Expose MSC4354 Sticky Events over the legacy (v3) /sync API. by reivilibre · Pull Request #19487 · element-hq/synapse

reivilibre · 2026-02-20T12:31:51Z

Follows: #19365

Part of: MSC4354 whose experimental feature tracking issue is #19409

Partially supersedes: #18968 (commit history too long to point at specific commits)

This pull request is commit-by-commit review friendly.

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>

MadLittleMods · 2026-03-03T17:06:51Z

+                    # remove sticky events that are in the timeline, else we will needlessly duplicate
+                    # events. This is particularly important given the risk of sticky events spam since
+                    # anyone can send sticky events, so halving the bandwidth on average for each sticky
+                    # event is helpful.


Is this part of the MSC?

Yes:

If a sticky event is in the timeline, it MAY be omitted from the sticky.events section. This ensures we minimise duplication in the /sync response JSON.

-- MSC4354 (permalink)

I'm also proposing we make this a MUST at matrix-org/matrix-spec-proposals#4354 (comment)

Feels like we should add some "as specced" or "As per MSC4354:" kind of comment in here. Still coming back to this after a second read

reivilibre · 2026-03-04T19:55:52Z

+    @patch.object(StickyEvent, "MAX_EVENTS_IN_SYNC", 3)
+    def test_pagination_with_many_sticky_events(self) -> None:
+        """
+        Test that pagination works correctly when there are more sticky events than
+        the intended limit.
+
+        The MSC doesn't define a limit or how to set one.
+        See thread: https://github.com/matrix-org/matrix-spec-proposals/pull/4354#discussion_r2885670008
+
+        But Synapse currently emits 100 at a time, controlled by `MAX_EVENTS_IN_SYNC`.
+        In this test we patch it to 3 (as sending 100 events is not very efficient).
+        """


Heeere's a real pagination test.

Note this does a cheeky patch to set the Synapse limit to 3 events.

MSC4354 doesn't define a limit or a way for the client to set one.
The MSC thread to track: matrix-org/matrix-spec-proposals#4354 (comment)

reivilibre · 2026-03-05T16:12:22Z

@@ -2225,6 +2284,7 @@ async def handle_room_entries(room_entry: "RoomSyncResultBuilder") -> None:
                ephemeral=ephemeral_by_room.get(room_entry.room_id, []),
                tags=tags_by_room.get(room_entry.room_id),


This async wasn't being used, so I thought it was enlightening/self-documenting to remove it.
Also renamed to may because it's just an approximation.

Just double-checking, the other manual checks here give us a definite answer?

MadLittleMods · 2026-03-05T20:22:13Z

+                    # remove sticky events that are in the timeline, else we will needlessly duplicate
+                    # events. This is particularly important given the risk of sticky events spam since
+                    # anyone can send sticky events, so halving the bandwidth on average for each sticky
+                    # event is helpful.


Feels like we should add some "as specced" or "As per MSC4354:" kind of comment in here. Still coming back to this after a second read

This PR contains the following updates: | Package | Update | Change | |---|---|---| | [element-hq/synapse](https://github.com/element-hq/synapse) | minor | `v1.149.1` → `v1.150.0` | --- ### Release Notes <details> <summary>element-hq/synapse (element-hq/synapse)</summary> ### [`v1.150.0`](https://github.com/element-hq/synapse/releases/tag/v1.150.0) [Compare Source](element-hq/synapse@v1.149.1...v1.150.0) ### Synapse 1.150.0 (2026-03-24) No significant changes since 1.150.0rc1. ### Synapse 1.150.0rc1 (2026-03-17) #### Features - Add experimental support for the [MSC4370](matrix-org/matrix-spec-proposals#4370) Federation API `GET /extremities` endpoint. ([#19314](element-hq/synapse#19314)) - [MSC4140: Cancellable delayed events](matrix-org/matrix-spec-proposals#4140): When persisting a delayed event to the timeline, include its `delay_id` in the event's `unsigned` section in `/sync` responses to the event sender. ([#19479](element-hq/synapse#19479)) - Expose [MSC4354 Sticky Events](matrix-org/matrix-spec-proposals#4354) over the legacy (v3) /sync API. ([#19487](element-hq/synapse#19487)) - When Matrix Authentication Service (MAS) integration is enabled, allow MAS to set the user locked status in Synapse. ([#19554](element-hq/synapse#19554)) #### Bugfixes - Fix `Build and push complement image` CI job pointing to non-existent image. ([#19523](element-hq/synapse#19523)) - Fix a bug introduced in v1.26.0 that caused deactivated, erased users to not be removed from the user directory. ([#19542](element-hq/synapse#19542)) #### Improved Documentation - In the Admin API documentation, always express path parameters as `/<param>` instead of as `/$param`. ([#19307](element-hq/synapse#19307)) - Update docs to clarify `outbound_federation_restricted_to` can also be used with the [Secure Border Gateway (SBG)](https://element.io/en/server-suite/secure-border-gateways). ([#19517](element-hq/synapse#19517)) - Unify Complement developer docs. ([#19518](element-hq/synapse#19518)) #### Internal Changes - Put membership updates in a background resumable task when changing the avatar or the display name. ([#19311](element-hq/synapse#19311)) - Add in-repo Complement test to sanity check Synapse version matches git checkout (testing what we think we are). ([#19476](element-hq/synapse#19476)) - Migrate `dev` dependencies to [PEP 735](https://peps.python.org/pep-0735/) dependency groups. ([#19490](element-hq/synapse#19490)) - Remove the optional `systemd-python` dependency and the `systemd` extra on the `synapse` package. ([#19491](element-hq/synapse#19491)) - Avoid re-computing the event ID when cloning events. ([#19527](element-hq/synapse#19527)) - Allow caching of the `/versions` and `/auth_metadata` public endpoints. ([#19530](element-hq/synapse#19530)) - Add a few labels to the number groupings in the `Processed request` logs. ([#19548](element-hq/synapse#19548)) </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).  Reviewed-on: https://gitea.alexlebens.dev/alexlebens/infrastructure/pulls/5040 Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net> Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

…-hq#19487) Follows: element-hq#19365 Part of: MSC4354 whose experimental feature tracking issue is element-hq#19409 Partially supersedes: element-hq#18968 --------- Signed-off-by: Olivier 'reivilibre' <oliverw@matrix.org>

…19591) Follows: #19487 Part of: MSC4354 whose experimental feature tracking issue is #19409 This PR implements the Sliding Sync (MSC4186) extension described in MSC4354, allowing sliding sync clients to receive sticky events in a reliable way. The logic is much the same as for oldschool sync (implementation in #19487), although in the sliding sync extension, the client can choose their own limit and must control their own pagination through an extra token in the extension request/response bodies. Note this does not yet send down existing sticky events in the room when the room has been newly-joined. This newly-discovered gap is tracked at #19662 and will be addressed for both current sync and MSC4186 SSS soon. --------- Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org> Co-authored-by: Eric Eastwood <erice@element.io>

@jason-famedly

Tested on NetBSD 10 amd64 with 2026Q2 environment. # Synapse 1.156.0 (2026-07-07) ## Features - Expose [MSC4354 Sticky Events](matrix-org/matrix-spec-proposals#4354) over [MSC4186 (Simplified) Sliding Sync](matrix-org/matrix-spec-proposals#4186). ([\#19591](element-hq/synapse#19591)) - Stabilize support for sending ephemeral events to application services, as per [MSC2409](matrix-org/matrix-spec-proposals#2409). Contributed by @jason-famedly @ Famedly. ([\#19758](element-hq/synapse#19758)) - Include `allowed_room_ids` in the `/summary` client-server API response for rooms with restricted join rules, as required by Matrix 1.15. Contributed by @FrenchGithubUser @famedly. ([\#19762](element-hq/synapse#19762)) - [MSC4140: Cancellable delayed events](matrix-org/matrix-spec-proposals#4140): Allow authentication on delayed event management endpoints (such as `/restart`) to bypass ratelimits for unauthenticated requests based on the client IP address. ([\#19794](element-hq/synapse#19794)) - Add new metric `synapse_non_deactivated_user_count` which tracks the number of non-deactivated users in the database, split by `app_service`. ([\#19848](element-hq/synapse#19848)) - The `GET /_matrix/client/unstable/org.matrix.msc1763/retention/configuration` endpoint is now provided when retention is enabled and `experimental_features.msc1763_enabled` is enabled, based on [MSC1763](matrix-org/matrix-spec-proposals#1763). ([\#19853](element-hq/synapse#19853)) - Add experimental support for [MSC4491: Invite reasons in room creation](matrix-org/matrix-spec-proposals#4491). ([\#19874](element-hq/synapse#19874)) # Synapse 1.155.0 (2026-06-16) # Synapse 1.154.0 (2026-06-04) ## Features - Add support for [MSC4452: Preview URL capabilities API](matrix-org/matrix-spec-proposals#4452) which exposes a `io.element.msc4452.preview_url` capability. If `experimental_features.msc4452_enabled` is `true`, the `/_matrix/(client/v1/media|media/v3)/preview_url` endpoint now responds with a 403 status code when the capability is disabled. ([\#19715](element-hq/synapse#19715)) # Synapse 1.153.0 (2026-05-19) ## Features - Make ACLs apply to EDUs per [MSC4163](matrix-org/matrix-spec-proposals#4163). ([\#18475](element-hq/synapse#18475)) - Stabilize [MSC3266: Room summary API](matrix-org/matrix-spec-proposals#3266), removing the experimental config flag `msc3266_enabled`. Contributed by @dasha-uwu. ([\#19720](element-hq/synapse#19720)) - Partial [MSC4311](matrix-org/matrix-spec-proposals#4311) implementation: `m.room.create` is now a required part of stripped `invite_state`/`knock_state` . Contributed by @FrenchGithubUser @famedly. ([\#19722](element-hq/synapse#19722)) - Expose `tombstoned` and `replacement_room` in room details on admin API endpoint `GET /_synapse/admin/v1/rooms/<room_id>`. Contributed by Noah Markert. ([\#19737](element-hq/synapse#19737)) # Synapse 1.152.1 (2026-05-07) # Synapse 1.152.0 (2026-04-28) ## Features - Add a ["Listing quarantined media changes" Admin API](https://element-hq.github.io/synapse/latest/admin_api/media_admin_api.html#listing-quarantined-media-changes) for retrieving a paginated record of when media became (un)quarantined. ([\#19558](element-hq/synapse#19558), [\#19677](element-hq/synapse#19677), [\#19694](element-hq/synapse#19694)) - Advertise [MSC4445](matrix-org/matrix-spec-proposals#4445) sync timeline order in `unstable_features`. ([\#19642](element-hq/synapse#19642)) - Report the Rust compiler version used in the Prometheus metrics. Contributed by Noah Markert. ([\#19643](element-hq/synapse#19643)) - Passthrough 'article' and 'profile' OpenGraph metadata on URL preview requests. ([\#19659](element-hq/synapse#19659)) - Add a way to re-sign local events with a new signing key. ([\#19668](element-hq/synapse#19668)) - Support [MSC4450: Identity Provider selection for User-Interactive Authentication with Legacy Single Sign-On](matrix-org/matrix-spec-proposals#4450). ([\#19693](element-hq/synapse#19693)) - Add experimental support for [MSC4242](matrix-org/matrix-spec-proposals#4242): State DAGs. Excludes federation support. ([\#19424](element-hq/synapse#19424)) - Adds [Admin API](https://element-hq.github.io/synapse/latest/usage/administration/admin_api/index.html) endpoints to list, fetch and delete user reports. ([\#19657](element-hq/synapse#19657)) - Reduce database disk space usage by pruning old rows from `device_lists_changes_in_room`. ([\#19473](element-hq/synapse#19473), [\#19709](element-hq/synapse#19709)) # Synapse 1.151.0 (2026-04-07) ## Features - Add stable support for [MSC4284](matrix-org/matrix-spec-proposals#4284) Policy Servers. ([\#19503](element-hq/synapse#19503)) - Update and stabilize support for [MSC2666](matrix-org/matrix-spec-proposals#2666): Get rooms in common with another user. Contributed by @tulir @ Beeper. ([\#19511](element-hq/synapse#19511)) - Updated experimental support for [MSC4388: Secure out-of-band channel for sign in with QR](matrix-org/matrix-spec-proposals#4388). ([\#19573](element-hq/synapse#19573)) - Stabilize `room_version` and `encryption` fields in the space/room `/hierarchy` API (part of [MSC3266](matrix-org/matrix-spec-proposals#3266)). ([\#19576](element-hq/synapse#19576)) - Introduce a [configuration option](https://element-hq.github.io/synapse/latest/usage/configuration/config_documentation.html#matrix_authentication_service) to allow using HTTP/2 over plaintext when Synapse connects to Matrix Authentication Service. ([\#19586](element-hq/synapse#19586)) ## Deprecations and Removals - Remove support for [MSC3852: Expose user agent information on Device](matrix-org/matrix-spec-proposals#3852) as the MSC was closed. ([\#19430](element-hq/synapse#19430)) # Synapse 1.150.0 (2026-03-24) ## Features - Add experimental support for the [MSC4370](matrix-org/matrix-spec-proposals#4370) Federation API `GET /extremities` endpoint. ([\#19314](element-hq/synapse#19314)) - [MSC4140: Cancellable delayed events](matrix-org/matrix-spec-proposals#4140): When persisting a delayed event to the timeline, include its `delay_id` in the event's `unsigned` section in `/sync` responses to the event sender. ([\#19479](element-hq/synapse#19479)) - Expose [MSC4354 Sticky Events](matrix-org/matrix-spec-proposals#4354) over the legacy (v3) /sync API. ([\#19487](element-hq/synapse#19487)) - When Matrix Authentication Service (MAS) integration is enabled, allow MAS to set the user locked status in Synapse. ([\#19554](element-hq/synapse#19554))

reivilibre changed the title ~~Expose [MSC4354 Sticky Events](https://github.com/matrix-org/matrix-spec-proposals/pull/4354) over the legacy (v3) /sync API.~~ Expose MSC4354 Sticky Events over the legacy (v3) /sync API. Feb 20, 2026

reivilibre marked this pull request as ready for review February 20, 2026 16:34

reivilibre requested a review from a team as a code owner February 20, 2026 16:34

MadLittleMods added the A-Sync label Feb 23, 2026

reivilibre added 4 commits February 27, 2026 20:14

Add get_sticky_events_in_rooms store function

63024c4

Expose MSC4354 sticky events in oldschool sync

69f76c3

Add endpoint test for sticky events in sync

c8174c9

Newsfile

48a42e8

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>

reivilibre force-pushed the rei/sticky_events_oldschool_sync branch from 7c4ca8e to 48a42e8 Compare February 27, 2026 20:15

MadLittleMods self-requested a review March 3, 2026 16:49

MadLittleMods reviewed Mar 3, 2026

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reivilibre added 4 commits March 4, 2026 18:55

fixup! Expose MSC4354 sticky events in oldschool sync

6c9c9fe

Comment why ignore history visibility

5f5570c

Add mathematical notation

a70e411

fixup! Add get_sticky_events_in_rooms store function

005fcda

reivilibre force-pushed the rei/sticky_events_oldschool_sync branch from ef5e852 to 005fcda Compare March 4, 2026 19:04

reivilibre added 5 commits March 4, 2026 19:48

fixup! Add get_sticky_events_in_rooms store function

4a42a56

Test commentary

e975caf

Reorder assertions

654cb1d

Reword test

6368a9e

Make a real pagination test

a4b09ab

reivilibre force-pushed the rei/sticky_events_oldschool_sync branch from b98a932 to a4b09ab Compare March 4, 2026 19:52

reivilibre commented Mar 4, 2026

View reviewed changes

XXX Move sticky_by_room condition

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reivilibre requested a review from MadLittleMods March 4, 2026 20:07

MadLittleMods approved these changes Mar 5, 2026

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Comment thread tests/rest/client/test_sync_sticky_events.py

Comment thread tests/rest/client/test_sync_sticky_events.py Outdated

Comment 'no change' no-op sync logic

35a0eb6

reivilibre commented Mar 5, 2026

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reivilibre requested a review from MadLittleMods March 5, 2026 16:12

Preferable test comment

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Merge branch 'develop' into rei/sticky_events_oldschool_sync

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MadLittleMods approved these changes Mar 5, 2026

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Comment 'As per MSC4354'

69a07ec

reivilibre merged commit 6e1ac55 into develop Mar 10, 2026
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reivilibre deleted the rei/sticky_events_oldschool_sync branch March 10, 2026 10:39

MadLittleMods mentioned this pull request Mar 16, 2026

MSC4140: update error responses #19539

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3 tasks

reivilibre mentioned this pull request Mar 20, 2026

Expose MSC4354 Sticky Events over MSC4186 (Simplified) Sliding Sync. #19591

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Just-Insane mentioned this pull request Mar 27, 2026

UnboundLocalError: now_token in /sync for appservice bots using MSC3202 (regression in v1.150.0) #19618

Closed

giles-labrys mentioned this pull request Apr 27, 2026

feat: add sticky events to SyncUpdate famedly/matrix-dart-sdk#2238

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MadLittleMods mentioned this pull request Jun 5, 2026

Document that the SQLite version included in Ubuntu LTS, aside from ESM-only versions, is included in our support policy. #19823

Merged

		@@ -2225,6 +2284,7 @@ async def handle_room_entries(room_entry: "RoomSyncResultBuilder") -> None:
		ephemeral=ephemeral_by_room.get(room_entry.room_id, []),
		tags=tags_by_room.get(room_entry.room_id),

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