Internet DRAFT - draft-sayre-2-way-rss
draft-sayre-2-way-rss
Network Working Group R. Sayre
Internet-Draft May 18, 2006
Expires: November 19, 2006
2-Way RSS
draft-sayre-2-way-rss-05
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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. The 2-Way RSS Model . . . . . . . . . . . . . . . . . . . . . 3
3. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Authoring . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. 2-Way RSS Feeds . . . . . . . . . . . . . . . . . . . . . . . 6
7. 2-Way Media RSS Feeds . . . . . . . . . . . . . . . . . . . . 7
8. Service Outlines . . . . . . . . . . . . . . . . . . . . . . . 9
9. The 2-Way RSS Namespace . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
2-Way RSS uses HTTP [RFC2616] and XML [XML 1.0] to publish and edit
Web resources.
1.1. Editor's Note
To discuss this draft, please join the 2-Way RSS mailing list [1].
Membership is open to all.
2. The 2-Way RSS Model
2-Way RSS uses HTTP to operate on collections of Web resources
represented by RSS feeds [RSS]. In 2-Way RSS, individual RSS items
have URIs [RFC3986]. This section illustrates the editing cycle for
RSS items.
o GET is used to retrieve an item or perform a read-only query.
o POST is used to create a new item.
o PUT is used to update an existing item.
o DELETE is used to remove an item.
3. Discovery
To discover the location of the feeds exposed by a 2-way RSS service,
the client must locate and request the Service Outline, an OPML 2.0
document [OPML2].
Client Server
| |
| 1.) GET Service Outline URI |
|------------------------------->|
| |
| 2.) Service OPML Document |
|<-------------------------------|
| |
1. The client sends a GET request to the Service Outline URI.
2. The server responds with an OPML 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.
4. Listing
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Once the client has discovered the location of a feed in the outline,
it can request a listing of the feed's items. However, a feed might
contain an extremely large number of items, so servers are likely to
list a small subset of them by default.
Client Server
| |
| 1.) GET to RSS Feed URI |
|------------------------------->|
| |
| 2.) 200 OK, RSS Feed Doc |
|<-------------------------------|
| |
1. The client sends a GET request to the RSS Feed's URI.
2. The server responds with an RSS Feed Document containing a full
or partial listing of the feed's membership.
5. 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 item.
5.1. Create
Client Server
| |
| 1.) POST Item to Feed URI |
|------------------------------->|
| |
| 2.) 201 Created @ Location |
|<-------------------------------|
| |
1. The client sends an RSS item to the server via HTTP POST. The
Request URI is that of the RSS Feed.
2. The server responds with a response of "201 Created" and a
"Location" header containing the URI of the newly-created RSS
item.
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5.2. Read
Client Server
| |
| 1.) GET to Item URI |
|------------------------------->|
| |
| 2.) 200 OK RSS Item |
|<-------------------------------|
| |
1. The client sends a GET request to the item's URI.
2. The server responds with an RSS item.
5.3. Update
Client Server
| |
| 1.) PUT to RSS Item URI |
|------------------------------->|
| |
| 2.) 200 OK |
|<-------------------------------|
| |
1. The client PUTs an updated RSS item to the item's URI.
2. The server responds with a successful status code.
5.4. Delete
Client Server
| |
| 1.) DELETE to Item URI |
|------------------------------->|
| |
| 2.) 204 No Content |
|<-------------------------------|
| |
1. The client sends a DELETE request to the item's URI.
2. The server responds with successful status code.
5.5. Success and Failure
HTTP defines classes of response. HTTP status codes of the form 2xx
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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.
6. 2-Way RSS Feeds
6.1. GET
RSS feeds can contain extremely large numbers of items. A naive
client such as a web spider or web browser would be overwhelmed if
the response to a GET contained every item 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 items
in the feed.
An example 2-Way RSS feed:
<rss xmlns:r="http://example.org/2006/02/2WayRSS">
<channel>
<title>The Baron in the Trees</title>
<link>http://example.org/trees.html</link>
<description>Recent posts.</description>
<!-- 0 or more item elements follow -->
<item>
<title>Chapter One</title>
<description>It was on the fifteenth of June, 1767,
that Cosimo Piovasco di Rondò, my brother,
sat among us for the last time.</description>
<guid>uuid:941e12b4-6eeb-4753-959d-0cbc51875387</guid>
<link>http://example.org/chapter1.html</link>
<r:link rel="edit" href="./item7.rss"/>
</item>
</channel>
</rss>
Each member item is represented by an <item> element, but those items
are not an editable representation of the each item. To retrieve the
source representation of the item, clients send a GET request to the
URI found in each item's edit link, an 'r:link' element Section 9.1
with an 'edit' relation.
6.2. POST
A 2-Way RSS feed also accepts POST requests. The client POSTs a new
item to the RSS feed. Some feeds only accept POST requests with
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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").
Example HTTP request creating a new item in a feed:
POST /wall HTTP/1.1
Host: example.org
User-Agent: Cosimo/1.0
Content-Type: text/xml
Content-Length: nnnn
<item xmlns:r="http://example.org/2006/02/2WayRSS">
<title>Chapter One</title>
<description>It started out simple...</description>
<guid>uuid:941e12b4-6eeb-4753-959d-0cbc51875387</guid>
<link>http://example.org/chapter1.html</link>
<r:link rel="edit" href="./item7.rss"/>
</item>
Example response.
HTTP/1.1 201 Created
Date: Mon, 21 Mar 2005 19:20:19 GMT
Server: CountBasic/1.0
ETag: "4c083-268-423f1dc6"
Location: http://example.org/items/foo13241234.xml
7. 2-Way Media RSS Feeds
The items within 2-way Media RSS Feeds do not represent uniform types
of content. For example, they might contain podcasts, JPEG images,
text documents, MPEG movies, or any other type of resource the server
allows.
7.1. GET
2-Way Media RSS Feeds return an RSS feed much like the textual 2-Way
RSS feeds described above, but with a few additions. The entries
also contain an <enclosure> element with a 'url' attribute pointing
to the media object. This URL can be used to edit the uploaded media
object, using PUT and DELETE. Such items may contain edit links used
to edit the item metadata.
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An example 2-Way Media RSS Feed:
<rss>
<channel>
<title>My Pics</title>
<link>http://example.org/pics</link>
<description>Recent photos.</description>
<!-- 0 or more item elements follow -->
<item>
<title>beach25</title>
<link>http://example.org/beach-pic1.html</link>
<guid>uuid:941e12b4-6eeb-4753-959d-0cbc51875387</guid>
<description>This was awesome.</description>
<enclosure url="http://example.org/beach.tiff"
length="15234"
type="image/tiff" />
</item>
</channel>
</rss>
Implementations require that each such item contain either a <title>
or <description> element. The value for the <title> element will
likely be provided by the client, as a way for users to associate
their local objects with those they have uploaded to the server (see
POST below).
7.2. POST
To add an item to a 2-Way Media RSS feed, clients POST the resource
to the Media feed's URL. Clients should provide a 'Title' request
header [OBJECT] to provide the server with a short string identifying
the object to users.
Clients may include a 'Content-Description' header [RFC2045]
providing a more complete description of the content. Data gleaned
from other entity headers, such as 'Keywords' [RFC2822] and 'From'
[RFC2616], may also be exposed in the RSS feed.
Servers may inspect the POSTed entity for additional metadata to be
exposed in an <item> element when listed in a 2-Way Media RSS feed.
For example, the server might inspect a JPEG file for EXIF headers
containing creator data.
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An example request:
POST /pics HTTP/1.1
Host: example.org
User-Agent: Cosimo/1.0
Content-Type: image/tiff
Content-Length: nnnn
Title: A trip to the beach
From: Bobby <bobby@example.org>
Keywords: beach, digginit, tags, mrpibb, redvines
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
<item>
<title>A trip to the beach</title>
<link>http://example.org/beach.jpg</link>
<guid>uuid:4019de8a-7d08-4ca7-aee4-1a7cb92f3173</guid>
<enclosure url="http://example.org/beach.tiff"
length="15234"
type="image/tiff" />
</item>
The server's response contains a 'Location' header that gives the URI
of the created media resource. The body of the response shows the
created item. The enclosure element contains more detailed
information about the created media resource.
8. Service Outlines
Many 2-Way RSS applications require a basic resource layout in order
to ease configuration requirements. Servers use Service Outline OPML
2.0 documents to convey information about related groups of 2-Way RSS
feeds. On a blogging service, for example, each group might
represent a distinct blog and associated resources. Normal RSS feeds
have a type attribute of 'rss'. 2-Way RSS feeds have a type attribute
of '2-way rss'. Read-only media feeds have a type attribute of
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'media rss', and 2-Way media feeds have a type attribute of '2-way
media rss'.
Example Service Outline document:
<opml version="2.0">
<head>
<title>My Blogs</title>
</head>
<body>
<outline text="Pretending to be Excited" type="2-way rss"
xmlUrl="http://example.org/pretend.rss"/>
<outline text="Quick Links" type="2-way rss"
xmlUrl="http://example.org/side.rss"/>
</body>
</opml>
Servers are not required to expose a Service Outline OPML 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 Outline OPML document shows the location of a
single feed:
<opml version="2.0">
<head>
<title>Flickr</title>
</head>
<body>
<outline text="My Pics" type="2-way media rss"
xmlUrl="http://example.org/pics.rss"/>
</body>
</opml>
If another 2-Way RSS feed is added, another element is added to the
Service Outline.
<opml version="2.0">
<head>
<title>Flickr</title>
</head>
<body>
<outline text="Pics" type="2-way media rss"
xmlUrl="http://example.org/pics.rss"/>
<outline text="Overwraught Prose" type="2-way rss"
xmlUrl="http://example.org/blog.rss"/>
</body>
</opml>
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More extensive services could require some amount of hierarchical
grouping.
<opml version="2.0">
<head>
<title>Flickr</title>
</head>
<body>
<outline text="Pics" type="2-way media rss"
xmlUrl="http://example.org/pics.rss"/>
<outline text="Crazy Delicious">
<outline text="Overwraught Prose" type="2-way rss"
xmlUrl="http://example.org/blog.rss"/>
<outline text="Still More Overwraught Prose" type="2-way rss"
xmlUrl="http://example.org/blog2.rss"/>
</outline>
</body>
</opml>
Many publishing systems include a categorization system. An outline
element with a type attribute value of 'categories' can be used to
list the available categories. In this example, the category feeds
are read-only.
<opml version="2.0">
<head>
<title>Flickr</title>
</head>
<body>
<outline text="Pics" type="2-way media rss"
xmlUrl="http://example.org/pics.rss"/>
<outline text="Categories" type="categories">
<outline text="Category 1" type="rss"
xmlUrl="http://example.org/cat/1"/>
<outline text="Category 2" type="rss"
xmlUrl="http://example.org/cat/2"/>
</outline>
</body>
</opml>
9. The 2-Way RSS Namespace
The 2-Way RSS namespace URI is 'http://example.org/2006/02/2WayRSS'
[@ will update]. The examples in this specifcation use the prefix
'r', but any prefix will do in practice.
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9.1. The 'r:link' Element
The syntax and semantics of the 'r:link' element are identical to the
XHTML link element [XHTML], except for the namespace, and one other
exception: the r:link element allows arbitrary attributes.
10. References
[OBJECT] Berners-Lee, T., "Object Header lines in HTTP", 1992,
<http://www.w3.org/Protocols/HTTP/Object_Headers.html>.
[OPML2] Winer, D., "OPML 2.0 Specification", March 2006,
<http://www.opml.org/spec2>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2616] 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.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RSS] Cadenhead, et al., "Really Simple Syndication -- RSS
Advisory Board Announcements", <http://www.rssboard.org/>.
[RSS091] Libby, D., "RSS 0.91 Spec, revision 3", June 1997, <http:/
/my.netscape.com/publish/formats/rss-spec-0.91.html>.
[RSS092] Winer, D., "RSS 0.92", December 2005,
<http://backend.userland.com/rss092>.
[RSS2] Winer, D., "RSS 2.0", July 2003,
<http://blogs.law.harvard.edu/tech/rss>.
[XHTML] Pemberton, S., "XHTML. 1.0 The Extensible HyperText Markup
Language (Second Edition)", W3C REC REC-xhtml1-20020801,
August 2002,
<http://www.w3.org/TR/2002/REC-xhtml1-20020801>.
[XML 1.0] Bray, T., Sperberg-McQueen, C., Paoli, J., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Third
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Edition)", W3C REC REC-xml-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204>.
[1] <http://groups.google.com/group/2-Way-RSS>
Appendix A. Acknowledgements
[@ will be updated prior to publication]
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Author's Address
Robert Sayre
Email: rfsayre@boswijck.com
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