HTTP Variants
draft-nottingham-variants-00

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Last updated 2017-09-28
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Network Working Group                                      M. Nottingham
Internet-Draft                                                    Fastly
Updates: 7234 (if approved)                           September 28, 2017
Intended status: Standards Track
Expires: April 1, 2018

                             HTTP Variants
                      draft-nottingham-variants-00

Abstract

   This specification introduces the HTTP "Variants" response header
   field to communicate what representations are available for a given
   resource.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   The issues list for this draft can be found at
   https://github.com/mnot/I-D/labels/variant.

   The most recent (often, unpublished) draft is at
   https://mnot.github.io/I-D/variant/.

   Recent changes are listed at https://github.com/mnot/I-D/commits/gh-
   pages/variant.

   See also the draft's current status in the IETF datatracker, at
   https://datatracker.ietf.org/doc/draft-nottingham-variant/.

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 April 1, 2018.

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Copyright Notice

   Copyright (c) 2017 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
   2.  The "Variants" HTTP Header Field  . . . . . . . . . . . . . .   4
     2.1.  Defining Content Negotiation Using Variants . . . . . . .   5
     2.2.  Cache Behaviour . . . . . . . . . . . . . . . . . . . . .   6
       2.2.1.  Relationship to Vary  . . . . . . . . . . . . . . . .   7
     2.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   7
       2.3.1.  Single Variant  . . . . . . . . . . . . . . . . . . .   7
       2.3.2.  Multiple Variants . . . . . . . . . . . . . . . . . .   8
       2.3.3.  Partial Coverage  . . . . . . . . . . . . . . . . . .   9
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Variants and Defined Content Negotiation Mechanisms   11
     A.1.  Content-Encoding  . . . . . . . . . . . . . . . . . . . .  11
     A.2.  Content-Language  . . . . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   HTTP proactive content negotiation ([RFC7231], Section 3.4.1) is
   starting to be used more widely again.  The most widely seen use -
   determining a response's content-coding - is being joined by renewed
   interest in negotiation for language and other, newer attributes (for
   example, see [I-D.ietf-httpbis-client-hints]).

   Successfully reusing negotiated responses that have been stored in a
   HTTP cache requires establishment of a secondary cache key

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   ([RFC7234], Section 4.1) using the Vary header ([RFC7231],
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