[MatrixRTC] Sticky Events support (MSC4354) #5017

toger5 · 2025-09-23T17:50:36Z

Depends on #5028

This PR adds support for sticky events in the MatrixRTCSession:

send sticky events instead of state events
update the call memberships based on sticky events instead of membership changes.
resend the current membership if the sticky event times out with an updated expiration ts (This is not the final solution. the sticky event timeout in iteself is enough. no expiration needed on the event content)

src/models/room.ts

toger5

temp review

spec/unit/models/room.spec.ts

src/models/room-sticky-events.ts

toger5 · 2025-09-30T15:26:24Z

src/matrixrtc/MatrixRTCSession.ts

+interface SessionMembershipsForRoomOpts {
+    listenForStickyEvents: boolean;
+    listenForMemberStateEvents: boolean;
+}


Wondering if we really want to make this configurable?
It would be great if we can just always make it listen to this?
Not sure its possible however...
Do you have an idea for a case where "always on" would break?

So you can do both at the same time? Or does it fall back to state on some trigger?
If this is temporary, it might be worth a comment to kill state as soon as event/sticky is deployed enough?

toger5 · 2025-09-30T15:35:31Z

src/matrixrtc/MatrixRTCSessionManager.ts

        }

        this.client.on(ClientEvent.Room, this.onRoom);
+        this.client.on(ClientEvent.Event, this.onEvent);


this in combination with:
this.roomSubset.on(RoomEvent.StickyEvents, this.onStickyEventUpdate);
will result in two calls to recalculateSessionMembers once via refreshRoom -> onRTCSessionMemberUpdate -> recalculateSessionMembers And a second time throughonStickyEventUpdate->`recalculateSessionMembers.

Or is there any check so one of them gets ignored?

A possible solution would be to check if the associated room already has a session (in onRoom) and if so, we do not call refresh room? So it only gets called on creating a new session?

This logic maybe should be applied to all of this file. refreshRoom should be: refreshSessionStore/Map and than we expect the session itself to listen to all the evnt updates. Listeners in the SessionManager only are responsible to find out if new sessions need to be created!

toger5 · 2025-10-07T13:25:41Z

I am relativly sure we are doing the right thing.
But I want to write down (and get confirmation) that we do expire call memberships if the sticky duration times out

Once a sticky event expires we emit the sticky map change action
if that action is emitted we recalculate the room
public static sessionMembershipsForSlot will get called as a consequence
this method will compute all the memberships based on the CURRENT SET OF matrix sticky events? (so if some event times out, it will not be in the CURRENT SET OF matrix sticky and hence will not be aprt of the memberships anymore?

Signed-off-by: Timo K <[email protected]>

spec/unit/matrixrtc/MembershipManager.spec.ts

Signed-off-by: Timo K <[email protected]>

src/matrixrtc/MembershipManager.ts

Half-Shot

Otherwise LGTM

Signed-off-by: Timo K <[email protected]>

BillCarsonFr · 2025-10-13T09:32:25Z

src/@types/event.ts

    [M_BEACON.name]: MBeaconEventContent;
    [M_POLL_START.name]: PollStartEventContent;
    [M_POLL_END.name]: PollEndEventContent;
+    [EventType.RTCMembership]: RtcMembershipData | { msc4354_sticky_key?: string };


Maybe add a TODO to try to use UnstableValue here too?

We should in a separate PR, yea. I'll open one to track it.

Drafted as #5042

BillCarsonFr · 2025-10-13T09:32:49Z

src/matrixrtc/MatrixRTCSession.ts

-     * Default: `false`.
-     * @deprecated does nothing anymore we always default to the new membership manager.
-     */
-    useNewMembershipManager?: boolean;


This was just deleting it since it did nothing. A bit cheeky but might as well drop it.

BillCarsonFr · 2025-10-13T09:56:11Z

src/matrixrtc/MatrixRTCSession.ts

+interface SessionMembershipsForRoomOpts {
+    listenForStickyEvents: boolean;
+    listenForMemberStateEvents: boolean;
+}


So you can do both at the same time? Or does it fall back to state on some trigger?
If this is temporary, it might be worth a comment to kill state as soon as event/sticky is deployed enough?

toger5 changed the title ~~Toger5/sticky-events~~ Sticky Events support for matrixRTC (MSC4354) Sep 23, 2025

toger5 force-pushed the toger5/sticky-events branch 2 times, most recently from 4ff6fb9 to dde4abb Compare September 23, 2025 17:57

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toger5 mentioned this pull request Sep 24, 2025

Add sticky event support element-hq/element-call#3513

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MSC4354: Sticky Events matrix-org/matrix-spec-proposals#4354

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MSC4140: Cancellable delayed events matrix-org/matrix-spec-proposals#4140

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Implement Sticky Events MSC

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Implement Sticky Events MSC4354 #5028

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Update sticky events to use NamespacedValue for later stable support. #5042

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toger5 commented Sep 23, 2025 •

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