Add admin API to get a list of federated rooms

changelog.d/11658.feature

@@ -0,0 +1 @@
+Add admin API to get a list of federated rooms.

docs/usage/administration/admin_api/federation.md

@@ -112,3 +112,63 @@ A response body like the following is returned:
 
 The response fields are the same like in the `destinations` array in
 [List of destinations](#list-of-destinations) response.
+
+## Destination rooms
+
+This API gets the rooms that federate with a specific remote server.
+
+The API is:
+
+```
+GET /_synapse/admin/v1/federation/destinations/<destination>/rooms
+```
+
+A response body like the following is returned:
+
+```json
+{
+   "rooms":[
+      {
+         "room_id": "!OGEhHVWSdvArJzumhm:matrix.org",
+         "stream_ordering": 8326
+      },
+      {
+         "room_id": "!xYvNcQPhnkrdUmYczI:matrix.org",
+         "stream_ordering": 93534
+      }
+   ],
+   "total": 2
+}
+```
+
+To paginate, check for `next_token` and if present, call the endpoint again
+with `from` set to the value of `next_token`. This will return a new page.
+
+If the endpoint does not return a `next_token` then there are no more destinations
+to paginate through.
+
+**Parameters**
+
+The following parameters should be set in the URL:
+
+- `destination` - Name of the remote server.
+
+The following query parameters are available:
+
+- `from` - Offset in the returned list. Defaults to `0`.
+- `limit` - Maximum amount of destinations to return. Defaults to `100`.
+- `dir` - Direction of room order by `room_id`. Either `f` for forwards or `b` for
+  backwards. Defaults to `f`.
+
+**Response**
+
+The following fields are returned in the JSON response body:
+
+- `rooms` - An array of objects, each containing information about a room.
+  Room objects contain the following fields:
+  - `room_id` - string - The ID of the room.
+  - `stream_ordering` - integer -  The stream ordering of the most recent
+    successfully-sent [PDU](understanding_synapse_through_grafana_graphs.md#federation)
+    to this destination in this room.
+- `next_token`: string representing a positive integer - Indication for pagination. See above.
+- `total` - integer - Total number of destinations.

synapse/rest/admin/__init__.py

@@ -41,7 +41,8 @@
     EventReportsRestServlet,
 )
 from synapse.rest.admin.federation import (
-    DestinationsRestServlet,
+    DestinationMembershipRestServlet,
+    DestinationRestServlet,
     ListDestinationsRestServlet,
 )
 from synapse.rest.admin.groups import DeleteGroupAdminRestServlet
@@ -267,7 +268,8 @@ def register_servlets(hs: "HomeServer", http_server: HttpServer) -> None:
     ListRegistrationTokensRestServlet(hs).register(http_server)
     NewRegistrationTokenRestServlet(hs).register(http_server)
     RegistrationTokenRestServlet(hs).register(http_server)
-    DestinationsRestServlet(hs).register(http_server)
+    DestinationMembershipRestServlet(hs).register(http_server)
+    DestinationRestServlet(hs).register(http_server)
     ListDestinationsRestServlet(hs).register(http_server)
 
     # Some servlets only get registered for the main process.

synapse/rest/admin/federation.py

@@ -90,7 +90,7 @@ async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         return HTTPStatus.OK, response
 
 
-class DestinationsRestServlet(RestServlet):
+class DestinationRestServlet(RestServlet):
     """Get details of a destination.
     This needs user to have administrator access in Synapse.
 
@@ -145,3 +145,59 @@ async def on_GET(
             }
 
         return HTTPStatus.OK, response
+
+
+class DestinationMembershipRestServlet(RestServlet):
+    """Get list of rooms of a destination.
+    This needs user to have administrator access in Synapse.
+
+    GET /_synapse/admin/v1/federation/destinations/<destination>/rooms?from=0&limit=10
+
+    returns:
+        200 OK with a list of rooms if success otherwise an error.
+
+    The parameters `from` and `limit` are required only for pagination.
+    By default, a `limit` of 100 is used.
+    """
+
+    PATTERNS = admin_patterns("/federation/destinations/(?P<destination>[^/]*)/rooms$")
+
+    def __init__(self, hs: "HomeServer"):
+        self._auth = hs.get_auth()
+        self._store = hs.get_datastore()
+
+    async def on_GET(
+        self, request: SynapseRequest, destination: str
+    ) -> Tuple[int, JsonDict]:
+        await assert_requester_is_admin(self._auth, request)
+
+        if not await self._store.is_destination_known(destination):
+            raise NotFoundError("Unknown destination")
+
+        start = parse_integer(request, "from", default=0)
+        limit = parse_integer(request, "limit", default=100)
+
+        if start < 0:
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Query parameter from must be a string representing a positive integer.",
+                errcode=Codes.INVALID_PARAM,
+            )
+
+        if limit < 0:
+            raise SynapseError(
+                HTTPStatus.BAD_REQUEST,
+                "Query parameter limit must be a string representing a positive integer.",
+                errcode=Codes.INVALID_PARAM,
+            )
+
+        direction = parse_string(request, "dir", default="f", allowed_values=("f", "b"))
+
+        rooms, total = await self._store.get_destination_rooms_paginate(
+            destination, start, limit, direction
+        )
+        response = {"rooms": rooms, "total": total}
+        if (start + limit) < total:
+            response["next_token"] = str(start + len(rooms))
+
+        return HTTPStatus.OK, response

synapse/storage/databases/main/transactions.py

@@ -561,6 +561,54 @@ def get_destinations_paginate_txn(
             "get_destinations_paginate_txn", get_destinations_paginate_txn
         )
 
+    async def get_destination_rooms_paginate(
+        self, destination: str, start: int, limit: int, direction: str = "f"
+    ) -> Tuple[List[JsonDict], int]:
+        """Function to retrieve a paginated list of destination's rooms.
+        This will return a json list of rooms and the
+        total number of rooms.
+
+        Args:
+            destination: the destination to query
+            start: start number to begin the query from
+            limit: number of rows to retrieve
+            direction: sort ascending or descending by room_id
+        Returns:
+            A tuple of a dict of rooms and a count of total rooms.
+        """
+
+        def get_destination_rooms_paginate_txn(
+            txn: LoggingTransaction,
+        ) -> Tuple[List[JsonDict], int]:
+
+            if direction == "b":
+                order = "DESC"
+            else:
+                order = "ASC"
+
+            sql = """
+                SELECT COUNT(*) as total_rooms
+                FROM destination_rooms
+                WHERE destination = ?
+                """
+            txn.execute(sql, [destination])
+            count = cast(Tuple[int], txn.fetchone())[0]
+
+            rooms = self.db_pool.simple_select_list_paginate_txn(
+                txn=txn,
+                table="destination_rooms",
+                orderby="room_id",
+                start=start,
+                limit=limit,
+                retcols=("room_id", "stream_ordering"),
+                order_direction=order,
+            )
+            return rooms, count
+
+        return await self.db_pool.runInteraction(
+            "get_destination_rooms_paginate_txn", get_destination_rooms_paginate_txn
+        )
+
     async def is_destination_known(self, destination: str) -> bool:
         """Check if a destination is known to the server."""
         result = await self.db_pool.simple_select_one_onecol(