Python: Listen on two ports

Question

import socket
backlog = 1 #Number of queues

sk_1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sk_2 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

local = {"port":1433}
internet = {"port":9999}

sk_1.bind (('', internet["port"]))
sk_1.listen(backlog)

sk_2.bind (('', local["port"]))
sk_2.listen(backlog)

Basically, I have this code. I am trying to listen on two ports: 1433 and 9999. But, this doesn't seems to work.

How can I listen on two ports, within the same python script??

Answer 1

The code so far is fine, as far as it goes (except that a backlog of 1 seems unduly strict), the problem of course comes when you try to accept a connection on either listening socket, since accept is normally a blocking call (and "polling" by trying to accept with short timeouts on either socket alternately will burn machine cycles to no good purpose).

select to the rescue!-) select.select (or on the better OSs select.poll or even select.epoll or select.kqueue... but, good old select.select works everywhere!-) will let you know which socket is ready and when, so you can accept appropriately. Along these lines, asyncore and asynchat provide a bit more organization (and third-party framework twisted, of course, adds a lot of such "asynchronous" functionality).

Alternatively, you can devote separate threads to servicing the two listening sockets, but in this case, if the different sockets' functionality needs to affect the same shared data structures, coordination (locking &c) may become ticklish. I would certainly recommend trying the async approach first -- it's actually simpler, as well as offering potential for substantially better performance!-)

Answer 2

The fancy-pants way to do this if you want to use Python std-lib would be to use SocketServer with the ThreadingMixin -- although the 'select' suggestion is probably the more efficient.

Even though we only define one ThreadedTCPRequestHandler you can easily repurpose it such that each listener has it's own unique handler and it should be fairly trivial to wrap the server/thread creation into a single method if thats the kind of thing you like.

#!/usr/bin/python

import threading
import time
import SocketServer

class ThreadedTCPRequestHandler(SocketServer.BaseRequestHandler):

    def handle(self):
        self.data = self.request.recv(1024).strip()
        print "%s wrote: " % self.client_address[0]
        print self.data
        self.request.send(self.data.upper())

class ThreadedTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
    pass

if __name__ == "__main__":

    HOST = ''
    PORT_A = 9999
    PORT_B = 9876

    server_A = ThreadedTCPServer((HOST, PORT_A), ThreadedTCPRequestHandler)
    server_B = ThreadedTCPServer((HOST, PORT_B), ThreadedTCPRequestHandler)

    server_A_thread = threading.Thread(target=server_A.serve_forever)
    server_B_thread = threading.Thread(target=server_B.serve_forever)

    server_A_thread.setDaemon(True)
    server_B_thread.setDaemon(True)

    server_A_thread.start()
    server_B_thread.start()

    while 1:
        time.sleep(1)