Network Working Group J. Gregorio, Ed.
Request for Comments: 5023 Google
Category: Standards Track B. de hOra, Ed.
NewBay Software
October 2007
The Atom Publishing Protocol
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Atom Publishing Protocol (AtomPub) is an application-level
protocol for publishing and editing Web resources. The protocol is
based on HTTP transfer of Atom-formatted representations. The Atom
format is documented in the Atom Syndication Format.
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RFC 5023 The Atom Publishing Protocol October 2007
Table of Contents
1. Introduction ....................................................4
2. Notational Conventions ..........................................4
2.1. XML-Related Conventions ....................................4
2.1.1. Referring to Information Items ......................4
2.1.2. RELAX NG Schema .....................................4
2.1.3. Use of "xml:base" and "xml:lang" ....................5
3. Terminology .....................................................5
4. Protocol Model ..................................................6
4.1. Identity and Naming ........................................6
4.2. Documents and Resource Classification ......................7
4.3. Control and Publishing .....................................8
4.4. Client Implementation Considerations .......................9
5. Protocol Operations .............................................9
5.1. Retrieving a Service Document .............................10
5.2. Listing Collection Members ................................10
5.3. Creating a Resource .......................................11
5.4. Editing a Resource ........................................11
5.4.1. Retrieving a Resource ..............................11
5.4.2. Editing a Resource .................................12
5.4.3. Deleting a Resource ................................12
5.5. Use of HTTP Response Codes ................................12
6. Protocol Documents .............................................13
6.1. Document Types ............................................13
6.2. Document Extensibility ....................................13
7. Category Documents .............................................14
7.1. Example ...................................................14
7.2. Element Definitions .......................................14
7.2.1. The "app:categories" Element .......................14
8. Service Documents ..............................................15
8.1. Workspaces ................................................16
8.2. Example ...................................................16
8.3. Element Definitions .......................................17
8.3.1. The "app:service" Element ..........................17
8.3.2. The "app:workspace" Element ........................18
8.3.3. The "app:collection" Element .......................18
8.3.4. The "app:accept" Element ...........................19
8.3.5. Usage in Atom Feed Documents .......................19
8.3.6. The "app:categories" Element .......................20
9. Creating and Editing Resources .................................20
9.1. Member URIs ...............................................20
9.2. Creating Resources with POST ..............................20
9.2.1. Example ............................................21
9.3. Editing Resources with PUT ................................22
9.4. Deleting Resources with DELETE ............................22
9.5. Caching and Entity Tags ...................................22
9.5.1. Example ............................................23
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RFC 5023 The Atom Publishing Protocol October 2007
9.6. Media Resources and Media Link Entries ....................25
9.6.1. Examples ...........................................26
9.7. The Slug Header ...........................................30
9.7.1. Slug Header Syntax .................................31
9.7.2. Example ............................................31
10. Listing Collections ...........................................32
10.1. Collection Partial Lists .................................32
10.2. The "app:edited" Element .................................33
11. Atom Format Link Relation Extensions ..........................34
11.1. The "edit" Link Relation .................................34
11.2. The "edit-media" Link Relation ...........................34
12. The Atom Format Type Parameter ................................34
12.1. The "type" parameter .....................................34
12.1.1. Conformance .......................................35
13. Atom Publishing Controls ......................................35
13.1. The "app:control" Element ................................35
13.1.1. The "app:draft" Element ...........................36
14. Securing the Atom Publishing Protocol .........................36
15. Security Considerations .......................................37
15.1. Denial of Service ........................................37
15.2. Replay Attacks ...........................................37
15.3. Spoofing Attacks .........................................37
15.4. Linked Resources .........................................38
15.5. Digital Signatures and Encryption ........................38
15.6. URIs and IRIs ............................................38
15.7. Code Injection and Cross Site Scripting ..................39
16. IANA Considerations ...........................................39
16.1. Content-Type Registration for 'application/atomcat+xml' ..39
16.2. Content-Type Registration for 'application/atomsvc+xml' ..40
16.3. Header Field Registration for 'SLUG' .....................42
16.4. The Link Relation Registration "edit" ....................42
16.5. The Link Relation Registration "edit-media" ..............42
16.6. The Atom Format Media Type Parameter .....................43
17. References ....................................................43
17.1. Normative References .....................................43
17.2. Informative References ...................................44
Appendix A. Contributors ..........................................46
Appendix B. RELAX NG Compact Schema ...............................46
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RFC 5023 The Atom Publishing Protocol October 2007
1. Introduction
The Atom Publishing Protocol is an application-level protocol for
publishing and editing Web Resources using HTTP [RFC2616] and XML 1.0
[REC-xml]. The protocol supports the creation of Web Resources and
provides facilities for:
o Collections: Sets of Resources, which can be retrieved in whole or
in part.
o Services: Discovery and description of Collections.
o Editing: Creating, editing, and deleting Resources.
The Atom Publishing Protocol is different from many contemporary
protocols in that the server is given wide latitude in processing
requests from clients. See Section 4.4 for more details.
2. 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 [RFC2119].
2.1. XML-Related Conventions
2.1.1. Referring to Information Items
Atom Protocol Document formats are specified in terms of the XML
Information Set [REC-xml-infoset], serialized as XML 1.0 [REC-xml].
The Infoset terms "Element Information Item" and "Attribute
Information Item" are shortened to "element" and "attribute"
respectively. Therefore, when this specification uses the term
"element", it is referring to an Element Information Item, and when
it uses the term "attribute", it is referring to an Attribute
Information Item.
2.1.2. RELAX NG Schema
Some sections of this specification are illustrated with fragments of
a non-normative RELAX NG Compact schema [RNC]. However, the text of
this specification provides the definition of conformance. Complete
schemas appear in Appendix B.
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RFC 5023 The Atom Publishing Protocol October 2007
2.1.3. Use of "xml:base" and "xml:lang"
XML elements defined by this specification MAY have an "xml:base"
attribute [REC-xmlbase]. When xml:base is used, it serves the
function described in Section 5.1.1 of URI Generic Syntax [RFC3986],
by establishing the base URI (or IRI, Internationalized Resource
Identifier [RFC3987]) for resolving relative references found within
the scope of the "xml:base" attribute.
Any element defined by this specification MAY have an "xml:lang"
attribute, whose content indicates the natural language for the
element and its descendants. Requirements regarding the content and
interpretation of "xml:lang" are specified in Section 2.12 of XML 1.0
[REC-xml].
3. Terminology
For convenience, this protocol can be referred to as the "Atom
Protocol" or "AtomPub". The following terminology is used by this
specification:
o URI - A Uniform Resource Identifier as defined in [RFC3986]. In
this specification, the phrase "the URI of a document" is
shorthand for "a URI which, when dereferenced, is expected to
produce that document as a representation".
o IRI - An Internationalized Resource Identifier as defined in
[RFC3987]. Before an IRI found in a document is used by HTTP, the
IRI is first converted to a URI. See Section 4.1.
o Resource - A network-accessible data object or service identified
by an IRI, as defined in [RFC2616]. See [REC-webarch] for further
discussion on Resources.
o relation (or "relation of") - Refers to the "rel" attribute value
of an atom:link element.
o Representation - An entity included with a request or response as
defined in [RFC2616].
o Collection - A Resource that contains a set of Member Resources.
Collections are represented as Atom Feeds. See Section 9.
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RFC 5023 The Atom Publishing Protocol October 2007
o Member (or Member Resource) - A Resource whose IRI is listed in a
Collection by an atom:link element with a relation of "edit" or
"edit-media". See Section 9.1. The protocol defines two kinds of
Members:
* Entry Resource - Members of a Collection that are represented
as Atom Entry Documents, as defined in [RFC4287].
* Media Resource - Members of a Collection that have
representations other than Atom Entry Documents.
o Media Link Entry - An Entry Resource that contains metadata about
a Media Resource. See Section 9.6.
o Workspace - A named group of Collections. See Section 8.1.
o Service Document - A document that describes the location and
capabilities of one or more Collections, grouped into Workspaces.
See Section 8.
o Category Document - A document that describes the categories
allowed in a Collection. See Section 7.
4. Protocol Model
The Atom Protocol specifies operations for publishing and editing
Resources using HTTP. It uses Atom-formatted representations to
describe the state and metadata of those Resources. It defines how
Collections of Resources can be organized, and it specifies formats
to support their discovery, grouping and categorization.
4.1. Identity and Naming
Atom Protocol documents allow the use of IRIs [RFC3987] as well as
URIs [RFC3986] to identify Resources. Before an IRI in a document is
used by HTTP, the IRI is first converted to a URI according to the
procedure defined in Section 3.1 of [RFC3987]. In accordance with
that specification, the conversion SHOULD be applied as late as
possible. Conversion does not imply Resource creation -- the IRI and
the URI into which it is converted identify the same Resource.
While the Atom Protocol specifies the formats of the representations
that are exchanged and the actions that can be performed on the IRIs
embedded in those representations, it does not constrain the form of
the URIs that are used. HTTP [RFC2616] specifies that the URI space
of each server is controlled by that server, and this protocol
imposes no further constraints on that control.
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RFC 5023 The Atom Publishing Protocol October 2007
4.2. Documents and Resource Classification
A Resource whose IRI is listed in a Collection is called a Member
Resource. The protocol defines two kinds of Member Resources --
Entry Resources and Media Resources. Entry Resources are represented
as Atom Entry Documents [RFC4287]. Media Resources can have
representations in any media type. A Media Resource is described
within a Collection using an Entry called a Media Link Entry. This
diagram shows the classification of Resources within the Atom
Protocol:
Member Resources
|
-----------------
| |
Entry Resources Media Resources
|
Media Link Entry
The Atom Protocol defines Collection Resources for managing and
organizing both kinds of Member Resource. A Collection is
represented by an Atom Feed Document. A Collection Feed's Entries
contain the IRIs of, and metadata about, the Collection's Member
Resources. A Collection Feed can contain any number of Entries,
which might represent all the Members of the Collection, or an
ordered subset of them (see Section 10.1). In the diagram of a
Collection below, there are two Entries. The first contains the IRI
of an Entry Resource. The second contains the IRIs of both a Media
Resource and a Media Link Entry, which contains the metadata for that
Media Resource:
Collection
|
o- Entry
| |
| o- Member Entry IRI (Entry Resource)
|
o- Entry
|
o- Member Entry IRI (Media Link Entry)
|
o- Media IRI (Media Resource)
The Atom Protocol does not make a distinction between Feeds used for
Collections and other Atom Feeds. The only mechanism that this
specification supplies for indicating that a Feed is a Collection
Feed is the presence of the Feed's IRI in a Service Document.
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Service Documents represent server-defined groups of Collections, and
are used to initialize the process of creating and editing Resources.
These groups of Collections are called Workspaces. Workspaces have
names, but no IRIs, and no specified processing model. The Service
Document can indicate which media types, and which categories, a
Collection will accept. In the diagram below, there are two
Workspaces each describing the IRIs, acceptable media types, and
categories for a Collection:
Service
o- Workspace
| |
| o- Collection
| |
| o- IRI, categories, media types
|
o- Workspace
|
o- Collection
|
o- IRI, categories, media types
4.3. Control and Publishing
The Atom Publishing Protocol uses HTTP methods to author Member
Resources as follows:
o GET is used to retrieve a representation of a known Resource.
o POST is used to create a new, dynamically named, Resource. When
the client submits non-Atom-Entry representations to a Collection
for creation, two Resources are always created -- a Media Entry
for the requested Resource, and a Media Link Entry for metadata
about the Resource that will appear in the Collection.
o PUT is used to edit a known Resource. It is not used for Resource
creation.
o DELETE is used to remove a known Resource.
The Atom Protocol only covers the creating, editing, and deleting of
Entry and Media Resources. Other Resources could be created, edited,
and deleted as the result of manipulating a Collection, but the
number of those Resources, their media types, and effects of Atom
Protocol operations on them are outside the scope of this
specification.
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RFC 5023 The Atom Publishing Protocol October 2007
Since all aspects of client-server interaction are defined in terms
of HTTP, [RFC2616] should be consulted for any areas not covered in
this specification.
4.4. Client Implementation Considerations
The Atom Protocol imposes few restrictions on the actions of servers.
Unless a constraint is specified here, servers can be expected to
vary in behavior, in particular around the manipulation of Atom
Entries sent by clients. For example, although this specification
only defines the expected behavior of Collections with respect to GET
and POST, this does not imply that PUT, DELETE, PROPPATCH, and others
are forbidden on Collection Resources -- only that this specification
does not define what the server's response would be to those methods.
Similarly, while some HTTP status codes are mentioned explicitly,
clients ought to be prepared to handle any status code from a server.
Servers can choose to accept, reject, delay, moderate, censor,
reformat, translate, relocate, or re-categorize the content submitted
to them. Only some of these choices are immediately relayed back to
the client in responses to client requests; other choices may only
become apparent later, in the feed or published entries. The same
series of requests to two different publishing sites can result in a
different series of HTTP responses, different resulting feeds, or
different entry contents.
As a result, client software has to be written flexibly to accept
what the server decides are the results of its submissions. Any
server response or server content modification not explicitly
forbidden by this specification or HTTP [RFC2616] is therefore
allowed.
5. Protocol Operations
While specific HTTP status codes are shown in the interaction
diagrams below, an AtomPub client should be prepared to handle any
status code. For example, a PUT to a Member URI could result in the
return of a "204 No Content" status code, which still indicates
success.
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RFC 5023 The Atom Publishing Protocol October 2007
5.1. Retrieving a Service Document
Client Server
| |
| 1.) GET to Service Document URI |
|------------------------------------------>|
| |
| 2.) 200 Ok |
| Service Document |
|<------------------------------------------|
| |
1. The client sends a GET request to the URI of the Service
Document.
2. The server responds with a Service Document enumerating the IRIs
of a group of Collections and the capabilities of those
Collections supported by the server. The content of this
document can vary based on aspects of the client request,
including, but not limited to, authentication credentials.
5.2. Listing Collection Members
To list the Members of a Collection, the client sends a GET request
to the URI of a Collection. An Atom Feed Document is returned whose
Entries contain the IRIs of Member Resources. The returned Feed may
describe all, or only a partial list, of the Members in a Collection
(see Section 10).
Client Server
| |
| 1.) GET to Collection URI |
|------------------------------->|
| |
| 2.) 200 Ok |
| Atom Feed Document |
|<-------------------------------|
| |
1. The client sends a GET request to the URI of the Collection.
2. The server responds with an Atom Feed Document containing the
IRIs of the Collection Members.
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RFC 5023 The Atom Publishing Protocol October 2007
5.3. Creating a Resource
Client Server
| |
| 1.) POST to Collection URI |
| Member Representation |
|------------------------------------------>|
| |
| 2.) 201 Created |
| Location: Member Entry URI |
|<------------------------------------------|
| |
1. The client POSTs a representation of the Member to the URI of the
Collection.
2. If the Member Resource was created successfully, the server
responds with a status code of 201 and a Location header that
contains the IRI of the newly created Entry Resource. Media
Resources could have also been created and their IRIs can be
found through the Entry Resource. See Section 9.6 for more
details.
5.4. Editing a Resource
Once a Resource has been created and its Member URI is known, that
URI can be used to retrieve, edit, and delete the Resource. Section
11 describes extensions to the Atom Syndication Format used in the
Atom Protocol for editing purposes.
5.4.1. Retrieving a Resource
Client Server
| |
| 1.) GET to Member URI |
|------------------------------------------>|
| |
| 2.) 200 Ok |
| Member Representation |
|<------------------------------------------|
| |
1. The client sends a GET request to the URI of a Member Resource to
retrieve its representation.
2. The server responds with the representation of the Member
Resource.
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RFC 5023 The Atom Publishing Protocol October 2007
5.4.2. Editing a Resource
Client Server
| |
| 1.) PUT to Member URI |
| Member Representation |
|------------------------------------------>|
| |
| 2.) 200 OK |
|<------------------------------------------|
1. The client sends a PUT request to store a representation of a
Member Resource.
2. If the request is successful, the server responds with a status
code of 200.
5.4.3. Deleting a Resource
Client Server
| |
| 1.) DELETE to Member URI |
|------------------------------------------>|
| |
| 2.) 200 OK |
|<------------------------------------------|
| |
1. The client sends a DELETE request to the URI of a Member
Resource.
2. If the deletion is successful, the server responds with a status
code of 200.
A different approach is taken for deleting Media Resources; see
Section 9.4 for details.
5.5. Use of HTTP Response Codes
The Atom Protocol uses the response status codes defined in HTTP to
indicate the success or failure of an operation. Consult the HTTP
specification [RFC2616] for detailed definitions of each status code.
Implementers are asked to note that according to the HTTP
specification, HTTP 4xx and 5xx response entities SHOULD include a
human-readable explanation of the error.
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RFC 5023 The Atom Publishing Protocol October 2007
6. Protocol Documents
6.1. Document Types
This specification defines two kinds of documents -- Category
Documents and Service Documents.
A Category Document (Section 7) contains lists of categories
specified using the "atom:category" element from the Atom Syndication
Format (see Section 4.2.2 of [RFC4287]).
A Service Document (Section 8) groups available Collections into
Workspaces.
The namespace name [REC-xml-names] for either kind of document is:
http://www.w3.org/2007/app
Atom Publishing Protocol XML Documents MUST be "namespace-well-
formed" as specified in Section 7 of [REC-xml-names].
This specification uses the prefix "app:" for the namespace name.
The prefix "atom:" is used for "http://www.w3.org/2005/Atom", the
namespace name of the Atom Syndication Format [RFC4287]. These
namespace prefixes are not semantically significant.
This specification does not define any DTDs for Atom Protocol
formats, and hence does not require them to be "valid" in the sense
used by [REC-xml].
6.2. Document Extensibility
Unrecognized markup in an Atom Publishing Protocol document is
considered "foreign markup" as defined in Section 6 of the Atom
Syndication Format [RFC4287]. Foreign markup can be used anywhere
within a Category or Service Document unless it is explicitly
forbidden. Processors that encounter foreign markup MUST NOT stop
processing and MUST NOT signal an error. Clients SHOULD preserve
foreign markup when transmitting such documents.
The namespace name "http://www.w3.org/2007/app" is reserved for
forward-compatible revisions of the Category and Service Document
types. This does not exclude the addition of elements and attributes
that might not be recognized by processors conformant to this
specification. Such unrecognized markup from the
"http://www.w3.org/2007/app" namespace MUST be treated as foreign
markup.
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RFC 5023 The Atom Publishing Protocol October 2007
7. Category Documents
Category Documents contain lists of categories described using the
"atom:category" element from the Atom Syndication Format [RFC4287].
Categories can also appear in Service Documents, where they indicate
the categories allowed in a Collection (see Section 8.3.6).
Category Documents are identified with the "application/atomcat+xml"
media type (see Section 16.1).
7.1. Example
This Category Document contains atom:category elements, with the
terms 'animal', 'vegetable', and 'mineral'. None of the categories
use the "label" attribute defined in [RFC4287]. They all inherit the
"http://example.com/cats/big3" "scheme" attribute declared on the
app:categories element. Therefore if the 'mineral' category were to
appear in an Atom Entry or Feed Document, it would appear as:
Main Site
My Blog Entries
Pictures
image/png
image/jpeg
image/gif
Sidebar Blog
Remaindered Links
application/atom+xml;type=entry
The Service Document above describes two Workspaces. The first
Workspace is called "Main Site", and has two Collections called "My
Blog Entries" and "Pictures", whose IRIs are
"http://example.org/blog/main" and "http://example.org/blog/pic"
respectively. The "Pictures" Collection includes three "accept"
elements indicating the types of image files the client can send to
the Collection to create new Media Resources (entries associated with
Media Resources are discussed in Section 9.6).
The second Workspace is called "Sidebar Blog" and has a single
Collection called "Remaindered Links" whose IRI is
"http://example.org/sidebar/list". The Collection has an "accept"
element whose content is "application/atom+xml;type=entry",
indicating it will accept Atom Entries from a client.
Within each of the two Entry Collections, the "categories" element
provides a list of available categories for Member Entries. In the
"My Blog Entries" Collection, the list of available categories is
available through the "href" attribute. The "Sidebar Blog"
Collection provides a category list within the Service Document, but
states the list is fixed, signaling a request from the server that
Entries be POSTed using only those two categories.
8.3. Element Definitions
8.3.1. The "app:service" Element
The root of a Service Document is the "app:service" element.
The app:service element is the container for service information
associated with one or more Workspaces. An app:service element MUST
contain one or more app:workspace elements.
namespace app = "http://www.w3.org/2007/app"
start = appService
appService =
element app:service {
appCommonAttributes,
( appWorkspace+
& extensionElement* )
}
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RFC 5023 The Atom Publishing Protocol October 2007
8.3.2. The "app:workspace" Element
Workspaces are server-defined groups of Collections. The "app:
workspace" element contains zero or more app:collection elements
describing the Collections of Resources available for editing.
appWorkspace =
element app:workspace {
appCommonAttributes,
( atomTitle
& appCollection*
& extensionSansTitleElement* )
}
atomTitle = element atom:title { atomTextConstruct }
8.3.2.1. The "atom:title" Element
The app:workspace element MUST contain one "atom:title" element (as
defined in [RFC4287]), giving a human-readable title for the
Workspace.
8.3.3. The "app:collection" Element
The "app:collection" element describes a Collection. The app:
collection element MUST contain one atom:title element.
The app:collection element MAY contain any number of app:accept
elements, indicating the types of representations accepted by the
Collection. The order of such elements is not significant.
The app:collection element MAY contain any number of app:categories
elements.
appCollection =
element app:collection {
appCommonAttributes,
attribute href { atomURI },
( atomTitle
& appAccept*
& appCategories*
& extensionSansTitleElement* )
}
8.3.3.1. The "href" Attribute
The app:collection element MUST contain an "href" attribute, whose
value gives the IRI of the Collection.
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RFC 5023 The Atom Publishing Protocol October 2007
8.3.3.2. The "atom:title" Element
The "atom:title" element is defined in [RFC4287] and gives a human-
readable title for the Collection.
8.3.4. The "app:accept" Element
The content of an "app:accept" element value is a media range as
defined in [RFC2616]. The media range specifies a type of
representation that can be POSTed to a Collection.
The app:accept element is similar to the HTTP Accept request-header
[RFC2616]. Media type parameters are allowed within app:accept, but
app:accept has no notion of preference -- "accept-params" or "q"
arguments, as specified in Section 14.1 of [RFC2616] are not
significant.
White space (as defined in [REC-xml]) around the app:accept element's
media range is insignificant and MUST be ignored.
A value of "application/atom+xml;type=entry" MAY appear in any app:
accept list of media ranges and indicates that Atom Entry Documents
can be POSTed to the Collection. If no app:accept element is
present, clients SHOULD treat this as equivalent to an app:accept
element with the content "application/atom+xml;type=entry".
If one app:accept element exists and is empty, clients SHOULD assume
that the Collection does not support the creation of new Entries.
appAccept =
element app:accept {
appCommonAttributes,
( text? )
}
8.3.5. Usage in Atom Feed Documents
The app:collection element MAY appear as a child of an atom:feed or
atom:source element in an Atom Feed Document. Its content identifies
a Collection by which new Entries can be added to appear in the feed.
When it appears in an atom:feed or atom:source element, the app:
collection element is considered foreign markup as defined in Section
6 of [RFC4287].
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RFC 5023 The Atom Publishing Protocol October 2007
8.3.6. The "app:categories" Element
The "app:categories" element provides a list of the categories that
can be applied to the members of a Collection. See Section 7.2.1 for
the detailed definition of app:categories.
The server MAY reject attempts to create or store members whose
categories are not present in its categories list. A Collection that
indicates the category set is open SHOULD NOT reject otherwise
acceptable members whose categories are not in its categories list.
The absence of an app:categories element means that the category
handling of the Collection is unspecified. A "fixed" category list
that contains zero categories indicates the Collection does not
accept category data.
9. Creating and Editing Resources
9.1. Member URIs
The Member URI allows clients to retrieve, edit, and delete a Member
Resource using HTTP's GET, PUT, and DELETE methods. Entry Resources
are represented as Atom Entry documents.
Member URIs appear in two places. They are returned in a Location
header after successful Resource creation using POST, as described in
Section 9.2 below. They can also appear in a Collection Feed's
Entries, as atom:link elements with a link relation of "edit".
A Member Entry SHOULD contain such an atom:link element with a link
relation of "edit", which indicates the Member URI.
9.2. Creating Resources with POST
To add members to a Collection, clients send POST requests to the URI
of the Collection.
Successful member creation is indicated with a 201 ("Created")
response code. When the Collection responds with a status code of
201, it SHOULD also return a response body, which MUST be an Atom
Entry Document representing the newly created Resource. Since the
server is free to alter the POSTed Entry, for example, by changing
the content of the atom:id element, returning the Entry can be useful
to the client, enabling it to correlate the client and server views
of the new Entry.
When a Member Resource is created, its Member Entry URI MUST be
returned in a Location header in the Collection's response.
Gregorio & de hOra Standards Track [Page 20]
RFC 5023 The Atom Publishing Protocol October 2007
If the creation request contained an Atom Entry Document, and the
subsequent response from the server contains a Content-Location
header that matches the Location header character-for-character, then
the client is authorized to interpret the response entity as being a
complete representation of the newly created Entry. Without a
matching Content-Location header, the client MUST NOT assume the
returned entity is a complete representation of the created Resource.
The request body sent with the POST need not be an Atom Entry. For
example, it might be a picture or a movie. Collections MAY return a
response with a status code of 415 ("Unsupported Media Type") to
indicate that the media type of the POSTed entity is not allowed or
supported by the Collection. For a discussion of the issues in
creating such content, see Section 9.6.
9.2.1. Example
Below, the client sends a POST request containing an Atom Entry
representation using the URI of the Collection:
POST /edit/ HTTP/1.1
Host: example.org
User-Agent: Thingio/1.0
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
Slug: First Post
Atom-Powered Robots Run Amok
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2003-12-13T18:30:02Z
John Doe Some text.
The server signals a successful creation with a status code of 201.
The response includes a Location header indicating the Member Entry
URI of the Atom Entry, and a representation of that Entry in the body
of the response.
HTTP/1.1 201 Created
Date: Fri, 7 Oct 2005 17:17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
Location: http://example.org/edit/first-post.atom
ETag: "c180de84f991g8"
Gregorio & de hOra Standards Track [Page 21]
RFC 5023 The Atom Publishing Protocol October 2007
Atom-Powered Robots Run Amok
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2003-12-13T18:30:02Z
John Doe Some text.
The Entry created and returned by the Collection might not match the
Entry POSTed by the client. A server MAY change the values of
various elements in the Entry, such as the atom:id, atom:updated, and
atom:author values, and MAY choose to remove or add other elements
and attributes, or change element content and attribute values.
9.3. Editing Resources with PUT
To edit a Member Resource, a client sends a PUT request to its Member
URI, as specified in [RFC2616].
To avoid unintentional loss of data when editing Member Entries or
Media Link Entries, an Atom Protocol client SHOULD preserve all
metadata that has not been intentionally modified, including unknown
foreign markup as defined in Section 6 of [RFC4287].
9.4. Deleting Resources with DELETE
To delete a Member Resource, a client sends a DELETE request to its
Member URI, as specified in [RFC2616]. The deletion of a Media Link
Entry SHOULD result in the deletion of the corresponding Media
Resource.
9.5. Caching and Entity Tags
Implementers are advised to pay attention to cache controls and to
make use of the mechanisms available in HTTP when editing Resources,
in particular, entity-tags as outlined in [NOTE-detect-lost-update].
Clients are not assured to receive the most recent representations of
Collection Members using GET if the server is authorizing
intermediaries to cache them.
Gregorio & de hOra Standards Track [Page 22]
RFC 5023 The Atom Publishing Protocol October 2007
9.5.1. Example
Below, the client creates a Member Entry using POST:
POST /myblog/entries HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
Slug: First Post
Atom-Powered Robots Run Amok
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2007-02-123T17:09:02Z
Captain Lansing It's something moving... solid metal
The server signals a successful creation with a status code of 201,
and returns an ETag header in the response. Because, in this case,
the server returned a Content-Location header and Location header
with the same value, the returned Entry representation can be
understood to be a complete representation of the newly created Entry
(see Section 9.2).
HTTP/1.1 201 Created
Date: Fri, 23 Feb 2007 21:17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry
Location: http://example.org/edit/first-post.atom
Content-Location: http://example.org/edit/first-post.atom
ETag: "e180ee84f0671b1"
Atom-Powered Robots Run Amok
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2007-02-123T17:09:02Z
Captain Lansing It's something moving... solid metal
The client can, if it wishes, use the returned ETag value to later
construct a "Conditional GET" as defined in [RFC2616]. In this case,
prior to editing, the client sends the ETag value for the Member
using the If-None-Match header.
Gregorio & de hOra Standards Track [Page 23]
RFC 5023 The Atom Publishing Protocol October 2007
GET /edit/first-post.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
If-None-Match: "e180ee84f0671b1"
If the Entry has not been modified, the response will be a status
code of 304 ("Not Modified"). This allows the client to determine
whether it still has the most recent representation of the Entry at
the time of editing.
HTTP/1.1 304 Not Modified
Date: Sat, 24 Feb 2007 13:17:11 GMT
After editing, the client can PUT the Entry and send the ETag entity
value in an If-Match header, informing the server to accept the entry
on the condition that the entity value sent still matches the
server's.
PUT /edit/first-post.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
If-Match: "e180ee84f0671b1"
Atom-Powered Robots Run Amok
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2007-02-24T16:34:06Z
Captain Lansing Update: it's a hoax!
The server however has since received a more recent copy than the
client's, and it responds with a status code of 412 ("Precondition
Failed").
HTTP/1.1 412 Precondition Failed
Date: Sat, 24 Feb 2007 16:34:11 GMT
This informs the client that the server has a more recent version of
the Entry and will not allow the sent entity to be stored.
Gregorio & de hOra Standards Track [Page 24]
RFC 5023 The Atom Publishing Protocol October 2007
9.6. Media Resources and Media Link Entries
A client can POST Media Resources as well as Entry Resources to a
Collection. If a server accepts such a request, then it MUST create
two new Resources -- one that corresponds to the entity sent in the
request, called the Media Resource, and an associated Member Entry,
called the Media Link Entry. Media Link Entries are represented as
Atom Entries, and appear in the Collection.
The Media Link Entry contains the metadata and IRI of the (perhaps
non-textual) Media Resource. The Media Link Entry thus makes the
metadata about the Media Resource separately available for retrieval
and alteration.
The server can signal the media types it will accept using the app:
accept element in the Service Document, as specified in Section
8.3.4.
Successful responses to creation requests MUST include the URI of the
Media Link Entry in the Location header. The Media Link Entry SHOULD
contain an atom:link element with a link relation of "edit-media"
that contains the Media Resource IRI. The Media Link Entry MUST have
an atom:content element with a "src" attribute. The value of the
"src" attribute is an IRI for the newly created Media Resource. It
is OPTIONAL that the IRI of the "src" attribute on the atom:content
element be the same as the Media Resource IRI. For example, the
"src" attribute value might instead be a link into a static cache or
content distribution network and not the Media Resource IRI.
Implementers are asked to note that [RFC4287] specifies that Atom
Entries MUST contain an atom:summary element. Thus, upon successful
creation of a Media Link Entry, a server MAY choose to populate the
atom:summary element (as well as any other mandatory elements such as
atom:id, atom:author, and atom:title) with content derived from the
POSTed entity or from any other source. A server might not allow a
client to modify the server-selected values for these elements.
For Resource creation, this specification only defines cases where
the POST body has an Atom Entry entity declared as an Atom media type
("application/atom+xml"), or a non-Atom entity declared as a non-Atom
media type. When a client is POSTing an Atom Entry to a Collection,
it may use a media type of either "application/atom+xml" or
"application/atom +xml;type=entry". This specification does not
specify any request semantics or server behavior in the case where
the POSTed media type is "application/atom+xml" but the body is
something other than an Atom Entry. In particular, what happens on
POSTing an Atom Feed Document to a Collection using the "application/
atom+xml" media type is undefined.
Gregorio & de hOra Standards Track [Page 25]
RFC 5023 The Atom Publishing Protocol October 2007
The Atom Protocol does not specify a means to create multiple
representations of the same Resource (for example, a PNG and a JPG of
the same image) either on creation or editing.
9.6.1. Examples
Below, the client sends a POST request containing a PNG image to the
URI of a Collection that accepts PNG images:
POST /edit/ HTTP/1.1
Host: media.example.org
Content-Type: image/png
Slug: The Beach
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...binary data...
The server signals a successful creation with a status code of 201.
The response includes a Location header indicating the Member URI of
the Media Link Entry and a representation of that entry in the body
of the response. The Media Link Entry includes a content element
with a "src" attribute. It also contains a link with a link relation
of "edit-media", specifying the IRI to be used for modifying the
Media Resource.
HTTP/1.1 201 Created
Date: Fri, 7 Oct 2005 17:17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
Location: http://example.org/media/edit/the_beach.atom
The Beach
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2005-10-07T17:17:08Z
Daffy
Gregorio & de hOra Standards Track [Page 26]
RFC 5023 The Atom Publishing Protocol October 2007
Later, the client sends a PUT request containing the new PNG using
the URI indicated in the Media Link Entry's "edit-media" link:
PUT /edit/the_beach.png HTTP/1.1
Host: media.example.org
Content-Type: image/png
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...binary data...
The server signals a successful edit with a status code of 200.
HTTP/1.1 200 Ok
Date: Fri, 8 Oct 2006 17:17:11 GMT
The client can edit the metadata for the picture. First GET the
Media Link Entry:
GET /media/edit/the_beach.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
The Media Link Entry is returned.
HTTP/1.1 200 Ok
Date: Fri, 7 Oct 2005 17:18:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
ETag: "c181bb840673b5"
The Beach
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2005-10-07T17:17:08Z
Daffy
The metadata can be updated, in this case to add a summary, and then
PUT back to the server.
Gregorio & de hOra Standards Track [Page 27]
RFC 5023 The Atom Publishing Protocol October 2007
PUT /media/edit/the_beach.atom HTTP/1.1
Host: example.org
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Type: application/atom+xml;type=entry
Content-Length: nnn
If-Match: "c181bb840673b5"
The Beach
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a
2005-10-07T17:17:08Z
Daffy
A nice sunset picture over the water.
The update was successful.
HTTP/1.1 200 Ok
Date: Fri, 7 Oct 2005 17:19:11 GMT
Content-Length: 0
Multiple Media Resources can be added to the Collection.
POST /edit/ HTTP/1.1
Host: media.example.org
Content-Type: image/png
Slug: The Pier
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...binary data...
The Resource is created successfully.
HTTP/1.1 201 Created
Date: Fri, 7 Oct 2005 17:17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
Location: http://example.org/media/edit/the_pier.atom
Gregorio & de hOra Standards Track [Page 28]
RFC 5023 The Atom Publishing Protocol October 2007
The Pier
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efe6b
2005-10-07T17:26:43Z
Daffy
The client can now create a new Atom Entry in the blog Entry
Collection that references the two newly created Media Resources.
POST /blog/ HTTP/1.1
Host: example.org
Content-Type: application/atom+xml;type=entry
Slug: A day at the beach
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
A fun day at the beach
urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6b
2005-10-07T17:40:02Z
Daffy
We had a good day at the beach.
Later we walked down to the pier.
The Resource is created successfully.
Gregorio & de hOra Standards Track [Page 29]
RFC 5023 The Atom Publishing Protocol October 2007
HTTP/1.1 200 Ok
Date: Fri, 7 Oct 2005 17:20:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=entry;charset="utf-8"
Location: http://example.org/blog/atom/a-day-at-the-beach.atom
A fun day at the beach
http://example.org/blog/a-day-at-the-beach.xhtml
2005-10-07T17:43:07Z
Daffy
We had a good day at the beach.
Later we walked down to the pier.
Note that the returned Entry contains a link with a relation of
"alternate" that points to the associated HTML page that was created
-- this is not required by this specification, but is included to
show the kinds of changes a server can make to an Entry.
9.7. The Slug Header
Slug is an HTTP entity-header whose presence in a POST to a
Collection constitutes a request by the client to use the header's
value as part of any URIs that would normally be used to retrieve the
to-be-created Entry or Media Resources.
Servers MAY use the value of the Slug header when creating the Member
URI of the newly created Resource, for instance, by using some or all
of the words in the value for the last URI segment. Servers MAY also
use the value when creating the atom:id, or as the title of a Media
Link Entry (see Section 9.6).
Gregorio & de hOra Standards Track [Page 30]
RFC 5023 The Atom Publishing Protocol October 2007
Servers MAY choose to ignore the Slug entity-header. Servers MAY
alter the header value before using it. For instance, a server might
filter out some characters or replace accented letters with non-
accented ones, replace spaces with underscores, change case, and so
on.
9.7.1. Slug Header Syntax
The syntax of the Slug header is defined using the augmented BNF
syntax defined in Section 2.1 of [RFC2616]:
LWS =
slugtext = %x20-7E | LWS
Slug = "Slug" ":" *slugtext
The field value is the percent-encoded value of the UTF-8 encoding of
the character sequence to be included (see Section 2.1 of [RFC3986]
for the definition of percent encoding, and [RFC3629] for the
definition of the UTF-8 encoding).
Implementation note: to produce the field value from a character
sequence, first encode it using the UTF-8 encoding, then encode all
octets outside the ranges %20-24 and %26-7E using percent encoding
(%25 is the ASCII encoding of "%", thus it needs to be escaped). To
consume the field value, first reverse the percent encoding, then run
the resulting octet sequence through a UTF-8 decoding process.
9.7.2. Example
Here is an example of the Slug header that uses percent-encoding to
represent the Unicode character U+00E8 (LATIN SMALL LETTER E WITH
GRAVE):
POST /myblog/entries HTTP/1.1
Host: example.org
Content-Type: image/png
Slug: The Beach at S%C3%A8te
Authorization: Basic ZGFmZnk6c2VjZXJldA==
Content-Length: nnn
...binary data...
See Section 9.2.1 for an example of the Slug header applied to the
creation of an Entry Resource.
Gregorio & de hOra Standards Track [Page 31]
RFC 5023 The Atom Publishing Protocol October 2007
10. Listing Collections
Collection Resources MUST provide representations in the form of Atom
Feed Documents whose Entries contain the IRIs of the Members in the
Collection. No distinction is made between Collection Feeds and
other kinds of Feeds -- a Feed might act both as a 'public' feed for
subscription purposes and as a Collection Feed.
Each Entry in the Feed Document SHOULD have an atom:link element with
a relation of "edit" (see Section 11.1).
The Entries in the returned Atom Feed SHOULD be ordered by their
"app:edited" property, with the most recently edited Entries coming
first in the document order. The app:edited value is not equivalent
to the HTTP Last-Modified header and cannot be used to determine the
freshness of cached responses.
Clients MUST NOT assume that an Atom Entry returned in the Feed is a
full representation of an Entry Resource and SHOULD perform a GET on
the URI of the Member Entry before editing it. See Section 9.5 for a
discussion on the implications of cache control directives when
obtaining entries.
10.1. Collection Partial Lists
Collections can contain large numbers of Resources. A client such as
a web spider or web browser might be overwhelmed if the response to a
GET contained every Entry in a Collection -- in turn the server might
also waste bandwidth and processing time on generating a response
that cannot be handled. For this reason, servers MAY respond to
Collection GET requests with a Feed Document containing a partial
list of the Collection's members, and a link to the next partial list
feed, if it exists. The first such partial list returned MUST
contain the most recently edited member Resources and MUST have an
atom:link with a "next" relation whose "href" value is the URI of the
next partial list of the Collection. This next partial list will
contain the next most recently edited set of Member Resources (and an
atom:link to the following partial list if it exists).
In addition to the "next" relation, partial list feeds MAY contain
link elements with "rel" attribute values of "previous", "first", and
"last", that can be used to navigate through the complete set of
entries in the Collection.
For instance, suppose a client is supplied the URI
"http://example.org/entries/go" of a Collection of Member Entries,
where the server as a matter of policy avoids generating Feed
Documents containing more than 10 Entries. The Atom Feed Document
Gregorio & de hOra Standards Track [Page 32]
RFC 5023 The Atom Publishing Protocol October 2007
for the Collection will then represent the first partial list of a
set of 10 linked Feed Documents. The "first" relation references the
initial Feed Document in the set and the "last" relation references
the final Feed Document in the set. Within each document, the
"previous" and "next" link relations reference the preceding and
subsequent documents.
...
The "previous" and "next" link elements for the partial list feed
located at "http://example.org/entries/2" would look like this:
...
10.2. The "app:edited" Element
The "app:edited" element is a Date construct (as defined by
[RFC4287]), whose content indicates the last time an Entry was
edited. If the entry has not been edited yet, the content indicates
the time it was created. Atom Entry elements in Collection Documents
SHOULD contain one app:edited element, and MUST NOT contain more than
one.
appEdited = element app:edited ( atomDateConstruct )
The server SHOULD change the value of this element every time an
Entry Resource or an associated Media Resource has been edited.
Gregorio & de hOra Standards Track [Page 33]
RFC 5023 The Atom Publishing Protocol October 2007
11. Atom Format Link Relation Extensions
11.1. The "edit" Link Relation
This specification adds the value "edit" to the Atom Registry of Link
Relations (see Section 7.1 of [RFC4287]). The value of "edit"
specifies that the value of the href attribute is the IRI of an
editable Member Entry. When appearing within an atom:entry, the href
IRI can be used to retrieve, update, and delete the Resource
represented by that Entry. An atom:entry MUST NOT contain more than
one "edit" link relation.
11.2. The "edit-media" Link Relation
This specification adds the value "edit-media" to the Atom Registry
of Link Relations (see Section 7.1 of [RFC4287]). When appearing
within an atom:entry, the value of the href attribute is an IRI that
can be used to modify a Media Resource associated with that Entry.
An atom:entry element MAY contain zero or more "edit-media" link
relations. An atom:entry MUST NOT contain more than one atom:link
element with a "rel" attribute value of "edit-media" that has the
same "type" and "hreflang" attribute values. All "edit-media" link
relations in the same Entry reference the same Resource. If a client
encounters multiple "edit-media" link relations in an Entry then it
SHOULD choose a link based on the client preferences for "type" and
"hreflang". If a client encounters multiple "edit-media" link
relations in an Entry and has no preference based on the "type" and
"hreflang" attributes then the client SHOULD pick the first "edit-
media" link relation in document order.
12. The Atom Format Type Parameter
The Atom Syndication Format [RFC4287] defines the "application/
atom+xml" media type to identify both Atom Feed and Atom Entry
Documents. Implementation experience has demonstrated that Atom Feed
and Entry Documents can have different processing models and that
there are situations where they need to be differentiated. This
specification defines a "type" parameter used to differentiate the
two types of Atom documents.
12.1. The "type" parameter
This specification defines a new "type" parameter for use with the
"application/atom+xml" media type. The "type" parameter has a value
of "entry" or "feed".
Neither the parameter name nor its value are case sensitive.
Gregorio & de hOra Standards Track [Page 34]
RFC 5023 The Atom Publishing Protocol October 2007
The value "entry" indicates that the media type identifies an Atom
Entry Document. The root element of the document MUST be atom:entry.
The value "feed" indicates that the media type identifies an Atom
Feed Document. The root element of the document MUST be atom:feed.
If not specified, the type is assumed to be unspecified, requiring
Atom processors to examine the root element to determine the type of
Atom document.
12.1.1. Conformance
New specifications MAY require that the "type" parameter be used to
identify the Atom Document type. Producers of Atom Entry Documents
SHOULD use the "type" parameter regardless of whether or not it is
mandatory. Producers of Atom Feed Documents MAY use the parameter.
Atom processors that do not recognize the "type" parameter MUST
ignore its value and examine the root element to determine the
document type.
Atom processors that do recognize the "type" parameter SHOULD detect
and report inconsistencies between the parameter's value and the
actual type of the document's root element.
13. Atom Publishing Controls
This specification defines an Atom Format Structured Extension, as
defined in Section 6 of [RFC4287], for publishing control within the
"http://www.w3.org/2007/app" namespace.
13.1. The "app:control" Element
namespace app = "http://www.w3.org/2007/app"
pubControl =
element app:control {
atomCommonAttributes,
pubDraft?
& extensionElement
}
pubDraft =
element app:draft { "yes" | "no" }
Gregorio & de hOra Standards Track [Page 35]
RFC 5023 The Atom Publishing Protocol October 2007
The "app:control" element MAY appear as a child of an atom:entry that
is being created or updated via the Atom Publishing Protocol. The
app:control element MUST appear only once in an Entry. The app:
control element is considered foreign markup as defined in Section 6
of [RFC4287].
The app:control element and its child elements MAY be included in
Atom Feed or Entry Documents.
The app:control element can contain an "app:draft" element as defined
below, and it can contain extension elements as defined in Section 6
of [RFC4287].
13.1.1. The "app:draft" Element
The inclusion of the "app:draft" element represents a request by the
client to control the visibility of a Member Resource. The app:draft
element MAY be ignored by the server.
The number of app:draft elements in app:control MUST be zero or one.
The content of an app:draft element MUST be one of "yes" or "no". If
the element contains "no", this indicates a client request that the
Member Resource be made publicly visible. If the app:draft element
is not present, then servers that support the extension MUST behave
as though an app:draft element containing "no" was sent.
14. Securing the Atom Publishing Protocol
The Atom Publishing Protocol is based on HTTP. Authentication
requirements for HTTP are covered in Section 11 of [RFC2616].
The use of authentication mechanisms to prevent POSTing or editing by
unknown or unauthorized clients is RECOMMENDED but not required.
When authentication is not used, clients and servers are vulnerable
to trivial spoofing, denial-of-service, and defacement attacks.
However, in some contexts, this is an acceptable risk.
The type of authentication deployed is a local decision made by the
server operator. Clients are likely to face authentication schemes
that vary across server deployments. At a minimum, client and server
implementations MUST be capable of being configured to use HTTP Basic
Authentication [RFC2617] in conjunction with a connection made with
TLS 1.0 [RFC2246] or a subsequent standards-track version of TLS
(such as [RFC4346]), supporting the conventions for using HTTP over
TLS described in [RFC2818].
Gregorio & de hOra Standards Track [Page 36]
RFC 5023 The Atom Publishing Protocol October 2007
The choice of authentication mechanism will impact interoperability.
The minimum level of security referenced above (Basic Authentication
with TLS) is considered good practice for Internet applications at
the time of publication of this specification and sufficient for
establishing a baseline for interoperability. Implementers are
encouraged to investigate and use alternative mechanisms regarded as
equivalently good or better at the time of deployment. It is
RECOMMENDED that clients be implemented in such a way that new
authentication schemes can be deployed.
Because this protocol uses HTTP response status codes as the primary
means of reporting the result of a request, servers are advised to
respond to unauthorized or unauthenticated requests using an
appropriate 4xx HTTP response code (e.g., 401 "Unauthorized" or 403
"Forbidden") in accordance with [RFC2617].
15. Security Considerations
The Atom Publishing Protocol is based on HTTP and thus subject to the
security considerations found in Section 15 of [RFC2616].
The threats listed in this section apply to many protocols that run
under HTTP. The Atompub Working Group decided that the protection
afforded by running authenticated HTTP under TLS (as described in
Section 14) was sufficient to mitigate many of the problems presented
by the attacks listed in this section.
15.1. Denial of Service
Atom Publishing Protocol server implementations need to take adequate
precautions to ensure malicious clients cannot consume excessive
server resources (CPU, memory, disk, etc.).
15.2. Replay Attacks
Atom Publishing Protocol server implementations are susceptible to
replay attacks. Specifically, this specification does not define a
means of detecting duplicate requests. Accidentally sent duplicate
requests are indistinguishable from intentional and malicious replay
attacks.
15.3. Spoofing Attacks
Atom Publishing Protocol implementations are susceptible to a variety
of spoofing attacks. Malicious clients might send Atom Entries
containing inaccurate information anywhere in the document.
Gregorio & de hOra Standards Track [Page 37]
RFC 5023 The Atom Publishing Protocol October 2007
15.4. Linked Resources
Atom Feed and Entry Documents can contain XML External Entities as
defined in Section 4.2.2 of [REC-xml]. Atom implementations are not
required to load external entities. External entities are subject to
the same security concerns as any network operation and can alter the
semantics of an Atom document. The same issues exist for Resources
linked to by Atom elements such as atom:link and atom:content.
15.5. Digital Signatures and Encryption
Atom Entry and Feed Documents can contain XML Digital Signatures
[REC-xmldsig-core] and can be encrypted using XML Encryption
[REC-xmlenc-core] as specified in Section 5 of [RFC4287]. Handling
of signatures and encrypted elements in Atom documents is discussed
in Sections 5 and 6.3 of [RFC4287].
Neither servers nor clients are under any obligation to support
encryption and digital signature of Entries or Feeds, although it is
certainly possible that in some installations, clients or servers
might require signing or encrypting of the documents exchanged in the
Atom Protocol.
Because servers are allowed (and in some cases, expected) to modify
the contents of an Entry Document before publishing it, signatures
within an entry are only likely to be useful to the server to which
the entry is being sent. Clients cannot assume that the signature
will be valid when viewed by a third party, or even that the server
will publish the client's signature.
A server is allowed to strip client-applied signatures, to strip
client-applied signatures and then re-sign with its own public key,
and to oversign an entry with its own public key. The meaning to a
third party of a signature applied by a server is the same as a
signature from anyone, as described in [RFC4287]. It is RECOMMENDED
that a server that is aware that it has changed any part of an Entry
Document that was signed by the client should strip that signature
before publishing the entry in order to prevent third parties from
trying to interpret a signature that cannot be validated.
15.6. URIs and IRIs
Atom Publishing Protocol implementations handle URIs and IRIs. See
Section 7 of [RFC3986] and Section 8 of [RFC3987] for security
considerations related to their handling and use.
Gregorio & de hOra Standards Track [Page 38]
RFC 5023 The Atom Publishing Protocol October 2007
The Atom Publishing Protocol leaves the server in control of minting
URIs. The use of any client-supplied data for creating new URIs is
subject to the same concerns as described in the next section.
15.7. Code Injection and Cross Site Scripting
Atom Feed and Entry Documents can contain a broad range of content
types including code that might be executable in some contexts.
Malicious clients could attempt to attack servers or other clients by
injecting code into a Collection Document's Entry or Media Resources.
Server implementations are strongly encouraged to verify that client-
supplied content is safe prior to accepting, processing, or
publishing it. In the case of HTML, experience indicates that
verification based on a white list of acceptable content is more
effective than a black list of forbidden content.
Additional information about XHTML and HTML content safety can be
found in Section 8.1 of [RFC4287].
16. IANA Considerations
This specification uses two new media types that conform to the
registry mechanism described in [RFC4288], a new message header that
conforms to the registry mechanism described in [RFC3864], and two
new link relations that conform to the registry mechanism described
in [RFC4287].
16.1. Content-Type Registration for 'application/atomcat+xml'
An Atom Publishing Protocol Category Document, when serialized as XML
1.0, can be identified with the following media type:
MIME media type name: application
MIME subtype name: atomcat+xml
Required parameters: None.
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], Section 3.2.
Gregorio & de hOra Standards Track [Page 39]
RFC 5023 The Atom Publishing Protocol October 2007
Security considerations: As defined in RFC 5023.
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
Section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: RFC 5023.
Applications that use this media type: No known applications
currently use this media type.
Additional information:
Magic number(s): As specified for "application/xml" in [RFC3023],
Section 3.2.
File extension: .atomcat
Fragment identifiers: As specified for "application/xml" in
[RFC3023], Section 5.
Base URI: As specified in [RFC3023], Section 6.
Macintosh file type code: TEXT
Person & email address to contact for further information:
Joe Gregorio
Intended usage: COMMON
Author/Change controller: IETF (iesg@ietf.org) Internet Engineering
Task Force
16.2. Content-Type Registration for 'application/atomsvc+xml'
An Atom Publishing Protocol Service Document, when serialized as XML
1.0, can be identified with the following media type:
MIME media type name: application
MIME subtype name: atomsvc+xml
Required parameters: None.
Gregorio & de hOra Standards Track [Page 40]
RFC 5023 The Atom Publishing Protocol October 2007
Optional parameters:
"charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in
[RFC3023].
Encoding considerations: Identical to those of "application/xml" as
described in [RFC3023], Section 3.2.
Security considerations: As defined in RFC 5023.
In addition, as this media type uses the "+xml" convention, it
shares the same security considerations as described in [RFC3023],
Section 10.
Interoperability considerations: There are no known interoperability
issues.
Published specification: RFC 5023.
Applications that use this media type: No known applications
currently use this media type.
Additional information:
Magic number(s): As specified for "application/xml" in [RFC3023],
Section 3.2.
File extension: .atomsvc
Fragment identifiers: As specified for "application/xml" in
[RFC3023], Section 5.
Base URI: As specified in [RFC3023], Section 6.
Macintosh file type code: TEXT
Person and email address to contact for further information: Joe
Gregorio
Intended usage: COMMON
Author/Change controller: IETF (iesg@ietf.org) Internet Engineering
Task Force
Gregorio & de hOra Standards Track [Page 41]
RFC 5023 The Atom Publishing Protocol October 2007
16.3. Header Field Registration for 'SLUG'
Header field name: SLUG
Applicable protocol: http [RFC2616]
Status: standard.
Author/Change controller: IETF (iesg@ietf.org) Internet Engineering
Task Force
Specification document(s): RFC 5023.
Related information: None.
16.4. The Link Relation Registration "edit"
Attribute Value: edit
Description: An IRI of an editable Member Entry. When appearing
within an atom:entry, the href IRI can be used to retrieve,
update, and delete the Resource represented by that Entry.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: Automated agents should take care when this
relation crosses administrative domains (e.g., the URI has a
different authority than the current document).
16.5. The Link Relation Registration "edit-media"
Attribute Value: edit-media
Description: An IRI of an editable Media Resource. When appearing
within an atom:entry, the href IRI can be used to retrieve,
update, and delete the Media Resource associated with that Entry.
Expected display characteristics: Undefined; this relation can be
used for background processing or to provide extended
functionality without displaying its value.
Security considerations: Automated agents should take care when this
relation crosses administrative domains (e.g., the URI has a
different authority than the current document).
Gregorio & de hOra Standards Track [Page 42]
RFC 5023 The Atom Publishing Protocol October 2007
16.6. The Atom Format Media Type Parameter
IANA has added a reference to this specification in the
'application/atom+xml' media type registration.
17. References
17.1. Normative References
[REC-xml] Yergeau, F., Paoli, J., Bray, T., Sperberg-McQueen, C.,
and E. Maler, "Extensible Markup Language (XML) 1.0
(Fourth Edition)", World Wide Web Consortium
Recommendation REC-xml-20060816, August 2006,
.
[REC-xml-infoset]
Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
.
[REC-xml-names]
Hollander, D., Bray, T., Tobin, R., and A. Layman,
"Namespaces in XML 1.0 (Second Edition)", World Wide Web
Consortium Recommendation REC-xml-names-20060816, August
2006, .
[REC-xmlbase]
Marsh, J., "XML Base", W3C REC W3C.REC-xmlbase-20010627,
June 2001,
.
[REC-xmldsig-core]
Solo, D., Reagle, J., and D. Eastlake, "XML-Signature
Syntax and Processing", World Wide Web Consortium
Recommendation REC-xmldsig-core-20020212, February 2002,
.
[REC-xmlenc-core]
Eastlake, D. and J. Reagle, "XML Encryption Syntax and
Processing", World Wide Web Consortium Recommendation REC-
xmlenc-core-20021210, December 2002,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Gregorio & de hOra Standards Track [Page 43]
RFC 5023 The Atom Publishing Protocol October 2007
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[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.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[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.
[RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
Format", RFC 4287, December 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
17.2. Informative References
[NOTE-detect-lost-update]
Nielsen, H. and D. LaLiberte, "Editing the Web: Detecting
the Lost Update Problem Using Unreserved Checkout", World
Wide Web Consortium NOTE NOTE-detect-lost-update, May
1999, .
[RNC] Clark, J., "RELAX NG Compact Syntax", December 2001,
.
Gregorio & de hOra Standards Track [Page 45]
RFC 5023 The Atom Publishing Protocol October 2007
Appendix A. Contributors
The content and concepts within are a product of the Atom community
and the Atompub Working Group.
Appendix B. RELAX NG Compact Schema
This appendix is informative.
The Relax NG schema explicitly excludes elements in the Atom Protocol
namespace that are not defined in this revision of the specification.
Requirements for Atom Protocol processors encountering such markup
are given in Sections 6.2 and 6.3 of [RFC4287].
The Schema for Service Documents:
# -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol
namespace app = "http://www.w3.org/2007/app"
namespace atom = "http://www.w3.org/2005/Atom"
namespace xsd = "http://www.w3.org/2001/XMLSchema"
namespace xhtml = "http://www.w3.org/1999/xhtml"
namespace local = ""
start = appService
# common:attrs
atomURI = text
appCommonAttributes =
attribute xml:base { atomURI }?,
attribute xml:lang { atomLanguageTag }?,
attribute xml:space {"default"|"preserved"}?,
undefinedAttribute*
atomCommonAttributes = appCommonAttributes
undefinedAttribute = attribute * - (xml:base | xml:space | xml:lang
| local:*) { text }
atomLanguageTag = xsd:string {
pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
}
Gregorio & de hOra Standards Track [Page 46]
RFC 5023 The Atom Publishing Protocol October 2007
atomDateConstruct =
appCommonAttributes,
xsd:dateTime
# app:service
appService =
element app:service {
appCommonAttributes,
( appWorkspace+
& extensionElement* )
}
# app:workspace
appWorkspace =
element app:workspace {
appCommonAttributes,
( atomTitle
& appCollection*
& extensionSansTitleElement* )
}
atomTitle = element atom:title { atomTextConstruct }
# app:collection
appCollection =
element app:collection {
appCommonAttributes,
attribute href { atomURI },
( atomTitle
& appAccept*
& appCategories*
& extensionSansTitleElement* )
}
# app:categories
atomCategory =
element atom:category {
atomCommonAttributes,
attribute term { text },
attribute scheme { atomURI }?,
attribute label { text }?,
undefinedContent
}
Gregorio & de hOra Standards Track [Page 47]
RFC 5023 The Atom Publishing Protocol October 2007
appInlineCategories =
element app:categories {
attribute fixed { "yes" | "no" }?,
attribute scheme { atomURI }?,
(atomCategory*,
undefinedContent)
}
appOutOfLineCategories =
element app:categories {
attribute href { atomURI },
undefinedContent
}
appCategories = appInlineCategories | appOutOfLineCategories
# app:accept
appAccept =
element app:accept {
appCommonAttributes,
( text? )
}
# Simple Extension
simpleSansTitleExtensionElement =
element * - (app:*|atom:title) {
text
}
simpleExtensionElement =
element * - (app:*) {
text
}
# Structured Extension
structuredSansTitleExtensionElement =
element * - (app:*|atom:title) {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
Gregorio & de hOra Standards Track [Page 48]
RFC 5023 The Atom Publishing Protocol October 2007
structuredExtensionElement =
element * - (app:*) {
(attribute * { text }+,
(text|anyElement)*)
| (attribute * { text }*,
(text?, anyElement+, (text|anyElement)*))
}
# Other Extensibility
extensionSansTitleElement =
simpleSansTitleExtensionElement|structuredSansTitleExtensionElement
extensionElement = simpleExtensionElement |
structuredExtensionElement
undefinedContent = (text|anyForeignElement)*
# Extensions
anyElement =
element * {
(attribute * { text }
| text
| anyElement)*
}
anyForeignElement =
element * - app:* {
(attribute * { text }
| text
| anyElement)*
}
atomPlainTextConstruct =
atomCommonAttributes,
attribute type { "text" | "html" }?,
text
atomXHTMLTextConstruct =
atomCommonAttributes,
attribute type { "xhtml" },
xhtmlDiv
atomTextConstruct = atomPlainTextConstruct | atomXHTMLTextConstruct
Gregorio & de hOra Standards Track [Page 49]
RFC 5023 The Atom Publishing Protocol October 2007
anyXHTML = element xhtml:* {
(attribute * { text }
| text
| anyXHTML)*
}
xhtmlDiv = element xhtml:div {
(attribute * { text }
| text
| anyXHTML)*
}
# EOF
The Schema for Category Documents:
# -*- rnc -*- # RELAX NG Compact Syntax Grammar for the Atom Protocol
namespace app = "http://www.w3.org/2007/app"
namespace atom = "http://www.w3.org/2005/Atom"
namespace xsd = "http://www.w3.org/2001/XMLSchema"
namespace local = ""
start = appCategories
atomCommonAttributes =
attribute xml:base { atomURI }?,
attribute xml:lang { atomLanguageTag }?,
undefinedAttribute*
undefinedAttribute = attribute * - (xml:base | xml:lang | local:*) {
text }
atomURI = text
atomLanguageTag = xsd:string {
pattern = "([A-Za-z]{1,8}(-[A-Za-z0-9]{1,8})*)?"
}
atomCategory =
element atom:category {
atomCommonAttributes,
attribute term { text },
attribute scheme { atomURI }?,
attribute label { text }?,
undefinedContent
}
Gregorio & de hOra Standards Track [Page 50]
RFC 5023 The Atom Publishing Protocol October 2007
appInlineCategories =
element app:categories {
attribute fixed { "yes" | "no" }?,
attribute scheme { atomURI }?,
(atomCategory*,
undefinedContent)
}
appOutOfLineCategories =
element app:categories {
attribute href { atomURI },
(empty)
}
appCategories = appInlineCategories | appOutOfLineCategories
# Extensibility
undefinedContent = (text|anyForeignElement)*
anyElement =
element * {
(attribute * { text }
| text
| anyElement)*
}
anyForeignElement =
element * - atom:* {
(attribute * { text }
| text
| anyElement)*
}
# EOF
Gregorio & de hOra Standards Track [Page 51]
RFC 5023 The Atom Publishing Protocol October 2007
Authors' Addresses
Joe Gregorio (editor)
Google
EMail: joe@bitworking.org
URI: http://bitworking.org/
Bill de hOra (editor)
NewBay Software
EMail: bill@dehora.net
URI: http://dehora.net/
Gregorio & de hOra Standards Track [Page 52]
RFC 5023 The Atom Publishing Protocol October 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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.
Gregorio & de hOra Standards Track [Page 53]
RFC, FYI, BCP