnloadEventCompleted` to wait until the `NetworkConfig.LoadSceneTimeOut` period before being triggered. (#1973)
+- Fixed issues when multiple `ConnectionApprovalCallback`s were registered (#1972)
+- Fixed a regression in serialization support: `FixedString`, `Vector2Int`, and `Vector3Int` types can now be used in NetworkVariables and RPCs again without requiring a `ForceNetworkSerializeByMemcpy<>` wrapper. (#1961)
+- Fixed generic types that inherit from NetworkBehaviour causing crashes at compile time. (#1976)
+- Fixed endless dialog boxes when adding a `NetworkBehaviour` to a `NetworkManager` or vice-versa. (#1947)
+- Fixed `NetworkAnimator` issue where it was only synchronizing parameters if the layer or state changed or was transitioning between states. (#1946)
+- Fixed `NetworkAnimator` issue where when it did detect a parameter had changed it would send all parameters as opposed to only the parameters that changed. (#1946)
+- Fixed `NetworkAnimator` issue where it was not always disposing the `NativeArray` that is allocated when spawned. (#1946)
+- Fixed `NetworkAnimator` issue where it was not taking the animation speed or state speed multiplier into consideration. (#1946)
+- Fixed `NetworkAnimator` issue where it was not properly synchronizing late joining clients if they joined while `Animator` was transitioning between states. (#1946)
+- Fixed `NetworkAnimator` issue where the server was not relaying changes to non-owner clients when a client was the owner. (#1946)
+- Fixed issue where the `PacketLoss` metric for tools would return the packet loss over a connection lifetime instead of a single frame. (#2004)
+
+## [1.0.0-pre.9] - 2022-05-10
+
+### Fixed
+
+- Fixed Hosting again after failing to host now works correctly (#1938)
+- Fixed NetworkManager to cleanup connected client lists after stopping (#1945)
+- Fixed NetworkHide followed by NetworkShow on the same frame works correctly (#1940)
+
+## [1.0.0-pre.8] - 2022-04-27
+
+### Changed
+
+- `unmanaged` structs are no longer universally accepted as RPC parameters because some structs (i.e., structs with pointers in them, such as `NativeList<T>`) can't be supported by the default memcpy struct serializer. Structs that are intended to be serialized across the network must add `INetworkSerializeByMemcpy` to the interface list (i.e., `struct Foo : INetworkSerializeByMemcpy`). This interface is empty and just serves to mark the struct as compatible with memcpy serialization. For external structs you can't edit, you can pass them to RPCs by wrapping them in `ForceNetworkSerializeByMemcpy<T>`. (#1901)
+- Changed requirement to register in-scene placed NetworkObjects with `NetworkManager` in order to respawn them.  In-scene placed NetworkObjects are now automatically tracked during runtime and no longer need to be registered as a NetworkPrefab.  (#1898)
+
+### Removed
+
+- Removed `SIPTransport` (#1870)
+- 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)
+- Fixed issue during client synchronization if 'ValidateSceneBeforeLoading' returned false it would halt the client synchronization process resulting in a client that was approved but not synchronized or fully connected with the server. (#1883)
+- Fixed an issue where UNetTransport.StartServer would return success even if the underlying transport failed to start (#854)
+- Passing generic types to RPCs no longer causes a native crash (#1901)
+- Fixed a compile failure when compiling against com.unity.nuget.mono-cecil >= 1.11.4 (#1920)
+- Fixed an issue where calling `Shutdown` on a `NetworkManager` that was already shut down would cause an immediate shutdown the next time it was started (basically the fix makes `Shutdown` idempotent). (#1877)
+
+## [1.0.0-pre.7] - 2022-04-06
 
 ### Added
 
@@ -15,9 +206,12 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Added `NetworkVariableWritePermission` to `NetworkVariableBase` and implemented `Owner` client writable netvars. (#1762)
 - `UnityTransport` settings can now be set programmatically. (#1845)
 - `FastBufferWriter` and Reader IsInitialized property. (#1859)
+- Prefabs can now be added to the network at **runtime** (i.e., from an addressable asset). If `ForceSamePrefabs` is false, this can happen after a connection has been formed. (#1882)
+- When `ForceSamePrefabs` is false, a configurable delay (default 1 second, configurable via `NetworkConfig.SpawnTimeout`) has been introduced to gracefully handle race conditions where a spawn call has been received for an object whose prefab is still being loaded. (#1882)
 
 ### Changed
 
+- Changed `NetcodeIntegrationTestHelpers` to use `UnityTransport` (#1870)
 - Updated `UnityTransport` dependency on `com.unity.transport` to 1.0.0 (#1849)
 
 ### Removed
@@ -27,6 +221,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `com.unity.collections` dependency from the package (#1849)
 
 ### Fixed
+
 - Fixed in-scene placed NetworkObjects not being found/ignored after a client disconnects and then reconnects. (#1850)
 - Fixed issue where `UnityTransport` send queues were not flushed when calling `DisconnectLocalClient` or `DisconnectRemoteClient`. (#1847)
 - Fixed NetworkBehaviour dependency verification check for an existing NetworkObject not searching from root parent transform relative GameObject. (#1841)
@@ -46,12 +241,12 @@ 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)
 
-### Changed
-
 ### Fixed
+
 - Fixed an issue where sometimes the first client to connect to the server could see messages from the server as coming from itself. (#1683)
 - Fixed an issue where clients seemed to be able to send messages to ClientId 1, but these messages would actually still go to the server (id 0) instead of that client. (#1683)
 - Improved clarity of error messaging when a client attempts to send a message to a destination other than the server, which isn't allowed. (#1683)
@@ -103,6 +298,7 @@ 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)
@@ -117,6 +313,7 @@ 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)
@@ -128,7 +325,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 - ResetTrigger function to NetworkAnimator (#1327)
 
-### Fixed 
+### Fixed
 
 - Overflow exception when syncing Animator state. (#1327)
 - Added `try`/`catch` around RPC calls, preventing exception from causing further RPC calls to fail (#1329)
@@ -153,7 +350,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Added `ClientNetworkTransform` sample to the SDK package (#1168)
 - Added `Bootstrap` sample to the SDK package (#1140)
 - Enhanced `NetworkSceneManager` implementation with additive scene loading capabilities (#1080, #955, #913)
-  - `NetworkSceneManager.OnSceneEvent` provides improved scene event notificaitons  
+  - `NetworkSceneManager.OnSceneEvent` provides improved scene event notificaitons
 - Enhanced `NetworkTransform` implementation with per axis/component based and threshold based state replication (#1042, #1055, #1061, #1084, #1101)
 - Added a jitter-resistent `BufferedLinearInterpolator<T>` for `NetworkTransform` (#1060)
 - Implemented `NetworkPrefabHandler` that provides support for object pooling and `NetworkPrefab` overrides (#1073, #1004, #977, #905,#749, #727)
@@ -210,7 +407,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `NetworkDictionary`, `NetworkSet` (#1149)
 - Removed `NetworkVariableSettings` (#1097)
 - Removed predefined `NetworkVariable<T>` types (#1093)
-    - Removed `NetworkVariableBool`, `NetworkVariableByte`, `NetworkVariableSByte`, `NetworkVariableUShort`, `NetworkVariableShort`, `NetworkVariableUInt`, `NetworkVariableInt`, `NetworkVariableULong`, `NetworkVariableLong`, `NetworkVariableFloat`, `NetworkVariableDouble`, `NetworkVariableVector2`, `NetworkVariableVector3`, `NetworkVariableVector4`, `NetworkVariableColor`, `NetworkVariableColor32`, `NetworkVariableRay`, `NetworkVariableQuaternion`
+  - Removed `NetworkVariableBool`, `NetworkVariableByte`, `NetworkVariableSByte`, `NetworkVariableUShort`, `NetworkVariableShort`, `NetworkVariableUInt`, `NetworkVariableInt`, `NetworkVariableULong`, `NetworkVariableLong`, `NetworkVariableFloat`, `NetworkVariableDouble`, `NetworkVariableVector2`, `NetworkVariableVector3`, `NetworkVariableVector4`, `NetworkVariableColor`, `NetworkVariableColor32`, `NetworkVariableRay`, `NetworkVariableQuaternion`
 - Removed `NetworkChannel` and `MultiplexTransportAdapter` (#1133)
 - Removed ILPP backend for 2019.4, minimum required version is 2020.3+ (#895)
 - `NetworkManager.NetworkConfig` had the following properties removed: (#1080)
@@ -282,14 +479,14 @@ This is the initial experimental Unity MLAPI Package, v0.1.0.
 - Integrated MLAPI with the Unity Profiler for versions 2020.2 and later:
   - Added new profiler modules for MLAPI that report important network data.
   - Attached the profiler to a remote player to view network data over the wire.
-- A test project is available for building and experimenting with MLAPI features. This project is available in the MLAPI GitHub [testproject folder](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/tree/release/0.1.0/testproject). 
+- A test project is available for building and experimenting with MLAPI features. This project is available in the MLAPI GitHub [testproject folder](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/tree/release/0.1.0/testproject).
 - Added a [MLAPI Community Contributions](https://github.com/Unity-Technologies/mlapi-community-contributions/tree/master/com.mlapi.contrib.extensions) new GitHub repository to accept extensions from the MLAPI community. Current extensions include moved MLAPI features for lag compensation (useful for Server Authoritative actions) and `TrackedObject`.
 
 ### Changed
 
 - [GitHub 520](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/520): MLAPI now uses the Unity Package Manager for installation management.
-- Added functionality and usability to `NetworkVariable`, previously called `NetworkVar`. Updates enhance options and fully replace the need for `SyncedVar`s. 
-- [GitHub 507](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/507): Reimplemented `NetworkAnimator`, which synchronizes animation states for networked objects. 
+- Added functionality and usability to `NetworkVariable`, previously called `NetworkVar`. Updates enhance options and fully replace the need for `SyncedVar`s.
+- [GitHub 507](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/507): Reimplemented `NetworkAnimator`, which synchronizes animation states for networked objects.
 - GitHub [444](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/444) and [455](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/455): Channels are now represented as bytes instead of strings.
 
 For users of previous versions of MLAPI, this release renames APIs due to refactoring. All obsolete marked APIs have been removed as per [GitHub 513](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/513) and [GitHub 514](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/514).
@@ -322,7 +519,7 @@ For users of previous versions of MLAPI, this release renames APIs due to refact
 
 ### Fixed
 
-- [GitHub 460](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/460): Fixed an issue for RPC where the host-server was not receiving RPCs from the host-client and vice versa without the loopback flag set in `NetworkingManager`. 
+- [GitHub 460](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/460): Fixed an issue for RPC where the host-server was not receiving RPCs from the host-client and vice versa without the loopback flag set in `NetworkingManager`.
 - Fixed an issue where data in the Profiler was incorrectly aggregated and drawn, which caused the profiler data to increment indefinitely instead of resetting each frame.
 - Fixed an issue the client soft-synced causing PlayMode client-only scene transition issues, caused when running the client in the editor and the host as a release build. Users may have encountered a soft sync of `NetworkedInstanceId` issues in the `SpawnManager.ClientCollectSoftSyncSceneObjectSweep` method.
 - [GitHub 458](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/458): Fixed serialization issues in `NetworkList` and `NetworkDictionary` when running in Server mode.
@@ -337,10 +534,10 @@ With a new release of MLAPI in Unity, some features have been removed:
 - SyncVars have been removed from MLAPI. Use `NetworkVariable`s in place of this functionality. <!-- MTT54 -->
 - [GitHub 527](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/527): Lag compensation systems and `TrackedObject` have moved to the new [MLAPI Community Contributions](https://github.com/Unity-Technologies/mlapi-community-contributions/tree/master/com.mlapi.contrib.extensions) repo.
 - [GitHub 509](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/509): Encryption has been removed from MLAPI. The `Encryption` option in `NetworkConfig` on the `NetworkingManager` is not available in this release. This change will not block game creation or running. A current replacement for this functionality is not available, and may be developed in future releases. See the following changes:
-    - Removed `SecuritySendFlags` from all APIs.
-    - Removed encryption, cryptography, and certificate configurations from APIs including `NetworkManager` and `NetworkConfig`.
-    - Removed "hail handshake", including `NetworkManager` implementation and `NetworkConstants` entries.
-    - Modified `RpcQueue` and `RpcBatcher` internals to remove encryption and authentication from reading and writing.
+  - Removed `SecuritySendFlags` from all APIs.
+  - Removed encryption, cryptography, and certificate configurations from APIs including `NetworkManager` and `NetworkConfig`.
+  - Removed "hail handshake", including `NetworkManager` implementation and `NetworkConstants` entries.
+  - Modified `RpcQueue` and `RpcBatcher` internals to remove encryption and authentication from reading and writing.
 - Removed the previous MLAPI Profiler editor window from Unity versions 2020.2 and later.
 - Removed previous MLAPI Convenience and Performance RPC APIs with the new standard RPC API. See [RFC #1](https://github.com/Unity-Technologies/com.unity.multiplayer.rfcs/blob/master/text/0001-std-rpc-api.md) for details.
 - [GitHub 520](https://github.com/Unity-Technologies/com.unity.multiplayer.mlapi/pull/520): Removed the MLAPI Installer.
@@ -353,7 +550,7 @@ With a new release of MLAPI in Unity, some features have been removed:
 - For `NetworkVariable`, the `NetworkDictionary` `List` and `Set` must use the `reliableSequenced` channel.
 - `NetworkObjects`s are supported but when spawning a prefab with nested child network objects you have to manually call spawn on them
 - `NetworkTransform` have the following issues:
-  - Replicated objects may have jitter. 
+  - Replicated objects may have jitter.
   - The owner is always authoritative about the object's position.
   - Scale is not synchronized.
 - Connection Approval is not called on the host client.

Components/Interpolator/BufferedLinearInterpolator.cs

@@ -4,14 +4,14 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
-
     /// <summary>
     /// Solves for incoming values that are jittered
     /// Partially solves for message loss. Unclamped lerping helps hide this, but not completely
     /// </summary>
-    /// <typeparam name="T"></typeparam>
-    internal abstract class BufferedLinearInterpolator<T> where T : struct
+    /// <typeparam name="T">The type of interpolated value</typeparam>
+    public abstract class BufferedLinearInterpolator<T> where T : struct
     {
+        internal float MaxInterpolationBound = 3.0f;
         private struct BufferedItem
         {
             public T Item;
@@ -24,6 +24,10 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// There's two factors affecting interpolation: buffering (set in NetworkManager's NetworkTimeSystem) and interpolation time, which is the amount of time it'll take to reach the target. This is to affect the second one.
+        /// </summary>
+        public float MaximumInterpolationTime = 0.1f;
 
         private const double k_SmallValue = 9.999999439624929E-11; // copied from Vector3's equal operator
 
@@ -69,6 +73,9 @@ namespace Unity.Netcode
 
         private bool InvalidState => m_Buffer.Count == 0 && m_LifetimeConsumedCount == 0;
 
+        /// <summary>
+        /// Resets interpolator to initial state
+        /// </summary>
         public void Clear()
         {
             m_Buffer.Clear();
@@ -76,6 +83,11 @@ namespace Unity.Netcode
             m_StartTimeConsumed = 0.0d;
         }
 
+        /// <summary>
+        /// Teleports current interpolation value to targetValue.
+        /// </summary>
+        /// <param name="targetValue">The target value to teleport instantly</param>
+        /// <param name="serverTime">The current server time</param>
         public void ResetTo(T targetValue, double serverTime)
         {
             m_LifetimeConsumedCount = 1;
@@ -89,7 +101,6 @@ namespace Unity.Netcode
             Update(0, serverTime, serverTime);
         }
 
-
         // todo if I have value 1, 2, 3 and I'm treating 1 to 3, I shouldn't interpolate between 1 and 3, I should interpolate from 1 to 2, then from 2 to 3 to get the best path
         private void TryConsumeFromBuffer(double renderTime, double serverTime)
         {
@@ -151,6 +162,7 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="deltaTime">time since call</param>
         /// <param name="serverTime">current server time</param>
+        /// <returns>The newly interpolated value of type 'T'</returns>
         public T Update(float deltaTime, NetworkTime serverTime)
         {
             return Update(deltaTime, serverTime.TimeTicksAgo(1).Time, serverTime.Time);
@@ -162,6 +174,7 @@ namespace Unity.Netcode
         /// <param name="deltaTime">time since last call</param>
         /// <param name="renderTime">our current time</param>
         /// <param name="serverTime">current server time</param>
+        /// <returns>The newly interpolated value of type 'T'</returns>
         public T Update(float deltaTime, double renderTime, double serverTime)
         {
             TryConsumeFromBuffer(renderTime, serverTime);
@@ -196,23 +209,26 @@ namespace Unity.Netcode
                         t = 0.0f;
                     }
 
-                    if (t > 3.0f) // max extrapolation
+                    if (t > MaxInterpolationBound) // max extrapolation
                     {
                         // TODO this causes issues with teleport, investigate
-                        // todo make this configurable
                         t = 1.0f;
                     }
                 }
 
                 var target = InterpolateUnclamped(m_InterpStartValue, m_InterpEndValue, t);
-                float maxInterpTime = 0.1f;
-                m_CurrentInterpValue = Interpolate(m_CurrentInterpValue, target, deltaTime / maxInterpTime); // second interpolate to smooth out extrapolation jumps
+                m_CurrentInterpValue = Interpolate(m_CurrentInterpValue, target, deltaTime / MaximumInterpolationTime); // second interpolate to smooth out extrapolation jumps
             }
 
             m_NbItemsReceivedThisFrame = 0;
             return m_CurrentInterpValue;
         }
 
+        /// <summary>
+        /// Add measurements to be used during interpolation. These will be buffered before being made available to be displayed as "latest value".
+        /// </summary>
+        /// <param name="newMeasurement">The new measurement value to use</param>
+        /// <param name="sentTime">The time to record for measurement</param>
         public void AddMeasurement(T newMeasurement, double sentTime)
         {
             m_NbItemsReceivedThisFrame++;
@@ -232,6 +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);
@@ -239,39 +257,75 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Gets latest value from the interpolator. This is updated every update as time goes by.
+        /// </summary>
+        /// <returns>The current interpolated value of type 'T'</returns>
         public T GetInterpolatedValue()
         {
             return m_CurrentInterpValue;
         }
 
+        /// <summary>
+        /// Method to override and adapted to the generic type. This assumes interpolation for that value will be clamped.
+        /// </summary>
+        /// <param name="start">The start value (min)</param>
+        /// <param name="end">The end value (max)</param>
+        /// <param name="time">The time value used to interpolate between start and end values (pos)</param>
+        /// <returns>The interpolated value</returns>
         protected abstract T Interpolate(T start, T end, float time);
+
+        /// <summary>
+        /// Method to override and adapted to the generic type. This assumes interpolation for that value will not be clamped.
+        /// </summary>
+        /// <param name="start">The start value (min)</param>
+        /// <param name="end">The end value (max)</param>
+        /// <param name="time">The time value used to interpolate between start and end values (pos)</param>
+        /// <returns>The interpolated value</returns>
         protected abstract T InterpolateUnclamped(T start, T end, float time);
     }
 
-
-    internal class BufferedLinearInterpolatorFloat : BufferedLinearInterpolator<float>
+    /// <inheritdoc />
+    /// <remarks>
+    /// This is a buffered linear interpolator for a <see cref="float"/> type value
+    /// </remarks>
+    public class BufferedLinearInterpolatorFloat : BufferedLinearInterpolator<float>
     {
+        /// <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 />
         protected override float Interpolate(float start, float end, float time)
         {
             return Mathf.Lerp(start, end, time);
         }
     }
 
-    internal class BufferedLinearInterpolatorQuaternion : BufferedLinearInterpolator<Quaternion>
+    /// <inheritdoc />
+    /// <remarks>
+    /// This is a buffered linear interpolator for a <see cref="Quaternion"/> type value
+    /// </remarks>
+    public class BufferedLinearInterpolatorQuaternion : BufferedLinearInterpolator<Quaternion>
     {
+        /// <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

@@ -5,77 +5,98 @@ namespace Unity.Netcode.Components
 {
     /// <summary>
     /// NetworkRigidbody allows for the use of <see cref="Rigidbody"/> on network objects. By controlling the kinematic
-    /// mode of the rigidbody and disabling it on all peers but the authoritative one.
+    /// mode of the <see cref="Rigidbody"/> and disabling it on all peers but the authoritative one.
     /// </summary>
     [RequireComponent(typeof(Rigidbody))]
     [RequireComponent(typeof(NetworkTransform))]
+    [AddComponentMenu("Netcode/Network Rigidbody")]
     public class NetworkRigidbody : NetworkBehaviour
     {
+        /// <summary>
+        /// Determines if we are server (true) or owner (false) authoritative
+        /// </summary>
+        private bool m_IsServerAuthoritative;
+
         private Rigidbody m_Rigidbody;
         private NetworkTransform m_NetworkTransform;
-
-        private bool m_OriginalKinematic;
         private RigidbodyInterpolation m_OriginalInterpolation;
 
-        // Used to cache the authority state of this rigidbody during the last frame
+        // Used to cache the authority state of this Rigidbody during the last frame
         private bool m_IsAuthority;
 
-        /// <summary>
-        /// Gets a bool value indicating whether this <see cref="NetworkRigidbody"/> on this peer currently holds authority.
-        /// </summary>
-        private bool HasAuthority => m_NetworkTransform.CanCommitToTransform;
-
         private void Awake()
         {
-            m_Rigidbody = GetComponent<Rigidbody>();
             m_NetworkTransform = GetComponent<NetworkTransform>();
+            m_IsServerAuthoritative = m_NetworkTransform.IsServerAuthoritative();
+
+            m_Rigidbody = GetComponent<Rigidbody>();
+            m_OriginalInterpolation = m_Rigidbody.interpolation;
+
+            // Set interpolation to none if NetworkTransform is handling interpolation, otherwise it sets it to the original value
+            m_Rigidbody.interpolation = m_NetworkTransform.Interpolate ? RigidbodyInterpolation.None : m_OriginalInterpolation;
+
+            // Turn off physics for the rigid body until spawned, otherwise
+            // clients can run fixed update before the first full
+            // NetworkTransform update
+            m_Rigidbody.isKinematic = true;
         }
 
-        private void FixedUpdate()
+        /// <summary>
+        /// For owner authoritative (i.e. ClientNetworkTransform)
+        /// we adjust our authority when we gain ownership
+        /// </summary>
+        public override void OnGainedOwnership()
         {
-            if (NetworkManager.IsListening)
-            {
-                if (HasAuthority != m_IsAuthority)
-                {
-                    m_IsAuthority = HasAuthority;
-                    UpdateRigidbodyKinematicMode();
-                }
-            }
+            UpdateOwnershipAuthority();
         }
 
-        // Puts the rigidbody in a kinematic non-interpolated mode on everyone but the server.
-        private void UpdateRigidbodyKinematicMode()
+        /// <summary>
+        /// For owner authoritative(i.e. ClientNetworkTransform)
+        /// we adjust our authority when we have lost ownership
+        /// </summary>
+        public override void OnLostOwnership()
         {
-            if (m_IsAuthority == false)
-            {
-                m_OriginalKinematic = m_Rigidbody.isKinematic;
-                m_Rigidbody.isKinematic = true;
+            UpdateOwnershipAuthority();
+        }
 
-                m_OriginalInterpolation = m_Rigidbody.interpolation;
-                // Set interpolation to none, the NetworkTransform component interpolates the position of the object.
-                m_Rigidbody.interpolation = RigidbodyInterpolation.None;
+        /// <summary>
+        /// Sets the authority differently depending upon
+        /// whether it is server or owner authoritative
+        /// </summary>
+        private void UpdateOwnershipAuthority()
+        {
+            if (m_IsServerAuthoritative)
+            {
+                m_IsAuthority = NetworkManager.IsServer;
             }
             else
             {
-                // Resets the rigidbody back to it's non replication only state. Happens on shutdown and when authority is lost
-                m_Rigidbody.isKinematic = m_OriginalKinematic;
-                m_Rigidbody.interpolation = m_OriginalInterpolation;
+                m_IsAuthority = IsOwner;
             }
+
+            // If you have authority then you are not kinematic
+            m_Rigidbody.isKinematic = !m_IsAuthority;
+
+            // Set interpolation of the Rigidbody based on authority
+            // With authority: let local transform handle interpolation
+            // Without authority: let the NetworkTransform handle interpolation
+            m_Rigidbody.interpolation = m_IsAuthority ? m_OriginalInterpolation : RigidbodyInterpolation.None;
         }
 
         /// <inheritdoc />
         public override void OnNetworkSpawn()
         {
-            m_IsAuthority = HasAuthority;
-            m_OriginalKinematic = m_Rigidbody.isKinematic;
-            m_OriginalInterpolation = m_Rigidbody.interpolation;
-            UpdateRigidbodyKinematicMode();
+            UpdateOwnershipAuthority();
         }
 
         /// <inheritdoc />
         public override void OnNetworkDespawn()
         {
-            UpdateRigidbodyKinematicMode();
+            m_Rigidbody.interpolation = m_OriginalInterpolation;
+            // Turn off physics for the rigid body until spawned, otherwise
+            // non-owners can run fixed updates before the first full
+            // NetworkTransform update and physics will be applied (i.e. gravity, etc)
+            m_Rigidbody.isKinematic = true;
         }
     }
 }

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;

Documentation~/Index.md

@@ -1,31 +0,0 @@
-# About Netcode for GameObjects
-
-Unity Netcode for GameObjects is a high-level networking library built to abstract networking. This allows developers to focus on the game rather than low level protocols and networking frameworks. 
-
-## Guides
-
-See guides below to install Unity Netcode for GameObjects, set up your project, and get started with your first networked game:
-
-* [Documentation](https://docs-multiplayer.unity3d.com/docs/getting-started/about-mlapi)
-* [Installation](https://docs-multiplayer.unity3d.com/docs/migration/install)
-* [First Steps](https://docs-multiplayer.unity3d.com/docs/tutorials/helloworld/helloworldintro)
-* [API Reference](https://docs-multiplayer.unity3d.com/docs/mlapi-api/introduction)
-
-# Technical details
-
-## Requirements
-
-This version of Netcode for GameObjects is compatible with the following Unity versions and platforms:
-
-* 2020.3 and later
-* Windows, Mac, Linux platforms
-
-## Document revision history
-
-|Date|Reason|
-|---|---|
-|March 10, 2021|Document created. Matches package version 0.1.0|
-|June 1, 2021|Update and add links for additional content. Matches patch version 0.1.0 and hotfixes.|
-|June 3, 2021|Update document to acknowledge Unity min version change. Matches package version 0.2.0|
-|August 5, 2021|Update product/package name|
-|September 9,2021|Updated the links and name of the file.|

Documentation~/index.md

@@ -0,0 +1,35 @@
+# About Netcode for GameObjects
+
+Netcode for GameObjects is a Unity package that provides networking capabilities to GameObject & MonoBehaviour workflows.
+
+## Guides
+
+See guides below to install Unity Netcode for GameObjects, set up your project, and get started with your first networked game:
+
+- [Documentation](https://docs-multiplayer.unity3d.com/netcode/current/about)
+- [Installation](https://docs-multiplayer.unity3d.com/netcode/current/migration/install)
+- [First Steps](https://docs-multiplayer.unity3d.com/netcode/current/tutorials/helloworld/helloworldintro)
+- [API Reference](https://docs-multiplayer.unity3d.com/netcode/current/api/introduction)
+
+# Technical details
+
+## Requirements
+
+Netcode for GameObjects targets the following Unity versions:
+- Unity 2020.3, 2021.1, 2021.2 and 2021.3
+
+On the following runtime platforms:
+- Windows, MacOS, and Linux
+- iOS and Android
+- Most closed platforms, such as consoles. Contact us for more information about specific closed platforms.
+
+## Document revision history
+
+|Date|Reason|
+|---|---|
+|March 10, 2021|Document created. Matches package version 0.1.0|
+|June 1, 2021|Update and add links for additional content. Matches patch version 0.1.0 and hotfixes.|
+|June 3, 2021|Update document to acknowledge Unity min version change. Matches package version 0.2.0|
+|August 5, 2021|Update product/package name|
+|September 9,2021|Updated the links and name of the file.|
+|April 20, 2022|Updated links|

Editor/CodeGen/CodeGenHelpers.cs

@@ -6,6 +6,7 @@ using System.Text;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 using Mono.Cecil.Rocks;
+using Unity.Collections;
 using Unity.CompilationPipeline.Common.Diagnostics;
 using Unity.CompilationPipeline.Common.ILPostProcessing;
 using UnityEngine;
@@ -14,6 +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;
@@ -27,6 +32,8 @@ namespace Unity.Netcode.Editor.CodeGen
         public static readonly string ServerRpcSendParams_FullName = typeof(ServerRpcSendParams).FullName;
         public static readonly string ServerRpcReceiveParams_FullName = typeof(ServerRpcReceiveParams).FullName;
         public static readonly string INetworkSerializable_FullName = typeof(INetworkSerializable).FullName;
+        public static readonly string INetworkSerializeByMemcpy_FullName = typeof(INetworkSerializeByMemcpy).FullName;
+        public static readonly string IUTF8Bytes_FullName = typeof(IUTF8Bytes).FullName;
         public static readonly string UnityColor_FullName = typeof(Color).FullName;
         public static readonly string UnityColor32_FullName = typeof(Color32).FullName;
         public static readonly string UnityVector2_FullName = typeof(Vector2).FullName;
@@ -77,6 +84,35 @@ namespace Unity.Netcode.Editor.CodeGen
             return false;
         }
 
+        public static string FullNameWithGenericParameters(this TypeReference typeReference, GenericParameter[] contextGenericParameters, TypeReference[] contextGenericParameterTypes)
+        {
+            var name = typeReference.FullName;
+            if (typeReference.HasGenericParameters)
+            {
+                name += "<";
+                for (var i = 0; i < typeReference.Resolve().GenericParameters.Count; ++i)
+                {
+                    if (i != 0)
+                    {
+                        name += ", ";
+                    }
+
+                    for (var j = 0; j < contextGenericParameters.Length; ++j)
+                    {
+                        if (typeReference.GenericParameters[i].FullName == contextGenericParameters[i].FullName)
+                        {
+                            name += contextGenericParameterTypes[i].FullName;
+                            break;
+                        }
+                    }
+                }
+
+                name += ">";
+            }
+
+            return name;
+        }
+
         public static bool HasInterface(this TypeReference typeReference, string interfaceTypeFullName)
         {
             if (typeReference.IsArray)
@@ -87,6 +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);
             }
@@ -348,5 +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) =>
-            compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName ||
-            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.Name == 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);
-            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerType);
-            foreach (var fieldInfo in messageWithHandlerType.GetFields())
+            TypeDefinition messageHandlerTypeDef = null;
+            TypeDefinition versionGetterTypeDef = null;
+            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 methodInfo in typeType.GetMethods())
+            foreach (var methodDef in typeTypeDef.Methods)
             {
-                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 fieldInfo in ilppMessageProviderType.GetFields(BindingFlags.Static | BindingFlags.NonPublic))
+            foreach (var fieldDef in ilppMessageProviderTypeDef.Fields)
             {
-                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 methodInfo in listType.GetMethods())
+            foreach (var methodDef in listTypeDef.Methods)
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
-                    case nameof(List<MessagingSystem.MessageWithHandler>.Add):
-                        m_List_Add_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                    case "Add":
+                        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 methodInfo in messagingSystemType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var methodDef in messagingSystemTypeDef.Methods)
             {
-                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
-        // 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)
+        // Creates a static module constructor (which is executed when the module is loaded) that registers all the message types in the assembly with MessagingSystem.
+        // This is the same behavior as annotating a static method with [ModuleInitializer] in standardized C# (that attribute doesn't exist in Unity, but the static module constructor still works).
         // https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.moduleinitializerattribute?view=net-5.0
         // https://web.archive.org/web/20100212140402/http://blogs.msdn.com/junfeng/archive/2005/11/19/494914.aspx
         private void CreateModuleInitializer(AssemblyDefinition assembly, List<TypeDefinition> 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

@@ -2,18 +2,14 @@ using System;
 using System.IO;
 using System.Linq;
 using System.Collections.Generic;
-using System.Reflection;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
-using Mono.Cecil.Rocks;
 using Unity.CompilationPipeline.Common.Diagnostics;
 using Unity.CompilationPipeline.Common.ILPostProcessing;
 using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostProcessor;
-using MethodAttributes = Mono.Cecil.MethodAttributes;
 
 namespace Unity.Netcode.Editor.CodeGen
 {
-
     internal sealed class INetworkSerializableILPP : ILPPInterface
     {
         public override ILPPInterface GetInstance() => this;
@@ -24,6 +20,30 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
+        private TypeReference ResolveGenericType(TypeReference type, List<TypeReference> typeStack)
+        {
+            var genericName = type.Name;
+            var lastType = (GenericInstanceType)typeStack[typeStack.Count - 1];
+            var resolvedType = lastType.Resolve();
+            typeStack.RemoveAt(typeStack.Count - 1);
+            for (var i = 0; i < resolvedType.GenericParameters.Count; ++i)
+            {
+                var parameter = resolvedType.GenericParameters[i];
+                if (parameter.Name == genericName)
+                {
+                    var underlyingType = lastType.GenericArguments[i];
+                    if (underlyingType.Resolve() == null)
+                    {
+                        return ResolveGenericType(underlyingType, typeStack);
+                    }
+
+                    return underlyingType;
+                }
+            }
+
+            return null;
+        }
+
         public override ILPostProcessResult Process(ICompiledAssembly compiledAssembly)
         {
             if (!WillProcess(compiledAssembly))
@@ -31,7 +51,6 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
-
             m_Diagnostics.Clear();
 
             // read
@@ -48,27 +67,31 @@ namespace Unity.Netcode.Editor.CodeGen
             {
                 try
                 {
-                    if (ImportReferences(mainModule))
-                    {
-                        var types = mainModule.GetTypes()
-                            .Where(t => t.Resolve().HasInterface(CodeGenHelpers.INetworkSerializable_FullName) && !t.Resolve().IsAbstract && t.Resolve().IsValueType)
-                            .ToList();
-                        // process `INetworkMessage` types
-                        if (types.Count == 0)
-                        {
-                            return null;
-                        }
+                    var structTypes = mainModule.GetTypes()
+                        .Where(t => t.Resolve().HasInterface(CodeGenHelpers.INetworkSerializeByMemcpy_FullName) && !t.Resolve().IsAbstract && !t.Resolve().HasGenericParameters && t.Resolve().IsValueType)
+                        .ToList();
 
-                        CreateModuleInitializer(assemblyDefinition, types);
-                    }
-                    else
+                    foreach (var type in structTypes)
                     {
-                        m_Diagnostics.AddError($"Cannot import references into main module: {mainModule.Name}");
+                        // We'll avoid some confusion by ensuring users only choose one of the two
+                        // serialization schemes - by method OR by memcpy, not both. We'll also do a cursory
+                        // check that INetworkSerializeByMemcpy types are unmanaged.
+                        if (type.HasInterface(CodeGenHelpers.INetworkSerializeByMemcpy_FullName))
+                        {
+                            if (type.HasInterface(CodeGenHelpers.INetworkSerializable_FullName))
+                            {
+                                m_Diagnostics.AddError($"{nameof(INetworkSerializeByMemcpy)} types may not implement {nameof(INetworkSerializable)} - choose one or the other.");
+                            }
+                            if (!type.IsValueType)
+                            {
+                                m_Diagnostics.AddError($"{nameof(INetworkSerializeByMemcpy)} types must be unmanaged types.");
+                            }
+                        }
                     }
                 }
                 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
@@ -93,75 +116,5 @@ namespace Unity.Netcode.Editor.CodeGen
 
             return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
         }
-
-        private MethodReference m_InitializeDelegates_MethodRef;
-
-        private const string k_InitializeMethodName = nameof(NetworkVariableHelper.InitializeDelegates);
-
-        private bool ImportReferences(ModuleDefinition moduleDefinition)
-        {
-
-            var helperType = typeof(NetworkVariableHelper);
-            foreach (var methodInfo in helperType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
-            {
-                switch (methodInfo.Name)
-                {
-                    case k_InitializeMethodName:
-                        m_InitializeDelegates_MethodRef = moduleDefinition.ImportReference(methodInfo);
-                        break;
-                }
-            }
-            return true;
-        }
-
-        private MethodDefinition GetOrCreateStaticConstructor(TypeDefinition typeDefinition)
-        {
-            var staticCtorMethodDef = typeDefinition.GetStaticConstructor();
-            if (staticCtorMethodDef == null)
-            {
-                staticCtorMethodDef = new MethodDefinition(
-                    ".cctor", // Static Constructor (constant-constructor)
-                    MethodAttributes.HideBySig |
-                    MethodAttributes.SpecialName |
-                    MethodAttributes.RTSpecialName |
-                    MethodAttributes.Static,
-                    typeDefinition.Module.TypeSystem.Void);
-                staticCtorMethodDef.Body.Instructions.Add(Instruction.Create(OpCodes.Ret));
-                typeDefinition.Methods.Add(staticCtorMethodDef);
-            }
-
-            return staticCtorMethodDef;
-        }
-
-        // Creates a static module constructor (which is executed when the module is loaded) that registers all the
-        // message types in the assembly with MessagingSystem.
-        // This is the same behavior as annotating a static method with [ModuleInitializer] in standardized
-        // C# (that attribute doesn't exist in Unity, but the static module constructor still works)
-        // https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.moduleinitializerattribute?view=net-5.0
-        // https://web.archive.org/web/20100212140402/http://blogs.msdn.com/junfeng/archive/2005/11/19/494914.aspx
-        private void CreateModuleInitializer(AssemblyDefinition assembly, List<TypeDefinition> networkSerializableTypes)
-        {
-            foreach (var typeDefinition in assembly.MainModule.Types)
-            {
-                if (typeDefinition.FullName == "<Module>")
-                {
-                    var staticCtorMethodDef = GetOrCreateStaticConstructor(typeDefinition);
-
-                    var processor = staticCtorMethodDef.Body.GetILProcessor();
-
-                    var instructions = new List<Instruction>();
-
-                    foreach (var type in networkSerializableTypes)
-                    {
-                        var method = new GenericInstanceMethod(m_InitializeDelegates_MethodRef);
-                        method.GenericArguments.Add(type);
-                        instructions.Add(processor.Create(OpCodes.Call, method));
-                    }
-
-                    instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));
-                    break;
-                }
-            }
-        }
     }
 }

Editor/CodeGen/RuntimeAccessModifiersILPP.cs

@@ -52,9 +52,6 @@ namespace Unity.Netcode.Editor.CodeGen
                         case nameof(NetworkBehaviour):
                             ProcessNetworkBehaviour(typeDefinition);
                             break;
-                        case nameof(NetworkVariableHelper):
-                            ProcessNetworkVariableHelper(typeDefinition);
-                            break;
                         case nameof(__RpcParams):
                             typeDefinition.IsPublic = true;
                             break;
@@ -103,17 +100,6 @@ namespace Unity.Netcode.Editor.CodeGen
             }
         }
 
-        private void ProcessNetworkVariableHelper(TypeDefinition typeDefinition)
-        {
-            foreach (var methodDefinition in typeDefinition.Methods)
-            {
-                if (methodDefinition.Name == nameof(NetworkVariableHelper.InitializeDelegates))
-                {
-                    methodDefinition.IsPublic = true;
-                }
-            }
-        }
-
         private void ProcessNetworkBehaviour(TypeDefinition typeDefinition)
         {
             foreach (var nestedType in typeDefinition.NestedTypes)

Editor/CodeGen/com.unity.netcode.editor.codegen.asmdef

@@ -2,11 +2,13 @@
     "name": "Unity.Netcode.Editor.CodeGen",
     "rootNamespace": "Unity.Netcode.Editor.CodeGen",
     "references": [
-        "Unity.Netcode.Runtime"
+        "Unity.Netcode.Runtime",
+        "Unity.Collections"
     ],
     "includePlatforms": [
         "Editor"
     ],
+    "excludePlatforms": [],
     "allowUnsafeCode": true,
     "overrideReferences": true,
     "precompiledReferences": [
@@ -15,5 +17,14 @@
         "Mono.Cecil.Pdb.dll",
         "Mono.Cecil.Rocks.dll"
     ],
-    "autoReferenced": false
+    "autoReferenced": false,
+    "defineConstraints": [],
+    "versionDefines": [
+        {
+            "name": "com.unity.nuget.mono-cecil",
+            "expression": "(0,1.11.4)",
+            "define": "CECIL_CONSTRAINTS_ARE_TYPE_REFERENCES"
+        }
+    ],
+    "noEngineReferences": false
 }

Editor/Configuration.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: 6b1ef235ca94b4bbd9a6456f44c69188
+guid: 52153943c346dd04e8712ab540ab9c22
 folderAsset: yes
 DefaultImporter:
   externalObjects: {}

Editor/Configuration/NetcodeForGameObjectsSettings.cs

@@ -0,0 +1,39 @@
+using UnityEditor;
+
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal class NetcodeForGameObjectsSettings
+    {
+        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);
+        }
+    }
+}

Editor/Configuration/NetcodeForGameObjectsSettings.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: e54b65208bd3bbe4eaf62ca0384ae21f
+guid: 2f9c9b10bc41a0e46ab71324dd0ac6e1
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/Configuration/NetcodeSettingsProvider.cs

@@ -0,0 +1,94 @@
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal static class NetcodeSettingsProvider
+    {
+        [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 = new NetcodeSettingsLabel("NetworkObject Helper Settings", 20);
+        internal static NetcodeSettingsToggle AutoAddNetworkObjectToggle = new NetcodeSettingsToggle("Auto-Add NetworkObjects", "When enabled, NetworkObjects are automatically added to GameObjects when NetworkBehaviours are added first.", 20);
+        internal static NetcodeSettingsLabel MultiplayerToolsLabel = new NetcodeSettingsLabel("Multiplayer Tools", 20);
+        internal static NetcodeSettingsToggle 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)
+        {
+            var autoAddNetworkObjectSetting = NetcodeForGameObjectsSettings.GetAutoAddNetworkObjectSetting();
+            var multiplayerToolsTipStatus = NetcodeForGameObjectsSettings.GetNetcodeInstallMultiplayerToolTips() == 0;
+            EditorGUI.BeginChangeCheck();
+            NetworkObjectsSectionLabel.DrawLabel();
+            autoAddNetworkObjectSetting = AutoAddNetworkObjectToggle.DrawToggle(autoAddNetworkObjectSetting);
+            MultiplayerToolsLabel.DrawLabel();
+            multiplayerToolsTipStatus = MultiplayerToolTipStatusToggle.DrawToggle(multiplayerToolsTipStatus);
+            if (EditorGUI.EndChangeCheck())
+            {
+                NetcodeForGameObjectsSettings.SetAutoAddNetworkObjectSetting(autoAddNetworkObjectSetting);
+                NetcodeForGameObjectsSettings.SetNetcodeInstallMultiplayerToolTips(multiplayerToolsTipStatus ? 0 : 1);
+            }
+        }
+    }
+
+    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;
+            AdjustLableSize(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)
+        {
+            AdjustLableSize(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 AdjustLableSize(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

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: 54c9647dc784a46bca664910f182491e
+guid: 6b373a89fcbd41444a97ebd1798b326f
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Editor/HiddenScriptEditor.cs

@@ -0,0 +1,81 @@
+using Unity.Netcode.Components;
+#if UNITY_UNET_PRESENT
+using Unity.Netcode.Transports.UNET;
+#endif
+using Unity.Netcode.Transports.UTP;
+using UnityEditor;
+
+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
+    {
+
+    }
+
+#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
@@ -33,8 +37,8 @@ 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_NetworkVariableFields.Add(fields[i].Name, fields[i]);
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
                 }
             }
         }
@@ -151,6 +155,8 @@ namespace Unity.Netcode.Editor
             }
         }
 
+
+        /// <inheritdoc/>
         public override void OnInspectorGUI()
         {
             if (!m_Initialized)
@@ -218,13 +224,21 @@ namespace Unity.Netcode.Editor
         /// </summary>
         private void OnEnable()
         {
+            // This can be null and throw an exception when running test runner in the editor
+            if (target == null)
+            {
+                return;
+            }
             // When we first add a NetworkBehaviour this editor will be enabled
             // so we go ahead and check for an already existing NetworkObject here
             CheckForNetworkObject((target as NetworkBehaviour).gameObject);
         }
 
-        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
-
+        /// <summary>
+        /// Recursively finds the root parent of a <see cref="Transform"/>
+        /// </summary>
+        /// <param name="transform">The current <see cref="Transform"/> we are inspecting for a parent</param>
+        /// <returns>the root parent for the first <see cref="Transform"/> passed into the method</returns>
         public static Transform GetRootParentTransform(Transform transform)
         {
             if (transform.parent == null || transform.parent == transform)
@@ -239,6 +253,8 @@ namespace Unity.Netcode.Editor
         /// does not already have a NetworkObject component.  If not it will notify
         /// the user that NetworkBehaviours require a NetworkObject.
         /// </summary>
+        /// <param name="gameObject"><see cref="GameObject"/> to start checking for a <see cref="NetworkObject"/></param>
+        /// <param name="networkObjectRemoved">used internally</param>
         public static void CheckForNetworkObject(GameObject gameObject, bool networkObjectRemoved = false)
         {
             // If there are no NetworkBehaviours or no gameObject, then exit early
@@ -249,11 +265,42 @@ namespace Unity.Netcode.Editor
 
             // Now get the root parent transform to the current GameObject (or itself)
             var rootTransform = GetRootParentTransform(gameObject.transform);
+            if (!rootTransform.TryGetComponent<NetworkManager>(out var networkManager))
+            {
+                networkManager = rootTransform.GetComponentInChildren<NetworkManager>();
+            }
+
+            // If there is a NetworkManager, then notify the user that a NetworkManager cannot have NetworkBehaviour components
+            if (networkManager != null)
+            {
+                var networkBehaviours = networkManager.gameObject.GetComponents<NetworkBehaviour>();
+                var networkBehavioursChildren = networkManager.gameObject.GetComponentsInChildren<NetworkBehaviour>();
+                if (networkBehaviours.Length > 0 || networkBehavioursChildren.Length > 0)
+                {
+                    if (EditorUtility.DisplayDialog("NetworkBehaviour or NetworkManager Cannot Be Added", $"{nameof(NetworkManager)}s cannot have {nameof(NetworkBehaviour)} components added to the root parent or any of its children." +
+                        $" Would you like to remove the NetworkManager or NetworkBehaviour?", "NetworkManager", "NetworkBehaviour"))
+                    {
+                        DestroyImmediate(networkManager);
+                    }
+                    else
+                    {
+                        foreach (var networkBehaviour in networkBehaviours)
+                        {
+                            DestroyImmediate(networkBehaviour);
+                        }
+
+                        foreach (var networkBehaviour in networkBehaviours)
+                        {
+                            DestroyImmediate(networkBehaviour);
+                        }
+                    }
+                    return;
+                }
+            }
 
             // Otherwise, check to see if there is any NetworkObject from the root GameObject down to all children.
             // If not, notify the user that NetworkBehaviours require that the relative GameObject has a NetworkObject component.
-            var networkObject = rootTransform.GetComponent<NetworkObject>();
-            if (networkObject == null)
+            if (!rootTransform.TryGetComponent<NetworkObject>(out var networkObject))
             {
                 networkObject = rootTransform.GetComponentInChildren<NetworkObject>();
 
@@ -263,7 +310,7 @@ 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 && NetcodeForGameObjectsSettings.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.");
@@ -272,7 +319,7 @@ 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, NetcodeForGameObjectsSettings.AutoAddNetworkObjectIfNoneExists))
                     {
                         gameObject.AddComponent<NetworkObject>();
                         var activeScene = UnityEngine.SceneManagement.SceneManager.GetActiveScene();
@@ -282,20 +329,5 @@ 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

@@ -3,14 +3,18 @@ using System.Collections.Generic;
 using UnityEditor;
 using UnityEngine;
 using UnityEditorInternal;
+using Unity.Netcode.Editor.Configuration;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// This <see cref="CustomEditor"/> handles the translation between the <see cref="NetworkConfig"/> and
+    /// the <see cref="NetworkManager"/> properties.
+    /// </summary>
     [CustomEditor(typeof(NetworkManager), true)]
     [CanEditMultipleObjects]
     public class NetworkManagerEditor : UnityEditor.Editor
     {
-        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
         private static GUIStyle s_CenteredWordWrappedLabelStyle;
         private static GUIStyle s_HelpBoxStyle;
 
@@ -200,6 +204,7 @@ namespace Unity.Netcode.Editor
             m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
         }
 
+        /// <inheritdoc/>
         public override void OnInspectorGUI()
         {
             Initialize();
@@ -209,18 +214,6 @@ 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();
@@ -363,10 +356,10 @@ namespace Unity.Netcode.Editor
             const string getToolsText = "Access additional tools for multiplayer development by installing the Multiplayer Tools package in the Package Manager.";
             const string openDocsButtonText = "Open Docs";
             const string dismissButtonText = "Dismiss";
-            const string targetUrl = "https://docs-multiplayer.unity3d.com/docs/tools/install-tools";
+            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 (NetcodeForGameObjectsSettings.GetNetcodeInstallMultiplayerToolTips() != 0)
             {
                 return;
             }
@@ -412,7 +405,7 @@ namespace Unity.Netcode.Editor
                 GUILayout.FlexibleSpace();
                 if (GUILayout.Button(dismissButtonText, dismissButtonStyle, GUILayout.ExpandWidth(false)))
                 {
-                    PlayerPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 1);
+                    NetcodeForGameObjectsSettings.SetNetcodeInstallMultiplayerToolTips(1);
                 }
                 EditorGUIUtility.AddCursorRect(GUILayoutUtility.GetLastRect(), MouseCursor.Link);
                 GUILayout.FlexibleSpace();

Editor/NetworkManagerHelper.cs

@@ -64,8 +64,12 @@ 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 +113,8 @@ 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

@@ -4,6 +4,9 @@ using UnityEditor;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// The <see cref="CustomEditor"/> for <see cref="NetworkObject"/>
+    /// </summary>
     [CustomEditor(typeof(NetworkObject), true)]
     [CanEditMultipleObjects]
     public class NetworkObjectEditor : UnityEditor.Editor
@@ -12,6 +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)
@@ -23,6 +28,7 @@ namespace Unity.Netcode.Editor
             m_NetworkObject = (NetworkObject)target;
         }
 
+        /// <inheritdoc/>
         public override void OnInspectorGUI()
         {
             Initialize();
@@ -91,7 +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/NetworkTransformEditor.cs

@@ -4,6 +4,9 @@ using Unity.Netcode.Components;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// The <see cref="CustomEditor"/> for <see cref="NetworkTransform"/>
+    /// </summary>
     [CustomEditor(typeof(NetworkTransform), true)]
     public class NetworkTransformEditor : UnityEditor.Editor
     {
@@ -28,6 +31,7 @@ namespace Unity.Netcode.Editor
         private static GUIContent s_RotationLabel = EditorGUIUtility.TrTextContent("Rotation");
         private static GUIContent s_ScaleLabel = EditorGUIUtility.TrTextContent("Scale");
 
+        /// <inheritdoc/>
         public void OnEnable()
         {
             m_SyncPositionXProperty = serializedObject.FindProperty(nameof(NetworkTransform.SyncPositionX));
@@ -46,6 +50,7 @@ namespace Unity.Netcode.Editor
             m_InterpolateProperty = serializedObject.FindProperty(nameof(NetworkTransform.Interpolate));
         }
 
+        /// <inheritdoc/>
         public override void OnInspectorGUI()
         {
             EditorGUILayout.LabelField("Syncing", EditorStyles.boldLabel);

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

@@ -1,12 +1,16 @@
 # Netcode for GameObjects
 
 [![Forums](https://img.shields.io/badge/unity--forums-multiplayer-blue)](https://forum.unity.com/forums/multiplayer.26/) [![Discord](https://img.shields.io/discord/449263083769036810.svg?label=discord&logo=discord&color=informational)](https://discord.gg/FM8SE9E)
-[![Website](https://img.shields.io/badge/docs-website-informational.svg)](https://docs-multiplayer.unity3d.com/) [![Api](https://img.shields.io/badge/docs-api-informational.svg)](https://docs-multiplayer.unity3d.com/docs/mlapi-api/introduction)
+[![Manual](https://img.shields.io/badge/docs-manual-informational.svg)](https://docs-multiplayer.unity3d.com/netcode/current/about) [![API](https://img.shields.io/badge/docs-api-informational.svg)](https://docs-multiplayer.unity3d.com/netcode/current/api/introduction)
 
-Netcode for GameObjects provides networking capabilities to GameObject & MonoBehaviour Unity workflows. The framework is interoperable with many low-level transports, including the official [Unity Transport Package](https://docs-multiplayer.unity3d.com/transport/1.0.0/introduction).
+Netcode for GameObjects is a Unity package that provides networking capabilities to GameObject & MonoBehaviour workflows. The framework is interoperable with many low-level transports, including the official [Unity Transport Package](https://docs-multiplayer.unity3d.com/transport/current/about).
 
 ### Getting Started
+
 Visit the [Multiplayer Docs Site](https://docs-multiplayer.unity3d.com/) for package & API documentation, as well as information about several samples which leverage the Netcode for GameObjects package.
 
+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
+
 For general questions, networking advice or discussions about Netcode for GameObjects, please join our [Discord Community](https://discord.gg/FM8SE9E) or create a post in the [Unity Multiplayer Forum](https://forum.unity.com/forums/multiplayer.26/).

Runtime/AssemblyInfo.cs

@@ -5,9 +5,11 @@ using System.Runtime.CompilerServices;
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
 [assembly: InternalsVisibleTo("TestProject.EditorTests")]
+[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 #endif
 [assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
 [assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.TestHelpers.Runtime")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+[assembly: InternalsVisibleTo("Unity.Multiplayer.Tools.Adapters.Ngo1WithUtp2")]

Runtime/Configuration/NetworkConfig.cs

@@ -53,9 +53,21 @@ namespace Unity.Netcode
         public uint TickRate = 30;
 
         /// <summary>
-        /// The amount of seconds to wait for handshake to complete before timing out a client
+        /// The amount of seconds for the server to wait for the connection approval handshake to complete before the client is disconnected.
+        ///
+        /// If the timeout is reached before approval is completed the client will be disconnected.
         /// </summary>
-        [Tooltip("The amount of seconds to wait for the handshake to complete before the client times out")]
+        /// <remarks>
+        /// The period begins after the <see cref="NetworkEvent.Connect"/> is received on the server.
+        /// The period ends once the server finishes processing a <see cref="ConnectionRequestMessage"/> from the client.
+        ///
+        /// This setting is independent of any Transport-level timeouts that may be in effect. It covers the time between
+        /// the connection being established on the Transport layer, the client sending a
+        /// <see cref="ConnectionRequestMessage"/>, and the server processing that message through <see cref="ConnectionApproval"/>.
+        ///
+        /// This setting is server-side only.
+        /// </remarks>
+        [Tooltip("The amount of seconds for the server to wait for the connection approval handshake to complete before the client is disconnected")]
         public int ClientConnectionBufferTimeout = 10;
 
         /// <summary>
@@ -128,18 +140,26 @@ namespace Unity.Netcode
         public int LoadSceneTimeOut = 120;
 
         /// <summary>
-        /// The amount of time a message should be buffered for without being consumed. If it is not consumed within this time, it will be dropped.
+        /// The amount of time a message should be buffered if the asset or object needed to process it doesn't exist yet. If the asset is not added/object is not spawned within this time, it will be dropped.
         /// </summary>
-        [Tooltip("The amount of time a message should be buffered for without being consumed. If it is not consumed within this time, it will be dropped")]
-        public float MessageBufferTimeout = 20f;
+        [Tooltip("The amount of time a message should be buffered if the asset or object needed to process it doesn't exist yet. If the asset is not added/object is not spawned within this time, it will be dropped")]
+        public float SpawnTimeout = 1f;
 
         /// <summary>
         /// Whether or not to enable network logs.
         /// </summary>
         public bool EnableNetworkLogs = true;
 
+        /// <summary>
+        /// The number of RTT samples that is kept as an average for calculations
+        /// </summary>
         public const int RttAverageSamples = 5; // number of RTT to keep an average of (plus one)
+
+        /// <summary>
+        /// The number of slots used for RTT calculations. This is the maximum amount of in-flight messages
+        /// </summary>
         public const int RttWindowSize = 64; // number of slots to use for RTT computations (max number of in-flight packets)
+
         /// <summary>
         /// Returns a base64 encoded version of the configuration
         /// </summary>

Runtime/Core/ComponentFactory.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// This class is used to support testable code by allowing any supported component used by NetworkManager to be replaced
+    /// with a mock component or a test version that overloads certain methods to change or record their behavior.
+    /// Components currently supported by ComponentFactory:
+    /// - IDeferredMessageManager
+    /// </summary>
+    internal static class ComponentFactory
+    {
+        internal delegate object CreateObjectDelegate(NetworkManager networkManager);
+
+        private static Dictionary<Type, CreateObjectDelegate> s_Delegates = new Dictionary<Type, CreateObjectDelegate>();
+
+        /// <summary>
+        /// Instantiates an instance of a given interface
+        /// </summary>
+        /// <param name="networkManager">The network manager</param>
+        /// <typeparam name="T">The interface to instantiate it with</typeparam>
+        /// <returns></returns>
+        public static T Create<T>(NetworkManager networkManager)
+        {
+            return (T)s_Delegates[typeof(T)](networkManager);
+        }
+
+        /// <summary>
+        /// Overrides the default creation logic for a given interface type
+        /// </summary>
+        /// <param name="creator">The factory delegate to create the instance</param>
+        /// <typeparam name="T">The interface type to override</typeparam>
+        public static void Register<T>(CreateObjectDelegate creator)
+        {
+            s_Delegates[typeof(T)] = creator;
+        }
+
+        /// <summary>
+        /// Reverts the creation logic for a given interface type to the default logic
+        /// </summary>
+        /// <typeparam name="T">The interface type to revert</typeparam>
+        public static void Deregister<T>()
+        {
+            s_Delegates.Remove(typeof(T));
+            SetDefaults();
+        }
+
+        /// <summary>
+        /// Initializes the default creation logic for all supported component types
+        /// </summary>
+        public static void SetDefaults()
+        {
+            SetDefault<IDeferredMessageManager>(networkManager => new DeferredMessageManager(networkManager));
+        }
+
+        private static void SetDefault<T>(CreateObjectDelegate creator)
+        {
+            if (!s_Delegates.ContainsKey(typeof(T)))
+            {
+                s_Delegates[typeof(T)] = creator;
+            }
+        }
+    }
+}

Runtime/Core/ComponentFactory.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: fda4c0eb89644fcea5416bbf98ea0ba0
+timeCreated: 1649966562

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);
 
@@ -235,14 +236,42 @@ 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)
                 {
-                    NetworkManager.NetworkMetrics.TrackRpcSent(
-                        client.Key,
-                        NetworkObject,
-                        rpcMethodName,
-                        __getTypeName(),
-                        rpcWriteSize);
+                    foreach (var targetClientId in clientRpcParams.Send.TargetClientIds)
+                    {
+                        NetworkManager.NetworkMetrics.TrackRpcSent(
+                            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
@@ -307,23 +347,29 @@ 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
             {
-                if (m_NetworkObject == null)
+                try
                 {
-                    m_NetworkObject = GetComponentInParent<NetworkObject>();
+                    if (m_NetworkObject == null)
+                    {
+                        m_NetworkObject = GetComponentInParent<NetworkObject>();
+                    }
+                }
+                catch (Exception)
+                {
+                    return null;
                 }
 
                 // ShutdownInProgress check:
@@ -331,7 +377,8 @@ namespace Unity.Netcode
                 // 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)
                     {
@@ -435,14 +482,41 @@ namespace Unity.Netcode
             IsSpawned = true;
             InitializeVariables();
             UpdateNetworkProperties();
-            OnNetworkSpawn();
+        }
+
+        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();
-            OnNetworkDespawn();
+            try
+            {
+                OnNetworkDespawn();
+            }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
         }
 
         /// <summary>
@@ -470,6 +544,7 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets called when the parent NetworkObject of this NetworkBehaviour's NetworkObject has changed
         /// </summary>
+        /// <param name="parentNetworkObject">the new <see cref="NetworkObject"/> parent</param>
         public virtual void OnNetworkObjectParentChanged(NetworkObject parentNetworkObject) { }
 
         private bool m_VarInit = false;
@@ -574,16 +649,30 @@ namespace Unity.Netcode
             NetworkVariableIndexesToResetSet.Clear();
         }
 
-        internal void PostNetworkVariableWrite()
+        internal void PostNetworkVariableWrite(bool forced = false)
         {
-            // mark any variables we wrote as no longer dirty
-            for (int i = 0; i < NetworkVariableIndexesToReset.Count; i++)
+            if (forced)
             {
-                NetworkVariableFields[NetworkVariableIndexesToReset[i]].ResetDirty();
+                // 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++)
+                {
+                    NetworkVariableFields[NetworkVariableIndexesToReset[i]].ResetDirty();
+                }
+            }
+
+            MarkVariablesDirty(false);
         }
 
-        internal void VariableUpdate(ulong targetClientId)
+        internal void PreVariableUpdate()
         {
             if (!m_VarInit)
             {
@@ -591,6 +680,10 @@ namespace Unity.Netcode
             }
 
             PreNetworkVariableWrite();
+        }
+
+        internal void VariableUpdate(ulong targetClientId)
+        {
             NetworkVariableUpdate(targetClientId, NetworkBehaviourId);
         }
 
@@ -637,7 +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
@@ -662,14 +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)
@@ -679,27 +780,47 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                bool canClientRead = NetworkVariableFields[j].CanClientRead(targetClientId);
 
-                if (canClientRead)
+                if (NetworkVariableFields[j].CanClientRead(targetClientId))
                 {
-                    var writePos = writer.Position;
-                    writer.WriteValueSafe((ushort)0);
-                    var startPos = writer.Position;
-                    NetworkVariableFields[j].WriteField(writer);
-                    var size = writer.Position - startPos;
-                    writer.Seek(writePos);
-                    writer.WriteValueSafe((ushort)size);
-                    writer.Seek(startPos + size);
+                    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);
+                        var size = writer.Position - startPos;
+                        writer.Seek(writePos);
+                        writer.WriteValueSafe((ushort)size);
+                        writer.Seek(startPos + size);
+                    }
+                    else
+                    {
+                        NetworkVariableFields[j].WriteField(writer);
+                    }
                 }
-                else
+                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)
             {
@@ -708,13 +829,23 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                reader.ReadValueSafe(out ushort varSize);
-                if (varSize == 0)
+                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)
@@ -751,8 +882,153 @@ 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
+        /// <see cref="OnDestroy"/> method!!
+        /// </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
@@ -764,6 +1040,7 @@ namespace Unity.Netcode
                 InitializeVariables();
             }
 
+
             for (int i = 0; i < NetworkVariableFields.Count; i++)
             {
                 NetworkVariableFields[i].Dispose();

Runtime/Core/NetworkBehaviourUpdater.cs

@@ -3,14 +3,22 @@ using Unity.Profiling;
 
 namespace Unity.Netcode
 {
+    /// <summary>
+    /// An helper class that helps NetworkManager update NetworkBehaviours and replicate them down to connected clients.
+    /// </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
@@ -18,59 +26,58 @@ 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();
-                    for (int i = 0; i < networkManager.ConnectedClientsList.Count; i++)
+                    foreach (var dirtyObj in m_DirtyNetworkObjects)
                     {
-                        var client = networkManager.ConnectedClientsList[i];
-                        var spawnedObjs = networkManager.SpawnManager.SpawnedObjectsList;
-                        m_Touched.UnionWith(spawnedObjs);
-                        foreach (var sobj in spawnedObjs)
+                        for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
                         {
-                            if (sobj.IsNetworkVisibleTo(client.ClientId))
+                            dirtyObj.ChildNetworkBehaviours[k].PreVariableUpdate();
+                        }
+
+                        for (int i = 0; i < networkManager.ConnectedClientsList.Count; i++)
+                        {
+                            var client = networkManager.ConnectedClientsList[i];
+
+                            if (dirtyObj.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);
                             }
                         }
                     }
-
-                    // Now, reset all the no-longer-dirty variables
-                    foreach (var sobj in networkManager.SpawnManager.SpawnedObjectsList)
-                    {
-                        for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
-                        {
-                            sobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                        }
-                    }
                 }
+                // Now, reset all the no-longer-dirty variables
+                foreach (var dirtyobj in m_DirtyNetworkObjects)
+                {
+                    dirtyobj.PostNetworkVariableWrite();
+                }
+                m_DirtyNetworkObjects.Clear();
             }
             finally
             {

Runtime/Core/NetworkUpdateLoop.cs

@@ -7,25 +7,55 @@ using UnityEngine.PlayerLoop;
 namespace Unity.Netcode
 {
     /// <summary>
-    /// Defines the required interface of a network update system being executed by the network update loop.
+    /// Defines the required interface of a network update system being executed by the <see cref="NetworkUpdateLoop"/>.
     /// </summary>
     public interface INetworkUpdateSystem
     {
+        /// <summary>
+        /// The update method that is being executed in the context of related <see cref="NetworkUpdateStage"/>.
+        /// </summary>
+        /// <param name="updateStage">The <see cref="NetworkUpdateStage"/> that is being executed.</param>
         void NetworkUpdate(NetworkUpdateStage updateStage);
     }
 
     /// <summary>
     /// Defines network update stages being executed by the network update loop.
+    /// See for more details on update stages:
+    /// https://docs.unity3d.com/ScriptReference/PlayerLoop.Initialization.html
     /// </summary>
     public enum NetworkUpdateStage : byte
     {
-        Unset = 0, // Default
+        /// <summary>
+        /// Default value
+        /// </summary>
+        Unset = 0,
+        /// <summary>
+        /// Very first initialization update
+        /// </summary>
         Initialization = 1,
+        /// <summary>
+        /// Invoked before Fixed update
+        /// </summary>
         EarlyUpdate = 2,
+        /// <summary>
+        /// Fixed Update (i.e. state machine, physics, animations, etc)
+        /// </summary>
         FixedUpdate = 3,
+        /// <summary>
+        /// Updated before the Monobehaviour.Update for all components is invoked
+        /// </summary>
         PreUpdate = 4,
+        /// <summary>
+        /// Updated when the Monobehaviour.Update for all components is invoked
+        /// </summary>
         Update = 5,
+        /// <summary>
+        /// Updated before the Monobehaviour.LateUpdate for all components is invoked
+        /// </summary>
         PreLateUpdate = 6,
+        /// <summary>
+        /// Updated after the Monobehaviour.LateUpdate for all components is invoked
+        /// </summary>
         PostLateUpdate = 7
     }
 
@@ -53,6 +83,7 @@ namespace Unity.Netcode
         /// <summary>
         /// Registers a network update system to be executed in all network update stages.
         /// </summary>
+        /// <param name="updateSystem">The <see cref="INetworkUpdateSystem"/> implementation to register for all network updates</param>
         public static void RegisterAllNetworkUpdates(this INetworkUpdateSystem updateSystem)
         {
             foreach (NetworkUpdateStage updateStage in Enum.GetValues(typeof(NetworkUpdateStage)))
@@ -64,6 +95,8 @@ namespace Unity.Netcode
         /// <summary>
         /// Registers a network update system to be executed in a specific network update stage.
         /// </summary>
+        /// <param name="updateSystem">The <see cref="INetworkUpdateSystem"/> implementation to register for all network updates</param>
+        /// <param name="updateStage">The <see cref="NetworkUpdateStage"/> being registered for the <see cref="INetworkUpdateSystem"/> implementation</param>
         public static void RegisterNetworkUpdate(this INetworkUpdateSystem updateSystem, NetworkUpdateStage updateStage = NetworkUpdateStage.Update)
         {
             var sysSet = s_UpdateSystem_Sets[updateStage];
@@ -94,6 +127,7 @@ namespace Unity.Netcode
         /// <summary>
         /// Unregisters a network update system from all network update stages.
         /// </summary>
+        /// <param name="updateSystem">The <see cref="INetworkUpdateSystem"/> implementation to deregister from all network updates</param>
         public static void UnregisterAllNetworkUpdates(this INetworkUpdateSystem updateSystem)
         {
             foreach (NetworkUpdateStage updateStage in Enum.GetValues(typeof(NetworkUpdateStage)))
@@ -105,6 +139,8 @@ namespace Unity.Netcode
         /// <summary>
         /// Unregisters a network update system from a specific network update stage.
         /// </summary>
+        /// <param name="updateSystem">The <see cref="INetworkUpdateSystem"/> implementation to deregister from all network updates</param>
+        /// <param name="updateStage">The <see cref="NetworkUpdateStage"/> to be deregistered from the <see cref="INetworkUpdateSystem"/> implementation</param>
         public static void UnregisterNetworkUpdate(this INetworkUpdateSystem updateSystem, NetworkUpdateStage updateStage = NetworkUpdateStage.Update)
         {
             var sysSet = s_UpdateSystem_Sets[updateStage];

Runtime/Exceptions/InvalidParentException.cs

@@ -7,8 +7,18 @@ namespace Unity.Netcode
     /// </summary>
     public class InvalidParentException : Exception
     {
+        /// <summary>
+        /// Constructor for <see cref="InvalidParentException"/>
+        /// </summary>
         public InvalidParentException() { }
+
+        /// <inheritdoc/>
+        /// <param name="message"></param>
         public InvalidParentException(string message) : base(message) { }
+
+        /// <inheritdoc/>
+        /// <param name="message"></param>
+        /// <param name="innerException"></param>
         public InvalidParentException(string message, Exception innerException) : base(message, innerException) { }
     }
 }

Runtime/Exceptions/SpawnStateException.cs

@@ -26,8 +26,15 @@ namespace Unity.Netcode
         public SpawnStateException(string message, Exception inner) : base(message, inner) { }
     }
 
+    /// <summary>
+    /// Exception thrown when a specified network channel is invalid
+    /// </summary>
     public class InvalidChannelException : Exception
     {
+        /// <summary>
+        /// Constructs an InvalidChannelException with a message
+        /// </summary>
+        /// <param name="message">the message</param>
         public InvalidChannelException(string message) : base(message) { }
     }
 }

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/Logging/NetworkLog.cs

@@ -14,8 +14,23 @@ namespace Unity.Netcode
         public static LogLevel CurrentLogLevel => NetworkManager.Singleton == null ? LogLevel.Normal : NetworkManager.Singleton.LogLevel;
 
         // internal logging
+
+        /// <summary>
+        /// Locally logs a info log with Netcode prefixing.
+        /// </summary>
+        /// <param name="message">The message to log</param>
         public static void LogInfo(string message) => Debug.Log($"[Netcode] {message}");
+
+        /// <summary>
+        /// Locally logs a warning log with Netcode prefixing.
+        /// </summary>
+        /// <param name="message">The message to log</param>
         public static void LogWarning(string message) => Debug.LogWarning($"[Netcode] {message}");
+
+        /// <summary>
+        /// Locally logs a error log with Netcode prefixing.
+        /// </summary>
+        /// <param name="message">The message to log</param>
         public static void LogError(string message) => Debug.LogError($"[Netcode] {message}");
 
         /// <summary>

Runtime/Messaging/BatchHeader.cs

@@ -3,7 +3,7 @@ namespace Unity.Netcode
     /// <summary>
     /// Header placed at the start of each message batch
     /// </summary>
-    internal struct BatchHeader
+    internal struct BatchHeader : INetworkSerializeByMemcpy
     {
         /// <summary>
         /// Total number of messages in the batch.

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
@@ -193,6 +220,7 @@ namespace Unity.Netcode
         /// <summary>
         /// Sends a named message to all clients
         /// </summary>
+        /// <param name="messageName">The message name to send</param>
         /// <param name="messageStream">The message stream containing the data</param>
         /// <param name="networkDelivery">The delivery type (QoS) to send data with</param>
         public void SendNamedMessageToAll(string messageName, FastBufferWriter messageStream, NetworkDelivery networkDelivery = NetworkDelivery.ReliableSequenced)
@@ -219,6 +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
             {
@@ -238,7 +280,7 @@ namespace Unity.Netcode
         /// Sends the named message
         /// </summary>
         /// <param name="messageName">The message name to send</param>
-        /// <param name="clientIds">The clients to send to, sends to everyone if null</param>
+        /// <param name="clientIds">The clients to send to</param>
         /// <param name="messageStream">The message stream containing the data</param>
         /// <param name="networkDelivery">The delivery type (QoS) to send data with</param>
         public void SendNamedMessage(string messageName, IReadOnlyList<ulong> clientIds, FastBufferWriter messageStream, NetworkDelivery networkDelivery = NetworkDelivery.ReliableSequenced)
@@ -250,7 +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;
@@ -263,6 +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/DeferredMessageManager.cs

@@ -0,0 +1,149 @@
+using System.Collections.Generic;
+using Unity.Collections;
+using Time = UnityEngine.Time;
+
+namespace Unity.Netcode
+{
+    internal class DeferredMessageManager : IDeferredMessageManager
+    {
+        protected struct TriggerData
+        {
+            public FastBufferReader Reader;
+            public MessageHeader Header;
+            public ulong SenderId;
+            public float Timestamp;
+            public int SerializedHeaderSize;
+        }
+        protected struct TriggerInfo
+        {
+            public float Expiry;
+            public NativeList<TriggerData> TriggerData;
+        }
+
+        protected readonly Dictionary<IDeferredMessageManager.TriggerType, Dictionary<ulong, TriggerInfo>> m_Triggers = new Dictionary<IDeferredMessageManager.TriggerType, Dictionary<ulong, TriggerInfo>>();
+
+        private readonly NetworkManager m_NetworkManager;
+
+        internal DeferredMessageManager(NetworkManager networkManager)
+        {
+            m_NetworkManager = networkManager;
+        }
+
+        /// <summary>
+        /// Defers processing of a message until the moment a specific networkObjectId is spawned.
+        /// This is to handle situations where an RPC or other object-specific message arrives before the spawn does,
+        /// either due to it being requested in OnNetworkSpawn before the spawn call has been executed
+        ///
+        /// There is a one second maximum lifetime of triggers to avoid memory leaks. After one second has passed
+        /// without the requested object ID being spawned, the triggers for it are automatically deleted.
+        /// </summary>
+        public virtual unsafe void DeferMessage(IDeferredMessageManager.TriggerType trigger, ulong key, FastBufferReader reader, ref NetworkContext context)
+        {
+            if (!m_Triggers.TryGetValue(trigger, out var triggers))
+            {
+                triggers = new Dictionary<ulong, TriggerInfo>();
+                m_Triggers[trigger] = triggers;
+            }
+
+            if (!triggers.TryGetValue(key, out var triggerInfo))
+            {
+                triggerInfo = new TriggerInfo
+                {
+                    Expiry = Time.realtimeSinceStartup + m_NetworkManager.NetworkConfig.SpawnTimeout,
+                    TriggerData = new NativeList<TriggerData>(Allocator.Persistent)
+                };
+                triggers[key] = triggerInfo;
+            }
+
+            triggerInfo.TriggerData.Add(new TriggerData
+            {
+                Reader = new FastBufferReader(reader.GetUnsafePtr(), Allocator.Persistent, reader.Length),
+                Header = context.Header,
+                Timestamp = context.Timestamp,
+                SenderId = context.SenderId,
+                SerializedHeaderSize = context.SerializedHeaderSize
+            });
+        }
+
+        /// <summary>
+        /// Cleans up any trigger that's existed for more than a second.
+        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
+        /// </summary>
+        public virtual unsafe void CleanupStaleTriggers()
+        {
+            foreach (var kvp in m_Triggers)
+            {
+                ulong* staleKeys = stackalloc ulong[kvp.Value.Count];
+                int index = 0;
+                foreach (var kvp2 in kvp.Value)
+                {
+                    if (kvp2.Value.Expiry < Time.realtimeSinceStartup)
+                    {
+                        staleKeys[index++] = kvp2.Key;
+                        PurgeTrigger(kvp.Key, kvp2.Key, kvp2.Value);
+                    }
+                }
+
+                for (var i = 0; i < index; ++i)
+                {
+                    kvp.Value.Remove(staleKeys[i]);
+                }
+            }
+        }
+
+        protected virtual void PurgeTrigger(IDeferredMessageManager.TriggerType triggerType, ulong key, TriggerInfo triggerInfo)
+        {
+            if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+            {
+                NetworkLog.LogWarning($"Deferred messages were received for a trigger of type {triggerType} with key {key}, but that trigger was not received within within {m_NetworkManager.NetworkConfig.SpawnTimeout} second(s).");
+            }
+
+            foreach (var data in triggerInfo.TriggerData)
+            {
+                data.Reader.Dispose();
+            }
+
+            triggerInfo.TriggerData.Dispose();
+        }
+
+        public virtual void ProcessTriggers(IDeferredMessageManager.TriggerType trigger, ulong key)
+        {
+            if (m_Triggers.TryGetValue(trigger, out var triggers))
+            {
+                // This must happen after InvokeBehaviourNetworkSpawn, otherwise ClientRPCs and other messages can be
+                // processed before the object is fully spawned. This must be the last thing done in the spawn process.
+                if (triggers.TryGetValue(key, out var triggerInfo))
+                {
+                    foreach (var deferredMessage in triggerInfo.TriggerData)
+                    {
+                        // Reader will be disposed within HandleMessage
+                        m_NetworkManager.MessagingSystem.HandleMessage(deferredMessage.Header, deferredMessage.Reader, deferredMessage.SenderId, deferredMessage.Timestamp, deferredMessage.SerializedHeaderSize);
+                    }
+
+                    triggerInfo.TriggerData.Dispose();
+                    triggers.Remove(key);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Cleans up any trigger that's existed for more than a second.
+        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
+        /// </summary>
+        public virtual void CleanupAllTriggers()
+        {
+            foreach (var kvp in m_Triggers)
+            {
+                foreach (var kvp2 in kvp.Value)
+                {
+                    foreach (var data in kvp2.Value.TriggerData)
+                    {
+                        data.Reader.Dispose();
+                    }
+                    kvp2.Value.TriggerData.Dispose();
+                }
+            }
+            m_Triggers.Clear();
+        }
+    }
+}

Runtime/Messaging/DeferredMessageManager.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: ac7f57f7d16a46e2aba65558e873727f
+timeCreated: 1649799187

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

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: c2e5a740c1abd4315801e3f26ecf8adb
+guid: d7742516058394f96999464f3ea32c71
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Runtime/Messaging/IDeferredMessageManager.cs

@@ -0,0 +1,35 @@
+namespace Unity.Netcode
+{
+    internal interface IDeferredMessageManager
+    {
+        internal enum TriggerType
+        {
+            OnSpawn,
+            OnAddPrefab,
+        }
+
+        /// <summary>
+        /// Defers processing of a message until the moment a specific networkObjectId is spawned.
+        /// This is to handle situations where an RPC or other object-specific message arrives before the spawn does,
+        /// either due to it being requested in OnNetworkSpawn before the spawn call has been executed
+        ///
+        /// There is a one second maximum lifetime of triggers to avoid memory leaks. After one second has passed
+        /// without the requested object ID being spawned, the triggers for it are automatically deleted.
+        /// </summary>
+        void DeferMessage(TriggerType trigger, ulong key, FastBufferReader reader, ref NetworkContext context);
+
+        /// <summary>
+        /// Cleans up any trigger that's existed for more than a second.
+        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
+        /// </summary>
+        void CleanupStaleTriggers();
+
+        void ProcessTriggers(TriggerType trigger, ulong key);
+
+        /// <summary>
+        /// Cleans up any trigger that's existed for more than a second.
+        /// These triggers were probably for situations where a request was received after a despawn rather than before a spawn.
+        /// </summary>
+        void CleanupAllTriggers();
+    }
+}

Runtime/Messaging/IDeferredMessageManager.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 7fb73a029c314763a04ebb015a07664d
+timeCreated: 1649966331

Runtime/Messaging/INetworkHooks.cs

@@ -91,8 +91,10 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="senderId">The source clientId</param>
         /// <param name="messageType">The type of the message</param>
+        /// <param name="messageContent">The FastBufferReader containing the message</param>
+        /// <param name="context">The NetworkContext the message is being processed in</param>
         /// <returns></returns>
-        bool OnVerifyCanReceive(ulong senderId, Type messageType);
+        bool OnVerifyCanReceive(ulong senderId, Type messageType, FastBufferReader messageContent, ref NetworkContext context);
 
         /// <summary>
         /// Called after a message is serialized, but before it's handled.

Runtime/Messaging/INetworkMessage.cs

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

Runtime/Messaging/MessageHeader.cs

@@ -3,7 +3,7 @@ namespace Unity.Netcode
     /// <summary>
     /// This is the header data that's serialized to the network when sending an <see cref="INetworkMessage"/>
     /// </summary>
-    internal struct MessageHeader
+    internal struct MessageHeader : INetworkSerializeByMemcpy
     {
         /// <summary>
         /// The byte representation of the message type. This is automatically assigned to each message

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -1,26 +1,30 @@
 namespace Unity.Netcode
 {
-    internal struct ChangeOwnershipMessage : INetworkMessage
+    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.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, ref context);
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);
                 return false;
             }
 

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);
-            reader.ReadValue(out NetworkTick);
+                // 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(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>()))
@@ -101,16 +145,24 @@ namespace Unity.Netcode
             {
                 // Note: Delegate creation allocates.
                 // Note: ToArray() also allocates. :(
-                networkManager.InvokeConnectionApproval(ConnectionData, senderId,
-                    (createPlayerObject, playerPrefabHash, approved, position, rotation) =>
+                var response = new NetworkManager.ConnectionApprovalResponse();
+                networkManager.ClientsToApprove[senderId] = response;
+
+                networkManager.ConnectionApprovalCallback(
+                    new NetworkManager.ConnectionApprovalRequest
                     {
-                        var localCreatePlayerObject = createPlayerObject;
-                        networkManager.HandleApproval(senderId, localCreatePlayerObject, playerPrefabHash, approved, position, rotation);
-                    });
+                        Payload = ConnectionData,
+                        ClientNetworkId = senderId
+                    }, response);
             }
             else
             {
-                networkManager.HandleApproval(senderId, networkManager.NetworkConfig.PlayerPrefab != null, null, true, null, null);
+                var response = new NetworkManager.ConnectionApprovalResponse
+                {
+                    Approved = true,
+                    CreatePlayerObject = networkManager.NetworkConfig.PlayerPrefab != null
+                };
+                networkManager.HandleConnectionApproval(senderId, response);
             }
         }
     }

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)
@@ -19,6 +21,11 @@ namespace Unity.Netcode
             }
 
             ObjectInfo.Deserialize(reader);
+            if (!networkManager.NetworkConfig.ForceSamePrefabs && !networkManager.SpawnManager.HasPrefab(ObjectInfo))
+            {
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnAddPrefab, ObjectInfo.Hash, reader, ref context);
+                return false;
+            }
             m_ReceivedNetworkVariableData = reader;
 
             return true;

Runtime/Messaging/Messages/DestroyObjectMessage.cs

@@ -1,22 +1,34 @@
 namespace Unity.Netcode
 {
-    internal struct DestroyObjectMessage : INetworkMessage
+    internal struct DestroyObjectMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
-        public ulong NetworkObjectId;
+        public int Version => 0;
 
-        public void Serialize(FastBufferWriter writer)
+        public ulong NetworkObjectId;
+        public bool DestroyGameObject;
+
+        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)
             {
                 return false;
             }
-            reader.ReadValueSafe(out this);
+
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            reader.ReadValueSafe(out DestroyGameObject);
+
+            if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
+            {
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);
+                return false;
+            }
             return true;
         }
 
@@ -30,7 +42,7 @@ namespace Unity.Netcode
             }
 
             networkManager.NetworkMetrics.TrackObjectDestroyReceived(context.SenderId, networkObject, context.MessageSize);
-            networkManager.SpawnManager.OnDespawnObject(networkObject, true);
+            networkManager.SpawnManager.OnDespawnObject(networkObject, DestroyGameObject);
         }
     }
 }

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);
-            writer.WriteValue(NetworkBehaviourIndex);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            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
                     {
@@ -54,11 +56,19 @@ namespace Unity.Netcode
                     networkVariable.CanClientRead(TargetClientId) &&
                     (NetworkBehaviour.NetworkManager.IsServer || networkVariable.CanClientWrite(NetworkBehaviour.NetworkManager.LocalClientId));
 
+                // Prevent the server from writing to the client that owns a given NetworkVariable
+                // Allowing the write would send an old value to the client and cause jitter
+                if (networkVariable.WritePerm == NetworkVariableWritePermission.Owner &&
+                    networkVariable.OwnerClientId() == TargetClientId)
+                {
+                    shouldWrite = false;
+                }
+
                 if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     if (!shouldWrite)
                     {
-                        BytePacker.WriteValueBitPacked(writer, 0);
+                        BytePacker.WriteValueBitPacked(writer, (ushort)0);
                     }
                 }
                 else
@@ -102,15 +112,10 @@ 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)))
-            {
-                throw new OverflowException($"Not enough data in the buffer to read {nameof(NetworkVariableDeltaMessage)}");
-            }
-
-            reader.ReadValue(out NetworkObjectId);
-            reader.ReadValue(out NetworkBehaviourIndex);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkBehaviourIndex);
 
             m_ReceivedNetworkVariableData = reader;
 
@@ -225,7 +230,7 @@ namespace Unity.Netcode
             }
             else
             {
-                networkManager.SpawnManager.TriggerOnSpawn(NetworkObjectId, m_ReceivedNetworkVariableData, ref context);
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, m_ReceivedNetworkVariableData, ref context);
             }
         }
     }

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);
-            writer.WriteValueSafe(IsReparented);
-            if (IsReparented)
-            {
-                writer.WriteValueSafe(IsLatestParentSet);
-                if (IsLatestParentSet)
-                {
-                    writer.WriteValueSafe((ulong)LatestParent);
-                }
-            }
+            get => ByteUtility.GetBit(m_BitField, 2);
+            set => ByteUtility.SetBit(ref m_BitField, 2, value);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        // 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)
+            {
+                if (IsLatestParentSet)
+                {
+                    BytePacker.WriteValueBitPacked(writer, LatestParent.Value);
+                }
+            }
+
+            // 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);
-            reader.ReadValueSafe(out IsReparented);
-            if (IsReparented)
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            reader.ReadValueSafe(out m_BitField);
+            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.SpawnManager.TriggerOnSpawn(NetworkObjectId, reader, ref context);
+                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.ApplyNetworkParenting();
+            networkObject.SetNetworkParenting(LatestParent, WorldPositionStays);
+            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

@@ -8,29 +8,22 @@ 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))
-            {
-                throw new OverflowException("Not enough space in the buffer to store RPC data.");
-            }
-
-            writer.WriteValue(metadata);
-            writer.WriteBytes(payload.GetUnsafePtr(), payload.Length);
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkBehaviourId);
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkRpcMethodId);
+            writer.WriteBytesSafe(payload.GetUnsafePtr(), payload.Length);
         }
 
         public static unsafe bool Deserialize(ref FastBufferReader reader, ref NetworkContext context, ref RpcMetadata metadata, ref FastBufferReader payload)
         {
-            int metadataSize = FastBufferWriter.GetWriteSize<RpcMetadata>();
-            if (!reader.TryBeginRead(metadataSize))
-            {
-                throw new InvalidOperationException("Not enough data in the buffer to read RPC meta.");
-            }
-
-            reader.ReadValue(out metadata);
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkBehaviourId);
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkRpcMethodId);
 
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(metadata.NetworkObjectId))
             {
-                networkManager.SpawnManager.TriggerOnSpawn(metadata.NetworkObjectId, reader, ref context);
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, metadata.NetworkObjectId, reader, ref context);
                 return false;
             }
 
@@ -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))
@@ -83,7 +76,7 @@ namespace Unity.Netcode
         }
     }
 
-    internal struct RpcMetadata
+    internal struct RpcMetadata : INetworkSerializeByMemcpy
     {
         public ulong NetworkObjectId;
         public ushort NetworkBehaviourId;
@@ -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

@@ -1,22 +1,24 @@
 namespace Unity.Netcode
 {
-    internal struct TimeSyncMessage : INetworkMessage
+    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

@@ -8,6 +8,11 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
+    internal class HandlerNotRegisteredException : SystemException
+    {
+        public HandlerNotRegisteredException() { }
+        public HandlerNotRegisteredException(string issue) : base(issue) { }
+    }
 
     internal class InvalidMessageStructureException : SystemException
     {
@@ -41,15 +46,22 @@ namespace Unity.Netcode
         }
 
         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];
-        private Type[] m_ReverseTypeMap = new Type[255];
+        // These array will grow as we need more message handlers. 4 is just a starting size.
+        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 +71,7 @@ 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 +80,40 @@ 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 +130,7 @@ 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);
@@ -136,11 +178,30 @@ namespace Unity.Netcode
             m_Hooks.Add(hooks);
         }
 
+        public void Unhook(INetworkHooks hooks)
+        {
+            m_Hooks.Remove(hooks);
+        }
+
         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 void HandleIncomingData(ulong clientId, ArraySegment<byte> data, float receiveTime)
@@ -208,11 +269,11 @@ namespace Unity.Netcode
             }
         }
 
-        private bool CanReceive(ulong clientId, Type messageType)
+        private bool CanReceive(ulong clientId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
         {
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
             {
-                if (!m_Hooks[hookIdx].OnVerifyCanReceive(clientId, messageType))
+                if (!m_Hooks[hookIdx].OnVerifyCanReceive(clientId, messageType, messageContent, ref context))
                 {
                     return false;
                 }
@@ -221,6 +282,55 @@ 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)
@@ -240,7 +350,7 @@ namespace Unity.Netcode
             };
 
             var type = m_ReverseTypeMap[header.MessageType];
-            if (!CanReceive(senderId, type))
+            if (!CanReceive(senderId, type, reader, ref context))
             {
                 reader.Dispose();
                 return;
@@ -254,18 +364,29 @@ namespace Unity.Netcode
             var handler = m_MessageHandlers[header.MessageType];
             using (reader)
             {
-                // No user-land message handler exceptions should escape the receive loop.
-                // If an exception is throw, the message is ignored.
-                // Example use case: A bad message is received that can't be deserialized and throws
-                // an OverflowException because it specifies a length greater than the number of bytes in it
-                // for some dynamic-length value.
-                try
+                // 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)
                 {
-                    handler.Invoke(reader, ref context, this);
+                    Debug.LogException(new HandlerNotRegisteredException(header.MessageType.ToString()));
                 }
-                catch (Exception e)
+                else
                 {
-                    Debug.LogException(e);
+                    // No user-land message handler exceptions should escape the receive loop.
+                    // If an exception is throw, the message is ignored.
+                    // Example use case: A bad message is received that can't be deserialized and throws
+                    // an OverflowException because it specifies a length greater than the number of bytes in it
+                    // for some dynamic-length value.
+                    try
+                    {
+                        handler.Invoke(reader, ref context, this);
+                    }
+                    catch (Exception e)
+                    {
+                        Debug.LogException(e);
+                    }
                 }
             }
             for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
@@ -309,7 +430,7 @@ 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)
@@ -320,10 +441,67 @@ 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)
                 {
@@ -361,16 +539,47 @@ namespace Unity.Netcode
                 return 0;
             }
 
-            var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FRAGMENTED_MESSAGE_MAX_SIZE : NON_FRAGMENTED_MESSAGE_MAX_SIZE;
+            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;
+                    }
+                }
 
-            using var tmpSerializer = new FastBufferWriter(NON_FRAGMENTED_MESSAGE_MAX_SIZE - FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp, maxSize - FastBufferWriter.GetWriteSize<MessageHeader>());
+                if (sentMessageVersions.Contains(messageVersion))
+                {
+                    continue;
+                }
 
-            message.Serialize(tmpSerializer);
+                sentMessageVersions.Add(messageVersion);
 
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds);
+                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, messageVersion);
+
+                var size = SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds, messageVersion);
+                largestSerializedSize = size > largestSerializedSize ? size : largestSerializedSize;
+            }
+
+            sentMessageVersions.Dispose();
+
+            return largestSerializedSize;
         }
 
-        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds)
+        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);
@@ -385,6 +594,25 @@ 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))
@@ -435,8 +663,22 @@ 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>

Runtime/Messaging/RpcParams.cs

@@ -3,21 +3,52 @@ using Unity.Collections;
 
 namespace Unity.Netcode
 {
+    /// <summary>
+    /// Server-Side RPC
+    /// Place holder.  <see cref="ServerRpcParams"/>
+    /// Note: Clients always send to one destination when sending RPCs to the server
+    /// so this structure is a place holder
+    /// </summary>
     public struct ServerRpcSendParams
     {
     }
 
+    /// <summary>
+    /// The receive parameters for server-side remote procedure calls
+    /// </summary>
     public struct ServerRpcReceiveParams
     {
+        /// <summary>
+        /// Server-Side RPC
+        /// The client identifier of the sender
+        /// </summary>
         public ulong SenderClientId;
     }
 
+    /// <summary>
+    /// Server-Side RPC
+    /// Can be used with any sever-side remote procedure call
+    /// Note: typically this is use primarily for the <see cref="ServerRpcReceiveParams"/>
+    /// </summary>
     public struct ServerRpcParams
     {
+        /// <summary>
+        /// The server RPC send parameters (currently a place holder)
+        /// </summary>
         public ServerRpcSendParams Send;
+
+        /// <summary>
+        /// The client RPC receive parameters provides you with the sender's identifier
+        /// </summary>
         public ServerRpcReceiveParams Receive;
     }
 
+    /// <summary>
+    /// Client-Side RPC
+    /// The send parameters, when sending client RPCs, provides you wil the ability to
+    /// target specific clients as a managed or unmanaged list:
+    /// <see cref="TargetClientIds"/> and <see cref="TargetClientIdsNativeArray"/>
+    /// </summary>
     public struct ClientRpcSendParams
     {
         /// <summary>
@@ -34,13 +65,32 @@ namespace Unity.Netcode
         public NativeArray<ulong>? TargetClientIdsNativeArray;
     }
 
+    /// <summary>
+    /// Client-Side RPC
+    /// Place holder.  <see cref="ServerRpcParams"/>
+    /// Note: Server will always be the sender, so this structure is a place holder
+    /// </summary>
     public struct ClientRpcReceiveParams
     {
     }
 
+    /// <summary>
+    /// Client-Side RPC
+    /// Can be used with any client-side remote procedure call
+    /// Note: Typically this is used primarily for sending to a specific list
+    /// of clients as opposed to the default (all).
+    /// <see cref="ClientRpcSendParams"/>
+    /// </summary>
     public struct ClientRpcParams
     {
+        /// <summary>
+        /// The client RPC send parameters provides you with the ability to send to a specific list of clients
+        /// </summary>
         public ClientRpcSendParams Send;
+
+        /// <summary>
+        /// The client RPC receive parameters (currently a place holder)
+        /// </summary>
         public ClientRpcReceiveParams Receive;
     }
 

Runtime/Metrics/MetricHooks.cs

@@ -52,7 +52,7 @@ namespace Unity.Netcode
             return true;
         }
 
-        public bool OnVerifyCanReceive(ulong senderId, Type messageType)
+        public bool OnVerifyCanReceive(ulong senderId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
         {
             return true;
         }

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;
-
-        static Dictionary<uint, string> s_SceneEventTypeNames;
-
-        static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
+        private const ulong k_MaxMetricsPerFrame = 1000L;
+        private static Dictionary<uint, string> s_SceneEventTypeNames;
+        private static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
 
         static NetworkMetrics()
         {
@@ -531,7 +528,7 @@ namespace Unity.Netcode
         }
     }
 
-        internal class NetcodeObserver
+    internal class NetcodeObserver
     {
         public static IMetricObserver Observer { get; } = MetricObserverFactory.Construct();
     }

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;
 
@@ -15,7 +15,7 @@ namespace Unity.Netcode
 
         public Object GetNetworkObject(ulong networkObjectId)
         {
-            if(m_NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(networkObjectId, out NetworkObject value))
+            if (m_NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(networkObjectId, out NetworkObject value))
             {
                 return value;
             }

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -24,16 +25,27 @@ namespace Unity.Netcode
         /// </summary>
         public event OnListChangedDelegate OnListChanged;
 
+        /// <summary>
+        /// Constructor method for <see cref="NetworkList"/>
+        /// </summary>
         public NetworkList() { }
 
+        /// <inheritdoc/>
+        /// <param name="values"></param>
+        /// <param name="readPerm"></param>
+        /// <param name="writePerm"></param>
         public NetworkList(IEnumerable<T> values = default,
             NetworkVariableReadPermission readPerm = DefaultReadPerm,
             NetworkVariableWritePermission writePerm = DefaultWritePerm)
             : base(readPerm, writePerm)
         {
-            foreach (var value in values)
+            // allow null IEnumerable<T> to mean "no values"
+            if (values != null)
             {
-                m_List.Add(value);
+                foreach (var value in values)
+                {
+                    m_List.Add(value);
+                }
             }
         }
 
@@ -41,7 +53,10 @@ namespace Unity.Netcode
         public override void ResetDirty()
         {
             base.ResetDirty();
-            m_DirtyEvents.Clear();
+            if (m_DirtyEvents.Length > 0)
+            {
+                m_DirtyEvents.Clear();
+            }
         }
 
         /// <inheritdoc />
@@ -51,6 +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)
         {
@@ -67,34 +94,35 @@ namespace Unity.Netcode
             writer.WriteValueSafe((ushort)m_DirtyEvents.Length);
             for (int i = 0; i < m_DirtyEvents.Length; i++)
             {
-                writer.WriteValueSafe(m_DirtyEvents[i].Type);
-                switch (m_DirtyEvents[i].Type)
+                var element = m_DirtyEvents.ElementAt(i);
+                writer.WriteValueSafe(element.Type);
+                switch (element.Type)
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
+                            NetworkVariableSerialization<T>.Write(writer, ref element.Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Insert:
                         {
-                            writer.WriteValueSafe(m_DirtyEvents[i].Index);
-                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
+                            writer.WriteValueSafe(element.Index);
+                            NetworkVariableSerialization<T>.Write(writer, ref element.Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
+                            NetworkVariableSerialization<T>.Write(writer, ref element.Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.RemoveAt:
                         {
-                            writer.WriteValueSafe(m_DirtyEvents[i].Index);
+                            writer.WriteValueSafe(element.Index);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Value:
                         {
-                            writer.WriteValueSafe(m_DirtyEvents[i].Index);
-                            NetworkVariable<T>.Write(writer, m_DirtyEvents[i].Value);
+                            writer.WriteValueSafe(element.Index);
+                            NetworkVariableSerialization<T>.Write(writer, ref element.Value);
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Clear:
@@ -112,7 +140,7 @@ namespace Unity.Netcode
             writer.WriteValueSafe((ushort)m_List.Length);
             for (int i = 0; i < m_List.Length; i++)
             {
-                NetworkVariable<T>.Write(writer, m_List[i]);
+                NetworkVariableSerialization<T>.Write(writer, ref m_List.ElementAt(i));
             }
         }
 
@@ -123,7 +151,8 @@ namespace Unity.Netcode
             reader.ReadValueSafe(out ushort count);
             for (int i = 0; i < count; i++)
             {
-                NetworkVariable<T>.Read(reader, out T value);
+                var value = new T();
+                NetworkVariableSerialization<T>.Read(reader, ref value);
                 m_List.Add(value);
             }
         }
@@ -139,7 +168,8 @@ namespace Unity.Netcode
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            NetworkVariable<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             m_List.Add(value);
 
                             if (OnListChanged != null)
@@ -160,15 +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);
-                            NetworkVariable<T>.Read(reader, out T value);
-                            m_List.InsertRangeWithBeginEnd(index, index + 1);
-                            m_List[index] = 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)
                             {
@@ -188,12 +228,14 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = m_List[index]
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            NetworkVariable<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)
                             {
@@ -220,6 +262,7 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -247,13 +290,15 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Value:
                         {
                             reader.ReadValueSafe(out int index);
-                            NetworkVariable<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");
@@ -282,6 +327,7 @@ namespace Unity.Netcode
                                     Value = value,
                                     PreviousValue = previousValue
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -304,6 +350,7 @@ namespace Unity.Netcode
                                 {
                                     Type = eventType
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -326,6 +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>()
@@ -341,6 +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>()
@@ -354,14 +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;
@@ -390,8 +455,21 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void Insert(int index, T item)
         {
-            m_List.InsertRangeWithBeginEnd(index, index + 1);
-            m_List[index] = 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>()
             {
@@ -406,6 +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>()
@@ -423,13 +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);
@@ -439,9 +531,13 @@ namespace Unity.Netcode
         private void HandleAddListEvent(NetworkListEvent<T> listEvent)
         {
             m_DirtyEvents.Add(listEvent);
+            MarkNetworkObjectDirty();
             OnListChanged?.Invoke(listEvent);
         }
 
+        /// <summary>
+        /// This is actually unused left-over from a previous interface
+        /// </summary>
         public int LastModifiedTick
         {
             get
@@ -451,6 +547,11 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Overridden <see cref="IDisposable"/> implementation.
+        /// CAUTION: If you derive from this class and override the <see cref="Dispose"/> method,
+        /// you **must** always invoke the base.Dispose() method!
+        /// </summary>
         public override void Dispose()
         {
             m_List.Dispose();

Runtime/NetworkVariable/NetworkVariable.cs

@@ -1,63 +1,15 @@
 using UnityEngine;
 using System;
-using System.Runtime.CompilerServices;
-using Unity.Collections.LowLevel.Unsafe;
 
 namespace Unity.Netcode
 {
     /// <summary>
     /// A variable that can be synchronized over the network.
     /// </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
     {
-        // Functions that know how to serialize INetworkSerializable
-        internal static void WriteNetworkSerializable<TForMethod>(FastBufferWriter writer, in TForMethod value)
-            where TForMethod : INetworkSerializable, new()
-        {
-            writer.WriteNetworkSerializable(value);
-        }
-        internal static void ReadNetworkSerializable<TForMethod>(FastBufferReader reader, out TForMethod value)
-            where TForMethod : INetworkSerializable, new()
-        {
-            reader.ReadNetworkSerializable(out value);
-        }
-
-        // Functions that serialize other types
-        private static void WriteValue<TForMethod>(FastBufferWriter writer, in TForMethod value)
-            where TForMethod : unmanaged
-        {
-            writer.WriteValueSafe(value);
-        }
-
-        private static void ReadValue<TForMethod>(FastBufferReader reader, out TForMethod value)
-            where TForMethod : unmanaged
-        {
-            reader.ReadValueSafe(out value);
-        }
-
-        internal delegate void WriteDelegate<TForMethod>(FastBufferWriter writer, in TForMethod value);
-
-        internal delegate void ReadDelegate<TForMethod>(FastBufferReader reader, out TForMethod value);
-
-        // These static delegates provide the right implementation for writing and reading a particular network variable type.
-        // For most types, these default to WriteValue() and ReadValue(), which perform simple memcpy operations.
-        //
-        // INetworkSerializableILPP will generate startup code that will set it to WriteNetworkSerializable()
-        // and ReadNetworkSerializable() for INetworkSerializable types, which will call NetworkSerialize().
-        //
-        // In the future we may be able to use this to provide packing implementations for floats and integers to optimize bandwidth usage.
-        //
-        // The reason this is done is to avoid runtime reflection and boxing in NetworkVariable - without this,
-        // NetworkVariable would need to do a `var is INetworkSerializable` check, and then cast to INetworkSerializable,
-        // *both* of which would cause a boxing allocation. Alternatively, NetworkVariable could have been split into
-        // NetworkVariable and NetworkSerializableVariable or something like that, which would have caused a poor
-        // user experience and an API that's easier to get wrong than right. This is a bit ugly on the implementation
-        // side, but it gets the best achievable user experience and performance.
-        internal static WriteDelegate<T> Write = WriteValue;
-        internal static ReadDelegate<T> Read = ReadValue;
-
-
         /// <summary>
         /// Delegate type for value changed event
         /// </summary>
@@ -69,7 +21,12 @@ namespace Unity.Netcode
         /// </summary>
         public OnValueChangedDelegate OnValueChanged;
 
-
+        /// <summary>
+        /// Constructor for <see cref="NetworkVariable{T}"/>
+        /// </summary>
+        /// <param name="value">initial value set that is of type T</param>
+        /// <param name="readPerm">the <see cref="NetworkVariableReadPermission"/> for this <see cref="NetworkVariable{T}"/></param>
+        /// <param name="writePerm">the <see cref="NetworkVariableWritePermission"/> for this <see cref="NetworkVariable{T}"/></param>
         public NetworkVariable(T value = default,
             NetworkVariableReadPermission readPerm = DefaultReadPerm,
             NetworkVariableWritePermission writePerm = DefaultWritePerm)
@@ -78,6 +35,9 @@ namespace Unity.Netcode
             m_InternalValue = value;
         }
 
+        /// <summary>
+        /// The internal value of the NetworkVariable
+        /// </summary>
         [SerializeField]
         private protected T m_InternalValue;
 
@@ -90,7 +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;
                 }
@@ -104,24 +64,14 @@ namespace Unity.Netcode
             }
         }
 
-        // Compares two values of the same unmanaged type by underlying memory
-        // Ignoring any overriden value checks
-        // Size is fixed
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe bool ValueEquals(ref T a, ref T b)
-        {
-            // get unmanaged pointers
-            var aptr = UnsafeUtility.AddressOf(ref a);
-            var bptr = UnsafeUtility.AddressOf(ref b);
-
-            // compare addresses
-            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(T)) == 0;
-        }
-
-
+        /// <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.
+        /// </summary>
+        /// <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);
@@ -143,12 +93,17 @@ namespace Unity.Netcode
         /// <param name="keepDirtyDelta">Whether or not the container should keep the dirty delta, or mark the delta as consumed</param>
         public override void ReadDelta(FastBufferReader reader, bool keepDirtyDelta)
         {
+            // todo:
+            // keepDirtyDelta marks a variable received as dirty and causes the server to send the value to clients
+            // In a prefect world, whether a variable was A) modified locally or B) received and needs retransmit
+            // would be stored in different fields
+
             T previousValue = m_InternalValue;
-            Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
 
             if (keepDirtyDelta)
             {
-                m_IsDirty = true;
+                SetDirty(true);
             }
 
             OnValueChanged?.Invoke(previousValue, m_InternalValue);
@@ -157,13 +112,13 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void ReadField(FastBufferReader reader)
         {
-            Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
         }
 
         /// <inheritdoc />
         public override void WriteField(FastBufferWriter writer)
         {
-            Write(writer, m_InternalValue);
+            NetworkVariableSerialization<T>.Write(writer, ref m_InternalValue);
         }
     }
 }

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -1,4 +1,5 @@
 using System;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -12,16 +13,36 @@ namespace Unity.Netcode
         /// </summary>
         internal const NetworkDelivery Delivery = NetworkDelivery.ReliableFragmentedSequenced;
 
+        /// <summary>
+        /// Maintains a link to the associated NetworkBehaviour
+        /// </summary>
         private protected NetworkBehaviour m_NetworkBehaviour;
 
+        /// <summary>
+        /// Initializes the NetworkVariable
+        /// </summary>
+        /// <param name="networkBehaviour">The NetworkBehaviour the NetworkVariable belongs to</param>
         public void Initialize(NetworkBehaviour networkBehaviour)
         {
             m_NetworkBehaviour = networkBehaviour;
         }
 
+        /// <summary>
+        /// The default read permissions
+        /// </summary>
         public const NetworkVariableReadPermission DefaultReadPerm = NetworkVariableReadPermission.Everyone;
+
+        /// <summary>
+        /// The default write permissions
+        /// </summary>
         public const NetworkVariableWritePermission DefaultWritePerm = NetworkVariableWritePermission.Server;
 
+        /// <summary>
+        /// The default constructor for <see cref="NetworkVariableBase"/> that can be used to create a
+        /// custom NetworkVariable.
+        /// </summary>
+        /// <param name="readPerm">the <see cref="NetworkVariableReadPermission"/> access settings</param>
+        /// <param name="writePerm">the <see cref="NetworkVariableWritePermission"/> access settings</param>
         protected NetworkVariableBase(
             NetworkVariableReadPermission readPerm = DefaultReadPerm,
             NetworkVariableWritePermission writePerm = DefaultWritePerm)
@@ -30,7 +51,11 @@ namespace Unity.Netcode
             WritePerm = writePerm;
         }
 
-        private protected bool m_IsDirty;
+        /// <summary>
+        /// The <see cref="m_IsDirty"/> property is used to determine if the
+        /// value of the `NetworkVariable` has changed.
+        /// </summary>
+        private bool m_IsDirty;
 
         /// <summary>
         /// Gets or sets the name of the network variable's instance
@@ -43,14 +68,29 @@ namespace Unity.Netcode
         /// </summary>
         public readonly NetworkVariableReadPermission ReadPerm;
 
+        /// <summary>
+        /// The write permission for this var
+        /// </summary>
         public readonly NetworkVariableWritePermission WritePerm;
 
         /// <summary>
         /// Sets whether or not the variable needs to be delta synced
         /// </summary>
+        /// <param name="isDirty">Whether or not the var is dirty</param>
         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>
@@ -70,6 +110,11 @@ namespace Unity.Netcode
             return m_IsDirty;
         }
 
+        /// <summary>
+        /// Gets if a specific client has permission to read the var or not
+        /// </summary>
+        /// <param name="clientId">The client id</param>
+        /// <returns>Whether or not the client has permission to read</returns>
         public bool CanClientRead(ulong clientId)
         {
             switch (ReadPerm)
@@ -78,10 +123,15 @@ 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;
             }
         }
 
+        /// <summary>
+        /// Gets if a specific client has permission to write the var or not
+        /// </summary>
+        /// <param name="clientId">The client id</param>
+        /// <returns>Whether or not the client has permission to write</returns>
         public bool CanClientWrite(ulong clientId)
         {
             switch (WritePerm)
@@ -94,6 +144,14 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Returns the ClientId of the owning client
+        /// </summary>
+        internal ulong OwnerClientId()
+        {
+            return m_NetworkBehaviour.NetworkObject.OwnerClientId;
+        }
+
         /// <summary>
         /// Writes the dirty changes, that is, the changes since the variable was last dirty, to the writer
         /// </summary>
@@ -119,6 +177,9 @@ namespace Unity.Netcode
         /// <param name="keepDirtyDelta">Whether or not the delta should be kept as dirty or consumed</param>
         public abstract void ReadDelta(FastBufferReader reader, bool keepDirtyDelta);
 
+        /// <summary>
+        /// Virtual <see cref="IDisposable"/> implementation
+        /// </summary>
         public virtual void Dispose()
         {
         }

Runtime/NetworkVariable/NetworkVariableHelper.cs

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

Runtime/NetworkVariable/NetworkVariablePermission.cs

@@ -1,14 +1,32 @@
 namespace Unity.Netcode
 {
+    /// <summary>
+    /// The permission types for reading a var
+    /// </summary>
     public enum NetworkVariableReadPermission
     {
+        /// <summary>
+        /// Everyone can read
+        /// </summary>
         Everyone,
+        /// <summary>
+        /// Only the owner and the server can read
+        /// </summary>
         Owner,
     }
 
+    /// <summary>
+    ///  The permission types for writing a var
+    /// </summary>
     public enum NetworkVariableWritePermission
     {
+        /// <summary>
+        /// Only the server can write
+        /// </summary>
         Server,
+        /// <summary>
+        /// Only the owner can write
+        /// </summary>
         Owner
     }
 }

Runtime/NetworkVariable/NetworkVariableSerialization.cs

@@ -0,0 +1,443 @@
+using System;
+using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Interface used by NetworkVariables to serialize them
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal interface INetworkVariableSerializer<T>
+    {
+        // Write has to be taken by ref here because of INetworkSerializable
+        // Open Instance Delegates (pointers to methods without an instance attached to them)
+        // require the first parameter passed to them (the instance) to be passed by ref.
+        // So foo.Bar() becomes BarDelegate(ref foo);
+        // 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, ref T value);
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class ShortSerializer : INetworkVariableSerializer<short>
+    {
+        public void Write(FastBufferWriter writer, ref short value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref short value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class UshortSerializer : INetworkVariableSerializer<ushort>
+    {
+        public void Write(FastBufferWriter writer, ref ushort value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ushort value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class IntSerializer : INetworkVariableSerializer<int>
+    {
+        public void Write(FastBufferWriter writer, ref int value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref int value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class UintSerializer : INetworkVariableSerializer<uint>
+    {
+        public void Write(FastBufferWriter writer, ref uint value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref uint value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class LongSerializer : INetworkVariableSerializer<long>
+    {
+        public void Write(FastBufferWriter writer, ref long value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref long value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class UlongSerializer : INetworkVariableSerializer<ulong>
+    {
+        public void Write(FastBufferWriter writer, ref ulong value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ulong value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Basic serializer for unmanaged types.
+    /// This covers primitives, built-in unity types, and IForceSerializeByMemcpy
+    /// Since all of those ultimately end up calling WriteUnmanagedSafe, this simplifies things
+    /// by calling that directly - thus preventing us from having to have a specific T that meets
+    /// the specific constraints that the various generic WriteValue calls require.
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal class UnmanagedTypeSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            writer.WriteUnmanagedSafe(value);
+        }
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            reader.ReadUnmanagedSafe(out value);
+        }
+    }
+
+    /// <summary>
+    /// Serializer for FixedStrings
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal class FixedStringSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INativeList<byte>, IUTF8Bytes
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            writer.WriteValueSafe(value);
+        }
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            reader.ReadValueSafeInPlace(ref value);
+        }
+    }
+
+    /// <summary>
+    /// Serializer for unmanaged INetworkSerializable types
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal class UnmanagedNetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INetworkSerializable
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
+            value.NetworkSerialize(bufferSerializer);
+        }
+        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();
+                }
+                value.NetworkSerialize(bufferSerializer);
+            }
+        }
+    }
+
+    /// <summary>
+    /// This class is used to register user serialization with NetworkVariables for types
+    /// that are serialized via user serialization, such as with FastBufferReader and FastBufferWriter
+    /// extension methods. Finding those methods isn't achievable efficiently at runtime, so this allows
+    /// users to tell NetworkVariable about those extension methods (or simply pass in a lambda)
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public class UserNetworkVariableSerialization<T>
+    {
+        /// <summary>
+        /// The write value delegate handler definition
+        /// </summary>
+        /// <param name="writer">The <see cref="FastBufferWriter"/> to write the value of type `T`</param>
+        /// <param name="value">The value of type `T` to be written</param>
+        public delegate void WriteValueDelegate(FastBufferWriter writer, in T value);
+
+        /// <summary>
+        /// The read value delegate handler definition
+        /// </summary>
+        /// <param name="reader">The <see cref="FastBufferReader"/> to read the value of type `T`</param>
+        /// <param name="value">The value of type `T` to be read</param>
+        public delegate void ReadValueDelegate(FastBufferReader reader, out T value);
+
+        /// <summary>
+        /// The <see cref="WriteValueDelegate"/> delegate handler declaration
+        /// </summary>
+        public static WriteValueDelegate WriteValue;
+
+        /// <summary>
+        /// The <see cref="ReadValueDelegate"/> delegate handler declaration
+        /// </summary>
+        public static ReadValueDelegate ReadValue;
+    }
+
+    /// <summary>
+    /// This class is instantiated for types that we can't determine ahead of time are serializable - types
+    /// that don't meet any of the constraints for methods that are available on FastBufferReader and
+    /// FastBufferWriter. These types may or may not be serializable through extension methods. To ensure
+    /// the user has time to pass in the delegates to UserNetworkVariableSerialization, the existence
+    /// of user serialization isn't checked until it's used, so if no serialization is provided, this
+    /// will throw an exception when an object containing the relevant NetworkVariable is spawned.
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    internal class FallbackSerializer<T> : INetworkVariableSerializer<T>
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null)
+            {
+                throw new ArgumentException($"Type {typeof(T).FullName} is not supported by {typeof(NetworkVariable<>).Name}. If this is a type you can change, then either implement {nameof(INetworkSerializable)} or mark it as serializable by memcpy by adding {nameof(INetworkSerializeByMemcpy)} to its interface list. If not, assign serialization code to {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.WriteValue)} and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+            }
+            UserNetworkVariableSerialization<T>.WriteValue(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null)
+            {
+                throw new ArgumentException($"Type {typeof(T).FullName} is not supported by {typeof(NetworkVariable<>).Name}. If this is a type you can change, then either implement {nameof(INetworkSerializable)} or mark it as serializable by memcpy by adding {nameof(INetworkSerializeByMemcpy)} to its interface list. If not, assign serialization code to {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.WriteValue)} and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+            }
+            UserNetworkVariableSerialization<T>.ReadValue(reader, out value);
+        }
+    }
+
+    /// <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
+    {
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
+#if UNITY_EDITOR
+        [InitializeOnLoadMethod]
+#endif
+        internal static void InitializeIntegerSerialization()
+        {
+            NetworkVariableSerialization<short>.Serializer = new ShortSerializer();
+            NetworkVariableSerialization<short>.AreEqual = NetworkVariableSerialization<short>.ValueEquals;
+            NetworkVariableSerialization<ushort>.Serializer = new UshortSerializer();
+            NetworkVariableSerialization<ushort>.AreEqual = NetworkVariableSerialization<ushort>.ValueEquals;
+            NetworkVariableSerialization<int>.Serializer = new IntSerializer();
+            NetworkVariableSerialization<int>.AreEqual = NetworkVariableSerialization<int>.ValueEquals;
+            NetworkVariableSerialization<uint>.Serializer = new UintSerializer();
+            NetworkVariableSerialization<uint>.AreEqual = NetworkVariableSerialization<uint>.ValueEquals;
+            NetworkVariableSerialization<long>.Serializer = new LongSerializer();
+            NetworkVariableSerialization<long>.AreEqual = NetworkVariableSerialization<long>.ValueEquals;
+            NetworkVariableSerialization<ulong>.Serializer = new UlongSerializer();
+            NetworkVariableSerialization<ulong>.AreEqual = NetworkVariableSerialization<ulong>.ValueEquals;
+        }
+
+        /// <summary>
+        /// Registeres an unmanaged type that will be serialized by a direct memcpy into a buffer
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_UnmanagedByMemcpy<T>() where T : unmanaged
+        {
+            NetworkVariableSerialization<T>.Serializer = new UnmanagedTypeSerializer<T>();
+        }
+
+        /// <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>
+    /// Support methods for reading/writing NetworkVariables
+    /// Because there are multiple overloads of WriteValue/ReadValue based on different generic constraints,
+    /// but there's no way to achieve the same thing with a class, this sets up various read/write schemes
+    /// based on which constraints are met by `T` using reflection, which is done at module load time.
+    /// </summary>
+    /// <typeparam name="T">The type the associated NetworkVariable is templated on</typeparam>
+    [Serializable]
+    public static class NetworkVariableSerialization<T>
+    {
+        internal static INetworkVariableSerializer<T> Serializer = new FallbackSerializer<T>();
+
+        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
+        {
+            // get unmanaged pointers
+            var aptr = UnsafeUtility.AddressOf(ref a);
+            var bptr = UnsafeUtility.AddressOf(ref b);
+
+            // compare addresses
+            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(TValueType)) == 0;
+        }
+
+        internal static bool EqualityEqualsObject<TValueType>(ref TValueType a, ref TValueType b) where TValueType : class, IEquatable<TValueType>
+        {
+            if (a == null)
+            {
+                return b == null;
+            }
+
+            if (b == null)
+            {
+                return false;
+            }
+
+            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)
+        {
+            Serializer.Write(writer, ref value);
+        }
+
+        internal static void Read(FastBufferReader reader, ref T value)
+        {
+            Serializer.Read(reader, ref value);
+        }
+    }
+}

Runtime/NetworkVariable/NetworkVariableSerialization.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 2c6ef5fdf2e94ec3b4ce8086d52700b3
+timeCreated: 1650985453

Runtime/Profiling/ProfilingHooks.cs

@@ -82,7 +82,7 @@ namespace Unity.Netcode
             return true;
         }
 
-        public bool OnVerifyCanReceive(ulong senderId, Type messageType)
+        public bool OnVerifyCanReceive(ulong senderId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
         {
             return true;
         }

Runtime/SceneManagement/ISceneManagerHandler.cs

@@ -1,4 +1,3 @@
-using System;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
@@ -10,19 +9,8 @@ namespace Unity.Netcode
     /// </summary>
     internal interface ISceneManagerHandler
     {
-        // Generic action to call when a scene is finished loading/unloading
-        struct SceneEventAction
-        {
-            internal uint SceneEventId;
-            internal Action<uint> EventAction;
-            internal void Invoke()
-            {
-                EventAction.Invoke(SceneEventId);
-            }
-        }
+        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventProgress sceneEventProgress);
 
-        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventAction sceneEventAction);
-
-        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventAction sceneEventAction);
+        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventProgress sceneEventProgress);
     }
 }

Runtime/SceneManagement/NetworkSceneManager.cs

@@ -12,6 +12,7 @@ namespace Unity.Netcode
     /// delegate type <see cref="NetworkSceneManager.SceneEventDelegate"/> uses this class to provide
     /// scene event status.<br/>
     /// <em>Note: This is only when <see cref="NetworkConfig.EnableSceneManagement"/> is enabled.</em><br/>
+    /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
     /// See also: <br/>
     /// <seealso cref="SceneEventType"/>
     /// </summary>
@@ -166,6 +167,7 @@ namespace Unity.Netcode
         /// <item><term><see cref="OnUnloadComplete"/> Invoked only when an <see cref="SceneEventType.UnloadComplete"/> event is being processed</term></item>
         /// <item><term><see cref="OnSynchronizeComplete"/> Invoked only when a <see cref="SceneEventType.SynchronizeComplete"/> event is being processed</term></item>
         /// </list>
+        /// <em>Note: Do not start new scene events within NetworkSceneManager scene event notification callbacks.</em><br/>
         /// </summary>
         public event SceneEventDelegate OnSceneEvent;
 
@@ -239,13 +241,15 @@ namespace Unity.Netcode
 
         /// <summary>
         /// Invoked when a <see cref="SceneEventType.Load"/> event is started by the server.<br/>
-        /// <em>Note: The server and connected client(s) will always receive this notification.</em>
+        /// <em>Note: The server and connected client(s) will always receive this notification.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnLoadDelegateHandler OnLoad;
 
         /// <summary>
         /// Invoked when a <see cref="SceneEventType.Unload"/> event is started by the server.<br/>
-        /// <em>Note: The server and connected client(s) will always receive this notification.</em>
+        /// <em>Note: The server and connected client(s) will always receive this notification.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnUnloadDelegateHandler OnUnload;
 
@@ -254,7 +258,8 @@ namespace Unity.Netcode
         /// after a client is approved for connection in order to synchronize the client with the currently loaded
         /// scenes and NetworkObjects.  This event signifies the beginning of the synchronization event.<br/>
         /// <em>Note: The server and connected client(s) will always receive this notification.
-        /// This event is generated on a per newly connected and approved client basis.</em>
+        /// This event is generated on a per newly connected and approved client basis.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnSynchronizeDelegateHandler OnSynchronize;
 
@@ -263,7 +268,8 @@ namespace Unity.Netcode
         /// This event signifies the end of an existing <see cref="SceneEventType.Load"/> event as it pertains
         /// to all clients connected when the event was started.  This event signifies that all clients (and server) have
         /// finished the <see cref="SceneEventType.Load"/> event.<br/>
-        /// <em>Note: this is useful to know when all clients have loaded the same scene (single or additive mode)</em>
+        /// <em>Note: this is useful to know when all clients have loaded the same scene (single or additive mode)</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnEventCompletedDelegateHandler OnLoadEventCompleted;
 
@@ -273,21 +279,24 @@ namespace Unity.Netcode
         /// to all clients connected when the event was started.  This event signifies that all clients (and server) have
         /// finished the <see cref="SceneEventType.Unload"/> event.<br/>
         /// <em>Note: this is useful to know when all clients have unloaded a specific scene.  The <see cref="LoadSceneMode"/> will
-        /// always be <see cref="LoadSceneMode.Additive"/> for this event.</em>
+        /// always be <see cref="LoadSceneMode.Additive"/> for this event.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnEventCompletedDelegateHandler OnUnloadEventCompleted;
 
         /// <summary>
         /// Invoked when a <see cref="SceneEventType.LoadComplete"/> event is generated by a client or server.<br/>
         /// <em>Note: The server receives this message from all clients (including itself).
-        /// Each client receives their own notification sent to the server.</em>
+        /// Each client receives their own notification sent to the server.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnLoadCompleteDelegateHandler OnLoadComplete;
 
         /// <summary>
         /// Invoked when a <see cref="SceneEventType.UnloadComplete"/> event is generated by a client or server.<br/>
         /// <em>Note: The server receives this message from all clients (including itself).
-        /// Each client receives their own notification sent to the server.</em>
+        /// Each client receives their own notification sent to the server.</em><br/>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnUnloadCompleteDelegateHandler OnUnloadComplete;
 
@@ -296,6 +305,7 @@ namespace Unity.Netcode
         /// <em> Note: The server receives this message from the client, but will never generate this event for itself.
         /// Each client receives their own notification sent to the server.  This is useful to know that a client has
         /// completed the entire connection sequence, loaded all scenes, and synchronized all NetworkObjects.</em>
+        /// <em>*** Do not start new scene events within scene event notification callbacks.</em><br/>
         /// </summary>
         public event OnSynchronizeCompleteDelegateHandler OnSynchronizeComplete;
 
@@ -319,30 +329,30 @@ namespace Unity.Netcode
         public VerifySceneBeforeLoadingDelegateHandler VerifySceneBeforeLoading;
 
         /// <summary>
-        ///  Proof of concept: Interface version that allows for the decoupling from
-        ///  the SceneManager's Load and Unload methods for testing purposes (potentially other future usage)
+        /// The SceneManagerHandler implementation
+        /// </summary>
+        internal ISceneManagerHandler SceneManagerHandler = new DefaultSceneManagerHandler();
+
+        /// <summary>
+        ///  The default SceneManagerHandler that interfaces between the SceneManager and NetworkSceneManager
         /// </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;
             }
         }
 
-        internal ISceneManagerHandler SceneManagerHandler = new DefaultSceneManagerHandler();
-        /// End of Proof of Concept
-
-
         internal readonly Dictionary<Guid, SceneEventProgress> SceneEventProgressTracking = new Dictionary<Guid, SceneEventProgress>();
 
         /// <summary>
@@ -425,6 +435,8 @@ namespace Unity.Netcode
         /// </summary>
         public void Dispose()
         {
+            SceneUnloadEventHandler.Shutdown();
+
             foreach (var keypair in SceneEventDataStore)
             {
                 if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
@@ -632,6 +644,12 @@ namespace Unity.Netcode
             return validated;
         }
 
+        /// <summary>
+        /// Used for NetcodeIntegrationTest testing in order to properly
+        /// assign the right loaded scene to the right client's ScenesLoaded list
+        /// </summary>
+        internal Func<string, Scene> OverrideGetAndAddNewlyLoadedSceneByName;
+
         /// <summary>
         /// Since SceneManager.GetSceneByName only returns the first scene that matches the name
         /// we must "find" a newly added scene by looking through all loaded scenes and determining
@@ -643,20 +661,27 @@ namespace Unity.Netcode
         /// <returns></returns>
         internal Scene GetAndAddNewlyLoadedSceneByName(string sceneName)
         {
-            for (int i = 0; i < SceneManager.sceneCount; i++)
+            if (OverrideGetAndAddNewlyLoadedSceneByName != null)
             {
-                var sceneLoaded = SceneManager.GetSceneAt(i);
-                if (sceneLoaded.name == sceneName)
+                return OverrideGetAndAddNewlyLoadedSceneByName.Invoke(sceneName);
+            }
+            else
+            {
+                for (int i = 0; i < SceneManager.sceneCount; i++)
                 {
-                    if (!ScenesLoaded.ContainsKey(sceneLoaded.handle))
+                    var sceneLoaded = SceneManager.GetSceneAt(i);
+                    if (sceneLoaded.name == sceneName)
                     {
-                        ScenesLoaded.Add(sceneLoaded.handle, sceneLoaded);
-                        return sceneLoaded;
+                        if (!ScenesLoaded.ContainsKey(sceneLoaded.handle))
+                        {
+                            ScenesLoaded.Add(sceneLoaded.handle, sceneLoaded);
+                            return sceneLoaded;
+                        }
                     }
                 }
-            }
 
-            throw new Exception($"Failed to find any loaded scene named {sceneName}!");
+                throw new Exception($"Failed to find any loaded scene named {sceneName}!");
+            }
         }
 
         /// <summary>
@@ -720,18 +745,18 @@ namespace Unity.Netcode
         /// </summary>
         /// <param name="globalObjectIdHash"></param>
         /// <returns></returns>
-        internal NetworkObject GetSceneRelativeInSceneNetworkObject(uint globalObjectIdHash)
+        internal NetworkObject GetSceneRelativeInSceneNetworkObject(uint globalObjectIdHash, int? networkSceneHandle)
         {
             if (ScenePlacedObjects.ContainsKey(globalObjectIdHash))
             {
-                if (ScenePlacedObjects[globalObjectIdHash].ContainsKey(SceneBeingSynchronized.handle))
+                var sceneHandle = SceneBeingSynchronized.handle;
+                if (networkSceneHandle.HasValue && networkSceneHandle.Value != 0)
                 {
-                    var inScenePlacedNetworkObject = ScenePlacedObjects[globalObjectIdHash][SceneBeingSynchronized.handle];
-
-                    // We can only have 1 duplicated globalObjectIdHash per scene instance, so remove it once it has been returned
-                    ScenePlacedObjects[globalObjectIdHash].Remove(SceneBeingSynchronized.handle);
-
-                    return inScenePlacedNetworkObject;
+                    sceneHandle = ServerSceneHandleToClientSceneHandle[networkSceneHandle.Value];
+                }
+                if (ScenePlacedObjects[globalObjectIdHash].ContainsKey(sceneHandle))
+                {
+                    return ScenePlacedObjects[globalObjectIdHash][sceneHandle];
                 }
             }
             return null;
@@ -859,16 +884,17 @@ namespace Unity.Netcode
         /// Callback for the <see cref="SceneEventProgress.OnComplete"/> <see cref="SceneEventProgress.OnCompletedDelegate"/> handler
         /// </summary>
         /// <param name="sceneEventProgress"></param>
-        /// <returns></returns>
         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 = m_NetworkManager.ConnectedClients.Keys.Except(sceneEventProgress.DoneClients).ToList();
+            sceneEventData.ClientsTimedOut = clientsThatTimedOut;
 
             var message = new SceneEventMessage
             {
@@ -889,8 +915,8 @@ namespace Unity.Netcode
                 SceneName = SceneNameFromHash(sceneEventProgress.SceneHash),
                 ClientId = NetworkManager.ServerClientId,
                 LoadSceneMode = sceneEventProgress.LoadSceneMode,
-                ClientsThatCompleted = sceneEventProgress.DoneClients,
-                ClientsThatTimedOut = m_NetworkManager.ConnectedClients.Keys.Except(sceneEventProgress.DoneClients).ToList(),
+                ClientsThatCompleted = clientsThatCompleted,
+                ClientsThatTimedOut = clientsThatTimedOut,
             });
 
             if (sceneEventData.SceneEventType == SceneEventType.LoadEventCompleted)
@@ -911,7 +937,7 @@ namespace Unity.Netcode
         /// Unloads an additively loaded scene.  If you want to unload a <see cref="LoadSceneMode.Single"/> mode loaded scene load another <see cref="LoadSceneMode.Single"/> scene.
         /// When applicable, the <see cref="AsyncOperation"/> is delivered within the <see cref="SceneEvent"/> via the <see cref="OnSceneEvent"/>
         /// </summary>
-        /// <param name="sceneName">scene name to unload</param>
+        /// <param name="scene"></param>
         /// <returns><see cref="SceneEventProgressStatus"/> (<see cref="SceneEventProgressStatus.Started"/> means it was successful)</returns>
         public SceneEventProgressStatus UnloadScene(Scene scene)
         {
@@ -945,11 +971,9 @@ namespace Unity.Netcode
             sceneEventProgress.SceneEventType = SceneEventType.UnloadEventCompleted;
 
             ScenesLoaded.Remove(scene.handle);
-
-            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(scene,
-                    new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventData.SceneEventId, EventAction = OnSceneUnloaded });
-
-            sceneEventProgress.SetSceneLoadOperation(sceneUnload);
+            sceneEventProgress.SceneEventId = sceneEventData.SceneEventId;
+            sceneEventProgress.OnSceneEventCompleted = OnSceneUnloaded;
+            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(scene, sceneEventProgress);
 
             // Notify local server that a scene is going to be unloaded
             OnSceneEvent?.Invoke(new SceneEvent()
@@ -993,9 +1017,10 @@ namespace Unity.Netcode
                     $"because the client scene handle {sceneHandle} was not found in ScenesLoaded!");
             }
             m_IsSceneEventActive = true;
-
-            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(ScenesLoaded[sceneHandle],
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventData.SceneEventId, EventAction = OnSceneUnloaded });
+            var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
+            sceneEventProgress.SceneEventId = sceneEventData.SceneEventId;
+            sceneEventProgress.OnSceneEventCompleted = OnSceneUnloaded;
+            var sceneUnload = SceneManagerHandler.UnloadSceneAsync(ScenesLoaded[sceneHandle], sceneEventProgress);
 
             ScenesLoaded.Remove(sceneHandle);
 
@@ -1021,6 +1046,12 @@ namespace Unity.Netcode
         /// </summary>
         private void OnSceneUnloaded(uint sceneEventId)
         {
+            // If we are shutdown or about to shutdown, then ignore this event
+            if (!m_NetworkManager.IsListening || m_NetworkManager.ShutdownInProgress)
+            {
+                return;
+            }
+
             var sceneEventData = SceneEventDataStore[sceneEventId];
             // First thing we do, if we are a server, is to send the unload scene event.
             if (m_NetworkManager.IsServer)
@@ -1033,7 +1064,7 @@ 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);
                 }
             }
 
@@ -1064,7 +1095,7 @@ namespace Unity.Netcode
 
         private void EmptySceneUnloadedOperation(uint sceneEventId)
         {
-            // Do nothing (this is a stub call since it is only used to flush all currently loaded scenes)
+            // Do nothing (this is a stub call since it is only used to flush all additively loaded scenes)
         }
 
         /// <summary>
@@ -1074,6 +1105,7 @@ namespace Unity.Netcode
         /// </summary>
         internal void UnloadAdditivelyLoadedScenes(uint sceneEventId)
         {
+            var sceneEventData = SceneEventDataStore[sceneEventId];
             // Unload all additive scenes while making sure we don't try to unload the base scene ( loaded in single mode ).
             var currentActiveScene = SceneManager.GetActiveScene();
             foreach (var keyHandleEntry in ScenesLoaded)
@@ -1081,17 +1113,11 @@ 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,
-                        new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = EmptySceneUnloadedOperation });
-
-                    OnSceneEvent?.Invoke(new SceneEvent()
-                    {
-                        AsyncOperation = sceneUnload,
-                        SceneEventType = SceneEventType.Unload,
-                        SceneName = keyHandleEntry.Value.name,
-                        LoadSceneMode = LoadSceneMode.Additive, // The only scenes unloaded are scenes that were additively loaded
-                        ClientId = NetworkManager.ServerClientId
-                    });
+                    var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
+                    sceneEventProgress.SceneEventId = sceneEventId;
+                    sceneEventProgress.OnSceneEventCompleted = EmptySceneUnloadedOperation;
+                    var sceneUnload = SceneManagerHandler.UnloadSceneAsync(keyHandleEntry.Value, sceneEventProgress);
+                    SceneUnloadEventHandler.RegisterScene(this, keyHandleEntry.Value, LoadSceneMode.Additive, sceneUnload);
                 }
             }
             // clear out our scenes loaded list
@@ -1104,6 +1130,7 @@ namespace Unity.Netcode
         /// When applicable, the <see cref="AsyncOperation"/> is delivered within the <see cref="SceneEvent"/> via <see cref="OnSceneEvent"/>
         /// </summary>
         /// <param name="sceneName">the name of the scene to be loaded</param>
+        /// <param name="loadSceneMode">how the scene will be loaded (single or additive mode)</param>
         /// <returns><see cref="SceneEventProgressStatus"/> (<see cref="SceneEventProgressStatus.Started"/> means it was successful)</returns>
         public SceneEventProgressStatus LoadScene(string sceneName, LoadSceneMode loadSceneMode)
         {
@@ -1124,12 +1151,12 @@ namespace Unity.Netcode
             sceneEventData.SceneEventType = SceneEventType.Load;
             sceneEventData.SceneHash = SceneHashFromNameOrPath(sceneName);
             sceneEventData.LoadSceneMode = loadSceneMode;
-
+            var sceneEventId = sceneEventData.SceneEventId;
             // This both checks to make sure the scene is valid and if not resets the active scene event
             m_IsSceneEventActive = ValidateSceneBeforeLoading(sceneEventData.SceneHash, loadSceneMode);
             if (!m_IsSceneEventActive)
             {
-                EndSceneEvent(sceneEventData.SceneEventId);
+                EndSceneEvent(sceneEventId);
                 return SceneEventProgressStatus.SceneFailedVerification;
             }
 
@@ -1142,15 +1169,16 @@ namespace Unity.Netcode
                 MoveObjectsToDontDestroyOnLoad();
 
                 // Now Unload all currently additively loaded scenes
-                UnloadAdditivelyLoadedScenes(sceneEventData.SceneEventId);
+                UnloadAdditivelyLoadedScenes(sceneEventId);
+
+                // Register the active scene for unload scene event notifications
+                SceneUnloadEventHandler.RegisterScene(this, SceneManager.GetActiveScene(), LoadSceneMode.Single);
             }
 
             // Now start loading the scene
-            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode,
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventData.SceneEventId, EventAction = OnSceneLoaded });
-
-            sceneEventProgress.SetSceneLoadOperation(sceneLoad);
-
+            sceneEventProgress.SceneEventId = sceneEventId;
+            sceneEventProgress.OnSceneEventCompleted = OnSceneLoaded;
+            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode, sceneEventProgress);
             // Notify the local server that a scene loading event has begun
             OnSceneEvent?.Invoke(new SceneEvent()
             {
@@ -1167,6 +1195,114 @@ namespace Unity.Netcode
             return sceneEventProgress.Status;
         }
 
+        /// <summary>
+        /// Helper class used to handle "odd ball" scene unload event notification scenarios
+        /// when scene switching.
+        /// </summary>
+        internal class SceneUnloadEventHandler
+        {
+            private static Dictionary<NetworkManager, List<SceneUnloadEventHandler>> s_Instances = new Dictionary<NetworkManager, List<SceneUnloadEventHandler>>();
+
+            internal static void RegisterScene(NetworkSceneManager networkSceneManager, Scene scene, LoadSceneMode loadSceneMode, AsyncOperation asyncOperation = null)
+            {
+                var networkManager = networkSceneManager.m_NetworkManager;
+                if (!s_Instances.ContainsKey(networkManager))
+                {
+                    s_Instances.Add(networkManager, new List<SceneUnloadEventHandler>());
+                }
+                var clientId = networkManager.IsServer ? NetworkManager.ServerClientId : networkManager.LocalClientId;
+                s_Instances[networkManager].Add(new SceneUnloadEventHandler(networkSceneManager, scene, clientId, loadSceneMode, asyncOperation));
+            }
+
+            private static void SceneUnloadComplete(SceneUnloadEventHandler sceneUnloadEventHandler)
+            {
+                if (sceneUnloadEventHandler == null || sceneUnloadEventHandler.m_NetworkSceneManager == null || sceneUnloadEventHandler.m_NetworkSceneManager.m_NetworkManager == null)
+                {
+                    return;
+                }
+                var networkManager = sceneUnloadEventHandler.m_NetworkSceneManager.m_NetworkManager;
+                if (s_Instances.ContainsKey(networkManager))
+                {
+                    s_Instances[networkManager].Remove(sceneUnloadEventHandler);
+                    if (s_Instances[networkManager].Count == 0)
+                    {
+                        s_Instances.Remove(networkManager);
+                    }
+                }
+            }
+
+            /// <summary>
+            /// Called by NetworkSceneManager when it is disposing
+            /// </summary>
+            internal static void Shutdown()
+            {
+                foreach (var instanceEntry in s_Instances)
+                {
+                    foreach (var instance in instanceEntry.Value)
+                    {
+                        instance.OnShutdown();
+                    }
+                    instanceEntry.Value.Clear();
+                }
+                s_Instances.Clear();
+            }
+
+            private NetworkSceneManager m_NetworkSceneManager;
+            private AsyncOperation m_AsyncOperation;
+            private LoadSceneMode m_LoadSceneMode;
+            private ulong m_ClientId;
+            private Scene m_Scene;
+            private bool m_ShuttingDown;
+
+            private void OnShutdown()
+            {
+                m_ShuttingDown = true;
+                SceneManager.sceneUnloaded -= SceneUnloaded;
+            }
+
+            private void SceneUnloaded(Scene scene)
+            {
+                if (m_Scene.handle == scene.handle && !m_ShuttingDown)
+                {
+                    if (m_NetworkSceneManager != null && m_NetworkSceneManager.m_NetworkManager != null)
+                    {
+                        m_NetworkSceneManager.OnSceneEvent?.Invoke(new SceneEvent()
+                        {
+                            AsyncOperation = m_AsyncOperation,
+                            SceneEventType = SceneEventType.UnloadComplete,
+                            SceneName = m_Scene.name,
+                            LoadSceneMode = m_LoadSceneMode,
+                            ClientId = m_ClientId
+                        });
+                        m_NetworkSceneManager.OnUnloadComplete?.Invoke(m_ClientId, m_Scene.name);
+                    }
+                    SceneManager.sceneUnloaded -= SceneUnloaded;
+                    SceneUnloadComplete(this);
+                }
+            }
+
+            private SceneUnloadEventHandler(NetworkSceneManager networkSceneManager, Scene scene, ulong clientId, LoadSceneMode loadSceneMode, AsyncOperation asyncOperation = null)
+            {
+                m_LoadSceneMode = loadSceneMode;
+                m_AsyncOperation = asyncOperation;
+                m_NetworkSceneManager = networkSceneManager;
+                m_ClientId = clientId;
+                m_Scene = scene;
+                SceneManager.sceneUnloaded += SceneUnloaded;
+                // Send the initial unload event notification
+                m_NetworkSceneManager.OnSceneEvent?.Invoke(new SceneEvent()
+                {
+                    AsyncOperation = m_AsyncOperation,
+                    SceneEventType = SceneEventType.Unload,
+                    SceneName = m_Scene.name,
+                    LoadSceneMode = m_LoadSceneMode,
+                    ClientId = clientId
+                });
+
+                m_NetworkSceneManager.OnUnload?.Invoke(networkSceneManager.m_NetworkManager.LocalClientId, m_Scene.name, null);
+            }
+        }
+
         /// <summary>
         /// Client Side:
         /// Handles both forms of scene loading
@@ -1201,10 +1337,15 @@ namespace Unity.Netcode
             if (sceneEventData.LoadSceneMode == LoadSceneMode.Single)
             {
                 IsSpawnedObjectsPendingInDontDestroyOnLoad = true;
-            }
 
-            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, sceneEventData.LoadSceneMode,
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = OnSceneLoaded });
+                // Register the active scene for unload scene event notifications
+                SceneUnloadEventHandler.RegisterScene(this, SceneManager.GetActiveScene(), LoadSceneMode.Single);
+
+            }
+            var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
+            sceneEventProgress.SceneEventId = sceneEventId;
+            sceneEventProgress.OnSceneEventCompleted = OnSceneLoaded;
+            var sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, sceneEventData.LoadSceneMode, sceneEventProgress);
 
             OnSceneEvent?.Invoke(new SceneEvent()
             {
@@ -1218,13 +1359,18 @@ namespace Unity.Netcode
             OnLoad?.Invoke(m_NetworkManager.LocalClientId, sceneName, sceneEventData.LoadSceneMode, sceneLoad);
         }
 
-
         /// <summary>
         /// Client and Server:
         /// Generic on scene loaded callback method to be called upon a scene loading
         /// </summary>
         private void OnSceneLoaded(uint sceneEventId)
         {
+            // If we are shutdown or about to shutdown, then ignore this event
+            if (!m_NetworkManager.IsListening || m_NetworkManager.ShutdownInProgress)
+            {
+                return;
+            }
+
             var sceneEventData = SceneEventDataStore[sceneEventId];
             var nextScene = GetAndAddNewlyLoadedSceneByName(SceneNameFromHash(sceneEventData.SceneHash));
             if (!nextScene.isLoaded || !nextScene.IsValid())
@@ -1295,6 +1441,9 @@ 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;
 
@@ -1330,7 +1479,7 @@ 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);
         }
@@ -1363,6 +1512,13 @@ namespace Unity.Netcode
             EndSceneEvent(sceneEventId);
         }
 
+        /// <summary>
+        /// Used for integration testing, due to the complexities of having all clients loading scenes
+        /// this is needed to "filter" out the scenes not loaded by NetworkSceneManager
+        /// (i.e. we don't want a late joining player to load all of the other client scenes)
+        /// </summary>
+        internal Func<Scene, bool> ExcludeSceneFromSychronization;
+
         /// <summary>
         /// Server Side:
         /// This is used for players that have just had their connection approved and will assure they are synchronized
@@ -1389,6 +1545,13 @@ namespace Unity.Netcode
             {
                 var scene = SceneManager.GetSceneAt(i);
 
+                // NetworkSceneManager does not synchronize scenes that are not loaded by NetworkSceneManager
+                // unless the scene in question is the currently active scene.
+                if (ExcludeSceneFromSychronization != null && !ExcludeSceneFromSychronization(scene))
+                {
+                    continue;
+                }
+
                 var sceneHash = SceneHashFromNameOrPath(scene.path);
 
                 // This would depend upon whether we are additive or not
@@ -1406,11 +1569,11 @@ namespace Unity.Netcode
                 {
                     continue;
                 }
-
                 sceneEventData.AddSceneToSynchronize(sceneHash, scene.handle);
             }
 
             sceneEventData.AddSpawnedNetworkObjects();
+            sceneEventData.AddDespawnedInSceneNetworkObjects();
 
             var message = new SceneEventMessage
             {
@@ -1446,12 +1609,9 @@ namespace Unity.Netcode
 
             var loadSceneMode = sceneHash == sceneEventData.SceneHash ? sceneEventData.LoadSceneMode : LoadSceneMode.Additive;
 
-            // Always check to see if the scene needs to be validated
-            if (!ValidateSceneBeforeLoading(sceneHash, loadSceneMode))
-            {
-                EndSceneEvent(sceneEventId);
-                return;
-            }
+            // Store the sceneHandle and hash
+            sceneEventData.NetworkSceneHandle = sceneHandle;
+            sceneEventData.ClientSceneHash = sceneHash;
 
             // If this is the beginning of the synchronization event, then send client a notification that synchronization has begun
             if (sceneHash == sceneEventData.SceneHash)
@@ -1468,9 +1628,16 @@ namespace Unity.Netcode
                 ScenePlacedObjects.Clear();
             }
 
-            // Store the sceneHandle and hash
-            sceneEventData.ClientSceneHandle = sceneHandle;
-            sceneEventData.ClientSceneHash = sceneHash;
+            // Always check to see if the scene needs to be validated
+            if (!ValidateSceneBeforeLoading(sceneHash, loadSceneMode))
+            {
+                HandleClientSceneEvent(sceneEventId);
+                if (m_NetworkManager.LogLevel == LogLevel.Developer)
+                {
+                    NetworkLog.LogInfo($"Client declined to load the scene {sceneName}, continuing with synchronization.");
+                }
+                return;
+            }
 
             var shouldPassThrough = false;
             var sceneLoad = (AsyncOperation)null;
@@ -1486,8 +1653,10 @@ namespace Unity.Netcode
             if (!shouldPassThrough)
             {
                 // If not, then load the scene
-                sceneLoad = SceneManagerHandler.LoadSceneAsync(sceneName, loadSceneMode,
-                new ISceneManagerHandler.SceneEventAction() { SceneEventId = sceneEventId, EventAction = ClientLoadedSynchronization });
+                var sceneEventProgress = new SceneEventProgress(m_NetworkManager);
+                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()
@@ -1532,9 +1701,9 @@ namespace Unity.Netcode
                 SceneManager.SetActiveScene(nextScene);
             }
 
-            if (!ServerSceneHandleToClientSceneHandle.ContainsKey(sceneEventData.ClientSceneHandle))
+            if (!ServerSceneHandleToClientSceneHandle.ContainsKey(sceneEventData.NetworkSceneHandle))
             {
-                ServerSceneHandleToClientSceneHandle.Add(sceneEventData.ClientSceneHandle, nextScene.handle);
+                ServerSceneHandleToClientSceneHandle.Add(sceneEventData.NetworkSceneHandle, nextScene.handle);
             }
             else
             {
@@ -1704,7 +1873,7 @@ namespace Unity.Netcode
 
                         if (SceneEventProgressTracking.ContainsKey(sceneEventData.SceneEventProgressId))
                         {
-                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].AddClientAsDone(clientId);
+                            SceneEventProgressTracking[sceneEventData.SceneEventProgressId].ClientFinishedSceneEvent(clientId);
                         }
                         EndSceneEvent(sceneEventId);
                         break;
@@ -1713,7 +1882,7 @@ 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()
@@ -1746,7 +1915,9 @@ namespace Unity.Netcode
                         // NetworkObjects
                         m_NetworkManager.InvokeOnClientConnectedCallback(clientId);
 
-                        if (sceneEventData.ClientNeedsReSynchronization() && !DisableReSynchronization)
+                        // Check to see if the client needs to resynchronize and before sending the message make sure the client is still connected to avoid
+                        // a potential crash within the MessageSystem (i.e. sending to a client that no longer exists)
+                        if (sceneEventData.ClientNeedsReSynchronization() && !DisableReSynchronization && m_NetworkManager.ConnectedClients.ContainsKey(clientId))
                         {
                             sceneEventData.SceneEventType = SceneEventType.ReSynchronize;
                             SendSceneEventData(sceneEventId, new ulong[] { clientId });
@@ -1847,7 +2018,11 @@ 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
@@ -1856,10 +2031,9 @@ namespace Unity.Netcode
             foreach (var networkObjectInstance in networkObjects)
             {
                 var globalObjectIdHash = networkObjectInstance.GlobalObjectIdHash;
-                var sceneHandle = networkObjectInstance.gameObject.scene.handle;
+                var sceneHandle = networkObjectInstance.GetSceneOriginHandle();
                 // We check to make sure the NetworkManager instance is the same one to be "NetcodeIntegrationTestHelpers" compatible and filter the list on a per scene basis (for additive scenes)
-                if (networkObjectInstance.IsSceneObject != false && networkObjectInstance.NetworkManager == m_NetworkManager && networkObjectInstance.gameObject.scene == sceneToFilterBy &&
-                    sceneHandle == sceneToFilterBy.handle)
+                if (networkObjectInstance.IsSceneObject != false && networkObjectInstance.NetworkManager == m_NetworkManager && sceneHandle == sceneToFilterBy.handle)
                 {
                     if (!ScenePlacedObjects.ContainsKey(globalObjectIdHash))
                     {

Runtime/SceneManagement/SceneEventData.cs

@@ -91,7 +91,7 @@ namespace Unity.Netcode
     {
         internal SceneEventType SceneEventType;
         internal LoadSceneMode LoadSceneMode;
-        internal Guid SceneEventProgressId;
+        internal ForceNetworkSerializeByMemcpy<Guid> SceneEventProgressId;
         internal uint SceneEventId;
 
 
@@ -100,7 +100,7 @@ namespace Unity.Netcode
 
         // Used by the client during synchronization
         internal uint ClientSceneHash;
-        internal int ClientSceneHandle;
+        internal int NetworkSceneHandle;
 
         /// Only used for <see cref="SceneEventType.Synchronize"/> scene events, this assures permissions when writing
         /// NetworkVariable information.  If that process changes, then we need to update this
@@ -118,6 +118,9 @@ namespace Unity.Netcode
         /// </summary>
         private List<NetworkObject> m_NetworkObjectsSync = new List<NetworkObject>();
 
+        private List<NetworkObject> m_DespawnedInSceneObjectsSync = new List<NetworkObject>();
+        private Dictionary<int, List<uint>> m_DespawnedInSceneObjects = new Dictionary<int, List<uint>>();
+
         /// <summary>
         /// Server Side Re-Synchronization:
         /// If there happens to be NetworkObjects in the final Event_Sync_Complete message that are no longer spawned,
@@ -240,7 +243,45 @@ 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();
+            // 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)
+                {
+                    m_DespawnedInSceneObjectsSync.Add(sobj);
+                }
+            }
         }
 
         /// <summary>
@@ -307,6 +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"/>)
@@ -318,7 +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)
@@ -372,7 +439,6 @@ namespace Unity.Netcode
             writer.WriteValueSafe(ScenesToSynchronize.ToArray());
             writer.WriteValueSafe(SceneHandlesToSynchronize.ToArray());
 
-
             // Store our current position in the stream to come back and say how much data we have written
             var positionStart = writer.Position;
 
@@ -383,17 +449,30 @@ namespace Unity.Netcode
             int totalBytes = 0;
 
             // Write the number of NetworkObjects we are serializing
-            writer.WriteValueSafe(m_NetworkObjectsSync.Count());
-            for (var i = 0; i < m_NetworkObjectsSync.Count(); ++i)
+            writer.WriteValueSafe(m_NetworkObjectsSync.Count);
+
+            // Serialize all NetworkObjects that are spawned
+            for (var i = 0; i < m_NetworkObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
                 var sceneObject = m_NetworkObjectsSync[i].GetMessageSceneObject(TargetClientId);
-                writer.WriteValueSafe(m_NetworkObjectsSync[i].gameObject.scene.handle);
                 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);
+            // Write the scene handle and GlobalObjectIdHash value
+            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
+            {
+                var noStart = writer.Position;
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
+                var noStop = writer.Position;
+                totalBytes += (int)(noStop - noStart);
+            }
+
             // Size Place Holder -- End
             var positionEnd = writer.Position;
             var bytesWritten = (uint)(positionEnd - (positionStart + sizeof(uint)));
@@ -423,8 +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);
@@ -433,6 +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);
@@ -450,7 +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)
             {
@@ -541,15 +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
             {
@@ -571,7 +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)
                 {
@@ -672,6 +767,90 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// For synchronizing any despawned in-scene placed NetworkObjects that were
+        /// despawned by the server during synchronization or scene loading
+        /// </summary>
+        private void DeserializeDespawnedInScenePlacedNetworkObjects()
+        {
+            // Process all de-spawned in-scene NetworkObjects for this network session
+            m_DespawnedInSceneObjects.Clear();
+            InternalBuffer.ReadValueSafe(out int despawnedObjectsCount);
+            var sceneCache = new Dictionary<int, Dictionary<uint, NetworkObject>>();
+
+            for (int i = 0; i < despawnedObjectsCount; i++)
+            {
+                // We just need to get the scene
+                InternalBuffer.ReadValueSafe(out int networkSceneHandle);
+                InternalBuffer.ReadValueSafe(out uint globalObjectIdHash);
+                var sceneRelativeNetworkObjects = new Dictionary<uint, NetworkObject>();
+                if (!sceneCache.ContainsKey(networkSceneHandle))
+                {
+                    if (m_NetworkManager.SceneManager.ServerSceneHandleToClientSceneHandle.ContainsKey(networkSceneHandle))
+                    {
+                        var localSceneHandle = m_NetworkManager.SceneManager.ServerSceneHandleToClientSceneHandle[networkSceneHandle];
+                        if (m_NetworkManager.SceneManager.ScenesLoaded.ContainsKey(localSceneHandle))
+                        {
+                            var objectRelativeScene = m_NetworkManager.SceneManager.ScenesLoaded[localSceneHandle];
+
+                            // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) =>
+                            c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#else
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) =>
+                            c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#endif
+
+
+                            foreach (var inSceneObject in inSceneNetworkObjects)
+                            {
+                                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);
+                        }
+                        else
+                        {
+                            UnityEngine.Debug.LogError($"In-Scene NetworkObject GlobalObjectIdHash ({globalObjectIdHash}) cannot find its relative local scene handle {localSceneHandle}!");
+                        }
+                    }
+                    else
+                    {
+                        UnityEngine.Debug.LogError($"In-Scene NetworkObject GlobalObjectIdHash ({globalObjectIdHash}) cannot find its relative NetworkSceneHandle {networkSceneHandle}!");
+                    }
+                }
+                else // Use the cached NetworkObjects if they exist
+                {
+                    sceneRelativeNetworkObjects = sceneCache[networkSceneHandle];
+                }
+
+                // Now find the in-scene NetworkObject with the current GlobalObjectIdHash we are looking for
+                if (sceneRelativeNetworkObjects.ContainsKey(globalObjectIdHash))
+                {
+                    // Since this is a NetworkObject that was never spawned, we just need to send a notification
+                    // out that it was despawned so users can make adjustments
+                    sceneRelativeNetworkObjects[globalObjectIdHash].InvokeBehaviourNetworkDespawn();
+                    if (!m_NetworkManager.SceneManager.ScenePlacedObjects.ContainsKey(globalObjectIdHash))
+                    {
+                        m_NetworkManager.SceneManager.ScenePlacedObjects.Add(globalObjectIdHash, new Dictionary<int, NetworkObject>());
+                    }
+
+                    if (!m_NetworkManager.SceneManager.ScenePlacedObjects[globalObjectIdHash].ContainsKey(sceneRelativeNetworkObjects[globalObjectIdHash].GetSceneOriginHandle()))
+                    {
+                        m_NetworkManager.SceneManager.ScenePlacedObjects[globalObjectIdHash].Add(sceneRelativeNetworkObjects[globalObjectIdHash].GetSceneOriginHandle(), sceneRelativeNetworkObjects[globalObjectIdHash]);
+                    }
+                }
+                else
+                {
+                    UnityEngine.Debug.LogError($"In-Scene NetworkObject GlobalObjectIdHash ({globalObjectIdHash}) could not be found!");
+                }
+            }
+        }
+
         /// <summary>
         /// Client Side:
         /// During the processing of a server sent Event_Sync, this method will be called for each scene once
@@ -683,26 +862,33 @@ namespace Unity.Netcode
         {
             try
             {
-                // Process all NetworkObjects for this scene
+                // Process all spawned NetworkObjects for this network session
                 InternalBuffer.ReadValueSafe(out int newObjectsCount);
-
                 for (int i = 0; i < newObjectsCount; i++)
                 {
-                    // We want to make sure for each NetworkObject we have the appropriate scene selected as the scene that is
-                    // currently being synchronized.  This assures in-scene placed NetworkObjects will use the right NetworkObject
-                    // from the list of populated <see cref="NetworkSceneManager.ScenePlacedObjects"/>
-                    InternalBuffer.ReadValueSafe(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))
+                    // If the sceneObject is in-scene placed, then set the scene being synchronized
+                    if (sceneObject.IsSceneObject)
                     {
-                        m_NetworkObjectsSync.Add(spawnedNetworkObject);
+                        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
             {

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 NetworkTime at the moment the scene switch was initiated by the server.
+        /// This is when the current scene event will have timed out
         /// </summary>
-        internal NetworkTime 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>
-        /// 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; }
+        internal Action<uint> OnSceneEventCompleted;
 
         /// <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; }
 
@@ -105,55 +105,195 @@ namespace Unity.Netcode
 
         internal LoadSceneMode LoadSceneMode;
 
+        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)
             {
                 m_NetworkManager = networkManager;
-                m_TimeOutCoroutine = m_NetworkManager.StartCoroutine(TimeOutSceneEventProgress());
-                TimeAtInitiation = networkManager.LocalTime;
+
+                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());
+                }
             }
             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)
+        /// during a scene event and if it does not complete within the scene loading time out period
+        /// it will time out the scene event.
+        /// </summary>
         internal IEnumerator TimeOutSceneEventProgress()
         {
-            yield return new WaitForSecondsRealtime(m_NetworkManager.NetworkConfig.LoadSceneTimeOut);
-            TimedOut = true;
-            CheckCompletion();
-        }
-
-        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();
-        }
-
-        internal void CheckCompletion()
-        {
-            if ((!IsCompleted && DoneClients.Count == m_NetworkManager.ConnectedClientsList.Count && m_SceneLoadOperation.isDone) || (!IsCompleted && TimedOut))
+            var waitForNetworkTick = new WaitForSeconds(1.0f / m_NetworkManager.NetworkConfig.TickRate);
+            while (!HasTimedOut())
             {
-                IsCompleted = true;
-                AreAllClientsDoneLoading = true;
+                yield return waitForNetworkTick;
 
-                // If OnComplete is not registered or it is and returns true then remove this from the progress tracking
-                if (OnComplete == null || (OnComplete != null && OnComplete.Invoke(this)))
+                TryFinishingSceneEventProgress();
+            }
+        }
+
+        /// <summary>
+        /// Sets the client's scene event progress to finished/true
+        /// </summary>
+        internal void ClientFinishedSceneEvent(ulong clientId)
+        {
+            if (ClientsProcessingSceneEvent.ContainsKey(clientId))
+            {
+                ClientsProcessingSceneEvent[clientId] = true;
+                TryFinishingSceneEventProgress();
+            }
+        }
+
+        /// <summary>
+        /// Determines if the scene event has finished for both
+        /// client(s) and server.
+        /// </summary>
+        /// <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()
+        {
+            // If the network session is terminated/terminating then finish tracking
+            // this scene event
+            if (!IsNetworkSessionActive())
+            {
+                return true;
+            }
+
+            // Clients skip over this
+            foreach (var clientStatus in ClientsProcessingSceneEvent)
+            {
+                if (!clientStatus.Value)
                 {
-                    m_NetworkManager.SceneManager.SceneEventProgressTracking.Remove(Guid);
+                    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);
                 }
-                m_NetworkManager.StopCoroutine(m_TimeOutCoroutine);
             }
         }
     }

Runtime/Serialization/BitCounter.cs

@@ -2,6 +2,9 @@ using System.Runtime.CompilerServices;
 
 namespace Unity.Netcode
 {
+    /// <summary>
+    /// Utility class to count the number of bytes or bits needed to serialize a value.
+    /// </summary>
     public static class BitCounter
     {
         // Since we don't have access to BitOperations.LeadingZeroCount() (which would have been the fastest)

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

@@ -1,13 +1,17 @@
+using System;
+using Unity.Collections;
+using UnityEngine;
+
 namespace Unity.Netcode
 {
     /// <summary>
     /// Two-way serializer wrapping FastBufferReader or FastBufferWriter.
-    /// 
+    ///
     /// Implemented as a ref struct for two reasons:
     /// 1. 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 out live the stack context in which they were
+    /// Ref structs help enforce both of those rules: they can't ref live the stack context in which they were
     /// created, and they're always passed by reference no matter what.
     ///
     /// BufferSerializer doesn't wrapp FastBufferReader or FastBufferWriter directly because it can't.
@@ -58,168 +62,526 @@ namespace Unity.Netcode
             return m_Implementation.GetFastBufferWriter();
         }
 
-        /// <summary>
-        /// Serialize an INetworkSerializable
-        /// 
-        /// Throws OverflowException if the end of the buffer has been reached.
-        /// Write buffers will grow up to the maximum allowable message size before throwing OverflowException.
-        /// </summary>
-        /// <param name="value">Value to serialize</param>
-        public void SerializeNetworkSerializable<T>(ref T value) where T : INetworkSerializable, new()
-        {
-            m_Implementation.SerializeNetworkSerializable(ref value);
-        }
 
         /// <summary>
-        /// Serialize a string.
-        ///
-        /// Note: Will ALWAYS allocate a new string when reading.
-        /// 
-        /// Throws OverflowException if the end of the buffer has been reached.
-        /// Write buffers will grow up to the maximum allowable message size before throwing OverflowException.
+        /// Read or write a string
         /// </summary>
-        /// <param name="s">Value to serialize</param>
-        /// <param name="oneByteChars">
-        /// If true, will truncate each char to one byte.
-        /// This is slower than two-byte chars, but uses less bandwidth.
-        /// </param>
-        public void SerializeValue(ref string s, bool oneByteChars = false)
-        {
-            m_Implementation.SerializeValue(ref s, oneByteChars);
-        }
+        /// <param name="s">The value to read/write</param>
+        /// <param name="oneByteChars">If true, characters will be limited to one-byte ASCII characters</param>
+        public void SerializeValue(ref string s, bool oneByteChars = false) => m_Implementation.SerializeValue(ref s, oneByteChars);
 
         /// <summary>
-        /// Serialize an array value.
-        ///
-        /// Note: Will ALWAYS allocate a new array when reading.
-        /// If you have a statically-sized array that you know is large enough, it's recommended to
-        /// serialize the size yourself and iterate serializing array members.
-        /// 
-        /// (This is because C# doesn't allow setting an array's length value, so deserializing
-        /// into an existing array of larger size would result in an array that doesn't have as many values
-        /// as its Length indicates it should.)
-        /// 
-        /// Throws OverflowException if the end of the buffer has been reached.
-        /// Write buffers will grow up to the maximum allowable message size before throwing OverflowException.
+        /// Read or write a single byte
         /// </summary>
-        /// <param name="array">Value to serialize</param>
-        public void SerializeValue<T>(ref T[] array) where T : unmanaged
-        {
-            m_Implementation.SerializeValue(ref array);
-        }
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref byte value) => m_Implementation.SerializeValue(ref value);
 
         /// <summary>
-        /// Serialize a single byte
-        /// 
-        /// Throws OverflowException if the end of the buffer has been reached.
-        /// Write buffers will grow up to the maximum allowable message size before throwing OverflowException.
+        /// Read or write a primitive value (int, bool, etc)
+        /// Accepts any value that implements the given interfaces, but is not guaranteed to work correctly
+        /// on values that are not primitives.
         /// </summary>
-        /// <param name="value">Value to serialize</param>
-        public void SerializeValue(ref byte value)
-        {
-            m_Implementation.SerializeValue(ref value);
-        }
+        /// <param name="value">The value to read/write</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>
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Implementation.SerializeValue(ref value);
 
         /// <summary>
-        /// Serialize an unmanaged type. Supports basic value types as well as structs.
-        /// The provided type will be copied to/from the buffer as it exists in memory.
-        /// 
-        /// Throws OverflowException if the end of the buffer has been reached.
-        /// Write buffers will grow up to the maximum allowable message size before throwing OverflowException.
+        /// Read or write an array of primitive values (int, bool, etc)
+        /// Accepts any value that implements the given interfaces, but is not guaranteed to work correctly
+        /// on values that are not primitives.
         /// </summary>
-        /// <param name="value">Value to serialize</param>
-        public void SerializeValue<T>(ref T value) where T : unmanaged
-        {
-            m_Implementation.SerializeValue(ref value);
-        }
+        /// <param name="value">The values to read/write</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>
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Implementation.SerializeValue(ref value);
 
         /// <summary>
-        /// Allows faster serialization by batching bounds checking.
-        /// When you know you will be writing multiple fields back-to-back and you know the total size,
-        /// you can call PreCheck() once on the total size, and then follow it with calls to
-        /// SerializeValuePreChecked() for faster serialization. Write buffers will grow during PreCheck()
-        /// if needed.
-        /// 
-        /// PreChecked serialization operations will throw OverflowException in editor and development builds if you
-        /// go past the point you've marked using PreCheck(). In release builds, OverflowException will not be thrown
-        /// for performance reasons, since the point of using PreCheck is to avoid bounds checking in the following
-        /// operations in release builds.
-        ///
-        /// To get the correct size to check for, use FastBufferWriter.GetWriteSize(value) or
-        /// FastBufferWriter.GetWriteSize&lt;type&gt;()
+        /// Read or write an enum value
         /// </summary>
-        /// <param name="amount">Number of bytes you plan to read or write</param>
-        /// <returns>True if the read/write can proceed, false otherwise.</returns>
+        /// <param name="value">The value to read/write</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>
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of enum values
+        /// </summary>
+        /// <param name="value">The value to read/write</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>
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a struct value implementing ISerializeByMemcpy
+        /// </summary>
+        /// <param name="value">The value to read/write</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>
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of struct values implementing ISerializeByMemcpy
+        /// </summary>
+        /// <param name="value">The values to read/write</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>
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a struct or class value implementing INetworkSerializable
+        /// </summary>
+        /// <param name="value">The value to read/write</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>
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of struct or class values implementing INetworkSerializable
+        /// </summary>
+        /// <param name="value">The values to read/write</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>
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Vector2 value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Vector2 value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Vector2 values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Vector2[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Vector3 value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Vector3 value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Vector3 values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Vector3[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Vector2Int value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Vector2Int value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Vector2Int values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Vector2Int[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Vector3Int value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Vector3Int value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Vector3Int values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Vector3Int[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Vector4 value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Vector4 value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Vector4 values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Vector4[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Quaternion value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Quaternion value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Quaternion values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Quaternion[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Color value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Color value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Color values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Color[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Color32 value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Color32 value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Color32 values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Color32[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Ray value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Ray value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Ray values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Ray[] value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a Ray2D value
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValue(ref Ray2D value) => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write an array of Ray2D values
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValue(ref Ray2D[] value) => m_Implementation.SerializeValue(ref value);
+
+        // There are many FixedString types, but all of them share the interfaces INativeList<bool> and IUTF8Bytes.
+        // INativeList<bool> provides the Length property
+        // IUTF8Bytes provides GetUnsafePtr()
+        // Those two are necessary to serialize FixedStrings efficiently
+        // - otherwise we'd just be memcpy'ing the whole thing even if
+        // most of it isn't used.
+        /// <summary>
+        /// Read or write a FixedString value
+        /// </summary>
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of FixedStrings</param>
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Implementation.SerializeValue(ref value);
+
+        /// <summary>
+        /// Read or write a NetworkSerializable value.
+        /// SerializeValue() is the preferred method to do this - this is provided for backward compatibility only.
+        /// </summary>
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeNetworkSerializable<T>(ref T value) where T : INetworkSerializable, new() => m_Implementation.SerializeNetworkSerializable(ref value);
+
+        /// <summary>
+        /// Performs an advance check to ensure space is available to read/write one or more values.
+        /// This provides a performance benefit for serializing multiple values using the
+        /// SerializeValuePreChecked methods. But note that the benefit is small and only likely to be
+        /// noticeable if serializing a very large number of items.
+        /// </summary>
+        /// <param name="amount"></param>
+        /// <returns></returns>
         public bool PreCheck(int amount)
         {
             return m_Implementation.PreCheck(amount);
         }
 
         /// <summary>
-        /// Serialize a string.
-        /// 
-        /// Note: Will ALWAYS allocate a new string when reading.
-        ///
-        /// Using the PreChecked versions of these functions requires calling PreCheck() ahead of time, and they should only
-        /// be called if PreCheck() returns true. This is an efficiency option, as it allows you to PreCheck() multiple
-        /// serialization operations in one function call instead of having to do bounds checking on every call.
+        /// Serialize a string, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
         /// </summary>
-        /// <param name="s">Value to serialize</param>
-        /// <param name="oneByteChars">
-        /// If true, will truncate each char to one byte.
-        /// This is slower than two-byte chars, but uses less bandwidth.
-        /// </param>
-        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false)
-        {
-            m_Implementation.SerializeValuePreChecked(ref s, oneByteChars);
-        }
+        /// <param name="s">The value to read/write</param>
+        /// <param name="oneByteChars">If true, characters will be limited to one-byte ASCII characters</param>
+        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false) => m_Implementation.SerializeValuePreChecked(ref s, oneByteChars);
 
         /// <summary>
-        /// Serialize an array value.
-        ///
-        /// Note: Will ALWAYS allocate a new array when reading.
-        /// If you have a statically-sized array that you know is large enough, it's recommended to
-        /// serialize the size yourself and iterate serializing array members.
-        /// 
-        /// (This is because C# doesn't allow setting an array's length value, so deserializing
-        /// into an existing array of larger size would result in an array that doesn't have as many values
-        /// as its Length indicates it should.)
-        ///
-        /// Using the PreChecked versions of these functions requires calling PreCheck() ahead of time, and they should only
-        /// be called if PreCheck() returns true. This is an efficiency option, as it allows you to PreCheck() multiple
-        /// serialization operations in one function call instead of having to do bounds checking on every call.
+        /// Serialize a byte, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
         /// </summary>
-        /// <param name="array">Value to serialize</param>
-        public void SerializeValuePreChecked<T>(ref T[] array) where T : unmanaged
-        {
-            m_Implementation.SerializeValuePreChecked(ref array);
-        }
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref byte value) => m_Implementation.SerializeValuePreChecked(ref value);
 
         /// <summary>
-        /// Serialize a single byte
-        ///
-        /// Using the PreChecked versions of these functions requires calling PreCheck() ahead of time, and they should only
-        /// be called if PreCheck() returns true. This is an efficiency option, as it allows you to PreCheck() multiple
-        /// serialization operations in one function call instead of having to do bounds checking on every call.
+        /// Serialize a primitive, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
         /// </summary>
-        /// <param name="value">Value to serialize</param>
-        public void SerializeValuePreChecked(ref byte value)
-        {
-            m_Implementation.SerializeValuePreChecked(ref value);
-        }
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The value to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution based on generic constraints</param>
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Implementation.SerializeValuePreChecked(ref value);
 
         /// <summary>
-        /// Serialize an unmanaged type. Supports basic value types as well as structs.
-        /// The provided type will be copied to/from the buffer as it exists in memory.
-        ///
-        /// Using the PreChecked versions of these functions requires calling PreCheck() ahead of time, and they should only
-        /// be called if PreCheck() returns true. This is an efficiency option, as it allows you to PreCheck() multiple
-        /// serialization operations in one function call instead of having to do bounds checking on every call.
+        /// Serialize an array of primitives, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
         /// </summary>
-        /// <param name="value">Value to serialize</param>
-        public void SerializeValuePreChecked<T>(ref T value) where T : unmanaged
-        {
-            m_Implementation.SerializeValuePreChecked(ref value);
-        }
+        /// <typeparam name="T">The network serializable types in an array</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of primitives</param>
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize an enum, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of enums</param>
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize an array of enums, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <typeparam name="T">The network serializable types in an array</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of enums</param>
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a struct, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of structs</param>
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize an array of structs, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <typeparam name="T">The network serializable types in an array</typeparam>
+        /// <param name="value">The values to read/write</param>
+        /// <param name="unused">An unused parameter used for enabling overload resolution of structs</param>
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector2, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector2 value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector2 array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValuePreChecked(ref Vector2[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector3, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector3 value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector3 array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValuePreChecked(ref Vector3[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector2Int, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector2Int value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector2Int array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The values to read/write</param>
+        public void SerializeValuePreChecked(ref Vector2Int[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector3Int, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector3Int value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector3Int array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector3Int[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector4, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector4 value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Vector4Array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Vector4[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Quaternion, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Quaternion value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Quaternion array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Quaternion[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Color, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Color value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Color array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Color[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Color32, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Color32 value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Color32 array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Color32[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Ray, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Ray value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Ray array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Ray[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Ray2D, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Ray2D value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        /// <summary>
+        /// Serialize a Ray2D array, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <param name="value">The value to read/write</param>
+        public void SerializeValuePreChecked(ref Ray2D[] value) => m_Implementation.SerializeValuePreChecked(ref value);
+
+        // There are many FixedString types, but all of them share the interfaces INativeList<bool> and IUTF8Bytes.
+        // INativeList<bool> provides the Length property
+        // IUTF8Bytes provides GetUnsafePtr()
+        // Those two are necessary to serialize FixedStrings efficiently
+        // - otherwise we'd just be memcpying the whole thing even if
+        // most of it isn't used.
+
+        /// <summary>
+        /// Serialize a FixedString, "pre-checked", which skips buffer checks.
+        /// In debug and editor builds, a check is made to ensure you've called "PreCheck" before
+        /// calling this. In release builds, calling this without calling "PreCheck" may read or write
+        /// past the end of the buffer, which will cause memory corruption and undefined behavior.
+        /// </summary>
+        /// <typeparam name="T">The network serializable type</typeparam>
+        /// <param name="value">The value to read/write</param>
+        /// <param name="unused">An unused parameter that can be used for enabling overload resolution for fixed strings</param>
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Implementation.SerializeValuePreChecked(ref value);
     }
 }

Runtime/Serialization/BufferSerializerReader.cs

@@ -1,4 +1,6 @@
 using System;
+using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -24,54 +26,77 @@ namespace Unity.Netcode
             throw new InvalidOperationException("Cannot retrieve a FastBufferWriter from a serializer where IsWriter = false");
         }
 
-        public void SerializeValue(ref string s, bool oneByteChars = false)
-        {
-            m_Reader.ReadValueSafe(out s, oneByteChars);
-        }
+        public void SerializeValue(ref string s, bool oneByteChars = false) => m_Reader.ReadValueSafe(out s, oneByteChars);
+        public void SerializeValue(ref byte value) => m_Reader.ReadByteSafe(out value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Reader.ReadValueSafe(out value);
+        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.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.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[] array) where T : unmanaged
-        {
-            m_Reader.ReadValueSafe(out array);
-        }
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Reader.ReadValueSafe(out value);
 
-        public void SerializeValue(ref byte value)
-        {
-            m_Reader.ReadByteSafe(out value);
-        }
+        public void SerializeValue(ref Vector2 value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector2[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector3 value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector3[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector2Int value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector2Int[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector3Int value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector3Int[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector4 value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Vector4[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Quaternion value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Quaternion[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Color value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Color[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Color32 value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Color32[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Ray value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Ray[] value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Ray2D value) => m_Reader.ReadValueSafe(out value);
+        public void SerializeValue(ref Ray2D[] value) => m_Reader.ReadValueSafe(out value);
 
-        public void SerializeValue<T>(ref T value) where T : unmanaged
-        {
-            m_Reader.ReadValueSafe(out value);
-        }
-
-        public void SerializeNetworkSerializable<T>(ref T value) where T : INetworkSerializable, new()
-        {
-            m_Reader.ReadNetworkSerializable(out value);
-        }
+        public void SerializeNetworkSerializable<T>(ref T value) where T : INetworkSerializable, new() => m_Reader.ReadNetworkSerializable(out value);
 
         public bool PreCheck(int amount)
         {
             return m_Reader.TryBeginRead(amount);
         }
 
-        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false)
-        {
-            m_Reader.ReadValue(out s, oneByteChars);
-        }
-
-        public void SerializeValuePreChecked<T>(ref T[] array) where T : unmanaged
-        {
-            m_Reader.ReadValue(out array);
-        }
-
-        public void SerializeValuePreChecked(ref byte value)
-        {
-            m_Reader.ReadValue(out value);
-        }
-
-        public void SerializeValuePreChecked<T>(ref T value) where T : unmanaged
-        {
-            m_Reader.ReadValue(out value);
-        }
+        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false) => m_Reader.ReadValue(out s, oneByteChars);
+        public void SerializeValuePreChecked(ref byte value) => m_Reader.ReadByte(out value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector2 value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector2[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector3 value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector3[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector2Int value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector2Int[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector3Int value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector3Int[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector4 value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Vector4[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Quaternion value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Quaternion[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Color value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Color[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Color32 value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Color32[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Ray value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Ray[] value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Ray2D value) => m_Reader.ReadValue(out value);
+        public void SerializeValuePreChecked(ref Ray2D[] value) => m_Reader.ReadValue(out value);
     }
 }

Runtime/Serialization/BufferSerializerWriter.cs

@@ -1,4 +1,6 @@
 using System;
+using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -24,25 +26,39 @@ namespace Unity.Netcode
             return m_Writer;
         }
 
-        public void SerializeValue(ref string s, bool oneByteChars = false)
-        {
-            m_Writer.WriteValueSafe(s, oneByteChars);
-        }
+        public void SerializeValue(ref string s, bool oneByteChars = false) => m_Writer.WriteValueSafe(s, oneByteChars);
+        public void SerializeValue(ref byte value) => m_Writer.WriteByteSafe(value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Writer.WriteValueSafe(value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Writer.WriteValue(value);
+        public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Writer.WriteValue(value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Writer.WriteValueSafe(value);
 
-        public void SerializeValue<T>(ref T[] array) where T : unmanaged
-        {
-            m_Writer.WriteValueSafe(array);
-        }
-
-        public void SerializeValue(ref byte value)
-        {
-            m_Writer.WriteByteSafe(value);
-        }
-
-        public void SerializeValue<T>(ref T value) where T : unmanaged
-        {
-            m_Writer.WriteValueSafe(value);
-        }
+        public void SerializeValue(ref Vector2 value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector2[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector3 value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector3[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector2Int value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector2Int[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector3Int value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector3Int[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector4 value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Vector4[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Quaternion value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Quaternion[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Color value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Color[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Color32 value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Color32[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Ray value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Ray[] value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Ray2D value) => m_Writer.WriteValueSafe(value);
+        public void SerializeValue(ref Ray2D[] value) => m_Writer.WriteValueSafe(value);
 
         public void SerializeNetworkSerializable<T>(ref T value) where T : INetworkSerializable, new()
         {
@@ -54,24 +70,37 @@ namespace Unity.Netcode
             return m_Writer.TryBeginWrite(amount);
         }
 
-        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false)
-        {
-            m_Writer.WriteValue(s, oneByteChars);
-        }
+        public void SerializeValuePreChecked(ref string s, bool oneByteChars = false) => m_Writer.WriteValue(s, oneByteChars);
+        public void SerializeValuePreChecked(ref byte value) => m_Writer.WriteByte(value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForPrimitives unused = default) where T : unmanaged, IComparable, IConvertible, IComparable<T>, IEquatable<T> => m_Writer.WriteValue(value);
 
-        public void SerializeValuePreChecked<T>(ref T[] array) where T : unmanaged
-        {
-            m_Writer.WriteValue(array);
-        }
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)
+            where T : unmanaged, INativeList<byte>, IUTF8Bytes => m_Writer.WriteValue(value);
 
-        public void SerializeValuePreChecked(ref byte value)
-        {
-            m_Writer.WriteByte(value);
-        }
-
-        public void SerializeValuePreChecked<T>(ref T value) where T : unmanaged
-        {
-            m_Writer.WriteValue(value);
-        }
+        public void SerializeValuePreChecked(ref Vector2 value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector2[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector3 value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector3[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector2Int value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector2Int[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector3Int value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector3Int[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector4 value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Vector4[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Quaternion value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Quaternion[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Color value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Color[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Color32 value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Color32[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Ray value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Ray[] value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Ray2D value) => m_Writer.WriteValue(value);
+        public void SerializeValuePreChecked(ref Ray2D[] value) => m_Writer.WriteValue(value);
     }
 }

Runtime/Serialization/BytePacker.cs

@@ -6,6 +6,7 @@ namespace Unity.Netcode
 {
     /// <summary>
     /// Utility class for packing values in serialization.
+    /// <seealso cref="ByteUnpacker"/> to unpack packed values.
     /// </summary>
     public static class BytePacker
     {
@@ -49,7 +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>
@@ -60,7 +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>
@@ -97,7 +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.
@@ -108,7 +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.
@@ -119,7 +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.
@@ -127,7 +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.
@@ -135,7 +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.
@@ -143,7 +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.
@@ -151,7 +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
@@ -281,196 +282,183 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void WriteValueBitPacked<T>(FastBufferWriter writer, T value) where T: unmanaged => writer.WriteValueSafe(value);
 #else
-
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const ushort BitPackedUshortMax = (1 << 15) - 1;
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const short BitPackedShortMax = (1 << 14) - 1;
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const short BitPackedShortMin = -(1 << 14);
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const uint BitPackedUintMax = (1 << 30) - 1;
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const int BitPackedIntMax = (1 << 29) - 1;
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const int BitPackedIntMin = -(1 << 29);
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const ulong BitPackedULongMax = (1L << 61) - 1;
+
+        /// <summary>
+        /// Obsolete value that no longer carries meaning. Do not use.
+        /// </summary>
         public const long BitPackedLongMax = (1L << 60) - 1;
+
+        /// <summary>
+        /// 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.
-        /// The first bit indicates whether the value is 1 byte or 2.
-        /// The sign bit takes up another bit.
-        /// That leaves 14 bits for the value.
-        /// A value greater than 2^14-1 or less than -2^14 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 after zig-zag encoding.
+        /// Writes a 16-bit signed short 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 two bits indicate whether the value is 1, 2, or 3 bytes.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
+        /// 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.
-        /// The first bit indicates whether the value is 1 byte or 2.
-        /// That leaves 15 bits for the value.
-        /// A value greater than 2^15-1 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
-        /// most significant bit.
+        /// Writes a 16-bit unsigned short to the buffer in a bit-encoded packed format.
+        /// The first two bits indicate whether the value is 1, 2, or 3 bytes.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
+        /// 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, ushort value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value >= BitPackedUshortMax)
+            if (value > (1 << 14) - 1)
             {
-                throw new ArgumentException("BitPacked ushorts must be <= 15 bits");
-            }
-#endif
-
-            if (value <= 0b0111_1111)
-            {
-                if (!writer.TryBeginWriteInternal(1))
+                if (!writer.TryBeginWriteInternal(3))
                 {
                     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.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
-        /// The sign bit takes up another bit.
-        /// That leaves 60 bits for the value.
-        /// A value greater than 2^60-1 or less than -2^60 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 four
-        /// most significant bits after zig-zag encoding.
+        /// Writes a 32-bit signed int 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 three bits indicate whether the value is 1, 2, 3, 4, or 5 bytes.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
+        /// 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.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
-        /// That leaves 31 bits for the value.
-        /// A value greater than 2^61-1 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 three
-        /// most significant bits.
+        /// 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, or 5 bytes.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
+        /// 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, ulong value)
+        public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value > BitPackedULongMax)
+            if (value > (1 << 29) - 1)
             {
-                throw new ArgumentException("BitPacked ulongs must be <= 61 bits");
+                if (!writer.TryBeginWriteInternal(5))
+                {
+                    throw new OverflowException("Writing past the end of the buffer");
+                }
+                writer.WriteByte(5);
+                writer.WriteValue(value);
+                return;
             }
-#endif
+
             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

@@ -4,14 +4,25 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
+    /// <summary>
+    /// Byte Unpacking Helper Class
+    /// Use this class to unpack values during deserialization for values that were packed.
+    /// <seealso cref="BytePacker"/> to pack unpacked values
+    /// </summary>
     public static class ByteUnpacker
     {
-
 #if UNITY_NETCODE_DEBUG_NO_PACKING
-        
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ReadValuePacked<T>(FastBufferReader reader, out T value) where T: unmanaged => reader.ReadValueSafe(out value);
 #else
+        /// <summary>
+        /// Read a packed enum value
+        /// </summary>
+        /// <param name="reader">The reader to read from</param>
+        /// <param name="value">The value that's read</param>
+        /// <typeparam name="TEnum">Type of enum to read</typeparam>
+        /// <exception cref="InvalidOperationException">Throws InvalidOperationException if an enum somehow ends up not being the size of a byte, short, int, or long (which should be impossible)</exception>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static unsafe void ReadValuePacked<TEnum>(FastBufferReader reader, out TEnum value) where TEnum : unmanaged, Enum
         {
@@ -46,7 +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);
         }
 
@@ -58,7 +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);
         }
 
@@ -97,11 +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)
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (short)Arithmetic.ZigZagDecode(readValue);
-        }
+        public static void ReadValuePacked(FastBufferReader reader, out short value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read an unsigned short (UInt16) as a varint from the stream.
@@ -109,11 +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)
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (ushort)readValue;
-        }
+        public static void ReadValuePacked(FastBufferReader reader, out ushort value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read a two-byte character as a varint from the stream.
@@ -123,7 +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;
         }
 
@@ -133,11 +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)
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (int)Arithmetic.ZigZagDecode(readValue);
-        }
+        public static void ReadValuePacked(FastBufferReader reader, out int value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read an unsigned int (UInt32) from the stream.
@@ -145,7 +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.
@@ -153,7 +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.
@@ -163,8 +162,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out long value)
         {
-            ReadUInt64Packed(reader, out ulong readValue);
-            value = Arithmetic.ZigZagDecode(readValue);
+            ReadValueBitPacked(reader, out value);
         }
 
         /// <summary>
@@ -302,7 +300,7 @@ namespace Unity.Netcode
 #endif
 
 #if UNITY_NETCODE_DEBUG_NO_PACKING
-        
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void ReadValueBitPacked<T>(FastBufferReader reader, T value) where T: unmanaged => reader.ReadValueSafe(out value);
 #else
@@ -329,7 +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");
@@ -338,17 +338,23 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
+                    ptr[0] = data[0];
+                    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>
@@ -374,7 +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");
@@ -383,26 +390,34 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    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>
@@ -428,7 +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");
@@ -437,109 +453,74 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    ptr[3] = data[3];
                     break;
                 case 5:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
-                    *(ptr + 4) = *(data + 4);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    ptr[3] = data[3];
+                    ptr[4] = data[4];
                     break;
                 case 6:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
-                    *(ptr + 4) = *(data + 4);
-                    *(ptr + 5) = *(data + 5);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    ptr[3] = data[3];
+                    ptr[4] = data[4];
+                    ptr[5] = data[5];
                     break;
                 case 7:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
-                    *(ptr + 4) = *(data + 4);
-                    *(ptr + 5) = *(data + 5);
-                    *(ptr + 6) = *(data + 6);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    ptr[3] = data[3];
+                    ptr[4] = data[4];
+                    ptr[5] = data[5];
+                    ptr[6] = data[6];
                     break;
                 case 8:
-                    *ptr = *data;
-                    *(ptr + 1) = *(data + 1);
-                    *(ptr + 2) = *(data + 2);
-                    *(ptr + 3) = *(data + 3);
-                    *(ptr + 4) = *(data + 4);
-                    *(ptr + 5) = *(data + 5);
-                    *(ptr + 6) = *(data + 6);
-                    *(ptr + 7) = *(data + 7);
+                    ptr[0] = data[0];
+                    ptr[1] = data[1];
+                    ptr[2] = data[2];
+                    ptr[3] = data[3];
+                    ptr[4] = data[4];
+                    ptr[5] = data[5];
+                    ptr[6] = data[6];
+                    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