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Network Working Group                                   J. Gregorio, Ed.
Internet-Draft                                                    Google
Intended status: Standards Track                             May 1, 2008
Expires: November 2, 2008

                    AtomPub Multipart Media Creation

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   This specification defines how an Atom Publishing Protocol collection
   should process multipart/related requests and also defines how a
   service announces that it accepts multipart/related entities.

Editorial Note

   To provide feedback on this Internet-Draft, join the Atom Protocol
   mailing list (http://www.imc.org/atom-protocol/) [1].

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . . . 3
     1.2.  Design Considerations . . . . . . . . . . . . . . . . . . . 3
     1.3.  Applicability . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Multipart Representations . . . . . . . . . . . . . . . . . . . 4
   4.  Service Document Extension  . . . . . . . . . . . . . . . . . . 4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Revision History . . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9

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1.  Introduction

   The Atom Publishing Protocol [RFC5023] defines Media Collections and
   how to create a Media Resource by POSTing the media to the Media
   Collection.  RFC 5023 does not define handling multipart/related
   [RFC2387] represenatations nor does it specify how the acceptance of
   such representations should be advertised in the Service Document.
   This specification covers both the processing and the Service
   Document aspects of handling multipart/related content.

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

1.2.  Design Considerations

   The primary objective of multipart/related POSTs is to reduce round-
   trips for creating Media Resources.  There will be three round trips
   in the typical Media Resource creation scenario; POST of the media,
   GET of the Media Link Entry, and subsequent PUT of the updated Media
   Link Entry.  This specification reduces that to just a single round-
   trip by allowing the client to package up the media and the
   associated Media Link Entry into a single multipart/related
   representation which is POSTed to the Media Collection.

   The design of the handling of multipart/related representations was
   aimed at backward compatibility, that is for non-multipart/related
   aware clients to fully function.  A second aim was to retain and
   utilize the expressiveness of the current app:accept element in the
   Service Document.  The last aim was to ease the burden on clients by
   allowing the mulitpart representation to be constructed in an order
   that was convenient for the client.

1.3.  Applicability

   The applicability of multipart/related representations to AtomPub
   Collections is restricted to just creating new entries in Media
   collections.  It does not specify the creation or use of a resource
   that supports a GET to return the multipart/related representation
   nor does it specify the creation or use of a resource that supports a
   PUT of a multipart/related representation.

2.  Terminology

   The terms Collection, Media Resource, Media Link Entry, and Service

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   Document are used as defined in [RFC5023].

3.  Multipart Representations

   This section covers the constraints on a multipart/related
   representation sent to a Media Collection.  Section 4 covers how a
   client discovers that a Media Collection accepts multipart/related

   A multipart/related POST to a Media Collection MUST be a valid
   multipart/related representation as defined by [RFC2387] and MUST
   contain two body parts.  One body part MUST be an Atom Entry with a
   media type of 'application/atom+xml' or 'application/
   atom+xml;type=entry'.  The other body part MUST be of a media type
   acceptable to the collection.  The order of the body parts and which
   one is the 'root' object are not relavant and an AtomPub service MUST
   accept otherwise valid multipart/related POST representations in
   either order.

   That is, if a client is creating a media resource of type image/png
   it can either POST a multipart/related representation with a type
   parameter of either "application/atom+xml;type=entry" or "image/png".
   If the optional start parameter is provided it MAY point, via
   Content-ID, to either the image/png or the application/atom+xml

   A successful POST of a multipart/related representation to a Media
   Collection proceeds as any successful Media Resource creation.  The
   non-Atom object is used to create the Media Resource and the Atom
   Entry object is used to create the Media Link Entry.  Media Resource
   creation proceeds as defined in Section 9.6 of [RFC5023] with a
   successful creation returning a 201 status code and a Location:
   header pointing to the newly created Media Link Entry.  All other
   aspects of [RFC5023] MUST be followed for Media Resource creation
   including Slug: header processing.

4.  Service Document Extension

   An AtomPub service announces that it will accept multipart/related
   POSTs by an extension to the app:accept element.  The 'multipart'
   attribute is boolean valued, either "yes" or "no", and a "yes"
   indicates that the collection accepts multipart/related POSTs for the
   value of the app:accept element.  The following example indicates a
   collection that allows the creation of resources with the Ogg
   Bitstream Format and will also accept them in multipart form.

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   <app:accept multipart="yes">application/ogg</app:accept>

   The 'multipart' attribute is foreign markup and will be ignored by
   clients that do not understand multipart/related uploads.  In
   addition it permits the full range of the app:accept element to be
   used.  The following indicates that the collection accepts any image
   media type and will also accept them in multipart form.

   <app:accept multipart="yes">image/*</app:accept>

   The 'multipart' attribute can only have values of "yes" or "no".  If
   not present the client MUST interpret the app:accept element as if
   the multipart attribute were present and had the value "no".

   The 'multipart' attribute allows clients that are unaware of
   multipart/related to continue to operate as normal since the
   multipart attribute is foreign markup.  The alternative, which was to
   put a multipart/related media type in the app:accept element loses
   flexibility since the 'type' parameter to the multipart/related media
   type accepts only media types and not media ranges.

5.  Examples

   Here is an example service document that contains two media
   collections.  The first collection accepts multipart/related POSTs
   for video media types only.  The second collection accepts multipart/
   related POSTs for image/jpeg and image/png media types.

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      <?xml version="1.0" encoding='utf-8'?>
      <service xmlns="http://www.w3.org/2007/app"
          <atom:title>Media Collections</atom:title>
              href="http://example.org/blog/main" >
            <atom:title>Mostly Media</atom:title>
            <accept multipart="yes">video/*</accept>
            <accept multipart="no" >text/*</accept>
            <accept                >audio/*</accept>
              href="http://example.org/blog/pic" >
            <atom:title>Pictures Only</atom:title>
            <accept multipart="yes">image/png</accept>
            <accept multipart="yes">image/gif</accept>

   Here is an example interaction of a client creating a new Media
   Resource in the Pictures Only media collection using a png image in a
   multipart/related representation.

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   POST /blog/pic HTTP/1.1
   Host: example.org
   Content-Length: nnnn
   content-type: multipart/related;
   slug: The Beach
   mime-version: 1.0

   Media Post
   Content-Type: application/atom+xml; charset="utf-8"
   MIME-Version: 1.0

   <?xml version="1.0"?>
   <entry xmlns="http://www.w3.org/2005/Atom">
     <title>The Beach</title>
     <summary type="text">
         A nice sunset picture over the water.
   Content-Type: image/gif
   MIME-Version: 1.0

   GIF89a...binary image data...

6.  Security Considerations

   The security considerations are the same as delineated in [RFC5023].

7.  IANA Considerations

   No IANA actions are required by this document.

8.  Normative References

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

   [RFC2387]  Levinson, E., "The MIME Multipart/Related Content-type",
              RFC 2387, August 1998.

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   [RFC5023]  Gregorio, J. and B. de hOra, "The Atom Publishing
              Protocol", RFC 5023, October 2007.

   [1]  <http://www.imc.org/atom-protocol/>

Appendix A.  Revision History

   00 - Initial Revision.

Author's Address

   Joe Gregorio (editor)

   Email: joe@bitworking.org
   URI:   http://bitworking.org/

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