fix: prevent exception when showing despawned NetworkObject - up port…

… of #3029 (#3030)

* fix

up-port of #3029

* test

up-port test of #3029 while also taking into consideration the two network topologies.

* update

Adding changelog entry.

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -12,6 +12,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 
 ### Fixed
 
+-Fixed issue where the `NetworkSpawnManager.HandleNetworkObjectShow` could throw an exception if one of the `NetworkObject` components to show was destroyed during the same frame. (#3030)
 - Fixed issue where the `NetworkManagerHelper` was continuing to check for hierarchy changes when in play mode. (#3026)
 
 ### Changed

com.unity.netcode.gameobjects/Runtime/Spawning/NetworkSpawnManager.cs

@@ -1581,20 +1581,46 @@ internal void HandleNetworkObjectShow()
             {
                 foreach (var entry in ClientsToShowObject)
                 {
-                    SendSpawnCallForObserverUpdate(entry.Value.ToArray(), entry.Key);
+                    if (entry.Key != null && entry.Key.IsSpawned)
+                    {
+                        try
+                        {
+                            SendSpawnCallForObserverUpdate(entry.Value.ToArray(), entry.Key);
+                        }
+                        catch (Exception ex)
+                        {
+                            if (NetworkManager.LogLevel <= LogLevel.Developer)
+                            {
+                                Debug.LogException(ex);
+                            }
+                        }
+                    }
                 }
                 ClientsToShowObject.Clear();
                 ObjectsToShowToClient.Clear();
                 return;
             }
 
-            // Handle NetworkObjects to show
+            // Server or Host handling of NetworkObjects to show
             foreach (var client in ObjectsToShowToClient)
             {
                 ulong clientId = client.Key;
                 foreach (var networkObject in client.Value)
                 {
-                    SendSpawnCallForObject(clientId, networkObject);
+                    if (networkObject != null && networkObject.IsSpawned)
+                    {
+                        try
+                        {
+                            SendSpawnCallForObject(clientId, networkObject);
+                        }
+                        catch (Exception ex)
+                        {
+                            if (NetworkManager.LogLevel <= LogLevel.Developer)
+                            {
+                                Debug.LogException(ex);
+                            }
+                        }
+                    }
                 }
             }
             ObjectsToShowToClient.Clear();

com.unity.netcode.gameobjects/Tests/Runtime/NetworkVisibilityTests.cs

@@ -14,9 +14,11 @@ namespace Unity.Netcode.RuntimeTests
     internal class NetworkVisibilityTests : NetcodeIntegrationTest
     {
 
-        protected override int NumberOfClients => 1;
+        protected override int NumberOfClients => 2;
         private GameObject m_TestNetworkPrefab;
         private bool m_SceneManagementEnabled;
+        private GameObject m_SpawnedObject;
+        private NetworkManager m_SessionOwner;
 
         public NetworkVisibilityTests(SceneManagementState sceneManagementState, NetworkTopologyTypes networkTopologyType) : base(networkTopologyType)
         {
@@ -27,7 +29,11 @@ protected override void OnServerAndClientsCreated()
         {
             m_TestNetworkPrefab = CreateNetworkObjectPrefab("Object");
             m_TestNetworkPrefab.AddComponent<NetworkVisibilityComponent>();
-            m_ServerNetworkManager.NetworkConfig.EnableSceneManagement = m_SceneManagementEnabled;
+            if (!UseCMBService())
+            {
+                m_ServerNetworkManager.NetworkConfig.EnableSceneManagement = m_SceneManagementEnabled;
+            }
+
             foreach (var clientNetworkManager in m_ClientNetworkManagers)
             {
                 clientNetworkManager.NetworkConfig.EnableSceneManagement = m_SceneManagementEnabled;
@@ -38,21 +44,58 @@ protected override void OnServerAndClientsCreated()
 
         protected override IEnumerator OnServerAndClientsConnected()
         {
-            SpawnObject(m_TestNetworkPrefab, m_ServerNetworkManager);
+            m_SessionOwner = UseCMBService() ? m_ClientNetworkManagers[0] : m_ServerNetworkManager;
+            m_SpawnedObject = SpawnObject(m_TestNetworkPrefab, m_SessionOwner);
 
             yield return base.OnServerAndClientsConnected();
         }
 
         [UnityTest]
         public IEnumerator HiddenObjectsTest()
         {
+            var expectedCount = UseCMBService() ? 2 : 3;
 #if UNITY_2023_1_OR_NEWER
-            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == 2);
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == expectedCount);
 #else
-            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == 2);
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == expectedCount);
 #endif
 
             Assert.IsFalse(s_GlobalTimeoutHelper.TimedOut, "Timed out waiting for the visible object count to equal 2!");
         }
+
+        [UnityTest]
+        public IEnumerator HideShowAndDeleteTest()
+        {
+            var expectedCount = UseCMBService() ? 2 : 3;
+#if UNITY_2023_1_OR_NEWER
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == expectedCount);
+#else
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == expectedCount);
+#endif
+            AssertOnTimeout("Timed out waiting for the visible object count to equal 2!");
+
+            var sessionOwnerNetworkObject = m_SpawnedObject.GetComponent<NetworkObject>();
+            var clientIndex = UseCMBService() ? 1 : 0;
+            sessionOwnerNetworkObject.NetworkHide(m_ClientNetworkManagers[clientIndex].LocalClientId);
+#if UNITY_2023_1_OR_NEWER
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == expectedCount - 1);
+#else
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == expectedCount - 1);
+#endif
+            AssertOnTimeout($"Timed out waiting for {m_SpawnedObject.name} to be hidden from client!");
+            var networkObjectId = sessionOwnerNetworkObject.NetworkObjectId;
+            sessionOwnerNetworkObject.NetworkShow(m_ClientNetworkManagers[clientIndex].LocalClientId);
+            sessionOwnerNetworkObject.Despawn(true);
+
+            // Expect no exceptions
+            yield return s_DefaultWaitForTick;
+
+            // Now force a scenario where it normally would have caused an exception
+            m_SessionOwner.SpawnManager.ObjectsToShowToClient.Add(m_ClientNetworkManagers[clientIndex].LocalClientId, new System.Collections.Generic.List<NetworkObject>());
+            m_SessionOwner.SpawnManager.ObjectsToShowToClient[m_ClientNetworkManagers[clientIndex].LocalClientId].Add(null);
+
+            // Expect no exceptions
+            yield return s_DefaultWaitForTick;
+        }
     }
 }