| Network Working Group | J.C. Gregorio, Editor |
| INTERNET DRAFT | BitWorking, Inc |
| <draft-ietf-atompub-protocol-02.txt> | R.F. Sayre, Editor |
| Category: Standards Track | Boswijck Memex Consulting |
| Expires: March 2005 | September 2004 |
The Atom Publishing Protocol
draft-ietf-atompub-protocol-02.txt
By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I 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 in March 2005.
Copyright (C) The Internet Society (2004). All Rights Reserved.
This memo presents a protocol for using XML (Extensible Markup Language) and HTTP (HyperText Transport Protocol) to edit content.
The Atom Publishing Protocol is an application-level protocol for publishing and editing Web resources belonging to periodically updated websites. The protocol at its core is the HTTP transport of Atom-formatted representations. The Atom format is documented in the Atom Syndication Format (draft-ietf-atompub-format-02.txt).
To provide feedback on this Internet-Draft, join the atom-syntax mailing list (http://www.imc.org/atom-syntax/index.html).
1
Introduction
1.1
Notational Conventions
1.2
Terminology
2
The Atom Publishing Protocol Model
3
Functional Specification
3.1
PostURI
3.1.1
Locating the PostURI
3.1.2
Request
3.1.3
Response
3.1.3.1
Response code 201
3.1.3.2
Response code 303
3.1.3.3
Response code 400
3.1.3.4
Response code 409
3.1.3.5
Response code 500
3.2
EditURI
3.2.1
Locating
3.2.2
Request
3.2.2.1
Successful Requests
3.2.2.2
Response code 301
3.2.2.3
Response code 307
3.2.2.4
Response code 401
3.2.2.5
Response code 409
3.2.2.6
Response code 410
3.2.2.7
Response code 500
3.3
FeedURI
3.3.1
Locating
3.3.2
Request
3.3.3
Response
3.3.3.1
Response code 301
3.3.3.2
Response code 307
3.4
ResourcePostURI
3.4.1
Locating
3.4.2
Request
3.4.3
Response
3.4.3.1
Response code 201
3.4.3.2
Response code 303
3.4.3.3
Response code 400
3.4.3.4
Response code 415
3.4.3.5
Response code 500
3.5
Link Tag
3.5.1
rel
3.5.2
href
3.5.3
title
3.5.4
type
3.6
Atom Request and Response Body Constraints
3.6.1
id
3.6.2
link
3.6.3
title
3.6.4
summary
3.6.5
content
3.6.6
issued
3.6.7
modified
3.6.8
created
3.6.9
author
3.6.10
contributor
3.6.11
generator
3.7
Securing the Atom Protocol
3.7.1
[@@TBD@@ CGI Authentication]
4
Security Considerations
5
IANA Considerations
6
Appendix A - SOAP Enabling
6.1
Servers
6.2
Clients
7
Appendix B - Examples
7.1
Example for a weblog
7.2
Example for a wiki
8
Revision History
9
Normative References
§
Author's Addresses
§
Intellectual Property and Copyright Statements
The Atom Publishing Protocol is an application-level protocol for publishing and editing Web resources using HTTP [RFC2616] and XML.
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 [RFC2119].
The Atom Publishing Protocol is an application-level protocol for publishing and editing Web resources. Using the common HTTP verbs provides a pattern for working with all such Web resources:
There are four major classes of URI [RFC2396] in this specification: PostURI, ResourcePostURI, FeedURI, and EditURI. This specification defines the expected actions for each of the methods listed. A URI MAY support methods not listed here. For example, an EditURI could support a POST or OPTIONS method. However, what those methods do is beyond the scope of this specification.
This document does not specify the form of the URIs that are used. The URI space of each server is controlled, as defined by HTTP, by the server alone. What this document does specify are the formats of the files that are exchanged and the actions that can be performed on the URIs embedded in those files.
The PostURI is used to create entries. These can be either full entries, such as a weblog post, or they can be comments, or even a wiki page. The client POSTs a filled-in Atom Entry to this URI. If the request is successful, one or more Web resources MAY be created. For example, POSTing an Atom entry to a PostURI may create two new Web resources, an HTML representation and an Atom representation.
The PostURI can be discovered in a link element with an @rel of 'service.post'. The link element containing a PostURI used to create a new entry MAY be discovered in three different places. The first place it may be found is in a <link> element in the 'head' element of an HTML document.
The second place a PostURI may be found an atom:link element that is a child of the atom:feed element. The third place a PostURI may be found is in the atom:link element of an atom:entry.
@@ TBD @@ - Discuss subordinate resources and what a PostURI means based on where the URI was found.
<link rel="service.post"
type="application/atom+xml"
href="URI for Posting goes here"
title="The name of the site." />
The request contains a filled-in Atom entry, subject to the constraints in section Section 3.6.
The possible status codes from a POST are 201, 303, 400, 404, 409, 410 and 500.
The Response MUST include a Location: header with the URI of the created resource. The URI returned must be the EditURI of the entry just created. The body of the response SHOULD contain the newly created entry. If the entry is present in the response body then it MUST conform to the same constraints listed for responses to a GET on an EditURI. User agents MUST NOT depend on the server returning a response body. If the server does return a response body then the user agents MUST NOT depend on the response body having a content-type of 'application/atom+xml". Note that the server may choose to omit the content in the response, particularly if it is large.
A 201 response MAY contain an ETag response header field indicating the current value of the entity tag for the requested variant just created.
If the entry returned is subsequently changed the user agent can update the entry by submitting it via PUT to the EditURI. If an ETag was returned with the creation of the entry then the user agent SHOULD include an If-Match: header in the request that contains that ETag.
The body of this response does not contain the filled-in Entry, but the filled-in Entry can be found under a different URI and can be retrieved using a GET method on that resource. The URI SHOULD be given by the Location field in the response.
Indicates that the server believes that the data sent constitutes an invalid request. As an example, the data posted may not be well-formed XML. The server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
The request contained a valid Atom Entry, but it conflicts with state on the server. The response SHOULD contain enough for information for the user to resolve the conflict.
[[@@TBD@@ more about response body format]]
Indicates that the server detected an internal error on the server processing this request (such as an unhandled exception). The server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
An EditURI is used to edit a single entry. Each entry that is editable MUST have a unique URI. This URI supports both GET and PUT and they are used in tandem for an editing cycle. The client GETs the representation which is formatted as an Atom entry. The client may then update the entry and then PUT it back to the same URI. The PUT will cause all the related resources to be updated, for example, the HTML representation.
Note that the value of the content element in the Atom entry does not have to exactly match the content element for the same entry when it is represented in an Atom feed. For example, a server may allow the client to post entries whose content is formatted as WikiML, yet the server may clean up such markup and transform it into well-formed XHTML before placing it in the publicly available Atom feed. Another scenario is summaries--the EditURI is for editing the full content of an entry, but the server may only present excerpts when it produces an Atom feed.
A client will send a DELETE to the EditURI to delete an entry.
For editing a site Entry, the link tag is used. Note that a link tag is used in both HTML and in the Atom format. A link tag of the following format points to the EditURI for a site. In HTML, the link tags for editing are always found in the head element, while in Atom they may appear as children of the entry elements.
<link rel="service.edit"
type="application/atom+xml"
href="URI for Editing goes here"
title="Readable desc of the entry." />
Note: The critical characteristic of this link tag is the @rel of 'service.edit' and the @type of 'application/atom+xml'.
A PUT request, and a GET response both contain a filled-in Atom entry, subject to the constraints in section Section 3.6.
The expected status codes from a GET are 200, 301, 307, and 500. 400, 404, and 410 are also possible.
The expected status codes from a PUT are 2xx, 301, 307, 500 and 501. 400, 404, 409, and 410 are also possible.
Servers MUST indicate successful GET requests with a 200 response.
Servers MUST indicate successful PUT requests with a 2xx response. Servers MAY include additional information in the PUT response. Clients SHOULD NOT expect any additional information in a PUT response.
The entry has moved permanently, the new URI is given in the Location header. The client SHOULD retry the GET using the URI returned in the Location header. When a PUT operation is attempted the user agent should prompt the user before attempting the PUT on the URI returned in the Location header.
The entry has moved temporarily, the new URI is given in the Location header. The client SHOULD retry the GET using the URI returned in the Location header. When a PUT operation is attempted the user agent should prompt the user before attempting the PUT on the URI returned in the Location header.
Indicates that the server believes that the data sent constitutes an invalid request. As an example, the data posted may not be well-formed XML. The server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
The request contained a valid Atom Entry, but it conflicts with the state of the resource, or other state on the server.
For example, a server could signal that the client has erred in this manner if it receives a request containing an atom:id element whose value differs from that of the resource found at the requested URI.
The response SHOULD contain enough for information for the user to resolve the conflict.
[[@@TBD@@ more about response body format ]]
Indicates that the requested resource is gone permanently. The client SHOULD NOT repeat the request.
Indicates that the server detected an internal error on the server processing this request (such as an unhandled exception). The server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
The FeedURI is used to retrieve a representation in Atom format. Note that this feed is different from a typical Atom feed in that it contains "link" elements for navigating and manipulating the content of the site. For example there should be a "link" element with rel="next" whose URI points to the next block of entries on the site. Similarly, the feed element can contain a "link" element with rel="service.post", the URI of which is a PostURI. Individual entries should contain "link" elements with rel="service.edit" whose URIs are EditURIs.
This document only uses some of the methods available for each type of URI. For example, the only method described by this document for the FeedURI is GET. Any other method may be supported by the URI types described, but defining their behavior is beyond the scope of this document. In this light you may notice that the PostURI only supports the POST method. It is possible, and allowable, that for some implementations the PostURI and the FeedURI are the same URI.
@@ Editor's Note: @@ Note that the "service.feed" takes the place of the Introspection File and the Search facet in previous versions of the specification. That is, facet discovery, which was previously done by inspecting the Introspection file is now done by looking for "link" tags with an attribute "rel" set to "service.[something]" in the "service.feed" file. At the same time the same representation replaces the search facet by having "link" tags that point to other feeds using well-known 'rel' attribute values such as 'next' and 'prev', or the search can branch in multiple directions by specifying multiple link tags with rel="service.feed" and having differing title attributes that announce the kind of search results in that feed.
A link tag of the following format points to the FeedURI.
<link rel="service.feed"
type="application/atom+xml"
href="URI goes here"
title="The name of the site." />
The request is a simple GET. No other verbs are currently specified for this URI.
The expected status codes from a GET are 200, 301, 307, and 500. 401, 404, and 410 are also possible.
The Feed has moved permanently, the new URI is given in the Location header. The client SHOULD do a GET on the URI returned in the Location header.
The Feed has moved temporarily, the new URI is given in the Location header. The client SHOULD do a GET on the URI returned in the Location header.
The ResourcePostURI is used to create new non-entry resources. The client POSTs a resource of the desired MIME type directly to this URI.
For creating a new non-entry resource, the link tag is used. Note that a link tag is used in both HTML and in the Atom format. A link tag of the following format points to the ResourcePostURI for a site. In HTML the link tags are always found in the head element, while in Atom they may appear as children of the Feed and entry elements.
<link rel="resource.post" href="URI for Resource Posting goes here" title="The name of the site.">
The request contains a resource, sent through a standard HTTP POST, e.g.:
POST /_do/exampleblog/post_resource HTTP/1.1 Host: www.example.com Content-Type: image/jpeg Content-Length: nnn ...raw bytes of image go here...
The expected status codes from a POST are 201, 303, 400, 415, and 500. 401, 404, 409, and 410 are also possible.
The response MUST include a Location: header with the URI of the created resource, i.e. the URI used to retrieve the resource representation in a subsequent HTTP GET. The server SHOULD omit the content of the resource in the response, since it would be redundant to return it to the client.
Similar to 201 but no caching is allowed. The response MUST include a Location: header.
Indicates that the server believes that the data sent constitutes an invalid request. The server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
The MIME type of the request entity is not supported by the server for this resource.
The response SHOULD contain enough for information for the user to resolve the conflict.
[[@@TBD@@ more about response body format ]]
Indicates that the server detected an internal error on the server processing this request (such as an unhandled exception). A short description of the error will appear on the status line itself. A longer description will appear in the body.
The link tag is used in both HTML and Atom formats. There are slight differences between the two usages. Here are the commonalities, differences, and a list of well-known values for the rel attribute.
The link tag in HTML documents appears in the 'head' of the document. The 'head' section only allows a linear list of 'link' tags. The Atom format allows 'link' tags as children of both the 'feed' element and of the 'entry' element. Note that this gives the information present in the link tag more context. For example ... @@ TBD @@
This attribute describes the relationship from the current document, be it HTML or Atom, to the anchor specified by the href attribute. The value of this attribute is a space-separated list of link types. Note that these values are case insensitive. When used in concert with type="application/atom+xml", the relations may be interpreted as follows.
URI of the resource being described by this link element.
Offers advisory information about the link. Rendered to the user to help them choose among a set of links with the same rel and type attributes.
The content type of the resource available at the URI given in the href attribute of the link element. Most of the link types in this specification are on type 'application/atom+xml'.
The Atom format is used as the representation of all the resources in this specification. As it is used in differing contexts, there are different constraints of which elements may be present, and how their values should be interpreted.
All instances of publishing Atom entries SHOULD be protected by authentication to prevent posting or editing by unknown sources. Atom servers and clients MUST support one of the following authentication mechanisms, and SHOULD support both.
Atom servers and clients MAY support encryption of the Atom session using TLS [RFC2246].
There are cases where an authentication mechanism may not be required, such as a publicly editable Wiki, or when using the PostURI to post comments to a site that does not require authentication to create comments.
This authentication method is included as part of the protocol to allow Atom servers and clients that cannot use HTTP Digest Authentication but where the user can both insert its own HTTP headers and create a CGI program to authenticate entries to the server. This scenario is common in environments where the user cannot control what services the server employs, but the user can write their own HTTP services.
Because Atom is a publishing protocol, it is important that only authorized users can create and edit entries.
The security of Atom is based on HTTP Digest Authentication and/or [@@TBD@@ CGI Authentication]. Any weaknesses in either of these authentication schemes will obviously affect the security of the Atom Publishing Protocol.
Both HTTP Digest Authentication and [@@TBD@@ CGI Authentication] are susceptible to dictionary-based attacks on the shared secret. If the shared secret is a password (instead of a random string with sufficient entropy), an attacker can determine the secret by exhaustively comparing the authenticating string with hashed results of the public string and dictionary entries.
See RFC 2617 for more detailed description of the security properties of HTTP Digest Authentication.
@@TBD@@ Talk here about using HTTP basic and digest authentication.
@@TBD@@ Talk here about denial of service attacks using large XML files, or the billion laughs DTD attack.
This document has no actions for IANA.
All servers SHOULD support the following alternate interface mechanisms to enable a wider variety of clients to interact with Atom Publishing Protocol servers. The following requirements are in addition to the ones listed in the Functional Specification Section. If a server supports SOAP Enabling then it MUST support all of the following.
Fill this in with an example for how all the above is used for a weblog. Start with main HTML page, link tag of type service.feed to the 'introspection' file. 1. Creating a new entry 2. Finding an old entry 3. editing an old entry 4. commenting on a entry (via HTML and Atom)
Fill this in like above but for a wiki.
draft-ietf-atompub-protocol-02 - Incorporates Pace409Response, PacePostLocationMust, and PaceSimpleResourcePosting.
draft-ietf-atompub-protocol-01 - Added in sections on Responses for the EditURI. Allow 2xx for response to EditURI PUTs. Elided all mentions of WSSE. Started adding in some normative references. Added the section "Securing the Atom Protocol". Clarified that it is possible that the PostURI and FeedURI could be the same URI. Cleaned up descriptions for Response codes 400 and 500.
Rev draft-ietf-atompub-protocol-00 - 5Jul2004 - Renamed the file and re-titled the document to conform to IETF submission guidelines. Changed MIME type to match the one selected for the Atom format. Numerous typographical fixes. We used to have two 'Introduction' sections. One of them was moved into the Abstract the other absorbed the Scope section. IPR and copyright notifications were added.
Rev 09 - 10Dec2003 - Added the section on SOAP enabled clients and servers.
Rev 08 - 01Dec2003 - Refactored the specification, merging the Introspection file into the feed format. Also dropped the distinction between the type of URI used to create new entries and the kind used to create comments. Dropped user preferences.
Rev 07 - 06Aug2003 - Removed the use of the RSD file for auto-discovery. Changed copyright until a final standards body is chosen. Changed query parameters for the search facet to all begin with atom- to avoid name collisions. Updated all the Entries to follow the 0.2 version. Changed the format of the search results and template file to a pure element based syntax.
Rev 06 - 24Jul2003 - Moved to PUT for updating Entries. Changed all the mime-types to application/x.atom+xml. Added template editing. Changed 'edit-entry' to 'create-entry' in the Introspection file to more accurately reflect it's purpose.
Rev 05 - 17Jul2003 - Renamed everything Echo into Atom. Added version numbers in the Revision history. Changed all the mime-types to application/atom+xml.
Rev 04 - 15Jul2003 - Updated the RSD version used from 0.7 to 1.0. Change the method of deleting an Entry from POSTing <delete/> to using the HTTP DELETE verb. Also changed the query interface to GET instead of POST. Moved Introspection Discovery to be up under Introspection. Introduced the term 'facet' for the services listed in the Introspection file.
Rev 03 - 10Jul2003 - Added a link to the Wiki near the front of the document. Added a section on finding an Entry. Retrieving an Entry now broken out into it's own section. Changed the HTTP status code for a successful editing of an Entry to 205.
Rev 02 - 7Jul2003 - Entries are no longer returned from POSTs, instead they are retrieved via GET. Cleaned up figure titles, as they are rendered poorly in HTML. All content-types have been changed to application/atom+xml.
Rev 01 - 5Jul2003 - Renamed from EchoAPI.html to follow the more commonly used format: draft-gregorio-NN.html. Renamed all references to URL to URI. Broke out introspection into it's own section. Added the Revision History section. Added more to the warning that the example URIs are not normative.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC2246] | Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 2246, January 1999. |
| [RFC2396] | Berners-Lee, T., Fielding, R.T. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. |
| [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.M., Hostetler, J.L., Lawrence, S.D., Leach, P.J., Luotonen, A. and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. |
| Joe Gregorio (editor) | |
| BitWorking, Inc | |
| 1002 Heathwood Dairy Rd. |
|
| Apex, NC 27502 | |
| US | |
| Phone: | +1 919 272 3764 |
| EMail: | joe@bitworking.com |
| URI: | http://bitworking.com/ |
| Robert Sayre (editor) | |
| Boswijck Memex Consulting | |
| 148 N 9th St. 4R |
|
| Brooklyn, NY 11211 | |
| US | |
| EMail: | rfsayre@boswijck.com |
| URI: | http://boswijck.com |
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.
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 (C) The Internet Society (2004). 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.
Funding for the RFC Editor function is currently provided by the Internet Society.