fix: ObjectDisposedException on NetworkManager after shutting down the Transport

com.unity.netcode.gameobjects/Runtime/Transports/UTP/UnityTransport.cs

@@ -1495,6 +1495,11 @@ public override bool StartServer()
         /// </summary>
         public override void Shutdown()
         {
+            if (m_NetworkManager && !m_NetworkManager.ShutdownInProgress)
+            {
+                Debug.LogWarning("Directly calling `UnityTransport.Shutdown()` results in unexpected shutdown behaviour. All pending events will be lost. Use `NetworkManager.Shutdown()` instead.");
+            }
+
             if (m_Driver.IsCreated)
             {
                 while (ProcessEvent() && m_Driver.IsCreated)
@@ -1519,6 +1524,7 @@ public override void Shutdown()
             DisposeInternals();
 
             m_ReliableReceiveQueues.Clear();
+            m_State = State.Disconnected;
 
             // We must reset this to zero because UTP actually re-uses clientIds if there is a clean disconnect
             m_ServerClientId = 0;

com.unity.netcode.gameobjects/Tests/Runtime/Transports/UnityTransportTestHelpers.cs

@@ -36,6 +36,24 @@ public static IEnumerator WaitForNetworkEvent(NetworkEvent type, List<TransportE
             Assert.Fail("Timed out while waiting for network event.");
         }
 
+        // Wait to ensure no event is sent.
+        public static IEnumerator EnsureNoNetworkEvent(List<TransportEvent> events, float timeout = MaxNetworkEventWaitTime)
+        {
+            int initialCount = events.Count;
+            float startTime = Time.realtimeSinceStartup;
+
+            while (Time.realtimeSinceStartup - startTime < timeout)
+            {
+                if (events.Count > initialCount)
+                {
+                    Assert.Fail("Received unexpected network event.");
+                }
+
+                yield return new WaitForSeconds(0.01f);
+            }
+        }
+
+
         // Common code to initialize a UnityTransport that logs its events.
         public static void InitializeTransport(out UnityTransport transport, out List<TransportEvent> events,
             int maxPayloadSize = UnityTransport.InitialMaxPayloadSize, int maxSendQueueSize = 0, NetworkFamily family = NetworkFamily.Ipv4)

com.unity.netcode.gameobjects/Tests/Runtime/Transports/UnityTransportTests.cs

@@ -499,5 +499,46 @@ public IEnumerator ReliablePayloadsCanBeLargerThanMaximum()
 
             yield return WaitForNetworkEvent(NetworkEvent.Data, m_Client1Events);
         }
+
+        public enum AfterShutdownAction
+        {
+            Send,
+            DisconnectRemoteClient,
+            DisconnectLocalClient,
+        }
+
+        [UnityTest]
+        public IEnumerator DoesNotActAfterShutdown([Values] AfterShutdownAction afterShutdownAction)
+        {
+            InitializeTransport(out m_Server, out m_ServerEvents);
+            InitializeTransport(out m_Client1, out m_Client1Events);
+
+            m_Server.StartServer();
+            m_Client1.StartClient();
+
+            yield return WaitForNetworkEvent(NetworkEvent.Connect, m_Client1Events);
+
+            m_Server.Shutdown();
+
+            if (afterShutdownAction == AfterShutdownAction.Send)
+            {
+                var data = new ArraySegment<byte>(new byte[16]);
+                m_Server.Send(m_Client1.ServerClientId, data, NetworkDelivery.Reliable);
+
+                yield return EnsureNoNetworkEvent(m_Client1Events);
+            }
+            else if (afterShutdownAction == AfterShutdownAction.DisconnectRemoteClient)
+            {
+                m_Server.DisconnectRemoteClient(m_Client1.ServerClientId);
+
+                LogAssert.Expect(LogType.Assert, "DisconnectRemoteClient should be called on a listening server");
+            }
+            else if (afterShutdownAction == AfterShutdownAction.DisconnectLocalClient)
+            {
+                m_Server.DisconnectLocalClient();
+
+                yield return EnsureNoNetworkEvent(m_Client1Events);
+            }
+        }
     }
 }