Internet DRAFT - draft-snell-link-method
draft-snell-link-method
Individual Submission J. Snell
Internet-Draft September 21, 2015
Intended status: Standards Track
Expires: March 24, 2016
HTTP Link and Unlink Methods
draft-snell-link-method-12
Abstract
This specification defines the semantics of the LINK and UNLINK HTTP
methods.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 24, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Link Relationships . . . . . . . . . . . . . . . . . . . . . 2
3. LINK . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. UNLINK . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Relationship to other HTTP Methods and Discoverability of
Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informational References . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This specification updates the HTTP LINK and UNLINK methods
originally defined in [RFC2068].
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in [RFC2119].
2. Link Relationships
The LINK and UNLINK methods are used to manage relationships between
resources. Those relationships are defined using the Link model
established in Section 3 of [RFC5988]. For every individual link,
the context IRI, link relation type, target IRI, and optional
collection of target attributes MUST be considered; that is, for any
effective request URI, there can exist at most one Link relationship
between any context and target IRI pairing with any given combination
of link relation type and target attributes.
Within LINK and UNLINK requests, a [RFC5988] Link header field is
used to describe a Link relationship to be managed. Any single LINK
or UNLINK request MAY contain multiple Link header fields, each of
which describes a separate relationship between a context IRI and
target IRI. When a LINK request contains multiple Link header
fields, the server MUST create all of the specified relationships or
not create any of them. Likewise, when an UNLINK request contains
multiple Link header fields, the server MUST either remove all the
specified relationship or not remove any of them.
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The target and context IRIs of a Link relationship are determined
following the requirements specified in Sections 5.1 and 5.2 of
[RFC5988].
When determining whether or not a relationship already exists between
a context IRI and target IRI, implementations will need to compare
the given IRIs with other, previously established relationships. To
do so, the implementation MUST first resolve the IRIs as required by
[RFC5988] and then compare on a case-sensitive, character-by-
character basis. For instance, the IRIs "http://example.org/foo" and
"http://example.org/Foo" MUST NOT be considered to be equivalent.
3. LINK
The LINK method is used to establish one or more relationships
between the resource identified by the effective request URI and one
or more other resources. Metadata contained within Link header
fields [RFC5988] provide information about the relationships being
established. A payload within a LINK request has no defined
semantics.
LINK requests are idempotent but are not safe. Establishing a
relationship causes an inherent change to the state of the target
resource. Note, however, that acceptance of a LINK request is
inherently noncomittal on the part of the server. That is, the
server MAY signal the acceptance of a LINK request without taking any
further action on it.
Any successful response (using a 2xx status code) to a LINK request
indicates that all of the Link relationships described in the request
have been established. No specific 2xx status code is required.
Responses to LINK requests are not cacheable. If a LINK request
passes through a cache that has one or more stored responses for the
effective request URI, those stored responses will be invalidated
(see Section 6 of [RFC7234]).
The semantics of the LINK method change to a "conditional LINK" if
the request message includes an If-Modified-Since, If-Unmodified-
Since, If-Match, If-None-Match, or If-Range header field ([RFC7232]).
A conditional LINK requests that the relationship be established only
under the circumstances described by the conditional header field(s).
4. UNLINK
The UNLINK method is used to remove one or more relationships between
the resource identified by the effective request URI and other
resources. Metadata contained within Link header fields [RFC5988]
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provide the information about the relationships that are to be
removed. A payload within an UNLINK request has no defined
semantics.
UNLINK request messages are idempotent but are not safe. Removing a
relationship causes an inherent change to the state of the target
resource. Note, however, that acceptance of an UNLINK request is
inherently noncomittal on the part of the server. That is, the
server MAY signal the acceptance of an UNLINK request without taking
any further action on it.
Any successful response (using a 2xx status code) to an UNLINK
request indicates that all of the Link relationships described in the
request have been removed. No specific 2xx status code is required.
Responses to UNLINK requests are not cacheable. If an UNLINK request
passes through a cache that has one or more stored responses for the
effective request URI, those stored responses will be invalidated
(see Section 6 of [RFC7234]).
The semantics of the UNLINK method change to a "conditional UNLINK"
if the request message includes an If-Modified-Since, If-Unmodified-
Since, If-Match, If-None-Match, or If-Range header field ([RFC7232]).
A conditional UNLINK requests that the relationship be established
only under the circumstances described by the conditional header
field(s).
5. Relationship to other HTTP Methods and Discoverability of Links
The use of the LINK and UNLINK request methods to manage
relationships between resources has no direct bearing on the use or
appearance of Link header fields within any other HTTP request or
response message involving the same effective request URI. Nor do
the methods have any direct normative impact on the use of link-like
structures within the resource representations returned by a server
for any particular resource.
Whether and how to represent relationships managed using LINK and
UNLINK is solely at the discretion of the server implementation.
This specification does not define a means of discovering or
enumerating the relationships that have been established using the
LINK request method.
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6. Example
There exists a broad range of possible use cases for the LINK and
UNLINK methods. The examples that follow illustrate a subset of
those cases.
Example 1: Creating two separate links between an image and the
profiles of two people associated with the image:
LINK /images/my_dog.jpg HTTP/1.1
Host: example.org
Link: <http://example.com/profiles/joe>; rel="tag"
Link: <http://example.com/profiles/sally>; rel="tag"
Possible response:
HTTP/1.1 202 Accepted
Example 2: Removing an existing Link relationship between two
resources:
UNLINK /images/my_dog.jpg HTTP/1.1
Host: example.org
Link: <http://example.com/profiles/sally>; rel="tag"
Possible response:
HTTP/1.1 204 No Content
Example 3: Establish a "pingback" or "trackback" style link to a blog
entry about an article
LINK /articles/an_interesting_article HTTP/1.1
Host: example.org
Link: <http://example.com/my_blog_post>; rel="mention"
Example 4: Establish a link between two semantically related
resources:
LINK /some-resource HTTP/1.1
Host: example.org
Link: <http://example.com/schemas/my_schema>; rel="describedBy"
Example 5: Add an existing resource to a collection:
LINK /some-collection-resource HTTP/1.1
Host: example.org
Link: <http://example.com/my-member-resource>; rel="item"
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Example 6: Link one resource to another that monitors its current
state (e.g. pub/sub)
LINK /my-resource HTTP/1.1
Host: example.org
Link: <http://example.com/my-monitor>; rel="monitor"
Example 7: Using the Link anchor attribute to change the context IRI
(in this example, a link relationship is established between the IRIs
"acct:joe@example.org" and "acct:sally@example.org")
LINK /my-resource HTTP/1.1
Host: example.org
Link: <acct:joe@example.org>; rel="follow";
anchor="acct:sally@example.org"
Example 8: Using fragment identifiers to establish links with
embedded resources. In this example, a link relationship is
established between "http://example.org/alice#me" and
"http://example.org/bob#me".
LINK /alice HTTP/1.1
Host: example.org
Link: <http://example.org/bob#me>; rel="knows"; anchor="#me"
7. Security Considerations
The LINK and UNLINK methods are subject to the same general security
considerations as all HTTP methods as described in [RFC7231].
Because the LINK and UNLINK methods MAY cause changes to a resource's
state, the server is responsible for determining the client's
authorization to make such changes.
8. IANA Considerations
IANA is requested to add the LINK and UNLINK methods to the permanent
registry at <http://www.iana.org/assignments/http-methods> (see
Section 8.1 of [RFC7231]).
+-------------+------+------------+---------------+
| Method Name | Safe | Idempotent | Specification |
+-------------+------+------------+---------------+
| LINK | No | Yes | Section 3 |
| UNLINK | No | Yes | Section 4 |
+-------------+------+------------+---------------+
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<http://www.rfc-editor.org/info/rfc5988>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
DOI 10.17487/RFC7232, June 2014,
<http://www.rfc-editor.org/info/rfc7232>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<http://www.rfc-editor.org/info/rfc7234>.
9.2. Informational References
[RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
RFC 2068, DOI 10.17487/RFC2068, January 1997,
<http://www.rfc-editor.org/info/rfc2068>.
Author's Address
James M Snell
Email: jasnell@gmail.com
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