Network Working Group R. Sayre Internet-Draft October 25, 2005 Expires: April 28, 2006 The Atom Publishing Protocol (Basic) draft-sayre-atompub-protocol-basic-05.txt 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. This document may not be modified, and derivative works of it may not be created. This document may only be posted in an Internet-Draft. 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 April 28, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo presents a protocol that uses XML and HTTP to publish and edit Web resources. Editorial Note To provide feedback on this Internet-Draft, join the atom-protocol mailing list . Sayre Expires April 28, 2006 [Page 1] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 3. The Atom Publishing Protocol Model . . . . . . . . . . . . . 3 4. APP Feeds . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Media Feeds . . . . . . . . . . . . . . . . . . . . . . . . 7 6. APP Outlines . . . . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . 10 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . 11 A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 B. Change History . . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . 13 Sayre Expires April 28, 2006 [Page 2] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 1. Introduction The Atom Publishing Protocol (APP) protocol uses HTTP [RFC2616] and XML [W3C.REC-xml-20040204] to publish and edit Web resources. 2. Notational Conventions The APP namespace is "http://purl.org/atom/app#". This specification refers to it by using the prefix "pub", but that prefix is arbitrary. The terms 'URI' and 'IRI' are shorthand for the identifiers specified in [RFC3986] and [RFC3987]. 3. The Atom Publishing Protocol Model The APP uses HTTP to operate on collections of Web resources represented by Atom feeds [AtomFormat]. This section illustrates the editing cycle for Atom entries. o GET is used to retrieve a representation of a resource or perform a read-only query. o POST is used to create a new, dynamically-named resource. o PUT is used to update a known resource. o DELETE is used to remove a resource. 3.1 Discovery To discover the location of the feeds exposed by an APP service, the client must locate and request an APP Outline (Section 6). APP Outlines describe the layout of an APP service. Client Server | | | 1.) GET Outline URI | |------------------------------->| | | | 2.) Service Outline Doc | |<-------------------------------| | | 1. The client sends a GET request to the Service Outline Resource. 2. The server responds with a APP Outline 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. Sayre Expires April 28, 2006 [Page 3] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 3.2 Listing Once the client has discovered the location of a feed in the outline, it can request a listing of the feed's entries. However, a feed might contain an extremely large number of entries, so servers are likely to list a small subset of them by default. Client Server | | | 1.) GET to Atom Feed URI | |------------------------------->| | | | 2.) 200 OK, Atom Feed Doc | |<-------------------------------| | | 1. The client sends a GET request to the Atom Feed's URI. 2. The server responds with an Atom Feed Document containing a full or partial listing of the feed's membership. 3.3 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 entry. 3.3.1 Create Client Server | | | 1.) POST Entry to Feed URI | |------------------------------->| | | | 2.) 201 Created @ Location | |<-------------------------------| | | 1. The client sends an Atom Entry to the server via HTTP POST. The Request URI is that of the Atom Feed. 2. The server responds with a response of "201 Created" and a "Location" header containing the URI of the newly-created Atom Entry. Sayre Expires April 28, 2006 [Page 4] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 3.3.2 Read Client Server | | | 1.) GET or HEAD to Entry URI | |------------------------------->| | | | 2.) 200 OK Atom Entry | |<-------------------------------| | | 1. The client sends a GET (or HEAD) request to the entry's URI. 2. The server responds with an Atom Entry document. 3.3.3 Update Client Server | | | 1.) PUT to Entry URI | |------------------------------->| | | | 2.) 200 OK | |<-------------------------------| | | 1. The client PUTs an updated Atom Entry Document to the entry's URI. 2. The server responds with a successful status code. 3.3.4 Delete Client Server | | | 1.) DELETE to Entry URI | |------------------------------->| | | | 2.) 204 No Content | |<-------------------------------| | | 1. The client sends a DELETE request to the entry's URI. 2. The server responds with successful status code. 3.4 Success and Failure HTTP defines classes of response. HTTP status codes of the form 2xx 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 Sayre Expires April 28, 2006 [Page 5] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 failed. Consult the HTTP specification for more detailed definitions of each status code. 4. APP Feeds 4.1 GET Feeds can contain extremely large numbers of resources. A naive client such as a web spider or web browser would be overwhelmed if the response to a GET contained every entry 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 entries in the feed. An example APP feed: My Posts1 urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6 2005-12-21T04:11:00-08:00 title 25 2005-12-21T04:11:00-08:00 Foo It started out looking simple enough... urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387 ... Each member entry is represented by an atom:entry element, but those entries are not an editable representation of the entry. To retrieve the source representation of the entry, clients send a GET request to the URI found in each entry's pub:edit element (see Section 4.3.1). Derived resources are located by examining an entry's atom:link elements. 4.2 POST An APP feed also accepts POST requests. The client POSTs a representation of the desired resource to the APP feed. Some feeds Sayre Expires April 28, 2006 [Page 6] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 only accept POST requests with certain media-types, so a POST MAY generate 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 request creating a new entry in a feed: POST /collection HTTP/1.1 Host: example.org User-Agent: Cosimo/1.0 Content-Type: application/atom+xml Content-Length: nnnn ...data... 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/foo13241234.atom APP feeds contain primarily textual content. Examples include weblogs, online journals, and wikis. Clients add entries by sending POST requests containing Atom Entry Documents. Existing entries are edited by sending HTTP requests to the URI found in an individual entry's pub:edit element. Servers can determine the processing necessary to interpret a request by examining the request's HTTP method. It is probably unwise to change an existing entry's atom:id value when issuing a PUT request. 4.3 Entry Extensions 4.3.1 The 'pub:edit' Element The pub:edit element is a child of atom:entry and has one attribute, 'href'. The value of this attribute is an IRI reference interpreted relative to xml:base. 4.3.2 The 'pub:control' Element The pub:control element is a child of atom:entry and is used to persist editing information and contains arbitrary markup. 5. Media Feeds The entries within Media Feeds are feeds do not represent uniform Sayre Expires April 28, 2006 [Page 7] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 types of content. For example, they might contain JPEG images, text documents, MPEG movies, and any other type of resource the server allows. 5.1 GET Media Feeds return an Atom feed much like Text Feeds, but with a few additions. The entries also contain an atom:content element with a 'src' attribute pointing to the media resource. This URI can be used to edit the uploaded media resource, using PUT and DELETE. Such entries may contain pub:edit elements used to edit the entry metadata. As with other entries, derived resources can be located by inspecting an entry's atom:link elements. An example Media Feed: My Posts1 Foo urn:uuid:ce61592c-14e2-4557-978e-dfbd444aefa6 2005-12-21T04:11:00-08:00 Title25 2005-12-21T04:11:00-08:00 urn:uuid:941e12b4-6eeb-4753-959d-0cbc51875387 This was awesome. ... The Atom Syndication Format requires that each such entry contain an atom:title and atom:summary element. This requirement can be challenging to meet without requiring users to enter tedious metadata, but servers should attempt to provide textual data about the resource in the interests of accessibility. The atom:title element will likely be provided by the client, as a way for users to associate their local resources with those they have uploaded to the server (see POST below). Sayre Expires April 28, 2006 [Page 8] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 5.2 POST To add an entry to a Media Feed, clients POST the resource to the Media Feed's URI. Clients should provide a 'Title' request header to provide the server with a short string identifying the resource to users. Clients may include a 'Content-Description' header [RFC2045] providing a more complete description of the content. In addition, servers may inspect the POSTed entity for additional metadata to be exposed in an atom:entry element when listed in a Media Feed. For example, the server might inspect a JPEG file for EXIF headers containing creator data. An example request: POST /collection HTTP/1.1 Host: example.org User-Agent: Cosimo/1.0 Content-Type: image/jpg Content-Length: nnnn Title: A Trip to the beach 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.jpg 6. APP Outlines In order for authoring to commence, a client must first discover the Atom Feeds offered by the server. The outline is an APP Outline Document [APPO]. The top level outline elements describe distinct groups of resources available on the server. For example, a user with an account containing three blogs would have 3 elements under the root element. There is no requirement that servers support multiple top-level outlines, and a feed may appear in more than one location in the document. Clients read APP feeds by visiting the URI located in the 'href' attribute of an element. This URI also serves as the Sayre Expires April 28, 2006 [Page 9] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 location a client POSTs new entries to. The 'class' attribute of the element indicates the type of feed. This specification defines two values for the 'class' attribute: o feed o media feed These values correspond to standard feeds and media feeds, respectively. An example APP Outline: 7. Security Considerations APP relies on HTTP Authentication. See [RFC2617] for a more detailed description of the security properties of HTTP Authentication. 8. References [APPO] Sayre, R., "APP Outline Format", work-in-progress, draft-sayre-atompub-protocol-outline-00, October 2005. [AtomFormat] Nottingham, M. and R. Sayre, "The Atom Syndication Format", work-in-progress, August 2005. [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. [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Sayre Expires April 28, 2006 [Page 10] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005. [W3C.REC-xml-20040204] Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T., and E. Maler, "Extensible Markup Language (XML) 1.0 (Third Edition)", W3C REC REC-xml-20040204, February 2004. Author's Address Robert Sayre Email: rfsayre@boswijck.com URI: http://boswijck.com Appendix A. Contributors This draft is a variant of the in-progress Atom Publishing Protocol specification from the IETF Atompub WG, and owes a debt to the WG's members. Appendix B. Change History -05: Death to collections! Switch APPO instead of XOXO. State the obvious about the extension elements. Remove RFC2119 reference. Change "Normative References" to "References". -04: Add pub:control element. Reword collection POST. Prophesize about atom:id. -03: Remove search/query capabilities added in -02 Drop round-tripping. Most of them were writable, some folks wanted to edit atom:updated, that leaves atom:id, and that seems foolish to try and edit, so go ahead and try it if you think you can. Sayre Expires April 28, 2006 [Page 11] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 Drop ordering... let the server pop things up if it wants to. -02: Add search/query capabilities. -01: Split from WG draft, cut SOAP, and much other cruft. -interlude: Becomes WG draft. -00: Split from WG draft Sayre Expires April 28, 2006 [Page 12] Internet-Draft The Atom Publishing Protocol (Basic) October 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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Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2005). 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. Sayre Expires April 28, 2006 [Page 13] Internet-Draft The Atom Publishing Protocol (Basic) October 2005 Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Sayre Expires April 28, 2006 [Page 14]