Rip out auth-event reconciliation code (#12943)

There is a corner in `_check_event_auth` (long known as "the weird corner") where, if we get an event with auth_events which don't match those we were expecting, we attempt to resolve the diffence between our state and the remote's with a state resolution.

This isn't specced, and there's general agreement we shouldn't be doing it.

However, it turns out that the faster-joins code was relying on it, so we need to introduce something similar (but rather simpler) for that.

3 files changed, 5 insertions, 154 deletions

diff --git a/tests/handlers/test_federation.py b/tests/handlers/test_federation.py
index 712933f9ca..8a0bb91f40 100644
--- a/tests/handlers/test_federation.py
+++ b/tests/handlers/test_federation.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import List, cast
+from typing import cast
 from unittest import TestCase
 
 from twisted.test.proto_helpers import MemoryReactor
@@ -50,8 +50,6 @@ class FederationTestCase(unittest.FederatingHomeserverTestCase):
         hs = self.setup_test_homeserver(federation_http_client=None)
         self.handler = hs.get_federation_handler()
         self.store = hs.get_datastores().main
-        self.state_storage_controller = hs.get_storage_controllers().state
-        self._event_auth_handler = hs.get_event_auth_handler()
         return hs
 
     def test_exchange_revoked_invite(self) -> None:
@@ -314,142 +312,6 @@ class FederationTestCase(unittest.FederatingHomeserverTestCase):
             )
         self.get_success(d)
 
-    def test_backfill_floating_outlier_membership_auth(self) -> None:
-        """
-        As the local homeserver, check that we can properly process a federated
-        event from the OTHER_SERVER with auth_events that include a floating
-        membership event from the OTHER_SERVER.
-
-        Regression test, see #10439.
-        """
-        OTHER_SERVER = "otherserver"
-        OTHER_USER = "@otheruser:" + OTHER_SERVER
-
-        # create the room
-        user_id = self.register_user("kermit", "test")
-        tok = self.login("kermit", "test")
-        room_id = self.helper.create_room_as(
-            room_creator=user_id,
-            is_public=True,
-            tok=tok,
-            extra_content={
-                "preset": "public_chat",
-            },
-        )
-        room_version = self.get_success(self.store.get_room_version(room_id))
-
-        prev_event_ids = self.get_success(self.store.get_prev_events_for_room(room_id))
-        (
-            most_recent_prev_event_id,
-            most_recent_prev_event_depth,
-        ) = self.get_success(self.store.get_max_depth_of(prev_event_ids))
-        # mapping from (type, state_key) -> state_event_id
-        assert most_recent_prev_event_id is not None
-        prev_state_map = self.get_success(
-            self.state_storage_controller.get_state_ids_for_event(
-                most_recent_prev_event_id
-            )
-        )
-        # List of state event ID's
-        prev_state_ids = list(prev_state_map.values())
-        auth_event_ids = prev_state_ids
-        auth_events = list(
-            self.get_success(self.store.get_events(auth_event_ids)).values()
-        )
-
-        # build a floating outlier member state event
-        fake_prev_event_id = "$" + random_string(43)
-        member_event_dict = {
-            "type": EventTypes.Member,
-            "content": {
-                "membership": "join",
-            },
-            "state_key": OTHER_USER,
-            "room_id": room_id,
-            "sender": OTHER_USER,
-            "depth": most_recent_prev_event_depth,
-            "prev_events": [fake_prev_event_id],
-            "origin_server_ts": self.clock.time_msec(),
-            "signatures": {OTHER_SERVER: {"ed25519:key_version": "SomeSignatureHere"}},
-        }
-        builder = self.hs.get_event_builder_factory().for_room_version(
-            room_version, member_event_dict
-        )
-        member_event = self.get_success(
-            builder.build(
-                prev_event_ids=member_event_dict["prev_events"],
-                auth_event_ids=self._event_auth_handler.compute_auth_events(
-                    builder,
-                    prev_state_map,
-                    for_verification=False,
-                ),
-                depth=member_event_dict["depth"],
-            )
-        )
-        # Override the signature added from "test" homeserver that we created the event with
-        member_event.signatures = member_event_dict["signatures"]
-
-        # Add the new member_event to the StateMap
-        updated_state_map = dict(prev_state_map)
-        updated_state_map[
-            (member_event.type, member_event.state_key)
-        ] = member_event.event_id
-        auth_events.append(member_event)
-
-        # build and send an event authed based on the member event
-        message_event_dict = {
-            "type": EventTypes.Message,
-            "content": {},
-            "room_id": room_id,
-            "sender": OTHER_USER,
-            "depth": most_recent_prev_event_depth,
-            "prev_events": prev_event_ids.copy(),
-            "origin_server_ts": self.clock.time_msec(),
-            "signatures": {OTHER_SERVER: {"ed25519:key_version": "SomeSignatureHere"}},
-        }
-        builder = self.hs.get_event_builder_factory().for_room_version(
-            room_version, message_event_dict
-        )
-        message_event = self.get_success(
-            builder.build(
-                prev_event_ids=message_event_dict["prev_events"],
-                auth_event_ids=self._event_auth_handler.compute_auth_events(
-                    builder,
-                    updated_state_map,
-                    for_verification=False,
-                ),
-                depth=message_event_dict["depth"],
-            )
-        )
-        # Override the signature added from "test" homeserver that we created the event with
-        message_event.signatures = message_event_dict["signatures"]
-
-        # Stub the /event_auth response from the OTHER_SERVER
-        async def get_event_auth(
-            destination: str, room_id: str, event_id: str
-        ) -> List[EventBase]:
-            return [
-                event_from_pdu_json(ae.get_pdu_json(), room_version=room_version)
-                for ae in auth_events
-            ]
-
-        self.handler.federation_client.get_event_auth = get_event_auth  # type: ignore[assignment]
-
-        with LoggingContext("receive_pdu"):
-            # Fake the OTHER_SERVER federating the message event over to our local homeserver
-            d = run_in_background(
-                self.hs.get_federation_event_handler().on_receive_pdu,
-                OTHER_SERVER,
-                message_event,
-            )
-        self.get_success(d)
-
-        # Now try and get the events on our local homeserver
-        stored_event = self.get_success(
-            self.store.get_event(message_event.event_id, allow_none=True)
-        )
-        self.assertTrue(stored_event is not None)
-
     @unittest.override_config(
         {"rc_invites": {"per_user": {"per_second": 0.5, "burst_count": 3}}}
     )
diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py
index 5eb0f243f7..9a48e9286f 100644
--- a/tests/rest/client/test_third_party_rules.py
+++ b/tests/rest/client/test_third_party_rules.py
@@ -21,7 +21,6 @@ from synapse.api.constants import EventTypes, LoginType, Membership
 from synapse.api.errors import SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.events import EventBase
-from synapse.events.snapshot import EventContext
 from synapse.events.third_party_rules import load_legacy_third_party_event_rules
 from synapse.rest import admin
 from synapse.rest.client import account, login, profile, room
@@ -113,14 +112,8 @@ class ThirdPartyRulesTestCase(unittest.FederatingHomeserverTestCase):
 
         # Have this homeserver skip event auth checks. This is necessary due to
         # event auth checks ensuring that events were signed by the sender's homeserver.
-        async def _check_event_auth(
-            origin: str,
-            event: EventBase,
-            context: EventContext,
-            *args: Any,
-            **kwargs: Any,
-        ) -> EventContext:
-            return context
+        async def _check_event_auth(origin: Any, event: Any, context: Any) -> None:
+            pass
 
         hs.get_federation_event_handler()._check_event_auth = _check_event_auth  # type: ignore[assignment]
 
diff --git a/tests/test_federation.py b/tests/test_federation.py
index 0cbef70bfa..779fad1f63 100644
--- a/tests/test_federation.py
+++ b/tests/test_federation.py
@@ -81,12 +81,8 @@ class MessageAcceptTests(unittest.HomeserverTestCase):
         self.handler = self.homeserver.get_federation_handler()
         federation_event_handler = self.homeserver.get_federation_event_handler()
 
-        async def _check_event_auth(
-            origin,
-            event,
-            context,
-        ):
-            return context
+        async def _check_event_auth(origin, event, context):
+            pass
 
         federation_event_handler._check_event_auth = _check_event_auth
         self.client = self.homeserver.get_federation_client()