tcp_proxy.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Mon Jun 22 19:15:47 2020

@author: edoardottt
"""

import sys
import socket
import threading


def server_loop(local_host, local_port, remote_host, remote_port, receive_first):

    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

    try:
        server.bind((local_port, local_host))
    except:
        print("[!!] Failed  to listen on {}:{}".format(local_host, local_port))
        print("[!!] Check for other listening sockets or correct permissions.")
        sys.exit(0)

    print("[*] Listening on {}:{}".format(local_host, local_port))

    server.listen(5)

    while True:
        client_socket, addr = server.accept()

        # print out the local connection information
        print("[==>] Received incoming connection from {}:{}".format(addr[0], addr[1]))

        # start a thread to talk to the remote host
        proxy_thread = threading.Thread(
            target=proxy_handler,
            args=(client_socket, remote_host, remote_port, receive_first),
        )

        proxy_thread.start()


# this is a pretty hex dumping function directly taken from
# the comments here:
# https://code.activestate.com/recipes/142812-hex-dumper/
def hexdump(src, length=16):
    result = []
    digits = 4 if isinstance(src, unicode) else 2

    for i in xrange(0, len(src), length):
        s = src[i : i + length]
        hexa = b" ".join(["{}0*X".format(digits, ord(x)) for x in s])
        text = b"".join([x if 0x20 <= ord(x) < 0x7F else b"." for x in s])
        result.append(b"{}04X {}-*s {}s".format(i, length * (digits + 1), hexa, text))

    print(b"\n".join(result))


def receive_from(connection):

    buffer = ""

    # We set a 2 second timeout; depending on your
    # target, this may  need to be adjusted
    connection.settimeout(2)

    try:
        # keep reading into the buffer until
        # there's no more data
        # or we time out
        while True:
            data = connection.recv(4096)
            if not data:
                break

            buffer += data

    except:
        pass

    return buffer


# modify any requests defined for the remote host
def request_handler(buffer):
    # perform packet modifications
    return buffer


# modify any responses destined for the local host
def response_handler(buffer):
    # perform packet modifications
    return buffer


def proxy_handler(client_socket, remote_host, remote_port, receive_first):

    # connect to the remote host
    remote_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    remote_socket.connect((remote_host, remote_port))

    # receive data from the remote end if necessary
    if receive_first:

        remote_buffer = receive_from(remote_socket)
        hexdump(remote_buffer)

        # send it to our response handler
        remote_buffer = response_handler(remote_buffer)

        # if we have data to send to out client, send it
        if len(remote_buffer):
            print("[<==] Sending {} bytes to localhost".format(len(remote_buffer)))
            client_socket.send(remote_buffer)

    # now lets loop  and read from local,
    # send to remote, send to local,
    # rinse, wash, repeat.
    while True:

        # read from local host
        local_buffer = receive_from(client_socket)

        if len(local_buffer):
            print("[==>] Received {} bytes from localhost".format(len(local_buffer)))
            hexdump(local_buffer)

            # send it to our request handler
            local_buffer = request_handler(local_buffer)

            # send off the data to the remote host
            remote_socket.send(local_buffer)
            print("[==>] Sent to remote.")

        # receive back the response
        remote_buffer = receive_from(remote_socket)

        if len(remote_buffer):

            print("[<==] Received {} bytes from remote".format(len(remote_buffer)))
            hexdump(remote_buffer)

            # send to our response handler
            remote_buffer = response_handler(remote_buffer)

            # send the response to the local socket
            client_socket.send(remote_buffer)

            print("[<==] Sent to localhost.")

        # if no more data on either side, close the connections
        if not len(local_buffer) or not len(remote_buffer):
            client_socket.close()
            remote_socket.close()
            print("[*] No more data. Closing connections.")

            break


def main():
    # no fancy command-line parsing here
    if len(sys.argv[1:]) != 5:
        print(
            "Usage: python3 proxy.py [localhost] [localport] [remotehost] [remoteport] [receive_first]"
        )
        print("Example: python3 proxy.py 127.0.0.1 9000 10.12.132.1 9000 True")

    # setup local listening parameters
    local_host = sys.argv[1]
    local_port = int(sys.argv[2])

    # setup remote target
    remote_host = sys.argv[3]
    remote_port = int(sys.argv[4])

    # this tells our proxy to connect and receive data
    # before sending to the remote host
    receive_first = sys.argv[5]

    if "True" in receive_first:
        receive_first = True
    else:
        receive_first = False

    # now spin up our listening socket
    server_loop(local_host, local_port, remote_host, remote_port, receive_first)


main()