Fixed message fragmentation issues caused by initial lobby syncing. The size of the initial message exceeds MTU if the host has a large number of subs, and apparently Lidgren doesn't attempt to handle fragmenting by default when sending the messages with the unreliable delivery method. Now the initial syncing message is sent only once with the reliable delivery method which should be able to handle fragmented messages.

Barotrauma/Source/Networking/GameServer.cs

@@ -922,6 +922,8 @@ namespace Barotrauma.Networking
 
         private void ClientWriteLobby(Client c)
         {
+            bool isInitialUpdate = false;
+
             NetOutgoingMessage outmsg = server.CreateMessage();
             outmsg.Write((byte)ServerPacketHeader.UPDATE_LOBBY);
 
@@ -939,6 +941,7 @@ namespace Barotrauma.Networking
                 outmsg.Write(c.lastRecvGeneralUpdate < 1);
                 if (c.lastRecvGeneralUpdate < 1)
                 {
+                    isInitialUpdate = true;
                     ClientWriteInitial(c, outmsg);
                 }
                 outmsg.Write((GameMain.NetLobbyScreen.SubList.SelectedData as Submarine).Name);
@@ -987,6 +990,20 @@ namespace Barotrauma.Networking
 
             outmsg.Write((byte)ServerNetObject.END_OF_MESSAGE);
 
+            if (isInitialUpdate)
+            {
+                //the initial update may be very large if the host has a large number
+                //of submarine files, so the message may have to be fragmented
+
+                //unreliable messages don't play nicely with fragmenting, so we'll send the message reliably
+                server.SendMessage(outmsg, c.Connection, NetDeliveryMethod.ReliableUnordered);
+
+                //and assume the message was received, so we don't have to keep resending
+                //these large initial messages until the client acknowledges receiving them
+                c.lastRecvGeneralUpdate++;
+            }
+            else
+            {
                 if (outmsg.LengthBytes > config.MaximumTransmissionUnit)
                 {
                     DebugConsole.ThrowError("Maximum packet size exceeded (" + outmsg.LengthBytes + " > " + config.MaximumTransmissionUnit + ")");
@@ -994,6 +1011,7 @@ namespace Barotrauma.Networking
 
                 server.SendMessage(outmsg, c.Connection, NetDeliveryMethod.Unreliable);
             }
+        }
 
         public bool StartGameClicked(GUIButton button, object obj)
         {