synapse/tests/http/federation/test_srv_resolver.py

#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
from typing import Dict, Generator, List, Tuple, cast
from unittest.mock import Mock

from twisted.internet import defer
from twisted.internet.defer import Deferred
from twisted.internet.error import ConnectError
from twisted.names import dns, error

from synapse.http.federation.srv_resolver import Server, SrvResolver
from synapse.logging.context import LoggingContext, current_context

from tests import unittest
from tests.utils import MockClock


class SrvResolverTestCase(unittest.TestCase):
    def test_resolve(self) -> None:
        dns_client_mock = Mock()

        service_name = b"test_service.example.com"
        host_name = b"example.com"

        answer_srv = dns.RRHeader(
            type=dns.SRV, payload=dns.Record_SRV(target=host_name)
        )

        result_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
        dns_client_mock.lookupService.return_value = result_deferred

        cache: Dict[bytes, List[Server]] = {}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        @defer.inlineCallbacks
        def do_lookup() -> Generator["Deferred[object]", object, List[Server]]:
            with LoggingContext("one") as ctx:
                resolve_d = resolver.resolve_service(service_name)
                result: List[Server]
                result = yield defer.ensureDeferred(resolve_d)  # type: ignore[assignment]

                # should have restored our context
                self.assertIs(current_context(), ctx)

                return result

        test_d = do_lookup()
        self.assertNoResult(test_d)

        dns_client_mock.lookupService.assert_called_once_with(service_name)

        result_deferred.callback(([answer_srv], None, None))

        servers = self.successResultOf(test_d)

        self.assertEqual(len(servers), 1)
        self.assertEqual(servers, cache[service_name])
        self.assertEqual(servers[0].host, host_name)

    @defer.inlineCallbacks
    def test_from_cache_expired_and_dns_fail(
        self,
    ) -> Generator["Deferred[object]", object, None]:
        dns_client_mock = Mock()
        dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())

        service_name = b"test_service.example.com"

        entry = Mock(spec_set=["expires", "priority", "weight"])
        entry.expires = 0
        entry.priority = 0
        entry.weight = 0

        cache = {service_name: [cast(Server, entry)]}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        servers: List[Server]
        servers = yield defer.ensureDeferred(
            resolver.resolve_service(service_name)
        )  # type: ignore[assignment]

        dns_client_mock.lookupService.assert_called_once_with(service_name)

        self.assertEqual(len(servers), 1)
        self.assertEqual(servers, cache[service_name])

    @defer.inlineCallbacks
    def test_from_cache(self) -> Generator["Deferred[object]", object, None]:
        clock = MockClock()

        dns_client_mock = Mock(spec_set=["lookupService"])
        dns_client_mock.lookupService = Mock(spec_set=[])

        service_name = b"test_service.example.com"

        entry = Mock(spec_set=["expires", "priority", "weight"])
        entry.expires = 999999999
        entry.priority = 0
        entry.weight = 0

        cache = {service_name: [cast(Server, entry)]}
        resolver = SrvResolver(
            dns_client=dns_client_mock, cache=cache, get_time=clock.time
        )

        servers: List[Server]
        servers = yield defer.ensureDeferred(
            resolver.resolve_service(service_name)
        )  # type: ignore[assignment]

        self.assertFalse(dns_client_mock.lookupService.called)

        self.assertEqual(len(servers), 1)
        self.assertEqual(servers, cache[service_name])

    @defer.inlineCallbacks
    def test_empty_cache(self) -> Generator["Deferred[object]", object, None]:
        dns_client_mock = Mock()

        dns_client_mock.lookupService.return_value = defer.fail(error.DNSServerError())

        service_name = b"test_service.example.com"

        cache: Dict[bytes, List[Server]] = {}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        with self.assertRaises(error.DNSServerError):
            yield defer.ensureDeferred(resolver.resolve_service(service_name))

    @defer.inlineCallbacks
    def test_name_error(self) -> Generator["Deferred[object]", object, None]:
        dns_client_mock = Mock()

        dns_client_mock.lookupService.return_value = defer.fail(error.DNSNameError())

        service_name = b"test_service.example.com"

        cache: Dict[bytes, List[Server]] = {}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        servers: List[Server]
        servers = yield defer.ensureDeferred(
            resolver.resolve_service(service_name)
        )  # type: ignore[assignment]

        self.assertEqual(len(servers), 0)
        self.assertEqual(len(cache), 0)

    def test_disabled_service(self) -> None:
        """
        test the behaviour when there is a single record which is ".".
        """
        service_name = b"test_service.example.com"

        lookup_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
        dns_client_mock = Mock()
        dns_client_mock.lookupService.return_value = lookup_deferred
        cache: Dict[bytes, List[Server]] = {}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        # Old versions of Twisted don't have an ensureDeferred in failureResultOf.
        resolve_d = defer.ensureDeferred(resolver.resolve_service(service_name))

        # returning a single "." should make the lookup fail with a ConenctError
        lookup_deferred.callback(
            (
                [dns.RRHeader(type=dns.SRV, payload=dns.Record_SRV(target=b"."))],
                None,
                None,
            )
        )

        self.failureResultOf(resolve_d, ConnectError)

    def test_non_srv_answer(self) -> None:
        """
        test the behaviour when the dns server gives us a spurious non-SRV response
        """
        service_name = b"test_service.example.com"

        lookup_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
        dns_client_mock = Mock()
        dns_client_mock.lookupService.return_value = lookup_deferred
        cache: Dict[bytes, List[Server]] = {}
        resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)

        # Old versions of Twisted don't have an ensureDeferred in successResultOf.
        resolve_d = defer.ensureDeferred(resolver.resolve_service(service_name))

        lookup_deferred.callback(
            (
                [
                    dns.RRHeader(type=dns.A, payload=dns.Record_A()),
                    dns.RRHeader(type=dns.SRV, payload=dns.Record_SRV(target=b"host")),
                ],
                None,
                None,
            )
        )

        servers = self.successResultOf(resolve_d)

        self.assertEqual(len(servers), 1)
        self.assertEqual(servers, cache[service_name])
        self.assertEqual(servers[0].host, b"host")