#! /usr/bin/env python
# dnsupdate.py
# Updates a dynamic dns-record using a TSIG key.

def get_ipaddress():
  # Connects to the dns server to determine which ip address
  # this host connects from
  import urllib
  remote = opener = urllib.FancyURLopener({})
  f = opener.open("http://www.wahlberg.se/~fredrik/ip.php")
  ip = f.read().strip()
  return ip

def main(msg):
  from optparse import OptionParser
  import sys
  # Define option parameters
  usage = "usage: %prog [-n] hostname [-i] ip adress [OPTIONS]"
  parser = OptionParser(usage)
  parser.add_option("-c", "--config", 
                    type="string",
                    help="File containing configuration data")
  parser.add_option("-d", "--domain", 
                    type="string",
                    help="Name of the domain to update")
  parser.add_option("-i", "--ipaddress", 
                    type="string",
                    help="IP-address of the host [auto detected]")
  parser.add_option("-k", "--keyname", 
                    type="string",
                    help="Name of the TSIG key")
  parser.add_option("-n", "--name", 
                    type="string",
                    help="Name of the host to update")
  parser.add_option("-p", "--password", 
                    type="string",
                    help="The TSIG key")
  parser.add_option("-t", "--ttl", 
                    type="int",
                    help="TTL in seconds")
  (options, args) = parser.parse_args()
  
  if options.config:
    msg['cfgfile'] = options.config

  msg = readcfg(msg)
  
  if options.domain:
    msg['domain'] = options.domain
  if options.ipaddress:
    msg['ipaddress'] = options.ipaddress
  else:
    msg['ipaddress'] = get_ipaddress()
  if options.keyname:
    msg['keyname'] = options.keyname
  if options.name:
    msg['hostname'] = options.name
  if options.password:
    msg['keysecret'] = options.password
  if options.ttl:
    msg['ttl'] = options.ttl
  
  #print msg
  update(msg)


def readcfg(msg):
  # Reads the config file for default info
  cfgfile = open(msg['cfgfile'], 'r')

  for line in cfgfile.readlines():
    (key, value) = line.split('\t', 1)
    msg[key] = value.strip()
  
  cfgfile.close()
  return msg

def update(msg):
  import dns.query
  import dns.tsigkeyring
  import dns.update
  import re
  import string
  # The update function connects to the dns server
  
  # Sanity check incoming data
  #global hostname, ipaddress, ttl
  msg['hostname'] = string.replace(msg['hostname'], "." + msg['domain'], '')
  if not re.search('^[12]?[0-9]?[0-9](\.[12]?[0-9]?[0-9]){3}$', msg['ipaddress']):
    print "Invalid ip address '%s'" % msg['ipaddress']
    return
  

  # The name of the key and the secret
  keyring = dns.tsigkeyring.from_text({
      msg['keyname']: msg['keysecret']
  })

  # dns.update.Update(name of domain, keyring, keyname)
  update = dns.update.Update(msg['domain'], keyring=keyring, keyname=msg['keyname'])

  # update.replace(hostname, ttl, record-type, new ip)
  update.replace(msg['hostname'], msg['ttl'], 'a', msg['ipaddress'])

  # doit, servername
  response = dns.query.tcp(update, 'nic.wahlberg.se')
  
  # Verify response
  if response.rcode() == 0:
    print "Host '%s.%s' has been added with ip address %s" % (msg['hostname'], msg['domain'], msg['ipaddress'])
  else:
    print "An error has occurred, the server returned:\n%s" % response

if __name__=="__main__":
  import os.path
  msg = {}
  msg['cfgfile'] = os.path.expanduser("~/.dnsupdaterc")
  main(msg)