fix: prevent exception when showing despawned or destroyed NetworkObject (#3029)

* fix

Adding protections against exceptions in the NetworkSpawnManager.HandleNetworkObjectShow method.

* test

validate the fix

* update

adding changelog entry.

* update

adding PR number to changelog entry.

* fix and style

Removing whitespace
Adding 2022.3 define for find objects.

com.unity.netcode.gameobjects/CHANGELOG.md

@@ -13,10 +13,12 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ### Fixed
 
 - Fixed issue where collections v2.2.x was not supported when using UTP v2.2.x within Unity v2022.3. (#3033)
+- Fixed issue where the `NetworkSpawnManager.HandleNetworkObjectShow` could throw an exception if one of the `NetworkObject` components to show was destroyed during the same frame. (#3029)
 - Fixed issue where the `NetworkManagerHelper` was continuing to check for hierarchy changes when in play mode. (#3027)
 
 ### Changed
 
+
 ## [1.11.0] - 2024-08-20
 
 ### Added

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

@@ -1152,7 +1152,24 @@ namespace Unity.Netcode
                 ulong clientId = client.Key;
                 foreach (var networkObject in client.Value)
                 {
-                    SendSpawnCallForObject(clientId, networkObject);
+                    // Ignore if null or not spawned (v1.x.x the server should only show what is spawned)
+                    if (networkObject != null && networkObject.IsSpawned)
+                    {
+                        // Prevent exceptions from interrupting this iteration
+                        // so the ObjectsToShowToClient list will be fully processed
+                        // and cleard.
+                        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

@@ -20,6 +20,8 @@ namespace Unity.Netcode.RuntimeTests
         private GameObject m_TestNetworkPrefab;
         private bool m_SceneManagementEnabled;
 
+        private GameObject m_SpawnedObject;
+
         public NetworkVisibilityTests(SceneManagementState sceneManagementState)
         {
             m_SceneManagementEnabled = sceneManagementState == SceneManagementState.SceneManagementEnabled;
@@ -40,7 +42,7 @@ namespace Unity.Netcode.RuntimeTests
 
         protected override IEnumerator OnServerAndClientsConnected()
         {
-            SpawnObject(m_TestNetworkPrefab, m_ServerNetworkManager);
+            m_SpawnedObject = SpawnObject(m_TestNetworkPrefab, m_ServerNetworkManager);
 
             yield return base.OnServerAndClientsConnected();
         }
@@ -54,7 +56,43 @@ namespace Unity.Netcode.RuntimeTests
             yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == 2);
 #endif
 
-            Assert.IsFalse(s_GlobalTimeoutHelper.TimedOut, "Timed out waiting for the visible object count to equal 2!");
+            AssertOnTimeout("Timed out waiting for the visible object count to equal 2!");
+        }
+
+
+        [UnityTest]
+        public IEnumerator HideShowAndDeleteTest()
+        {
+#if UNITY_2023_1_OR_NEWER
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == 2);
+#else
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == 2);
+#endif
+            AssertOnTimeout("Timed out waiting for the visible object count to equal 2!");
+
+            var serverNetworkObject = m_SpawnedObject.GetComponent<NetworkObject>();
+
+            serverNetworkObject.NetworkHide(m_ClientNetworkManagers[0].LocalClientId);
+
+#if UNITY_2023_1_OR_NEWER
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsByType<NetworkVisibilityComponent>(FindObjectsSortMode.None).Where((c) => c.IsSpawned).Count() == 1);
+#else
+            yield return WaitForConditionOrTimeOut(() => Object.FindObjectsOfType<NetworkVisibilityComponent>().Where((c) => c.IsSpawned).Count() == 1);
+#endif
+            AssertOnTimeout($"Timed out waiting for {m_SpawnedObject.name} to be hidden from client!");
+            var networkObjectId = serverNetworkObject.NetworkObjectId;
+            serverNetworkObject.NetworkShow(m_ClientNetworkManagers[0].LocalClientId);
+            serverNetworkObject.Despawn(true);
+
+            // Expect no exceptions
+            yield return s_DefaultWaitForTick;
+
+            // Now force a scenario where it normally would have caused an exception
+            m_ServerNetworkManager.SpawnManager.ObjectsToShowToClient.Add(m_ClientNetworkManagers[0].LocalClientId, new System.Collections.Generic.List<NetworkObject>());
+            m_ServerNetworkManager.SpawnManager.ObjectsToShowToClient[m_ClientNetworkManagers[0].LocalClientId].Add(null);
+
+            // Expect no exceptions
+            yield return s_DefaultWaitForTick;
         }
     }
 }