Add sticky event support #3513

toger5 · 2025-09-24T12:45:57Z

This uses the newly merged sticky event work. Largely this just adds a new setting to enable it when starting a call. Sticky events will always work if someone else on the call enables it.

Testing options

Netilify

use the linked netlify build https://pr3513--element-call.netlify.app/
open the netlify url WITH a homeserver url parameter to link your custom homeserver (example: https://localhost:3000?homeserver=https%3A%2F%2Ftest.com encoding is of course needed)
start a call with this link (using the homeserver url param) (in multiple browser envs (private, non private OR firefox container extension)

Locally

pull/download this PR/branch
start the docker dev env via yarn backend (synapse, livekit sfu, nginx, jwt authorizationService...)
(in a new terminal) start EC yarn dev

Now it should "just work" to do calls on https://localhost:3000

BillCarsonFr

So this is added a new lab option?
It is just for Netlify? so why a review?

BillCarsonFr · 2025-10-10T11:16:30Z

src/home/useGroupCallRooms.ts

+  }
+
+  // There was call membership events at some point in the timeline.
+  return timeline.getEvents().some(


There is no API to get the sticky events? Having the sticky key doesn't make the event sticky.
I am a bit lost with what this method is expecting to do

BillCarsonFr · 2025-10-10T11:21:23Z

src/home/useGroupCallRooms.ts

+  }
+
+  // There was call membership events at some point in the timeline.
+  return timeline.getEvents().some(


What is this method exactly? Try some heuristic to see if a room is a call room? like type": "org.matrix.msc3417.call"?

Or if there might be an active call?
And now it is checking for possible past sticky events (but potentially not anymore sticky)?
I don't get what this doing and what for

Half-Shot · 2025-10-13T08:18:04Z

It is just for Netlify? so why a review?

Sorry failed to change the title 🤦

- use new js-sdk - use custom synapse - don't filter rooms by existing call state events Signed-off-by: Timo K <[email protected]>

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

… toger5/sticky-events-version

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

toger5

I think the following might make sense:

since sticky events imply the new event format it also implies multi-sfu (new event format does not have a oldest member transport)
rename the dev option to: use sticky m.rtc.member` events
Always use multi sfu when stikcy evnets are activated (gray out the multi sfu option)
Currently turning multi-sfu off and sticky on results in not sending any transport at all

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

toger5 · 2025-10-20T15:16:20Z

I think this might be ready to merge @robintown

src/rtcSessionHelpers.ts

robintown · 2025-10-21T04:46:30Z

src/rtcSessionHelpers.ts

      membershipEventExpiryMs:
        matrixRtcSessionConfig?.membership_event_expiry_ms,
      useExperimentalToDeviceTransport,
+      unstableSendStickyEvents: preferStickyEvents.getValue(),


Could be nice to have preferStickyEvents be an explicit parameter of enterRtcSession, like multiSfu is, so we can easily turn on sticky events in the middle of a call when dogfooding

we would still need to rejoin and setup a new membership manager. I am not sure its worth the effort?

Sure but with the scope.reconcile method already used for starting and stopping the membership managers as needed, this ends up being pretty trivial.

Incidentally I see it as necessary to make the CallViewModel also aware of the relationship between multiSfu and preferStickyEvents (the fact that one force-enables the other), otherwise it would pass the wrong transport to enterRtcSession. So I just committed e313cf0 which handles both these things. Does it look reasonable to you?

robintown · 2025-10-21T04:58:31Z

src/home/useGroupCallRooms.ts

+
+  // Check for *active* calls using sticky events.
+  for (const sticky of room._unstable_getStickyEvents()) {
+    if (sticky.getType() === EventType.GroupCallMemberPrefix) {


Presumably we should refer to RTCMembership here rather than GroupCallMemberPrefix (though TBH we could probably replace this entire function body with return true; and it would be fine… we're definitely not aiming to support using the SPA in cases where the homeserver is also used by messenger apps… well, maybe we are with the guest access use case, but I don't think we'll care about giving guest access users a home page at all.)

100%.
Lets keep the function in for now. There might be some use for it in the guest case and it is very detangled from the rest of element-call -> not complexifying the codebase. (just makes it larger)

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

CallViewModel would pass the wrong transport to enterRtcSession when the user enabled sticky events but didn't manually enable multi-SFU mode as well. This likely would've added some confusion to our attempts to test these modes.

robintown

I think this looks pretty much ready now. But just one thing I want to get clarity on (for my future reference as we eventually roll the Matrix 2.0 changes out to the public):

Largely this just adds a new setting to enable it when starting a call. Sticky events will always work if someone else on the call enables it.

From what I can tell by looking at the matrix-js-sdk diff, it's not the case that it switches membership manager implementations when another participant sending sticky events is detected. Do you mean that the setting enables sending sticky events, but receiving sticky events will always work?

robintown · 2025-10-21T17:09:27Z

src/rtcSessionHelpers.ts

      membershipEventExpiryMs:
        matrixRtcSessionConfig?.membership_event_expiry_ms,
      useExperimentalToDeviceTransport,
+      unstableSendStickyEvents: preferStickyEvents.getValue(),


Sure but with the scope.reconcile method already used for starting and stopping the membership managers as needed, this ends up being pretty trivial.

Incidentally I see it as necessary to make the CallViewModel also aware of the relationship between multiSfu and preferStickyEvents (the fact that one force-enables the other), otherwise it would pass the wrong transport to enterRtcSession. So I just committed e313cf0 which handles both these things. Does it look reasonable to you?

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

toger5 · 2025-10-22T10:53:16Z

I added another todo comment so we can dont forget discussion the transport$ naming. I am not exactly sure transport makes so much sense considering it now includes the sticky option.

I will merge this into the main multi sfu branch as it is now however so we have less branches to handle.

github-actions bot deployed to Netlify September 24, 2025 12:57 View deployment

kegsay mentioned this pull request Sep 24, 2025

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

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4 tasks

Half-Shot self-assigned this Sep 25, 2025

Half-Shot marked this pull request as ready for review October 6, 2025 08:58

Half-Shot requested a review from a team as a code owner October 6, 2025 08:58

Half-Shot requested a review from robintown October 6, 2025 08:58

github-actions bot deployed to Netlify October 6, 2025 08:59 View deployment

BillCarsonFr reviewed Oct 10, 2025

View reviewed changes

Half-Shot changed the title ~~[Netlify] Add sticky event support~~ Add sticky event support Oct 13, 2025

toger5 and others added 7 commits October 13, 2025 11:56

add sticky event support

4bfe5c5

- use new js-sdk - use custom synapse - don't filter rooms by existing call state events Signed-off-by: Timo K <[email protected]>

enable sticky events in the joinSessionConfig

2dcb823

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

Remove unused useNewMembershipmanager setting

f3abcb6

Add prefer sticky setting]

3ffaf33

Fixup call detection logic to allow sticky events

1546c04

lint

abcf300

update docker image

6580555

Half-Shot force-pushed the toger5/sticky-events-version branch from eb586a5 to 6580555 Compare October 13, 2025 10:58

Half-Shot changed the base branch from livekit to voip-team/rebased-multiSFU October 13, 2025 10:59

Half-Shot added 3 commits October 13, 2025 12:05

More tidy

b90bf7d

Merge remote-tracking branch 'origin/voip-team/rebased-multiSFU' into…

3337768

… toger5/sticky-events-version

update checksum

a9586fe

github-actions bot deployed to Netlify October 15, 2025 14:40 View deployment

bump js-sdk fix sticky events type

b34bee0

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

github-actions bot deployed to Netlify October 15, 2025 15:50 View deployment

fix demo

63be993

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

github-actions bot deployed to Netlify October 15, 2025 23:04 View deployment

toger5 commented Oct 20, 2025

View reviewed changes

always use multi sfu if we are using sticky events.

e523776

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

github-actions bot deployed to Netlify October 20, 2025 15:08 View deployment

robintown reviewed Oct 21, 2025

View reviewed changes

toger5 requested a review from robintown October 21, 2025 12:15

review

e0c0923

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

github-actions bot deployed to Netlify October 21, 2025 12:18 View deployment

lint

49d5a54

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

github-actions bot deployed to Netlify October 21, 2025 12:46 View deployment

github-actions bot deployed to Netlify October 21, 2025 17:11 View deployment

robintown approved these changes Oct 21, 2025

View reviewed changes

Fix test type errors

bd94e41

github-actions bot deployed to Netlify October 21, 2025 17:21 View deployment

add todo comment

3e0e1cc

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

github-actions bot deployed to Netlify October 22, 2025 10:52 View deployment

toger5 merged commit 5526cd7 into voip-team/rebased-multiSFU Oct 22, 2025
14 of 16 checks passed

Add sticky event support #3513

Add sticky event support #3513

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toger5 commented Sep 24, 2025 • edited by Half-Shot Loading Uh oh! There was an error while loading. Please reload this page.

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Half-Shot commented Oct 13, 2025

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toger5 commented Oct 20, 2025

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toger5 commented Oct 22, 2025

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toger5 commented Sep 24, 2025 •

edited by Half-Shot

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