Rewrite tcp stream on the fly: how complicated is it? How about dropping a stream?

Question

I am trying to write a tcp stream tunnel (similar to the default SSH descriptors), but with one exception, I have to rewrite certain information as it goes through.

I'm sure there is something similar there, but I could not find it. I have three main questions:

• Is there an easy way to save tcp stream for monitoring? (for example, using netcat or ssh -r / -l / -D or using some other alltogether utility)
• How hard is it to rewrite the stream on the fly?

Edit: The rewritten information will only be initial authentication.

Answer 1

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< > socat -v -x tcp-l: 8080, fork, reuseaddr tcp: localhost: 80 2 > log

http://localhost:8080/ http://localhost:80/, log.

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public class ForwardAndChangeCaseThread extends Thread {
    private Socket in, out;
    public ForwardAndChangeCaseThread(Socket in, Socket out) {
        this.in = in; this.out = out;
    }
    public void run() {
        byte[] buf = new byte[4096];
        InputStream in = this.in.getInputStream();
        OutputStream out = this.out.getOutputStream();
        int count;
        while ((count = in.read(buf)) > 0) {
            for (int i = 0; i < count; i++)
                if (buf[i] >= 0x40) buf[i] ^= 0x20;
            out.write(buf, 0, count);
        }
    }
}
public class TcpForwarder {
    public static void main(String[] args) {
        ServerSocket listen = new ServerSocket(8080, 1);
        for (;;) {
            Socket local = listen.accept();
            Socket remote = new Socket("localhost", 80);
            new ForwardAndChangeCaseThread(local, remote).start();
            new ForwardAndChangeCaseThread(remote, local).start();
        }
    }
}

Answer 2

Ettercap TCP.

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Answer 3

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• StreamModule

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Answer 4

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