IP Address change notifier

ip_checker.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

__author__ = "Ryan McGuire ([email protected])"
__date__   = "Wed Sep  1 22:05:31 2010"

#Check the current external IP address
#If it has changed, email me the new one (via cron)
#Update the dynamic DNS provider

#This is used on my router, where the real external IP address
#is assigned directly to my NIC. This script won't work on a NAT'd box.

import socket
import fcntl
import struct
import sys
import urllib2

last_ip_file = "/storage/var/lib/ip_checker/last_ip.txt"
dyndns_update = "http://USERNAME:[email protected]/nic/update?hostname=YOUR_DYNAMIC_HOSTNAME"

def get_ip_address(ifname):
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    return socket.inet_ntoa(fcntl.ioctl(
            s.fileno(),
            0x8915,  # SIOCGIFADDR
            struct.pack('256s', ifname[:15])
    )[20:24])

def check_ip_change():
    current_ip = get_ip_address("red")
    with open(last_ip_file) as f:
        last_ip = f.read()
    if current_ip != last_ip:
        #The IP changed
        with open(last_ip_file, "w") as f:
            f.write(current_ip)
        #Email the new IP (via cron)
        print("Sentry external IP address changed: {ip}".format(ip=current_ip))
        #Update the dyndns record
        urllib2.urlopen(dyndns_update).read()
        return 1
    return 0

if __name__ == '__main__':
    sys.exit(check_ip_change())