RE: question about QPACK decode framing

Brian Swander <briansw@microsoft.com> Thu, 01 November 2018 15:27 UTC

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From: Brian Swander <briansw@microsoft.com>
To: Dmitri Tikhonov <dtikhonov@litespeedtech.com>, Matthew Cox <macox@microsoft.com>
CC: "quic@ietf.org" <quic@ietf.org>
Subject: RE: question about QPACK decode framing
Thread-Topic: question about QPACK decode framing
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Date: Thu, 1 Nov 2018 15:27:09 +0000
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>From our read of the current drafts:

It seems that in the drafts that the HEADERS frame is only for the compressed headers being sent on a real stream.
The encoder and decoder streams for QPACK are just the raw encodings as described in the QPACK spec without extra framing.  
If so, then on the decoding on the decoder stream, there is no way to know (a priori) that we have a complete set of headers, since there is no overall header length available.

Can someone please clarify.

Thanks
bs


-----Original Message-----
From: Dmitri Tikhonov <dtikhonov@litespeedtech.com>; 
Sent: Wednesday, October 31, 2018 2:15 PM
To: Brian Swander <briansw@microsoft.com>;
Cc: quic@ietf.org
Subject: Re: question about QPACK decode framing

Hi Brian,

(I am assuming you're talking about processing the header block.)

The header block is in the HQ "HEADERS" frame which has a length.
Depending on your implementation, you may be able to tell if you have the complete header block buffered.

  - Dmitri.

On Wed, Oct 31, 2018 at 08:57:27PM +0000, Brian Swander wrote:
> Is there a way to determine that we are decoding a complete set of headers a priori?   I.e. is the "headers length" encoded anywhere?   Or does decode (control stream) just have to handle the case where we only have a partial header, and we just pend and wait for more data before continuing?
> 
> Thanks
> bs