synapse/tests/http/test_matrixfederationclient.py

# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# 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 Any, Dict, Generator
from unittest.mock import ANY, Mock, create_autospec

from netaddr import IPSet
from parameterized import parameterized

from twisted.internet import defer
from twisted.internet.defer import Deferred, TimeoutError
from twisted.internet.error import ConnectingCancelledError, DNSLookupError
from twisted.test.proto_helpers import MemoryReactor, StringTransport
from twisted.web.client import Agent, ResponseNeverReceived
from twisted.web.http import HTTPChannel
from twisted.web.http_headers import Headers

from synapse.api.errors import HttpResponseException, RequestSendFailed
from synapse.http.matrixfederationclient import (
    ByteParser,
    MatrixFederationHttpClient,
    MatrixFederationRequest,
)
from synapse.logging.context import (
    SENTINEL_CONTEXT,
    LoggingContext,
    LoggingContextOrSentinel,
    current_context,
)
from synapse.server import HomeServer
from synapse.util import Clock

from tests.replication._base import BaseMultiWorkerStreamTestCase
from tests.server import FakeTransport
from tests.test_utils import FakeResponse
from tests.unittest import HomeserverTestCase, override_config


def check_logcontext(context: LoggingContextOrSentinel) -> None:
    current = current_context()
    if current is not context:
        raise AssertionError("Expected logcontext %s but was %s" % (context, current))


class FederationClientTests(HomeserverTestCase):
    def make_homeserver(self, reactor: MemoryReactor, clock: Clock) -> HomeServer:
        hs = self.setup_test_homeserver(reactor=reactor, clock=clock)
        return hs

    def prepare(
        self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer
    ) -> None:
        self.cl = MatrixFederationHttpClient(self.hs, None)
        self.reactor.lookups["testserv"] = "1.2.3.4"

    def test_client_get(self) -> None:
        """
        happy-path test of a GET request
        """

        @defer.inlineCallbacks
        def do_request() -> Generator["Deferred[object]", object, object]:
            with LoggingContext("one") as context:
                fetch_d = defer.ensureDeferred(
                    self.cl.get_json("testserv:8008", "foo/bar")
                )

                # Nothing happened yet
                self.assertNoResult(fetch_d)

                # should have reset logcontext to the sentinel
                check_logcontext(SENTINEL_CONTEXT)

                try:
                    fetch_res = yield fetch_d
                    return fetch_res
                finally:
                    check_logcontext(context)

        test_d = do_request()

        self.pump()

        # Nothing happened yet
        self.assertNoResult(test_d)

        # Make sure treq is trying to connect
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (host, port, factory, _timeout, _bindAddress) = clients[0]
        self.assertEqual(host, "1.2.3.4")
        self.assertEqual(port, 8008)

        # complete the connection and wire it up to a fake transport
        protocol = factory.buildProtocol(None)
        transport = StringTransport()
        protocol.makeConnection(transport)

        # that should have made it send the request to the transport
        self.assertRegex(transport.value(), b"^GET /foo/bar")
        self.assertRegex(transport.value(), b"Host: testserv:8008")

        # Deferred is still without a result
        self.assertNoResult(test_d)

        # Send it the HTTP response
        res_json = b'{ "a": 1 }'
        protocol.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Server: Fake\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: %i\r\n"
            b"\r\n"
            b"%s" % (len(res_json), res_json)
        )

        self.pump()

        res = self.successResultOf(test_d)

        # check the response is as expected
        self.assertEqual(res, {"a": 1})

    def test_dns_error(self) -> None:
        """
        If the DNS lookup returns an error, it will bubble up.
        """
        d = defer.ensureDeferred(
            self.cl.get_json("testserv2:8008", "foo/bar", timeout=10000)
        )
        self.pump()

        f = self.failureResultOf(d)
        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertIsInstance(f.value.inner_exception, DNSLookupError)

    def test_client_connection_refused(self) -> None:
        d = defer.ensureDeferred(
            self.cl.get_json("testserv:8008", "foo/bar", timeout=10000)
        )

        self.pump()

        # Nothing happened yet
        self.assertNoResult(d)

        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (host, port, factory, _timeout, _bindAddress) = clients[0]
        self.assertEqual(host, "1.2.3.4")
        self.assertEqual(port, 8008)
        e = Exception("go away")
        factory.clientConnectionFailed(None, e)
        self.pump(0.5)

        f = self.failureResultOf(d)

        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertIs(f.value.inner_exception, e)

    def test_client_never_connect(self) -> None:
        """
        If the HTTP request is not connected and is timed out, it'll give a
        ConnectingCancelledError or TimeoutError.
        """
        d = defer.ensureDeferred(
            self.cl.get_json("testserv:8008", "foo/bar", timeout=10000)
        )

        self.pump()

        # Nothing happened yet
        self.assertNoResult(d)

        # Make sure treq is trying to connect
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        self.assertEqual(clients[0][0], "1.2.3.4")
        self.assertEqual(clients[0][1], 8008)

        # Deferred is still without a result
        self.assertNoResult(d)

        # Push by enough to time it out
        self.reactor.advance(10.5)
        f = self.failureResultOf(d)

        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertIsInstance(
            f.value.inner_exception, (ConnectingCancelledError, TimeoutError)
        )

    def test_client_connect_no_response(self) -> None:
        """
        If the HTTP request is connected, but gets no response before being
        timed out, it'll give a ResponseNeverReceived.
        """
        d = defer.ensureDeferred(
            self.cl.get_json("testserv:8008", "foo/bar", timeout=10000)
        )

        self.pump()

        # Nothing happened yet
        self.assertNoResult(d)

        # Make sure treq is trying to connect
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        self.assertEqual(clients[0][0], "1.2.3.4")
        self.assertEqual(clients[0][1], 8008)

        conn = Mock()
        client = clients[0][2].buildProtocol(None)
        client.makeConnection(conn)

        # Deferred is still without a result
        self.assertNoResult(d)

        # Push by enough to time it out
        self.reactor.advance(10.5)
        f = self.failureResultOf(d)

        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertIsInstance(f.value.inner_exception, ResponseNeverReceived)

    def test_client_ip_range_blocklist(self) -> None:
        """Ensure that Synapse does not try to connect to blocked IPs"""

        # Set up the ip_range blocklist
        self.hs.config.server.federation_ip_range_blocklist = IPSet(
            ["127.0.0.0/8", "fe80::/64"]
        )
        self.reactor.lookups["internal"] = "127.0.0.1"
        self.reactor.lookups["internalv6"] = "fe80:0:0:0:0:8a2e:370:7337"
        self.reactor.lookups["fine"] = "10.20.30.40"
        cl = MatrixFederationHttpClient(self.hs, None)

        # Try making a GET request to a blocked IPv4 address
        # ------------------------------------------------------
        # Make the request
        d = defer.ensureDeferred(cl.get_json("internal:8008", "foo/bar", timeout=10000))

        # Nothing happened yet
        self.assertNoResult(d)

        self.pump(1)

        # Check that it was unable to resolve the address
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 0)

        f = self.failureResultOf(d)
        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertIsInstance(f.value.inner_exception, DNSLookupError)

        # Try making a POST request to a blocked IPv6 address
        # -------------------------------------------------------
        # Make the request
        d = defer.ensureDeferred(
            cl.post_json("internalv6:8008", "foo/bar", timeout=10000)
        )

        # Nothing has happened yet
        self.assertNoResult(d)

        # Move the reactor forwards
        self.pump(1)

        # Check that it was unable to resolve the address
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 0)

        # Check that it was due to a blocked DNS lookup
        f = self.failureResultOf(d, RequestSendFailed)
        self.assertIsInstance(f.value.inner_exception, DNSLookupError)

        # Try making a GET request to an allowed IPv4 address
        # ----------------------------------------------------------
        # Make the request
        d = defer.ensureDeferred(cl.post_json("fine:8008", "foo/bar", timeout=10000))

        # Nothing has happened yet
        self.assertNoResult(d)

        # Move the reactor forwards
        self.pump(1)

        # Check that it was able to resolve the address
        clients = self.reactor.tcpClients
        self.assertNotEqual(len(clients), 0)

        # Connection will still fail as this IP address does not resolve to anything
        f = self.failureResultOf(d, RequestSendFailed)
        self.assertIsInstance(f.value.inner_exception, ConnectingCancelledError)

    def test_client_gets_headers(self) -> None:
        """
        Once the client gets the headers, _request returns successfully.
        """
        request = MatrixFederationRequest(
            method="GET", destination="testserv:8008", path="foo/bar"
        )
        d = defer.ensureDeferred(self.cl._send_request(request, timeout=10000))

        self.pump()

        conn = Mock()
        clients = self.reactor.tcpClients
        client = clients[0][2].buildProtocol(None)
        client.makeConnection(conn)

        # Deferred does not have a result
        self.assertNoResult(d)

        # Send it the HTTP response
        client.dataReceived(b"HTTP/1.1 200 OK\r\nServer: Fake\r\n\r\n")

        # We should get a successful response
        r = self.successResultOf(d)
        self.assertEqual(r.code, 200)

    @parameterized.expand(["get_json", "post_json", "delete_json", "put_json"])
    def test_timeout_reading_body(self, method_name: str) -> None:
        """
        If the HTTP request is connected, but gets no response before being
        timed out, it'll give a RequestSendFailed with can_retry.
        """
        method = getattr(self.cl, method_name)
        d = defer.ensureDeferred(method("testserv:8008", "foo/bar", timeout=10000))

        self.pump()

        conn = Mock()
        clients = self.reactor.tcpClients
        client = clients[0][2].buildProtocol(None)
        client.makeConnection(conn)

        # Deferred does not have a result
        self.assertNoResult(d)

        # Send it the HTTP response
        client.dataReceived(
            b"HTTP/1.1 200 OK\r\nContent-Type: application/json\r\n"
            b"Server: Fake\r\n\r\n"
        )

        # Push by enough to time it out
        self.reactor.advance(10.5)
        f = self.failureResultOf(d)

        self.assertIsInstance(f.value, RequestSendFailed)
        self.assertTrue(f.value.can_retry)
        self.assertIsInstance(f.value.inner_exception, defer.TimeoutError)

    def test_client_requires_trailing_slashes(self) -> None:
        """
        If a connection is made to a client but the client rejects it due to
        requiring a trailing slash. We need to retry the request with a
        trailing slash. Workaround for Synapse <= v0.99.3, explained in #3622.
        """
        d = defer.ensureDeferred(
            self.cl.get_json("testserv:8008", "foo/bar", try_trailing_slash_on_400=True)
        )

        # Send the request
        self.pump()

        # there should have been a call to connectTCP
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (_host, _port, factory, _timeout, _bindAddress) = clients[0]

        # complete the connection and wire it up to a fake transport
        client = factory.buildProtocol(None)
        conn = StringTransport()
        client.makeConnection(conn)

        # that should have made it send the request to the connection
        self.assertRegex(conn.value(), b"^GET /foo/bar")

        # Clear the original request data before sending a response
        conn.clear()

        # Send the HTTP response
        client.dataReceived(
            b"HTTP/1.1 400 Bad Request\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: 59\r\n"
            b"\r\n"
            b'{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}'
        )

        # We should get another request with a trailing slash
        self.assertRegex(conn.value(), b"^GET /foo/bar/")

        # Send a happy response this time
        client.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: 2\r\n"
            b"\r\n"
            b"{}"
        )

        # We should get a successful response
        r = self.successResultOf(d)
        self.assertEqual(r, {})

    def test_client_does_not_retry_on_400_plus(self) -> None:
        """
        Another test for trailing slashes but now test that we don't retry on
        trailing slashes on a non-400/M_UNRECOGNIZED response.

        See test_client_requires_trailing_slashes() for context.
        """
        d = defer.ensureDeferred(
            self.cl.get_json("testserv:8008", "foo/bar", try_trailing_slash_on_400=True)
        )

        # Send the request
        self.pump()

        # there should have been a call to connectTCP
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (_host, _port, factory, _timeout, _bindAddress) = clients[0]

        # complete the connection and wire it up to a fake transport
        client = factory.buildProtocol(None)
        conn = StringTransport()
        client.makeConnection(conn)

        # that should have made it send the request to the connection
        self.assertRegex(conn.value(), b"^GET /foo/bar")

        # Clear the original request data before sending a response
        conn.clear()

        # Send the HTTP response
        client.dataReceived(
            b"HTTP/1.1 404 Not Found\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: 2\r\n"
            b"\r\n"
            b"{}"
        )

        # We should not get another request
        self.assertEqual(conn.value(), b"")

        # We should get a 404 failure response
        self.failureResultOf(d)

    def test_client_sends_body(self) -> None:
        defer.ensureDeferred(
            self.cl.post_json(
                "testserv:8008", "foo/bar", timeout=10000, data={"a": "b"}
            )
        )

        self.pump()

        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        client = clients[0][2].buildProtocol(None)
        server = HTTPChannel()

        client.makeConnection(FakeTransport(server, self.reactor))
        server.makeConnection(FakeTransport(client, self.reactor))

        self.pump(0.1)

        self.assertEqual(len(server.requests), 1)
        request = server.requests[0]
        content = request.content.read()
        self.assertEqual(content, b'{"a":"b"}')

    def test_closes_connection(self) -> None:
        """Check that the client closes unused HTTP connections"""
        d = defer.ensureDeferred(self.cl.get_json("testserv:8008", "foo/bar"))

        self.pump()

        # there should have been a call to connectTCP
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (_host, _port, factory, _timeout, _bindAddress) = clients[0]

        # complete the connection and wire it up to a fake transport
        client = factory.buildProtocol(None)
        conn = StringTransport()
        client.makeConnection(conn)

        # that should have made it send the request to the connection
        self.assertRegex(conn.value(), b"^GET /foo/bar")

        # Send the HTTP response
        client.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: 2\r\n"
            b"\r\n"
            b"{}"
        )

        # We should get a successful response
        r = self.successResultOf(d)
        self.assertEqual(r, {})

        self.assertFalse(conn.disconnecting)

        # wait for a while
        self.reactor.advance(120)

        self.assertTrue(conn.disconnecting)

    @parameterized.expand([(b"",), (b"foo",), (b'{"a": Infinity}',)])
    def test_json_error(self, return_value: bytes) -> None:
        """
        Test what happens if invalid JSON is returned from the remote endpoint.
        """

        test_d = defer.ensureDeferred(self.cl.get_json("testserv:8008", "foo/bar"))

        self.pump()

        # Nothing happened yet
        self.assertNoResult(test_d)

        # Make sure treq is trying to connect
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (host, port, factory, _timeout, _bindAddress) = clients[0]
        self.assertEqual(host, "1.2.3.4")
        self.assertEqual(port, 8008)

        # complete the connection and wire it up to a fake transport
        protocol = factory.buildProtocol(None)
        transport = StringTransport()
        protocol.makeConnection(transport)

        # that should have made it send the request to the transport
        self.assertRegex(transport.value(), b"^GET /foo/bar")
        self.assertRegex(transport.value(), b"Host: testserv:8008")

        # Deferred is still without a result
        self.assertNoResult(test_d)

        # Send it the HTTP response
        protocol.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Server: Fake\r\n"
            b"Content-Type: application/json\r\n"
            b"Content-Length: %i\r\n"
            b"\r\n"
            b"%s" % (len(return_value), return_value)
        )

        self.pump()

        f = self.failureResultOf(test_d)
        self.assertIsInstance(f.value, RequestSendFailed)

    def test_too_big(self) -> None:
        """
        Test what happens if a huge response is returned from the remote endpoint.
        """

        test_d = defer.ensureDeferred(self.cl.get_json("testserv:8008", "foo/bar"))

        self.pump()

        # Nothing happened yet
        self.assertNoResult(test_d)

        # Make sure treq is trying to connect
        clients = self.reactor.tcpClients
        self.assertEqual(len(clients), 1)
        (host, port, factory, _timeout, _bindAddress) = clients[0]
        self.assertEqual(host, "1.2.3.4")
        self.assertEqual(port, 8008)

        # complete the connection and wire it up to a fake transport
        protocol = factory.buildProtocol(None)
        transport = StringTransport()
        protocol.makeConnection(transport)

        # that should have made it send the request to the transport
        self.assertRegex(transport.value(), b"^GET /foo/bar")
        self.assertRegex(transport.value(), b"Host: testserv:8008")

        # Deferred is still without a result
        self.assertNoResult(test_d)

        # Send it a huge HTTP response
        protocol.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Server: Fake\r\n"
            b"Content-Type: application/json\r\n"
            b"\r\n"
        )

        self.pump()

        # should still be waiting
        self.assertNoResult(test_d)

        sent = 0
        chunk_size = 1024 * 512
        while not test_d.called:
            protocol.dataReceived(b"a" * chunk_size)
            sent += chunk_size
            self.assertLessEqual(sent, ByteParser.MAX_RESPONSE_SIZE)

        self.assertEqual(sent, ByteParser.MAX_RESPONSE_SIZE)

        f = self.failureResultOf(test_d)
        self.assertIsInstance(f.value, RequestSendFailed)

        self.assertTrue(transport.disconnecting)

    def test_build_auth_headers_rejects_falsey_destinations(self) -> None:
        with self.assertRaises(ValueError):
            self.cl.build_auth_headers(None, b"GET", b"https://example.com")
        with self.assertRaises(ValueError):
            self.cl.build_auth_headers(b"", b"GET", b"https://example.com")
        with self.assertRaises(ValueError):
            self.cl.build_auth_headers(
                None, b"GET", b"https://example.com", destination_is=b""
            )
        with self.assertRaises(ValueError):
            self.cl.build_auth_headers(
                b"", b"GET", b"https://example.com", destination_is=b""
            )

    @override_config(
        {
            "federation": {
                "client_timeout": "180s",
                "max_long_retry_delay": "100s",
                "max_short_retry_delay": "7s",
                "max_long_retries": 20,
                "max_short_retries": 5,
            }
        }
    )
    def test_configurable_retry_and_delay_values(self) -> None:
        self.assertEqual(self.cl.default_timeout_seconds, 180)
        self.assertEqual(self.cl.max_long_retry_delay_seconds, 100)
        self.assertEqual(self.cl.max_short_retry_delay_seconds, 7)
        self.assertEqual(self.cl.max_long_retries, 20)
        self.assertEqual(self.cl.max_short_retries, 5)


class FederationClientProxyTests(BaseMultiWorkerStreamTestCase):
    def default_config(self) -> Dict[str, Any]:
        conf = super().default_config()
        conf["instance_map"] = {
            "main": {"host": "testserv", "port": 8765},
            "federation_sender": {"host": "testserv", "port": 1001},
        }
        return conf

    @override_config({"outbound_federation_restricted_to": ["federation_sender"]})
    def test_proxy_requests_through_federation_sender_worker(self) -> None:
        """
        Test that all outbound federation requests go through the `federation_sender`
        worker
        """
        # Mock out the `MatrixFederationHttpClient` of the `federation_sender` instance
        # so we can act like some remote server responding to requests
        mock_client_on_federation_sender = Mock()
        mock_agent_on_federation_sender = create_autospec(Agent, spec_set=True)
        mock_client_on_federation_sender.agent = mock_agent_on_federation_sender

        # Create the `federation_sender` worker
        self.federation_sender = self.make_worker_hs(
            "synapse.app.generic_worker",
            {"worker_name": "federation_sender"},
            federation_http_client=mock_client_on_federation_sender,
        )

        # Fake `remoteserv:8008` responding to requests
        mock_agent_on_federation_sender.request.side_effect = (
            lambda *args, **kwargs: defer.succeed(
                FakeResponse.json(
                    payload={
                        "foo": "bar",
                    }
                )
            )
        )

        # This federation request from the main process should be proxied through the
        # `federation_sender` worker off to the remote server
        test_request_from_main_process_d = defer.ensureDeferred(
            self.hs.get_federation_http_client().get_json("remoteserv:8008", "foo/bar")
        )

        # Pump the reactor so our deferred goes through the motions
        self.pump()

        # Make sure that the request was proxied through the `federation_sender` worker
        mock_agent_on_federation_sender.request.assert_called_once_with(
            b"GET",
            b"matrix-federation://remoteserv:8008/foo/bar",
            headers=ANY,
            bodyProducer=ANY,
        )

        # Make sure the response is as expected back on the main worker
        res = self.successResultOf(test_request_from_main_process_d)
        self.assertEqual(res, {"foo": "bar"})

    @override_config({"outbound_federation_restricted_to": ["federation_sender"]})
    def test_proxy_request_with_network_error_through_federation_sender_worker(
        self,
    ) -> None:
        """
        Test that when the outbound federation request fails with a network related
        error, a sensible error makes its way back to the main process.
        """
        # Mock out the `MatrixFederationHttpClient` of the `federation_sender` instance
        # so we can act like some remote server responding to requests
        mock_client_on_federation_sender = Mock()
        mock_agent_on_federation_sender = create_autospec(Agent, spec_set=True)
        mock_client_on_federation_sender.agent = mock_agent_on_federation_sender

        # Create the `federation_sender` worker
        self.federation_sender = self.make_worker_hs(
            "synapse.app.generic_worker",
            {"worker_name": "federation_sender"},
            federation_http_client=mock_client_on_federation_sender,
        )

        # Fake `remoteserv:8008` responding to requests
        mock_agent_on_federation_sender.request.side_effect = (
            lambda *args, **kwargs: defer.fail(ResponseNeverReceived("fake error"))
        )

        # This federation request from the main process should be proxied through the
        # `federation_sender` worker off to the remote server
        test_request_from_main_process_d = defer.ensureDeferred(
            self.hs.get_federation_http_client().get_json("remoteserv:8008", "foo/bar")
        )

        # Pump the reactor so our deferred goes through the motions. We pump with 10
        # seconds (0.1 * 100) so the `MatrixFederationHttpClient` runs out of retries
        # and finally passes along the error response.
        self.pump(0.1)

        # Make sure that the request was proxied through the `federation_sender` worker
        mock_agent_on_federation_sender.request.assert_called_with(
            b"GET",
            b"matrix-federation://remoteserv:8008/foo/bar",
            headers=ANY,
            bodyProducer=ANY,
        )

        # Make sure we get some sort of error back on the main worker
        failure_res = self.failureResultOf(test_request_from_main_process_d)
        self.assertIsInstance(failure_res.value, RequestSendFailed)
        self.assertIsInstance(failure_res.value.inner_exception, HttpResponseException)

    @override_config({"outbound_federation_restricted_to": ["federation_sender"]})
    def test_proxy_requests_and_discards_hop_by_hop_headers(self) -> None:
        """
        Test to make sure hop-by-hop headers and addional headers defined in the
        `Connection` header are discarded when proxying requests
        """
        # Mock out the `MatrixFederationHttpClient` of the `federation_sender` instance
        # so we can act like some remote server responding to requests
        mock_client_on_federation_sender = Mock()
        mock_agent_on_federation_sender = create_autospec(Agent, spec_set=True)
        mock_client_on_federation_sender.agent = mock_agent_on_federation_sender

        # Create the `federation_sender` worker
        self.federation_sender = self.make_worker_hs(
            "synapse.app.generic_worker",
            {"worker_name": "federation_sender"},
            federation_http_client=mock_client_on_federation_sender,
        )

        # Fake `remoteserv:8008` responding to requests
        mock_agent_on_federation_sender.request.side_effect = lambda *args, **kwargs: defer.succeed(
            FakeResponse(
                code=200,
                body=b'{"foo": "bar"}',
                headers=Headers(
                    {
                        "Content-Type": ["application/json"],
                        "Connection": ["close, X-Foo, X-Bar"],
                        # Should be removed because it's defined in the `Connection` header
                        "X-Foo": ["foo"],
                        "X-Bar": ["bar"],
                        # Should be removed because it's a hop-by-hop header
                        "Proxy-Authorization": "abcdef",
                    }
                ),
            )
        )

        # This federation request from the main process should be proxied through the
        # `federation_sender` worker off to the remote server
        test_request_from_main_process_d = defer.ensureDeferred(
            self.hs.get_federation_http_client().get_json_with_headers(
                "remoteserv:8008", "foo/bar"
            )
        )

        # Pump the reactor so our deferred goes through the motions
        self.pump()

        # Make sure that the request was proxied through the `federation_sender` worker
        mock_agent_on_federation_sender.request.assert_called_once_with(
            b"GET",
            b"matrix-federation://remoteserv:8008/foo/bar",
            headers=ANY,
            bodyProducer=ANY,
        )

        res, headers = self.successResultOf(test_request_from_main_process_d)
        header_names = set(headers.keys())

        # Make sure the response does not include the hop-by-hop headers
        self.assertNotIn(b"X-Foo", header_names)
        self.assertNotIn(b"X-Bar", header_names)
        self.assertNotIn(b"Proxy-Authorization", header_names)
        # Make sure the response is as expected back on the main worker
        self.assertEqual(res, {"foo": "bar"})