The Cache HTTP Response Header
draft-nottingham-cache-header-00

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Network Working Group                                      M. Nottingham
Internet-Draft                                                    Fastly
Intended status: Standards Track                       September 7, 2018
Expires: March 11, 2019

                     The Cache HTTP Response Header
                    draft-nottingham-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_

   The issues list for this draft can be found at
   https://github.com/mnot/I-D/labels/cache-header [1].

   The most recent (often, unpublished) draft is at
   https://mnot.github.io/I-D/cache-header/ [2].

   Recent changes are listed at https://github.com/mnot/I-D/commits/gh-
   pages/cache-header [3].

   See also the draft's current status in the IETF datatracker, at
   https://datatracker.ietf.org/doc/draft-nottingham-cache-header/ [4].

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."

   This Internet-Draft will expire on March 11, 2019.

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Copyright Notice

   Copyright (c) 2018 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  . . . . . . . . . . . . . . . . . . . . . . . .   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

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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
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