Extensible Prioritization Scheme for HTTP
draft-kazuho-httpbis-priority-03

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HTTP                                                              K. Oku
Internet-Draft                                                    Fastly
Intended status: Standards Track                               L. Pardue
Expires: May 8, 2020                                          Cloudflare
                                                       November 05, 2019

               Extensible Prioritization Scheme for HTTP
                    draft-kazuho-httpbis-priority-03

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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on May 8, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of

Oku & Pardue               Expires May 8, 2020                  [Page 1]
Internet-Draft  Extensible Prioritization Scheme for HTTP  November 2019

   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Motivation for Replacing HTTP/2 Priorities  . . . . . . . . .   4
   3.  Negotiating Priorities  . . . . . . . . . . . . . . . . . . .   5
     3.1.  The SETTINGS_PRIORITIES SETTINGS Parameter  . . . . . . .   5
     3.2.  Defined Prioritization Scheme Values  . . . . . . . . . .   6
       3.2.1.  H2_TREE . . . . . . . . . . . . . . . . . . . . . . .   6
       3.2.2.  URGENCY . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  The Priority HTTP Header Field  . . . . . . . . . . . . . . .   7
     4.1.  urgency . . . . . . . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  prerequisite  . . . . . . . . . . . . . . . . . . . .   8
       4.1.2.  default . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.3.  supplementary . . . . . . . . . . . . . . . . . . . .   8
       4.1.4.  background  . . . . . . . . . . . . . . . . . . . . .   9
     4.2.  progressive . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Reprioritization  . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  HTTP/2 PRIORITY_UPDATE Frame  . . . . . . . . . . . . . .  11
     5.2.  HTTP/3 PRIORITY_UPDATE Frame  . . . . . . . . . . . . . .  11
   6.  Merging Client- and Server-Driven Parameters  . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     7.1.  Fairness and Coalescing Intermediaries  . . . . . . . . .  13
   8.  Considerations  . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Why use an End-to-End Header Field? . . . . . . . . . . .  14
     8.2.  Why do Urgencies Have Meanings? . . . . . . . . . . . . .  14
     8.3.  Can an Intermediary Send its own Signal?  . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  HTTP Prioritization Scheme Registry . . . . . . . . . . .  16
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  18
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  19
     B.1.  Since draft-kazuho-httpbis-priority-02  . . . . . . . . .  19