SETTINGS_HTTP3_PRIORITY_MASK? | Re: SETTINGS_PRIORITY_SCHEME | Re: Setting to disable HTTP/2 Priorities

Kari Hurtta <hurtta-ietf@elmme-mailer.org> Wed, 31 July 2019 18:37 UTC

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To: Lucas Pardue <lucaspardue.24.7@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
Date: Wed, 31 Jul 2019 21:34:17 +0300 (EEST)
From: Kari Hurtta <hurtta-ietf@elmme-mailer.org>
CC: Kari Hurtta <hurtta-ietf@elmme-mailer.org>, HTTP Working Group <ietf-http-wg@w3.org>, Dmitri Tikhonov <dtikhonov@litespeedtech.com>, Brad Lassey <lassey@chromium.org>, Kari Hurtta <khurtta@welho.com>
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Subject: SETTINGS_HTTP3_PRIORITY_MASK? | Re: SETTINGS_PRIORITY_SCHEME | Re: Setting to disable HTTP/2 Priorities
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> Hi Kari,
> 
> On Tue, Jul 30, 2019 at 4:52 PM Kari Hurtta <hurtta-ietf@elmme-mailer.org>;
> wrote:
> 
> > Why boolean ("ENABLE") ?
> 
> 
> > I suggests SETTINGS Parameter
> >
> > SETTINGS_PRIORITY_SCHEME
> >

> >
> > That is:
> >     Suggest SETTINGS_PRIORITY_SCHEME once
> >     and send SETTINGS_PRIORITY_SCHEME second time
> >     after that when you agreed with peer.
> >
> >
> > That makes SETTINGS_PRIORITY_SCHEME switch to
> > new priority scheme (when that is defined).
> >
> 
> Boolean gives us the MVP for moving away from RFC7540 priorities. The

( what is MVP ? )

> suggestion to allow also signalling "something else" is valid and has been
> mentioned by some others, thanks for sharing your thoughts.
> My personal concern is that making this too complicated may result in it
> not getting exercised in practice. This, to my mind, includes picking
> something that is a fit for HTTP/3 too.
> 
> How would you feel about an an alternative design that uses two settings?
> I.e. one for RFC750 enablement, and another to enable a specific
> prioritisation scheme.
> 
> HTTP/3 allows only one SETTINGS frame in each direction, so using that as a
> negotiation mechanism has problems. Boolean unilateral adverts work better
> in that case. We might want to say that HTTP/3 has RFC7540 priorities
> always default to disabled and not specify a setting in the core draft to
> enable them. Then, using additional boolean settings per scheme would allow
> a more common approach to priority scheme selection across H2 and H3.
> 
> Regards
> Lucas

I perhaps interpret this incorrectly, but I try reword your design.

So  HTTP/2 you have SETTINGS paramaters

 • SETTINGS_PROVIDE_HTTP2_PRIORITIES (aka SETTINGS_ENABLE_HTTP2_PRIORITIES)
 • SETTINGS_HTTP3_PRIORITY_MASK

and on HTTP/3 you have on SETTINGS paramater

 • SETTINGS_HTTP3_PRIORITY_MASK


where SETTINGS_HTTP3_PRIORITY_MASK is enable mask (or bitmask) of
HTTP/3 priority schemes which sender of SETTINGS frame support.

Because SETTINGS_HTTP3_PRIORITY_MASK does not include bit for
HTTP/2 tree priorites, HTTP/3 does not support them.

Available HTTP/3 priority schemes is intersection (or "binary and")
between sent and received SETTINGS_HTTP3_PRIORITY_MASK.


Because HTTP/3 there is only one SETTINGS frame per direction,
sending of SETTINGS_HTTP3_PRIORITY_MASK can not delayed until
SETTINGS_HTTP3_PRIORITY_MASK received from peer is learned.

Therefore SETTINGS frame can not used to indicate selected
priority scheme (if there more than one priority scheme available).


So I assume that HTTP/3 client indicates selected priority scheme
by just using it.

I my guess correct?


( If priority mask style desing is allowed to include bit
  for HTTP/2 tree priorites, then SETTINGS_PROVIDE_HTTP2_PRIORITIES
  and SETTINGS_HTTP3_PRIORITY_MASK SETTINGS parameters
  collapse to one SETTINGS paramater:

    SETTINGS_PRIORITY_MASK

)

/ Kari Hurtta