Skip to main content

TCP Tunnel + Sniffer

Objective​

Write a simple cli which takes two arguments, --from {socket-addr-a} and --to {socket-addr-b}. On starting the program, it should start a TCP server at socket-addr-a. Then, for every connection made to socket-addr-a, it should make a TCP connection to socket-addr-b and create a TCP tunnel. Whenever a TCP packet comes from the client, it should print the packet as bytes to the console, and then pass on the packet to the server at socket-addr-b. It should then wait for the server's response, print it, and pass it onto the client.

CLIENT <-> TCP TUNNEL <-> SERVER (at socket-addr-b).

Bonus​

  • Separate out the cli from the actual library logic, allowing other developers to use it in their programs and build upon it.
  • Add the option of passing a kind of encoder/decoder function while initializing the TCP tunnel via the library. This function will run with the packet bytes as the arguments, allowing the user to do more than just print those bytes. (E.g. maybe the user wants to save those bytes to a log file, or perform some transformations on it). Here, user refers to a developer using your library.

Pseudo Code​

listener = tcp.listen(socket-addr-a)

loop {
  client = listener.accept_next_connection()
  handle_client(client)
}

default_msg_cb = (bytes, from_server=false) => {
  prefix = from_server ? "Server -> " : "Client ->"

  console.log(`${prefix} ${bytes}`)
}

handleClient = (client, msg_cb = default_msg_cb) => {
   server_conn = tcp.connect(socket-addr-b)

   loop {
      client_msg = client.await_next_message()
      msg_cb(client_msg, false)
      server_conn.send(msg)
      server_msg = server_conn.await_next_message()
      msg_cb(server_msg, true)
      client.send(server_msg)
   }
}

Tips​

Reference Program​

Resources​