synapse/tests/http/test_matrixfederationclient.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]
#
#
import io
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.internet.testing 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.api.ratelimiting import Ratelimiter
from synapse.config._base import ConfigError
from synapse.config.ratelimiting import RatelimitSettings
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.clock 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[Any]", object, object]:
            with LoggingContext(
                name="one",
                server_name=self.hs.hostname,
            ) 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)

    def test_authed_media_redirect_response(self) -> None:
        """
        Validate that, when following a `Location` redirect, the
        maximum size is _not_ set to the initial response `Content-Length` and
        the media file can be downloaded.
        """
        limiter = Ratelimiter(
            store=self.hs.get_datastores().main,
            clock=self.clock,
            cfg=RatelimitSettings(key="", per_second=0.17, burst_count=1048576),
        )

        output_stream = io.BytesIO()

        d = defer.ensureDeferred(
            self.cl.federation_get_file(
                "testserv:8008", "path", output_stream, limiter, "127.0.0.1", 10000
            )
        )

        self.pump()

        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)

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

        redirect_data = b"\r\n\r\n--6067d4698f8d40a0a794ea7d7379d53a\r\nContent-Type: application/json\r\n\r\n{}\r\n--6067d4698f8d40a0a794ea7d7379d53a\r\nLocation: http://testserv:8008/ab/c1/2345.txt\r\n\r\n--6067d4698f8d40a0a794ea7d7379d53a--\r\n\r\n"
        protocol.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Server: Fake\r\n"
            b"Content-Length: %i\r\n"
            b"Content-Type: multipart/mixed; boundary=6067d4698f8d40a0a794ea7d7379d53a\r\n\r\n"
            % (len(redirect_data))
        )
        protocol.dataReceived(redirect_data)

        # Still no result, not followed the redirect yet
        self.assertNoResult(d)

        # Now send the response returned by the server at `Location`
        clients = self.reactor.tcpClients
        (host, port, factory, _timeout, _bindAddress) = clients[1]
        self.assertEqual(host, "1.2.3.4")
        self.assertEqual(port, 8008)
        protocol = factory.buildProtocol(None)
        transport = StringTransport()
        protocol.makeConnection(transport)

        # make sure the length is longer than the initial response
        data = b"Hello world!" * 30
        protocol.dataReceived(
            b"HTTP/1.1 200 OK\r\n"
            b"Server: Fake\r\n"
            b"Content-Length: %i\r\n"
            b"Content-Type: text/plain\r\n"
            b"\r\n"
            b"%s\r\n"
            b"\r\n" % (len(data), data)
        )

        # We should get a successful response
        length, _, _ = self.successResultOf(d)
        self.assertEqual(length, len(data))
        self.assertEqual(output_stream.getvalue(), data)

    @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\nServer: 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
        https://github.com/matrix-org/synapse/issues/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\nServer: Fake\r\nContent-Type: application/json\r\n\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"],
            "worker_replication_secret": "secret",
        }
    )
    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.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"],
            "worker_replication_secret": "secret",
        }
    )
    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.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)
        self.assertEqual(failure_res.value.inner_exception.code, 502)

    @override_config(
        {
            "outbound_federation_restricted_to": ["federation_sender"],
            "worker_replication_secret": "secret",
        }
    )
    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.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"],
                            "X-Test": ["test"],
                            # Define some hop-by-hop headers (try with varying casing to
                            # make sure we still match-up the headers)
                            "Connection": ["close, X-fOo, X-Bar, X-baz"],
                            # Should be removed because it's defined in the `Connection` header
                            "X-Foo": ["foo"],
                            "X-Bar": ["bar"],
                            # (not in canonical case)
                            "x-baZ": ["baz"],
                            # Should be removed because it's a hop-by-hop header
                            "Proxy-Authorization": "abcdef",
                            # Should be removed because it's a hop-by-hop header (not in canonical case)
                            "transfer-EnCoDiNg": "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.assertIncludes(
            header_names,
            {
                b"Content-Type",
                b"X-Test",
                # Default headers from Twisted
                b"Date",
                b"Server",
            },
            exact=True,
        )
        # Make sure the response is as expected back on the main worker
        self.assertEqual(res, {"foo": "bar"})

    @override_config(
        {
            "outbound_federation_restricted_to": ["federation_sender"],
            # `worker_replication_secret` is set here so that the test setup is able to pass
            # but the actual homserver creation test is in the test body below
            "worker_replication_secret": "secret",
        }
    )
    def test_not_able_to_proxy_requests_through_federation_sender_worker_when_no_secret_configured(
        self,
    ) -> None:
        """
        Test that we aren't able to proxy any outbound federation requests when
        `worker_replication_secret` is not configured.
        """
        with self.assertRaises(ConfigError):
            # Create the `federation_sender` worker
            self.make_worker_hs(
                "synapse.app.generic_worker",
                {
                    "worker_name": "federation_sender",
                    # Test that we aren't able to proxy any outbound federation requests
                    # when `worker_replication_secret` is not configured.
                    "worker_replication_secret": None,
                },
            )

    @override_config(
        {
            "outbound_federation_restricted_to": ["federation_sender"],
            "worker_replication_secret": "secret",
        }
    )
    def test_not_able_to_proxy_requests_through_federation_sender_worker_when_wrong_auth_given(
        self,
    ) -> None:
        """
        Test that we aren't able to proxy any outbound federation requests when the
        wrong authorization is given.
        """
        # 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.make_worker_hs(
            "synapse.app.generic_worker",
            {
                "worker_name": "federation_sender",
                # Test that we aren't able to proxy any outbound federation requests
                # when `worker_replication_secret` is wrong.
                "worker_replication_secret": "wrong",
            },
            federation_http_client=mock_client_on_federation_sender,
        )

        # This federation request from the main process should be proxied through the
        # `federation_sender` worker off but will fail here because it's using the wrong
        # authorization.
        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 *NOT* proxied through the `federation_sender`
        # worker
        mock_agent_on_federation_sender.request.assert_not_called()

        failure_res = self.failureResultOf(test_request_from_main_process_d)
        self.assertIsInstance(failure_res.value, HttpResponseException)
        self.assertEqual(failure_res.value.code, 401)