it is done

core/src/mindustry/net/Registrator.java

@@ -0,0 +1,45 @@
+package mindustry.net;
+
+import arc.struct.ObjectIntMap;
+import arc.func.Prov;
+import mindustry.net.Packets.*;
+
+public class Registrator{
+    private static ClassEntry[] classes = {
+    new ClassEntry(StreamBegin.class, StreamBegin::new),
+    new ClassEntry(StreamChunk.class, StreamChunk::new),
+    new ClassEntry(WorldStream.class, WorldStream::new),
+    new ClassEntry(ConnectPacket.class, ConnectPacket::new),
+    new ClassEntry(InvokePacket.class, InvokePacket::new)
+    };
+    private static ObjectIntMap<Class> ids = new ObjectIntMap<>();
+
+    static{
+        if(classes.length > 127) throw new RuntimeException("Can't have more than 127 registered classes!");
+        for(int i = 0; i < classes.length; i++){
+            ids.put(classes[i].type, i);
+        }
+    }
+
+    public static ClassEntry getByID(byte id){
+        return classes[id];
+    }
+
+    public static byte getID(Class<?> type){
+        return (byte)ids.get(type, -1);
+    }
+
+    public static ClassEntry[] getClasses(){
+        return classes;
+    }
+
+    public static class ClassEntry{
+        public final Class<?> type;
+        public final Prov<?> constructor;
+
+        public <T extends Packet> ClassEntry(Class<T> type, Prov<T> constructor){
+            this.type = type;
+            this.constructor = constructor;
+        }
+    }
+}