MSC4075: MatrixRTC Call Ringing

[toger5]

Rendered

To-do:

• How do you decline a call?
• Implementations using revised format from 04635eb (#4075)
• This looks very similar to m.call.invite but with much less info. Have we taken into account learnings from this existing capability?

Dependencies:

• MSC4143: MatrixRTC #4143

Implementations:

• Element Web
  • sending rings: Add ringing for matrixRTC matrix-react-sdk#11870
  • ringing: Add ringing for matrixRTC matrix-react-sdk#11870
• Ruma
  • notify event support: Add CallNotify event as described by MSC4075 ruma/ruma#1704
• Element X
  • android sending rings
  • android ringing
  • ios sending rings
  • ios ringing
• Extensible events fallback
  • Element web
  • Element X ios
  • Element X android

[uhoreg]

@toger5 You've added some implementations in the PR description. Do these implement the MSC in full, or are there parts of the MSC that are still lacking implementation?

[toger5]

Yes it's implemented in full. At least on the platforms shown in the description (EW).

There are optional configurations that are still missing. (Allowing to send a notification to a specific subset of users) but the API for this is already part of the SDK. There is no ui for this however and we are not sure we want that in EW.

[td-famedly]

Instead of hardcoding 10 seconds, I am assuming the clients could probably just look at the lifetime field for the invite event mapped to call_id from the notify event.

[toger5]

Which invite event are you referring to? The general idea is to allow the receiver to choose a ring duration and not the sender.
So reading from any event would result in someone else choosing how long you device should ring.

[td-famedly]

The general idea is to allow the receiver to choose a ring duration and not the sender.

To me that sounds a bit counter intuitive, f.ex I would not want to stop ringing the device after 10 seconds if the m.call.invite lifetime was 60 seconds and I can still pick up the call. Or does the "stop ringing after 10 seconds" also automatically send a reject then? (might be out of scope for this PR)

[toger5]

This is independent of the legacy call invite event. It is just what we use for matrix RTC sessions where there is no enforced call buildup procedure. (You just post your state event)
So most likely there is no call.invite event which lifetime could be used. The call notify event is the one that could include a lifetime. But we decided against that as described in the msc and the comment above.
It's also a slightly different semantic since the calling participant can stay in the call for however long they desire. Where a call invite has a Lifetime.