perf: avoid boxing for getting message id (#1144)

* perf: avoid boxing for getting message id

* Update Assets/Mirror/Runtime/MessagePacker.cs

Co-Authored-By: MichalPetryka <35800402+MichalPetryka@users.noreply.github.com>

* Update Assets/Mirror/Runtime/NetworkConnection.cs

Co-Authored-By: MichalPetryka <35800402+MichalPetryka@users.noreply.github.com>

Assets/Mirror/Runtime/MessagePacker.cs

@@ -59,8 +59,11 @@ public static byte[] PackMessage(int msgType, MessageBase msg)
         //    and do an allocation free send before recycling it.
         public static void Pack<T>(T message, NetworkWriter writer) where T : IMessageBase
         {
-            // write message type
-            int msgType = GetId(message.GetType());
+            // if it is a value type,  just use typeof(T) to avoid boxing
+            // this works because value types cannot be derived
+            // if it is a reference type (for example IMessageBase),
+            // ask the message for the real type
+            int msgType = GetId(typeof(T).IsValueType ? typeof(T) : message.GetType());
             writer.WriteUInt16((ushort)msgType);
 
             // serialize message into writer

Assets/Mirror/Runtime/NetworkConnection.cs

@@ -386,8 +386,12 @@ internal bool InvokeHandler(int msgType, NetworkReader reader, int channelId)
             // get writer from pool
             NetworkWriter writer = NetworkWriterPool.GetWriter();
 
-            // pack and invoke
-            int msgType = MessagePacker.GetId(msg.GetType());
+            // if it is a value type,  just use typeof(T) to avoid boxing
+            // this works because value types cannot be derived
+            // if it is a reference type (for example IMessageBase),
+            // ask the message for the real type
+            int msgType = MessagePacker.GetId(typeof(T).IsValueType ? typeof(T) : msg.GetType());
+
             MessagePacker.Pack(msg, writer);
             ArraySegment<byte> segment = writer.ToArraySegment();
             bool result = InvokeHandler(msgType, new NetworkReader(segment), channelId);