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Versions: 00 01 02

Network Working Group                                            J. Arwe
Internet-Draft                                               S. Speicher
Intended status: Standards Track                                     IBM
Expires: January 30, 2014                                       E. Wilde
                                                         EMC Corporation
                                                           July 29, 2013


                      The Accept-Post HTTP Header
                       draft-wilde-accept-post-00

Abstract

   This specification defines a new HTTP response header field Accept-
   Post, which indicates server support for specific media types for
   entity bodies in HTTP POST requests.

Note to Readers

   This draft should be discussed on the apps-discuss mailing list [9].

   Online access to all versions and files is available on github [10].

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/.

   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 January 30, 2014.

Copyright Notice

   Copyright (c) 2013 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  The Accept-Post Response Header Field . . . . . . . . . . . . . 3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  The Accept-Post Response Header . . . . . . . . . . . . . . 4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     5.1.  Linked Data Platform  . . . . . . . . . . . . . . . . . . . 4
     5.2.  Atom Publishing Protocol  . . . . . . . . . . . . . . . . . 4
     5.3.  Additional Information in Error Responses . . . . . . . . . 5
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   8.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Non-Normative References  . . . . . . . . . . . . . . . . . 6
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
























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1.  Introduction

   This specification defines a new HTTP response header field Accept-
   Post, which indicates server support for specific media types for
   entity bodies in HTTP POST requests.  This header field is comparable
   to the Accept-Patch response header field specified together with the
   HTTP PATCH method [4] (notice, however, that while Accept-Patch is
   defined to only list specific media types, Accept-Post reuses the
   "media range" concept of HTTP's Accept header and thus allows media
   type wildcards as well).


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].


3.  The Accept-Post Response Header Field

   This specification introduces a new response header field Accept-Post
   used to specify the document formats accepted by the server in HTTP
   POST requests.  Accept-Post SHOULD appear in the OPTIONS response for
   any resource that supports the use of the POST method.  The presence
   of the Accept-Post header in response to any method is an implicit
   indication that POST is allowed on the resource identified by the
   Request-URI.  The presence of a specific document format in this
   header indicates that that specific format is allowed on the resource
   identified by the Request-URI.

   The syntax for Accept-Post headers, using the ABNF syntax defined in
   Section 2.1 of RFC 2616 [2], is given by the following definition.
   Accept-Post = "Accept-Post" ":" #( media-range [ accept-params ] )

   The Accept-Post header specifies a media range as defined by HTTP
   [2].  The media range specifies a type of representation that can be
   POSTed to the Request-URI.

   The app:accept element is similar to the HTTP Accept request header
   field [2].  Media type parameters are allowed within Accept-Post, but
   Accept-Post has no notion of preference - "accept-params" or "q"
   arguments, as specified in Section 14.1 of [2], are not significant.


4.  IANA Considerations





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4.1.  The Accept-Post Response Header

   The Accept-Post response header should be added to the permanent
   registry of message header fields (see [3]).


5.  Examples

   Accept-Post extends the way in which interaction information can be
   exposed in HTTP itself.  The following sections contain some examples
   how this can be used in concrete HTTP-based services.

5.1.  Linked Data Platform

   The Linked Data Platform (LDP) [5] describes a set of best practices
   and simple approach for a read-write Linked Data architecture, based
   on HTTP access to Web resources that describe their state using the
   RDF data model.  LDP defines LDP Containers (LDPC) and LDP Resources
   (LDPR).  Adding new LDPRs to an LDPC is done by sending an HTTP POST
   request to the LDPC.  An LDPC can constrain the media types it is
   accepting for these POST requests, and MUST expose its support for
   accepted media types via Accept-Post.

   In fact, the Accept-Post header was initially developed within the
   W3C's LDP Working Group (LDPWG), see Appendix A for acknowledgements.
   It was then decided that the header itself might be useful in other
   contexts as well, and thus should be specified in a standalone
   document.

5.2.  Atom Publishing Protocol

   The Atom Publishing Protocol (AtomPub) [6] defines a model of
   interacting with collections and members, based on representations
   using the Atom [7] syntax.  AtomPub allows clients to create new
   collection members by using HTTP POST, with the request being sent to
   the collection URI.  AtomPub servers can limit the media types they
   accept in these POST requests, and the accepted media types are
   listed in an "AtomPub service document".

   The Accept-Post header field does allow an AtomPub server to
   advertise its support for specific media types in interactions with
   the collection resource, without the need for a client to locate the
   service document and interact with it.  This increases the visibility
   of the "POST to Create" model of AtomPub, and makes it easier for
   clients to find out about the capabilities of a specific collection.

   While the AtomPub protocol cannot be changed retroactively, this
   additional way of exposing interaction guidance could make it easier



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   for clients to interact with AtomPub services that do support the
   Accept-Post header field.  For those that do not support Accept-Post,
   clients would still have to rely on using the information contained
   in the service document (including the sometimes tricky issue of how
   to locate the service document for a given collection).

5.3.  Additional Information in Error Responses

   If a client POSTs an unsupported POST document, it is possible for
   the server to use Accept-Post to indicate the supported media types.
   These can be specified using a 415 (Unsupported Media Type) response
   when the client sends a POST document format that the server does not
   support for the resource identified by the Request-URI.  Such a
   response then MAY include an Accept-Post response header notify the
   client what POST document media types are supported.


6.  Implementation Status

   Note to RFC Editor: Please remove this section before publication.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 6982 [8].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to RFC 6982, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

      ...


7.  Security Considerations

   The Accept-Post header may expose information that a server would
   prefer to not publish.  In such a case, a server can simply stop



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   exposing the header, in which case HTTP interactions would be back to
   the level of standard HTTP (i.e., with no indication what kind of
   media types a resource accepts in POST requests).


8.  Open Issues

   Note to RFC Editor: Please remove this section before publication.

   o  Accept-Post currently uses the "media range" concept of HTTP's
      Accept header field.  An alternative would be only support fully
      specified media types, which is what the Accept-Patch header field
      is doing.  This latter solution is more constrained, and fails to
      address some uses cases, such as AtomPub's way of exposing
      collection support for POST requests.


9.  References

9.1.  Normative References

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

   [2]  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.

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

9.2.  Non-Normative References

   [4]  Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC 5789,
        March 2010.

   [5]  Speicher, S. and J. Arwe, "Linked Data Platform 1.0", World Wide
        Web Consortium WD WD-ldp-20130307, March 2013,
        <http://www.w3.org/TR/2013/WD-ldp-20130307>.

   [6]  Gregorio, J. and B. de hOra, "The Atom Publishing Protocol",
        RFC 5023, October 2007.

   [7]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication
        Format", RFC 4287, December 2005.

   [8]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code:



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        The Implementation Status Section", RFC 6982, July 2013.

URIs

   [9]   <https://www.ietf.org/mailman/listinfo/apps-discuss>

   [10]  <https://github.com/dret/I-D/tree/master/accept-post>


Appendix A.  Acknowledgements

   This work has been done in the context of the W3C Linked Data
   Platform Working Group (LDPWG) [5].  Thanks for comments and
   suggestions provided by the working group as a whole.


Authors' Addresses

   John Arwe
   IBM

   Email: johnarwe@us.ibm.com


   Steve Speicher
   IBM

   Email: sspeiche@us.ibm.com


   Erik Wilde
   EMC Corporation
   6801 Koll Center Parkway
   Pleasanton, CA 94566
   U.S.A.

   Phone: +1-925-6006244
   Email: erik.wilde@emc.com
   URI:   http://dret.net/netdret/












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