Good latency proxy? (TMnetsim causing stream corruption!)

Networking & Multiplayer
#1

I’m currently writing an unofficial multiplayer mod for the game Starsector. (great game btw! and a bargain for $10)

For simplicity* I’m making the game simulation(and fp) deterministic, syncing the peers, and transmitting just user-originated events using a lock-step model, with input delay appropriate to the latency between peers.
*(simplicity is of paramount importance because the entire mod is going to be bytecode injected, meaning there are practical limitations upon how much of the codebase I can interact with.)

To this end I created a prototype to test how well the lock-step model handles at various latencies. (using the tool TMnetsim as a latency proxy)
It seemed to work fine with low latencies, but exhibited weird data corruption at higher latencies.
After much hair pulling I determined it couldn’t possibly be my code, and wrote the below code as a sanity test to confirm TMnetsim is a useless piece of crap.

So 2 questions:

  1. The below code should work perfectly, right? (obviously with the relevant ports redirected)
  2. As TMnetsim appears to be a piece of unreliable crap, can anyone suggest a good tool for introducing semi-realistic latency between connections? (I could of course write one… but given the plethora of multiplayer games surely such tools already exist?!)

import java.io.IOException;
import java.net.Socket;

public class Client {

	public static void main(String[] args) throws IOException {
		Socket s = new Socket("localhost", 9665);

		new Thread(new SocketReader(s)).start();

		new Thread(new SocketWriter(s)).start();
	}

}


import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
	public static void main(String[] args) throws IOException {
		Socket s = new ServerSocket(9765).accept();

		new Thread(new SocketReader(s)).start();

		new Thread(new SocketWriter(s)).start();
	}

}



import java.io.DataInputStream;
import java.io.IOException;
import java.net.Socket;

class SocketReader implements Runnable {

	Socket s;

	public SocketReader(Socket s) {
		this.s = s;
	}

	@Override
	public void run() {
		try {
			DataInputStream dis = new DataInputStream(s.getInputStream());
			int counter = 0;

			while (true) {
				int val = dis.readInt();
				if (val != counter) {
					throw new RuntimeException("stream corruption! Expected: " + counter + " received: " + val);
				}
				counter++;
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;

class SocketWriter implements Runnable {

	Socket s;

	public SocketWriter(Socket s) {
		this.s = s;
	}

	@Override
	public void run() {

		try {
			DataOutputStream dos = new DataOutputStream(s.getOutputStream());
			int counter = 0;
			
			while (true) {
				dos.writeInt(counter);
				counter++;
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}