Subject: Fwd: New Version Notification for draft-ietf-httpbis-priority-02.txt

From: Lucas Pardue <[email-masked]>
Date: Thu, 1 Oct 2020 13:03:24 +0100

Hi Folks,

Kazuho and I have just cut a new version of Extensible Priorities. We think
this is a good interop target and for visibility I'd like to highlight the
notable points.

Following the WG discussion (and consensus) about header and frame signals,
we have been able to make progress on changes that we had proposed during
the interim meeting in May 2020 [1]. There has been feedback in the
meantime, details are a little different but the HTTP/3 PRIORITY_UPDATE
frame has changed format, which is a breaking change. The change from ASCII
art to QUIC-style frame definition can make this hard to spot: we've
dropped the bit field and encoded the prioritization target in the frame
type codepoint. To avoid clashes with the old codepoint (and failures that
might cause, especially for any deployments in the wild), we've moved the
frame types to 0xF0700 and 0xF0701. A future draft could move these back.

Since PRIORITY_UPDATE can be used to signal initial priority, we've added
some text to explain how a server should treat that. There's a little bit
more work left there but we hope some implementation experience will help
us refine the recommendations.

We've also added more exposition and guidance about how servers should
treat the Extensible Priority signal. It's tempting to get very
prescriptive here but we've kept the ethos of HTTP/2's server scheduling
guidance: signals are hints. We've highlighted some pitfall edge-cases that
servers should consider avoiding, no doubt there are some more we might
discover during interop testing.

To summarise: the priority scheme remains the same, we've tweaked frame
signals a bit and added more requirements about how to handle them, and
we've added more text to help server implementers. We encourage people to
take a look and try this out.

Kind regards
Lucas on behalf of Extensible Priorities editors

[1] -
https://github.com/httpwg/wg-materials/blob/gh-pages/interim-20-05/priorities.pdf

---------- Forwarded message ---------
From: <[email-masked]>
Date: Thu, Oct 1, 2020 at 12:17 PM
Subject: New Version Notification for draft-ietf-httpbis-priority-02.txt
To: Lucas Pardue <[email-masked]>, Kazuho Oku <
[email-masked]>

A new version of I-D, draft-ietf-httpbis-priority-02.txt
has been successfully submitted by Lucas Pardue and posted to the
IETF repository.

Name:           draft-ietf-httpbis-priority
Revision:       02
Title:          Extensible Prioritization Scheme for HTTP
Document date:  2020-10-01
Group:          httpbis
Pages:          22
URL:            https://www.ietf.org/id/draft-ietf-httpbis-priority-02.txt
Status:
https://datatracker.ietf.org/doc/draft-ietf-httpbis-priority/
Htmlized:
https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-priority
Htmlized:       https://tools.ietf.org/html/draft-ietf-httpbis-priority-02
Diff:
https://www.ietf.org/rfcdiff?url2=draft-ietf-httpbis-priority-02

Abstract:
   This document describes a scheme for prioritizing HTTP responses.
   This scheme expresses the priority of each HTTP response using
   absolute values, rather than as a relative relationship between a
   group of HTTP responses.

   This document defines the Priority header field for communicating the
   initial priority in an HTTP version-independent manner, as well as
   HTTP/2 and HTTP/3 frames for reprioritizing the responses.  These
   share a common format structure that is designed to provide future
   extensibility.

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