Re: Questions about QPACK

Dmitri Tikhonov <dtikhonov@litespeedtech.com> Thu, 21 November 2019 16:25 UTC

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Date: Thu, 21 Nov 2019 11:25:47 -0500
From: Dmitri Tikhonov <dtikhonov@litespeedtech.com>
To: Bence Béky <bnc@chromium.org>
Cc: Jiuhai Zhang <jiuhai.zhang@gmail.com>, quic@ietf.org, 78690842@qq.com
Subject: Re: Questions about QPACK
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On Thu, Nov 21, 2019 at 09:57:24AM -0500, Bence Béky wrote:
> > Q1:why we send N bit to peer? it seems we don't need to send the
> > bit, if sender don't want to put in dynamic table.
> 
> QPACK is hop-to-hop, that is, client to intermediary, intermediary to
> intermediary, intermediary to server, all separately (and the other
> way around).  Intermediary can be locally installed
> firewall/antivirus, proxy, reverse proxy, load balancer etc.
> Intermediaries are allowed to recompress headers using different
> algorithms using QPACK, or they might relay to an HTTP/2 connection
> using HPACK, etc.  The N bit is to inform intermediaries whether the
> original sender of the headers deems that the header MUST always be
> encoded using literals.

The HPACK RFC has a whole subsection [1] dedicated to the never-indexed
literals.  The QPACK draft refers to (and subsumes?) [2] the HPACK's
security considerations.

  - Dmitri.

1. https://tools.ietf.org/html/rfc7541#section-7.1.3
2. https://tools.ietf.org/html/draft-ietf-quic-qpack-11#section-7