Properly typecheck types.http (#14988)

* Tweak http types in Synapse

AFACIS these are correct, and they make mypy happier on tests.http.

* Type hints for test_proxyagent

* type hints for test_srv_resolver

* test_matrix_federation_agent

* tests.http.server._base

* tests.http.__init__

* tests.http.test_additional_resource

* tests.http.test_client

* tests.http.test_endpoint

* tests.http.test_matrixfederationclient

* tests.http.test_servlet

* tests.http.test_simple_client

* tests.http.test_site

* One fixup in tests.server

* Untyped defs

* Changelog

* Fixup syntax for Python 3.7

* Fix olddeps syntax

* Use a twisted IPv4 addr for dummy_address

* Fix typo, thanks Sean

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

* Remove redundant `Optional`

---------

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

2 files changed, 123 insertions, 79 deletions

diff --git a/tests/http/federation/test_matrix_federation_agent.py b/tests/http/federation/test_matrix_federation_agent.py
index 992d8f94fd..acfdcd3bca 100644
--- a/tests/http/federation/test_matrix_federation_agent.py
+++ b/tests/http/federation/test_matrix_federation_agent.py
@@ -14,7 +14,7 @@
 import base64
 import logging
 import os
-from typing import Iterable, Optional
+from typing import Any, Awaitable, Callable, Generator, List, Optional, cast
 from unittest.mock import Mock, patch
 
 import treq
@@ -24,14 +24,19 @@ from zope.interface import implementer
 
 from twisted.internet import defer
 from twisted.internet._sslverify import ClientTLSOptions, OpenSSLCertificateOptions
-from twisted.internet.interfaces import IProtocolFactory
+from twisted.internet.defer import Deferred
+from twisted.internet.endpoints import _WrappingProtocol
+from twisted.internet.interfaces import (
+    IOpenSSLClientConnectionCreator,
+    IProtocolFactory,
+)
 from twisted.internet.protocol import Factory
 from twisted.protocols.tls import TLSMemoryBIOFactory, TLSMemoryBIOProtocol
 from twisted.web._newclient import ResponseNeverReceived
 from twisted.web.client import Agent
 from twisted.web.http import HTTPChannel, Request
 from twisted.web.http_headers import Headers
-from twisted.web.iweb import IPolicyForHTTPS
+from twisted.web.iweb import IPolicyForHTTPS, IResponse
 
 from synapse.config.homeserver import HomeServerConfig
 from synapse.crypto.context_factory import FederationPolicyForHTTPS
@@ -42,11 +47,21 @@ from synapse.http.federation.well_known_resolver import (
     WellKnownResolver,
     _cache_period_from_headers,
 )
-from synapse.logging.context import SENTINEL_CONTEXT, LoggingContext, current_context
+from synapse.logging.context import (
+    SENTINEL_CONTEXT,
+    LoggingContext,
+    LoggingContextOrSentinel,
+    current_context,
+)
+from synapse.types import ISynapseReactor
 from synapse.util.caches.ttlcache import TTLCache
 
 from tests import unittest
-from tests.http import TestServerTLSConnectionFactory, get_test_ca_cert_file
+from tests.http import (
+    TestServerTLSConnectionFactory,
+    dummy_address,
+    get_test_ca_cert_file,
+)
 from tests.server import FakeTransport, ThreadedMemoryReactorClock
 from tests.utils import default_config
 
@@ -54,15 +69,17 @@ logger = logging.getLogger(__name__)
 
 
 # Once Async Mocks or lambdas are supported this can go away.
-def generate_resolve_service(result):
-    async def resolve_service(_):
+def generate_resolve_service(
+    result: List[Server],
+) -> Callable[[Any], Awaitable[List[Server]]]:
+    async def resolve_service(_: Any) -> List[Server]:
         return result
 
     return resolve_service
 
 
 class MatrixFederationAgentTests(unittest.TestCase):
-    def setUp(self):
+    def setUp(self) -> None:
         self.reactor = ThreadedMemoryReactorClock()
 
         self.mock_resolver = Mock()
@@ -75,8 +92,12 @@ class MatrixFederationAgentTests(unittest.TestCase):
 
         self.tls_factory = FederationPolicyForHTTPS(config)
 
-        self.well_known_cache = TTLCache("test_cache", timer=self.reactor.seconds)
-        self.had_well_known_cache = TTLCache("test_cache", timer=self.reactor.seconds)
+        self.well_known_cache: TTLCache[bytes, Optional[bytes]] = TTLCache(
+            "test_cache", timer=self.reactor.seconds
+        )
+        self.had_well_known_cache: TTLCache[bytes, bool] = TTLCache(
+            "test_cache", timer=self.reactor.seconds
+        )
         self.well_known_resolver = WellKnownResolver(
             self.reactor,
             Agent(self.reactor, contextFactory=self.tls_factory),
@@ -89,8 +110,8 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self,
         client_factory: IProtocolFactory,
         ssl: bool = True,
-        expected_sni: bytes = None,
-        tls_sanlist: Optional[Iterable[bytes]] = None,
+        expected_sni: Optional[bytes] = None,
+        tls_sanlist: Optional[List[bytes]] = None,
     ) -> HTTPChannel:
         """Builds a test server, and completes the outgoing client connection
         Args:
@@ -116,8 +137,8 @@ class MatrixFederationAgentTests(unittest.TestCase):
         if ssl:
             server_factory = _wrap_server_factory_for_tls(server_factory, tls_sanlist)
 
-        server_protocol = server_factory.buildProtocol(None)
-
+        server_protocol = server_factory.buildProtocol(dummy_address)
+        assert server_protocol is not None
         # now, tell the client protocol factory to build the client protocol (it will be a
         # _WrappingProtocol, around a TLSMemoryBIOProtocol, around an
         # HTTP11ClientProtocol) and wire the output of said protocol up to the server via
@@ -125,7 +146,8 @@ class MatrixFederationAgentTests(unittest.TestCase):
         #
         # Normally this would be done by the TCP socket code in Twisted, but we are
         # stubbing that out here.
-        client_protocol = client_factory.buildProtocol(None)
+        client_protocol = client_factory.buildProtocol(dummy_address)
+        assert isinstance(client_protocol, _WrappingProtocol)
         client_protocol.makeConnection(
             FakeTransport(server_protocol, self.reactor, client_protocol)
         )
@@ -136,6 +158,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         )
 
         if ssl:
+            assert isinstance(server_protocol, TLSMemoryBIOProtocol)
             # fish the test server back out of the server-side TLS protocol.
             http_protocol = server_protocol.wrappedProtocol
             # grab a hold of the TLS connection, in case it gets torn down
@@ -144,6 +167,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
             http_protocol = server_protocol
             tls_connection = None
 
+        assert isinstance(http_protocol, HTTPChannel)
         # give the reactor a pump to get the TLS juices flowing (if needed)
         self.reactor.advance(0)
 
@@ -159,12 +183,14 @@ class MatrixFederationAgentTests(unittest.TestCase):
         return http_protocol
 
     @defer.inlineCallbacks
-    def _make_get_request(self, uri: bytes):
+    def _make_get_request(
+        self, uri: bytes
+    ) -> Generator["Deferred[object]", object, IResponse]:
         """
         Sends a simple GET request via the agent, and checks its logcontext management
         """
         with LoggingContext("one") as context:
-            fetch_d = self.agent.request(b"GET", uri)
+            fetch_d: Deferred[IResponse] = self.agent.request(b"GET", uri)
 
             # Nothing happened yet
             self.assertNoResult(fetch_d)
@@ -172,8 +198,9 @@ class MatrixFederationAgentTests(unittest.TestCase):
             # should have reset logcontext to the sentinel
             _check_logcontext(SENTINEL_CONTEXT)
 
+            fetch_res: IResponse
             try:
-                fetch_res = yield fetch_d
+                fetch_res = yield fetch_d  # type: ignore[misc, assignment]
                 return fetch_res
             except Exception as e:
                 logger.info("Fetch of %s failed: %s", uri.decode("ascii"), e)
@@ -216,7 +243,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         request: Request,
         content: bytes,
         headers: Optional[dict] = None,
-    ):
+    ) -> None:
         """Check that an incoming request looks like a valid .well-known request, and
         send back the response.
         """
@@ -237,16 +264,16 @@ class MatrixFederationAgentTests(unittest.TestCase):
         because it is created too early during setUp
         """
         return MatrixFederationAgent(
-            reactor=self.reactor,
+            reactor=cast(ISynapseReactor, self.reactor),
             tls_client_options_factory=self.tls_factory,
-            user_agent="test-agent",  # Note that this is unused since _well_known_resolver is provided.
+            user_agent=b"test-agent",  # Note that this is unused since _well_known_resolver is provided.
             ip_whitelist=IPSet(),
             ip_blacklist=IPSet(),
             _srv_resolver=self.mock_resolver,
             _well_known_resolver=self.well_known_resolver,
         )
 
-    def test_get(self):
+    def test_get(self) -> None:
         """happy-path test of a GET request with an explicit port"""
         self._do_get()
 
@@ -254,11 +281,11 @@ class MatrixFederationAgentTests(unittest.TestCase):
         os.environ,
         {"https_proxy": "proxy.com", "no_proxy": "testserv"},
     )
-    def test_get_bypass_proxy(self):
+    def test_get_bypass_proxy(self) -> None:
         """test of a GET request with an explicit port and bypass proxy"""
         self._do_get()
 
-    def _do_get(self):
+    def _do_get(self) -> None:
         """test of a GET request with an explicit port"""
         self.agent = self._make_agent()
 
@@ -318,7 +345,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
     @patch.dict(
         os.environ, {"https_proxy": "http://proxy.com", "no_proxy": "unused.com"}
     )
-    def test_get_via_http_proxy(self):
+    def test_get_via_http_proxy(self) -> None:
         """test for federation request through a http proxy"""
         self._do_get_via_proxy(expect_proxy_ssl=False, expected_auth_credentials=None)
 
@@ -326,7 +353,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         os.environ,
         {"https_proxy": "http://user:pass@proxy.com", "no_proxy": "unused.com"},
     )
-    def test_get_via_http_proxy_with_auth(self):
+    def test_get_via_http_proxy_with_auth(self) -> None:
         """test for federation request through a http proxy with authentication"""
         self._do_get_via_proxy(
             expect_proxy_ssl=False, expected_auth_credentials=b"user:pass"
@@ -335,7 +362,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
     @patch.dict(
         os.environ, {"https_proxy": "https://proxy.com", "no_proxy": "unused.com"}
     )
-    def test_get_via_https_proxy(self):
+    def test_get_via_https_proxy(self) -> None:
         """test for federation request through a https proxy"""
         self._do_get_via_proxy(expect_proxy_ssl=True, expected_auth_credentials=None)
 
@@ -343,7 +370,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         os.environ,
         {"https_proxy": "https://user:pass@proxy.com", "no_proxy": "unused.com"},
     )
-    def test_get_via_https_proxy_with_auth(self):
+    def test_get_via_https_proxy_with_auth(self) -> None:
         """test for federation request through a https proxy with authentication"""
         self._do_get_via_proxy(
             expect_proxy_ssl=True, expected_auth_credentials=b"user:pass"
@@ -353,7 +380,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self,
         expect_proxy_ssl: bool = False,
         expected_auth_credentials: Optional[bytes] = None,
-    ):
+    ) -> None:
         """Send a https federation request via an agent and check that it is correctly
             received at the proxy and client. The proxy can use either http or https.
         Args:
@@ -418,10 +445,12 @@ class MatrixFederationAgentTests(unittest.TestCase):
         # now we make another test server to act as the upstream HTTP server.
         server_ssl_protocol = _wrap_server_factory_for_tls(
             _get_test_protocol_factory()
-        ).buildProtocol(None)
+        ).buildProtocol(dummy_address)
+        assert isinstance(server_ssl_protocol, TLSMemoryBIOProtocol)
 
         # Tell the HTTP server to send outgoing traffic back via the proxy's transport.
         proxy_server_transport = proxy_server.transport
+        assert proxy_server_transport is not None
         server_ssl_protocol.makeConnection(proxy_server_transport)
 
         # ... and replace the protocol on the proxy's transport with the
@@ -451,6 +480,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
 
         # now there should be a pending request
         http_server = server_ssl_protocol.wrappedProtocol
+        assert isinstance(http_server, HTTPChannel)
         self.assertEqual(len(http_server.requests), 1)
 
         request = http_server.requests[0]
@@ -491,7 +521,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         json = self.successResultOf(treq.json_content(response))
         self.assertEqual(json, {"a": 1})
 
-    def test_get_ip_address(self):
+    def test_get_ip_address(self) -> None:
         """
         Test the behaviour when the server name contains an explicit IP (with no port)
         """
@@ -526,7 +556,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_ipv6_address(self):
+    def test_get_ipv6_address(self) -> None:
         """
         Test the behaviour when the server name contains an explicit IPv6 address
         (with no port)
@@ -562,7 +592,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_ipv6_address_with_port(self):
+    def test_get_ipv6_address_with_port(self) -> None:
         """
         Test the behaviour when the server name contains an explicit IPv6 address
         (with explicit port)
@@ -598,7 +628,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_hostname_bad_cert(self):
+    def test_get_hostname_bad_cert(self) -> None:
         """
         Test the behaviour when the certificate on the server doesn't match the hostname
         """
@@ -651,7 +681,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         failure_reason = e.value.reasons[0]
         self.assertIsInstance(failure_reason.value, VerificationError)
 
-    def test_get_ip_address_bad_cert(self):
+    def test_get_ip_address_bad_cert(self) -> None:
         """
         Test the behaviour when the server name contains an explicit IP, but
         the server cert doesn't cover it
@@ -684,7 +714,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         failure_reason = e.value.reasons[0]
         self.assertIsInstance(failure_reason.value, VerificationError)
 
-    def test_get_no_srv_no_well_known(self):
+    def test_get_no_srv_no_well_known(self) -> None:
         """
         Test the behaviour when the server name has no port, no SRV, and no well-known
         """
@@ -740,7 +770,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_well_known(self):
+    def test_get_well_known(self) -> None:
         """Test the behaviour when the .well-known delegates elsewhere"""
         self.agent = self._make_agent()
 
@@ -802,7 +832,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.well_known_cache.expire()
         self.assertNotIn(b"testserv", self.well_known_cache)
 
-    def test_get_well_known_redirect(self):
+    def test_get_well_known_redirect(self) -> None:
         """Test the behaviour when the server name has no port and no SRV record, but
         the .well-known has a 300 redirect
         """
@@ -892,7 +922,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.well_known_cache.expire()
         self.assertNotIn(b"testserv", self.well_known_cache)
 
-    def test_get_invalid_well_known(self):
+    def test_get_invalid_well_known(self) -> None:
         """
         Test the behaviour when the server name has an *invalid* well-known (and no SRV)
         """
@@ -945,7 +975,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_well_known_unsigned_cert(self):
+    def test_get_well_known_unsigned_cert(self) -> None:
         """Test the behaviour when the .well-known server presents a cert
         not signed by a CA
         """
@@ -969,7 +999,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
             ip_blacklist=IPSet(),
             _srv_resolver=self.mock_resolver,
             _well_known_resolver=WellKnownResolver(
-                self.reactor,
+                cast(ISynapseReactor, self.reactor),
                 Agent(self.reactor, contextFactory=tls_factory),
                 b"test-agent",
                 well_known_cache=self.well_known_cache,
@@ -999,7 +1029,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
             b"_matrix._tcp.testserv"
         )
 
-    def test_get_hostname_srv(self):
+    def test_get_hostname_srv(self) -> None:
         """
         Test the behaviour when there is a single SRV record
         """
@@ -1041,7 +1071,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_get_well_known_srv(self):
+    def test_get_well_known_srv(self) -> None:
         """Test the behaviour when the .well-known redirects to a place where there
         is a SRV.
         """
@@ -1101,7 +1131,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_idna_servername(self):
+    def test_idna_servername(self) -> None:
         """test the behaviour when the server name has idna chars in"""
         self.agent = self._make_agent()
 
@@ -1163,7 +1193,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_idna_srv_target(self):
+    def test_idna_srv_target(self) -> None:
         """test the behaviour when the target of a SRV record has idna chars"""
         self.agent = self._make_agent()
 
@@ -1206,7 +1236,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         self.reactor.pump((0.1,))
         self.successResultOf(test_d)
 
-    def test_well_known_cache(self):
+    def test_well_known_cache(self) -> None:
         self.reactor.lookups["testserv"] = "1.2.3.4"
 
         fetch_d = defer.ensureDeferred(
@@ -1262,7 +1292,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         r = self.successResultOf(fetch_d)
         self.assertEqual(r.delegated_server, b"other-server")
 
-    def test_well_known_cache_with_temp_failure(self):
+    def test_well_known_cache_with_temp_failure(self) -> None:
         """Test that we refetch well-known before the cache expires, and that
         it ignores transient errors.
         """
@@ -1341,7 +1371,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         r = self.successResultOf(fetch_d)
         self.assertEqual(r.delegated_server, None)
 
-    def test_well_known_too_large(self):
+    def test_well_known_too_large(self) -> None:
         """A well-known query that returns a result which is too large should be rejected."""
         self.reactor.lookups["testserv"] = "1.2.3.4"
 
@@ -1367,7 +1397,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
         r = self.successResultOf(fetch_d)
         self.assertIsNone(r.delegated_server)
 
-    def test_srv_fallbacks(self):
+    def test_srv_fallbacks(self) -> None:
         """Test that other SRV results are tried if the first one fails."""
         self.agent = self._make_agent()
 
@@ -1427,7 +1457,7 @@ class MatrixFederationAgentTests(unittest.TestCase):
 
 
 class TestCachePeriodFromHeaders(unittest.TestCase):
-    def test_cache_control(self):
+    def test_cache_control(self) -> None:
         # uppercase
         self.assertEqual(
             _cache_period_from_headers(
@@ -1464,7 +1494,7 @@ class TestCachePeriodFromHeaders(unittest.TestCase):
             0,
         )
 
-    def test_expires(self):
+    def test_expires(self) -> None:
         self.assertEqual(
             _cache_period_from_headers(
                 Headers({b"Expires": [b"Wed, 30 Jan 2019 07:35:33 GMT"]}),
@@ -1491,14 +1521,14 @@ class TestCachePeriodFromHeaders(unittest.TestCase):
         self.assertEqual(_cache_period_from_headers(Headers({b"Expires": [b"0"]})), 0)
 
 
-def _check_logcontext(context):
+def _check_logcontext(context: LoggingContextOrSentinel) -> None:
     current = current_context()
     if current is not context:
         raise AssertionError("Expected logcontext %s but was %s" % (context, current))
 
 
 def _wrap_server_factory_for_tls(
-    factory: IProtocolFactory, sanlist: Iterable[bytes] = None
+    factory: IProtocolFactory, sanlist: Optional[List[bytes]] = None
 ) -> IProtocolFactory:
     """Wrap an existing Protocol Factory with a test TLSMemoryBIOFactory
     The resultant factory will create a TLS server which presents a certificate
@@ -1537,7 +1567,7 @@ def _get_test_protocol_factory() -> IProtocolFactory:
     return server_factory
 
 
-def _log_request(request: str):
+def _log_request(request: str) -> None:
     """Implements Factory.log, which is expected by Request.finish"""
     logger.info(f"Completed request {request}")
 
@@ -1547,6 +1577,8 @@ class TrustingTLSPolicyForHTTPS:
     """An IPolicyForHTTPS which checks that the certificate belongs to the
     right server, but doesn't check the certificate chain."""
 
-    def creatorForNetloc(self, hostname, port):
+    def creatorForNetloc(
+        self, hostname: bytes, port: int
+    ) -> IOpenSSLClientConnectionCreator:
         certificateOptions = OpenSSLCertificateOptions()
         return ClientTLSOptions(hostname, certificateOptions.getContext())
diff --git a/tests/http/federation/test_srv_resolver.py b/tests/http/federation/test_srv_resolver.py
index 77ce8432ac..7748f56ee6 100644
--- a/tests/http/federation/test_srv_resolver.py
+++ b/tests/http/federation/test_srv_resolver.py
@@ -12,7 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-
+from typing import Dict, Generator, List, Tuple, cast
 from unittest.mock import Mock
 
 from twisted.internet import defer
@@ -20,7 +20,7 @@ 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 SrvResolver
+from synapse.http.federation.srv_resolver import Server, SrvResolver
 from synapse.logging.context import LoggingContext, current_context
 
 from tests import unittest
@@ -28,7 +28,7 @@ from tests.utils import MockClock
 
 
 class SrvResolverTestCase(unittest.TestCase):
-    def test_resolve(self):
+    def test_resolve(self) -> None:
         dns_client_mock = Mock()
 
         service_name = b"test_service.example.com"
@@ -38,18 +38,19 @@ class SrvResolverTestCase(unittest.TestCase):
             type=dns.SRV, payload=dns.Record_SRV(target=host_name)
         )
 
-        result_deferred = Deferred()
+        result_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
         dns_client_mock.lookupService.return_value = result_deferred
 
-        cache = {}
+        cache: Dict[bytes, List[Server]] = {}
         resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)
 
         @defer.inlineCallbacks
-        def do_lookup():
+        def do_lookup() -> Generator["Deferred[object]", object, List[Server]]:
 
             with LoggingContext("one") as ctx:
                 resolve_d = resolver.resolve_service(service_name)
-                result = yield defer.ensureDeferred(resolve_d)
+                result: List[Server]
+                result = yield defer.ensureDeferred(resolve_d)  # type: ignore[assignment]
 
                 # should have restored our context
                 self.assertIs(current_context(), ctx)
@@ -70,7 +71,9 @@ class SrvResolverTestCase(unittest.TestCase):
         self.assertEqual(servers[0].host, host_name)
 
     @defer.inlineCallbacks
-    def test_from_cache_expired_and_dns_fail(self):
+    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())
 
@@ -81,10 +84,13 @@ class SrvResolverTestCase(unittest.TestCase):
         entry.priority = 0
         entry.weight = 0
 
-        cache = {service_name: [entry]}
+        cache = {service_name: [cast(Server, entry)]}
         resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)
 
-        servers = yield defer.ensureDeferred(resolver.resolve_service(service_name))
+        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)
 
@@ -92,7 +98,7 @@ class SrvResolverTestCase(unittest.TestCase):
         self.assertEqual(servers, cache[service_name])
 
     @defer.inlineCallbacks
-    def test_from_cache(self):
+    def test_from_cache(self) -> Generator["Deferred[object]", object, None]:
         clock = MockClock()
 
         dns_client_mock = Mock(spec_set=["lookupService"])
@@ -105,12 +111,15 @@ class SrvResolverTestCase(unittest.TestCase):
         entry.priority = 0
         entry.weight = 0
 
-        cache = {service_name: [entry]}
+        cache = {service_name: [cast(Server, entry)]}
         resolver = SrvResolver(
             dns_client=dns_client_mock, cache=cache, get_time=clock.time
         )
 
-        servers = yield defer.ensureDeferred(resolver.resolve_service(service_name))
+        servers: List[Server]
+        servers = yield defer.ensureDeferred(
+            resolver.resolve_service(service_name)
+        )  # type: ignore[assignment]
 
         self.assertFalse(dns_client_mock.lookupService.called)
 
@@ -118,45 +127,48 @@ class SrvResolverTestCase(unittest.TestCase):
         self.assertEqual(servers, cache[service_name])
 
     @defer.inlineCallbacks
-    def test_empty_cache(self):
+    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 = {}
+        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):
+    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 = {}
+        cache: Dict[bytes, List[Server]] = {}
         resolver = SrvResolver(dns_client=dns_client_mock, cache=cache)
 
-        servers = yield defer.ensureDeferred(resolver.resolve_service(service_name))
+        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):
+    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()
+        lookup_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
         dns_client_mock = Mock()
         dns_client_mock.lookupService.return_value = lookup_deferred
-        cache = {}
+        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.
@@ -173,16 +185,16 @@ class SrvResolverTestCase(unittest.TestCase):
 
         self.failureResultOf(resolve_d, ConnectError)
 
-    def test_non_srv_answer(self):
+    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()
+        lookup_deferred: "Deferred[Tuple[List[dns.RRHeader], None, None]]" = Deferred()
         dns_client_mock = Mock()
         dns_client_mock.lookupService.return_value = lookup_deferred
-        cache = {}
+        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.