The Key HTTP Response Header Field
draft-ietf-httpbis-key-00

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Document Type Active Internet-Draft (httpbis WG)
Last updated 2015-10-18
Replaces draft-fielding-http-key
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httpbis Working Group                                        R. Fielding
Internet-Draft                                Adobe Systems Incorporated
Intended status: Standards Track                           M. Nottingham
Expires: April 21, 2016                                 October 19, 2015

                   The Key HTTP Response Header Field
                       draft-ietf-httpbis-key-00

Abstract

   The 'Key' header field for HTTP responses allows an origin server to
   describe the secondary cache key ([RFC7234], section 4.1) for a
   resource, by conveying what is effectively a short algorithm that can
   be used upon later requests to determine if a stored response is
   reusable for a given request.

   Key has the advantage of avoiding an additional round trip for
   validation whenever a new request differs slightly, but not
   significantly, from prior requests.

   Key also informs user agents of the request characteristics that
   might result in different content, which can be useful if the user
   agent is not sending request header fields in order to reduce the
   risk of fingerprinting.

Note to Readers

   The issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/key .

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on April 21, 2016.

Fielding & Nottingham    Expires April 21, 2016                 [Page 1]
Internet-Draft                     Key                      October 2015

Copyright Notice

   Copyright (c) 2015 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
   2.  The "Key" Response Header Field . . . . . . . . . . . . . . .   4
     2.1.  Relationship with Vary  . . . . . . . . . . . . . . . . .   5
     2.2.  Calculating a Secondary Cache Key . . . . . . . . . . . .   6
       2.2.1.  Creating a Header Field Value . . . . . . . . . . . .   8
       2.2.2.  Failing Parameter Processing  . . . . . . . . . . . .   8
     2.3.  Key Parameters  . . . . . . . . . . . . . . . . . . . . .   8
       2.3.1.  div . . . . . . . . . . . . . . . . . . . . . . . . .   9
       2.3.2.  partition . . . . . . . . . . . . . . . . . . . . . .  10
       2.3.3.  match . . . . . . . . . . . . . . . . . . . . . . . .  11
       2.3.4.  substr  . . . . . . . . . . . . . . . . . . . . . . .  12
       2.3.5.  param . . . . . . . . . . . . . . . . . . . . . . . .  13
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     3.1.  Procedure . . . . . . . . . . . . . . . . . . . . . . . .  14
     3.2.  Registrations . . . . . . . . . . . . . . . . . . . . . .  14
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   In HTTP caching [RFC7234], the Vary response header field effectively
   modifies the key used to store and access a response to include
   information from the request's headers.  This "secondary cache key"
   allows proactive content negotiation [RFC7231] to work with caches.

Fielding & Nottingham    Expires April 21, 2016                 [Page 2]
Internet-Draft                     Key                      October 2015

   Vary's operation is generic; it works well when caches understand the
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