com.unity.netcode.gameobjects@1.7.0

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).

## [1.7.0] - 2023-10-11

### Added

- exposed NetworkObject.GetNetworkBehaviourAtOrderIndex as a public API (#2724)
- Added context menu tool that provides users with the ability to quickly update the GlobalObjectIdHash value for all in-scene placed prefab instances that were created prior to adding a NetworkObject component to it. (#2707)
- Added methods NetworkManager.SetPeerMTU and NetworkManager.GetPeerMTU to be able to set MTU sizes per-peer (#2676)
- Added `GenerateSerializationForGenericParameterAttribute`, which can be applied to user-created Network Variable types to ensure the codegen generates serialization for the generic types they wrap. (#2694)
- Added `GenerateSerializationForTypeAttribute`, which can be applied to any class or method to ensure the codegen generates serialization for the specific provided type. (#2694)
- Exposed `NetworkVariableSerialization<T>.Read`, `NetworkVariableSerialization<T>.Write`, `NetworkVariableSerialization<T>.AreEqual`, and `NetworkVariableSerialization<T>.Duplicate` to further support the creation of user-created network variables by allowing users to access the generated serialization methods and serialize generic types efficiently without boxing. (#2694)
- Added `NetworkVariableBase.MarkNetworkBehaviourDirty` so that user-created network variable types can mark their containing `NetworkBehaviour` to be processed by the update loop. (#2694)

### Fixed

- Fixed issue where the server side `NetworkSceneManager` instance was not adding the currently active scene to its list of scenes loaded. (#2723)
- Generic NetworkBehaviour types no longer result in compile errors or runtime errors (#2720)
- Rpcs within Generic NetworkBehaviour types can now serialize parameters of the class's generic types (but may not have generic types of their own) (#2720)
- Errors are no longer thrown when entering play mode with domain reload disabled (#2720)
- NetworkSpawn is now correctly called each time when entering play mode with scene reload disabled (#2720)
- NetworkVariables of non-integer types will no longer break the inspector (#2714)
- NetworkVariables with NonSerializedAttribute will not appear in the inspector (#2714)
- Fixed issue where `UnityTransport` would attempt to establish WebSocket connections even if using UDP/DTLS Relay allocations when the build target was WebGL. This only applied to working in the editor since UDP/DTLS can't work in the browser. (#2695)
- Fixed issue where a `NetworkBehaviour` component's `OnNetworkDespawn` was not being invoked on the host-server side for an in-scene placed `NetworkObject` when a scene was unloaded (during a scene transition) and the `NetworkBehaviour` component was positioned/ordered before the `NetworkObject` component. (#2685)
- Fixed issue where `SpawnWithObservers` was not being honored when `NetworkConfig.EnableSceneManagement` was disabled. (#2682)
- Fixed issue where `NetworkAnimator` was not internally tracking changes to layer weights which prevented proper layer weight synchronization back to the original layer weight value. (#2674)
- Fixed "writing past the end of the buffer" error when calling ResetDirty() on managed network variables that are larger than 256 bytes when serialized. (#2670)
- Fixed issue where generation of the `DefaultNetworkPrefabs` asset was not enabled by default. (#2662)
- Fixed issue where the `GlobalObjectIdHash` value could be updated but the asset not marked as dirty. (#2662)
- Fixed issue where the `GlobalObjectIdHash` value of a (network) prefab asset could be assigned an incorrect value when editing the prefab in a temporary scene. (#2662)
- Fixed issue where the `GlobalObjectIdHash` value generated after creating a (network) prefab from an object constructed within the scene would not be the correct final value in a stand alone build. (#2662)

### Changed

- Updated dependency on `com.unity.transport` to version 1.4.0. (#2716)

Runtime/Core/NetworkBehaviour.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using Unity.Collections;
 using UnityEngine;
 
+
 namespace Unity.Netcode
 {
     /// <summary>
@@ -11,6 +12,18 @@ namespace Unity.Netcode
     public abstract class NetworkBehaviour : MonoBehaviour
     {
 #pragma warning disable IDE1006 // disable naming rule violation check
+
+        // RuntimeAccessModifiersILPP will make this `public`
+        internal delegate void RpcReceiveHandler(NetworkBehaviour behaviour, FastBufferReader reader, __RpcParams parameters);
+
+        // RuntimeAccessModifiersILPP will make this `public`
+        internal static readonly Dictionary<Type, Dictionary<uint, RpcReceiveHandler>> __rpc_func_table = new Dictionary<Type, Dictionary<uint, RpcReceiveHandler>>();
+
+#if DEVELOPMENT_BUILD || UNITY_EDITOR
+        // RuntimeAccessModifiersILPP will make this `public`
+        internal static readonly Dictionary<Type, Dictionary<uint, string>> __rpc_name_table = new Dictionary<Type, Dictionary<uint, string>>();
+#endif
+
         // RuntimeAccessModifiersILPP will make this `protected`
         internal enum __RpcExecStage
         {
@@ -97,7 +110,7 @@ namespace Unity.Netcode
 
             bufferWriter.Dispose();
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
+            if (__rpc_name_table[GetType()].TryGetValue(rpcMethodId, out var rpcMethodName))
             {
                 NetworkManager.NetworkMetrics.TrackRpcSent(
                     NetworkManager.ServerClientId,
@@ -228,7 +241,7 @@ namespace Unity.Netcode
 
             bufferWriter.Dispose();
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
+            if (__rpc_name_table[GetType()].TryGetValue(rpcMethodId, out var rpcMethodName))
             {
                 if (clientRpcParams.Send.TargetClientIds != null)
                 {
@@ -532,6 +545,23 @@ namespace Unity.Netcode
             OnGainedOwnership();
         }
 
+        /// <summary>
+        /// Invoked on all clients, override this method to be notified of any
+        /// ownership changes (even if the instance was niether the previous or
+        /// newly assigned current owner). 
+        /// </summary>
+        /// <param name="previous">the previous owner</param>
+        /// <param name="current">the current owner</param>
+        protected virtual void OnOwnershipChanged(ulong previous, ulong current)
+        {
+
+        }
+
+        internal void InternalOnOwnershipChanged(ulong previous, ulong current)
+        {
+            OnOwnershipChanged(previous, current);
+        }
+
         /// <summary>
         /// Gets called when we loose ownership of this object
         /// </summary>
@@ -565,6 +595,25 @@ namespace Unity.Netcode
             // ILPP generates code for all NetworkBehaviour subtypes to initialize each type's network variables.
         }
 
+#pragma warning disable IDE1006 // disable naming rule violation check
+        // RuntimeAccessModifiersILPP will make this `protected`
+        internal virtual void __initializeRpcs()
+#pragma warning restore IDE1006 // restore naming rule violation check
+        {
+            // ILPP generates code for all NetworkBehaviour subtypes to initialize each type's RPCs.
+        }
+
+#pragma warning disable IDE1006 // disable naming rule violation check
+        // RuntimeAccessModifiersILPP will make this `protected`
+        internal void __registerRpc(uint hash, RpcReceiveHandler handler, string rpcMethodName)
+#pragma warning restore IDE1006 // restore naming rule violation check
+        {
+            __rpc_func_table[GetType()][hash] = handler;
+#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            __rpc_name_table[GetType()][hash] = rpcMethodName;
+#endif
+        }
+
 #pragma warning disable IDE1006 // disable naming rule violation check
         // RuntimeAccessModifiersILPP will make this `protected`
         // Using this method here because ILPP doesn't seem to let us do visibility modification on properties.
@@ -583,6 +632,14 @@ namespace Unity.Netcode
 
             m_VarInit = true;
 
+            if (!__rpc_func_table.ContainsKey(GetType()))
+            {
+                __rpc_func_table[GetType()] = new Dictionary<uint, RpcReceiveHandler>();
+#if UNITY_EDITOR || DEVELOPMENT_BUILD
+                __rpc_name_table[GetType()] = new Dictionary<uint, string>();
+#endif
+                __initializeRpcs();
+            }
             __initializeVariables();
 
             {

Runtime/Core/NetworkManager.cs

@@ -15,6 +15,9 @@ namespace Unity.Netcode
     [AddComponentMenu("Netcode/Network Manager", -100)]
     public class NetworkManager : MonoBehaviour, INetworkUpdateSystem
     {
+        // TODO: Deprecate...
+        // The following internal values are not used, but because ILPP makes them public in the assembly, they cannot
+        // be removed thanks to our semver validation.
 #pragma warning disable IDE1006 // disable naming rule violation check
 
         // RuntimeAccessModifiersILPP will make this `public`
@@ -491,6 +494,15 @@ namespace Unity.Netcode
                 }
             }
         }
+
+        private void ModeChanged(PlayModeStateChange change)
+        {
+            if (IsListening && change == PlayModeStateChange.ExitingPlayMode)
+            {
+                // Make sure we are not holding onto anything in case domain reload is disabled
+                ShutdownInternal();
+            }
+        }
 #endif
 
         /// <summary>
@@ -539,6 +551,9 @@ namespace Unity.Netcode
             NetworkConfig?.InitializePrefabs();
 
             UnityEngine.SceneManagement.SceneManager.sceneUnloaded += OnSceneUnloaded;
+#if UNITY_EDITOR
+            EditorApplication.playModeStateChanged += ModeChanged;
+#endif
         }
 
         private void OnEnable()
@@ -581,7 +596,12 @@ namespace Unity.Netcode
 
         /// <summary>
         /// Sets the maximum size of a single non-fragmented message (or message batch) passed through the transport.
-        /// This should represent the transport's MTU size, minus any transport-level overhead.
+        /// This should represent the transport's default MTU size, minus any transport-level overhead.
+        /// This value will be used for any remote endpoints that haven't had per-endpoint MTUs set.
+        /// This value is also used as the size of the temporary buffer used when serializing
+        /// a single message (to avoid serializing multiple times when sending to multiple endpoints),
+        /// and thus should be large enough to ensure it can hold each message type.
+        /// This value defaults to 1296.
         /// </summary>
         /// <param name="size"></param>
         public int MaximumTransmissionUnitSize
@@ -590,6 +610,34 @@ namespace Unity.Netcode
             get => MessageManager.NonFragmentedMessageMaxSize;
         }
 
+        /// <summary>
+        /// Set the maximum transmission unit for a specific peer.
+        /// This determines the maximum size of a message batch that can be sent to that client.
+        /// If not set for any given client, <see cref="MaximumTransmissionUnitSize"/> will be used instead.
+        /// </summary>
+        /// <param name="clientId"></param>
+        /// <param name="size"></param>
+        public void SetPeerMTU(ulong clientId, int size)
+        {
+            MessageManager.PeerMTUSizes[clientId] = size;
+        }
+
+        /// <summary>
+        /// Queries the current MTU size for a client.
+        /// If no MTU has been set for that client, will return <see cref="MaximumTransmissionUnitSize"/>
+        /// </summary>
+        /// <param name="clientId"></param>
+        /// <returns></returns>
+        public int GetPeerMTU(ulong clientId)
+        {
+            if (MessageManager.PeerMTUSizes.TryGetValue(clientId, out var ret))
+            {
+                return ret;
+            }
+
+            return MessageManager.NonFragmentedMessageMaxSize;
+        }
+
         /// <summary>
         /// Sets the maximum size of a message (or message batch) passed through the transport with the ReliableFragmented delivery.
         /// Warning: setting this value too low may result in the SDK becoming non-functional with projects that have a large number of NetworkBehaviours or NetworkVariables, as the SDK relies on the transport's ability to fragment some messages when they grow beyond the MTU size.

Runtime/Core/NetworkObject.cs

@@ -1,9 +1,18 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
+#if UNITY_EDITOR
+using UnityEditor;
+#if UNITY_2021_2_OR_NEWER
+using UnityEditor.SceneManagement;
+#else
+using UnityEditor.Experimental.SceneManagement;
+#endif
+#endif
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
+
 namespace Unity.Netcode
 {
     /// <summary>
@@ -37,30 +46,171 @@ namespace Unity.Netcode
             }
         }
 
-        private bool m_IsPrefab;
-
 #if UNITY_EDITOR
-        private void OnValidate()
+        private const string k_GlobalIdTemplate = "GlobalObjectId_V1-{0}-{1}-{2}-{3}";
+
+        /// <summary>
+        /// Object Types <see href="https://docs.unity3d.com/ScriptReference/GlobalObjectId.html"/>
+        /// Parameter 0 of <see cref="k_GlobalIdTemplate"/>
+        /// </summary>
+        // 0 = Null (when considered a null object type we can ignore)
+        // 1 = Imported Asset
+        // 2 = Scene Object
+        // 3 = Source Asset.
+        private const int k_NullObjectType = 0;
+        private const int k_ImportedAssetObjectType = 1;
+        private const int k_SceneObjectType = 2;
+        private const int k_SourceAssetObjectType = 3;
+
+        [ContextMenu("Refresh In-Scene Prefab Instances")]
+        internal void RefreshAllPrefabInstances()
         {
-            GenerateGlobalObjectIdHash();
+            var instanceGlobalId = GlobalObjectId.GetGlobalObjectIdSlow(this);
+            if (!PrefabUtility.IsPartOfAnyPrefab(this) || instanceGlobalId.identifierType != k_ImportedAssetObjectType)
+            {
+                EditorUtility.DisplayDialog("Network Prefab Assets Only", "This action can only be performed on a network prefab asset.", "Ok");
+                return;
+            }
+
+            // Handle updating the currently active scene
+            var networkObjects = FindObjectsByType<NetworkObject>(FindObjectsInactive.Include, FindObjectsSortMode.None);
+            foreach (var networkObject in networkObjects)
+            {
+                networkObject.OnValidate();
+            }
+            NetworkObjectRefreshTool.ProcessActiveScene();
+
+            // Refresh all build settings scenes
+            var activeScene = SceneManager.GetActiveScene();
+            foreach (var editorScene in EditorBuildSettings.scenes)
+            {
+                // skip disabled scenes and the currently active scene
+                if (!editorScene.enabled || activeScene.path == editorScene.path)
+                {
+                    continue;
+                }
+                // Add the scene to be processed
+                NetworkObjectRefreshTool.ProcessScene(editorScene.path, false);
+            }
+
+            // Process all added scenes
+            NetworkObjectRefreshTool.ProcessScenes();
         }
 
-        internal void GenerateGlobalObjectIdHash()
+        private void OnValidate()
         {
             // do NOT regenerate GlobalObjectIdHash for NetworkPrefabs while Editor is in PlayMode
-            if (UnityEditor.EditorApplication.isPlaying && !string.IsNullOrEmpty(gameObject.scene.name))
+            if (EditorApplication.isPlaying && !string.IsNullOrEmpty(gameObject.scene.name))
             {
                 return;
             }
 
             // do NOT regenerate GlobalObjectIdHash if Editor is transitioning into or out of PlayMode
-            if (!UnityEditor.EditorApplication.isPlaying && UnityEditor.EditorApplication.isPlayingOrWillChangePlaymode)
+            if (!EditorApplication.isPlaying && EditorApplication.isPlayingOrWillChangePlaymode)
             {
                 return;
             }
 
-            var globalObjectIdString = UnityEditor.GlobalObjectId.GetGlobalObjectIdSlow(this).ToString();
-            GlobalObjectIdHash = XXHash.Hash32(globalObjectIdString);
+            // Get a global object identifier for this network prefab
+            var globalId = GetGlobalId();
+
+
+            // if the identifier type is 0, then don't update the GlobalObjectIdHash
+            if (globalId.identifierType == k_NullObjectType)
+            {
+                return;
+            }
+
+            var oldValue = GlobalObjectIdHash;
+            GlobalObjectIdHash = globalId.ToString().Hash32();
+
+            // If the GlobalObjectIdHash value changed, then mark the asset dirty
+            if (GlobalObjectIdHash != oldValue)
+            {
+                // Check if this is an in-scnee placed NetworkObject (Special Case for In-Scene Placed)
+                if (!IsEditingPrefab() && gameObject.scene.name != null && gameObject.scene.name != gameObject.name)
+                {
+                    // Sanity check to make sure this is a scene placed object
+                    if (globalId.identifierType != k_SceneObjectType)
+                    {
+                        // This should never happen, but in the event it does throw and error
+                        Debug.LogError($"[{gameObject.name}] is detected as an in-scene placed object but its identifier is of type {globalId.identifierType}! **Report this error**");
+                    }
+
+                    // If this is a prefab instance
+                    if (PrefabUtility.IsPartOfAnyPrefab(this))
+                    {
+                        // We must invoke this in order for the modifications to get saved with the scene (does not mark scene as dirty)
+                        PrefabUtility.RecordPrefabInstancePropertyModifications(this);
+                    }
+                }
+                else // Otherwise, this is a standard network prefab asset so we just mark it dirty for the AssetDatabase to update it
+                {
+                    EditorUtility.SetDirty(this);
+                }
+            }
+        }
+
+        private bool IsEditingPrefab()
+        {
+            // Check if we are directly editing the prefab
+            var stage = PrefabStageUtility.GetPrefabStage(gameObject);
+
+            // if we are not editing the prefab directly (or a sub-prefab), then return the object identifier
+            if (stage == null || stage.assetPath == null)
+            {
+                return false;
+            }
+            return true;
+        }
+
+        private GlobalObjectId GetGlobalId()
+        {
+            var instanceGlobalId = GlobalObjectId.GetGlobalObjectIdSlow(this);
+
+            // If not editing a prefab, then just use the generated id
+            if (!IsEditingPrefab())
+            {
+                return instanceGlobalId;
+            }
+
+            // If the asset doesn't exist at the given path, then return the object identifier
+            var prefabStageAssetPath = PrefabStageUtility.GetPrefabStage(gameObject).assetPath;
+            // If (for some reason) the asset path is null return the generated id
+            if (prefabStageAssetPath == null)
+            {
+                return instanceGlobalId;
+            }
+
+            var theAsset = AssetDatabase.LoadAssetAtPath<NetworkObject>(prefabStageAssetPath);
+            // If there is no asset at that path (for some odd/edge case reason), return the generated id
+            if (theAsset == null)
+            {
+                return instanceGlobalId;
+            }
+
+            // If we can't get the asset GUID and/or the file identifier, then return the object identifier
+            if (!AssetDatabase.TryGetGUIDAndLocalFileIdentifier(theAsset, out var guid, out long localFileId))
+            {
+                return instanceGlobalId;
+            }
+
+            // Note: If we reached this point, then we are most likely opening a prefab to edit.
+            // The instanceGlobalId will be constructed as if it is a scene object, however when it
+            // is serialized its value will be treated as a file asset (the "why" to the below code).
+
+            // Construct an imported asset identifier with the type being a source asset object type
+            var prefabGlobalIdText = string.Format(k_GlobalIdTemplate, k_SourceAssetObjectType, guid, (ulong)localFileId, 0);
+
+            // If we can't parse the result log an error and return the instanceGlobalId
+            if (!GlobalObjectId.TryParse(prefabGlobalIdText, out var prefabGlobalId))
+            {
+                Debug.LogError($"[GlobalObjectId Gen] Failed to parse ({prefabGlobalIdText}) returning default ({instanceGlobalId})! ** Please Report This Error **");
+                return instanceGlobalId;
+            }
+
+            // Otherwise, return the constructed identifier for the source prefab asset
+            return prefabGlobalId;
         }
 #endif // UNITY_EDITOR
 
@@ -684,6 +834,21 @@ namespace Unity.Netcode
             }
         }
 
+        internal void InvokeOwnershipChanged(ulong previous, ulong next)
+        {
+            for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
+            {
+                if (ChildNetworkBehaviours[i].gameObject.activeInHierarchy)
+                {
+                    ChildNetworkBehaviours[i].InternalOnOwnershipChanged(previous, next);
+                }
+                else
+                {
+                    Debug.LogWarning($"{ChildNetworkBehaviours[i].gameObject.name} is disabled! Netcode for GameObjects does not support disabled NetworkBehaviours! The {ChildNetworkBehaviours[i].GetType().Name} component was skipped during ownership assignment!");
+                }
+            }
+        }
+
         internal void InvokeBehaviourOnNetworkObjectParentChanged(NetworkObject parentNetworkObject)
         {
             for (int i = 0; i < ChildNetworkBehaviours.Count; i++)
@@ -1190,7 +1355,7 @@ namespace Unity.Netcode
             return 0;
         }
 
-        internal NetworkBehaviour GetNetworkBehaviourAtOrderIndex(ushort index)
+        public NetworkBehaviour GetNetworkBehaviourAtOrderIndex(ushort index)
         {
             if (index >= ChildNetworkBehaviours.Count)
             {

Runtime/Core/NetworkObjectRefreshTool.cs

@@ -0,0 +1,118 @@
+#if UNITY_EDITOR
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UnityEditor.SceneManagement;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// This is a helper tool to update all in-scene placed instances of a prefab that 
+    /// originally did not have a NetworkObject component but one was added to the prefab
+    /// later.
+    /// </summary>
+    internal class NetworkObjectRefreshTool
+    {
+        private static List<string> s_ScenesToUpdate = new List<string>();
+        private static bool s_ProcessScenes;
+        private static bool s_CloseScenes;
+
+        internal static Action AllScenesProcessed;
+
+        internal static void ProcessScene(string scenePath, bool processScenes = true)
+        {
+            if (!s_ScenesToUpdate.Contains(scenePath))
+            {
+                if (s_ScenesToUpdate.Count == 0)
+                {
+                    EditorSceneManager.sceneOpened += EditorSceneManager_sceneOpened;
+                    EditorSceneManager.sceneSaved += EditorSceneManager_sceneSaved;
+                }
+                s_ScenesToUpdate.Add(scenePath);
+            }
+            s_ProcessScenes = processScenes;
+        }
+
+        internal static void ProcessActiveScene()
+        {
+            var activeScene = SceneManager.GetActiveScene();
+            if (s_ScenesToUpdate.Contains(activeScene.path) && s_ProcessScenes)
+            {
+                SceneOpened(activeScene);
+            }
+        }
+
+        internal static void ProcessScenes()
+        {
+            if (s_ScenesToUpdate.Count != 0)
+            {
+                s_CloseScenes = true;
+                var scenePath = s_ScenesToUpdate.First();
+                EditorSceneManager.OpenScene(scenePath, OpenSceneMode.Additive);
+            }
+            else
+            {
+                s_CloseScenes = false;
+                EditorSceneManager.sceneSaved -= EditorSceneManager_sceneSaved;
+                EditorSceneManager.sceneOpened -= EditorSceneManager_sceneOpened;
+                AllScenesProcessed?.Invoke();
+            }
+        }
+
+        private static void FinishedProcessingScene(Scene scene, bool refreshed = false)
+        {
+            if (s_ScenesToUpdate.Contains(scene.path))
+            {
+                // Provide a log of all scenes that were modified to the user
+                if (refreshed)
+                {
+                    Debug.Log($"Refreshed and saved updates to scene: {scene.name}");
+                }
+                s_ProcessScenes = false;
+                s_ScenesToUpdate.Remove(scene.path);
+
+                if (scene != SceneManager.GetActiveScene())
+                {
+                    EditorSceneManager.CloseScene(scene, s_CloseScenes);
+                }
+                ProcessScenes();
+            }
+        }
+
+        private static void EditorSceneManager_sceneSaved(Scene scene)
+        {
+            FinishedProcessingScene(scene, true);
+        }
+
+        private static void SceneOpened(Scene scene)
+        {
+            if (s_ScenesToUpdate.Contains(scene.path))
+            {
+                if (s_ProcessScenes)
+                {
+                    if (!EditorSceneManager.MarkSceneDirty(scene))
+                    {
+                        Debug.Log($"Scene {scene.name} did not get marked as dirty!");
+                        FinishedProcessingScene(scene);
+                    }
+                    else
+                    {
+                        EditorSceneManager.SaveScene(scene);
+                    }
+                }
+                else
+                {
+                    FinishedProcessingScene(scene);
+                }
+            }
+        }
+
+        private static void EditorSceneManager_sceneOpened(Scene scene, OpenSceneMode mode)
+        {
+            SceneOpened(scene);
+        }
+    }
+}
+#endif // UNITY_EDITOR

Runtime/Core/NetworkObjectRefreshTool.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d24d5e8371c3cca4890e2713bdeda288
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Messaging/GenerateSerializationForGenericParameterAttribute.cs

@@ -0,0 +1,82 @@
+using System;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Marks a generic parameter in this class as a type that should be serialized through
+    /// <see cref="NetworkVariableSerialization{T}"/>. This enables the use of the following methods to support
+    /// serialization within a Network Variable type:
+    /// <br/>
+    /// <br/>
+    /// <see cref="NetworkVariableSerialization{T}"/>.<see cref="NetworkVariableSerialization{T}.Read"/>
+    /// <br/>
+    /// <see cref="NetworkVariableSerialization{T}"/>.<see cref="NetworkVariableSerialization{T}.Write"/>
+    /// <br/>
+    /// <see cref="NetworkVariableSerialization{T}"/>.<see cref="NetworkVariableSerialization{T}.AreEqual"/>
+    /// <br/>
+    /// <see cref="NetworkVariableSerialization{T}"/>.<see cref="NetworkVariableSerialization{T}.Duplicate"/>
+    /// <br/>
+    /// <br/>
+    /// The parameter is indicated by index (and is 0-indexed); for example:
+    /// <br/>
+    /// <code>
+    /// [SerializesGenericParameter(1)]
+    /// public class MyClass&lt;TTypeOne, TTypeTwo&gt;
+    /// {
+    /// }
+    /// </code>
+    /// <br/>
+    /// This tells the code generation for <see cref="NetworkVariableSerialization{T}"/> to generate
+    /// serialized code for <b>TTypeTwo</b> (generic parameter 1).
+    /// <br/>
+    /// <br/>
+    /// Note that this is primarily intended to support subtypes of <see cref="NetworkVariableBase"/>,
+    /// and as such, the type resolution is done by examining fields of <see cref="NetworkBehaviour"/>
+    /// subclasses. If your type is not used in a <see cref="NetworkBehaviour"/>, the codegen will
+    /// not find the types, even with this attribute.
+    /// <br/>
+    /// <br/>
+    /// This attribute is properly inherited by subclasses. For example:
+    /// <br/>
+    /// <code>
+    /// [SerializesGenericParameter(0)]
+    /// public class MyClass&lt;T&gt;
+    /// {
+    /// }
+    /// <br/>
+    /// public class MySubclass1 : MyClass&lt;Foo&gt;
+    /// {
+    /// }
+    /// <br/>
+    /// public class MySubclass2&lt;T&gt; : MyClass&lt;T&gt;
+    /// {
+    /// }
+    /// <br/>
+    /// [SerializesGenericParameter(1)]
+    /// public class MySubclass3&lt;TTypeOne, TTypeTwo&gt; : MyClass&lt;TTypeOne&gt;
+    /// {
+    /// }
+    /// <br/>
+    /// public class MyBehaviour : NetworkBehaviour
+    /// {
+    ///     public MySubclass1 TheValue;
+    ///     public MySubclass2&lt;Bar&gt; TheValue;
+    ///     public MySubclass3&lt;Baz, Qux&gt; TheValue;
+    /// }
+    /// </code>
+    /// <br/>
+    /// The above code will trigger generation of serialization code for <b>Foo</b> (passed directly to the
+    /// base class), <b>Bar</b> (passed indirectly to the base class), <b>Baz</b> (passed indirectly to the base class),
+    /// and <b>Qux</b> (marked as serializable in the subclass).
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = true)]
+    public class GenerateSerializationForGenericParameterAttribute : Attribute
+    {
+        internal int ParameterIndex;
+
+        public GenerateSerializationForGenericParameterAttribute(int parameterIndex)
+        {
+            ParameterIndex = parameterIndex;
+        }
+    }
+}

Runtime/Messaging/GenerateSerializationForGenericParameterAttribute.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 18cdaa9c2f6446279b0c5948fcd34eec
+timeCreated: 1694029524

Runtime/Messaging/GenerateSerializationForTypeAttribute.cs

@@ -0,0 +1,26 @@
+using System;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Specifies a specific type that needs serialization to be generated by codegen.
+    /// This is only needed in special circumstances where manual serialization is being done.
+    /// If you are making a generic network variable-style class, use <see cref="GenerateSerializationForGenericParameterAttribute"/>.
+    /// <br />
+    /// <br />
+    /// This attribute can be attached to any class or method anywhere in the codebase and
+    /// will trigger codegen to generate serialization code for the provided type. It only needs
+    /// to be included once type per codebase, but including it multiple times for the same type
+    /// is safe.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method, AllowMultiple = true)]
+    public class GenerateSerializationForTypeAttribute : Attribute
+    {
+        internal Type Type;
+
+        public GenerateSerializationForTypeAttribute(Type type)
+        {
+            Type = type;
+        }
+    }
+}

Runtime/Messaging/GenerateSerializationForTypeAttribute.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 1bd80306706f4054b9ba514a72076df5
+timeCreated: 1694103021

Runtime/Messaging/ILPPMessageProvider.cs

@@ -1,4 +1,7 @@
 using System.Collections.Generic;
+#if UNITY_EDITOR
+using UnityEditor;
+#endif
 
 namespace Unity.Netcode
 {
@@ -13,5 +16,24 @@ namespace Unity.Netcode
         {
             return __network_message_types;
         }
+
+#if UNITY_EDITOR
+        [InitializeOnLoadMethod]
+        public static void NotifyOnPlayStateChange()
+        {
+            EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
+        }
+
+        public static void OnPlayModeStateChanged(PlayModeStateChange change)
+        {
+            if (change == PlayModeStateChange.ExitingPlayMode)
+            {
+                // Clear out the network message types, because ILPP-generated RuntimeInitializeOnLoad code will
+                // run again and add more messages to it.
+                __network_message_types.Clear();
+            }
+        }
+
+#endif
     }
 }

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -60,6 +60,8 @@ namespace Unity.Netcode
                 }
             }
 
+            networkObject.InvokeOwnershipChanged(originalOwner, OwnerClientId);
+
             networkManager.NetworkMetrics.TrackOwnershipChangeReceived(context.SenderId, networkObject, context.MessageSize);
         }
     }

Runtime/Messaging/Messages/ConnectionApprovedMessage.cs

@@ -37,6 +37,9 @@ namespace Unity.Netcode
             BytePacker.WriteValueBitPacked(writer, NetworkTick);
 
             uint sceneObjectCount = 0;
+
+            // When SpawnedObjectsList is not null then scene management is disabled. Provide a list of
+            // all observed and spawned NetworkObjects that the approved client needs to synchronize.
             if (SpawnedObjectsList != null)
             {
                 var pos = writer.Position;
@@ -45,7 +48,7 @@ namespace Unity.Netcode
                 // Serialize NetworkVariable data
                 foreach (var sobj in SpawnedObjectsList)
                 {
-                    if (sobj.CheckObjectVisibility == null || sobj.CheckObjectVisibility(OwnerClientId))
+                    if (sobj.SpawnWithObservers && (sobj.CheckObjectVisibility == null || sobj.CheckObjectVisibility(OwnerClientId)))
                     {
                         sobj.Observers.Add(OwnerClientId);
                         var sceneObject = sobj.GetMessageSceneObject(OwnerClientId);

Runtime/Messaging/Messages/RpcMessages.cs

@@ -34,7 +34,7 @@ namespace Unity.Netcode
                 return false;
             }
 
-            if (!NetworkManager.__rpc_func_table.ContainsKey(metadata.NetworkRpcMethodId))
+            if (!NetworkBehaviour.__rpc_func_table[networkBehaviour.GetType()].ContainsKey(metadata.NetworkRpcMethodId))
             {
                 return false;
             }
@@ -42,7 +42,7 @@ namespace Unity.Netcode
             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))
+            if (NetworkBehaviour.__rpc_name_table[networkBehaviour.GetType()].TryGetValue(metadata.NetworkRpcMethodId, out var rpcMethodName))
             {
                 networkManager.NetworkMetrics.TrackRpcReceived(
                     context.SenderId,
@@ -67,7 +67,7 @@ namespace Unity.Netcode
 
             try
             {
-                NetworkManager.__rpc_func_table[metadata.NetworkRpcMethodId](networkBehaviour, payload, rpcParams);
+                NetworkBehaviour.__rpc_func_table[networkBehaviour.GetType()][metadata.NetworkRpcMethodId](networkBehaviour, payload, rpcParams);
             }
             catch (Exception ex)
             {
@@ -75,7 +75,7 @@ namespace Unity.Netcode
                 if (networkManager.LogLevel == LogLevel.Developer)
                 {
                     Debug.Log($"RPC Table Contents");
-                    foreach (var entry in NetworkManager.__rpc_func_table)
+                    foreach (var entry in NetworkBehaviour.__rpc_func_table[networkBehaviour.GetType()])
                     {
                         Debug.Log($"{entry.Key} | {entry.Value.Method.Name}");
                     }

Runtime/Messaging/NetworkMessageManager.cs

@@ -99,6 +99,8 @@ namespace Unity.Netcode
         public int NonFragmentedMessageMaxSize = DefaultNonFragmentedMessageMaxSize;
         public int FragmentedMessageMaxSize = int.MaxValue;
 
+        public Dictionary<ulong, int> PeerMTUSizes = new Dictionary<ulong, int>();
+
         internal struct MessageWithHandler
         {
             public Type MessageType;
@@ -497,6 +499,7 @@ namespace Unity.Netcode
             m_SendQueues.Remove(clientId);
 
             m_PerClientMessageVersions.Remove(clientId);
+            PeerMTUSizes.Remove(clientId);
         }
 
         internal void CleanupDisconnectedClients()
@@ -678,6 +681,21 @@ namespace Unity.Netcode
                     continue;
                 }
 
+                var startSize = NonFragmentedMessageMaxSize;
+                if (delivery != NetworkDelivery.ReliableFragmentedSequenced)
+                {
+                    if (PeerMTUSizes.TryGetValue(clientId, out var clientMaxSize))
+                    {
+                        maxSize = clientMaxSize;
+                    }
+                    startSize = maxSize;
+                    if (tmpSerializer.Position >= maxSize)
+                    {
+                        Debug.LogError($"MTU size for {clientId} is too small to contain a message of type {typeof(TMessageType).FullName}");
+                        continue;
+                    }
+                }
+
                 for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                 {
                     m_Hooks[hookIdx].OnBeforeSendMessage(clientId, ref message, delivery);
@@ -686,7 +704,7 @@ namespace Unity.Netcode
                 var sendQueueItem = m_SendQueues[clientId];
                 if (sendQueueItem.Length == 0)
                 {
-                    sendQueueItem.Add(new SendQueueItem(delivery, NonFragmentedMessageMaxSize, Allocator.TempJob, maxSize));
+                    sendQueueItem.Add(new SendQueueItem(delivery, startSize, Allocator.TempJob, maxSize));
                     sendQueueItem.ElementAt(0).Writer.Seek(sizeof(NetworkBatchHeader));
                 }
                 else
@@ -694,7 +712,7 @@ namespace Unity.Netcode
                     ref var lastQueueItem = ref sendQueueItem.ElementAt(sendQueueItem.Length - 1);
                     if (lastQueueItem.NetworkDelivery != delivery || lastQueueItem.Writer.MaxCapacity - lastQueueItem.Writer.Position < tmpSerializer.Length + headerSerializer.Length)
                     {
-                        sendQueueItem.Add(new SendQueueItem(delivery, NonFragmentedMessageMaxSize, Allocator.TempJob, maxSize));
+                        sendQueueItem.Add(new SendQueueItem(delivery, startSize, Allocator.TempJob, maxSize));
                         sendQueueItem.ElementAt(sendQueueItem.Length - 1).Writer.Seek(sizeof(NetworkBatchHeader));
                     }
                 }

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -1,7 +1,6 @@
 using System;
 using System.Collections.Generic;
 using Unity.Collections;
-using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -9,6 +8,7 @@ namespace Unity.Netcode
     /// Event based NetworkVariable container for syncing Lists
     /// </summary>
     /// <typeparam name="T">The type for the list</typeparam>
+    [GenerateSerializationForGenericParameter(0)]
     public class NetworkList<T> : NetworkVariableBase where T : unmanaged, IEquatable<T>
     {
         private NativeList<T> m_List = new NativeList<T>(64, Allocator.Persistent);
@@ -68,14 +68,7 @@ namespace Unity.Netcode
 
         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.BehaviourUpdater.AddForUpdate(m_NetworkBehaviour.NetworkObject);
+            MarkNetworkBehaviourDirty();
         }
 
         /// <inheritdoc />

Runtime/NetworkVariable/NetworkVariable.cs

@@ -8,6 +8,7 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">the unmanaged type for <see cref="NetworkVariable{T}"/> </typeparam>
     [Serializable]
+    [GenerateSerializationForGenericParameter(0)]
     public class NetworkVariable<T> : NetworkVariableBase
     {
         /// <summary>
@@ -146,8 +147,11 @@ namespace Unity.Netcode
             // Therefore, we set the m_PreviousValue field to a duplicate of the current
             // field, so that our next dirty check is made against the current "not dirty"
             // value.
-            m_HasPreviousValue = true;
-            NetworkVariableSerialization<T>.Serializer.Duplicate(m_InternalValue, ref m_PreviousValue);
+            if (!m_HasPreviousValue || !NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref m_PreviousValue))
+            {
+                m_HasPreviousValue = true;
+                NetworkVariableSerialization<T>.Duplicate(m_InternalValue, ref m_PreviousValue);
+            }
         }
 
         /// <summary>

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -88,17 +88,22 @@ namespace Unity.Netcode
 
             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.BehaviourUpdater.AddForUpdate(m_NetworkBehaviour.NetworkObject);
+                MarkNetworkBehaviourDirty();
             }
         }
 
+        protected void MarkNetworkBehaviourDirty()
+        {
+            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.BehaviourUpdater.AddForUpdate(m_NetworkBehaviour.NetworkObject);
+        }
+
         /// <summary>
         /// Resets the dirty state and marks the variable as synced / clean
         /// </summary>

Runtime/NetworkVariable/NetworkVariableSerialization.cs

@@ -514,7 +514,7 @@ namespace Unity.Netcode
 
         public void Duplicate(in T value, ref T duplicatedValue)
         {
-            using var writer = new FastBufferWriter(256, Allocator.Temp);
+            using var writer = new FastBufferWriter(256, Allocator.Temp, int.MaxValue);
             var refValue = value;
             Write(writer, ref refValue);
 
@@ -580,11 +580,16 @@ namespace Unity.Netcode
     /// <typeparam name="T"></typeparam>
     internal class FallbackSerializer<T> : INetworkVariableSerializer<T>
     {
+        private void ThrowArgumentError()
+        {
+            throw new ArgumentException($"Serialization has not been generated for type {typeof(T).FullName}. This can be addressed by adding a [{nameof(GenerateSerializationForGenericParameterAttribute)}] to your generic class that serializes this value (if you are using one), adding [{nameof(GenerateSerializationForTypeAttribute)}(typeof({typeof(T).FullName})] to the class or method that is attempting to serialize it, or creating a field on a {nameof(NetworkBehaviour)} of type {nameof(NetworkVariable<T>)}. If this error continues to appear after doing one of those things and this is a type you can change, then either implement {nameof(INetworkSerializable)} or mark it as serializable by memcpy by adding {nameof(INetworkSerializeByMemcpy)} to its interface list to enable automatic serialization generation. If not, assign serialization code to {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.WriteValue)}, {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.DuplicateValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+        }
+
         public void Write(FastBufferWriter writer, ref T value)
         {
             if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null || UserNetworkVariableSerialization<T>.DuplicateValue == null)
             {
-                throw new ArgumentException($"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)}, {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.DuplicateValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+                ThrowArgumentError();
             }
             UserNetworkVariableSerialization<T>.WriteValue(writer, value);
         }
@@ -592,7 +597,7 @@ namespace Unity.Netcode
         {
             if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null || UserNetworkVariableSerialization<T>.DuplicateValue == null)
             {
-                throw new ArgumentException($"Type {typeof(T).FullName} is not supported by {typeof(NetworkVariable<>).Name}. If this is a type you can change, then either implement {nameof(INetworkSerializable)} or mark it as serializable by memcpy by adding {nameof(INetworkSerializeByMemcpy)} to its interface list. If not, assign serialization code to {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.WriteValue)}, {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.DuplicateValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+                ThrowArgumentError();
             }
             UserNetworkVariableSerialization<T>.ReadValue(reader, out value);
         }
@@ -606,7 +611,7 @@ namespace Unity.Netcode
         {
             if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null || UserNetworkVariableSerialization<T>.DuplicateValue == null)
             {
-                throw new ArgumentException($"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)}, {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.ReadValue)}, and {nameof(UserNetworkVariableSerialization<T>)}.{nameof(UserNetworkVariableSerialization<T>.DuplicateValue)}, or if it's serializable by memcpy (contains no pointers), wrap it in {typeof(ForceNetworkSerializeByMemcpy<>).Name}.");
+                ThrowArgumentError();
             }
             UserNetworkVariableSerialization<T>.DuplicateValue(value, ref duplicatedValue);
         }
@@ -841,8 +846,95 @@ namespace Unity.Netcode
     {
         internal static INetworkVariableSerializer<T> Serializer = new FallbackSerializer<T>();
 
-        internal delegate bool EqualsDelegate(ref T a, ref T b);
-        internal static EqualsDelegate AreEqual;
+        /// <summary>
+        /// A callback to check if two values are equal.
+        /// </summary>
+        public delegate bool EqualsDelegate(ref T a, ref T b);
+
+        /// <summary>
+        /// Uses the most efficient mechanism for a given type to determine if two values are equal.
+        /// For types that implement <see cref="IEquatable{T}"/>, it will call the Equals() method.
+        /// For unmanaged types, it will do a bytewise memory comparison.
+        /// For other types, it will call the == operator.
+        /// <br/>
+        /// <br/>
+        /// Note: If you are using this in a custom generic class, please make sure your class is
+        /// decorated with <see cref="GenerateSerializationForGenericParameterAttribute"/> so that codegen can
+        /// initialize the serialization mechanisms correctly. If your class is NOT
+        /// generic, it is better to check their equality yourself.
+        /// </summary>
+        public static EqualsDelegate AreEqual { get; internal set; }
+
+        /// <summary>
+        /// Serialize a value using the best-known serialization method for a generic value.
+        /// Will reliably serialize any value that is passed to it correctly with no boxing.
+        /// <br/>
+        /// <br/>
+        /// Note: If you are using this in a custom generic class, please make sure your class is
+        /// decorated with <see cref="GenerateSerializationForGenericParameterAttribute"/> so that codegen can
+        /// initialize the serialization mechanisms correctly. If your class is NOT
+        /// generic, it is better to use FastBufferWriter directly.
+        /// <br/>
+        /// <br/>
+        /// If the codegen is unable to determine a serializer for a type,
+        /// <see cref="UserNetworkVariableSerialization{T}"/>.<see cref="UserNetworkVariableSerialization{T}.WriteValue"/> is called, which, by default,
+        /// will throw an exception, unless you have assigned a user serialization callback to it at runtime.
+        /// </summary>
+        /// <param name="writer"></param>
+        /// <param name="value"></param>
+        public static void Write(FastBufferWriter writer, ref T value)
+        {
+            Serializer.Write(writer, ref value);
+        }
+
+        /// <summary>
+        /// Deserialize a value using the best-known serialization method for a generic value.
+        /// Will reliably deserialize any value that is passed to it correctly with no boxing.
+        /// For types whose deserialization can be determined by codegen (which is most types),
+        /// GC will only be incurred if the type is a managed type and the ref value passed in is `null`,
+        /// in which case a new value is created; otherwise, it will be deserialized in-place.
+        /// <br/>
+        /// <br/>
+        /// Note: If you are using this in a custom generic class, please make sure your class is
+        /// decorated with <see cref="GenerateSerializationForGenericParameterAttribute"/> so that codegen can
+        /// initialize the serialization mechanisms correctly. If your class is NOT
+        /// generic, it is better to use FastBufferReader directly.
+        /// <br/>
+        /// <br/>
+        /// If the codegen is unable to determine a serializer for a type,
+        /// <see cref="UserNetworkVariableSerialization{T}"/>.<see cref="UserNetworkVariableSerialization{T}.ReadValue"/> is called, which, by default,
+        /// will throw an exception, unless you have assigned a user deserialization callback to it at runtime.
+        /// </summary>
+        /// <param name="reader"></param>
+        /// <param name="value"></param>
+        public static void Read(FastBufferReader reader, ref T value)
+        {
+            Serializer.Read(reader, ref value);
+        }
+
+        /// <summary>
+        /// Duplicates a value using the most efficient means of creating a complete copy.
+        /// For most types this is a simple assignment or memcpy.
+        /// For managed types, this is will serialize and then deserialize the value to ensure
+        /// a correct copy.
+        /// <br/>
+        /// <br/>
+        /// Note: If you are using this in a custom generic class, please make sure your class is
+        /// decorated with <see cref="GenerateSerializationForGenericParameterAttribute"/> so that codegen can
+        /// initialize the serialization mechanisms correctly. If your class is NOT
+        /// generic, it is better to duplicate it directly.
+        /// <br/>
+        /// <br/>
+        /// If the codegen is unable to determine a serializer for a type,
+        /// <see cref="UserNetworkVariableSerialization{T}"/>.<see cref="UserNetworkVariableSerialization{T}.DuplicateValue"/> is called, which, by default,
+        /// will throw an exception, unless you have assigned a user duplication callback to it at runtime.
+        /// </summary>
+        /// <param name="value"></param>
+        /// <param name="duplicatedValue"></param>
+        public static void Duplicate(in T value, ref T duplicatedValue)
+        {
+            Serializer.Duplicate(value, ref duplicatedValue);
+        }
 
         // Compares two values of the same unmanaged type by underlying memory
         // Ignoring any overridden value checks
@@ -1001,15 +1093,21 @@ namespace Unity.Netcode
         {
             return a == b;
         }
+    }
 
-        internal static void Write(FastBufferWriter writer, ref T value)
+    // RuntimeAccessModifiersILPP will make this `public`
+    // This is just pass-through to NetworkVariableSerialization<T> but is here becaues I could not get ILPP
+    // to generate code that would successfully call Type<T>.Method(T), but it has no problem calling Type.Method<T>(T)
+    internal class RpcFallbackSerialization
+    {
+        public static void Write<T>(FastBufferWriter writer, ref T value)
         {
-            Serializer.Write(writer, ref value);
+            NetworkVariableSerialization<T>.Write(writer, ref value);
         }
 
-        internal static void Read(FastBufferReader reader, ref T value)
+        public static void Read<T>(FastBufferReader reader, ref T value)
         {
-            Serializer.Read(reader, ref value);
+            NetworkVariableSerialization<T>.Read(reader, ref value);
         }
     }
 }

Runtime/SceneManagement/NetworkSceneManager.cs

@@ -740,6 +740,14 @@ namespace Unity.Netcode
             // Since NetworkManager is now always migrated to the DDOL we will use this to get the DDOL scene
             DontDestroyOnLoadScene = networkManager.gameObject.scene;
 
+            // Since the server tracks loaded scenes, we need to add the currently active scene
+            // to the list of scenes that can be unloaded.
+            if (networkManager.IsServer)
+            {
+                var activeScene = SceneManager.GetActiveScene();
+                ScenesLoaded.Add(activeScene.handle, activeScene);
+            }
+
             // Add to the server to client scene handle table
             UpdateServerClientSceneHandle(DontDestroyOnLoadScene.handle, DontDestroyOnLoadScene.handle, DontDestroyOnLoadScene);
         }

Runtime/Spawning/NetworkSpawnManager.cs

@@ -257,6 +257,7 @@ namespace Unity.Netcode
                 throw new SpawnStateException("Object is not spawned");
             }
 
+            var previous = networkObject.OwnerClientId;
             // Assign the new owner
             networkObject.OwnerClientId = clientId;
 
@@ -286,6 +287,12 @@ namespace Unity.Netcode
                     NetworkManager.NetworkMetrics.TrackOwnershipChangeSent(client.Key, networkObject, size);
                 }
             }
+
+            // After we have sent the change ownership message to all client observers, invoke the ownership changed notification.
+            /// !!Important!!
+            /// This gets called specifically *after* sending the ownership message so any additional messages that need to proceed an ownership
+            /// change can be sent from NetworkBehaviours that override the <see cref="NetworkBehaviour.OnOwnershipChanged"></see>
+            networkObject.InvokeOwnershipChanged(previous, clientId);
         }
 
         internal bool HasPrefab(NetworkObject.SceneObject sceneObject)

Runtime/Transports/UTP/BatchedSendQueue.cs

@@ -242,7 +242,7 @@ namespace Unity.Netcode.Transports.UTP
         /// Fill the given <see cref="DataStreamWriter"/> with as many bytes from the queue as
         /// possible, disregarding message boundaries.
         /// </summary>
-        ///<remarks>
+        /// <remarks>
         /// This does NOT actually consume anything from the queue. That is, calling this method
         /// does not reduce the length of the queue. Callers are expected to call
         /// <see cref="Consume"/> with the value returned by this method afterwards if the data can
@@ -252,15 +252,17 @@ namespace Unity.Netcode.Transports.UTP
         /// this could lead to reading messages from a corrupted queue.
         /// </remarks>
         /// <param name="writer">The <see cref="DataStreamWriter"/> to write to.</param>
+        /// <param name="maxBytes">Max number of bytes to copy (0 means writer capacity).</param>
         /// <returns>How many bytes were written to the writer.</returns>
-        public int FillWriterWithBytes(ref DataStreamWriter writer)
+        public int FillWriterWithBytes(ref DataStreamWriter writer, int maxBytes = 0)
         {
             if (!IsCreated || Length == 0)
             {
                 return 0;
             }
 
-            var copyLength = Math.Min(writer.Capacity, Length);
+            var maxLength = maxBytes == 0 ? writer.Capacity : Math.Min(maxBytes, writer.Capacity);
+            var copyLength = Math.Min(maxLength, Length);
 
             unsafe
             {

Runtime/Transports/UTP/UnityTransport.cs

@@ -727,6 +727,7 @@ namespace Unity.Netcode.Transports.UTP
             public SendTarget Target;
             public BatchedSendQueue Queue;
             public NetworkPipeline ReliablePipeline;
+            public int MTU;
 
             public void Execute()
             {
@@ -749,7 +750,7 @@ namespace Unity.Netcode.Transports.UTP
                     // in the stream (the send queue does that automatically) we are sure they'll be
                     // reassembled properly at the other end. This allows us to lift the limit of ~44KB
                     // on reliable payloads (because of the reliable window size).
-                    var written = pipeline == ReliablePipeline ? Queue.FillWriterWithBytes(ref writer) : Queue.FillWriterWithMessages(ref writer);
+                    var written = pipeline == ReliablePipeline ? Queue.FillWriterWithBytes(ref writer, MTU) : Queue.FillWriterWithMessages(ref writer);
 
                     result = Driver.EndSend(writer);
                     if (result == written)
@@ -783,12 +784,21 @@ namespace Unity.Netcode.Transports.UTP
             {
                 return;
             }
+
+            var mtu = 0;
+            if (NetworkManager)
+            {
+                var ngoClientId = NetworkManager.ConnectionManager.TransportIdToClientId(sendTarget.ClientId);
+                mtu = NetworkManager.GetPeerMTU(ngoClientId);
+            }
+
             new SendBatchedMessagesJob
             {
                 Driver = m_Driver.ToConcurrent(),
                 Target = sendTarget,
                 Queue = queue,
-                ReliablePipeline = m_ReliableSequencedPipeline
+                ReliablePipeline = m_ReliableSequencedPipeline,
+                MTU = mtu,
             }.Run();
         }
 
@@ -1560,6 +1570,21 @@ namespace Unity.Netcode.Transports.UTP
             }
 #endif
 
+#if UTP_TRANSPORT_2_1_ABOVE
+            if (m_ProtocolType == ProtocolType.RelayUnityTransport)
+            {
+                if (m_UseWebSockets && m_RelayServerData.IsWebSocket == 0)
+                {
+                    Debug.LogError("Transport is configured to use WebSockets, but Relay server data isn't. Be sure to use \"wss\" as the connection type when creating the server data (instead of \"dtls\" or \"udp\").");
+                }
+
+                if (!m_UseWebSockets && m_RelayServerData.IsWebSocket != 0)
+                {
+                    Debug.LogError("Relay server data indicates usage of WebSockets, but \"Use WebSockets\" checkbox isn't checked under \"Unity Transport\" component.");
+                }
+            }
+#endif
+
 #if UTP_TRANSPORT_2_0_ABOVE
             if (m_UseWebSockets)
             {
@@ -1567,7 +1592,7 @@ namespace Unity.Netcode.Transports.UTP
             }
             else
             {
-#if UNITY_WEBGL
+#if UNITY_WEBGL && !UNITY_EDITOR
                 Debug.LogWarning($"WebSockets were used even though they're not selected in NetworkManager. You should check {nameof(UseWebSockets)}', on the Unity Transport component, to silence this warning.");
                 driver = NetworkDriver.Create(new WebSocketNetworkInterface(), m_NetworkSettings);
 #else

Runtime/com.unity.netcode.runtime.asmdef

@@ -36,6 +36,11 @@
             "name": "com.unity.transport",
             "expression": "2.0.0-exp",
             "define": "UTP_TRANSPORT_2_0_ABOVE"
+        },
+        {
+            "name": "com.unity.transport",
+            "expression": "2.1.0",
+            "define": "UTP_TRANSPORT_2_1_ABOVE"
         }
     ]
 }