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 +645,8 @@ 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 +660,8 @@ 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")
@@ -713,6 +716,8 @@ 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"],
+            "im.nheko.summary.encryption": stats["encryption"],
         }
 
         # Federation requests need to provide additional information so the
@@ -812,9 +817,51 @@ 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
+                        # key.
+                        room.pop("allowed_room_ids", None)
+
+                        # If there was a requester, add their membership.
+                        # We keep the membership in the local membership table
+                        # unless the room is purged even for remote rooms.
+                        if requester:
+                            (
+                                membership,
+                                _,
+                            ) = await self._store.get_local_current_membership_for_user_in_room(
+                                requester, room_id
+                            )
+                            room["membership"] = membership or "leave"
+
+                        return room
+
+            raise NotFoundError("Room not found or is not accessible")
 
         return room_summary
 

tests/handlers/test_room_summary.py

@@ -1092,3 +1092,29 @@ def test_visibility(self):
         )
         result = self.get_success(self.handler.get_room_summary(user2, self.room))
         self.assertEqual(result.get("room_id"), self.room)
+
+    def test_fed(self):
+        """
+        Return data over federation and ensure that it is handled properly.
+        """
+        fed_hostname = self.hs.hostname + "2"
+        fed_room = "#fed_room:" + fed_hostname
+
+        requested_room_entry = _RoomEntry(
+            fed_room,
+            {"room_id": fed_room, "world_readable": True},
+        )
+
+        async def summarize_remote_room_hierarchy(_self, room, suggested_only):
+            return requested_room_entry, {}, set()
+
+        with mock.patch(
+            "synapse.handlers.room_summary.RoomSummaryHandler._summarize_remote_room_hierarchy",
+            new=summarize_remote_room_hierarchy,
+        ):
+            result = self.get_success(
+                self.handler.get_room_summary(
+                    self.user, fed_room, remote_room_hosts=[fed_hostname]
+                )
+            )
+        self.assertEqual(result.get("room_id"), fed_room)