dnsupdate/dnsupdate.py

#! /usr/bin/env python
# dnsupdate.py
# A utility to update dynamic dns-records using a TSIG key.


def checkerror(msg, show=""):
  # Determine if there are any errors reported
  if len(msg['error']) > 0:
    if show and not msg.has_key('quiet'):
      for error in msg['error']:
        print "Error: %s" % error
      print "Use -h option for help"
    return 1
  else:
    return 0



def get_ipaddress():
  # Connect to a remote server to determine which IP address
  # this host connects from
  import re
  import urllib
  opener = urllib.FancyURLopener({})
  try:
    f = opener.open(msg['ipurl'])
    page = f.read()
    res = re.search('[12]?[0-9]?[0-9](\.[12]?[0-9]?[0-9]){3}', page)
    ip = res.group()
    return ip
  except:
    msg['error'].append("Could not determine IP address automatically,\n       use -i switch to enter manually")



def getparams(msg):
  # Read command line parameters and input values 
  # OptionParser is part of Python 2.3 and called optik if installed under
  # Python 2.x
  try:
    from optparse import OptionParser
  except:
    from optik import OptionParser
  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 name server")
  parser.add_option("-d", "--domain", 
                    type="string",
                    help="Domain to update")
  parser.add_option("--force", 
                    action="store_true",
                    help="Force the action, do not check if update is necessary")
  parser.add_option("-i", "--ipaddress", 
                    type="string",
                    help="Public IP address for this host [auto detected]")
  parser.add_option("-k", "--keyname", 
                    type="string",
                    help="Name of the TSIG key")
  parser.add_option("-n", "--hostname", 
                    type="string",
                    help="Hostname to publish")
  parser.add_option("--nameserver", 
                    type="string",
                    help="IP address to the name server")
  parser.add_option("-q", "--quiet", 
                    action="store_true",
                    help="Quit mode")
  parser.add_option("-s", "--keysecret", 
                    type="string",
                    help="TSIG key")
  parser.add_option("--showcfg", 
                    action="store_true",
                    help="Display config file data")
  parser.add_option("-u", "--ipurl", 
                    type="string",
                    help="URL to the server which detects the public IP address")
  parser.add_option("-t", "--ttl", 
                    type="int",
                    help="TTL in seconds")
  parser.add_option("-v", "--verbose", 
                    action="store_true",
                    help="Print progress information")
                    
  (options, args) = parser.parse_args()
  
  if options.config:
    msg['cfgfile'] = options.config

  msg = readcfg(msg)

  # Populate the basic params
  base_params = ['delete',
                 'domain',
                 'force',
                 'hostname',
                 'keyname',
                 'keysecret',
                 'nameserver', 
                 'quiet',
                 'showcfg',
                 'ttl',
                 'ipurl']

  for param in base_params:
    if eval('options.' + param):
      msg[param] = eval('options.' + param)

  # These parameters needs special handling
  if options.ipaddress:
    msg['ipaddress'] = options.ipaddress
  else:
    ip = get_ipaddress()
    if ip:
      msg['ipaddress'] = ip

  if options.verbose and msg.has_key('quiet'):
    del msg['quiet']

  return msg



def readcfg(msg, show=""):
  # Read the config file for pre configured values
  import os.path
  if not msg.has_key('cfgfile'):
    if os.path.exists(os.path.expanduser("~/.dnsupdaterc")):
      cfgfile = open(os.path.expanduser("~/.dnsupdaterc"), 'r')
    elif os.path.exists("/etc/dnsupdaterc"):
      cfgfile = open("/etc/dnsupdaterc", 'r')
    else:
      return msg
  else:
    if not os.path.exists(msg['cfgfile']):
      if show:
        checkerror(msg, show="errors")
      msg['error'].append("No such file; '%s'" % msg['cfgfile'])
      return msg
    cfgfile = open(msg['cfgfile'], 'r')

  if show:
    print "Current configuration values:"
    
  for line in cfgfile.readlines():
    line = line.strip()
    if line.find("#", 0, 1) == 0 or not line:
      continue
    (key, value) = line.split('\t', 1)
    if show:
      print "%s: %s" % (key.strip(), value.strip())
    if not value.strip().lower() == "false":
      msg[key.strip()] = value.strip()
  
  cfgfile.close()
  return msg



def update(msg):
  # The update function connects to the dns server
  import dns.query
  import dns.tsigkeyring
  import dns.update
  import binascii # for exception handling in keyring generation
  import socket # for exception handling in server communictions

  # The name of the key and the secret 
  try: 
    keyring = dns.tsigkeyring.from_text({
      msg['keyname']: msg['keysecret']
    })
  except binascii.Error:
    msg['error'].append("Your password is incorrect.")
    return 

  # 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, msg['nameserver'])
  except socket.error:
    msg['error'].append("An error occurred in the server communication.")
    return 
  except dns.tsig.BadSignature:
    msg['error'].append("Your password could not be verified.\n       Check your password and keyname.")
    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:
      msg['error'].append("Update denied, server responded %s" % dns.rcode.to_text(response.rcode()))



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', 'nameserver', '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):
  # Check if the ip address exists and if it needs an update
  import dns.resolver
  ip = ""
  host = msg['hostname'] + "." + msg['domain']
  try:
    res = dns.resolver.Resolver()
    res.nameservers = [msg['nameserver']]
    ans = res.query(host)
    for res in ans:
      ip = res.to_text()
  except dns.exception.Timeout:
    msg['error'].append("Connection timeout, could not connect to name server.\n")
  except dns.resolver.NXDOMAIN:
    pass

  if ip == msg['ipaddress'] and not msg.has_key('delete'):
    msg['error'].append("Name server already up to date")
  elif ip == "" and msg.has_key('delete'):
    msg['error'].append("Name server does not recognise the hostname")
  
  return msg

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

  getparams(msg)

  if msg.has_key('showcfg'):
    readcfg(msg, show="config")
    sys.exit(0)
    
  validate(msg)
  
  err = checkerror(msg)
  if err == 0:
    if not msg.has_key('force'):
      verify_ip(msg)

  err = checkerror(msg)
  if err == 0:
    update(msg)
    err = checkerror(msg)
    if err == 0:
      syslog.openlog("dnsupdate")
      for error in msg['error']:
        syslog.syslog(syslog.LOG_ERR, error)
      syslog.closelog()
      sys.exit(0)

  err = checkerror(msg, show="errors")
  syslog.openlog("dnsupdate")
  for error in msg['error']:
    syslog.syslog(syslog.LOG_ERR, error)
  syslog.closelog()
  sys.exit(1)