MaimMim Man in the middle minetest interceptor

- prototype
- between client and server, allow to capture all exchanges and potentially change them
- created to capture server maps in laby
- first test get only MapBlock, support version serialization version 28
  - prepartion for 29 with zstd but untested.

java/org/artisanlogiciel/games/minetest/net/MiM.java

@@ -0,0 +1,127 @@
+package org.artisanlogiciel.games.minetest.net;
+
+import org.artisanlogiciel.games.minetest.core.PacketException;
+
+import java.io.IOException;
+import java.net.*;
+
+/**
+ * Man in the middle UDP
+ * very simple for one client only
+ */
+
+public class MiM {
+
+    DatagramSocket serverSocket;
+    boolean running = false;
+    InetSocketAddress serverAddress;
+    // will be captured, incoming address & port
+    SocketAddress fromClient = null;
+    int localPort;
+    PacketHandler handler = null;
+
+    public MiM(int myPort, InetSocketAddress remoteAddress)
+    {
+        localPort = myPort;
+        serverAddress = remoteAddress;
+    }
+
+    public void launch()
+    {
+        // ServerSocket socket = new ServerSocket()
+        try {
+            handler = new PacketHandler();
+            serverSocket = new DatagramSocket(localPort);
+            DatagramSocket in = serverSocket;
+            SocketAddress fromServer = serverAddress;
+            Thread toServer = new Thread( () -> {runFromToServer(in,fromServer);});
+            running = true;
+            toServer.start();
+        }
+        catch(Exception e)
+        {
+            System.out.println("problem");
+            e.printStackTrace(System.err);
+            running = false;
+        }
+    }
+
+    public void stop()
+    {
+        running = false;
+    }
+
+    public void runFromToServer(DatagramSocket in, SocketAddress fromServer) {
+        try {
+
+            while (running) {
+                // quick way, a new buffer at each reception
+                // to handle split packets that are buffered
+                byte[] buf = new byte[4096];
+                SocketAddress toRemote = null;
+                DatagramPacket packet = new DatagramPacket(buf, buf.length);
+                in.receive(packet);
+                SocketAddress from = packet.getSocketAddress();
+                if ( from.equals(fromServer)) {
+                    // no client yet
+                    if ( fromClient == null )
+                    {
+                        continue;
+                    }
+                    fromServer(buf,packet.getLength());
+                    toRemote = fromClient;
+                }
+                else
+                {
+                    // record client
+                    // later on to be smart : could try to record peer id ?
+                    // will add a constraint : only one auth at a time
+                    if ( fromClient == null ) {
+                        fromClient = from;
+                    }
+                    fromClient(buf,packet.getLength());
+                    toRemote = fromServer;
+                }
+                packet = new DatagramPacket(buf, packet.getLength(), toRemote);
+                in.send(packet);
+            }
+        }
+        catch( IOException ioException)
+        {
+            //
+            System.out.println("oops");
+        }
+        // socket.close();
+    }
+
+    void fromServer(byte[] buffer, int length)
+    {
+        try {
+            // reply from server
+            if (handler != null) {
+                handler.fromServer(buffer, length);
+            }
+        }
+        catch (PacketException packetException)
+        {
+            //
+        }
+    }
+
+    void fromClient(byte[] buffer, int length)
+    {
+        try {
+            // reply from client
+            if (handler != null) {
+                handler.fromClient(buffer, length);
+            }
+        }
+        catch (PacketException packetException)
+        {
+            //
+        }
+
+    }
+
+
+}