Sliding Sync: Exclude partially stated rooms if we must await full state (#17538)

Previously, we just had very basic partial room exclusion based on
whether we were lazy-loading room members. Now with this PR, we added
`must_await_full_state(...)` with rules to check if we have a we're only
requesting `required_state` which is completely satisfied even with
partial state.

Partially-stated rooms should have all state events except for remote
membership events so if we require a remote membership event anywhere,
then we need to return `True`.

changelog.d/17538.bugfix

@@ -0,0 +1 @@
+Better exclude partially stated rooms if we must await full state in experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint.

synapse/handlers/sliding_sync.py

@@ -24,6 +24,7 @@ from itertools import chain
 from typing import (
     TYPE_CHECKING,
     Any,
+    Callable,
     Dict,
     Final,
     List,
@@ -366,6 +367,73 @@ class RoomSyncConfig:
                     else:
                         self.required_state_map[state_type].add(state_key)
 
+    def must_await_full_state(
+        self,
+        is_mine_id: Callable[[str], bool],
+    ) -> bool:
+        """
+        Check if we have a we're only requesting `required_state` which is completely
+        satisfied even with partial state, then we don't need to `await_full_state` before
+        we can return it.
+
+        Also see `StateFilter.must_await_full_state(...)` for comparison
+
+        Partially-stated rooms should have all state events except for remote membership
+        events so if we require a remote membership event anywhere, then we need to
+        return `True` (requires full state).
+
+        Args:
+            is_mine_id: a callable which confirms if a given state_key matches a mxid
+               of a local user
+        """
+        wildcard_state_keys = self.required_state_map.get(StateValues.WILDCARD)
+        # Requesting *all* state in the room so we have to wait
+        if (
+            wildcard_state_keys is not None
+            and StateValues.WILDCARD in wildcard_state_keys
+        ):
+            return True
+
+        # If the wildcards don't refer to remote user IDs, then we don't need to wait
+        # for full state.
+        if wildcard_state_keys is not None:
+            for possible_user_id in wildcard_state_keys:
+                if not possible_user_id[0].startswith(UserID.SIGIL):
+                    # Not a user ID
+                    continue
+
+                localpart_hostname = possible_user_id.split(":", 1)
+                if len(localpart_hostname) < 2:
+                    # Not a user ID
+                    continue
+
+                if not is_mine_id(possible_user_id):
+                    return True
+
+        membership_state_keys = self.required_state_map.get(EventTypes.Member)
+        # We aren't requesting any membership events at all so the partial state will
+        # cover us.
+        if membership_state_keys is None:
+            return False
+
+        # If we're requesting entirely local users, the partial state will cover us.
+        for user_id in membership_state_keys:
+            if user_id == StateValues.ME:
+                continue
+            # We're lazy-loading membership so we can just return the state we have.
+            # Lazy-loading means we include membership for any event `sender` in the
+            # timeline but since we had to auth those timeline events, we will have the
+            # membership state for them (including from remote senders).
+            elif user_id == StateValues.LAZY:
+                continue
+            elif user_id == StateValues.WILDCARD:
+                return False
+            elif not is_mine_id(user_id):
+                return True
+
+        # Local users only so the partial state will cover us.
+        return False
+
 
 class StateValues:
     """
@@ -395,6 +463,7 @@ class SlidingSyncHandler:
         self.device_handler = hs.get_device_handler()
         self.push_rules_handler = hs.get_push_rules_handler()
         self.rooms_to_exclude_globally = hs.config.server.rooms_to_exclude_from_sync
+        self.is_mine_id = hs.is_mine_id
 
         self.connection_store = SlidingSyncConnectionStore()
 
@@ -575,19 +644,10 @@ class SlidingSyncHandler:
                     # Since creating the `RoomSyncConfig` takes some work, let's just do it
                     # once and make a copy whenever we need it.
                     room_sync_config = RoomSyncConfig.from_room_config(list_config)
-                    membership_state_keys = room_sync_config.required_state_map.get(
-                        EventTypes.Member
-                    )
-                    # Also see `StateFilter.must_await_full_state(...)` for comparison
-                    lazy_loading = (
-                        membership_state_keys is not None
-                        and StateValues.LAZY in membership_state_keys
-                    )
 
-                    if not lazy_loading:
+                    # Exclude partially-stated rooms if we must wait for the room to be
-                        # Exclude partially-stated rooms unless the `required_state`
+                    # fully-stated
-                        # only has `["m.room.member", "$LAZY"]` for membership
+                    if room_sync_config.must_await_full_state(self.is_mine_id):
-                        # (lazy-loading room members).
                         filtered_sync_room_map = {
                             room_id: room
                             for room_id, room in filtered_sync_room_map.items()
@@ -654,6 +714,12 @@ class SlidingSyncHandler:
         # Handle room subscriptions
         if has_room_subscriptions and sync_config.room_subscriptions is not None:
             with start_active_span("assemble_room_subscriptions"):
+                # Find which rooms are partially stated and may need to be filtered out
+                # depending on the `required_state` requested (see below).
+                partial_state_room_map = await self.store.is_partial_state_room_batched(
+                    sync_config.room_subscriptions.keys()
+                )
+
                 for (
                     room_id,
                     room_subscription,
@@ -677,12 +743,20 @@ class SlidingSyncHandler:
                     )
 
                     # Take the superset of the `RoomSyncConfig` for each room.
-                    #
-                    # Update our `relevant_room_map` with the room we're going to display
-                    # and need to fetch more info about.
                     room_sync_config = RoomSyncConfig.from_room_config(
                         room_subscription
                     )
+
+                    # Exclude partially-stated rooms if we must wait for the room to be
+                    # fully-stated
+                    if room_sync_config.must_await_full_state(self.is_mine_id):
+                        if partial_state_room_map.get(room_id):
+                            continue
+
+                    all_rooms.add(room_id)
+
+                    # Update our `relevant_room_map` with the room we're going to display
+                    # and need to fetch more info about.
                     existing_room_sync_config = relevant_room_map.get(room_id)
                     if existing_room_sync_config is not None:
                         existing_room_sync_config.combine_room_sync_config(

tests/rest/client/sliding_sync/test_rooms_required_state.py

@@ -631,8 +631,7 @@ class SlidingSyncRoomsRequiredStateTestCase(SlidingSyncBase):
 
     def test_rooms_required_state_partial_state(self) -> None:
         """
-        Test partially-stated room are excluded unless `rooms.required_state` is
+        Test partially-stated room are excluded if they require full state.
-        lazy-loading room members.
         """
         user1_id = self.register_user("user1", "pass")
         user1_tok = self.login(user1_id, "pass")
@@ -649,59 +648,195 @@ class SlidingSyncRoomsRequiredStateTestCase(SlidingSyncBase):
             mark_event_as_partial_state(self.hs, join_response2["event_id"], room_id2)
         )
 
-        # Make the Sliding Sync request (NOT lazy-loading room members)
+        # Make the Sliding Sync request with examples where `must_await_full_state()` is
+        # `False`
         sync_body = {
             "lists": {
-                "foo-list": {
+                "no-state-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 0,
+                },
+                "other-state-list": {
                     "ranges": [[0, 1]],
                     "required_state": [
                         [EventTypes.Create, ""],
                     ],
                     "timeline_limit": 0,
                 },
+                "lazy-load-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        [EventTypes.Create, ""],
+                        # Lazy-load room members
+                        [EventTypes.Member, StateValues.LAZY],
+                        # Local member
+                        [EventTypes.Member, user2_id],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "local-members-only-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        # Own user ID
+                        [EventTypes.Member, user1_id],
+                        # Local member
+                        [EventTypes.Member, user2_id],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "me-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        # Own user ID
+                        [EventTypes.Member, StateValues.ME],
+                        # Local member
+                        [EventTypes.Member, user2_id],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "wildcard-type-local-state-key-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        ["*", user1_id],
+                        # Not a user ID
+                        ["*", "foobarbaz"],
+                        # Not a user ID
+                        ["*", "foo.bar.baz"],
+                        # Not a user ID
+                        ["*", "@foo"],
+                    ],
+                    "timeline_limit": 0,
+                },
+            }
+        }
+        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+
+        # The list should include both rooms now because we don't need full state
+        for list_key in response_body["lists"].keys():
+            self.assertIncludes(
+                set(response_body["lists"][list_key]["ops"][0]["room_ids"]),
+                {room_id2, room_id1},
+                exact=True,
+                message=f"Expected all rooms to show up for list_key={list_key}. Response "
+                + str(response_body["lists"][list_key]),
+            )
+
+        # Take each of the list variants and apply them to room subscriptions to make
+        # sure the same rules apply
+        for list_key in sync_body["lists"].keys():
+            sync_body_for_subscriptions = {
+                "room_subscriptions": {
+                    room_id1: {
+                        "required_state": sync_body["lists"][list_key][
+                            "required_state"
+                        ],
+                        "timeline_limit": 0,
+                    },
+                    room_id2: {
+                        "required_state": sync_body["lists"][list_key][
+                            "required_state"
+                        ],
+                        "timeline_limit": 0,
+                    },
+                }
+            }
+            response_body, _ = self.do_sync(sync_body_for_subscriptions, tok=user1_tok)
+
+            self.assertIncludes(
+                set(response_body["rooms"].keys()),
+                {room_id2, room_id1},
+                exact=True,
+                message=f"Expected all rooms to show up for test_key={list_key}.",
+            )
+
+        # =====================================================================
+
+        # Make the Sliding Sync request with examples where `must_await_full_state()` is
+        # `True`
+        sync_body = {
+            "lists": {
+                "wildcard-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        ["*", "*"],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "wildcard-type-remote-state-key-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        ["*", "@some:remote"],
+                        # Not a user ID
+                        ["*", "foobarbaz"],
+                        # Not a user ID
+                        ["*", "foo.bar.baz"],
+                        # Not a user ID
+                        ["*", "@foo"],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "remote-member-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        # Own user ID
+                        [EventTypes.Member, user1_id],
+                        # Remote member
+                        [EventTypes.Member, "@some:remote"],
+                        # Local member
+                        [EventTypes.Member, user2_id],
+                    ],
+                    "timeline_limit": 0,
+                },
+                "lazy-but-remote-member-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [
+                        # Lazy-load room members
+                        [EventTypes.Member, StateValues.LAZY],
+                        # Remote member
+                        [EventTypes.Member, "@some:remote"],
+                    ],
+                    "timeline_limit": 0,
+                },
             }
         }
         response_body, _ = self.do_sync(sync_body, tok=user1_tok)
 
         # Make sure the list includes room1 but room2 is excluded because it's still
         # partially-stated
-        self.assertListEqual(
+        for list_key in response_body["lists"].keys():
-            list(response_body["lists"]["foo-list"]["ops"]),
+            self.assertIncludes(
-            [
+                set(response_body["lists"][list_key]["ops"][0]["room_ids"]),
-                {
+                {room_id1},
-                    "op": "SYNC",
+                exact=True,
-                    "range": [0, 1],
+                message=f"Expected only fully-stated rooms to show up for list_key={list_key}. Response "
-                    "room_ids": [room_id1],
+                + str(response_body["lists"][list_key]),
-                }
-            ],
-            response_body["lists"]["foo-list"],
             )
 
-        # Make the Sliding Sync request (with lazy-loading room members)
+        # Take each of the list variants and apply them to room subscriptions to make
-        sync_body = {
+        # sure the same rules apply
-            "lists": {
+        for list_key in sync_body["lists"].keys():
-                "foo-list": {
+            sync_body_for_subscriptions = {
-                    "ranges": [[0, 1]],
+                "room_subscriptions": {
-                    "required_state": [
+                    room_id1: {
-                        [EventTypes.Create, ""],
+                        "required_state": sync_body["lists"][list_key][
-                        # Lazy-load room members
+                            "required_state"
-                        [EventTypes.Member, StateValues.LAZY],
+                        ],
+                        "timeline_limit": 0,
+                    },
+                    room_id2: {
+                        "required_state": sync_body["lists"][list_key][
+                            "required_state"
                         ],
                         "timeline_limit": 0,
                     },
                 }
             }
-        response_body, _ = self.do_sync(sync_body, tok=user1_tok)
+            response_body, _ = self.do_sync(sync_body_for_subscriptions, tok=user1_tok)
 
-        # The list should include both rooms now because we're lazy-loading room members
+            self.assertIncludes(
-        self.assertListEqual(
+                set(response_body["rooms"].keys()),
-            list(response_body["lists"]["foo-list"]["ops"]),
+                {room_id1},
-            [
+                exact=True,
-                {
+                message=f"Expected only fully-stated rooms to show up for test_key={list_key}.",
-                    "op": "SYNC",
-                    "range": [0, 1],
-                    "room_ids": [room_id2, room_id1],
-                }
-            ],
-            response_body["lists"]["foo-list"],
             )