Re: SETTINGS_ENABLE_HTTP2_PRIORITIES default value | Re: Setting to disable HTTP/2 Priorities

Lucas Pardue <lucaspardue.24.7@gmail.com> Wed, 31 July 2019 19:16 UTC

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From: Lucas Pardue <lucaspardue.24.7@gmail.com>
Date: Wed, 31 Jul 2019 20:14:24 +0100
Message-ID: <CALGR9oYddEX+GeA9yTXD+hH9ufdUC7qSpo2MW8-UcXUNqEgM-Q@mail.gmail.com>
To: Kari Hurtta <hurtta-ietf@elmme-mailer.org>
Cc: HTTP Working Group <ietf-http-wg@w3.org>, Willy Tarreau <w@1wt.eu>, Brad Lassey <lassey@chromium.org>
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Subject: Re: SETTINGS_ENABLE_HTTP2_PRIORITIES default value | Re: Setting to disable HTTP/2 Priorities
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On Wed, 31 Jul 2019, 20:10 Kari Hurtta, <hurtta-ietf@elmme-mailer.org>;
wrote:

> > The aim is to maintain todays default behavior of endpoints supporting
> H2.
> > This is achieved by defining the initial value of the setting as 1;
> > endpoints "opt out" by sending 0.
> >
> >Do you think we have mis-specced this compared to our aim?
>
>
> There is  "If a client or server does not send the setting, the peer
> SHOULD NOT make any assumptions about its support for HTTP/2 priorities.".
>
>
> https://datatracker.ietf.org/doc/draft-lassey-priority-setting/?include_text=1
>
> ------------
> 3.  The SETTINGS_ENABLE_HTTP2_PRIORITIES SETTINGS Parameter
>
>    This document adds a new SETTINGS parameter to those defined by
>    [RFC7540], Section 6.5.2.
>
>    The new parameter name is SETTINGS_ENABLE_HTTP2_PRIORITIES.  The
>    value of the parameter MUST be 0 or 1 to indicate not supporting or
>    supporting HTTP/2 priorities respectively.  If either side sends the
>    parameter with a value of 0, clients SHOULD NOT send priority frames
>    and servers SHOULD NOT make any assumptions based on the presence or
>    lack thereof of priority frames.  If both sides send the parameter
>    with a value of 1, then both parties MAY use HTTP/2 priorities as
>    they see fit.  A sender MUST NOT send the parameter with the value of
>    0 after previously sending a value of 1.  If a client or server does
>    not send the setting, the peer SHOULD NOT make any assumptions about
>    its support for HTTP/2 priorities.
> -------------
>
> This section indicates that default value is undefined, because it says
> that if SETTINGS_ENABLE_HTTP2_PRIORITIES is not seen, the peer SHOULD NOT
> make any assumptions about other ends support for HTTP/2 priorities.
>
> -------------
> 4.1.  A New HTTP/2 Setting
>
>    This document registers an entry in the "HTTP/2 Settings" registry
>    that was established by Section 11.3 of [RFC7540].
>
>    Name: SETTINGS_ENABLE_HTTP2_PRIORITIES
>
>    Code: 0xTBD
>
>    Initial Value: 1
>
>    Specification: This document
> --------------
>
> If initial value for SETTINGS_ENABLE_HTTP2_PRIORITIES is really 1,
> then peer may assume that other ends supports HTTP/2 priorities
> until SETTINGS_ENABLE_HTTP2_PRIORITIES is seen.
>
> So there is inconsistence between chapters.
>
> / Kari Hurtta
>

Agreed. We should tighten this up for something that is practically
deployable and meets the needs of implementers. Ideally we can take
feedback so far and iterate through the design team process.

Cheers
Lucas

>