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


def checkerror(msg):
  if len(msg['error']) > 0:
    if not msg.has_key('quiet'):
      for error in msg['error']:
        print "Error: %s" % error
      print "Use -h for help"
    return 1
  else:
    return 0


def get_ipaddress():
  # Connect to the dns server to determine which ip address
  # this host connects from
  import urllib
  remote = opener = urllib.FancyURLopener({})
  try:
    f = opener.open("http://www.wahlberg.se/~fredrik/ip.php")
    ip = f.read().strip()
    return ip
  except:
    msg['error'].append("Could not determine ip address automatically,\nuse -i switch to enter manually")



def getparams(msg):
  from optparse import OptionParser
  import sys
  # Define option parameters
  usage = "usage: %prog [OPTIONS]"
  parser = OptionParser(usage)
  parser.add_option("-c", "--config", 
                    type="string",
                    help="Alternate config file")
  parser.add_option("--delete", 
                    action="store_true",
                    help="Remove the host from the zone")
  parser.add_option("-d", "--domain", 
                    type="string",
                    help="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="Hostname of local machine")
  parser.add_option("-p", "--password", 
                    type="string",
                    help="TSIG key")
  parser.add_option("-q", "--quiet", 
                    action="store_true",
                    help="Quit mode")
  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.ipaddress:
    msg['ipaddress'] = options.ipaddress
  else:
    ip = get_ipaddress()
    if ip:
      msg['ipaddress'] = ip

  if options.delete:
    msg['delete'] = options.delete
  if options.domain:
    msg['domain'] = options.domain
  if options.keyname:
    msg['keyname'] = options.keyname
  if options.name:
    msg['hostname'] = options.name
  if options.password:
    msg['keysecret'] = options.password
  if options.quiet:
    msg['quiet'] = options.quiet
  if options.ttl:
    msg['ttl'] = options.ttl
    
 
  return msg



def readcfg(msg):
  import os.path
  # Reads the config file for default info
  if not msg.has_key('cfgfile'):
    if os.path.exists(os.path.expanduser("~/.dnsupdaterc")):
      cfgfile = open(os.path.expanduser("~/.dnsupdaterc"), 'r')
    else:
      return msg
  else:
    if not os.path.exists(msg['cfgfile']):
      msg['error'].append("No such file: %s" % msg['cfgfile'])
      return msg
    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
  # The update function connects to the dns server
  
  # 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'])

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

  # doit, servername
  try: 
    response = dns.query.tcp(update, '217.78.32.198')
  except:
    msg['error'].append("An error has occurred, check your keyname and password.")
    return 
  
  # Verify response
  if not msg.has_key('quiet'):
    if response.rcode() == 0:
      if msg.has_key("delete"):
        print "Host '%s.%s' has been deleted" % (msg['hostname'], msg['domain'])
      else:
        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



def validate(msg):
  import re
  import string
  # Verify all required data is present and sanity check incoming data
  req_vals = ['domain', 'hostname', 'ipaddress', 'keyname', 'keysecret', 'ttl']
  for value in req_vals:
    if not msg.has_key(value):
      msg['error'].append('Missing "%s" parameter' % value)
  
  #global hostname, ipaddress, ttl
  if msg.has_key('hostname') and msg.has_key('domain'):
    msg['hostname'] = string.replace(msg['hostname'], "." + msg['domain'], '')
  
  if msg.has_key('ipaddress'):
    if not re.search('^[12]?[0-9]?[0-9](\.[12]?[0-9]?[0-9]){3}$', msg['ipaddress']):
      msg['error'].append("Invalid ip address '%s'" % msg['ipaddress'])

  return msg  


def verify_ip(msg):
  import dns.resolver
  try:
    ans = dns.resolver.query(msg['hostname'] + "." + msg['domain'], 'A')
    for res in ans:
      ip = res.to_text()
  except:
    ip = ""
  
  if ip == msg['ipaddress'] and not msg.has_key('delete'):
    msg['error'].append("Nameserver already up to date")
  elif ip == "" and msg.has_key('delete'):
    msg['error'].append("Nameserver does not recognise the hostname")
  
  return msg

if __name__=="__main__":
  import sys
  msg = {}
  msg['error'] = []

  getparams(msg)
  validate(msg)
  verify_ip(msg)
  err = checkerror(msg)
  if err == 0:
    update(msg)
    checkerror(msg)
    if err == 0:
      sys.exit(0)

  sys.exit(1)