Network Working Group J. Arwe
Internet-Draft S. Speicher
Intended status: Standards Track IBM
Expires: February 6, 2015 E. Wilde
UC Berkeley
Aug 5, 2014
The Accept-Post HTTP Header
draft-wilde-accept-post-03
Abstract
This specification defines a new HTTP response header field Accept-
Post, which indicates server support for specific media types for
entity bodies in HTTP POST requests.
Note to Readers
This draft should be discussed on the apps-discuss mailing list [1].
Online access to all versions and files is available on github [2].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on February 6, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Accept-Post Response Header Field . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.1. The Accept-Post Response Header . . . . . . . . . . . . . 4
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Atom Publishing Protocol . . . . . . . . . . . . . . . . . 4
5.2. Linked Data Platform . . . . . . . . . . . . . . . . . . . 5
5.3. Additional Information in Error Responses . . . . . . . . 5
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 6
6.1. Eclipse Lyo . . . . . . . . . . . . . . . . . . . . . . . 6
6.2. RWW.I/O . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.3. Tivoli Workload Automation . . . . . . . . . . . . . . . . 8
6.4. Jazz for Service Management . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. From -03 to -04 . . . . . . . . . . . . . . . . . . . . . 10
9.2. From -02 to -03 . . . . . . . . . . . . . . . . . . . . . 10
9.3. From -01 to -02 . . . . . . . . . . . . . . . . . . . . . 10
9.4. From -00 to -01 . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This specification defines a new HTTP response header field Accept-
Post, which indicates server support for specific media types for
entity bodies in HTTP POST requests. This header field is comparable
to the Accept-Patch response header field specified together with the
HTTP PATCH method [RFC5789] (notice, however, that while Accept-Patch
is defined to only list specific media types, Accept-Post reuses the
"media range" concept of HTTP's Accept header and thus allows media
type wildcards as well).
2. Terminology
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 RFC 2119 [RFC2119].
3. The Accept-Post Response Header Field
This specification introduces a new response header field Accept-Post
used to specify the document formats accepted by the server in HTTP
POST requests. Accept-Post SHOULD appear in the OPTIONS response for
any resource that supports the use of the POST method. The presence
of the Accept-Post header in response to any method is an implicit
indication that POST is allowed on the resource identified by the
Request-URI. The presence of a specific document format in this
header indicates that this specific format is allowed on the resource
identified by the Request-URI.
The syntax for Accept-Post headers, using the ABNF [RFC5234] syntax
defined in Section 5.3.2 of HTTP/1.1 [RFC7231], is given by the
following definition:
Accept-Post = #( media-range [ accept-params ] )
(Please note that this ABNF differs from the one given in Section
5.3.2 of RFC 7231 [RFC7231], which includes the header field name.)
The Accept-Post header specifies a media range as defined by HTTP
[RFC7231]. The media range specifies a type of representation that
can be POSTed to the Request-URI.
The app:accept element is similar to the HTTP Accept request header
field [RFC7231]. Media type parameters are allowed within Accept-
Post, but Accept-Post has no notion of preference - "accept-params"
or "q" arguments, as specified in Section 5.3.2 of [RFC7231], are not
significant.
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4. IANA Considerations
This specification defines a response header field for the Hypertext
Transfer Protocol (HTTP) that has been registered with the Internet
Assigned Numbers Authority (IANA) following the "Registration
Procedures for Message Header Fields" [RFC3864].
4.1. The Accept-Post Response Header
The Accept-Post response header should be added to the permanent
registry of message header fields (see [RFC3864]), taking into
account the guidelines given by HTTP/1.1 [RFC7231].
Header Field Name: Accept-Post
Applicable Protocol: Hypertext Transfer Protocol (HTTP)
Status: Standard
Author/Change controller: IETF
Specification document(s): RFC XXXX
5. Examples
Accept-Post extends the way in which interaction information can be
exposed in HTTP itself. The following sections contain some examples
how this can be used in concrete HTTP-based services. Based on the
first example of AtomPub Section 5.1, when sending a GET request to
the URI of a collection, the following response could be sent, if the
server decided to support Accept-Post headers:
HTTP/1.1 201 OK
Date: Fri, 23 Feb 2007 21:17:11 GMT
Content-Length: nnn
Content-Type: application/atom+xml;type=feed
Accept-Post: image/gif, image/jpeg, image/png
In this response to the GET request of a collection URI, the server
indicates that this particular collection accepts new entries in the
form of GIF, JPEG, or PNG images. No parameters are used, which
means that there is no server-specified preference among those media
types.
5.1. Atom Publishing Protocol
The Atom Publishing Protocol (AtomPub) [RFC5023] defines a model of
interacting with collections and members, based on representations
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using the Atom [RFC4287] syntax. AtomPub allows clients to create
new collection members by using HTTP POST, with the request being
sent to the collection URI. AtomPub servers can limit the media
types they accept in these POST requests, and the accepted media
types are listed in an "AtomPub service document".
The Accept-Post header field does allow an AtomPub server to
advertise its support for specific media types in interactions with
the collection resource, without the need for a client to locate the
service document and interact with it. This increases the visibility
of the "POST to Create" model of AtomPub, and makes it easier for
clients to find out about the capabilities of a specific collection.
While the AtomPub protocol cannot be changed retroactively, this
additional way of exposing interaction guidance could make it easier
for clients to interact with AtomPub services that do support the
Accept-Post header field. For those that do not support Accept-Post,
clients would still have to rely on using the information contained
in the service document (including the sometimes tricky issue of how
to locate the service document for a given collection).
5.2. Linked Data Platform
The Linked Data Platform (LDP) [W3C.WD-ldp-20140311] describes a set
of best practices and simple approach for a read-write Linked Data
architecture, based on HTTP access to Web resources that describe
their state using the RDF data model. LDP defines LDP Containers
(LDPC) and LDP Resources (LDPR). Adding new LDPRs to an LDPC is done
by sending an HTTP POST request to the LDPC. An LDPC can constrain
the media types it is accepting for these POST requests, and should
expose its support for accepted media types via Accept-Post.
In fact, the Accept-Post header was initially developed within the
W3C's LDP Working Group (LDPWG), see Appendix A for acknowledgements.
It was then decided that the header itself might be useful in other
contexts as well, and thus should be specified in a standalone
document.
5.3. Additional Information in Error Responses
If a client POSTs an unsupported POST document, it is possible for
the server to use Accept-Post to indicate the supported media types.
These can be specified using a 415 (Unsupported Media Type) response
when the client sends a POST document format that the server does not
support for the resource identified by the Request-URI. Such a
response then MAY include an Accept-Post response header notify the
client what POST document media types are supported.
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This example applies to all resources supporting a limited set of
media types for POST requests, such as the ones listed in the
previous to sections. In both AtomPub and LDP, it would be possible
for a server to include an Accept-Post header in a 415 response to a
failed POST request, and indicate the media types that are accepted
for POST requests.
6. Implementation Status
Note to RFC Editor: Please remove this section before publication.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in RFC 6982
[RFC6982]. The description of implementations in this section is
intended to assist the IETF in its decision processes in progressing
drafts to RFCs. Please note that the listing of any individual
implementation here does not imply endorsement by the IETF.
Furthermore, no effort has been spent to verify the information
presented here that was supplied by IETF contributors. This is not
intended as, and must not be construed to be, a catalog of available
implementations or their features. Readers are advised to note that
other implementations may exist.
According to RFC 6982, "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
6.1. Eclipse Lyo
Organization: IBM developed and contributed to the Eclipse Lyo
project [3].
Name: Eclipse Lyo "LDP reference implementation" [4]
Description: A very simple reference implementation for W3C Linked
Data Platform (LDP) using some base Java technologies such as
JAX-RS 2.0 and Apache Jena. The goals of this reference
implementation is to experiment with validating the concepts in
the specification and understanding what a SDK might look like to
build LDP-compliant servers. Additional goal is to validate the
approach for usage in OSLC4J SDK for building OSLC [5] clients and
servers.
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Maturity: Early prototype/alpha.
Coverage: All parts of the specification were covered for server
requirements.
Licensing: Freely distributable (Eclipse Public License (EPL) [6]
and Eclipse Distribution License (EDL) [7]).
Implementation Experience: Experience is only from the server
perspective of generating the HTTP response header. It was
trivial using JAX-RS 2.0 mechanism using a ContainerResponseFilter
on all responses. More details about this approach are described
in this blog post [8].
Contact: Steve Speicher <[email protected]>
6.2. RWW.I/O
Organization: No particular organization. The work done is part
of project RWW.I/O [9].
Name: RWW.I/O - personal linked data storage.
Description: A minimal support for LDP is now included in RWW.I/O,
which is a personal linked data storage space, following the
structure of a Unix file system. Currently, only LDPCs are
supported, since the LDPRs are always files or directories that
are being managed through RESTful operations. RWW.I/O encourages
the use of .meta files to semantically describe non-LD resources
(e.g. images, html, js, css, etc.), and the use of .acl files for
access control rules using the WAC vocabulary. Both .meta and
.acl should be used per file (i.e. photo.jpg will have a
.meta.photo.jpg and a .acl.photo.jpg).
Maturity: Beta until more features from LDP spec are included (if
necessary).
Coverage: LDPCs on the server side, pagination and Accept-Post
header. You can test LDPC support like this: curl -H "Accept:
text/turtle" https://deiu.rww.io/public/?p=1 ; You can test
Accept-Post header like this: curl -v -X OPTIONS -H "Accept: text/
turtle" https://deiu.rww.io/public/
Licensing: MIT license. Source code is available on GitHub [10].
Implementation Experience: Implementing current LDP features in
RWW.I/O was trivial. I've also decided to add the Accept-Post
header to HEAD replies, as it helps to reduce the number of
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requests for a client trying to discover more information about
the server.
Contact: Andrei Sambra <[email protected]>
6.3. Tivoli Workload Automation
Organization: IBM [11]
Name: Tivoli Workload Automation [12]
Description: An existing scheduling product that already
implements the OSLC Automation specification [13] (both client and
server roles), including creation factories for Automation
Requests that accept HTTP POST requests. Since OSLC Automation
offers no programmatic way for clients to know which media types
are supported by the server, clients are limited in practice to
those required by OSLC Automation (RDF/XML), or to making
optimistic requests using other RDF media types.
Maturity: Early prototype/alpha
Coverage: All parts of the specification were covered for server
and client requirements.
Licensing: proprietary
Implementation Experience: Experience from the server perspective
of generating the HTTP response header is that it was trivial
using JAX-RS annotations to add another response header. Client
parsing of the header presented no new problems, since the syntax
is almost identical to the server-side processing of an Accept
header.
Contact: John Arwe <[email protected]>
6.4. Jazz for Service Management
Organization: IBM [11]
Name: Jazz for Service Management Registry Services
Description: An existing component bundled with multiple existing
Cloud and Smarter Infrastructure (formerly branded as Tivoli)
products. It already supports multiple resource collections that
use HTTP POST requests to create new member resources, e.g.
"registration records". Given that clients have no existing means
by which they can know which media types the server supports, and
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given that Registry Services has been adding new media types over
the past few months as part of its continuous delivery process,
Accept-Post is a natural fit to enable looser client coupling.
Maturity: Early prototype/alpha
Coverage: All parts of the specification were covered for server
requirements.
Licensing: proprietary
Implementation Experience: Experience is only from the server
perspective of generating the HTTP response header. It was easy
to add a new header using JAX-RS annotations.
Contact: John Arwe <[email protected]>
7. Security Considerations
The Accept-Post header may expose information that a server would
prefer to not publish. In such a case, a server can simply stop
exposing the header, in which case HTTP interactions would be back to
the level of standard HTTP (i.e., with no indication what kind of
media types a resource accepts in POST requests).
8. Open Issues
Note to RFC Editor: Please remove this section before publication.
o Accept-Post currently uses the "media range" concept of HTTP's
Accept header field. An alternative would be only support fully
specified media types, which is what the Accept-Patch header field
is doing. This latter solution is more constrained, and fails to
address some uses cases, such as AtomPub's way of exposing
collection support for POST requests.
o While "accept-post" is currently defined in the "HTTP Link Hints"
draft [I-D.nottingham-link-hint], it would be good to align the
way in which they work. Currently, the "accept-post" of link
hints allows a list of specific media types, whereas the Accept-
Post header field may contain "media ranges".
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9. Change Log
Note to RFC Editor: Please remove this section before publication.
9.1. From -03 to -04
o Updating references (removing RFC 2616, adding new HTTP/1.1 RFCs).
9.2. From -02 to -03
o Adding reference to RFC 5234 (ABNF).
o Updating references.
o Adding proper registration template.
9.3. From -01 to -02
o Added header field example.
o Updated author address.
o Adding more entries to the "Implementation Status" section.
9.4. From -00 to -01
o Changed ABNF for header field from RFC 2616 to HTTPbis convention
(only specify the header field value grammar).
o Added implementations (all from the LDP community for now).
o Added open issue for aligning accept-post as defined by the "HTTP
Link Hints" draft.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
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10.2. Informative References
[I-D.nottingham-link-hint]
Nottingham, M., "HTTP Link Hints",
draft-nottingham-link-hint-00 (work in progress),
June 2013.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, December 2005.
[RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
Protocol", RFC 5023, October 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
July 2013.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
(HTTP/1.1): Semantics and Content", RFC 7231, June 2014.
[W3C.WD-ldp-20140311]
Speicher, S., Arwe, J., and A. Malhotra, "Linked Data
Platform 1.0", World Wide Web Consortium LastCall WD-ldp-
20140311, March 2014,
<http://www.w3.org/TR/2014/WD-ldp-20140311>.
URIs
[1] <https://www.ietf.org/mailman/listinfo/apps-discuss>
[2] <https://github.com/dret/I-D/tree/master/accept-post>
[3] <http://eclipse.org/lyo>
[4] <http://wiki.eclipse.org/Lyo/BuildLDPSample>
[5] <http://open-services.net>
[6] <http://www.eclipse.org/legal/epl-v10.html>
[7] <http://www.eclipse.org/org/documents/edl-v10.php>
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[8] <http://stevespeicher.blogspot.com/2013/08/
supporting-accept-post-in-jax-rs.html>
[9] <https://rww.io/>
[10] <https://github.com/deiu/rww.io>
[11] <http://www.ibm.com/>
[12] <https://www.ibm.com/developerworks/community/forums/html/
topic?id=f403c299-c1c6-4da8-8b12-f3b72de54a1a>
[13] <http://open-services.net/wiki/automation/
OSLC-Automation-Specification-Version-2.0/>
Appendix A. Acknowledgements
Thanks for comments and suggestions provided by Martin Duerst, Barry
Leiba, Mark Nottingham, and Julian Reschke.
This work has been done in the context of the W3C Linked Data
Platform Working Group (LDPWG) [W3C.WD-ldp-20140311]; thanks for
comments and suggestions provided by the working group as a whole.
Authors' Addresses
John Arwe
IBM
Email: [email protected]
Steve Speicher
IBM
Email: [email protected]
Erik Wilde
UC Berkeley
Email: [email protected]
URI: http://dret.net/netdret/
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