Python 2 non blocking asyncore port forwarding TCP proxy

s.py

#!/usr/bin/env python
#
# s.py - a simple port forwarder using asyncore
#
# by Yusuke Shinyama, *public domain*
# http://www.unixuser.org/~euske/python/s.py
#

import sys, socket, asyncore


##  Server
##
class Server(asyncore.dispatcher):
  
  def __init__(self, port, destaddr, bindaddr="127.0.0.1"):
    asyncore.dispatcher.__init__(self)
    self.destaddr = destaddr
    self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
    self.set_reuse_addr()
    self.bind((bindaddr, port))
    self.listen(1)
    self.session = 0
    print >>sys.stderr, "Listening: %s:%d" % (bindaddr, port)
    return
  
  def handle_accept(self):
    (conn, (addr,port)) = self.accept()
    print >>sys.stderr, "Accepted:", addr
    Proxy(conn, self.session).connect_remote(self.destaddr)
    self.session += 1
    return


##  Proxy
##
class Proxy(asyncore.dispatcher):
  
  def __init__(self, sock, session):
    self.session = session
    self.sendbuffer = ""
    self.client = None
    self.disp("BEGIN")
    asyncore.dispatcher.__init__(self, sock)
    return

  # overridable methods
  def local2remote(self, s):
    print ">>> %r" % s
    return s
  def remote2local(self, s):
    print "<<< %r" % s
    return s

  def connect_remote(self, addr):
    assert not self.client, "already connected"
    self.addr = addr
    self.disp("(connecting to %s:%d)" % self.addr)
    self.client = Client(self)
    self.client.connect(addr)
    return

  def disconnect_remote(self):
    assert self.client, "not connected"
    self.client.close()
    self.client = None
    return
  
  def disp(self, s):
    print >>sys.stderr, "SESSION %s:" % self.session, s
    return
  
  def remote_connected(self):
    self.disp("(connected to remote %s:%d)" % self.addr)
    return
  
  def remote_closed(self):
    self.disp("(closed by remote %s:%d)" % self.addr)
    self.client = None
    if not self.sendbuffer:
      self.handle_close()
    return

  def remote_error(self):
    self.disp("(error by remote %s:%d)" % self.addr)
    return
  
  def remote_read(self, data):
    if data:
      data = self.remote2local(data)
      if data:
        self.sendbuffer += data
    return
  
  def handle_read(self):
    data = self.recv(8192)
    if data:
      data = self.local2remote(data)
      if data and self.client:
        self.client.remote_write(data)
    return
  
  def writable(self):
    return 0 < len(self.sendbuffer)
  
  def handle_write(self):
    n = self.send(self.sendbuffer)
    self.sendbuffer = self.sendbuffer[n:]
    if not self.sendbuffer and not self.client:
      self.handle_close()
    return
  
  def handle_close(self):
    if self.client:
      self.disp("(closed by local)")
      self.disconnect_remote()
    self.close()
    self.disp("END")
    return


##  Client
##
class Client(asyncore.dispatcher):

  def __init__(self, proxy):
    self.proxy = proxy
    self.sendbuffer = ""
    asyncore.dispatcher.__init__(self)
    self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
    return

  def handle_connect(self):
    self.proxy.remote_connected()
    return

  def handle_close(self):
    self.proxy.remote_closed()
    self.close()
    return

  def handle_error(self):
    self.proxy.remote_error()
    return

  def handle_read(self):
    self.proxy.remote_read(self.recv(8192))
    return

  def remote_write(self, data):
    self.sendbuffer += data
    return

  def writable(self):
    return 0 < len(self.sendbuffer)

  def handle_write(self):
    n = self.send(self.sendbuffer)
    self.sendbuffer = self.sendbuffer[n:]
    return


# main
if __name__=='__main__':
  if len(sys.argv) < 4:
    print >>sys.stderr, "usage: s.py local_port remote_host remote_port"
    sys.exit(2)
  Server(int(sys.argv[1]), (sys.argv[2], int(sys.argv[3])))
  asyncore.loop()

Saving it because finding an actually working Python TCP proxy was quite hard ...