#!/usr/bin/python
#
# dyndns.py
#
# a simple ssh based dyndns updater for bind zone files
#
# Copyright (C) 2013 Christian Pointner <equinox@spreadspace.org>
#
# This file is part of dyndns.py.
#
# dyndns.py is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# any later version.
#
# dyndns.py is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with dyndns.py. If not, see <http://www.gnu.org/licenses/>.
#

from easyzone import easyzone
import subprocess

import sys
import os
import re

#
domain = '{{ dyndns.domain }}.'
zonefile = '{{ dyndns.zone_file }}'
rndc = '/usr/sbin/rndc'
###
# add this to the authorized key file of a system user
# the user needs to be a member of the bind group and must
# have write permissions to the zone file

# no-agent-forwarding,no-port-forwarding,no-pty,no-X11-forwarding,no-user-rc,command="/usr/local/bin/dyndns.py <allowed names>" ssh-rsa ...
###

if ('SSH_CLIENT' in os.environ) and ('SSH_ORIGINAL_COMMAND' in os.environ):
    sshclient = os.environ['SSH_CLIENT']
    sshcmd = os.environ['SSH_ORIGINAL_COMMAND']
else:
    sys.stdout.write("Error: not an SSH connection\n")
    sys.exit(1)

name = sshcmd.split()[0]
if name not in set(sys.argv[1:]):
    sys.stdout.write("Error: you are not allowed to update '%s'\n" % name)
    sys.exit(1)

ip = sshclient.split()[0]
if not re.match(r'^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$', ip):
    sys.stdout.write("Error: not a valid IPv4 address\n")
    sys.exit(1)

name = name + '.' + domain
zone = easyzone.zone_from_file(domain, zonefile)
zone.add_name(name)
records = zone.names[name].records('A', create=True, ttl=60)
for item in records.get_items():
    if item == ip:
        sys.stdout.write("Ok: nothing changed\n")
        sys.exit(0)

    records.delete(item)

records.add(ip)
zone.save(autoserial=True)

cmd = [rndc, 'reload', domain]
p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
output = ''
for line in p.stdout.readlines():
    output = output + line

r = p.wait()
if r != 0:
    sys.stdout.write("Error: rndc returned %d\n\n%s" % (r, output))
else:
    sys.stdout.write("Ok: " + output)