Implement MSC4497: Filter state events by type in /state endpoint

changelog.d/19899.feature

@@ -0,0 +1,2 @@
+Implemement MSC4497: Filter state events by type in /state endpoint. Requests to `/_matrix/client/v3/rooms/!../state` can now be
+made with a `cc.koja.types` key to filter to only specific state types.

synapse/config/experimental.py

@@ -622,6 +622,10 @@ def read_config(
         # MSC4455: Preview URL capability
         # Tracked in: https://github.com/element-hq/synapse/issues/19719
         self.msc4452_enabled: bool = experimental.get("msc4452_enabled", False)
-
         # MSC4491: Invite reasons in room creation
         self.msc4491_enabled: bool = experimental.get("msc4491_enabled", False)
+
+        # MSC4497: State event type filter
+        self.msc4497_state_event_type_filter: bool = experimental.get(
+            "msc4497_state_event_type_filter", False
+        )

synapse/rest/client/room.py

@@ -25,7 +25,7 @@
 import re
 from enum import Enum
 from http import HTTPStatus
-from typing import TYPE_CHECKING, Awaitable
+from typing import TYPE_CHECKING, Awaitable, Mapping, Sequence
 from urllib import parse as urlparse
 
 import attr
@@ -990,15 +990,25 @@ def __init__(self, hs: "HomeServer"):
         super().__init__()
         self.message_handler = hs.get_message_handler()
         self.auth = hs.get_auth()
+        self.experimental_config = hs.config.experimental
 
     @cancellable
     async def on_GET(
         self, request: SynapseRequest, room_id: str
     ) -> tuple[int, list[JsonDict]]:
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
+        args: Mapping[bytes, Sequence[bytes]] = request.args  # type: ignore
+        type_filter = (
+            parse_strings_from_args(args, "cc.koja.types", required=False)
+            if self.experimental_config.msc4497_state_event_type_filter
+            else None
+        )
         # Get all the current state for this room
         events = await self.message_handler.get_state_events(
             room_id=room_id,
+            state_filter=StateFilter.from_types((x, None) for x in type_filter)
+            if type_filter is not None
+            else None,
             requester=requester,
         )
         return 200, events

tests/rest/client/test_rooms.py

@@ -601,6 +601,35 @@ def test_get_state_format_event(self) -> None:
         self.assertEqual(channel.json_body["state_key"], self.user_id)
         self.assertTrue(type(channel.json_body["origin_server_ts"]) is int)
 
+    def test_get_state_type_filter_single(self) -> None:
+        """MSC4497: filtering by a single type returns only that event type."""
+        self.hs.config.experimental.msc4497_state_event_type_filter = True
+        room_id = self.helper.create_room_as(self.user_id)
+        channel = self.make_request(
+            "GET",
+            "/rooms/%s/state?cc.koja.types=m.room.create" % room_id,
+        )
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.result["body"])
+        self.assertEqual(
+            [event["type"] for event in channel.json_list],
+            ["m.room.create"],
+        )
+
+    def test_get_state_type_filter_multiple(self) -> None:
+        """MSC4497: filtering by multiple types returns only those event types."""
+        self.hs.config.experimental.msc4497_state_event_type_filter = True
+        room_id = self.helper.create_room_as(self.user_id)
+        channel = self.make_request(
+            "GET",
+            "/rooms/%s/state?cc.koja.types=m.room.create&cc.koja.types=m.room.member"
+            % room_id,
+        )
+        self.assertEqual(channel.code, HTTPStatus.OK, channel.result["body"])
+        self.assertCountEqual(
+            [event["type"] for event in channel.json_list],
+            ["m.room.create", "m.room.member"],
+        )
+
 
 class RoomsMemberListTestCase(RoomBase):
     """Tests /rooms/$room_id/members/list REST events."""