#!/usr/bin/python

import socket
import select
import sys
import os

def tcpbug(listenaddr, destaddr, outputfd):
    listen = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    listen.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    listen.bind(listenaddr)
    listen.listen(1)
    
    client, addr = listen.accept()

    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.connect(destaddr)

    cwbuf = swbuf = outbuf = ''
    
    while client or server or outbuf:
	readset = []
	if client:
	    readset.append(client)
	if server:
	    readset.append(server)
	    
	writeset = []
	if cwbuf and client:
	    writeset.append(client)
	if swbuf and server:
	    writeset.append(server)
	if outbuf:
	    writeset.append(outputfd)

	readset, writeset, e = select.select(readset, writeset, [])

	if client in readset:
	    data = client.recv(2000)
	    if data:
		swbuf = swbuf + data
		outbuf = outbuf + 'C%d\n%s' % (len(data), data)
	    else:
		client = None

	if server in readset:
	    data = server.recv(2000)
	    if data:
		cwbuf = cwbuf + data
		outbuf = outbuf + 'S%d\n%s' % (len(data), data)
	    else:
		server = None
    
	if client in writeset:
	    n = client.send(cwbuf)
	    cwbuf = cwbuf[n:]

	if server in writeset:
	    n = server.send(swbuf)
	    swbuf = swbuf[n:]

	if outputfd in writeset:
	    n = os.write(outputfd, outbuf)
	    outbuf = outbuf[n:]
	    
	if client and not cwbuf and not server:
	    client.close()
	    client = None

	if server and not swbuf and not client:
	    server.close()
	    server = None

def main():
    try:
	lport = int(sys.argv[1])
	dhost = sys.argv[2]
	dport = int(sys.argv[3])
    except (IndexError, ValueError):
	sys.stderr.write('Usage: %s listenport desthost destport\n'
			 % sys.argv[0])
	exit(1)

    tcpbug(('', lport), (dhost, dport), 1)

if __name__ == '__main__':
    main()