Handling of rejected datachannel m-lines

[fippo]

We have a minor web compat problem with the handling of rejected datachannel SDP.
This fiddle demonstrates it:
https://jsfiddle.net/fippo/ra7t85ez/1/

In Chrome the datachannel with label "data" is closed, ondatachannel fires once with "data2"
In Firefox ondatachannel fires with both "data" and "data2" datachannels.

Which one is correct? https://www.rfc-editor.org/rfc/rfc8829.html#name-applying-an-answer does not cover the case of a rejected m= line (the fiddle actually rejects in the offer with some SDP munging but that is superficial I think)

Further:

• are subsequent offers allowed to attempt negotiating SCTP again? It seems both Chrome and Firefox allow this.
• should creating the second datachannel trigger ONN? Firefox' answer seems to be "yes" which seems sensible.

[juberti]

I tend to think that any dcs that were created ahead of the rejected dc offer should be killed, otherwise you have no way of knowing that the dcs were rejected. So Chrome's behavior seems better to me.

Yes, I think subsequent offers should be able to try again (why not?)
Yes, second DC creation should trigger ONN.

[fippo]

A corollary which might be worth pointing out: closing all local data channels should not reject a negotiated application m-line. That doesn't save you much anyway.

[fippo]

@docfaraday thoughts?