#! /usr/bin/env python

import os, sys
from socket import *
from fcntl import ioctl
from select import select
import getopt, struct

MAGIC_WORD = "EknathVenkataramani"

TUNSETIFF = 0x400454ca
IFF_TUN   = 0x0001
IFF_TAP   = 0x0002

TUNMODE = IFF_TUN
MODE = 0
DEBUG = 0

def usage(status=0):
    print "Usage: tunproxy [-s port|-c targetip:port] [-e]"
    sys.exit(status)

opts = getopt.getopt(sys.argv[1:],"s:c:ehd")

for opt,optarg in opts[0]:
	if opt == "-h":
		usage()
	elif opt == "-d":
		DEBUG += 1
	elif opt == "-s":
		'''Server Mode> So get pinged by client and then send data'''
		MODE = 1
		PORT = int(optarg)
	elif opt == "-c":
		'''CLient Mode. So ping the server and receive the data'''
		MODE = 2
		IP,PORT = optarg.split(":")
		PORT = int(PORT)
		peer = (IP,PORT)
	elif opt == "-e":
		TUNMODE = IFF_TAP

if MODE == 0:
    usage(1)


f = os.open("/dev/net/tun", os.O_RDWR)
'''tun is the interface which processes IP packets'''

ifs = ioctl(f, TUNSETIFF, struct.pack("16sH", "eknathtun%d", TUNMODE))
'''Create the TUN interface'''

ifname = ifs[:16].strip("\x00")
'''Get the interface name'''
print "Allocated interface %s!" % ifname

s = socket(AF_INET, SOCK_DGRAM)
'''Open socket for communication'''
try:
	if MODE == 1:'''Used while receiving data (ping packet)'''

		s.bind(("", PORT))
		while 1:
			word,peer = s.recvfrom(1500)
			'''_1500_ is the buffer size, indicating the maxmum size of data to be received at once
			_word_ is a string representing the data received and _peer_ is the address of the socket sending the data'''
			if word == MAGIC_WORD:
				break
			print "Bad magic word for %s:%i" % peer
		s.sendto(MAGIC_WORD, peer)
		'''peer is the name of the destination '''

	else:'''Used while sending data (ping packet)'''
		s.sendto(MAGIC_WORD, peer)
		'''peer is the destination to send the data. In this case this comes from the command line arg and is a tuple containing the (destinationIP,port#)'''
		word,peer = s.recvfrom(1500)
		'''_1500_ is the buffer size, indicating the maxmum size of data to be received at once'''
		'''_word_ is a string representing the data received and _peer_ is the address of the socket sending the data'''
		if word != MAGIC_WORD:
			print "Bad magic word for %s:%i" % peer
			sys.exit(2)
	print "Connection with %s:%i established" % peer

	while 1:
		r = select([f,s],[],[])[0][0]
		'''wait until _f_ or _s_ is ready for reading '''
		if r == f:
			if DEBUG: os.write(1,">")
			s.sendto(os.read(f,1500),peer)
		else:
			buf,p = s.recvfrom(1500)
			if p != peer:
				print "Got packet from %s:%i instead of %s:%i" % (p+peer)
				continue
			if DEBUG: os.write(1,"<")
			os.write(f, buf)
except KeyboardInterrupt:
    print "Exitting....!"