Client communicates event syncing errors to the server

This should help

Barotrauma/BarotraumaClient/Source/Networking/GameClient.cs

@@ -1646,5 +1646,23 @@ namespace Barotrauma.Networking
             Vote(VoteType.EndRound, tickBox.Selected);
             return false;
         }
+
+        public void ReportError(ClientNetError error,UInt16 expectedID=0,UInt16 eventID=0,UInt16 entityID=0)
+        {
+            NetOutgoingMessage outMsg = client.CreateMessage();
+            outMsg.Write((byte)error);
+            switch (error)
+            {
+                case ClientNetError.MISSING_EVENT:
+                    outMsg.Write(expectedID);
+                    outMsg.Write(eventID);
+                    break;
+                case ClientNetError.MISSING_ENTITY:
+                    outMsg.Write(eventID);
+                    outMsg.Write(entityID);
+                    break;
+            }
+            client.SendMessage(outMsg, NetDeliveryMethod.ReliableUnordered);
+        }
     }
 }

Barotrauma/BarotraumaClient/Source/Networking/NetEntityEvent/ClientEntityEventManager.cs

@@ -170,9 +170,14 @@ namespace Barotrauma.Networking
                         {
                             DebugConsole.NewMessage(
                                 "Received msg " + thisEventID + " (waiting for " + (lastReceivedID + 1) + ")",
-                                thisEventID < lastReceivedID + 1
+                                NetIdUtils.IdMoreRecent(thisEventID, (UInt16)(lastReceivedID + 1))
-                                    ? Microsoft.Xna.Framework.Color.Yellow
+                                    ? Microsoft.Xna.Framework.Color.Red
-                                    : Microsoft.Xna.Framework.Color.Red);
+                                    : Microsoft.Xna.Framework.Color.Yellow);
+                        }
+                        
+                        if (NetIdUtils.IdMoreRecent(thisEventID, (UInt16)(lastReceivedID + 1)))
+                        {
+                            GameMain.Client.ReportError(ClientNetError.MISSING_EVENT, expectedID: (UInt16)(lastReceivedID + 1), eventID: thisEventID);
                         }
                     }
                     else if (entity == null)
@@ -180,6 +185,7 @@ namespace Barotrauma.Networking
                         DebugConsole.NewMessage(
                             "Received msg " + thisEventID + ", entity " + entityID + " not found",
                             Microsoft.Xna.Framework.Color.Red);
+                        GameMain.Client.ReportError(ClientNetError.MISSING_ENTITY, eventID: thisEventID, entityID: entityID);
                     }
                     
                     msg.Position += msgLength * 8;

Barotrauma/BarotraumaShared/Source/Networking/GameServer.cs

@@ -590,6 +590,9 @@ namespace Barotrauma.Networking
                         fileSender.ReadFileRequest(inc);
                     }
                     break;
+                case ClientPacketHeader.ERROR:
+                    HandleClientError(inc);
+                    break;
             }            
         }
         
@@ -608,6 +611,47 @@ namespace Barotrauma.Networking
             return userID;
         }
 
+        private void HandleClientError(NetIncomingMessage inc)
+        {
+            Client c = ConnectedClients.Find(x => x.Connection == inc.SenderConnection);
+
+            string errorStr = "Unhandled error report";
+
+            ClientNetError error = (ClientNetError)inc.ReadByte();
+            switch (error)
+            {
+                case ClientNetError.MISSING_EVENT:
+                    UInt16 expectedID = inc.ReadUInt16();
+                    UInt16 receivedID = inc.ReadUInt16();
+                    errorStr = "Expecting event id " + expectedID.ToString() + ", received " + receivedID.ToString();
+                    break;
+                case ClientNetError.MISSING_ENTITY:
+                    UInt16 eventID = inc.ReadUInt16();
+                    UInt16 entityID = inc.ReadUInt16();
+                    Entity entity = Entity.FindEntityByID(entityID);
+                    if (entity == null)
+                    {
+                        errorStr = "Received an update for an entity that doesn't exist (event id " + eventID.ToString() + ", entity id " + entityID.ToString() + ")";
+                    }
+                    else if (entity is Character character)
+                    {
+                        errorStr = "Missing character " + character.Name + " (event id " + eventID.ToString() + ", entity id " + entityID.ToString() + ")";
+                    }
+                    else if (entity is Item item)
+                    {
+                        errorStr = "Missing item " + item.Name + " (event id " + eventID.ToString() + ", entity id " + entityID.ToString() + ")";
+                    }
+                    else
+                    {
+                        errorStr = "Missing entity " + entity.ToString() + " (event id " + eventID.ToString() + ", entity id " + entityID.ToString() + ")";
+                    }
+                    break;
+            }
+
+            GameServer.Log(c.Name+" has reported an error: "+errorStr, ServerLog.MessageType.Error);
+            KickClient(c, errorStr);
+        }
+
         private void ClientReadLobby(NetIncomingMessage inc)
         {
             Client c = ConnectedClients.Find(x => x.Connection == inc.SenderConnection);

Barotrauma/BarotraumaShared/Source/Networking/NetworkMember.cs

@@ -17,7 +17,9 @@ namespace Barotrauma.Networking
         FILE_REQUEST,   //request a (submarine) file from the server
         
         RESPONSE_STARTGAME, //tell the server whether you're ready to start
-        SERVER_COMMAND      //tell the server to end a round or kick/ban someone (special permissions required)
+        SERVER_COMMAND,     //tell the server to end a round or kick/ban someone (special permissions required)
+
+        ERROR           //tell the server that an error occurred
     }
     enum ClientNetObject
     {
@@ -29,6 +31,12 @@ namespace Barotrauma.Networking
         ENTITY_STATE
     }
 
+    enum ClientNetError
+    {
+        MISSING_EVENT, //client was expecting a previous event
+        MISSING_ENTITY //client can't find an entity of a certain ID
+    }
+
     enum ServerPacketHeader
     {
         AUTH_RESPONSE,      //tell the player if they require a password to log in