PSA: Changing Datachannel ID allocation time

[Harald Alvestrand]

Back in 2019, we discovered that the standard's allocation of DataChannel ID was logically unsound (https://github.com/w3c/webrtc-pc/issues/1818). The unsound part was that we could not know if a channel ID was valid before knowing the number of streams available, and this was not possible to know before SCTP offer/answer had completed.

This was fixed in spec PR https://github.com/w3c/webrtc-pc/pull/2222, which moved the allocation of IDs to the completion of the SCTP setup. However, implementations were slow to catch up - as of today, Chrome still allocates IDs at offer/answer completion, and WPT tests still verify that this happens.

I am looking at making this change (for other reasons), but am wondering if anyone knows that they will be affected by delaying the allocation of channel ID from offer/answer completion to SCTP setup completion?

Harald