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Re: RTCSdpType "rollback" and why sdp field is needed?

From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Sun, 6 Aug 2017 11:44:45 +0200
Message-ID: <CALiegfk1Dk8=OTwKCziSN4-0dxgvArTM=WqocXKkPYUrMq2pTg@mail.gmail.com>
To: "public-webrtc@w3.org" <public-webrtc@w3.org>
On Sun, Aug 6, 2017 at 11:12 AM, Iñaki Baz Castillo <ibc@aliax.net> wrote:
> Hi,
>
> When calling setLocalDescription() or setRemoteDescription() with {
> type: "rollback" , sdp: ??? }, what is sdp field supposed to have?
>
> Note that sdp field in RTCSessionDescriptionInit is not
> nullable/optional, so what is it supposed to hold when using type
> "rollback" and why is it needed at all such a sdp field?

Sorry, I understood it wrong. The spec clearly says:

> sdp of type DOMStringThe string representation of the SDP [SDP]; if type is rollback, this member is unused.


Now, if there is any Safari developer reading this (sorry, I won't
send my computer "sysdiagnose" to Apple, as your bug tracker requests,
to just report a WebRTC signaling issue), here an issue:


1) pc.setRemoteDescription(offer)

offer just includes a m=video with VP8 (not supported by Safari).

2) pc.setRemoteDescription() is then rejected. So let's try rollback:

3) pc.setRemoteDescription({ type: "rollback", sdp: "" })

4) It's rejected with "Description type incompatible with current
signaling state".

Obviously pc.signalingState was "have-remote-offer" after step 2)
above. That's why I want to perform a rollback.

If there something I misunderstand regarding the rollback mechanism?
AFAIU it's designed to be called when pc.signalingState is not
"stable", am I wrong?



-- 
Iñaki Baz Castillo
<ibc@aliax.net>
Received on Sunday, 6 August 2017 09:45:30 UTC

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