Prefer Header for HTTP
draft-snell-http-prefer-13

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Network Working Group                                           J. Snell
Internet-Draft                                           August 21, 2012
Intended status: Standards Track
Expires: February 22, 2013

                         Prefer Header for HTTP
                       draft-snell-http-prefer-13

Abstract

   This specification defines an HTTP header field that can be used by a
   client to request that certain behaviors be implemented by a server
   while processing a request.

Status of this Memo

   This Internet-Draft is submitted to IETF 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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 22, 2013.

Copyright Notice

   Copyright (c) 2012 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
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   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.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  3
   2.  The Prefer Request Header Field  . . . . . . . . . . . . . . .  3
     2.1.  Content Negotiation and Cache Considerations . . . . . . .  5
     2.2.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  The "return-asynch" Preference . . . . . . . . . . . . . . . .  5
   4.  The "return-representation" Preference . . . . . . . . . . . .  6
   5.  The "return-minimal" Preference  . . . . . . . . . . . . . . .  7
   6.  The "wait" Preference  . . . . . . . . . . . . . . . . . . . .  8
   7.  The "strict" and "lenient" Processing Preferences  . . . . . .  9
   8.  Registered Preferences . . . . . . . . . . . . . . . . . . . . 10
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  The Registry of Preferences  . . . . . . . . . . . . . . . 11
       9.1.1.  Initial Registry Contents  . . . . . . . . . . . . . . 12
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   11. Normative References . . . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14

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1.  Introduction

   This specification defines a new HTTP request header field that can
   be used by clients to request optional behaviors be applied by a
   server during the processing the request.

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are to be interpreted as described in [RFC2119].

1.1.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234] and includes, by reference, the "word", "OWS",
   "BWS" rules and the #rule extension as defined within Sections 1.2
   and 3.2.4 of [I-D.ietf-httpbis-p1-messaging].

2.  The Prefer Request Header Field

   The Prefer request-header field is used to indicate that particular
   server behaviors are preferred by the client, but not required for
   successful completion of the request.  Prefer is similar in nature to
   the Expect header field defined by Section 9.3 of
   [I-D.ietf-httpbis-p2-semantics] with the exception that servers are
   allowed to ignore stated preferences.

     Prefer     = "Prefer" ":" 1#preference
     preference = token [ BWS "=" BWS word ]
                  *( OWS ";" [ OWS parameter ] )
     parameter  = token [ BWS "=" BWS word ]

   This header field is defined with an extensible syntax to allow for
   future values included in the Registry of Preferences (Section 9.1).
   A server that does not recognize or is unable to comply with