notify_listener.py

import datetime
import logging
import globals

import socket

import dns.flags
import dns.message
import dns.rdataclass
import dns.rdatatype
import dns.name

from typing import cast


def listen_for_notify():
	address = globals.config.listen_ip
	port    = globals.config.listen_port

	if not isinstance(port,int):
		message = "port value must be an int. check config.json. exiting."
		logging.fatal(message)
		raise Exception(message)

	s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
	s.bind((address, port))
	message = f"listener created at {datetime.datetime.now().strftime(globals.timestamp_format)}."
	logging.info(message)
	while True:
		(wire, address) = s.recvfrom(512)
		notify = dns.message.from_wire(wire)

		error_happened = True
		try:
			soa = notify.find_rrset(notify.answer, notify.question[0].name, dns.rdataclass.IN, dns.rdatatype.SOA)

			# Do something with the SOA RR here
			error_happened = False
		except KeyError:
			# No SOA RR in the answer section.
			pass

		server_ip = address[0]
		domain_name  = soa.name.to_text(True)
		serial = soa[0].serial
		message = f"notify received at {datetime.datetime.now().strftime(globals.timestamp_format)} local time from server {server_ip} for domain {domain_name} with serial number {serial}."
		print(message)
		logging.info(message)

		response = dns.message.make_response(notify)  # type: dns.message.Message
		response.flags |= dns.flags.AA
		wire = response.to_wire(cast(dns.name.Name, response))
		s.sendto(wire, address)

		if error_happened:
			message = f"an unknown communications error happened while listening for notify."
			logging.error(message)
			continue

		if server_ip not in globals.config.notify_servers:
			message = f"notify received from '{server_ip}', but it is not in our list of 'notify_servers'. skipping."
			logging.warning(message)
			continue

		if domain_name not in globals.config.domains_to_manage:
			message = f"notify received for domain '{domain_name}', but it is not in our list of 'domains_to_manage'. skipping."
			logging.warning(message)
			continue

		# we are listening for this domain
		globals.wq.put((domain_name,serial))