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Network Working Group                                     P. Saint-Andre
Internet-Draft                                 XMPP Standards Foundation
Intended status: Informational                             J. Hildebrand
Expires: November 8, 2008                                   Jabber, Inc.
                                                                B. Wyman
                                                             May 7, 2008


  Atomsub: Transporting Atom Notifications over the Publish-Subscribe
   Extension to the Extensible Messaging and Presence Protocol (XMPP)
                   draft-saintandre-atompub-notify-07

Status of this Memo

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   applicable patent or other IPR claims of which he or she is aware
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   This Internet-Draft will expire on November 8, 2008.

Abstract

   This memo describes a method for notifying interested parties about
   changes in syndicated information encapsulated in the Atom feed
   format, where such notifications are delivered via an extension to
   the Extensible Messaging and Presence Protocol (XMPP) for publish-
   subscribe functionality.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Process Flows  . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Notification of Entry Creation . . . . . . . . . . . . . .  5
     2.3.  Notification of Entry Modification . . . . . . . . . . . .  9
     2.4.  Notification of Entry Deletion . . . . . . . . . . . . . . 12
   3.  Implementation Notes . . . . . . . . . . . . . . . . . . . . . 13
     3.1.  Association Between User and Pubsub Node . . . . . . . . . 13
     3.2.  Generation of ItemIDs  . . . . . . . . . . . . . . . . . . 13
     3.3.  Handling of Duplicate Entries  . . . . . . . . . . . . . . 13
     3.4.  Notifications Matching Multiple Subscriptions  . . . . . . 13
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
   Intellectual Property and Copyright Statements . . . . . . . . . . 17






























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1.  Introduction

1.1.  Overview

   The Atom Publishing Format and Protocol Working Group has developed
   two technologies relevant to content syndication:

   1.  An XML data format for syndication of information about
       periodically-updated resources (such as weblog entries and news
       stories) available on the World Wide Web (see [ATOM-FORMAT]).
   2.  A protocol for publishing, editing, deleting, and otherwise
       managing such resources (see [ATOM-PROTOCOL]).

   Content syndication follows a classic "observer" or "publish-
   subscribe" software design pattern: a person or application publishes
   information to a "channel", and an event notification (or the data
   itself) is broadcasted to all those who are interested in knowing
   when such information is published or modified.  On the Internet
   today, publication of periodically-updated resources is handled by
   means of standard technologies such as [HTTP], and it is not
   envisioned that this will change since [ATOM-PROTOCOL] specifies the
   use of HTTP for publication.  However, existing methods for learning
   that a resource has been updated are currently limited to "polling"
   for changes via HTTP, which is inherently inefficient.  What is
   needed is a technology that can be relied on to "push" information
   only when a resource undergoes a state change, and only to those who
   are interested in learning about such state changes.

   One possible technology for doing so is email, since [SMTP] provides
   a way to initiate the sending of information from "publishers" to
   "subscribers" (think, for example, of email lists such as those used
   to announce newly-published RFCs).  While email is one possible
   solution, it is not necessarily the best solution for Atom; in
   particular, [ATOM-FORMAT] defines an XML data format for content
   syndication, which implies that it might be beneficial to use a
   native XML delivery mechanism rather than to attach a special XML
   media type to email messages.  Thankfully, a specialized XML delivery
   protocol has been developed through the IETF: the Extensible
   Messaging and Presence Protocol (XMPP) as specified in [XMPP-CORE].
   XMPP has the added benefit of being optimized for near-real-time data
   delivery, which may be important in applications of Atom that require
   subscribers to be notified about syndicated content in a highly
   timely manner.

   While the semantics of a normal XMPP <message/> element may be
   suitable for Atom content notifications, there also exists an XMPP
   extension that provides more structured communications in the context
   of information "channels" or "nodes" of the kind that are used in



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   typical content syndication technologies, where an interested entity
   can subscribe to that channel or node and thus receive notifications
   related to the topic of interest.  This extension is specified in
   [XMPP-PUBSUB] and may be especially useful for delivering
   notifications related to changes in Atom resources.  Therefore, this
   memo describes a method for notifying interested parties about
   changes in syndicated information encapsulated in the Atom feed
   format, where such notifications are delivered via the XMPP publish-
   subscribe extension.

1.2.  Terminology

   This document inherits terminology from [ATOM-FORMAT], [XMPP-CORE],
   and [XMPP-PUBSUB].

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


2.  Process Flows

2.1.  Overview

   The following process flows demonstrate how Atom-formatted data
   (specifically, feed entries) can be delivered using the XMPP pubsub
   extension.  The actors in these process flows are an application and
   one or more XMPP users.  The application acts as a translator between
   HTTP and XMPP, since it generates XMPP pubsub requests when certain
   events occur at an Atom-aware HTTP service (e.g., an HTTP POST to
   create a new dynamic resource).  The XMPP pubsub service then
   translates those pubsub requests into notifications that are sent to
   a potentially large number of XMPP users who have subscribed to such
   events (e.g., who have asked to receive an XMPP notification whenever
   a new dynamic resource is created for a certain Atom "channel").  Of
   course, an XMPP user is not necessarily a human, and could represent
   another application on the XMPP network (e.g., a chatroom, a bot, or
   a content management system).

   Note well that an HTTP user (e.g., a weblog author) would still
   publish information using the methods defined in [ATOM-PROTOCOL]; the
   process flows described herein enable the HTTP service with which an
   HTTP user interacts to generate notifications that are delivered via
   an XMPP pubsub service to a potentially large number of XMPP users
   who want to receive such information.

   We can visualize the architecture as follows:



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            +-----------+
            | HTTP User |
            +-----------+
                  |
                  | [Atom API]
                  |
           +--------------+
           | HTTP Service |
           +--------------+
                  |
                  | [XMPP Pubsub]
                  |
       +---------------------+
       | XMPP Pubsub Service |
       +---------------------+
                  |
                  | [XMPP Pubsub]
                  |
         +--------+-------+
         |                |
   +-----------+     +-----------+
   | XMPP User |     | XMPP User |
   +-----------+     +-----------+

   In the examples shown below, we stipulate the following particulars:

   o  The XMPP address of the HTTP Service is "atompub.example.org".
   o  The XMPP address of the XMPP Pubsub Service is
      "pubsub.example.com".
   o  The NodeID of the XMPP pubsub node to which the HTTP Service
      publishes and to which the XMPP Users subscribe is "an-atom-node".
   o  The ItemID of the XMPP pubsub item published by the HTTP Service
      is "70b2a83be71dfca04df91133d953fb22b41b4267".
   o  The XMPP addresses of the XMPP Users who are subscribed to the
      node are "alice@example.net" and "bob@example.com".

2.2.  Notification of Entry Creation

   An implementation MUST support notifications related to creation of
   an entry.

   When a content author publishes a new dynamic resource, many entities
   may be interested in learning that the resource is now available.
   The process flow is as follows:

   o  Author publishes a new entry to the HTTP service via the Atom API.





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   o  The HTTP service sends data for the new Atom entry in an XMPP
      pubsub "publish" request to a specific node at the XMPP pubsub
      service.  (Note: If the entry may be copied from one feed to
      another, e.g., in the generation of "synthetic" feeds, the entry
      SHOULD contain an atom:source element to ensure consistent
      metadata.)
   o  The XMPP pubsub service sends an XMPP message notification to each
      XMPP entity that is subscribed to the pubsub node.

   The result is that the XMPP subscribers will receive something close
   to real-time notification whenever a new feed entry has been
   published.

   Obviously the first step is out of scope for this memo, since it is
   described in [ATOM-PROTOCOL].  The XMPP protocols for the last two
   steps are shown below.

   First the HTTP service sends an XMPP pubsub "publish" request to the
   XMPP pubsub service:
































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   <iq type='set'
       from='atompub.example.org'
       to='pubsub.example.com'
       id='publish1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <publish node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amuck</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:30:02Z</updated>
           </entry>
         </item>
       </publish>
     </pubsub>
   </iq>

   The XMPP pubsub service then sends a pubsub notification to each XMPP
   subscriber; depending on pubsub node configuration, the notification
   may or may not contain the Atom payload (we assume here that the
   payload will be included).

   <message from='pubsub.example.com'
            to='alice@example.net'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>



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               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amuck</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:30:02Z</updated>
           </entry>
         </item>
        </items>
     </event>
   </message>

   <message from='pubsub.example.com'
            to='bob@example.com'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amuck</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>



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             <updated>2003-12-13T18:30:02Z</updated>
           </entry>
         </item>
        </items>
     </event>
   </message>

2.3.  Notification of Entry Modification

   An implementation SHOULD support notifications related to
   modification of an entry.

   When a content author updates an existing dynamic resource, many
   entities may be interested in learning that the resource has been
   modified.  The process flow is as follows:

   o  Author updates an existing entry at the HTTP service via the Atom
      API.
   o  The HTTP service sends data for the updated Atom entry in an XMPP
      pubsub "publish" request to a specific node at the XMPP pubsub
      service, specifying the same Item ID as previously supplied.
      (Note: If the entry may be copied from one feed to another, e.g.,
      in the generation of "synthetic" feeds, the entry SHOULD contain
      an atom:source element to ensure consistent metadata.)
   o  The XMPP pubsub service sends an XMPP message notification to each
      XMPP entity that is subscribed to the pubsub node.

   First the HTTP service sends an XMPP pubsub "publish" request to the
   XMPP pubsub service (note the modified title and time):






















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   <iq type='set'
       from='atompub.example.org'
       to='pubsub.example.com'
       id='publish2'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <publish node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amok</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:31:03Z</updated>
           </entry>
         </item>
       </publish>
     </pubsub>
   </iq>

   Subject to node configuration and/or subscription options, each XMPP
   subscriber would then receive a pubsub notification, which may or may
   not contain the Atom payload.

   <message from='pubsub.example.com'
            to='alice@example.net'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'



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                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amok</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:31:03Z</updated>
           </entry>
         </item>
        </items>
     </event>
   </message>

   <message from='pubsub.example.com'
            to='bob@example.com'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amok</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:31:03Z</updated>



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           </entry>
         </item>
        </items>
     </event>
   </message>

2.4.  Notification of Entry Deletion

   An implementation MAY support notifications related to deletion of an
   entry.

   If a content author deletes an existing dynamic resource, many
   entities may be interested in learning that the resource is no longer
   available.  The process flow is as follows:

   o  Author deletes an existing entry at the HTTP service via the Atom
      API.
   o  The HTTP service sends an XMPP pubsub "retract" request to a
      specific node at the XMPP pubsub service, specifying the same Item
      ID as previously supplied.
   o  The XMPP pubsub service sends an XMPP message notification to each
      XMPP entity that is subscribed to the pubsub node.

   First the HTTP service sends an XMPP pubsub "retract" request to the
   XMPP pubsub service:

   <iq type='set'
       from='atompub.example.org'
       to='pubsub.example.com'
       id='delete1'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <retract node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'/>
       </retract>
     </pubsub>
   </iq>

   Subject to node configuration and/or subscription options, each XMPP
   subscriber would then receive a pubsub notification that the item was
   deleted.











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   <message from='pubsub.example.com'
            to='alice@example.net'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <retract id='70b2a83be71dfca04df91133d953fb22b41b4267'/>
        </items>
     </event>
   </message>

   <message from='pubsub.example.com'
            to='bob@example.com'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <retract id='70b2a83be71dfca04df91133d953fb22b41b4267'/>
        </items>
     </event>
   </message>


3.  Implementation Notes

3.1.  Association Between User and Pubsub Node

   As explained in [XMPP-PUBSUB], a notification MAY include an XMPP
   SHIM Stanza Headers and Internet Metadata [XMPP-SHIM] header named
   "Reply-To" that specifies the JabberID of the publishing entity.
   Alternatively, as described in [XMPP-PEP], the XMPP server of the
   publishing entity MAY enable the publishing entity to associate a
   virtual pubsub service with the JabberID of its account, obviating
   the need for a separate pubsub service.

3.2.  Generation of ItemIDs

   The pubsub ItemIDs MUST conform to the rules defined in
   [XMPP-PUBSUB].  One possible method for generating a unique ItemID is
   to concatenate the XMPP address of the pubsub service, the pubsub
   node to which the item is published, and the atom:id of the feed
   entry, then hash the resulting string using the [SHA1] algorithm.

3.3.  Handling of Duplicate Entries

   It is the responsibility of the receiving application to remove or
   ignore duplicate entries that might be received from multiple feeds.

3.4.  Notifications Matching Multiple Subscriptions

   An XMPP entity may subscribe to a publish-subscribe node multiple
   times (e.g., once for each of several keywords), in which case a



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   single notification may match one or more subscriptions.  In order to
   specify which of one or more subscriptions are matched, the
   notification message SHOULD specify the subscription IDs using the
   header syntax defined in [XMPP-SHIM] and the "pubsub#subid" header
   defined in [XMPP-PUBSUB], as shown at the end of the following
   example.

   <message from='pubsub.example.com'
            to='alice@example.net'>
     <event xmlns='http://jabber.org/protocol/pubsub#event'>
       <items node='an-atom-node'>
         <item id='70b2a83be71dfca04df91133d953fb22b41b4267'>
           <entry xmlns='http://www.w3.org/2005/Atom'>
             <source>
               <title>Example Feed</title>
               <link href='http://example.org/'/>
               <link rel='self'
                     type='application/atom+xml'
                     href='http://example.org/atom.xml'/>
               <id>tag:example.org,2003:home</id>
               <updated>2003-12-13T18:30:02Z</updated>
               <author>
                 <name>John Doe</name>
               </author>
             </source>
             <title>Atom-Powered Robots Run Amok</title>
             <summary>Asimov's First Law horribly violated!</summary>
             <link rel='alternate'
                   type='text/html'
                   href='http://example.org/2003/12/13/atom03'/>
             <id>tag:example.org,2003:entry-32397</id>
             <published>2003-12-13T18:30:02Z</published>
             <updated>2003-12-13T18:31:03Z</updated>
           </entry>
         </item>
        </items>
     </event>
     <headers xmlns='http://jabber.org/protocol/shim'>
       <header name='pubsub#subid'>123-abc</header>
       <header name='pubsub#subid'>004-yyy</header>
     </headers>
   </message>


4.  Security Considerations

   Detailed security considerations for the relevant protocols profiled
   in this memo are given in [ATOM-FORMAT], [XMPP-CORE], and



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   [XMPP-PUBSUB]; this memo introduces no new security concerns above
   and beyond those described in the foregoing specifications.


5.  References

5.1.  Normative References

   [ATOM-FORMAT]
              Nottingham, M. and R. Sayre, "The Atom Syndication
              Format", RFC 4287, December 2005.

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

   [XMPP-CORE]
              Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [XMPP-PUBSUB]
              Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
              Subscribe", XSF XEP 0060, March 2008.

5.2.  Informative References

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

   [HTTP]     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.

   [SHA1]     Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, September 2001.

   [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.

   [XMPP-PEP]
              Saint-Andre, P. and K. Smith, "Personal Eventing via
              Pubsub", XSF XEP 0163, September 2007.

   [XMPP-SHIM]
              Saint-Andre, P. and J. Hildebrand, "Stanza Headers and
              Internet Metadata (SHIM)", XSF XEP 0131, July 2006.





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Authors' Addresses

   Peter Saint-Andre
   XMPP Standards Foundation

   Email: stpeter@jabber.org
   URI:   https://stpeter.im/


   Joe Hildebrand
   Jabber, Inc.

   Email: jhildebrand@jabber.com


   Bob Wyman

   Email: bob@wyman.us

































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