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()