Changelog

I can't see why erased senders makes a difference here?

changelog.d/15228.bugfix

@@ -0,0 +1 @@
+Temp changelog entry (TODO).

synapse/handlers/federation.py

@@ -392,7 +392,7 @@ class FederationHandler:
                 get_prev_content=False,
             )
 
-            # We set `check_history_visibility_only` as we might otherwise get false
+            # We unset `filter_out_erased_senders` as we might otherwise get false
             # positives from users having been erased.
             filtered_extremities = await filter_events_for_server(
                 self._storage_controllers,
@@ -400,7 +400,7 @@ class FederationHandler:
                 self.server_name,
                 events_to_check,
                 redact=False,
-                check_history_visibility_only=True,
+                filter_out_erased_senders=False,
             )
             if filtered_extremities:
                 extremities_to_request.append(bp.event_id)

synapse/visibility.py

@@ -14,7 +14,17 @@
 # limitations under the License.
 import logging
 from enum import Enum, auto
-from typing import Collection, Dict, FrozenSet, List, Optional, Tuple
+from typing import (
+    Collection,
+    Dict,
+    FrozenSet,
+    List,
+    Mapping,
+    Optional,
+    Sequence,
+    Set,
+    Tuple,
+)
 
 import attr
 from typing_extensions import Final
@@ -565,21 +575,32 @@ async def filter_events_for_server(
     storage: StorageControllers,
     target_server_name: str,
     local_server_name: str,
-    events: List[EventBase],
+    events: Sequence[EventBase],
     redact: bool = True,
-    check_history_visibility_only: bool = False,
+    filter_out_erased_senders: bool = True,
 ) -> List[EventBase]:
-    """Filter a list of events based on whether given server is allowed to
+    """Filter a list of events based on whether the target server is allowed to
     see them.
 
+    For a fully stated room, the target server is allowed to see an event E if:
+      - the state at E has world readable or shared history vis, OR
+      - the state at E says that the target server is in the room.
+
+    For a partially stated room, the target server is allowed to see E if:
+      - E was created by this homeserver, AND:
+          - the partial state at E has world readable or shared history vis, OR
+          - the partial state at E says that the target server is in the room.
+
+    TODO: state before or state after?
+
     Args:
         storage
-        server_name
+        target_server_name
+        local_server_name
         events
-        redact: Whether to return a redacted version of the event, or
-            to filter them out entirely.
-        check_history_visibility_only: Whether to only check the
-            history visibility, rather than things like if the sender has been
+        redact: Controls what to do with events which have been filtered out.
+            If True, include their redacted forms; if False, omit them entirely.
+        filter_out_erased_senders: If true, also filter out events whose sender has been
             erased. This is used e.g. during pagination to decide whether to
             backfill or not.
 
@@ -587,7 +608,7 @@ async def filter_events_for_server(
         The filtered events.
     """
 
-    def is_sender_erased(event: EventBase, erased_senders: Dict[str, bool]) -> bool:
+    def is_sender_erased(event: EventBase, erased_senders: Mapping[str, bool]) -> bool:
         if erased_senders and erased_senders[event.sender]:
             logger.info("Sender of %s has been erased, redacting", event.event_id)
             return True
@@ -616,7 +637,7 @@ async def filter_events_for_server(
         # server has no users in the room: redact
         return False
 
-    if not check_history_visibility_only:
+    if filter_out_erased_senders:
         erased_senders = await storage.main.are_users_erased(e.sender for e in events)
     else:
         # We don't want to check whether users are erased, which is equivalent
@@ -631,44 +652,49 @@ async def filter_events_for_server(
     # otherwise a room could be fully joined after we retrieve those, which would then bypass
     # this check but would base the filtering on an outdated view of the membership events.
 
-    partial_state_invisible_events = set()
-    if not check_history_visibility_only:
-        for e in events:
-            sender_domain = get_domain_from_id(e.sender)
-            if (
-                sender_domain != local_server_name
-                and await storage.main.is_partial_state_room(e.room_id)
-            ):
-                partial_state_invisible_events.add(e)
+    partial_state_invisible_event_ids: Set[str] = set()
+    maybe_visible_events: List[EventBase] = []
+    for e in events:
+        sender_domain = get_domain_from_id(e.sender)
+        if (
+            sender_domain != local_server_name
+            and await storage.main.is_partial_state_room(e.room_id)
+        ):
+            partial_state_invisible_event_ids.add(e.event_id)
+        else:
+            maybe_visible_events.append(e)
 
     # Let's check to see if all the events have a history visibility
     # of "shared" or "world_readable". If that's the case then we don't
     # need to check membership (as we know the server is in the room).
-    event_to_history_vis = await _event_to_history_vis(storage, events)
+    event_to_history_vis = await _event_to_history_vis(storage, maybe_visible_events)
 
     # for any with restricted vis, we also need the memberships
     event_to_memberships = await _event_to_memberships(
         storage,
         [
             e
-            for e in events
+            for e in maybe_visible_events
             if event_to_history_vis[e.event_id]
             not in (HistoryVisibility.SHARED, HistoryVisibility.WORLD_READABLE)
         ],
         target_server_name,
     )
 
-    to_return = []
-    for e in events:
+    def include_event_in_output(e: EventBase) -> bool:
+        if e.event_id in partial_state_invisible_event_ids:
+            return False
+
         erased = is_sender_erased(e, erased_senders)
         visible = check_event_is_visible(
             event_to_history_vis[e.event_id], event_to_memberships.get(e.event_id, {})
         )
 
-        if e in partial_state_invisible_events:
-            visible = False
+        return visible and not erased
 
-        if visible and not erased:
+    to_return = []
+    for e in events:
+        if include_event_in_output(e):
             to_return.append(e)
         elif redact:
             to_return.append(prune_event(e))

tests/federation/test_federation_catch_up.py

@@ -1,4 +1,5 @@
-from typing import Callable, List, Optional, Tuple
+from typing import Callable, Collection, List, Optional, Tuple
+from unittest import mock
 from unittest.mock import Mock
 
 from twisted.test.proto_helpers import MemoryReactor
@@ -500,3 +501,77 @@ class FederationCatchUpTestCases(FederatingHomeserverTestCase):
         self.assertEqual(len(sent_pdus), 1)
         self.assertEqual(sent_pdus[0].event_id, event_2.event_id)
         self.assertFalse(per_dest_queue._catching_up)
+
+    def test_catch_up_is_not_blocked_by_partial_state_room(self) -> None:
+        """Detects (part of?) https://github.com/matrix-org/synapse/issues/15220."""
+        # ARRANGE:
+        # - a local user (u1)
+        # - a room with which contains u1 and two remote users, @u2:host2 and @u3:other
+        # - events in that room such that
+        #   - history visibility is restricted
+        #   - u1 sent message events
+        #   - afterwards, u3 sent a remote event
+        # - catchup to begin for host2
+        per_dest_queue, sent_pdus = self.make_fake_destination_queue()
+
+        self.register_user("u1", "you the one")
+        u1_token = self.login("u1", "you the one")
+        room = self.helper.create_room_as("u1", tok=u1_token)
+        self.helper.send_state(
+            room_id=room,
+            event_type="m.room.history_visibility",
+            body={"history_visibility": "joined"},
+            tok=u1_token,
+        )
+        self.get_success(
+            event_injection.inject_member_event(self.hs, room, "@u2:host2", "join")
+        )
+        self.get_success(
+            event_injection.inject_member_event(self.hs, room, "@u3:other", "join")
+        )
+
+        # create some events
+        event_id_1 = self.helper.send(room, "hello", tok=u1_token)["event_id"]
+        event_id_2 = self.helper.send(room, "world", tok=u1_token)["event_id"]
+        # pretend that u3 changes their displayname
+        event_id_3 = self.get_success(
+            event_injection.inject_member_event(self.hs, room, "@u3:other", "join")
+        ).event_id
+
+        # destination_rooms should already be populated, but let us pretend that we already
+        # sent (successfully) up to and including event id 1
+        event_1 = self.get_success(self.hs.get_datastores().main.get_event(event_id_1))
+        assert event_1.internal_metadata.stream_ordering is not None
+        self.get_success(
+            self.hs.get_datastores().main.set_destination_last_successful_stream_ordering(
+                "host2", event_1.internal_metadata.stream_ordering
+            )
+        )
+
+        # Mock event 3 as having partial state
+        self.get_success(
+            event_injection.mark_event_as_partial_state(self.hs, event_id_3, room)
+        )
+
+        # Fail the test if we block on full state for event 3.
+        async def mock_await_full_state(event_ids: Collection[str]) -> None:
+            if event_id_3 in event_ids:
+                raise AssertionError("Tried to await full state for event_id_3")
+
+        # ACT
+        with mock.patch.object(
+            self.hs.get_storage_controllers().state._partial_state_events_tracker,
+            "await_full_state",
+            mock_await_full_state,
+        ):
+            self.get_success(per_dest_queue._catch_up_transmission_loop())
+
+        # ASSERT
+        # We should have:
+        # - not sent event 3: it's not ours, and the room is partial stated
+        # - fallen back to sending event 2: it's the most recent event in the room
+        #   we tried to send to host2
+        # - completed catch-up
+        self.assertEqual(len(sent_pdus), 1)
+        self.assertEqual(sent_pdus[0].event_id, event_id_2)
+        self.assertFalse(per_dest_queue._catching_up)

tests/test_utils/event_injection.py

@@ -102,3 +102,34 @@ async def create_event(
     context = await unpersisted_context.persist(event)
 
     return event, context
+
+
+async def mark_event_as_partial_state(
+    hs: synapse.server.HomeServer,
+    event_id: str,
+    room_id: str,
+) -> None:
+    """
+    (Falsely) mark an event as having partial state.
+
+    Naughty, but occasionally useful when checking that partial state doesn't
+    block something from happening.
+
+    If the event already has partial state, this insert will fail (event_id is unique
+    in this table).
+    """
+    store = hs.get_datastores().main
+    await store.db_pool.simple_upsert(
+        table="partial_state_rooms",
+        keyvalues={"room_id": room_id},
+        values={},
+        insertion_values={"room_id": room_id},
+    )
+
+    await store.db_pool.simple_insert(
+        table="partial_state_events",
+        values={
+            "room_id": room_id,
+            "event_id": event_id,
+        },
+    )