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Individual Submission                                           J. Snell
Internet-Draft                                        September 17, 2007
Expires: March 20, 2008


                         Prefer Header for HTTP
                       draft-snell-http-prefer-00

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This specification defines a new HTTP header that can be used by a
   client to request that certain behaviors be implemented by a server
   during the processing a request.









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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  The Prefer Request Header . . . . . . . . . . . . . . . . . . . 3
   3.  The "return-no-content" Preference  . . . . . . . . . . . . . . 3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 4
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 4
   Appendix B.  Changes  . . . . . . . . . . . . . . . . . . . . . . . 5
   Appendix C.  Notes to RFC Editor  . . . . . . . . . . . . . . . . . 5
   Appendix D.  Editorial Notes  . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5
   Intellectual Property and Copyright Statements  . . . . . . . . . . 6





































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1.  Introduction

   This specification defines a new HTTP header that can be used by a
   client to request that certain behaviors be implemented by a server
   during the processing a 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].


2.  The Prefer Request Header

   The Prefer request-header is used to indicate that particular server
   behaviors are preferred, but not required, by the client.  Prefer is
   similar in nature to the Expect header defined by [RFC2616] with the
   exception that servers are allowed to ignore a clients stated
   preferences.

     Prefer       =  "Prefer" ":" 1#preference

     preference  =  "no-content" | "content-returned" |
                    preference-extension
     preference-extension =  token [ "=" ( token | quoted-string )
                             *prefer-params ]
     prefer-params =  ";" token [ "=" ( token | quoted-string ) ]

   This header is defined with an extensible syntax to allow for future
   extensions.  A server that does not understand or is unable to comply
   with any of the preference values in the Prefer field of a request
   MUST ignore those values and MUST NOT stop processing or signal an
   error.

   Comparison of preference values is case-insensitive for unquoted
   tokens and is case-sensitive for quoted-string preference-extensions.

   The Prefer mechanism is hop-by-hop: that is, an HTTP proxy MAY choose
   to honor a preference even if the origin server does not.  However,
   the Prefer request-header itself is end-to-end; it MUST be forwarded
   if the request is forwarded.


3.  The "return-no-content" Preference

   The "return-no-content" token indicates that the client prefers that
   the server not include an entity in the response to a successful
   request.  Typically, such responses would use the 204 No Content
   status code as defined in Section 10.2.5 of [RFC2616], but other



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   status codes can be used as appropriate.


4.  IANA Considerations

   The 'Prefer' request header should be added to the permanent registry
   (see [RFC3864]).


       Header field name: Prefer

       Applicable Protocol: HTTP

       Status: standard

       Author/Change controller: IETF

       Specification document: this specification


5.  Security Considerations

   Specific preferences requested by a client can introduce security
   considerations and concerns beyond those discussed in [RFC2616].
   Implementors must refer to the specifications and descriptions of
   those preferences to determine the security considerations relevant
   to each.


6.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.


Appendix A.  Acknowledgements

   The author greatfully acknowledges the input from the IETF HTTP
   mailing list on the development of this document.




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Appendix B.  Changes

   TODO


Appendix C.  Notes to RFC Editor

   The RFC Editor should remove this section and the Changes section.


Appendix D.  Editorial Notes

   We need to determine how new preference codes are created/registered


Author's Address

   James M Snell


   Phone:
   Email: jasnell@gmail.com
   URI:   http://www.snellspace.com




























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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
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