Return some room data in Sliding Sync `/sync` (#17320)

 - Timeline events
 - Stripped `invite_state`

Based on [MSC3575](https://github.com/matrix-org/matrix-spec-proposals/pull/3575): Sliding Sync

1 files changed, 18 insertions, 0 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index b997d82d71..f937fd4698 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -836,3 +836,21 @@ def maybe_upsert_event_field(
             del container[key]
 
     return upsert_okay
+
+
+def strip_event(event: EventBase) -> JsonDict:
+    """
+    Used for "stripped state" events which provide a simplified view of the state of a
+    room intended to help a potential joiner identify the room (relevant when the user
+    is invited or knocked).
+
+    Stripped state events can only have the `sender`, `type`, `state_key` and `content`
+    properties present.
+    """
+
+    return {
+        "type": event.type,
+        "state_key": event.state_key,
+        "content": event.content,
+        "sender": event.sender,
+    }