Using proxy and multiple sockets in python

Question

I'm writing a proxy with tcp connection that listens to multiple ports from a client and forward it to a server.

The problem is that the software hangs on the sock.accept.

Maybe I'm doing a messy logic here, but I need a client that connects to a PC, and that PC connects to another device. So I wrote that small proxy, and I get INVALID ARGUMENT ERROR in socket.accept()

import select
import socket
import threading

class Proxy(object):

    def __init__(self, ip, ports):
        self._ip = ip
        self._sockets = []
        self._proxy = {}

        for port in ports:
            self._proxy[port] = self.add_socket(port)

    def add_socket(self, port=None):
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        if port:
            # sock.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
            sock.bind(('0.0.0.0',port))
        self._sockets.append(sock)
        return sock

    def get_client(self, src_sock, src_addr):
        src_ip, src_port = src_addr
        _, dst_port = src_sock.getsockname()

        if src_ip == self._ip:
            # got packet from device
            dst_addr = ("10.8.8.210", dst_port)
        else:
            # got packet from client
            dst_addr = self._ip, dst_port
            print(">", src_port, dst_addr)
        dst_sock = self._proxy[src_port]
        return dst_sock, dst_addr

    def run(self):
        while True:
            read_list, _, _ = select.select(self._sockets, [], [])

            if read_list:
                for sock in read_list:
                    try:

                        conn, addr = sock.accept()
                        data  = conn.recvfrom(16*2024)
                        # print("got data from {} {}".format(sock, addr))
                        dst_sock, dst_addr = self.get_client(sock, addr)
                       # print("forwarding data from {} to {}".format(addr, dst_addr, len(data)))
                        dst_sock.sendto(data, dst_addr)
                    except:
                        raise # pass # print("no recipient for data")
        for s in self._sockets:
             s.close()

ports = [30001,30002,30003, 30070, 30071,30072,30075]
p = Proxy("192.168.2.10", ports)                    
p.run()

You can only accept from a socket in listening state. And sendto and recvfrom are normally used for UDP (type=socket.SOCK_DGRAM) sockets. Before building a multi port proxy, just try to send one packet from one side to the other one... — Serge Ballesta
– Serge Ballesta, Commented Dec 21, 2018 at 15:10
Thanks so much I got it :), but I have another issues with ports that are not defined — andre
– andre, Commented Dec 21, 2018 at 15:11
Your question is unclear. You do not say if you want UDP or TCP, and you do not explain the logic behind your code. I am sorry because I have tried to understand what you are trying to setup, but I could not. — Serge Ballesta
– Serge Ballesta, Commented Dec 21, 2018 at 15:17

Dan D. · Accepted Answer · 2018-12-21 14:53:28Z

1

You have to call listen on the socket before accept:

adding sock.listen(1) to add_socket after bind

 sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 sock.bind(('0.0.0.0', port))
 sock.listen(1)
 self._sockets.append(sock)

then allows you to call accept without the error. You may want to set the listen backlog to a greater number.

answered Dec 21, 2018 at 14:53

Dan D.

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4 Comments

andre Over a year ago

With that code, I need to bind to EVERY port that my src client is using.. how can I fix that ?

andre Over a year ago

Keyerror 51083 not found. line 49 dst_sock = self._proxy[src_port]

andre Over a year ago

I hope you tell me the solution for this problem

andre Over a year ago

Whenever I add the required port, I needed to add 10000 ports to make it running, and the ports are changing

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