Merge remote-tracking branch 'origin/develop' into matrix-org-hotfixes

CHANGES.md

@@ -1,3 +1,10 @@
+# Synapse 1.116.0 (2024-10-01)
+
+No significant changes since 1.116.0rc2.
+
+
+
+
 # Synapse 1.116.0rc2 (2024-09-26)
 
 ### Features

changelog.d/17628.doc

@@ -0,0 +1 @@
+Clarify the docstring of `test_forget_when_not_left`.

changelog.d/17709.doc

@@ -0,0 +1 @@
+Add documentation note about PYTHONMALLOC for accurate jemalloc memory tracking. Contributed by @hensg.

changelog.d/17717.feature

@@ -0,0 +1 @@
+Add config option `redis.password_path`.

changelog.d/17776.doc

@@ -0,0 +1 @@
+Explain how load balancing works for `federation_sender_instances`.

changelog.d/17779.bugfix

@@ -0,0 +1 @@
+Fix a rare bug introduced in v1.29.0 where invalidating a user's access token from a worker could raise an error.

changelog.d/17780.bugfix

@@ -0,0 +1 @@
+In the response to `GET /_matrix/client/versions`, set the `unstable_features` flag for MSC4140 to `false` when server configuration disables support for delayed events.

changelog.d/17787.misc

@@ -0,0 +1 @@
+Sliding sync minor performance speed up using new table.

changelog.d/17788.misc

@@ -0,0 +1 @@
+Sliding sync minor performance improvement by omitting unchanged data from incremental responses.

changelog.d/17789.misc

@@ -0,0 +1 @@
+Speed up sliding sync when there are many active subscriptions.

debian/changelog

@@ -1,3 +1,9 @@
+matrix-synapse-py3 (1.116.0) stable; urgency=medium
+
+  * New Synapse release 1.116.0.
+
+ -- Synapse Packaging team <packages@matrix.org>  Tue, 01 Oct 2024 11:14:07 +0100
+
 matrix-synapse-py3 (1.116.0~rc2) stable; urgency=medium
 
   * New synapse release 1.116.0rc2.

docs/usage/administration/admin_faq.md

@@ -255,6 +255,8 @@ line to `/etc/default/matrix-synapse`:
 
     LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2
 
+*Note*: You may need to set `PYTHONMALLOC=malloc` to ensure that `jemalloc` can accurately calculate memory usage. By default, Python uses its internal small-object allocator, which may interfere with jemalloc's ability to track memory consumption correctly. This could prevent the [cache_autotuning](../configuration/config_documentation.md#caches-and-associated-values) feature from functioning as expected, as the Python allocator may not reach the memory threshold set by `max_cache_memory_usage`, thus not triggering the cache eviction process.
+
 This made a significant difference on Python 2.7 - it's unclear how
 much of an improvement it provides on Python 3.x.
 

docs/usage/configuration/config_documentation.md

@@ -4370,6 +4370,12 @@ a `federation_sender_instances` map. Doing so will remove handling of this funct
 the main process. Multiple workers can be added to this map, in which case the work is
 balanced across them. 
 
+The way that the load balancing works is any outbound federation request will be assigned 
+to a federation sender worker based on the hash of the destination server name. This
+means that all requests being sent to the same destination will be processed by the same
+worker instance. Multiple `federation_sender_instances` are useful if there is a federation
+with multiple servers.
+
 This configuration setting must be shared between all workers handling federation
 sending, and if changed all federation sender workers must be stopped at the same time
 and then started, to ensure that all instances are running with the same config (otherwise
@@ -4518,6 +4524,9 @@ This setting has the following sub-options:
 * `path`: The full path to a local Unix socket file. **If this is used, `host` and
  `port` are ignored.** Defaults to `/tmp/redis.sock'
 * `password`: Optional password if configured on the Redis instance.
+* `password_path`: Alternative to `password`, reading the password from an
+   external file. The file should be a plain text file, containing only the
+   password. Synapse reads the password from the given file once at startup.
 * `dbid`: Optional redis dbid if needs to connect to specific redis logical db.
 * `use_tls`: Whether to use tls connection. Defaults to false.
 * `certificate_file`: Optional path to the certificate file
@@ -4531,13 +4540,16 @@ This setting has the following sub-options:
 
   _Changed in Synapse 1.85.0: Added path option to use a local Unix socket_
 
+  _Changed in Synapse 1.116.0: Added password\_path_
+
 Example configuration:
 ```yaml
 redis:
   enabled: true
   host: localhost
   port: 6379
-  password: <secret_password>
+  password_path: <path_to_the_password_file>
+  # OR password: <secret_password>
   dbid: <dbid>
   #use_tls: True
   #certificate_file: <path_to_the_certificate_file>

poetry.lock

@@ -1974,13 +1974,13 @@ six = ">=1.5"
 
 [[package]]
 name = "python-multipart"
-version = "0.0.10"
+version = "0.0.12"
 description = "A streaming multipart parser for Python"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "python_multipart-0.0.10-py3-none-any.whl", hash = "sha256:2b06ad9e8d50c7a8db80e3b56dab590137b323410605af2be20d62a5f1ba1dc8"},
+    {file = "python_multipart-0.0.12-py3-none-any.whl", hash = "sha256:43dcf96cf65888a9cd3423544dd0d75ac10f7aa0c3c28a175bbcd00c9ce1aebf"},
-    {file = "python_multipart-0.0.10.tar.gz", hash = "sha256:46eb3c6ce6fdda5fb1a03c7e11d490e407c6930a2703fe7aef4da71c374688fa"},
+    {file = "python_multipart-0.0.12.tar.gz", hash = "sha256:045e1f98d719c1ce085ed7f7e1ef9d8ccc8c02ba02b5566d5f7521410ced58cb"},
 ]
 
 [[package]]

pyproject.toml

@@ -97,7 +97,7 @@ module-name = "synapse.synapse_rust"
 
 [tool.poetry]
 name = "matrix-synapse"
-version = "1.116.0rc2"
+version = "1.116.0"
 description = "Homeserver for the Matrix decentralised comms protocol"
 authors = ["Matrix.org Team and Contributors <packages@matrix.org>"]
 license = "AGPL-3.0-or-later"

synapse/config/redis.py

@@ -21,10 +21,15 @@
 
 from typing import Any
 
-from synapse.config._base import Config
+from synapse.config._base import Config, ConfigError, read_file
 from synapse.types import JsonDict
 from synapse.util.check_dependencies import check_requirements
 
+CONFLICTING_PASSWORD_OPTS_ERROR = """\
+You have configured both `redis.password` and `redis.password_path`.
+These are mutually incompatible.
+"""
+
 
 class RedisConfig(Config):
     section = "redis"
@@ -43,6 +48,17 @@ class RedisConfig(Config):
         self.redis_path = redis_config.get("path", None)
         self.redis_dbid = redis_config.get("dbid", None)
         self.redis_password = redis_config.get("password")
+        redis_password_path = redis_config.get("password_path")
+        if redis_password_path:
+            if self.redis_password:
+                raise ConfigError(CONFLICTING_PASSWORD_OPTS_ERROR)
+            self.redis_password = read_file(
+                redis_password_path,
+                (
+                    "redis",
+                    "password_path",
+                ),
+            ).strip()
 
         self.redis_use_tls = redis_config.get("use_tls", False)
         self.redis_certificate = redis_config.get("certificate_file", None)

synapse/handlers/sliding_sync/__init__.py

@@ -49,6 +49,7 @@ from synapse.types import (
     Requester,
     SlidingSyncStreamToken,
     StateMap,
+    StrCollection,
     StreamKeyType,
     StreamToken,
 )
@@ -293,7 +294,6 @@ class SlidingSyncHandler:
             # to record rooms as having updates even if there might not actually
             # be anything new for the user (e.g. due to event filters, events
             # having happened after the user left, etc).
-            unsent_room_ids = []
             if from_token:
                 # The set of rooms that the client (may) care about, but aren't
                 # in any list range (or subscribed to).
@@ -305,6 +305,15 @@ class SlidingSyncHandler:
                 # TODO: Replace this with something faster. When we land the
                 # sliding sync tables that record the most recent event
                 # positions we can use that.
+                unsent_room_ids: StrCollection
+                if await self.store.have_finished_sliding_sync_background_jobs():
+                    unsent_room_ids = await (
+                        self.store.get_rooms_that_have_updates_since_sliding_sync_table(
+                            room_ids=missing_rooms,
+                            from_key=from_token.stream_token.room_key,
+                        )
+                    )
+                else:
                     missing_event_map_by_room = (
                         await self.store.get_room_events_stream_for_rooms(
                             room_ids=missing_rooms,
@@ -1048,22 +1057,42 @@ class SlidingSyncHandler:
                     )
                 )
 
-        # Figure out the last bump event in the room
+        # Figure out the last bump event in the room. If the bump stamp hasn't
-        #
+        # changed we omit it from the response.
-        # By default, just choose the membership event position for any non-join membership
+        bump_stamp = None
-        bump_stamp = room_membership_for_user_at_to_token.event_pos.stream
+
+        always_return_bump_stamp = (
+            # We use the membership event position for any non-join
+            room_membership_for_user_at_to_token.membership != Membership.JOIN
+            # We didn't fetch any timeline events but we should still check for
+            # a bump_stamp that might be somewhere
+            or limited is None
+            # There might be a bump event somewhere before the timeline events
+            # that we fetched, that we didn't previously send down
+            or limited is True
+            # Always give the client some frame of reference if this is the
+            # first time they are seeing the room down the connection
+            or initial
+        )
+
         # If we're joined to the room, we need to find the last bump event before the
         # `to_token`
         if room_membership_for_user_at_to_token.membership == Membership.JOIN:
-            # Try and get a bump stamp, if not we just fall back to the
+            # Try and get a bump stamp
-            # membership token.
             new_bump_stamp = await self._get_bump_stamp(
-                room_id, to_token, timeline_events
+                room_id,
+                to_token,
+                timeline_events,
+                check_outside_timeline=always_return_bump_stamp,
             )
             if new_bump_stamp is not None:
                 bump_stamp = new_bump_stamp
 
-        if bump_stamp < 0:
+        if bump_stamp is None and always_return_bump_stamp:
+            # By default, just choose the membership event position for any non-join membership
+            bump_stamp = room_membership_for_user_at_to_token.event_pos.stream
+
+        if bump_stamp is not None and bump_stamp < 0:
             # We never want to send down negative stream orderings, as you can't
             # sensibly compare positive and negative stream orderings (they have
             # different meanings).
@@ -1156,14 +1185,23 @@ class SlidingSyncHandler:
 
     @trace
     async def _get_bump_stamp(
-        self, room_id: str, to_token: StreamToken, timeline: List[EventBase]
+        self,
+        room_id: str,
+        to_token: StreamToken,
+        timeline: List[EventBase],
+        check_outside_timeline: bool,
     ) -> Optional[int]:
-        """Get a bump stamp for the room, if we have a bump event
+        """Get a bump stamp for the room, if we have a bump event and it has
+        changed.
 
         Args:
             room_id
             to_token: The upper bound of token to return
             timeline: The list of events we have fetched.
+            limited: If the timeline was limited.
+            check_outside_timeline: Whether we need to check for bump stamp for
+                events before the timeline if we didn't find a bump stamp in
+                the timeline events.
         """
 
         # First check the timeline events we're returning to see if one of
@@ -1183,6 +1221,11 @@ class SlidingSyncHandler:
                 if new_bump_stamp > 0:
                     return new_bump_stamp
 
+        if not check_outside_timeline:
+            # If we are not a limited sync, then we know the bump stamp can't
+            # have changed.
+            return None
+
         # We can quickly query for the latest bump event in the room using the
         # sliding sync tables.
         latest_room_bump_stamp = await self.store.get_latest_bump_stamp_for_room(

synapse/handlers/sliding_sync/room_lists.py

@@ -500,6 +500,16 @@ class SlidingSyncRoomLists:
                 # depending on the `required_state` requested (see below).
                 partial_state_rooms = await self.store.get_partial_rooms()
 
+                # Fetch any rooms that we have not already fetched from the database.
+                subscription_sliding_sync_rooms = (
+                    await self.store.get_sliding_sync_room_for_user_batch(
+                        user_id,
+                        sync_config.room_subscriptions.keys()
+                        - room_membership_for_user_map.keys(),
+                    )
+                )
+                room_membership_for_user_map.update(subscription_sliding_sync_rooms)
+
                 for (
                     room_id,
                     room_subscription,
@@ -507,17 +517,11 @@ class SlidingSyncRoomLists:
                     # Check if we have a membership for the room, but didn't pull it out
                     # above. This could be e.g. a leave that we don't pull out by
                     # default.
-                    current_room_entry = (
+                    current_room_entry = room_membership_for_user_map.get(room_id)
-                        await self.store.get_sliding_sync_room_for_user(
-                            user_id, room_id
-                        )
-                    )
                     if not current_room_entry:
                         # TODO: Handle rooms the user isn't in.
                         continue
 
-                    room_membership_for_user_map[room_id] = current_room_entry
-
                     all_rooms.add(room_id)
 
                     # Take the superset of the `RoomSyncConfig` for each room.

synapse/http/client.py

@@ -1039,7 +1039,7 @@ class _MultipartParserProtocol(protocol.Protocol):
         self.deferred = deferred
         self.boundary = boundary
         self.max_length = max_length
-        self.parser = None
+        self.parser: Optional[multipart.MultipartParser] = None
         self.multipart_response = MultipartResponse()
         self.has_redirect = False
         self.in_json = False
@@ -1097,7 +1097,7 @@ class _MultipartParserProtocol(protocol.Protocol):
                         self.deferred.errback()
                     self.file_length += end - start
 
-            callbacks = {
+            callbacks: "multipart.multipart.MultipartCallbacks" = {
                 "on_header_field": on_header_field,
                 "on_header_value": on_header_value,
                 "on_part_data": on_part_data,
@@ -1113,7 +1113,7 @@ class _MultipartParserProtocol(protocol.Protocol):
             self.transport.abortConnection()
 
         try:
-            self.parser.write(incoming_data)  # type: ignore[attr-defined]
+            self.parser.write(incoming_data)
         except Exception as e:
             logger.warning(f"Exception writing to multipart parser: {e}")
             self.deferred.errback()

synapse/replication/http/push.py

@@ -48,7 +48,7 @@ class ReplicationRemovePusherRestServlet(ReplicationEndpoint):
 
     """
 
-    NAME = "add_user_account_data"
+    NAME = "remove_pusher"
     PATH_ARGS = ("user_id",)
     CACHE = False
 

synapse/rest/client/sync.py

@@ -1010,11 +1010,13 @@ class SlidingSyncRestServlet(RestServlet):
         serialized_rooms: Dict[str, JsonDict] = {}
         for room_id, room_result in rooms.items():
             serialized_rooms[room_id] = {
-                "bump_stamp": room_result.bump_stamp,
                 "notification_count": room_result.notification_count,
                 "highlight_count": room_result.highlight_count,
             }
 
+            if room_result.bump_stamp is not None:
+                serialized_rooms[room_id]["bump_stamp"] = room_result.bump_stamp
+
             if room_result.joined_count is not None:
                 serialized_rooms[room_id]["joined_count"] = room_result.joined_count
 

synapse/rest/client/versions.py

@@ -172,7 +172,7 @@ class VersionsRestServlet(RestServlet):
                         )
                     ),
                     # MSC4140: Delayed events
-                    "org.matrix.msc4140": True,
+                    "org.matrix.msc4140": bool(self.config.server.max_event_delay_ms),
                     # MSC4151: Report room API (Client-Server API)
                     "org.matrix.msc4151": self.config.experimental.msc4151_enabled,
                     # Simplified sliding sync

synapse/storage/databases/main/roommember.py

@@ -1499,6 +1499,57 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
             "get_sliding_sync_room_for_user", get_sliding_sync_room_for_user_txn
         )
 
+    async def get_sliding_sync_room_for_user_batch(
+        self, user_id: str, room_ids: StrCollection
+    ) -> Dict[str, RoomsForUserSlidingSync]:
+        """Get the sliding sync room entry for the given user and rooms."""
+
+        if not room_ids:
+            return {}
+
+        def get_sliding_sync_room_for_user_batch_txn(
+            txn: LoggingTransaction,
+        ) -> Dict[str, RoomsForUserSlidingSync]:
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "m.room_id", room_ids
+            )
+            sql = f"""
+                SELECT m.room_id, m.sender, m.membership, m.membership_event_id,
+                    r.room_version,
+                    m.event_instance_name, m.event_stream_ordering,
+                    m.has_known_state,
+                    COALESCE(j.room_type, m.room_type),
+                    COALESCE(j.is_encrypted, m.is_encrypted)
+                FROM sliding_sync_membership_snapshots AS m
+                INNER JOIN rooms AS r USING (room_id)
+                LEFT JOIN sliding_sync_joined_rooms AS j ON (j.room_id = m.room_id AND m.membership = 'join')
+                WHERE m.forgotten = 0
+                    AND {clause}
+                    AND user_id = ?
+            """
+            args.append(user_id)
+            txn.execute(sql, args)
+
+            return {
+                row[0]: RoomsForUserSlidingSync(
+                    room_id=row[0],
+                    sender=row[1],
+                    membership=row[2],
+                    event_id=row[3],
+                    room_version_id=row[4],
+                    event_pos=PersistedEventPosition(row[5], row[6]),
+                    has_known_state=bool(row[7]),
+                    room_type=row[8],
+                    is_encrypted=row[9],
+                )
+                for row in txn
+            }
+
+        return await self.db_pool.runInteraction(
+            "get_sliding_sync_room_for_user_batch",
+            get_sliding_sync_room_for_user_batch_txn,
+        )
+
 
 class RoomMemberBackgroundUpdateStore(SQLBaseStore):
     def __init__(

synapse/storage/databases/main/stream.py

@@ -751,6 +751,48 @@ class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
             if self._events_stream_cache.has_entity_changed(room_id, from_id)
         }
 
+    async def get_rooms_that_have_updates_since_sliding_sync_table(
+        self,
+        room_ids: StrCollection,
+        from_key: RoomStreamToken,
+    ) -> StrCollection:
+        """Return the rooms that probably have had updates since the given
+        token (changes that are > `from_key`)."""
+        # If the stream change cache is valid for the stream token, we can just
+        # use the result of that.
+        if from_key.stream >= self._events_stream_cache.get_earliest_known_position():
+            return self._events_stream_cache.get_entities_changed(
+                room_ids, from_key.stream
+            )
+
+        def get_rooms_that_have_updates_since_sliding_sync_table_txn(
+            txn: LoggingTransaction,
+        ) -> StrCollection:
+            sql = """
+                SELECT room_id
+                FROM sliding_sync_joined_rooms
+                WHERE {clause}
+                    AND event_stream_ordering > ?
+            """
+
+            results: Set[str] = set()
+            for batch in batch_iter(room_ids, 1000):
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "room_id", batch
+                )
+
+                args.append(from_key.stream)
+                txn.execute(sql.format(clause=clause), args)
+
+                results.update(row[0] for row in txn)
+
+            return results
+
+        return await self.db_pool.runInteraction(
+            "get_rooms_that_have_updates_since_sliding_sync_table",
+            get_rooms_that_have_updates_since_sliding_sync_table_txn,
+        )
+
     async def paginate_room_events_by_stream_ordering(
         self,
         *,

synapse/types/handlers/sliding_sync.py

@@ -158,6 +158,7 @@ class SlidingSyncResult:
                 name changes to mark the room as unread and bump it to the top. For
                 encrypted rooms, we just have to consider any activity as a bump because we
                 can't see the content and the client has to figure it out for themselves.
+                This may not be included if there hasn't been a change.
             joined_count: The number of users with membership of join, including the client's
                 own user ID. (same as sync `v2 m.joined_member_count`)
             invited_count: The number of users with membership of invite. (same as sync v2
@@ -193,7 +194,7 @@ class SlidingSyncResult:
         limited: Optional[bool]
         # Only optional because it won't be included for invite/knock rooms with `stripped_state`
         num_live: Optional[int]
-        bump_stamp: int
+        bump_stamp: Optional[int]
         joined_count: Optional[int]
         invited_count: Optional[int]
         notification_count: int

tests/config/test_load.py

@@ -19,13 +19,23 @@
 # [This file includes modifications made by New Vector Limited]
 #
 #
+import tempfile
+from typing import Callable
+
 import yaml
+from parameterized import parameterized
 
 from synapse.config import ConfigError
+from synapse.config._base import RootConfig
 from synapse.config.homeserver import HomeServerConfig
 
 from tests.config.utils import ConfigFileTestCase
 
+try:
+    import hiredis
+except ImportError:
+    hiredis = None  # type: ignore
+
 
 class ConfigLoadingFileTestCase(ConfigFileTestCase):
     def test_load_fails_if_server_name_missing(self) -> None:
@@ -116,3 +126,49 @@ class ConfigLoadingFileTestCase(ConfigFileTestCase):
         self.add_lines_to_config(["trust_identity_server_for_password_resets: true"])
         with self.assertRaises(ConfigError):
             HomeServerConfig.load_config("", ["-c", self.config_file])
+
+    @parameterized.expand(
+        [
+            "turn_shared_secret_path: /does/not/exist",
+            "registration_shared_secret_path: /does/not/exist",
+            *["redis:\n  enabled: true\n  password_path: /does/not/exist"]
+            * (hiredis is not None),
+        ]
+    )
+    def test_secret_files_missing(self, config_str: str) -> None:
+        self.generate_config()
+        self.add_lines_to_config(["", config_str])
+
+        with self.assertRaises(ConfigError):
+            HomeServerConfig.load_config("", ["-c", self.config_file])
+
+    @parameterized.expand(
+        [
+            (
+                "turn_shared_secret_path: {}",
+                lambda c: c.voip.turn_shared_secret,
+            ),
+            (
+                "registration_shared_secret_path: {}",
+                lambda c: c.registration.registration_shared_secret,
+            ),
+            *[
+                (
+                    "redis:\n  enabled: true\n  password_path: {}",
+                    lambda c: c.redis.redis_password,
+                )
+            ]
+            * (hiredis is not None),
+        ]
+    )
+    def test_secret_files_existing(
+        self, config_line: str, get_secret: Callable[[RootConfig], str]
+    ) -> None:
+        self.generate_config_and_remove_lines_containing("registration_shared_secret")
+        with tempfile.NamedTemporaryFile(buffering=0) as secret_file:
+            secret_file.write(b"53C237")
+
+            self.add_lines_to_config(["", config_line.format(secret_file.name)])
+            config = HomeServerConfig.load_config("", ["-c", self.config_file])
+
+            self.assertEqual(get_secret(config), "53C237")

tests/handlers/test_room_member.py

@@ -380,7 +380,7 @@ class RoomMemberMasterHandlerTestCase(HomeserverTestCase):
         )
 
     def test_forget_when_not_left(self) -> None:
-        """Tests that a user cannot not forgets a room that has not left."""
+        """Tests that a user cannot forget a room that they are still in."""
         self.get_failure(self.handler.forget(self.alice_ID, self.room_id), SynapseError)
 
     def test_nonlocal_room_user_action(self) -> None:

tests/rest/client/sliding_sync/test_rooms_meta.py

@@ -1096,6 +1096,92 @@ class SlidingSyncRoomsMetaTestCase(SlidingSyncBase):
 
         self.assertGreater(response_body["rooms"][room_id]["bump_stamp"], 0)
 
+    def test_rooms_bump_stamp_no_change_incremental(self) -> None:
+        """Test that the bump stamp is omitted if there has been no change"""
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(
+            user1_id,
+            tok=user1_tok,
+        )
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 100,
+                }
+            }
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Initial sync so we expect to see a bump stamp
+        self.assertIn("bump_stamp", response_body["rooms"][room_id1])
+
+        # Send an event that is not in the bump events list
+        self.helper.send_event(
+            room_id1, type="org.matrix.test", content={}, tok=user1_tok
+        )
+
+        response_body, from_token = self.do_sync(
+            sync_body, since=from_token, tok=user1_tok
+        )
+
+        # There hasn't been a change to the bump stamps, so we ignore it
+        self.assertNotIn("bump_stamp", response_body["rooms"][room_id1])
+
+    def test_rooms_bump_stamp_change_incremental(self) -> None:
+        """Test that the bump stamp is included if there has been a change, even
+        if its not in the timeline"""
+
+        user1_id = self.register_user("user1", "pass")
+        user1_tok = self.login(user1_id, "pass")
+
+        room_id1 = self.helper.create_room_as(
+            user1_id,
+            tok=user1_tok,
+        )
+
+        # Make the Sliding Sync request
+        sync_body = {
+            "lists": {
+                "foo-list": {
+                    "ranges": [[0, 1]],
+                    "required_state": [],
+                    "timeline_limit": 2,
+                }
+            }
+        }
+        response_body, from_token = self.do_sync(sync_body, tok=user1_tok)
+
+        # Initial sync so we expect to see a bump stamp
+        self.assertIn("bump_stamp", response_body["rooms"][room_id1])
+        first_bump_stamp = response_body["rooms"][room_id1]["bump_stamp"]
+
+        # Send a bump event at the start.
+        self.helper.send(room_id1, "test", tok=user1_tok)
+
+        # Send events that are not in the bump events list to fill the timeline
+        for _ in range(5):
+            self.helper.send_event(
+                room_id1, type="org.matrix.test", content={}, tok=user1_tok
+            )
+
+        response_body, from_token = self.do_sync(
+            sync_body, since=from_token, tok=user1_tok
+        )
+
+        # There was a bump event in the timeline gap, so we should see the bump
+        # stamp be updated.
+        self.assertIn("bump_stamp", response_body["rooms"][room_id1])
+        second_bump_stamp = response_body["rooms"][room_id1]["bump_stamp"]
+
+        self.assertGreater(second_bump_stamp, first_bump_stamp)
+
     def test_rooms_bump_stamp_invites(self) -> None:
         """
         Test that `bump_stamp` is present and points to the membership event,

tests/rest/client/test_delayed_events.py

@@ -8,11 +8,12 @@ from parameterized import parameterized
 from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.errors import Codes
-from synapse.rest.client import delayed_events, room
+from synapse.rest.client import delayed_events, room, versions
 from synapse.server import HomeServer
 from synapse.types import JsonDict
 from synapse.util import Clock
 
+from tests import unittest
 from tests.unittest import HomeserverTestCase
 
 PATH_PREFIX = "/_matrix/client/unstable/org.matrix.msc4140/delayed_events"
@@ -21,6 +22,21 @@ _HS_NAME = "red"
 _EVENT_TYPE = "com.example.test"
 
 
+class DelayedEventsUnstableSupportTestCase(HomeserverTestCase):
+    servlets = [versions.register_servlets]
+
+    def test_false_by_default(self) -> None:
+        channel = self.make_request("GET", "/_matrix/client/versions")
+        self.assertEqual(channel.code, 200, channel.result)
+        self.assertFalse(channel.json_body["unstable_features"]["org.matrix.msc4140"])
+
+    @unittest.override_config({"max_event_delay_duration": "24h"})
+    def test_true_if_enabled(self) -> None:
+        channel = self.make_request("GET", "/_matrix/client/versions")
+        self.assertEqual(channel.code, 200, channel.result)
+        self.assertTrue(channel.json_body["unstable_features"]["org.matrix.msc4140"])
+
+
 class DelayedEventsTestCase(HomeserverTestCase):
     """Tests getting and managing delayed events."""