The Priority HTTP Header Field
draft-kazuho-httpbis-priority-00

• Status
• IESG evaluation record
• IESG writeups
• Email expansions
• History

• Versions
• 00

HTTP                                                              K. Oku
Internet-Draft                                                    Fastly
Intended status: Standards Track                               L. Pardue
Expires: January 9, 2020                                      Cloudflare
                                                           July 08, 2019

                     The Priority HTTP Header Field
                    draft-kazuho-httpbis-priority-00

Abstract

   This document describes the Priority HTTP header field.  This header
   field can be used by endpoints to specify the absolute precedence of
   an HTTP response in an HTTP-version-independent way.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 9, 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Oku & Pardue             Expires January 9, 2020                [Page 1]
Internet-Draft       The Priority HTTP Header Field            July 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The Priority HTTP Header Field  . . . . . . . . . . . . . . .   3
     2.1.  urgency . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  progressive . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Merging Client- and Server-Driven Parameters  . . . . . . . .   5
   4.  Coexistence with HTTP/2 Priorities  . . . . . . . . . . . . .   6
     4.1.  The SETTINGS_HEADER_BASED_PRIORITY SETTINGS Parameter . .   6
   5.  Considerations  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Why use an End-to-End Header Field? . . . . . . . . . . .   6
     5.2.  Why are there Only Three Levels of Urgency? . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   It is common for an HTTP ([RFC7230]) resource representation to have
   relationships to one or more other resources.  Clients will often
   discover these relationships while processing a retrieved
   representation, leading to further retrieval requests.  Meanwhile,
   the nature of the relationship determines whether the client is
   blocked from continuing to process locally available resources.  For
   example, visual rendering of an HTML document could be blocked by the
   retrieval of a CSS file that the document refers to.  In contrast,
   inline images do not block rendering and get drawn progressively as
   the chunks of the images arrive.

   To provide meaningful representation of a document at the earliest
   moment, it is important for an HTTP server to prioritize the HTTP
   responses, or the chunks of those HTTP responses, that it sends.

   HTTP/2 ([RFC7540]) provides such a prioritization scheme.  A client
   sends a series of PRIORITY frames to communicate to the server a
   "priority tree"; this represents the client's preferred ordering and
   weighted distribution of the bandwidth among the HTTP responses.
   However, the design has shortcomings:

   o  Its complexity has led to varying levels of support by HTTP/2
      clients and servers.

Oku & Pardue             Expires January 9, 2020                [Page 2]
Internet-Draft       The Priority HTTP Header Field            July 2019