Network Working Group J. Snell
Internet-Draft December 14, 2004
Expires: June 14, 2005
The Atom Notification Protocol
draft-snell-atompub-notification-00
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Abstract
This memo presents a protocol for posting notifications of new or
updated content using a combination of the Atom Syndication Format
and HTTP POSTs.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Notational Conventions . . . . . . . . . . . . . . . . . . 3
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Atom Notification Protocol Model . . . . . . . . . . . . . 3
3. Functional Specification . . . . . . . . . . . . . . . . . . . 3
3.1 NotificationURI . . . . . . . . . . . . . . . . . . . . . 3
3.1.1 Locating the NotificationURI . . . . . . . . . . . . . 4
3.1.2 Request . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.3 Response . . . . . . . . . . . . . . . . . . . . . . . 5
4. Atom Syntax Extensions . . . . . . . . . . . . . . . . . . . . 5
4.1 "atom:notification" Element . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
The Atom Notification Protocol is an application-level protocol for
posting notification of new or updated content using HTTP and the
Atom Syndication Format.
1.1 Notational Conventions
The 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 [1].
1.2 Terminology
Atom Entry: An Atom Entry is a fragment of a full Atom feed. In this
case, the fragment is a single 'entry' element and all its child
elements. Each Atom Entry describes a single Web resource, providing
metadata and optionally a textual representation of that resource.
Atom Feed: In the context of an Atom Notification, an Atom Feed is a
minimal "atom:feed" element containing an "atom:head" element and no
"atom:entry" elements.
NotificationURI: A URI that is used to receive notifications about
new or updated Atom entries.
2. The Atom Notification Protocol Model
The Atom Notification Protocol has been designed to complement the
Atom Publishing Protocol by providing the means of sending
notifications when Atom-based content is created or updated.
The Atom Notification Protocol works by POSTing Atom Entries or Atom
Feeds to a NotificationURI using HTTP POST.
As is the case with the Atom Publishing Protocol, this document does
not seek to specify the form of the URIs that are used. This
document does, however, specify the formats of the entities posted to
those URIs.
3. Functional Specification
3.1 NotificationURI
The NotificationURI is used to POST notifications. A notification
consists of a single Atom Entry or Atom Feed. The notification is
essentially a one-way operation that implies no semantics or action
on the part of the receiver.
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3.1.1 Locating the NotificationURI
The NotificationURI can be discovered in one of two ways.
First, with an link element with a @rel of 'service.notification' in
the "head" element of an HTML document.
<link rel="service.notification"
type="application/atom+xml"
href="NotificationURI Goes Here"
title="The Title of the Site" />
Second, using a "atom:notification" element as described in section
4.1.
3.1.2 Request
The request contains a filled-in Atom Entry or Atom Feed.
A notification request containing an Atom Entry is intended to notify
the receiving endpoint that a specific entry has been created or
updated.
A notification request containing an Atom Feed is intended to notify
the receiving endpoint that a specific feed has been created or
updated.
Atom Entries POSTed to a NotificationURI MAY contain a "atom:head"
element that identifies the feed to which the entry belongs.
Atom Feeds POSTed to a NotificationURI MUST NOT contain any
"atom:entry" elements and SHOULD consist of only a minimal
"atom:head" element using as few optional elements as possible.
<?xml version="1.0" encoding="utf-8"?>
<feed version="draft-ietf-atompub-format-03: do not deploy"
xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">
<head>
<title>Example Feed</title>
<link href="http://example.org/"/>
<updated>2003-12-13T18:30:02Z</updated>
<author>
<name>John Doe</name>
</author>
</head>
</feed>
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3.1.3 Response
The possible HTTP status codes from a POST are 202, 400 or 500.
3.1.3.1 Response Code 202
A response code of 202 indicates that the notification was
successfully received and accepted. The body of the message SHOULD
be empty.
3.1.3.2 Response Code 400
A response code of 400 indicates that the server believes the data
sent constitutes an invalid request. For example, the data received
may not be a well-formed Atom entry or feed. The server SHOULD
include an entity containing an explanation of the error situation
and whether it is a temporary or permanent condition.
3.1.3.3 Response Code 500
A response code of 500 indicates that the server detected an internal
error while processing the notification request. The server SHOULD
include an entity containing an explanation of the error situation,
and whether it is a temporary or permanent condition.
4. Atom Syntax Extensions
4.1 "atom:notification" Element
The "atom:notification" element is a Service construct that conveys
the URI used to receive notifications related to an entry or feed.
No more than one "atom:notification" element may be added to the
"atom:head" or "atom:entry" elements. The "atom:notification"
element uses the same namespace URI as the Atom core elements.
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<?xml version="1.0" encoding="utf-8"?>
<feed version="draft-ietf-atompub-format-03: do not deploy"
xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-03">
<head>
<title>Example Feed</title>
<link href="http://example.org/"/>
<updated>2003-12-13T18:30:02Z</updated>
<author>
<name>John Doe</name>
</author>
<notification href="http://example.org/notificationURI" />
</head>
<entry>
<title>Atom-Powered Robots Run Amok</title>
<link href="http://example.org/2003/12/13/atom03"/>
<id>vemmi://example.org/2003/32397</id>
<updated>2003-12-13T18:30:02Z</updated>
<notification href="http://example.org/2003/32397/notificationURI" />
</entry>
</feed>
5. Security Considerations
The decision of whether or not to secure the Atom Notification
Protocol will be made on a case-by-case decision. Some notification
endpoints may be restricted to known authenticated users while others
will be open for anyone who wishes to post notifications. If a given
NotificationURI is restricted, the same authentication mechanisms
used by the Atom Publishing Protocol SHOULD be used. Because of
this, the Notification Protocol is open to the same threats as the
Publication Protocol.
One particular challenge that implementors of NotificationURI
endpoints will need to be aware of is the potential for denial of
service attacks and notification spamming. This document shall not
deal with potential solutions to such attacks.
6. IANA Considerations
This document has no actions for IANA.
7 References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Gregorio, J., Ed. and R. Sayre, Ed., "The Atom Publishing
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Protocol", draft-ietf-atompub-protocol-02 (work in progress),
September 2004.
[3] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication
Format", draft-ietf-atompub-format-03 (work in progress),
October 2004.
Author's Address
James M Snell
EMail: james@snellspace.com
URI: http://www.snellspace.com
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