#!/usr/bin/python2.7
"""Dynamic DNS script. Expects URLs from routers in the form
https://info.colgarra.priv.at/dyndns/dyndns.py?username=<username>&password=<pass>&hostname=<domain>&myip=<ipaddr>
"""

import re
import cgi
import pwd
from subprocess import call
import ipaddr


# Configuration
PASSWORD = 'hygCithOrs5'
ZONE = '.dyn.colgarra.priv.at'
DEBUG = False


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


fields = cgi.FieldStorage()

# the following fields are supported by most dyndns providers
# if a parameter is not provided, the .getvalue method returns None
username = fields.getvalue('username')
password = fields.getvalue('password')
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')


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

class AuthError(DynDnsError):
	returncode = 'badauth'

class UsernameMissing(AuthError):
	pass

class UsernameInvalid(AuthError):
	pass

class PasswordMissing(AuthError):
	pass

class PasswordWrong(AuthError):
	pass

class HostnameError(DynDnsError):
	returncode = 'notfqdn'

class HostnameMissing(HostnameError):
	pass

class PasswordWrong(HostnameError):
	pass

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

class IpMissing(IpError):
	pass

class IpInvalid(IpError):
	pass

try:
	# check username
	if username is None:
		raise UsernameMissing()
	try:
		user_info = pwd.getpwnam(username)
	except KeyError:
		raise UsernameInvalid()
	if user_info.pw_uid < 1000:
		raise UsernameInvalid()

	# check password
	if password is None:
		raise PasswordMissing()
	if password != PASSWORD:
		raise PasswordWrong()

	# 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()
	if hostname.endswith(ZONE):
		hostname = hostname[:-len(ZONE)]

	# check IP address
	if myip is None:
		raise IpMissing()
	try:
		ip = ipaddr.IPAddress(myip) # throws an exception if the IP address is not valid
	except ValueError:
		raise IpInvalid()
	if isinstance(ip, ipaddr.IPv4Address):
		iptype = 'A'
	elif isinstance(ip, ipaddr.IPv6Address):
		iptype = 'AAAA'
	else:
		raise IpInvalid() # should never happen

	# access granted
	print "Content-Type: text/html"
	print
	call(['sudo', '/usr/local/bin/nsupdate_dyndns', hostname, myip, iptype])
	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"
	print
	print error.returncode