Re-introduce the outbound federation proxy (#15913)

Allow configuring the set of workers to proxy outbound federation traffic through (`outbound_federation_restricted_to`).

This is useful when you have a worker setup with `federation_sender` instances responsible for sending outbound federation requests and want to make sure *all* outbound federation traffic goes through those instances. Before this change, the generic workers would still contact federation themselves for things like profile lookups, backfill, etc. This PR allows you to set more strict access controls/firewall for all workers and only allow the `federation_sender`'s to contact the outside world.

tests/test_server.py

@@ -38,7 +38,7 @@ from tests.http.server._base import test_disconnect
 from tests.server import (
     FakeChannel,
     FakeSite,
-    ThreadedMemoryReactorClock,
+    get_clock,
     make_request,
     setup_test_homeserver,
 )
@@ -46,12 +46,11 @@ from tests.server import (
 
 class JsonResourceTests(unittest.TestCase):
     def setUp(self) -> None:
-        self.reactor = ThreadedMemoryReactorClock()
-        self.hs_clock = Clock(self.reactor)
+        reactor, clock = get_clock()
+        self.reactor = reactor
         self.homeserver = setup_test_homeserver(
             self.addCleanup,
-            federation_http_client=None,
-            clock=self.hs_clock,
+            clock=clock,
             reactor=self.reactor,
         )
 
@@ -209,7 +208,13 @@ class JsonResourceTests(unittest.TestCase):
 
 class OptionsResourceTests(unittest.TestCase):
     def setUp(self) -> None:
-        self.reactor = ThreadedMemoryReactorClock()
+        reactor, clock = get_clock()
+        self.reactor = reactor
+        self.homeserver = setup_test_homeserver(
+            self.addCleanup,
+            clock=clock,
+            reactor=self.reactor,
+        )
 
         class DummyResource(Resource):
             isLeaf = True
@@ -242,6 +247,7 @@ class OptionsResourceTests(unittest.TestCase):
             "1.0",
             max_request_body_size=4096,
             reactor=self.reactor,
+            hs=self.homeserver,
         )
 
         # render the request and return the channel
@@ -344,7 +350,8 @@ class WrapHtmlRequestHandlerTests(unittest.TestCase):
             await self.callback(request)
 
     def setUp(self) -> None:
-        self.reactor = ThreadedMemoryReactorClock()
+        reactor, _ = get_clock()
+        self.reactor = reactor
 
     def test_good_response(self) -> None:
         async def callback(request: SynapseRequest) -> None:
@@ -462,9 +469,9 @@ class DirectServeJsonResourceCancellationTests(unittest.TestCase):
     """Tests for `DirectServeJsonResource` cancellation."""
 
     def setUp(self) -> None:
-        self.reactor = ThreadedMemoryReactorClock()
-        self.clock = Clock(self.reactor)
-        self.resource = CancellableDirectServeJsonResource(self.clock)
+        reactor, clock = get_clock()
+        self.reactor = reactor
+        self.resource = CancellableDirectServeJsonResource(clock)
         self.site = FakeSite(self.resource, self.reactor)
 
     def test_cancellable_disconnect(self) -> None:
@@ -496,9 +503,9 @@ class DirectServeHtmlResourceCancellationTests(unittest.TestCase):
     """Tests for `DirectServeHtmlResource` cancellation."""
 
     def setUp(self) -> None:
-        self.reactor = ThreadedMemoryReactorClock()
-        self.clock = Clock(self.reactor)
-        self.resource = CancellableDirectServeHtmlResource(self.clock)
+        reactor, clock = get_clock()
+        self.reactor = reactor
+        self.resource = CancellableDirectServeHtmlResource(clock)
         self.site = FakeSite(self.resource, self.reactor)
 
     def test_cancellable_disconnect(self) -> None: