#!/usr/bin/python
"""Dynamic DNS script. Expects URLs from routers in the form
http://dyndns.colgarra.priv.at/nic/update?hostname=<domain>&myip=<ipaddr>
"""
import os
import re
import cgi
from subprocess import call
import ipaddr


# Configuration
DEBUG = False


# Just for debugging:
if DEBUG:
	import cgitb
	cgitb.enable()


# Base class for our exceptions
class DynDnsError(Exception):
	pass

class HostnameError(DynDnsError):
	returncode = 'notfqdn'

class HostnameMissing(HostnameError):
	pass

class PasswordWrong(HostnameError):
	pass

class MyipError(DynDnsError):
	returncode = 'badip' # not documented at dyn.com

class MyipMissing(MyipError):
	pass

class MyipInvalid(MyipError):
	pass

class OfflineInvalid(DynDnsError):
	returncode = 'badparam' # not documented at dyn.com

class NsupdateError(DynDnsError):
	returncode = 'nohost'


fields = cgi.FieldStorage()

# the following fields are supported by most dyndns providers
# if a parameter is not provided, the .getvalue method returns None
hostname = fields.getvalue('hostname')
myip     = fields.getvalue('myip')
wildcard = fields.getvalue('wildcard')
mx       = fields.getvalue('mx')
backmx   = fields.getvalue('backmx')
offline  = fields.getvalue('offline')
system   = fields.getvalue('system')
url      = fields.getvalue('url')


try:
	# check hostname
	if hostname is None:
		raise HostnameMissing()
	if re.match(r'[-0-9a-z]+(\.[-0-9a-z]+)*$', hostname) is None:
		raise HostnameInvalid()

	# strip zone
	hostname = hostname.strip()

	# check offline
	if offline is None or offline.lower() == 'no':
		offline = False
	elif offline.lower() == 'yes':
		offline = True
	else:
		raise OfflineInvalid()

	# check IP address
	if not offline:
		if myip is None:
			# try HTTP_X_FORWARDED_FOR
			myip = os.environ.get('HTTP_X_FORWARDED_FOR')
			if not myip: # empty string if not present
				# try REMOTE_ADDR
				myip = os.environ.get('REMOTE_ADDR')
				if not myip: # empty string if not present
					raise MyipMissing()
	if not myip is None:
		try:
			ipaddr.IPAddress(myip) # throws an exception if the IP address is not valid
		except ValueError:
			raise MyipInvalid()

	# update bind
	call_params = ['sudo', 'tdyndns_update']
	if offline:
		call_params.append('--delete')
	if myip is not None:
		call_params.extend(['--ip', myip])
	call_params.append(hostname)
	retcode = call(call_params)
	if retcode != 0:
		raise NsupdateError()

	# return success
	print "Content-Type: text/html"
	print
	print "good"
	# Note: we should return 'nochg' in case the IP has not changed, however we don't know yet.


except DynDnsError as error:
	print "Content-Type: text/html"
	print "Status: 200 OK"
	print
	print error.returncode