Internet DRAFT - draft-reschke-http-cice
draft-reschke-http-cice
Network Working Group J. Reschke
Internet-Draft greenbytes
Intended status: Standards Track March 9, 2015
Expires: September 10, 2015
Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding
draft-reschke-http-cice-02
Abstract
In HTTP, "Content Codings" allow for payload encodings such as for
compression or integrity checks. In particular, the "gzip" content
coding is widely used for payload data sent in response messages.
Content Codings can be used in request messages as well, however
discoverability is not on par with response messages. This document
extends the HTTP "Accept-Encoding" header field for use in responses.
Editorial Note (To be removed by RFC Editor before publication)
Distribution of this document is unlimited. Although this is not a
work item of the HTTPbis Working Group, comments should be sent to
the Hypertext Transfer Protocol (HTTP) mailing list at
ietf-http-wg@w3.org [1], which may be joined by sending a message
with subject "subscribe" to ietf-http-wg-request@w3.org [2].
Discussions of the HTTPbis Working Group are archived at
<http://lists.w3.org/Archives/Public/ietf-http-wg/>.
XML versions and latest edits for this document are available from
<http://greenbytes.de/tech/webdav/#draft-reschke-http-cice>.
The changes in this draft are summarized in Appendix A.2.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Extensions to 'Accept-Encoding' Header Field . . . . . . . . . 3
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . 6
A.1. draft-reschke-http-cice-00 . . . . . . . . . . . . . . . . 6
A.2. draft-reschke-http-cice-01 . . . . . . . . . . . . . . . . 6
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1. Introduction
In HTTP, "Content Codings" allow for payload encodings such as for
compression or integrity checks ([RFC7231], Section 3.1.2). In
particular, the "gzip" content coding is widely used for payload data
sent in response messages.
Content Codings can be used in request messages as well, however
discoverability is not on par with response messages. This document
extends the HTTP "Accept-Encoding" header field ([RFC7231], Section
5.3.4) for use in responses.
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].
This document reuses terminology used in the base HTTP
specifications, namely Section 2 of [RFC7230] and Section 3.1.2 of
[RFC7231].
3. Extensions to 'Accept-Encoding' Header Field
Section 5.3.4 of [RFC7231] defines "Accept-Encoding" as a request
header field only.
This specification extends that definition to allow "Accept-Encoding"
as a response header field as well. When present, it indicates what
content codings a resource was willing to accept at the time of the
response. A field value that only contains "identity" implies that
no content codings are supported.
Note that this information is specific to the specific request. The
set of supported encodings might be different for other resources on
the same server, could also change depending on other aspects of the
request (such as the request method), or might change in the future.
Section 6.5.13 of [RFC7231] defines status code 415 (Unsupported
Media Type) to apply to both media type and content coding related
problems.
Servers that fail a request due to an unsupported content coding
SHOULD respond with a 415 status and SHOULD include an "Accept-
Encoding" header field in that response, allowing clients to
distinguish between content coding related issues and media type
related issues. In order to avoid confusion with media type related
problems, servers that fail a request with a 415 status for reasons
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unrelated to content codings SHOULD NOT include the "Accept-Encoding"
header field.
While sending "Accept-Encoding" in a 415 (Unsupported Media Type)
response will be the most common use case, it is not restricted to
this particular status code. For instance, a server might include it
in a 2xx response when a request payload was big enough to justity
use of a compression coding, but the client failed to do so.
4. Example
Client submits a POST request using Content-Encoding "compress"
([RFC7231], Section 3.1.2.1):
POST /edit/ HTTP/1.1
Host: example.org
Content-Type: application/atom+xml;type=entry
Content-Encoding: compress
...compressed payload...
Server rejects request because it only allows the "gzip" content
coding:
HTTP/1.1 415 Unsupported Media Type
Date: Fri, 09 May 2014 11:43:53 GMT
Accept-Encoding: gzip
Content-Length: 68
Content-Type: text/plain
This resource only supports the "gzip" content coding in requests.
...at which point the client can retry the request with the supported
"gzip" content coding.
Alternatively, a server that does not support any content codings in
requests could answer with:
HTTP/1.1 415 Unsupported Media Type
Date: Fri, 09 May 2014 11:43:53 GMT
Accept-Encoding: identity
Content-Length: 61
Content-Type: text/plain
This resource does not support content codings in requests.
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5. Deployment Considerations
Servers that do not support content codings in requests already are
required to fail a request that does use a content coding. Section
6.5.13 of [RFC7231] recommends to use the status code 415
(Unsupported Media Type), so the only change needed is to include the
"Accept-Encoding" header field with value "identity" in that
response.
Servers that do support some content codings are required to fail
requests with unsupported content codings as well. To be compliant
with this specification, servers will need to use the status code 415
(Unsupported Media Type) to signal the problem, and will have to
include an "Accept-Encoding" header field that enumerates the content
codings that are supported. As the set of supported content codings
usually is static and small, adding the header field ought to be
trivial.
6. Security Considerations
This specification does not introduce any new security considerations
beyond those discussed in Section 9 of [RFC7231].
7. IANA Considerations
HTTP header fields are registered within the "Message Headers"
registry located at
<http://www.iana.org/assignments/message-headers>, as defined by
[BCP90].
This document updates the definition of the "Accept-Encoding" header
field, so the "Permanent Message Header Field Names" registry shall
be updated accordingly:
+-----------------+----------+----------+---------------------------+
| Header Field | Protocol | Status | Reference |
| Name | | | |
+-----------------+----------+----------+---------------------------+
| Accept-Encoding | http | standard | [RFC7231], Section 5.3.4, |
| | | | extended by Section 3 of |
| | | | this document |
+-----------------+----------+----------+---------------------------+
8. Acknowledgements
Thanks go to the members of the and HTTPbis Working Group, namely
Amos Jeffries, Mark Nottingham, and Ted Hardie.
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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, March 1997.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, June 2014.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
June 2014.
9.2. Informative References
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
URIs
[1] <mailto:ietf-http-wg@w3.org>
[2] <mailto:ietf-http-wg-request@w3.org?subject=subscribe>
Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. draft-reschke-http-cice-00
Clarified that the information returned in Accept-Encoding is per
resource, not per server.
Added some deployment considerations.
Updated HTTP/1.1 references.
A.2. draft-reschke-http-cice-01
Restrict the scope of A-E from "future requests" to "at the time of
this request".
Mention use of A-E in responses other than 415.
Recommend not to include A-E in a 415 response unless there was
actually a problem related to content coding.
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Author's Address
Julian F. Reschke
greenbytes GmbH
Hafenweg 16
Muenster, NW 48155
Germany
EMail: julian.reschke@greenbytes.de
URI: http://greenbytes.de/tech/webdav/
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