Re: [rtcweb] Data channel: Handling of packets on unknown channels

[Michael Tuexen <[e-mail]>]

> On 28. Jun 2018, at 17:01, Harald Alvestrand <[e-mail]> wrote:
> 
> Den 28. juni 2018 16:35, skrev Michael Tuexen:
>>> On 28. Jun 2018, at 16:22, Harald Alvestrand <[e-mail]> wrote:
>>> 
>>> Den 28. juni 2018 14:51, skrev Michael Tuexen:
>>>>> On 28. Jun 2018, at 13:30, Harald Alvestrand <[e-mail]> wrote:
>>>>> 
>>>>> In considering the datachannel API, we encountered one interesting race
>>>>> condition:
>>>>> 
>>>>> A: <configure for datachannel>
>>>>> 
>>>>> A: CreateOffer(), SetLocalDescription(), send SDP
>>>>> 
>>>>> B: SetRemoteDescription, CreateAnswer, SetLocalDescription, send SDP
>>>>> 
>>>>> B: Configure an externally defined data channel, with #3249
>>>>> 
>>>>> B: Send a message on #3249
>>>>> 
>>>>> A: SetRemoteDescription
>>>>> 
>>>>> A: Wait a while (THE PAUSE)
>>>>> 
>>>>> A: Configure #3249
>>>>> 
>>>>> Now, if a message comes in to A on #3249 during THE PAUSE, what is the
>>>>> implementation to do?
>>>> Isn't that some kind or error condition?
>>>> 
>>>> If that it true, one could apply:
>>>> 
>>>>  If a message with an unsupported PPID is received or some error
>>>>  condition related to the received message is detected by the receiver
>>>>  (for example, illegal ordering), the receiver SHOULD close the
>>>>  corresponding data channel.  This implies in particular that
>>>>  extensions using additional PPIDs can't be used without prior
>>>>  negotiation.
>>> 
>>> 
>>> The receiver can't close the datachannel if the datachannel doesn't
>>> exist yet, so this doesn't work for that case.
>> I was assuming that the SCTP receives a user message on a stream. When
>> this message is delivered to its upper layer, doesn't this layer know
>> that there is no data channel? I would assume that this layer triggers
>> the stream reset procedure. I'm not saying that the user (for example
>> via a JS API) is involved... I'm more talking about implementing this
>> iside the browser..
> 
> 
> Exactly, it could close the stream, but it can't close the data channel
> since it doesn't exist.
Well, I can run the procedure and the peer will get an indication that
something isn't working well.
> 
> I think closing the stream would be a mistake, since that would make the
> outcome about whether you end up with the datachannel or not racy;
> discarding data will give you a working datachannel once A gets around
> to configuring it.
But if the user configures a reliable data channel, the user does not
get the service that was required...

Best regards
Michael
>