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>

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

View reviewed changes

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

543a97e

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

MadLittleMods approved these changes Mar 5, 2026

View reviewed changes

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

View reviewed changes

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

Preferable test comment

2c33715

Merge branch 'develop' into rei/sticky_events_oldschool_sync

a6b0ce1

MadLittleMods approved these changes Mar 5, 2026

View reviewed changes

Comment 'As per MSC4354'

69a07ec

reivilibre merged commit 6e1ac55 into develop Mar 10, 2026
79 of 81 checks passed

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

Open

3 tasks

reivilibre mentioned this pull request Mar 20, 2026

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

Open

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

Open

giles-labrys mentioned this pull request Apr 27, 2026

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

Open

		@@ -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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reivilibre commented Feb 20, 2026

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