port forwarding via python socket

port-forwarding.py

#!/usr/bin/env python3
# Tcp Port Forwarding (Reverse Proxy)
# Author : WangYihang <wangyihanger@gmail.com>

'''
 +-----------------------------+         +---------------------------------------------+         +--------------------------------+
 |     My Laptop (Alice)       |         |            Intermediary Server (Bob)        |         |    Internal Server (Carol)     |
 +-----------------------------+         +----------------------+----------------------+         +--------------------------------+
 | $ ssh -p 1022 carol@1.2.3.4 |<------->|    IF 1: 1.2.3.4     |  IF 2: 192.168.1.1   |<------->|       IF 1: 192.168.1.2        |
 | carol@1.2.3.4's password:   |         +----------------------+----------------------+         +--------------------------------+
 | carol@hostname:~$ whoami    |         | $ python pf.py --listen-host 1.2.3.4 \      |         | 192.168.1.2:22(OpenSSH Server) |
 | carol                       |         |                --listen-port 1022 \         |         +--------------------------------+
 +-----------------------------+         |                --connect-host 192.168.1.2 \ |
                                         |                --connect-port 22            |
                                         +---------------------------------------------+
'''

import socket
import threading
import argparse
import logging


format = '%(asctime)s - %(filename)s:%(lineno)d - %(levelname)s: %(message)s'
logging.basicConfig(level=logging.INFO, format=format)


def handle(buffer, direction, src_address, src_port, dst_address, dst_port):
    '''
    intercept the data flows between local port and the target port
    '''
    if direction:
        logging.debug(f"{src_address, src_port} -> {dst_address, dst_port} {len(buffer)} bytes")
    else:
        logging.debug(f"{src_address, src_port} <- {dst_address, dst_port} {len(buffer)} bytes")
    return buffer


def transfer(src, dst, direction):
    src_address, src_port = src.getsockname()
    dst_address, dst_port = dst.getsockname()
    while True:
        try:
            buffer = src.recv(4096)
            if len(buffer) == 0:
                break
            dst.send(handle(buffer, direction, src_address, src_port, dst_address, dst_port))
        except Exception as e:
            logging.error(repr(e))
            break
    logging.warning(f"Closing connect {src_address, src_port}! ")
    src.close()
    logging.warning(f"Closing connect {dst_address, dst_port}! ")
    dst.close()


def server(local_host, local_port, remote_host, remote_port):
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    server_socket.bind((local_host, local_port))
    server_socket.listen(0x40)
    logging.info(f"Server started {local_host, local_port}")
    logging.info(f"Connect to {local_host, local_port} to get the content of {remote_host, remote_port}")
    while True:
        src_socket, src_address = server_socket.accept()
        logging.info(f"[Establishing] {src_address} -> {local_host, local_port} -> ? -> {remote_host, remote_port}")
        try:
            dst_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            dst_socket.connect((remote_host, remote_port))
            logging.info(f"[OK] {src_address} -> {local_host, local_port} -> {dst_socket.getsockname()} -> {remote_host, remote_port}")
            s = threading.Thread(target=transfer, args=(dst_socket, src_socket, False))
            r = threading.Thread(target=transfer, args=(src_socket, dst_socket, True))
            s.start()
            r.start()
        except Exception as e:
            logging.error(repr(e))


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--listen-host", help="the host to listen", required=True)
    parser.add_argument("--listen-port", type=int, help="the port to bind", required=True)
    parser.add_argument("--connect-host", help="the target host to connect", required=True)
    parser.add_argument("--connect-port", type=int, help="the target port to connect", required=True)
    args = parser.parse_args()
    server(args.listen_host, args.listen_port,
           args.connect_host, args.connect_port)


if __name__ == "__main__":
    main()

The program communicates with the base, there is no call to the "transfer" function. Why?

@kristow31

See line 70-71, the target function of threading.Thread is function transfer.

In addition, please refer to the document of the Python threading package.

target is the callable object to be invoked by the run() method. Defaults to None, meaning nothing is called.

Hello everyone,
I really like port forwarding and what you can do with it.
Here is my Python port forwarding version that I've made recently, inspired by @wangyihan script :D

• Using socket & Asyncio:
  https://github.com/medram/port-forwarding/blob/with-asyncio/port_forwarding.py
• Using sockets & Selectors:
  https://github.com/medram/port-forwarding/blob/with-selectors/port_forwarding.py

I hope you like it.

By the way, it support HTTP Custom & HTTP injection (for fake Websocket upgrade reply).

what about udp ?

usage: 213.py [-h] --listen-host LISTEN_HOST --listen-port LISTEN_PORT
--connect-host CONNECT_HOST --connect-port CONNECT_PORT
213.py: error: the following arguments are required: --listen-host, --listen-port, --connect-host, --connect-port
Help, how to fix that?

line 45, if len(buffer) == 0, there would be endless loop

@ruanhao thanks for pointing out this bug, fixed.

Why do we need --listen-host parameter ? 127.0.0.1 won't always do ?

Why do we need --listen-host parameter ? 127.0.0.1 won't always do ?

there is need for 0.0.0.0