#/usr/bin/python
import os,sys
import nfqueue
from scapy.all import *
import socket


class MyQueue:
	def __init__(self):
		self.q = nfqueue.queue()

	def process(self, i, payload):
		data = payload.get_data()
		p = IP(data)

		#SYN-ACK
		if not p[TCP].flags == 18:
			return 0

		print "Crafting Fake ACK"
		fake = IP(src=p[IP].dst, dst=p[IP].src)/TCP(sport=p[TCP].dport, dport=p[TCP].sport, flags="A", seq=p[TCP].ack+1, ack=p[TCP].seq+2)
	
		print "Sending..."
		send(fake)

		#Accept the final SYN-ACK
		print "Accepting real ACK"
		payload.set_verdict(nfqueue.NF_ACCEPT)

	def main(self):
		self.q.open()
		self.q.bind(socket.AF_INET)
		self.q.set_callback(self.process)
		self.q.create_queue(0)
		try:
			self.q.try_run()
		except KeyboardInterrupt:
			print "Exiting..."
			self.q.unbind(socket.AF_INET)
			self.q.close()
			sys.exit(1)



MyQueue().main()