The Cache HTTP Response Header
draft-ietf-httpbis-cache-header-00

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Last updated 2019-03-04 (latest revision 2019-01-27)
Replaces draft-nottingham-cache-header
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HTTP Working Group                                         M. Nottingham
Internet-Draft                                                    Fastly
Intended status: Standards Track                        January 27, 2019
Expires: July 31, 2019

                     The Cache HTTP Response Header
                   draft-ietf-httpbis-cache-header-00

Abstract

   To aid debugging, HTTP caches often append headers to a response
   detailing how they handled the request.  This specification codifies
   that practice and updates it for HTTP's current caching model.

Note to Readers

   _RFC EDITOR: please remove this section before publication_

   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 https://httpwg.org/ [2];
   source code and issues list for this draft can be found at
   https://github.com/httpwg/http-extensions/labels/cache-header [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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 31, 2019.

Nottingham                Expires July 31, 2019                 [Page 1]
Internet-Draft                Cache Header                  January 2019

Copyright Notice

   Copyright (c) 2019 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  The Cache HTTP Response Header  . . . . . . . . . . . . . . .   3
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   7
     4.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   To aid debugging, HTTP caches often append headers to a response
   detailing how they handled the request.

   Unfortunately, the semantics of these headers are often unclear, and
   both the semantics and syntax used vary greatly between
   implementations.

   This specification defines a single, new HTTP response header field,
   "Cache" for this purpose.

   For example:

  Cache: HIT_FRESH; node="reverse-proxy.example.com:80";
                    key="https://example.com/foo|Accept-Encoding:gzip",
         HIT_STALE; node="FooCDN parent"; fresh=-45; age=200; latency=3,
         MISS; node="FooCDN edge"; fresh=-45; age=200; latency=98

Nottingham                Expires July 31, 2019                 [Page 2]
Internet-Draft                Cache Header                  January 2019

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document uses ABNF as defined in [RFC5234], along with the "%s"
   extension for case sensitivity defined in [RFC7405].

2.  The Cache HTTP Response Header

   The Cache HTTP response header indicates the handling of the request
   corresponding to the response it occurs within by caches along the
   path.

   Its value is a Parameterised List
   [I-D.ietf-httpbis-header-structure]:

   Cache   = sh-param-list

   Each member of the parameterised list represents a cache that has
   handled the request.

   The first member of the list represents the cache closest to the
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