test_zeroconf.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-


""" Unit tests for zeroconf.py """

import copy
import logging
import socket
import struct
import time
import unittest
from threading import Event

import zeroconf as r
from zeroconf import (
    DNSHinfo,
    DNSText,
    ServiceBrowser,
    ServiceInfo,
    ServiceStateChange,
    Zeroconf,
    ZeroconfServiceTypes,
)

log = logging.getLogger('zeroconf')
original_logging_level = [None]


def setup_module():
    original_logging_level[0] = log.level
    log.setLevel(logging.DEBUG)


def teardown_module():
    log.setLevel(original_logging_level[0])


class TestDunder(unittest.TestCase):

    def test_dns_text_repr(self):
        # There was an issue on Python 3 that prevented DNSText's repr
        # from working when the text was longer than 10 bytes
        text = DNSText('irrelevant', None, 0, 0, b'12345678901')
        repr(text)

        text = DNSText('irrelevant', None, 0, 0, b'123')
        repr(text)

    def test_dns_hinfo_repr_eq(self):
        hinfo = DNSHinfo('irrelevant', r._TYPE_HINFO, 0, 0, 'cpu', 'os')
        assert hinfo == hinfo
        repr(hinfo)

    def test_dns_pointer_repr(self):
        pointer = r.DNSPointer(
            'irrelevant', r._TYPE_PTR, r._CLASS_IN, r._DNS_TTL, '123')
        repr(pointer)

    def test_dns_address_repr(self):
        address = r.DNSAddress('irrelevant', r._TYPE_SOA, r._CLASS_IN, 1, b'a')
        repr(address)

    def test_dns_question_repr(self):
        question = r.DNSQuestion(
            'irrelevant', r._TYPE_SRV, r._CLASS_IN | r._CLASS_UNIQUE)
        repr(question)
        assert not question != question

    def test_dns_service_repr(self):
        service = r.DNSService(
            'irrelevant', r._TYPE_SRV, r._CLASS_IN, r._DNS_TTL, 0, 0, 80, b'a')
        repr(service)

    def test_dns_record_abc(self):
        record = r.DNSRecord('irrelevant', r._TYPE_SRV, r._CLASS_IN, r._DNS_TTL)
        self.assertRaises(r.AbstractMethodException, record.__eq__, record)
        self.assertRaises(r.AbstractMethodException, record.write, None)

    def test_service_info_dunder(self):
        type_ = "_test-srvc-type._tcp.local."
        name = "xxxyyy"
        registration_name = "%s.%s" % (name, type_)
        info = ServiceInfo(
            type_, registration_name,
            socket.inet_aton("10.0.1.2"), 80, 0, 0,
            None, "ash-2.local.")

        assert not info != info
        repr(info)

    def test_dns_outgoing_repr(self):
        dns_outgoing = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        repr(dns_outgoing)


class PacketGeneration(unittest.TestCase):

    def test_parse_own_packet_simple(self):
        generated = r.DNSOutgoing(0)
        r.DNSIncoming(generated.packet())

    def test_parse_own_packet_simple_unicast(self):
        generated = r.DNSOutgoing(0, 0)
        r.DNSIncoming(generated.packet())

    def test_parse_own_packet_flags(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        r.DNSIncoming(generated.packet())

    def test_parse_own_packet_question(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        generated.add_question(r.DNSQuestion("testname.local.", r._TYPE_SRV,
                                             r._CLASS_IN))
        r.DNSIncoming(generated.packet())

    def test_match_question(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        question = r.DNSQuestion("testname.local.", r._TYPE_SRV, r._CLASS_IN)
        generated.add_question(question)
        parsed = r.DNSIncoming(generated.packet())
        self.assertEqual(len(generated.questions), 1)
        self.assertEqual(len(generated.questions), len(parsed.questions))
        self.assertEqual(question, parsed.questions[0])

    def test_suppress_answer(self):
        query_generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        question = r.DNSQuestion("testname.local.", r._TYPE_SRV, r._CLASS_IN)
        query_generated.add_question(question)
        answer1 = r.DNSService(
            "testname1.local.", r._TYPE_SRV, r._CLASS_IN, r._DNS_TTL, 0, 0, 80, "foo.local.")
        staleanswer2 = r.DNSService(
            "testname2.local.", r._TYPE_SRV, r._CLASS_IN, r._DNS_TTL/2, 0, 0, 80, "foo.local.")
        answer2 = r.DNSService(
            "testname2.local.", r._TYPE_SRV, r._CLASS_IN, r._DNS_TTL, 0, 0, 80, "foo.local.")
        query_generated.add_answer_at_time(answer1, 0)
        query_generated.add_answer_at_time(staleanswer2, 0)
        query = r.DNSIncoming(query_generated.packet())

        # Should be suppressed
        response = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        response.add_answer(query, answer1)
        assert len(response.answers) == 0

        # Should not be suppressed, TTL in query is too short
        response.add_answer(query, answer2)
        assert len(response.answers) == 1

        # Should not be suppressed, name is different
        tmp = copy.copy(answer1)
        tmp.name = "testname3.local."
        response.add_answer(query, tmp)
        assert len(response.answers) == 2

        # Should not be suppressed, type is different
        tmp = copy.copy(answer1)
        tmp.type = r._TYPE_A
        response.add_answer(query, tmp)
        assert len(response.answers) == 3

        # Should not be suppressed, class is different
        tmp = copy.copy(answer1)
        tmp.class_ = r._CLASS_NONE
        response.add_answer(query, tmp)
        assert len(response.answers) == 4

        # ::TODO:: could add additional tests for DNSAddress, DNSHinfo, DNSPointer, DNSText, DNSService

    def test_dns_hinfo(self):
        generated = r.DNSOutgoing(0)
        generated.add_additional_answer(
            DNSHinfo('irrelevant', r._TYPE_HINFO, 0, 0, 'cpu', 'os'))
        parsed = r.DNSIncoming(generated.packet())
        self.assertEqual(parsed.answers[0].cpu, u'cpu')
        self.assertEqual(parsed.answers[0].os, u'os')

        generated = r.DNSOutgoing(0)
        generated.add_additional_answer(
            DNSHinfo('irrelevant', r._TYPE_HINFO, 0, 0, 'cpu', 'x' * 257))
        self.assertRaises(r.NamePartTooLongException, generated.packet)


class PacketForm(unittest.TestCase):

    def test_transaction_id(self):
        """ID must be zero in a DNS-SD packet"""
        generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        bytes = generated.packet()
        id = bytes[0] << 8 | bytes[1]
        self.assertEqual(id, 0)

    def test_query_header_bits(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_QUERY)
        bytes = generated.packet()
        flags = bytes[2] << 8 | bytes[3]
        self.assertEqual(flags, 0x0)

    def test_response_header_bits(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        bytes = generated.packet()
        flags = bytes[2] << 8 | bytes[3]
        self.assertEqual(flags, 0x8000)

    def test_numbers(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        bytes = generated.packet()
        (numQuestions, numAnswers, numAuthorities,
         numAdditionals) = struct.unpack('!4H', bytes[4:12])
        self.assertEqual(numQuestions, 0)
        self.assertEqual(numAnswers, 0)
        self.assertEqual(numAuthorities, 0)
        self.assertEqual(numAdditionals, 0)

    def test_numbers_questions(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        question = r.DNSQuestion("testname.local.", r._TYPE_SRV, r._CLASS_IN)
        for i in range(10):
            generated.add_question(question)
        bytes = generated.packet()
        (numQuestions, numAnswers, numAuthorities,
         numAdditionals) = struct.unpack('!4H', bytes[4:12])
        self.assertEqual(numQuestions, 10)
        self.assertEqual(numAnswers, 0)
        self.assertEqual(numAuthorities, 0)
        self.assertEqual(numAdditionals, 0)


class Names(unittest.TestCase):

    def test_long_name(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        question = r.DNSQuestion("this.is.a.very.long.name.with.lots.of.parts.in.it.local.",
                                 r._TYPE_SRV, r._CLASS_IN)
        generated.add_question(question)
        r.DNSIncoming(generated.packet())

    def test_exceedingly_long_name(self):
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        name = "%slocal." % ("part." * 1000)
        question = r.DNSQuestion(name, r._TYPE_SRV, r._CLASS_IN)
        generated.add_question(question)
        r.DNSIncoming(generated.packet())

    def test_exceedingly_long_name_part(self):
        name = "%s.local." % ("a" * 1000)
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        question = r.DNSQuestion(name, r._TYPE_SRV, r._CLASS_IN)
        generated.add_question(question)
        self.assertRaises(r.NamePartTooLongException, generated.packet)

    def test_same_name(self):
        name = "paired.local."
        generated = r.DNSOutgoing(r._FLAGS_QR_RESPONSE)
        question = r.DNSQuestion(name, r._TYPE_SRV, r._CLASS_IN)
        generated.add_question(question)
        generated.add_question(question)
        r.DNSIncoming(generated.packet())

    def test_lots_of_names(self):

        # instantiate a zeroconf instance
        zc = Zeroconf(interfaces=['127.0.0.1'])

        # create a bunch of servers
        type_ = "_my-service._tcp.local."
        name = 'a wonderful service'
        server_count = 300
        self.generate_many_hosts(zc, type_, name, server_count)

        # verify that name changing works
        self.verify_name_change(zc, type_, name, server_count)

        # we are going to monkey patch the zeroconf send to check packet sizes
        old_send = zc.send

        # needs to be a list so that we can modify it in our phony send
        longest_packet = [0, None]

        def send(out, addr=r._MDNS_ADDR, port=r._MDNS_PORT):
            """Sends an outgoing packet."""
            packet = out.packet()
            if longest_packet[0] < len(packet):
                longest_packet[0] = len(packet)
                longest_packet[1] = out
            old_send(out, addr=addr, port=port)

        # monkey patch the zeroconf send
        zc.send = send

        # dummy service callback
        def on_service_state_change(zeroconf, service_type, state_change, name):
            pass

        # start a browser
        browser = ServiceBrowser(zc, type_, [on_service_state_change])

        # wait until the browse request packet has maxed out in size
        sleep_count = 0
        while sleep_count < 100 and \
                longest_packet[0] < r._MAX_MSG_ABSOLUTE - 100:
            sleep_count += 1
            time.sleep(0.1)

        browser.cancel()
        time.sleep(0.5)

        import zeroconf
        zeroconf.log.debug('sleep_count %d, sized %d',
                           sleep_count, longest_packet[0])

        # now the browser has sent at least one request, verify the size
        assert longest_packet[0] <= r._MAX_MSG_ABSOLUTE
        assert longest_packet[0] >= r._MAX_MSG_ABSOLUTE - 100

        # mock zeroconf's logger warning() and debug()
        from unittest.mock import patch
        patch_warn = patch('zeroconf.log.warning')
        patch_debug = patch('zeroconf.log.debug')
        mocked_log_warn = patch_warn.start()
        mocked_log_debug = patch_debug.start()

        # now that we have a long packet in our possession, let's verify the
        # exception handling.
        out = longest_packet[1]
        out.data.append(b'\0' * 1000)

        # mock the zeroconf logger and check for the correct logging backoff
        call_counts = mocked_log_warn.call_count, mocked_log_debug.call_count
        # try to send an oversized packet
        zc.send(out)
        assert mocked_log_warn.call_count == call_counts[0] + 1
        assert mocked_log_debug.call_count == call_counts[0]
        zc.send(out)
        assert mocked_log_warn.call_count == call_counts[0] + 1
        assert mocked_log_debug.call_count == call_counts[0] + 1

        # force a receive of an oversized packet
        packet = out.packet()
        s = zc._respond_sockets[0]

        # mock the zeroconf logger and check for the correct logging backoff
        call_counts = mocked_log_warn.call_count, mocked_log_debug.call_count
        # force receive on oversized packet
        s.sendto(packet, 0, (r._MDNS_ADDR, r._MDNS_PORT))
        s.sendto(packet, 0, (r._MDNS_ADDR, r._MDNS_PORT))
        time.sleep(2.0)
        zeroconf.log.debug('warn %d debug %d was %s',
                           mocked_log_warn.call_count,
                           mocked_log_debug.call_count,
                           call_counts)
        assert mocked_log_debug.call_count > call_counts[0]

        # close our zeroconf which will close the sockets
        zc.close()

        # pop the big chunk off the end of the data and send on a closed socket
        out.data.pop()
        zc._GLOBAL_DONE = False

        # mock the zeroconf logger and check for the correct logging backoff
        call_counts = mocked_log_warn.call_count, mocked_log_debug.call_count
        # send on a closed socket (force a socket error)
        zc.send(out)
        zeroconf.log.debug('warn %d debug %d was %s',
                           mocked_log_warn.call_count,
                           mocked_log_debug.call_count,
                           call_counts)
        assert mocked_log_warn.call_count > call_counts[0]
        assert mocked_log_debug.call_count > call_counts[0]
        zc.send(out)
        zeroconf.log.debug('warn %d debug %d was %s',
                           mocked_log_warn.call_count,
                           mocked_log_debug.call_count,
                           call_counts)
        assert mocked_log_debug.call_count > call_counts[0] + 2

        mocked_log_warn.stop()
        mocked_log_debug.stop()

    def verify_name_change(self, zc, type_, name, number_hosts):
        desc = {'path': '/~paulsm/'}
        info_service = ServiceInfo(
            type_, '%s.%s' % (name, type_), socket.inet_aton("10.0.1.2"),
            80, 0, 0, desc, "ash-2.local.")

        # verify name conflict
        self.assertRaises(
            r.NonUniqueNameException,
            zc.register_service, info_service)

        zc.register_service(info_service, allow_name_change=True)
        assert info_service.name.split('.')[0] == '%s-%d' % (
            name, number_hosts + 1)

    def generate_many_hosts(self, zc, type_, name, number_hosts):
        records_per_server = 2
        block_size = 25
        number_hosts = int(((number_hosts - 1) / block_size + 1)) * block_size
        for i in range(1, number_hosts + 1):
            next_name = name if i == 1 else '%s-%d' % (name, i)
            self.generate_host(zc, next_name, type_)
            if i % block_size == 0:
                sleep_count = 0
                while sleep_count < 40 and \
                        i * records_per_server > len(
                            zc.cache.entries_with_name(type_)):
                    sleep_count += 1
                    time.sleep(0.05)

    @staticmethod
    def generate_host(zc, host_name, type_):
        name = '.'.join((host_name, type_))
        out = r.DNSOutgoing(r._FLAGS_QR_RESPONSE | r._FLAGS_AA)
        out.add_answer_at_time(
            r.DNSPointer(type_, r._TYPE_PTR, r._CLASS_IN,
                         r._DNS_TTL, name), 0)
        out.add_answer_at_time(
            r.DNSService(type_, r._TYPE_SRV, r._CLASS_IN,
                         r._DNS_TTL, 0, 0, 80,
                         name), 0)
        zc.send(out)


class Framework(unittest.TestCase):

    def test_launch_and_close(self):
        rv = r.Zeroconf(interfaces=r.InterfaceChoice.All)
        rv.close()
        rv = r.Zeroconf(interfaces=r.InterfaceChoice.Default)
        rv.close()


class Exceptions(unittest.TestCase):

    browser = None

    @classmethod
    def setUpClass(cls):
        cls.browser = Zeroconf(interfaces=['127.0.0.1'])

    @classmethod
    def tearDownClass(cls):
        cls.browser.close()
        cls.browser = None

    def test_bad_service_info_name(self):
        self.assertRaises(
            r.BadTypeInNameException,
            self.browser.get_service_info, "type", "type_not")

    def test_bad_service_names(self):
        bad_names_to_try = (
            '',
            'local',
            '_tcp.local.',
            '_udp.local.',
            '._udp.local.',
            '_@._tcp.local.',
            '_A@._tcp.local.',
            '_x--x._tcp.local.',
            '_-x._udp.local.',
            '_x-._tcp.local.',
            '_22._udp.local.',
            '_2-2._tcp.local.',
            '_1234567890-abcde._udp.local.',
            '\x00._x._udp.local.',
        )
        for name in bad_names_to_try:
            self.assertRaises(
                r.BadTypeInNameException,
                self.browser.get_service_info, name, 'x.' + name)

    def test_good_instance_names(self):
        good_names_to_try = (
            '.._x._tcp.local.',
            'x.sub._http._tcp.local.',
            '6d86f882b90facee9170ad3439d72a4d6ee9f511._zget._http._tcp.local.'
        )
        for name in good_names_to_try:
            r.service_type_name(name)

    def test_bad_types(self):
        bad_names_to_try = (
            '._x._tcp.local.',
            'a' * 64 + '._sub._http._tcp.local.',
            'a' * 62 + u'â._sub._http._tcp.local.',
        )
        for name in bad_names_to_try:
            self.assertRaises(
                r.BadTypeInNameException, r.service_type_name, name)

    def test_bad_sub_types(self):
        bad_names_to_try = (
            '_sub._http._tcp.local.',
            '._sub._http._tcp.local.',
            '\x7f._sub._http._tcp.local.',
            '\x1f._sub._http._tcp.local.',
        )
        for name in bad_names_to_try:
            self.assertRaises(
                r.BadTypeInNameException, r.service_type_name, name)

    def test_good_service_names(self):
        good_names_to_try = (
            '_x._tcp.local.',
            '_x._udp.local.',
            '_12345-67890-abc._udp.local.',
            'x._sub._http._tcp.local.',
            'a' * 63 + '._sub._http._tcp.local.',
            'a' * 61 + u'â._sub._http._tcp.local.',
        )
        for name in good_names_to_try:
            r.service_type_name(name)


class TestDnsIncoming(unittest.TestCase):

    def test_incoming_exception_handling(self):
        generated = r.DNSOutgoing(0)
        packet = generated.packet()
        packet = packet[:8] + b'deadbeef' + packet[8:]
        parsed = r.DNSIncoming(packet)
        parsed = r.DNSIncoming(packet)
        assert parsed.valid is False

    def test_incoming_unknown_type(self):
        generated = r.DNSOutgoing(0)
        answer = r.DNSAddress('a', r._TYPE_SOA, r._CLASS_IN, 1, b'a')
        generated.add_additional_answer(answer)
        packet = generated.packet()
        parsed = r.DNSIncoming(packet)
        assert len(parsed.answers) == 0
        assert parsed.is_query() != parsed.is_response()

    def test_incoming_ipv6(self):
        # ::TODO:: could use a test here if we add IPV6 record handling
        # ie: _TYPE_AAAA
        pass


class TestDNSCache(unittest.TestCase):

    def test_order(self):
        record1 = r.DNSAddress('a', r._TYPE_SOA, r._CLASS_IN, 1, b'a')
        record2 = r.DNSAddress('a', r._TYPE_SOA, r._CLASS_IN, 1, b'b')
        cache = r.DNSCache()
        cache.add(record1)
        cache.add(record2)
        entry = r.DNSEntry('a', r._TYPE_SOA, r._CLASS_IN)
        cached_record = cache.get(entry)
        self.assertEqual(cached_record, record2)


class ServiceTypesQuery(unittest.TestCase):

    def test_integration_with_listener(self):

        type_ = "_test-srvc-type._tcp.local."
        name = "xxxyyy"
        registration_name = "%s.%s" % (name, type_)

        zeroconf_registrar = Zeroconf(interfaces=['127.0.0.1'])
        desc = {'path': '/~paulsm/'}
        info = ServiceInfo(
            type_, registration_name,
            socket.inet_aton("10.0.1.2"), 80, 0, 0,
            desc, "ash-2.local.")
        zeroconf_registrar.register_service(info)

        try:
            service_types = ZeroconfServiceTypes.find(
                interfaces=['127.0.0.1'], timeout=0.5)
            assert type_ in service_types
            service_types = ZeroconfServiceTypes.find(
                zc=zeroconf_registrar, timeout=0.5)
            assert type_ in service_types

        finally:
            zeroconf_registrar.close()

    def test_integration_with_subtype_and_listener(self):
        subtype_ = "_subtype._sub"
        type_ = "_type._tcp.local."
        name = "xxxyyy"
        # Note: discovery returns only DNS-SD type not subtype
        discovery_type = "%s.%s" % (subtype_, type_)
        registration_name = "%s.%s" % (name, type_)

        zeroconf_registrar = Zeroconf(interfaces=['127.0.0.1'])
        desc = {'path': '/~paulsm/'}
        info = ServiceInfo(
            discovery_type, registration_name,
            socket.inet_aton("10.0.1.2"), 80, 0, 0,
            desc, "ash-2.local.")
        zeroconf_registrar.register_service(info)

        try:
            service_types = ZeroconfServiceTypes.find(
                interfaces=['127.0.0.1'], timeout=0.5)
            assert discovery_type in service_types
            service_types = ZeroconfServiceTypes.find(
                zc=zeroconf_registrar, timeout=0.5)
            assert discovery_type in service_types

        finally:
            zeroconf_registrar.close()


class ListenerTest(unittest.TestCase):

    def test_integration_with_listener_class(self):

        service_added = Event()
        service_removed = Event()

        subtype_name = "My special Subtype"
        type_ = "_http._tcp.local."
        subtype = subtype_name + "._sub." + type_
        name = "xxxyyy"
        registration_name = "%s.%s" % (name, type_)

        class MyListener:
            def add_service(self, zeroconf, type, name):
                zeroconf.get_service_info(type, name)
                service_added.set()

            def remove_service(self, zeroconf, type, name):
                service_removed.set()

        listener = MyListener()
        zeroconf_browser = Zeroconf(interfaces=['127.0.0.1'])
        zeroconf_browser.add_service_listener(subtype, listener)

        properties = dict(
            prop_none=None,
            prop_string=b'a_prop',
            prop_float=1.0,
            prop_blank=b'a blanked string',
            prop_true=1,
            prop_false=0,
        )

        zeroconf_registrar = Zeroconf(interfaces=['127.0.0.1'])
        desc = {'path': '/~paulsm/'}
        desc.update(properties)
        info_service = ServiceInfo(
            subtype, registration_name,
            socket.inet_aton("10.0.1.2"), 80, 0, 0,
            desc, "ash-2.local.")
        zeroconf_registrar.register_service(info_service)

        try:
            service_added.wait(1)
            assert service_added.is_set()

            # short pause to allow multicast timers to expire
            time.sleep(2)

            # clear the answer cache to force query
            for record in zeroconf_browser.cache.entries():
                zeroconf_browser.cache.remove(record)

            # get service info without answer cache
            info = zeroconf_browser.get_service_info(type_, registration_name)

            assert info.properties[b'prop_none'] is False
            assert info.properties[b'prop_string'] == properties['prop_string']
            assert info.properties[b'prop_float'] is False
            assert info.properties[b'prop_blank'] == properties['prop_blank']
            assert info.properties[b'prop_true'] is True
            assert info.properties[b'prop_false'] is False

            info = zeroconf_browser.get_service_info(subtype, registration_name)
            assert info.properties[b'prop_none'] is False

            zeroconf_registrar.unregister_service(info_service)
            service_removed.wait(1)
            assert service_removed.is_set()
        finally:
            zeroconf_registrar.close()
            zeroconf_browser.remove_service_listener(listener)
            zeroconf_browser.close()


def test_integration():
    service_added = Event()
    service_removed = Event()
    unexpected_ttl = Event()
    got_query = Event()

    type_ = "_http._tcp.local."
    registration_name = "xxxyyy.%s" % type_

    def on_service_state_change(zeroconf, service_type, state_change, name):
        if name == registration_name:
            if state_change is ServiceStateChange.Added:
                service_added.set()
            elif state_change is ServiceStateChange.Removed:
                service_removed.set()

    zeroconf_browser = Zeroconf(interfaces=['127.0.0.1'])

    # we are going to monkey patch the zeroconf send to check packet sizes
    old_send = zeroconf_browser.send

    time_offset = 0

    def current_time_millis():
        """Current system time in milliseconds"""
        return time.time() * 1000 + time_offset * 1000

    expected_ttl = r._DNS_TTL

    # needs to be a list so that we can modify it in our phony send
    nbr_queries = [0, None]

    def send(out, addr=r._MDNS_ADDR, port=r._MDNS_PORT):
        """Sends an outgoing packet."""
        pout = r.DNSIncoming(out.packet())

        for answer in pout.answers:
            nbr_queries[0] += 1
            if not answer.ttl > expected_ttl / 2:
                unexpected_ttl.set()

        got_query.set()
        old_send(out, addr=addr, port=port)

    # monkey patch the zeroconf send
    zeroconf_browser.send = send

    # monkey patch the zeroconf current_time_millis
    r.current_time_millis = current_time_millis

    service_added = Event()
    service_removed = Event()

    browser = ServiceBrowser(zeroconf_browser, type_, [on_service_state_change])

    zeroconf_registrar = Zeroconf(interfaces=['127.0.0.1'])
    desc = {'path': '/~paulsm/'}
    info = ServiceInfo(
        type_, registration_name,
        socket.inet_aton("10.0.1.2"), 80, 0, 0,
        desc, "ash-2.local.")
    zeroconf_registrar.register_service(info)

    try:
        service_added.wait(1)
        assert service_added.is_set()

        sleep_count = 0
        while nbr_queries[0] < 50:
            time_offset += expected_ttl / 4
            zeroconf_browser.notify_all()
            sleep_count += 1
            got_query.wait(1)
            got_query.clear()
        assert not unexpected_ttl.is_set()

        # Don't remove service, allow close() to cleanup

    finally:
        zeroconf_registrar.close()
        browser.cancel()
        zeroconf_browser.close()