HTTP Client Hints
draft-ietf-httpbis-client-hints-06

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HTTP Working Group                                           I. Grigorik
Internet-Draft                                                    Google
Intended status: Experimental                              July 16, 2018
Expires: January 17, 2019

                           HTTP Client Hints
                 draft-ietf-httpbis-client-hints-06

Abstract

   An increasing diversity of Web-connected devices and software
   capabilities has created a need to deliver optimized content for each
   device.

   This specification defines an extensible and configurable set of HTTP
   request header fields, colloquially known as Client Hints, to address
   this.  They are intended to be used as input to proactive content
   negotiation; just as the Accept header field allows user agents to
   indicate what formats they prefer, Client Hints allow user agents to
   indicate device and agent specific preferences.

Note to Readers

   Discussion of this draft takes place on the HTTP working group
   mailing list (ietf-http-wg@w3.org), which is archived at
   https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].

   Working Group information can be found at http://httpwg.github.io/
   [2]; source code and issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/client-hints [3].

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 https://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 17, 2019.

Grigorik                Expires January 17, 2019                [Page 1]
Internet-Draft              HTTP Client Hints                  July 2018

Copyright Notice

   Copyright (c) 2018 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
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
   2.  Client Hint Request Header Fields . . . . . . . . . . . . . .   4
     2.1.  Sending Client Hints  . . . . . . . . . . . . . . . . . .   4
     2.2.  Server Processing of Client Hints . . . . . . . . . . . .   4
       2.2.1.  Advertising Support via Accept-CH Header Field  . . .   5
       2.2.2.  The Accept-CH-Lifetime Header Field . . . . . . . . .   5
       2.2.3.  Interaction with Caches . . . . . . . . . . . . . . .   6
   3.  Client Hints  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  The DPR Header Field  . . . . . . . . . . . . . . . . . .   6
       3.1.1.  Confirming Selected DPR . . . . . . . . . . . . . . .   7
     3.2.  The Width Header Field  . . . . . . . . . . . . . . . . .   7
     3.3.  The Viewport-Width Header Field . . . . . . . . . . . . .   7
   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Accept-CH . . . . . . . . . . . . . . . . . . . . . . . .   9
     6.2.  Accept-CH-Lifetime  . . . . . . . . . . . . . . . . . . .   9
     6.3.  Content-DPR . . . . . . . . . . . . . . . . . . . . . . .  10
     6.4.  DPR . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.5.  Viewport-Width  . . . . . . . . . . . . . . . . . . . . .  10
     6.6.  Width . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Interaction with Key Response Header Field . . . . .  12
   Appendix B.  Changes  . . . . . . . . . . . . . . . . . . . . . .  12
     B.1.  Since -00 . . . . . . . . . . . . . . . . . . . . . . . .  12