RTCDataChannel: transition to `closing`?

Lennart has raised the question as to how an application determines that a remote peer has called RTCDataChannel.close() in Issue https://github.com/w3c/webrtc-pc/issues/1827 .

The specification appears to indicate that this causes a peer receiving an incoming stream reset to transition the RTCDataChannel readyState to closing, with no resulting event (e.g. onclose event handler is not fired). Adding an onclosing event handler seems icky.

Looking at RFC 6525 and Section 6.7 of draft-ietf-rtcweb-data-channel, one way to handle this would be to have receipt of an incoming stream reset cause readyState to transition to closed. The receipt of an incoming stream reset causes an outgoing stream reset to be sent. While after sending an outgoing stream reset the peer could transition readyState to closing and await receipt of a re-configuration response with a result of success prior to transitioning readyState to closed, after sending the outgoing stream reset, data can neither be sent nor received so closed might be more appropriate.

"6.7. Closing a Data Channel

Closing of a data channel MUST be signaled by resetting the corresponding outgoing streams [RFC6525]. This means that if one side decides to close the data channel, it resets the corresponding outgoing stream. When the peer sees that an incoming stream was reset, it also resets its corresponding outgoing stream. Once this is completed, the data channel is closed. Resetting a stream sets the Stream Sequence Numbers (SSNs) of the stream back to 'zero' with a corresponding notification to the application layer that the reset has been performed. Streams are available for reuse after a reset has been performed.

[RFC6525] also guarantees that all the messages are delivered (or abandoned) before the stream is reset."

w3c / ortc

RTCDataChannel: transition to `closing`? #838