Sliding Sync: Reset forgotten status when membership changes (like rejoining a room) (#17835)

Reset `sliding_sync_membership_snapshots` -> `forgotten` status when
membership changes (like rejoining a room).

Fix https://github.com/element-hq/synapse/issues/17781

### What was the problem before?

Previously, if someone used `/forget` on one of their rooms, it would
update `sliding_sync_membership_snapshots` as expected but when someone
rejoined the room (or had any membership change), the upsert didn't
overwrite and reset the `forgotten` status so it remained `forgotten`
and invisible down the Sliding Sync endpoint.

changelog.d/17835.bugfix

@@ -0,0 +1 @@
+Fix a bug in [MSC4186](https://github.com/matrix-org/matrix-spec-proposals/pull/4186) Sliding Sync that would cause rooms to stay forgotten and hidden even after rejoining.

synapse/storage/databases/main/events.py

@@ -1863,10 +1863,10 @@ class PersistEventsStore:
             txn.execute_batch(
                 f"""
                 INSERT INTO sliding_sync_membership_snapshots
-                    (room_id, user_id, sender, membership_event_id, membership, event_stream_ordering, event_instance_name
+                    (room_id, user_id, sender, membership_event_id, membership, forgotten, event_stream_ordering, event_instance_name
                     {("," + ", ".join(sliding_sync_snapshot_keys)) if sliding_sync_snapshot_keys else ""})
                 VALUES (
-                    ?, ?, ?, ?, ?,
+                    ?, ?, ?, ?, ?, ?,
                     (SELECT stream_ordering FROM events WHERE event_id = ?),
                     (SELECT COALESCE(instance_name, 'master') FROM events WHERE event_id = ?)
                     {("," + ", ".join("?" for _ in sliding_sync_snapshot_values)) if sliding_sync_snapshot_values else ""}
@@ -1876,6 +1876,7 @@ class PersistEventsStore:
                     sender = EXCLUDED.sender,
                     membership_event_id = EXCLUDED.membership_event_id,
                     membership = EXCLUDED.membership,
+                    forgotten = EXCLUDED.forgotten,
                     event_stream_ordering = EXCLUDED.event_stream_ordering
                     {("," + ", ".join(f"{key} = EXCLUDED.{key}" for key in sliding_sync_snapshot_keys)) if sliding_sync_snapshot_keys else ""}
                 """,
@@ -1886,6 +1887,9 @@ class PersistEventsStore:
                         membership_info.sender,
                         membership_info.membership_event_id,
                         membership_info.membership,
+                        # Since this is a new membership, it isn't forgotten anymore (which
+                        # matches how Synapse currently thinks about the forgotten status)
+                        0,
                         # XXX: We do not use `membership_info.membership_event_stream_ordering` here
                         # because it is an unreliable value. See XXX note above.
                         membership_info.membership_event_id,
@@ -2901,6 +2905,9 @@ class PersistEventsStore:
                     "sender": event.sender,
                     "membership_event_id": event.event_id,
                     "membership": event.membership,
+                    # Since this is a new membership, it isn't forgotten anymore (which
+                    # matches how Synapse currently thinks about the forgotten status)
+                    "forgotten": 0,
                     "event_stream_ordering": event.internal_metadata.stream_ordering,
                     "event_instance_name": event.internal_metadata.instance_name,
                 }

synapse/storage/databases/main/events_bg_updates.py

@@ -304,6 +304,12 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
             _BackgroundUpdates.SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_BG_UPDATE,
             self._sliding_sync_membership_snapshots_bg_update,
         )
+        # Add a background update to fix data integrity issue in the
+        # `sliding_sync_membership_snapshots` -> `forgotten` column
+        self.db_pool.updates.register_background_update_handler(
+            _BackgroundUpdates.SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_FIX_FORGOTTEN_COLUMN_BG_UPDATE,
+            self._sliding_sync_membership_snapshots_fix_forgotten_column_bg_update,
+        )
 
         # We want this to run on the main database at startup before we start processing
         # events.
@@ -2429,6 +2435,118 @@ class EventsBackgroundUpdatesStore(StreamWorkerStore, StateDeltasStore, SQLBaseS
 
         return len(memberships_to_update_rows)
 
+    async def _sliding_sync_membership_snapshots_fix_forgotten_column_bg_update(
+        self, progress: JsonDict, batch_size: int
+    ) -> int:
+        """
+        Background update to update the `sliding_sync_membership_snapshots` ->
+        `forgotten` column to be in sync with the `room_memberships` table.
+
+        Because of previously flawed code (now fixed); any room that someone has
+        forgotten and subsequently re-joined or had any new membership on, we need to go
+        and update the column to match the `room_memberships` table as it has fallen out
+        of sync.
+        """
+        last_event_stream_ordering = progress.get(
+            "last_event_stream_ordering", -(1 << 31)
+        )
+
+        def _txn(
+            txn: LoggingTransaction,
+        ) -> int:
+            """
+            Returns:
+                The number of rows updated.
+            """
+
+            # To simplify things, we can just recheck any row in
+            # `sliding_sync_membership_snapshots` with `forgotten=1`
+            txn.execute(
+                """
+                SELECT
+                    s.room_id,
+                    s.user_id,
+                    s.membership_event_id,
+                    s.event_stream_ordering,
+                    m.forgotten
+                FROM sliding_sync_membership_snapshots AS s
+                INNER JOIN room_memberships AS m ON (s.membership_event_id = m.event_id)
+                WHERE s.event_stream_ordering > ?
+                    AND s.forgotten = 1
+                ORDER BY s.event_stream_ordering ASC
+                LIMIT ?
+                """,
+                (last_event_stream_ordering, batch_size),
+            )
+
+            memberships_to_update_rows = cast(
+                List[Tuple[str, str, str, int, int]],
+                txn.fetchall(),
+            )
+            if not memberships_to_update_rows:
+                return 0
+
+            # Assemble the values to update
+            #
+            # (room_id, user_id)
+            key_values: List[Tuple[str, str]] = []
+            # (forgotten,)
+            value_values: List[Tuple[int]] = []
+            for (
+                room_id,
+                user_id,
+                _membership_event_id,
+                _event_stream_ordering,
+                forgotten,
+            ) in memberships_to_update_rows:
+                key_values.append(
+                    (
+                        room_id,
+                        user_id,
+                    )
+                )
+                value_values.append((forgotten,))
+
+            # Update all of the rows in one go
+            self.db_pool.simple_update_many_txn(
+                txn,
+                table="sliding_sync_membership_snapshots",
+                key_names=("room_id", "user_id"),
+                key_values=key_values,
+                value_names=("forgotten",),
+                value_values=value_values,
+            )
+
+            # Update the progress
+            (
+                _room_id,
+                _user_id,
+                _membership_event_id,
+                event_stream_ordering,
+                _forgotten,
+            ) = memberships_to_update_rows[-1]
+            self.db_pool.updates._background_update_progress_txn(
+                txn,
+                _BackgroundUpdates.SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_FIX_FORGOTTEN_COLUMN_BG_UPDATE,
+                {
+                    "last_event_stream_ordering": event_stream_ordering,
+                },
+            )
+
+            return len(memberships_to_update_rows)
+
+        num_rows = await self.db_pool.runInteraction(
+            "_sliding_sync_membership_snapshots_fix_forgotten_column_bg_update",
+            _txn,
+        )
+
+        if not num_rows:
+            await self.db_pool.updates._end_background_update(
+                _BackgroundUpdates.SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_FIX_FORGOTTEN_COLUMN_BG_UPDATE
+            )
+
+        return num_rows
+
 
 def _resolve_stale_data_in_sliding_sync_tables(
     txn: LoggingTransaction,

synapse/storage/databases/main/roommember.py

@@ -1375,6 +1375,7 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
                 keyvalues={"user_id": user_id, "room_id": room_id},
                 updatevalues={"forgotten": 1},
             )
+            # Handle updating the `sliding_sync_membership_snapshots` table
             self.db_pool.simple_update_txn(
                 txn,
                 table="sliding_sync_membership_snapshots",

synapse/storage/schema/__init__.py

@@ -153,6 +153,8 @@ Changes in SCHEMA_VERSION = 87
 Changes in SCHEMA_VERSION = 88
     - MSC4140: Add `delayed_events` table that keeps track of events that are to
       be posted in response to a resettable timeout or an on-demand action.
+    - Add background update to fix data integrity issue in the
+      `sliding_sync_membership_snapshots` -> `forgotten` column
 """
 
 

synapse/storage/schema/main/delta/88/02_fix_sliding_sync_membership_snapshots_forgotten_column.sql

@@ -0,0 +1,21 @@
+--
+-- This file is licensed under the Affero General Public License (AGPL) version 3.
+--
+-- Copyright (C) 2024 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>.
+
+-- Add a background update to update the `sliding_sync_membership_snapshots` ->
+-- `forgotten` column to be in sync with the `room_memberships` table.
+--
+-- For any room that someone has forgotten and subsequently re-joined or had any new
+-- membership on, we need to go and update the column to match the `room_memberships`
+-- table as it has fallen out of sync.
+INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
+  (8802, 'sliding_sync_membership_snapshots_fix_forgotten_column_bg_update', '{}');

synapse/types/storage/__init__.py

@@ -45,3 +45,6 @@ class _BackgroundUpdates:
     SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_BG_UPDATE = (
         "sliding_sync_membership_snapshots_bg_update"
     )
+    SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_FIX_FORGOTTEN_COLUMN_BG_UPDATE = (
+        "sliding_sync_membership_snapshots_fix_forgotten_column_bg_update"
+    )

tests/rest/client/sliding_sync/test_sliding_sync.py

@@ -240,6 +240,7 @@ class SlidingSyncBase(unittest.HomeserverTestCase):
         self,
         invitee_user_id: str,
         unsigned_invite_room_state: Optional[List[StrippedStateEvent]],
+        invite_room_id: Optional[str] = None,
     ) -> str:
         """
         Create a fake invite for a remote room and persist it.
@@ -252,19 +253,23 @@ class SlidingSyncBase(unittest.HomeserverTestCase):
             invitee_user_id: The person being invited
             unsigned_invite_room_state: List of stripped state events to assist the
                 receiver in identifying the room.
+            invite_room_id: Optional remote room ID to be invited to. When unset, we
+                will generate one.
 
         Returns:
             The room ID of the remote invite room
         """
         store = self.hs.get_datastores().main
 
+        if invite_room_id is None:
             invite_room_id = f"!test_room{self._remote_invite_count}:remote_server"
 
         invite_event_dict = {
             "room_id": invite_room_id,
             "sender": "@inviter:remote_server",
             "state_key": invitee_user_id,
-            "depth": 1,
+            # Just keep advancing the depth
+            "depth": self._remote_invite_count,
             "origin_server_ts": 1,
             "type": EventTypes.Member,
             "content": {"membership": Membership.INVITE},
@@ -679,6 +684,112 @@ class SlidingSyncTestCase(SlidingSyncBase):
             exact=True,
         )
 
+    def test_rejoin_forgotten_room(self) -> None:
+        """
+        Make sure we can see a forgotten room again if we rejoin (or any new membership
+        like an invite) (no longer forgotten)
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # User1 joins the room
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            }
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+        # We should see the room (like normal)
+        self.assertIncludes(
+            set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+            {room_id},
+            exact=True,
+        )
+
+        # Leave and forget the room
+        self.helper.leave(room_id, user1_id, tok=user1_tok)
+        # User1 forgets the room
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # Re-join the room
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        # We should see the room again after re-joining
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+        self.assertIncludes(
+            set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+            {room_id},
+            exact=True,
+        )
+
+    def test_invited_to_forgotten_remote_room(self) -> None:
+        """
+        Make sure we can see a forgotten room again if we are invited again
+        (remote/federated out-of-band memberships)
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        # Create a remote room invite (out-of-band membership)
+        room_id = self._create_remote_invite_room_for_user(user1_id, None)
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 99]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                }
+            }
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+        # We should see the room (like normal)
+        self.assertIncludes(
+            set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+            {room_id},
+            exact=True,
+        )
+
+        # Leave and forget the room
+        self.helper.leave(room_id, user1_id, tok=user1_tok)
+        # User1 forgets the room
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # Get invited to the room again
+        # self.helper.join(room_id, user1_id, tok=user1_tok)
+        self._create_remote_invite_room_for_user(user1_id, None, invite_room_id=room_id)
+
+        # We should see the room again after re-joining
+        response_body, _ = self.do_sync(sync_body, since=from_token, tok=user1_tok)
+        self.assertIncludes(
+            set(response_body["lists"]["foo-list"]["ops"][0]["room_ids"]),
+            {room_id},
+            exact=True,
+        )
+
     def test_ignored_user_invites_initial_sync(self) -> None:
         """
         Make sure we ignore invites if they are from one of the `m.ignored_user_list` on

tests/rest/client/test_rooms.py

@@ -2894,6 +2894,68 @@ class RoomMembershipReasonTestCase(unittest.HomeserverTestCase):
         self.assertEqual(event_content.get("reason"), reason, channel.result)
 
 
+class RoomForgottenTestCase(unittest.HomeserverTestCase):
+    """
+    Test forget/forgotten rooms
+    """
+
+    servlets = [
+        synapse.rest.admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.store = hs.get_datastores().main
+
+    def test_room_not_forgotten_after_unban(self) -> None:
+        """
+        Test what happens when someone is banned from a room, they forget the room, and
+        some time later are unbanned.
+
+        Currently, when they are unbanned, the room isn't forgotten anymore which may or
+        may not be expected.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        # User1 is banned and forgets the room
+        self.helper.ban(room_id, src=user2_id, targ=user1_id, tok=user2_tok)
+        # User1 forgets the room
+        self.get_success(self.store.forget(user1_id, room_id))
+
+        # The room should show up as forgotten
+        forgotten_room_ids = self.get_success(
+            self.store.get_forgotten_rooms_for_user(user1_id)
+        )
+        self.assertIncludes(forgotten_room_ids, {room_id}, exact=True)
+
+        # Unban user1
+        self.helper.change_membership(
+            room=room_id,
+            src=user2_id,
+            targ=user1_id,
+            membership=Membership.LEAVE,
+            tok=user2_tok,
+        )
+
+        # Room is no longer forgotten because it's a new membership
+        #
+        # XXX: Is this how we actually want it to behave? It seems like ideally, the
+        # room forgotten status should only be reset when the user decides to join again
+        # (or is invited/knocks). This way the room remains forgotten for any ban/leave
+        # transitions.
+        forgotten_room_ids = self.get_success(
+            self.store.get_forgotten_rooms_for_user(user1_id)
+        )
+        self.assertIncludes(forgotten_room_ids, set(), exact=True)
+
+
 class LabelsTestCase(unittest.HomeserverTestCase):
     servlets = [
         synapse.rest.admin.register_servlets_for_client_rest_resource,

tests/storage/test_sliding_sync_tables.py

@@ -5014,3 +5014,106 @@ class SlidingSyncTablesCatchUpBackgroundUpdatesTestCase(SlidingSyncTablesTestCas
             },
             exact=True,
         )
+
+
+class SlidingSyncMembershipSnapshotsTableFixForgottenColumnBackgroundUpdatesTestCase(
+    SlidingSyncTablesTestCaseBase
+):
+    """
+    Test the background updates that fixes `sliding_sync_membership_snapshots` ->
+    `forgotten` column.
+    """
+
+    def test_membership_snapshots_fix_forgotten_column_background_update(self) -> None:
+        """
+        Test that the background update, updates the `sliding_sync_membership_snapshots`
+        -> `forgotten` column to be in sync with the `room_memberships` table.
+        """
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+        user2_id = self.register_user("user2", "pass")
+        user2_tok = self.login(user2_id, "pass")
+
+        room_id = self.helper.create_room_as(user2_id, tok=user2_tok, is_public=True)
+        # User1 joins the room
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        # Leave and forget the room
+        self.helper.leave(room_id, user1_id, tok=user1_tok)
+        # User1 forgets the room
+        channel = self.make_request(
+            "POST",
+            f"/_matrix/client/r0/rooms/{room_id}/forget",
+            content={},
+            access_token=user1_tok,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+
+        # Re-join the room
+        self.helper.join(room_id, user1_id, tok=user1_tok)
+
+        # Reset `sliding_sync_membership_snapshots` table as if the `forgotten` column
+        # got out of sync from the `room_memberships` table from the previous flawed
+        # code.
+        self.get_success(
+            self.store.db_pool.simple_update_one(
+                table="sliding_sync_membership_snapshots",
+                keyvalues={"room_id": room_id, "user_id": user1_id},
+                updatevalues={"forgotten": 1},
+                desc="sliding_sync_membership_snapshots.test_membership_snapshots_fix_forgotten_column_background_update",
+            )
+        )
+
+        # Insert and run the background update.
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                {
+                    "update_name": _BackgroundUpdates.SLIDING_SYNC_MEMBERSHIP_SNAPSHOTS_FIX_FORGOTTEN_COLUMN_BG_UPDATE,
+                    "progress_json": "{}",
+                },
+            )
+        )
+        self.store.db_pool.updates._all_done = False
+        self.wait_for_background_updates()
+
+        # Make sure the table is populated
+
+        sliding_sync_membership_snapshots_results = (
+            self._get_sliding_sync_membership_snapshots()
+        )
+        self.assertIncludes(
+            set(sliding_sync_membership_snapshots_results.keys()),
+            {
+                (room_id, user1_id),
+                (room_id, user2_id),
+            },
+            exact=True,
+        )
+        state_map = self.get_success(
+            self.storage_controllers.state.get_current_state(room_id)
+        )
+        # Holds the info according to the current state when the user joined.
+        #
+        # We only care about checking on user1 as that's what we reset and expect to be
+        # correct now
+        self.assertEqual(
+            sliding_sync_membership_snapshots_results.get((room_id, user1_id)),
+            _SlidingSyncMembershipSnapshotResult(
+                room_id=room_id,
+                user_id=user1_id,
+                sender=user1_id,
+                membership_event_id=state_map[(EventTypes.Member, user1_id)].event_id,
+                membership=Membership.JOIN,
+                event_stream_ordering=state_map[
+                    (EventTypes.Member, user1_id)
+                ].internal_metadata.stream_ordering,
+                has_known_state=True,
+                room_type=None,
+                room_name=None,
+                is_encrypted=False,
+                tombstone_successor_room_id=None,
+                # We should see the room as no longer forgotten
+                forgotten=False,
+            ),
+        )