Re: reserved bit from Flags field | … | Re: Setting to disable HTTP/2 Priorities

Lucas Pardue <lucaspardue.24.7@gmail.com> Fri, 09 August 2019 12:08 UTC

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From: Lucas Pardue <lucaspardue.24.7@gmail.com>
Date: Fri, 9 Aug 2019 13:05:23 +0100
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To: Kari Hurtta <hurtta-ietf@elmme-mailer.org>
Cc: HTTP Working Group <ietf-http-wg@w3.org>, Matthew Kerwin <matthew@kerwin.net.au>, Brad Lassey <lassey@chromium.org>, Dmitri Tikhonov <dtikhonov@litespeedtech.com>
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On Fri, Aug 9, 2019 at 12:40 PM Kari Hurtta <hurtta-ietf@elmme-mailer.org>;
wrote:

> Kari Hurtta <hurtta-ietf@elmme-mailer.org>;: (Fri Aug  9 14:14:06 2019)
> > Also new type codes for HEADERS and PRIORITY frames need similar
> negotiation
> > (because accounting of frames and HPACK is affected; they can not just
> > ignored as unknwon frame type codes are ignored).
>
> Or actually only HPACK is affected.
>
> ( Only DATA frames are flow control controlled. )
>
> If only new PRIORITY frame (type code) is introduced, but no changes on
> HEADER frame
> (or no new HEADER frame (type code)), then negation is not needed before
> sending frame.
>
> / Kari Hurtta
>

It really depends. The absence of priority fields in HEADERS *is* priority
information for HTTP/2's default priority scheme.

Negotiation provides feedback. Without it, a client that opportunistically
sends new_priority_scheme instructions and neglects to send the default
priority scheme's instructions may cause unintended behaviour when the
server ignores the new signal and instead prioritizes everything to the
root with the same weight. That results in a round-robin priority scheme
which is demonstrably worse for web browsing performance.