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](https://github.com/matrix-org/matrix-spec-proposals/pull/3575):
Sliding Sync

Follow-up to https://github.com/element-hq/synapse/pull/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.

1 files changed, 28 insertions, 1 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index f937fd4698..54f94add4d 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -49,7 +49,7 @@ from synapse.api.errors import Codes, SynapseError
 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