Port forwarding capture on localhost with WireShark

Question

Is it possible to do a simple, port forwarding type capture on localhost (Windows) with WireShark?

I have been using the following Java code to do this:

package tapnet;

import java.net.*;
import java.io.*;

public class tapnet {

    public static String getHexString(byte[] buffer, int buflen) {
        StringBuffer sb = new StringBuffer();
        for (int i=0; i < buflen; i++ ) {
            String hexByte = "00" + Integer.toHexString(buffer[i]);
            sb.append(hexByte.substring(hexByte.length()-2));
        }
        return sb.toString();
    }

    public static void forwardComms(Socket fromClient, Socket toServer) throws Exception {
        byte[] buffer;
        int buflen;
        InputStream clientIn = fromClient.getInputStream();
        InputStream serverIn = toServer.getInputStream();
        OutputStream clientOut = fromClient.getOutputStream();
        OutputStream serverOut = toServer.getOutputStream();

        while (true) {
            Long waitTime = 0L;
            while ((clientIn.available() == 0) && (serverIn.available() == 0)) {
                Thread.currentThread().sleep(1);
                waitTime = waitTime + 1;
            }
            System.out.println("QUIET for "+waitTime+" ms");
            if (clientIn.available() > 0) {
                buflen = clientIn.available();
                buffer = new byte[buflen];
                clientIn.read(buffer,0,buflen);
                System.out.println("CLIENT: "+getHexString(buffer,buflen));
                serverOut.write(buffer,0,buflen);
            }
            if (serverIn.available() > 0) {
                buflen = serverIn.available();
                buffer = new byte[buflen];
                serverIn.read(buffer,0,buflen);
                System.out.println("SERVER: "+getHexString(buffer,buflen));
                clientOut.write(buffer,0,buflen);
            }
        }
    }

    public static void main(String[] args) throws Exception {
        if (args.length < 2) {
            System.out.println("Usage: tapnet.tapnet <serverPort> <clientPort> [<serverHost>]");
            System.exit(1);
        }

        int serverPort = Integer.valueOf(args[0]);
        int clientPort = Integer.valueOf(args[1]);

        String serverHost = "127.0.0.1";

        if (args.length == 3) {
            serverHost = args[2];
        }

        System.out.println(clientPort + " to " + serverHost + ":" + serverPort);

        ServerSocket listenPort = new ServerSocket(clientPort);
        while (true) {
            Socket fromClient = listenPort.accept();
            Socket toServer = new Socket(serverHost,serverPort);
            forwardComms(fromClient,toServer);
        }
    }
}

However, I would prefer to use WireShark so I can use the filtering, etc.

How can I set up something similar in WireShark?

Answer 1

I don't think WireShark can do forwarding. However, if you only want to capture packets then the correct filter on the ports should do the job.

If I understand the question thought, you need to filter packets before forwarding them (ie forward only HTTP content). In that case you can use libpcap Java wrappers to do the job (jpcap or pcap4j). A similar question forwarding port 4444 to 3306 can be found here.

Finally, if you just need to forward packets after all, without filtering them and doesn't need to be in Java you might wanna have a look at NetCat for windows (to save you the development and testing).

Hope it helps