Network Working Group P. Saint-Andre Internet-Draft Jabber Software Foundation Expires: July 15, 2005 J. Hildebrand Jabber, Inc. B. Wyman PubSub.com January 14, 2005 Transporting Atom Notifications over the Extensible Messaging and Presence Protocol (XMPP) draft-saintandre-atompub-notify-02 Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. 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 become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." 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 15, 2005. Copyright Notice Copyright (C) The Internet Society (2005). 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 Saint-Andre, et al. Expires July 15, 2005 [Page 1] Internet-Draft ATOM-PUBSUB January 2005 the Extensible Messaging and Presence Protocol (XMPP) for publish-subscribe functionality. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Discussion Venue . . . . . . . . . . . . . . . . . . . . . 4 2. Process Flows . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Notification of Entry Creation . . . . . . . . . . . . . . 5 2.2 Notification of Entry Modification . . . . . . . . . . . . 7 2.3 Notification of Entry Deletion . . . . . . . . . . . . . . 9 3. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5.1 Normative References . . . . . . . . . . . . . . . . . . . . 11 5.2 Informative References . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . 13 Saint-Andre, et al. Expires July 15, 2005 [Page 2] Internet-Draft ATOM-PUBSUB January 2005 1. Introduction 1.1 Overview The Atom Publishing Format and Protocol Working Group has been chartered to develop two technologies relevant to content syndication: 1. A data format for syndication of information about periodically-updated resources (such as weblog entries and news stories) available on the World Wide Web. 2. A protocol for publishing, editing, deleting, and otherwise managing such resources. Content syndication follows a classic "observer" or "publish-subscribe" 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 information is published or modified for that channel. 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 element may be suitable for Atom content notifications, there also exists an XMPP extension that provides more structured communications in the context Saint-Andre, et al. Expires July 15, 2005 [Page 3] Internet-Draft ATOM-PUBSUB January 2005 of information "channels" or "nodes" of the kind that are used in content syndication. 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], [ATOM-PROTOCOL], [XMPP-CORE], and [XMPP-PUBSUB]. The capitalized 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 [TERMS]. 1.3 Discussion Venue The authors welcomes discussion and comments related to the topics presented in this document. The preferred forum is the mailing list, for which subscription information and archive links are available at . 2. Process Flows 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 Saint-Andre, et al. Expires July 15, 2005 [Page 4] Internet-Draft ATOM-PUBSUB January 2005 who want to receive such information. We can visualize the architecture as follows: +-----------+ | HTTP User | +-----------+ | | [Atom API] | +--------------+ | HTTP Service | +--------------+ | | [XMPP Pubsub] | +---------------------+ | XMPP Pubsub Service | +---------------------+ | | [XMPP Pubsub] | +-----------+ | XMPP User | +-----------+ 2.1 Notification of Entry Creation 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. 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:head 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 Saint-Andre, et al. Expires July 15, 2005 [Page 5] Internet-Draft ATOM-PUBSUB January 2005 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: Example Feed 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amuck vemmi://example.org/2003/32397 2003-12-13T18:30:02Z 2003-12-13T18:30:02Z 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 delivered). Saint-Andre, et al. Expires July 15, 2005 [Page 6] Internet-Draft ATOM-PUBSUB January 2005 Example Feed 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amuck vemmi://example.org/2003/32397 2003-12-13T18:30:02Z 2003-12-13T18:30:02Z 2.2 Notification of Entry Modification 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:head 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): Saint-Andre, et al. Expires July 15, 2005 [Page 7] Internet-Draft ATOM-PUBSUB January 2005 Example Feed 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok vemmi://example.org/2003/32397 2003-12-13T18:30:02Z 2003-12-13T18:31:03Z 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. Saint-Andre, et al. Expires July 15, 2005 [Page 8] Internet-Draft ATOM-PUBSUB January 2005 Example Feed 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok vemmi://example.org/2003/32397 2003-12-13T18:30:02Z 2003-12-13T18:31:03Z 2.3 Notification of Entry Deletion 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: Saint-Andre, et al. Expires July 15, 2005 [Page 9] Internet-Draft ATOM-PUBSUB January 2005 Subject to node configuration and/or subscription options, each XMPP subscriber would then receive a pubsub notification that the item was deleted. 3. Implementation Notes 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. It is the responsibility of the receiving application to remove or ignore duplicate entries that might be received from multiple feeds. 4. Security Considerations Detailed security considerations for the relevant protocols profiled in this memo are given in [ATOM-FORMAT], [ATOM-PROTOCOL], [XMPP-CORE], and [XMPP-PUBSUB]; this memo introduces no new security concerns above and beyond those described in the foregoing specifications. 5. References Saint-Andre, et al. Expires July 15, 2005 [Page 10] Internet-Draft ATOM-PUBSUB January 2005 5.1 Normative References [ATOM-FORMAT] Nottingham, M., "The Atom Syndication Format", draft-ietf-atompub-format-04 (work in progress), January 2005. [ATOM-PROTOCOL] Gregorio, J., "The Atom Publishing Protocol", draft-ietf-atompub-protocol-02 (work in progress), October 2004. [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., "Publish-Subscribe", JSF JEP 0060, July 2004. 5.2 Informative References [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. [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [SHA1] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 (SHA1)", RFC 3174, September 2001. Authors' Addresses Peter Saint-Andre Jabber Software Foundation EMail: stpeter@jabber.org Joe Hildebrand Jabber, Inc. EMail: jhildebrand@jabber.com Saint-Andre, et al. Expires July 15, 2005 [Page 11] Internet-Draft ATOM-PUBSUB January 2005 Bob Wyman PubSub.com EMail: bob@wyman.us Saint-Andre, et al. Expires July 15, 2005 [Page 12] Internet-Draft ATOM-PUBSUB January 2005 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 might or might not be available; nor does it represent that it has 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. 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