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 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 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 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. Saint-Andre, et al. Expires November 8, 2008 [Page 1] Internet-Draft ATOMSUB May 2008 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 Saint-Andre, et al. Expires November 8, 2008 [Page 2] Internet-Draft ATOMSUB May 2008 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 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 Saint-Andre, et al. Expires November 8, 2008 [Page 3] Internet-Draft ATOMSUB May 2008 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: Saint-Andre, et al. Expires November 8, 2008 [Page 4] Internet-Draft ATOMSUB May 2008 +-----------+ | 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. Saint-Andre, et al. Expires November 8, 2008 [Page 5] Internet-Draft ATOMSUB May 2008 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: Saint-Andre, et al. Expires November 8, 2008 [Page 6] Internet-Draft ATOMSUB May 2008 Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amuck Asimov's First Law horribly violated! tag:example.org,2003:entry-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 included). Example Feed Saint-Andre, et al. Expires November 8, 2008 [Page 7] Internet-Draft ATOMSUB May 2008 tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amuck Asimov's First Law horribly violated! tag:example.org,2003:entry-32397 2003-12-13T18:30:02Z 2003-12-13T18:30:02Z Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amuck Asimov's First Law horribly violated! tag:example.org,2003:entry-32397 2003-12-13T18:30:02Z Saint-Andre, et al. Expires November 8, 2008 [Page 8] Internet-Draft ATOMSUB May 2008 2003-12-13T18:30:02Z 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): Saint-Andre, et al. Expires November 8, 2008 [Page 9] Internet-Draft ATOMSUB May 2008 Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok Asimov's First Law horribly violated! tag:example.org,2003:entry-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. Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok Asimov's First Law horribly violated! tag:example.org,2003:entry-32397 2003-12-13T18:30:02Z 2003-12-13T18:31:03Z Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok Asimov's First Law horribly violated! tag:example.org,2003:entry-32397 2003-12-13T18:30:02Z 2003-12-13T18:31:03Z Saint-Andre, et al. Expires November 8, 2008 [Page 11] Internet-Draft ATOMSUB May 2008 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: Subject to node configuration and/or subscription options, each XMPP subscriber would then receive a pubsub notification that the item was deleted. Saint-Andre, et al. Expires November 8, 2008 [Page 12] Internet-Draft ATOMSUB May 2008 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 Saint-Andre, et al. Expires November 8, 2008 [Page 13] Internet-Draft ATOMSUB May 2008 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. Example Feed tag:example.org,2003:home 2003-12-13T18:30:02Z John Doe Atom-Powered Robots Run Amok Asimov's First Law horribly violated! tag:example.org,2003:entry-32397 2003-12-13T18:30:02Z 2003-12-13T18:31:03Z
123-abc
004-yyy
 4. Security Considerations Detailed security considerations for the relevant protocols profiled in this memo are given in [ATOM-FORMAT], [XMPP-CORE], and Saint-Andre, et al. Expires November 8, 2008 [Page 14] Internet-Draft ATOMSUB May 2008 [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. Saint-Andre, et al. Expires November 8, 2008 [Page 15] Internet-Draft ATOMSUB May 2008 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 Saint-Andre, et al. Expires November 8, 2008 [Page 16] Internet-Draft ATOMSUB May 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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, THE IETF TRUST 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. Intellectual Property 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. 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. Saint-Andre, et al. Expires November 8, 2008 [Page 17]