Cache Digests for HTTP/2
draft-ietf-httpbis-cache-digest-02

Document Type Active Internet-Draft (httpbis WG)
Last updated 2017-07-27 (latest revision 2017-05-29)
Replaces draft-kazuho-h2-cache-digest
Stream IETF
Intended RFC status Experimental
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Stream WG state In WG Last Call
Document shepherd Patrick McManus
IESG IESG state I-D Exists
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Send notices to Patrick McManus <mcmanus@ducksong.com>
HTTP Working Group                                                K. Oku
Internet-Draft                                             DeNA Co, Ltd.
Intended status: Experimental                              M. Nottingham
Expires: December 1, 2017                                   May 30, 2017

                        Cache Digests for HTTP/2
                   draft-ietf-httpbis-cache-digest-02

Abstract

   This specification defines a HTTP/2 frame type to allow clients to
   inform the server of their cache's contents.  Servers can then use
   this to inform their choices of what to push to clients.

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/ .

   Working Group information can be found at http://httpwg.github.io/ ;
   source code and issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/cache-digest .

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/.

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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on December 1, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Oku & Nottingham        Expires December 1, 2017                [Page 1]
Internet-Draft          Cache Digests for HTTP/2                May 2017

   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The CACHE_DIGEST Frame  . . . . . . . . . . . . . . . . . . .   3
     2.1.  Client Behavior . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Computing the Digest-Value  . . . . . . . . . . . . .   5
       2.1.2.  Computing a Hash Value  . . . . . . . . . . . . . . .   6
     2.2.  Server Behavior . . . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Querying the Digest for a Value . . . . . . . . . . .   7
   3.  The ACCEPT_CACHE_DIGEST SETTINGS Parameter  . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Encoding the CACHE_DIGEST frame as an HTTP Header  .  12
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .  13
   Appendix C.  Changes  . . . . . . . . . . . . . . . . . . . . . .  13
     C.1.  Since draft-ietf-httpbis-cache-digest-01  . . . . . . . .  13
     C.2.  Since draft-ietf-httpbis-cache-digest-00  . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   HTTP/2 [RFC7540] allows a server to "push" synthetic request/response
   pairs into a client's cache optimistically.  While there is strong
   interest in using this facility to improve perceived Web browsing
   performance, it is sometimes counterproductive because the client
   might already have cached the "pushed" response.

   When this is the case, the bandwidth used to "push" the response is
   effectively wasted, and represents opportunity cost, because it could
   be used by other, more relevant responses.  HTTP/2 allows a stream to
   be cancelled by a client using a RST_STREAM frame in this situation,
   but there is still at least one round trip of potentially wasted
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