tcp_proxy.py

import sys
import socket
import threading

HEX_FILTER = ''.join(
    [(len(repr(chr(i))) == 3) and chr(i) or '.' for i in range(256)]
)

def hexdump(src, length=16, show=True):
    if isinstance(src, bytes):
        src = src.decode()

    results = list()
    for i in range(0, len(src), length):
        word = str(src[i:i+length])

        printable = word.translate(HEX_FILTER)
        hexa = ''.join([f'{ord(c):02x}' for c in word])
        hexwidth = length*3
        results.append(f'{i:04x} {hexa:<{hexwidth}} {printable}')
    if show:
        for line in results:
            print(line)
    else:
        return results
    
def receive_from(connection):
    buffer = b''
    connection.settimeout(5)
    try:
        while True:
            data = connection.recv(4096)
            if not data:
                break
            buffer += data
    except Exception as e:
        pass
    return buffer

def request_handler(buffer):
    # perform packet modifications
    return buffer

def response_handler(buffer):
    # perform packet mods
    return buffer

def proxy_handler(client_socket, remote_host, remote_port, receive_first):
    remote_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    remote_socket.connect((remote_host, int(remote_port)))

    if receive_first:
        remote_buffer = receive_from(remote_socket)
        hexdump(remote_buffer)

    remote_buffer = response_handler(remote_buffer)
    if len(remote_buffer):
        line = f"[==>] Received {len(remote_buffer)}"
        client_socket.send(remote_buffer)
    
    while True:
        local_buffer = receive_from(client_socket)
        if len(local_buffer):
            line = f"[==>] Received {len(local_buffer)} bytes from local host"
            print(line)
            hexdump(local_buffer)

            local_buffer = request_handler(local_buffer)
            remote_socket.send(local_buffer)
            print("[==> Sent to remote]")

        remote_buffer = receive_from(remote_socket)
        if len(remote_buffer):
            print(f"[==>] Received {len(remote_buffer)} from remote") 
            hexdump(remote_buffer)

            remote_buffer = response_handler(remote_buffer)
            client_socket.send(remote_buffer)
            print("[==>] Sent to host.")

        if not len(local_buffer) or not len(remote_buffer):
            client_socket.close()
            remote_socket.close()
            print("[*] no more data")
            break

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_host, int(local_port)))
    except Exception as e:
        print(f'problem on bind: {e}')

        print(f'!! Failed to listen on {local_host}:{local_port}')
        print(f'!! Check for other listening sockets or correct permissions')
        sys.exit()
    print(f'[*] Listening on {local_host}:{local_port}')
    server.listen(5)
    while True:
        client_socket, addr = server.accept()
        # print out local conneciton information
        line = f"> Received Incoming connect from {addr[0]}:{addr[1]}"
        print(line)
        #start a thread to talk to remote host
        proxy_thread = threading.Thread(
            target=proxy_handler,
            args=(client_socket,remote_host,remote_port,receive_first)
        )
        proxy_thread.start()

def main():
    if len(sys.argv[1:]) != 5:
        print('''
                Usage: ./tcp_proxy.py [local host] [localport] [remotehost] [remoteport] [receive_first]
                Example: ./tcp_proxy.py 127.0.0.1 9000 1.12.132.1 9000 True
              ''')
        sys.exit()
    local_host = sys.argv[1]
    local_port = sys.argv[2]
    remote_host = sys.argv[3]
    remote_port = sys.argv[4]
    receive_first = sys.argv[5]

    if "true" in receive_first.lower():
        receive_first = True
    else:
        receive_first = False
    
    server_loop(local_host, local_port, remote_host, remote_port, receive_first)

if __name__ == "__main__":
    main()