Support MSC3266 room summaries over federation

changelog.d/11507.feature

@@ -0,0 +1 @@
+Support [MSC3266](https://github.com/matrix-org/matrix-doc/pull/3266) room summaries over federation.

synapse/handlers/room_summary.py

@@ -630,7 +630,7 @@ async def _is_local_room_accessible(
         return False
 
     async def _is_remote_room_accessible(
-        self, requester: str, room_id: str, room: JsonDict
+        self, requester: Optional[str], room_id: str, room: JsonDict
     ) -> bool:
         """
         Calculate whether the room received over federation should be shown to the requester.
@@ -645,7 +645,7 @@ async def _is_remote_room_accessible(
         due to an invite, etc.
 
         Args:
-            requester: The user requesting the summary.
+            requester: The user requesting the summary. If not passed only world readability is checked.
             room_id: The room ID returned over federation.
             room: The summary of the room returned over federation.
 
@@ -659,6 +659,8 @@ async def _is_remote_room_accessible(
             or room.get("world_readable") is True
         ):
             return True
+        elif not requester:
+            return False
 
         # Check if the user is a member of any of the allowed rooms from the response.
         allowed_rooms = room.get("allowed_room_ids")
@@ -713,8 +715,12 @@ async def _build_room_entry(self, room_id: str, for_federation: bool) -> JsonDic
             ),
             "guest_can_join": stats["guest_access"] == "can_join",
             "room_type": create_event.content.get(EventContentFields.ROOM_TYPE),
+            "im.nheko.summary.version": stats["version"],
         }
 
+        if stats["encryption"]:
+            entry["im.nheko.summary.encryption"] = stats["encryption"]
+
         # Federation requests need to provide additional information so the
         # requested server is able to filter the response appropriately.
         if for_federation:
@@ -812,15 +818,50 @@ async def get_room_summary(
 
                 room_summary["membership"] = membership or "leave"
         else:
-            # TODO federation API, descoped from initial unstable implementation
-            #      as MSC needs more maturing on that side.
-            raise SynapseError(400, "Federation is not currently supported.")
+            # Reuse the hierarchy query over federation
+            if remote_room_hosts is None:
+                raise SynapseError(400, "Missing via to query remote room")
+
+            (
+                room_entry,
+                children_room_entries,
+                inaccessible_children,
+            ) = await self._summarize_remote_room_hierarchy(
+                _RoomQueueEntry(room_id, remote_room_hosts),
+                suggested_only=True,
+            )
+
+            if room_entry:
+                room = room_entry.room
+                fed_room_id = room_entry.room_id
+
+                if fed_room_id == room_id:
+                    # The results over federation might include rooms that the we,
+                    # as the requesting server, are allowed to see, but the requesting
+                    # user is not permitted to see.
+                    #
+                    # Filter the returned results to only what is accessible to the user.
+                    if await self._is_remote_room_accessible(
+                        requester, fed_room_id, room
+                    ):
+                        # Before returning to the client, remove the allowed_room_ids
+                        # and allowed_spaces keys.
+                        room.pop("allowed_room_ids", None)
+                        room.pop("allowed_spaces", None)
+
+                        # A remote room can't be in the joined state
+                        room["membership"] = "leave"
+
+                        return room
+
+            raise NotFoundError("Room not found or is not accessible")
 
         return room_summary
 
 
 @attr.s(frozen=True, slots=True, auto_attribs=True)
 class _RoomQueueEntry:
+
     # The room ID of this entry.
     room_id: str
     # The server to query if the room is not known locally.