server.py

#!/usr/bin/env python
#
# Proof of Concept: UDP Hole Punching
# Two client connect to a server and get redirected to each other.
#
# This is the rendezvous server.
#
# Koen Bollen <meneer koenbollen nl>
# 2010 GPL
#

import socket
import struct
import sys

def addr2bytes( addr ):
    """Convert an address pair to a hash."""
    host, port = addr
    try:
        host = socket.gethostbyname( host )
    except (socket.gaierror, socket.error):
        raise ValueError, "invalid host"
    try:
        port = int(port)
    except ValueError:
        raise ValueError, "invalid port"
    bytes  = socket.inet_aton( host )
    bytes += struct.pack( "H", port )
    return bytes

def main():
    port = 4653
    try:
        port = int(sys.argv[1])
    except (IndexError, ValueError):
        pass

    sockfd = socket.socket( socket.AF_INET, socket.SOCK_DGRAM )
    sockfd.bind( ("", port) )
    print "listening on *:%d (udp)" % port

    poolqueue = {}
    while True:
        data, addr = sockfd.recvfrom(32)
        print "connection from %s:%d" % addr

        pool = data.strip()
        sockfd.sendto( "ok "+pool, addr )
        data, addr = sockfd.recvfrom(2)
        if data != "ok":
            continue

        print "request received for pool:", pool

        try:
            a, b = poolqueue[pool], addr
            sockfd.sendto( addr2bytes(a), b )
            sockfd.sendto( addr2bytes(b), a )
            print "linked", pool
            del poolqueue[pool]
        except KeyError:
            poolqueue[pool] = addr

if __name__ == "__main__":
    main()

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