HTTP Client Hints
draft-ietf-httpbis-client-hints-10

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HTTP Working Group                                           I. Grigorik
Internet-Draft                                                  Y. Weiss
Intended status: Experimental                                     Google
Expires: August 21, 2020                               February 18, 2020

                           HTTP Client Hints
                   draft-ietf-httpbis-client-hints-10

Abstract

   HTTP defines proactive content negotiation to allow servers to select
   the appropriate response for a given request, based upon the user
   agent's characteristics, as expressed in request headers.  In
   practice, clients are often unwilling to send those request headers,
   because it is not clear whether they will be used, and sending them
   impacts both performance and privacy.

   This document defines an Accept-CH response header that servers can
   use to advertise their use of request headers for proactive content
   negotiation, along with a set of guidelines for the creation of such
   headers, colloquially known as "Client Hints."

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."

Grigorik & Weiss         Expires August 21, 2020                [Page 1]
Internet-Draft              HTTP Client Hints              February 2020

   This Internet-Draft will expire on August 21, 2020.

Copyright Notice

   Copyright (c) 2020 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 . . . . . . . . . . . .   5
   3.  Advertising Server Support  . . . . . . . . . . . . . . . . .   5
     3.1.  The Accept-CH Response Header Field . . . . . . . . . . .   5
       3.1.1.  Interaction with Caches . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
     4.1.  Information Exposure  . . . . . . . . . . . . . . . . . .   6
     4.2.  Deployment and Security Risks . . . . . . . . . . . . . .   8
     4.3.  Abuse Detection . . . . . . . . . . . . . . . . . . . . .   8
   5.  Cost of Sending Hints . . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  Accept-CH . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Interaction with Variants Response Header Field  . .  11
   Appendix B.  Changes  . . . . . . . . . . . . . . . . . . . . . .  11
     B.1.  Since -00 . . . . . . . . . . . . . . . . . . . . . . . .  11
     B.2.  Since -01 . . . . . . . . . . . . . . . . . . . . . . . .  11
     B.3.  Since -02 . . . . . . . . . . . . . . . . . . . . . . . .  11
     B.4.  Since -03 . . . . . . . . . . . . . . . . . . . . . . . .  11
     B.5.  Since -04 . . . . . . . . . . . . . . . . . . . . . . . .  11
     B.6.  Since -05 . . . . . . . . . . . . . . . . . . . . . . . .  11