Python は、TCP/IP プロトコルでのポート転送とリダイレクトの例を実装します。

#!/usr/bin/env python
import sys, socket, time, threading

loglock = threading.Lock()
def log(msg):
  loglock.acquire()
  try:
    print '[%s]: \n%s\n' % (time.ctime(), msg.strip())
    sys.stdout.flush()
  finally:
    loglock.release()

class PipeThread(threading.Thread):
  def __init__(self, source, target):
    threading.Thread.__init__(self)
    self.source = source
    self.target = target

  def run(self):
    while True:
      try:
        data = self.source.recv(1024)
        log(data)
        if not data: break
        self.target.send(data)
      except:
        break
    log('PipeThread done')

class Forwarding(threading.Thread):
  def __init__(self, port, targethost, targetport):
    threading.Thread.__init__(self)
    self.targethost = targethost
    self.targetport = targetport
    self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    self.sock.bind(('0.0.0.0', port))
    self.sock.listen(10)
  def run(self):
    while True:
      client_fd, client_addr = self.sock.accept()
      target_fd = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      target_fd.connect((self.targethost, self.targetport))
      log('new connect')
      # two direct pipe
      PipeThread(target_fd, client_fd).start()
      PipeThread(client_fd, target_fd).start()


if __name__ == '__main__':
  print 'Starting'
  import sys
  try:
    port = int(sys.argv[1])
    targethost = sys.argv[2]
    try: targetport = int(sys.argv[3])
    except IndexError: targetport = port
  except (ValueError, IndexError):
    print 'Usage: %s port targethost [targetport]' % sys.argv[0]
    sys.exit(1)

  #sys.stdout = open('forwaring.log', 'w')
  Forwarding(port, targethost, targetport).start()