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Atompub Working Group                                           R. Sayre
Internet-Draft                                          January 24, 2006
Expires: July 28, 2006


                  The Atom Publishing Protocol (Basic)
                 draft-sayre-atompub-protocol-basic-06

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 28, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This memo presents a protocol that uses XML and HTTP to publish and
   edit Web resources.










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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Notational Conventions . . . . . . . . . . . . . . . . . . . .  3
   3.  The Atom Publishing Protocol Model . . . . . . . . . . . . . .  3
   4.  Discovery  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   5.  Listing  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   6.  Authoring  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   7.  Atom Protocol Feeds  . . . . . . . . . . . . . . . . . . . . .  6
   8.  Media Feeds  . . . . . . . . . . . . . . . . . . . . . . . . .  8
   9.  Service Description  . . . . . . . . . . . . . . . . . . . . . 10
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   12. Informative References . . . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 15
   Appendix B.  Change History  . . . . . . . . . . . . . . . . . . . 15
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17

































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1.  Introduction

   The Atom Publishing Protocol uses HTTP [RFC2616] and XML [W3C.REC-
   xml-20040204] to publish and edit Web resources.


2.  Notational Conventions

   The Atom Protocol namespace is "http://purl.org/atom/app#".  This
   specification refers to it by using the prefix "pub", but that prefix
   is arbitrary.

   The terms 'URI' and 'IRI' are shorthand for the identifiers specified
   in [RFC3986] and [RFC3987].


3.  The Atom Publishing Protocol Model

   The Atom Protocol uses HTTP to operate on collections of Web
   resources represented by Atom feeds [AtomFormat].  This section
   illustrates the editing cycle for Atom entries.
   o  GET is used to retrieve a representation of a resource or perform
      a read-only query.
   o  POST is used to create a new, dynamically-named resource.
   o  PUT is used to update a known resource.
   o  DELETE is used to remove a resource.


4.  Discovery

   To discover the location of the feeds exposed by an Atom Protocol
   service, the client must locate and request a Service Description
   Document (Section 6).


      Client                      Server
      |                                |
      |  1.) GET Service URI           |
      |------------------------------->|
      |                                |
      |  2.) Service Description Doc   |
      |<-------------------------------|
      |                                |


   1.  The client sends a GET request to the Service Description URI.





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   2.  The server responds with a Service Description Document
       containing the locations of feeds provided by the service.  The
       content of this document can vary based on aspects of the client
       request, including, but not limited to, authentication
       credentials.


5.  Listing

   Once the client has discovered the location of a feed in the outline,
   it can request a listing of the feed's entries.  However, a feed
   might contain an extremely large number of entries, so servers are
   likely to list a small subset of them by default.


      Client                      Server
      |                                |
      |  1.) GET to Atom Feed URI      |
      |------------------------------->|
      |                                |
      |  2.) 200 OK, Atom Feed Doc     |
      |<-------------------------------|
      |                                |


   1.  The client sends a GET request to the Atom Feed's URI.
   2.  The server responds with an Atom Feed Document containing a full
       or partial listing of the feed's membership.


6.  Authoring

   After locating a feed, a client can add entries by sending a POST
   request to the feed; other changes are accomplished by sending HTTP
   requests to each entry.

6.1.  Create


      Client                      Server
      |                                |
      |  1.) POST Entry to Feed URI    |
      |------------------------------->|
      |                                |
      |  2.) 201 Created @ Location    |
      |<-------------------------------|
      |                                |




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   1.  The client sends an Atom Entry to the server via HTTP POST.  The
       Request URI is that of the Atom Feed.
   2.  The server responds with a response of "201 Created" and a
       "Location" header containing the URI of the newly-created Atom
       Entry.

6.2.  Read


      Client                      Server
      |                                |
      |  1.) GET or HEAD to Entry URI  |
      |------------------------------->|
      |                                |
      |  2.) 200 OK Atom Entry         |
      |<-------------------------------|
      |                                |


   1.  The client sends a GET (or HEAD) request to the entry's URI.
   2.  The server responds with an Atom Entry document.

6.3.  Update


      Client                      Server
      |                                |
      |  1.) PUT to Entry URI          |
      |------------------------------->|
      |                                |
      |  2.) 200 OK                    |
      |<-------------------------------|
      |                                |


   1.  The client PUTs an updated Atom Entry Document to the entry's
       URI.
   2.  The server responds with a successful status code.

6.4.  Delete


      Client                      Server
      |                                |
      |  1.) DELETE to Entry URI       |
      |------------------------------->|
      |                                |
      |  2.) 204 No Content            |



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      |<-------------------------------|
      |                                |


   1.  The client sends a DELETE request to the entry's URI.
   2.  The server responds with successful status code.

6.5.  Success and Failure

   HTTP defines classes of response.  HTTP status codes of the form 2xx
   signal that a request was successful.  HTTP status codes of the form
   4xx or 5xx signal that an error has occurred, and the request has
   failed.  Consult the HTTP specification for more detailed definitions
   of each status code.


7.  Atom Protocol Feeds

7.1.  GET

   Feeds can contain extremely large numbers of resources.  A naive
   client such as a web spider or web browser would be overwhelmed if
   the response to a GET contained every entry in the feed, and the
   server would waste large amounts of bandwidth and processing time on
   clients unable to handle the response.  As a result, responses to a
   simple GET request represent a server-determined subset of the
   entries in the feed.
























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   An example Atom Protocol feed:


          <feed xmlns="http://www.w3.org/2005/Atom"
                xmlns:pub="http://purl.org/atom/app#">
            <title>My Posts1</title>
            <id>urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6</id>
            <updated>2005-12-21T04:11:00-08:00</updated>
            <!-- 0 or more atom:entry elements follow -->
            <entry>
              <title type="text">title 25</title>
              <updated>2005-12-21T04:11:00-08:00</updated>
              <author>
                <name>Foo</name>
              </author>
              <summary>It started out looking simple enough...</summary>
              <id>urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387</id>
              <pub:edit href="./entry7.atom"/>
              <link href="/permalink7.html" />
             </entry>
             ...
          </feed>


   Each member entry is represented by an atom:entry element, but those
   entries are not an editable representation of the entry.  To retrieve
   the source representation of the entry, clients send a GET request to
   the URI found in each entry's pub:edit element (see Section 4.3.1).
   Derived resources are located by examining an entry's atom:link
   elements.

7.2.  POST

   An Atom Protocol feed also accepts POST requests.  The client POSTs a
   representation of the desired resource to the APP feed.  Some feeds
   only accept POST requests with certain media-types, so a POST request
   could result in a response with a status code of 415 ("Unsupported
   Media Type").  In the case of a successful creation, the status code
   is 201 ("Created").












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   Example request creating a new entry in a feed:


          POST /collection HTTP/1.1
          Host: example.org
          User-Agent: Cosimo/1.0
          Content-Type: application/atom+xml
          Content-Length: nnnn

          ...data...


   Example response.


          HTTP/1.1 201 Created
          Date: Mon, 21 Mar 2005 19:20:19 GMT
          Server: CountBasic/2.0
          ETag: "4c083-268-423f1dc6"
          Location: http://example.org/stuff/foo13241234.atom



8.  Media Feeds

   The entries within Media Feeds do not represent uniform types of
   content.  For example, they might contain JPEG images, text
   documents, MPEG movies, or any other type of resource the server
   allows.

8.1.  GET

   Media Feeds return an Atom feed much like the textual Atom Protcol
   feeds described above, but with a few additions.  The entries also
   contain an atom:content element with a 'src' attribute pointing to
   the media resource.  This URI can be used to edit the uploaded media
   resource, using PUT and DELETE.  Such entries may contain edit links
   used to edit the entry metadata.  As with any Atom entry, related and
   derived resources can be located by inspecting an entry's atom:link
   elements.











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   An example Media Feed:


          <feed xmlns="http://www.w3.org/2005/Atom"
                xmlns:pub="http://purl.org/atom/app#">
            <title>My Posts1</title>
            <author>
               <name>Foo</name>
            </author>
            <id>urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6</id>
            <updated>2005-12-21T04:11:00-08:00</updated>
            <!-- 0 or more atom:entry elements follow -->
            <entry>
              <title type="text">Title25</title>
              <updated>2005-12-21T04:11:00-08:00</updated>
              <id>urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387</id>
              <link href="/permalink7.html" type="text/html" />
              <link href="/stuff/public/beach.jpg" type="image/jpg"
                    title="Low res public version" />
              <summary>This was awesome.</summary>
              <content src="http://example.org/beach.tiff" />
            </entry>
            ...
          </feed>


   The Atom Syndication Format requires that each such entry contain an
   atom:title and atom:summary element.  This requirement can be
   challenging to meet without requiring users to enter tedious
   metadata, but servers should attempt to provide textual data about
   the resource in the interests of accessibility.  The atom:title
   element will likely be provided by the client, as a way for users to
   associate their local resources with those they have uploaded to the
   server (see POST below).

8.2.  POST

   To add an entry to a Media Feed, clients POST the resource to the
   Media Feed's URI.  Clients should provide a 'Title' request header to
   provide the server with a short string identifying the resource to
   users.  Clients may include a 'Content-Description' header [RFC2045]
   providing a more complete description of the content.  In addition,
   servers may inspect the POSTed entity for additional metadata to be
   exposed in an atom:entry element when listed in a Media Feed.  For
   example, the server might inspect a JPEG file for EXIF headers
   containing creator data.





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   An example request:


          POST /collection HTTP/1.1
          Host: example.org
          User-Agent: Cosimo/1.0
          Content-Type: image/tiff
          Content-Length: nnnn
          Title: A Trip to the beach
          Content-Description: It was so fun.

          ...binary data...


   An example response:


          HTTP/1.1 201 Created
          Date: Mon, 21 Mar 2005 19:20:19 GMT
          Server: CountBasic/2.0
          ETag: "4c083-268-423f1dc6"
          Location: http://example.org/stuff/beach.tiff


   [@@ deal with response ambiguity noted in WG]


9.  Service Description

   Many Atom Protocol applications require a basic resource layout in
   order to ease configuration requirements.  Servers use Service
   Description documents to convey information about related groups of
   Atom Protocol feeds.  On a blogging service, for example, each group
   might represent a distinct blog and associated resources.

   Example Service Description document:


      <app xmlns="http://purl.org/atom/app#">
        <service name="My Blog" class="feed"
         href="http://example.com/entries">
         <service name="Photos" class="media feed"
          href="http://example.com/photos"/>
         <service name="Drafts" class="feed"
          href="http://example.com/drafts"/>
        </service>
        <service class="feed" name="Sidebar Blog"
         href="http://example.org/details"/>



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      </app>


   Servers are not required to expose a Service Description document,
   but experimental deployment experience has shown that a single
   document which signals some basic information about the server's
   configuration can greatly simplify client implementations.  The
   simplest useful Service Description document shows the location of a
   single resource:


      <app>
        <service name="My Blog" class="feed"
         href="http://blog.example.com/app.cgi"/>
      </app>


   If another service is added, the document can be upgraded to reflect
   new resources.


      <app>
        <service name="My Blog" class="feed"
         href="http://blog.example.com/app.cgi"/>
        <service name="Another Blog" class="feed"
         href="http://another.example.com/app.cgi"/>
      </app>


   Finally, more extensive services could require some amount of
   hierarchical grouping.


      <app>
        <service name="My Blog" class="feed"
         href="http://blog.example.com/app.cgi">
          <service name="Photos" class="media feed"
           href="http://example.com/photos"/>
        </service>
        <service name="Other Things">
          <service name="Another Blog" class="feed"
           href="http://another.example.com/app.cgi"/>
          <service name="A Third Blog" class="feed"
           href="http://third.example.com/app.cgi"/>
        </service>
      </app>





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   This example shows that links to APP feeds can appear in <service>
   elements used to group other resources.  The <service> element named
   "Other Things" does not contain an 'href' attribute, so it functions
   as a simple named group of the services it contains.

9.1.  Categories

   [@@ tbd]

9.2.  Document Format

   Service Description documents MUST be well-formed XML [W3C.REC-xml-
   20040204].

   The root element of an APP Service Description Document is "<app>".
   This specification does not define any attributes of the <app>
   element, but the element can have any number of attributes.

   Zero or more <service> elements appear as child elements of <app>.
   Also, <service> elements may contain zero or more <service> elements.
   This specification defines three attributes of the <service> element.
   <service> elements contain at least a 'name' or 'href' attribute.
   Additional service properties too large or structured to include in
   attribute values could appear as child elements of the service
   element.

   <app> elements can contain any number of elements that are not
   <service> elements, and <service> elements can contain any number of
   elements that are not <service> elements.

9.2.1.  The 'name' Attribute

   The 'name' attribute contains a short string describing the service
   element.  Entities such as "&amp;" and "&lt;" represent their
   corresponding characters ("&" and "<" respectively), not markup.

9.2.2.  The 'href' Attribute

   The 'href' attribute contains an IRI reference interpreted relative
   to the in-scope base IRI [RFC3987].  Most protocols require URIs
   [RFC3986], so IRIs usually need to be converted to URIs before being
   dereferenced.

9.2.3.  The 'class' Attribute

   The 'class' attribute contains a space-separated list of strings used
   to classify the service element.  This specification defines two
   values for the 'class' attribute:



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   o  feed
   o  media feed

   These values correspond to standard feeds and media feeds,
   respectively.  If the 'class' attribute is not present, the <service>
   element can be processed as if the attribute were present with a
   value of 'feed'.

9.2.4.  Relax NG Schema

   Service Description documents conform to the schema below.


      default namespace = "http://purl.org/atom/app#"
      start = app

      app = element app {
        anyAttribute*,
        (service* & anyElement*)
      }

      service = element service {
        (nameAtt | hrefAtt), anyAttribute*,
        (service* & anyElement*)
      }

      nameAtt = attribute name { text }
      hrefAtt = attribute href { text }
      classAtt = attribute class { text }

      anyElement = element * { (anyAttribute | text | anyElement)* }
      anyAttribute = attribute * { text }


9.2.5.  Extending Service Description

   The Service Description document format can be freely extended by
   adding attributes and elements not defined by this specification.

   Valid Service Description document with extensions:


      <app xmlns="http://purl.org/atom/app#" foo="bar">
        <blog-userid>42</blog-userid>
        <service name="Baz" qux="hmmm" href="http://example.com">
          <some-other-extension>hmm</some-other-extension>
        </service>
      </app>



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   Additional service properties too large or structured to include in
   attribute values could appear as child elements of the <service> or
   <app> elements. <app> elements may contain any number of elements
   that are not <service> elements, and <service> elements may contain
   any number of elements that are not <service> elements.

9.2.6.  User Agent Conformance

   Foreign markup is markup not defined by this specification.

   Software consuming Service Description documents must not halt
   processing when any foreign markup is encountered.  Software may
   ignore the markup and process any content of foreign elements as
   though the surrounding markup were not present.  For example,
   software may process


      <app>
        <workspace>
          <service name="My Blog"
           href="http://example.com/entries">
            <service name="Photos" class="media feed"
             href="http://example.com/jpgs"/>
            <view title="Archives" seek="...">
            <view title="2005" href="..." />
              ...
            </view>
          </service>
        </workspace>
      </app>


   as though the <workspace> and <view> elements were not present.

   Software conforming to this specification may halt processing when
   documents that do not conform to the schema are encountered.


10.  IANA Considerations

   [@@ fill out in for application/sd+xml (service description)]


11.  Security Considerations







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12.  Informative References


Appendix A.  Acknowledgements

   This draft is a variant of the in-progress Atom Publishing Protocol
   specification from the IETF Atompub WG, and owes a debt to the WG's
   members.


Appendix B.  Change History
   -06:  Change service description format.
      Change IPR terms to full3978
   -interlude:  More unproductive WG thrashing.
   -05:  Death to collections!
      Switch APPO instead of XOXO.
      State the obvious about the extension elements.
      Remove RFC2119 reference.
      Change "Normative References" to "References".
   -04:  Add pub:control element.
      Reword collection POST.
      Prophesize about atom:id.
   -03:  Remove search/query capabilities added in -02 Drop round-
      tripping.  Most of them were writable, some folks wanted to edit
      atom:updated, that leaves atom:id, and that seems foolish to try
      and edit, so go ahead and try it if you think you can.
   -02:  Add search/query capabilities.
   -01:  Split from WG draft, cut SOAP, and much other cruft.
   -interlude:  Becomes WG draft.
   -00:  Split from WG draft.





















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Author's Address

   Robert Sayre

   Email: rfsayre@boswijck.com














































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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
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   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Disclaimer of Validity

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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