SimpleProxy.java

//DEPS info.picocli:picocli:4.7.5
//JAVA 21

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.Callable;
import picocli.CommandLine;
import picocli.CommandLine.Command;

public class SimpleProxy implements Callable<Integer> {
  
  @CommandLine.Option(names = "--port", description = "Set the port of the listening server", defaultValue = "43812")
  private int port;
  
  private ServerSocket serverSocket = null;

  @Override
  public Integer call() throws Exception {
    serverSocket = new ServerSocket(port);
    System.out.println("Proxy server listening on " + serverSocket.getInetAddress() + ":" + serverSocket.getLocalPort());
    return 0;
  }

  public void listen() throws IOException {
    System.out.println("Starting the proxy server");
    while (true) {
        Socket clientSocket = serverSocket.accept();
        System.out.println("Accepted connection from client: " + clientSocket.getInetAddress());
        Thread proxyThread = new Thread(() -> handleClient(clientSocket));
        proxyThread.start();
    }
  }
  
  private void handleClient(Socket clientSocket) { 
    try {
        // Simulate connection reset by closing the client socket immediately
        //clientSocket.close();
        serverSocket.close();
        System.out.println("Connection closed for client: " + clientSocket.getInetAddress());
        return; // Exit the method after simulating the reset
    } catch (IOException e) {
        e.printStackTrace();
    }
}
  public static void main(String[] args) throws IOException {
    SimpleProxy proxy = new SimpleProxy();
    new CommandLine(proxy).execute(args);
    proxy.listen();
  }
}