Add ETag header support to /state

changelog.d/17974.feature

@@ -0,0 +1 @@
+Add ETag header to the /rooms/$room_id/state endpoint, and return no content on cache hit.

synapse/handlers/message.py

@@ -19,6 +19,7 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
+import hashlib
 import logging
 import random
 from http import HTTPStatus
@@ -173,7 +174,8 @@ async def get_state_events(
         room_id: str,
         state_filter: Optional[StateFilter] = None,
         at_token: Optional[StreamToken] = None,
-    ) -> List[dict]:
+        last_hash: Optional[str] = None,
+    ) -> Tuple[List[dict], Optional[str]]:
         """Retrieve all state events for a given room. If the user is
         joined to the room then return the current state. If the user has
         left the room return the state events from when they left. If an explicit
@@ -190,6 +192,8 @@ async def get_state_events(
                 state based on the current_state_events table.
         Returns:
             A list of dicts representing state events. [{}, {}, {}]
+            A hash of the state IDs representing the state events. This is only calculated if
+            no at_token is given and the user is joined to the room.
         Raises:
             NotFoundError (404) if the at token does not yield an event
 
@@ -200,6 +204,7 @@ async def get_state_events(
             state_filter = StateFilter.all()
 
         user_id = requester.user.to_string()
+        hash = None
 
         if at_token:
             last_event_id = (
@@ -239,6 +244,14 @@ async def get_state_events(
                 state_ids = await self._state_storage_controller.get_current_state_ids(
                     room_id, state_filter=state_filter
                 )
+
+                hash = hashlib.sha1(
+                    ",".join(state_ids.values()).encode("utf-8")
+                ).hexdigest()
+                # If the requester's hash matches ours, their cache is up to date and we can skip
+                # fetching events.
+                if last_hash == hash:
+                    return [], hash
                 room_state = await self.store.get_events(state_ids.values())
             elif membership == Membership.LEAVE:
                 # If the membership is not JOIN, then the event ID should exist.
@@ -257,7 +270,7 @@ async def get_state_events(
             self.clock.time_msec(),
             config=SerializeEventConfig(requester=requester),
         )
-        return events
+        return events, hash
 
     async def _user_can_see_state_at_event(
         self, user_id: str, room_id: str, event_id: str

synapse/rest/client/room.py

@@ -715,7 +715,7 @@ async def on_GET(
         membership = parse_string(request, "membership")
         not_membership = parse_string(request, "not_membership")
 
-        events = await handler.get_state_events(
+        events, _ = await handler.get_state_events(
             room_id=room_id,
             requester=requester,
             at_token=at_token,
@@ -835,13 +835,22 @@ def __init__(self, hs: "HomeServer"):
     @cancellable
     async def on_GET(
         self, request: SynapseRequest, room_id: str
-    ) -> Tuple[int, List[JsonDict]]:
+    ) -> Tuple[int, Optional[List[JsonDict]]]:
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
+        existing_hash = request.getHeader(b"If-None-Match")
+
         # Get all the current state for this room
-        events = await self.message_handler.get_state_events(
+        events, hash = await self.message_handler.get_state_events(
             room_id=room_id,
             requester=requester,
+            # Trim quotes from hash.
+            last_hash=existing_hash.decode("ascii")[1:-1] if existing_hash else None,
         )
+        request.setHeader(b"ETag", f'"{hash}"'.encode("ascii"))
+
+        if len(events) == 0:
+            return 304, None
+
         return 200, events
 
 

tests/rest/client/test_rooms.py

@@ -552,6 +552,64 @@ def test_get_state_event_cancellation(self) -> None:
         self.assertEqual(HTTPStatus.OK, channel.code, msg=channel.result["body"])
         self.assertEqual(channel.json_body, {"membership": "join"})
 
+    def test_get_state_etag_match(self) -> None:
+        """Test that `/rooms/$room_id/state` returns a NOT_MODIFIED response when provided with the correct ETag."""
+        room_id = self.helper.create_room_as(self.user_id)
+        channel = self.make_request(
+            "GET",
+            "/rooms/%s/state" % room_id,
+        )
+
+        etagheader = channel.headers.getRawHeaders(b"ETag")
+        self.assertEqual(HTTPStatus.OK, channel.code, msg=channel.result["body"])
+        assert etagheader
+        channel2 = self.make_request(
+            "GET",
+            "/rooms/%s/state" % room_id,
+            custom_headers=[
+                (
+                    b"If-None-Match",
+                    etagheader[0],
+                ),
+            ],
+        )
+        self.assertEqual(
+            HTTPStatus.NOT_MODIFIED,
+            channel2.code,
+            "Responds with not modified when provided with the correct ETag",
+        )
+        self.assertEqual(
+            etagheader,
+            channel2.headers.getRawHeaders(b"ETag"),
+            "returns the same etag",
+        )
+
+    def test_get_state_etag_nonmatch(self) -> None:
+        """Test that `/rooms/$room_id/state` returns a normal response to an unrecognised ETag."""
+        room_id = self.helper.create_room_as(self.user_id)
+        channel = self.make_request(
+            "GET",
+            "/rooms/%s/state" % room_id,
+            custom_headers=(
+                (
+                    b"If-None-Match",
+                    '"notavalidetag"',
+                ),
+            ),
+        )
+
+        self.assertEqual(HTTPStatus.OK, channel.code, msg=channel.result["body"])
+        self.assertCountEqual(
+            [state_event["type"] for state_event in channel.json_list],
+            {
+                "m.room.create",
+                "m.room.power_levels",
+                "m.room.join_rules",
+                "m.room.member",
+                "m.room.history_visibility",
+            },
+        )
+
 
 class RoomsMemberListTestCase(RoomBase):
     """Tests /rooms/$room_id/members/list REST events."""