Sliding Sync: Update filters to be robust against remote invite rooms (#17450)

Update `filters.is_encrypted` and `filters.types`/`filters.not_types` to
be robust when dealing with remote invite rooms in Sliding Sync.

Part of
[MSC3575](matrix-org/matrix-spec-proposals#3575):
Sliding Sync

Follow-up to #17434

We now take into account current state, fallback to stripped state
for invite/knock rooms, then historical state. If we can't determine
the info needed to filter a room (either from state or stripped state),
it is filtered out.

Author: MadLittleMods

changelog.d/17450.bugfix

@@ -0,0 +1 @@
+Update experimental [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575) Sliding Sync `/sync` endpoint to handle invite/knock rooms when filtering.

synapse/api/constants.py

@@ -225,6 +225,11 @@ class EventContentFields:
     # This is deprecated in MSC2175.
     ROOM_CREATOR: Final = "creator"
 
+    # The version of the room for `m.room.create` events.
+    ROOM_VERSION: Final = "room_version"
+
+    ROOM_NAME: Final = "name"
+
     # Used in m.room.guest_access events.
     GUEST_ACCESS: Final = "guest_access"
 
@@ -237,6 +242,9 @@ class EventContentFields:
     # an unspecced field added to to-device messages to identify them uniquely-ish
     TO_DEVICE_MSGID: Final = "org.matrix.msgid"
 
+    # `m.room.encryption`` algorithm field
+    ENCRYPTION_ALGORITHM: Final = "algorithm"
+
 
 class EventUnsignedContentFields:
     """Fields found inside the 'unsigned' data on events"""

synapse/events/__init__.py

@@ -554,3 +554,22 @@ def relation_from_event(event: EventBase) -> Optional[_EventRelation]:
             aggregation_key = None
 
     return _EventRelation(parent_id, rel_type, aggregation_key)
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class StrippedStateEvent:
+    """
+    A stripped down state event. Usually used for remote invite/knocks so the user can
+    make an informed decision on whether they want to join.
+
+    Attributes:
+        type: Event `type`
+        state_key: Event `state_key`
+        sender: Event `sender`
+        content: Event `content`
+    """
+
+    type: str
+    state_key: str
+    sender: str
+    content: Dict[str, Any]

synapse/events/utils.py

@@ -49,7 +49,7 @@
 from synapse.api.room_versions import RoomVersion
 from synapse.types import JsonDict, Requester
 
-from . import EventBase, make_event_from_dict
+from . import EventBase, StrippedStateEvent, make_event_from_dict
 
 if TYPE_CHECKING:
     from synapse.handlers.relations import BundledAggregations
@@ -854,3 +854,30 @@ def strip_event(event: EventBase) -> JsonDict:
         "content": event.content,
         "sender": event.sender,
     }
+
+
+def parse_stripped_state_event(raw_stripped_event: Any) -> Optional[StrippedStateEvent]:
+    """
+    Given a raw value from an event's `unsigned` field, attempt to parse it into a
+    `StrippedStateEvent`.
+    """
+    if isinstance(raw_stripped_event, dict):
+        # All of these fields are required
+        type = raw_stripped_event.get("type")
+        state_key = raw_stripped_event.get("state_key")
+        sender = raw_stripped_event.get("sender")
+        content = raw_stripped_event.get("content")
+        if (
+            isinstance(type, str)
+            and isinstance(state_key, str)
+            and isinstance(sender, str)
+            and isinstance(content, dict)
+        ):
+            return StrippedStateEvent(
+                type=type,
+                state_key=state_key,
+                sender=sender,
+                content=content,
+            )
+
+    return None