Use PDUs for stripped state over federation

As per MSC4311 updates.

synapse/events/utils.py

@@ -870,7 +870,7 @@ def maybe_upsert_event_field(
     return upsert_okay
 
 
-def strip_event(event: EventBase) -> JsonDict:
+def strip_event(event: EventBase, for_federation: Optional[bool] = False) -> 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
@@ -879,13 +879,10 @@ def strip_event(event: EventBase) -> JsonDict:
     Stripped state events can only have the `sender`, `type`, `state_key` and `content`
     properties present.
     """
-    # MSC4311: Ensure the create event is available on invites and knocks.
-    # TODO: Implement the rest of MSC4311
-    if (
-        event.room_version.msc4291_room_ids_as_hashes
-        and event.type == EventTypes.Create
-        and event.get_state_key() == ""
-    ):
+    # MSC4311 makes all stripped state events fully-formed PDUs over federation,
+    # especially the `m.room.create` event.
+    # TODO: Implement the validation component of MSC4311
+    if for_federation:
         return event.get_pdu_json()
 
     return {

synapse/federation/federation_client.py

@@ -1336,10 +1336,16 @@ class FederationClient(FederationBase):
         room_id: str,
         event_id: str,
         pdu: EventBase,
+        stripped_state: List[JsonDict],
     ) -> EventBase:
         room_version = await self.store.get_room_version(room_id)
 
-        content = await self._do_send_invite(destination, pdu, room_version)
+        content = await self._do_send_invite(
+            destination,
+            pdu,
+            room_version,
+            stripped_state,
+        )
 
         pdu_dict = content["event"]
 
@@ -1360,7 +1366,11 @@ class FederationClient(FederationBase):
         return pdu
 
     async def _do_send_invite(
-        self, destination: str, pdu: EventBase, room_version: RoomVersion
+        self,
+        destination: str,
+        pdu: EventBase,
+        room_version: RoomVersion,
+        stripped_state: List[JsonDict],
     ) -> JsonDict:
         """Actually sends the invite, first trying v2 API and falling back to
         v1 API if necessary.
@@ -1383,7 +1393,7 @@ class FederationClient(FederationBase):
                 content={
                     "event": pdu.get_pdu_json(time_now),
                     "room_version": room_version.identifier,
-                    "invite_room_state": pdu.unsigned.get("invite_room_state", []),
+                    "invite_room_state": stripped_state,
                 },
             )
         except HttpResponseException as e:

synapse/federation/federation_server.py

@@ -907,7 +907,7 @@ class FederationServer(FederationBase):
         # related to the room while the knock request is pending.
         stripped_room_state = (
             await self.store.get_stripped_room_state_from_event_context(
-                context, self._room_prejoin_state_types
+                context, self._room_prejoin_state_types, for_federation=True,
             )
         )
         return {"knock_room_state": stripped_room_state}

synapse/handlers/federation.py

@@ -547,7 +547,7 @@ class FederationHandler:
 
         return False
 
-    async def send_invite(self, target_host: str, event: EventBase) -> EventBase:
+    async def send_invite(self, target_host: str, event: EventBase, stripped_state: List[JsonDict]) -> EventBase:
         """Sends the invite to the remote server for signing.
 
         Invites must be signed by the invitee's server before distribution.
@@ -558,6 +558,7 @@ class FederationHandler:
                 room_id=event.room_id,
                 event_id=event.event_id,
                 pdu=event,
+                stripped_state=stripped_state,
             )
         except RequestSendFailed:
             raise SynapseError(502, f"Can't connect to server {target_host}")

synapse/handlers/message.py

@@ -1973,8 +1973,17 @@ class EventCreationHandler:
                         # way? If we have been invited by a remote server, we need
                         # to get them to sign the event.
 
+                        # As of MSC4311, "stripped" state events are formatted differently
+                        # over federation.
+                        stripped_state_fed = await self.store.get_stripped_room_state_from_event_context(
+                            context,
+                            self.room_prejoin_state_types,
+                            membership_user_id=event.sender,
+                            for_federation=True,
+                        )
+
                         returned_invite = await federation_handler.send_invite(
-                            invitee.domain, event
+                            invitee.domain, event, stripped_state_fed,
                         )
                         event.unsigned.pop("room_state", None)
 

synapse/storage/databases/main/events_worker.py

@@ -1094,6 +1094,7 @@ class EventsWorkerStore(SQLBaseStore):
         context: EventContext,
         state_keys_to_include: StateFilter,
         membership_user_id: Optional[str] = None,
+        for_federation: Optional[bool] = False,
     ) -> List[JsonDict]:
         """
         Retrieve the stripped state from a room, given an event context to retrieve state
@@ -1110,6 +1111,8 @@ class EventsWorkerStore(SQLBaseStore):
                 events of. This is useful when generating the stripped state of a room for
                 invites. We want to send membership events of the inviter, so that the
                 invitee can display the inviter's profile information if the room lacks any.
+            for_federation: When True, the stripped state events will be returned as PDUs
+                as per MSC4311. When False, the stripped client format is used.
 
         Returns:
             A list of dictionaries, each representing a stripped state event from the room.
@@ -1134,7 +1137,7 @@ class EventsWorkerStore(SQLBaseStore):
 
         state_to_include = await self.get_events(selected_state_ids.values())
 
-        return [strip_event(e) for e in state_to_include.values()]
+        return [strip_event(e, for_federation) for e in state_to_include.values()]
 
     def _maybe_start_fetch_thread(self) -> None:
         """Starts an event fetch thread if we are not yet at the maximum number."""