TCP server-to-server tunnel

tunnel_s2s.py

import select
import socket
import sys

tcp_ip = '0.0.0.0'
tcp_port1 = int(sys.argv[1])
tcp_port2 = int(sys.argv[2])

s1 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s1.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s1.bind((tcp_ip, tcp_port1))
s1.listen(1)
s2 = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s2.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s2.bind((tcp_ip, tcp_port2))
s2.listen(1)

conns = []
conn_reciprocates = {}
while True:
    inputs = [s1, s2] + conns
    outputs = []
    readable, writable, exceptional = select.select(inputs, outputs, inputs, 1.0)
    if s1 in readable and s2 in readable:
        connA, addrA = s1.accept()
        connB, addrB = s2.accept()
        print 'Connecting %s with %s' % (connA.getpeername(), connB.getpeername())
        conns.append(connA)
        conns.append(connB)
        conn_reciprocates[connA] = connB
        conn_reciprocates[connB] = connA

    for conn in readable:
        if conn in (s1, s2):
            continue
        rconn = conn_reciprocates[conn]
        data = conn.recv(8192)
        if len(data) < 1:
            exceptional.append(conn)
            continue
        print 'Forwarded %d bytes from %s to %s' % (len(data), conn.getpeername(), rconn.getpeername())
        rconn.send(data)

    rexceptional = []
    for conn in exceptional:
        assert conn not in (s1, s2)
        if conn in rexceptional: # processed already
            continue
        rconn = conn_reciprocates[conn]
        #print 'Disconnected %s from %s' % (conn.getpeername(), rconn.getpeername())
        rconn.close()
        conns.remove(conn)
        conns.remove(rconn)
        del conn_reciprocates[conn]
        del conn_reciprocates[rconn]
        rexceptional.append(rconn)