Internet DRAFT - draft-ietf-httpbis-cice
draft-ietf-httpbis-cice
HTTP Working Group J. Reschke
Internet-Draft greenbytes
Intended status: Standards Track September 8, 2015
Expires: March 11, 2016
Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding
draft-ietf-httpbis-cice-03
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,
to indicate the content codings that are supported in requests.
Editorial Note (To be removed by RFC Editor before publication)
Discussion of this draft takes place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org), which is archived at
<https://lists.w3.org/Archives/Public/ietf-http-wg/>.
Working Group information can be found at
<https://tools.ietf.org/wg/httpbis/> and <http://httpwg.github.io/>;
source code and issues list for this draft can be found at
<https://github.com/httpwg/http-extensions>.
The changes in this draft are summarized in Appendix A.6.
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
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This Internet-Draft will expire on March 11, 2016.
Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Using the 'Accept-Encoding' Header Field in Responses . . . . . 3
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Header Field Registry . . . . . . . . . . . . . . . . . . . 5
7.2. Status Code Registry . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . 7
A.1. Since draft-reschke-http-cice-00 . . . . . . . . . . . . . 7
A.2. Since draft-reschke-http-cice-01 . . . . . . . . . . . . . 7
A.3. Since draft-reschke-http-cice-02 . . . . . . . . . . . . . 7
A.4. Since draft-ietf-httpbis-cice-00 . . . . . . . . . . . . . 7
A.5. Since draft-ietf-httpbis-cice-01 . . . . . . . . . . . . . 8
A.6. Since draft-ietf-httpbis-cice-02 . . . . . . . . . . . . . 8
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 8
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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 ([RFC7230], Section 4.2) 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, to indicate the content codings that are
supported in requests. It furthermore updates the definition of
status code 415 (Unsupported Media Type) ([RFC7231], Section 6.5.13),
recommending to include the "Accept-Encoding" header field when
appropriate.
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 defined in the base HTTP
specifications, namely Section 2 of [RFC7230] and Section 3.1.2 of
[RFC7231].
3. Using the 'Accept-Encoding' Header Field in Responses
Section 5.3.4 of [RFC7231] defines "Accept-Encoding" as a request
header field only.
This specification expands that definition to allow "Accept-Encoding"
as a response header field as well. When present in a response, it
indicates what content codings the resource was willing to accept in
the associated request. A field value that only contains "identity"
implies that no content codings were supported.
Note that this information is specific to the associated request; the
set of supported encodings might be different for other resources on
the same server, and could change over time or depend on other
aspects of the request (such as the request method).
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
ought to respond with a 415 status and ought to include an "Accept-
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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
unrelated to content codings MUST NOT include the "Accept-Encoding"
header field.
It is expected that the most common use of "Accept-Encoding" in
responses will have the 415 (Unsupported Media Type) status code, in
response to optimistic use of a content coding by clients. However,
the header field can also be used to indicate to clients that content
codings are supported, to optimize future interactions. For example,
a resource might include it in a 2xx response when the request
payload was big enough to justify use of a compression coding, but
the client failed do so.
4. Example
A client submits a POST request using the "compress" content coding
([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...
The 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:
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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.
5. Deployment Considerations
Servers that do not support content codings in requests already are
required to fail a request that uses a content coding. Section
6.5.13 of [RFC7231] defines the status code 415 (Unsupported Media
Type) for this purpose, 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
is usually static and small, adding the header field ought to be
trivial.
6. Security Considerations
This specification only adds discovery of supported content codings
and diagnostics for requests failing due to unsupported content
codings. As such, it doesn't introduce any new security
considerations over those already present in HTTP/1.1 (Section 9 of
[RFC7231]) and HTTP/2 (Section 10 of [RFC7540]).
However, the point of better discoverability and diagnostics is to
make it easier to use content codings in requests. This might lead
to increased usage of compression codings such as gzip (Section 4.2
of [RFC7230]), which, when used over a secure channel, can enable
side-channel attacks such as BREACH (see Section 10.6 of [RFC7540]
and [BREACH]). At the time of publication, it was unclear how
BREACH-like attacks can be applied to compression in HTTP requests.
7. IANA Considerations
7.1. Header Field Registry
HTTP header fields are registered within the "Message Headers"
registry located at
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<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 ought
to be updated accordingly:
+-----------------+----------+----------+---------------------------+
| Header Field | Protocol | Status | Reference |
| Name | | | |
+-----------------+----------+----------+---------------------------+
| Accept-Encoding | http | standard | [RFC7231], Section 5.3.4, |
| | | | and Section 3 of this |
| | | | document |
+-----------------+----------+----------+---------------------------+
7.2. Status Code Registry
HTTP status codes are registered within the "Status Code" registry
located at <http://www.iana.org/assignments/http-status-codes>.
This document updates the definition of the status code 415
(Unsupported Media Type), so the "Status Code" registry ought to be
updated accordingly:
+-------+------------------+----------------------------------------+
| Value | Description | Reference |
+-------+------------------+----------------------------------------+
| 415 | Unsupported | [RFC7231], Section 6.5.13, and |
| | Media Type | Section 3 of this document |
+-------+------------------+----------------------------------------+
8. References
8.1. 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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
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DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
8.2. Informative References
[BCP90] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004, <http://www.rfc-editor.org/info/bcp90>.
[BREACH] Gluck, Y., Harris, N., and A. Prado, "BREACH: Reviving the
CRIME Attack", July 2013, <http://breachattack.com/
resources/
BREACH%20-%20SSL,%20gone%20in%2030%20seconds.pdf>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. Since 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. Since 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.
A.3. Since draft-reschke-http-cice-02
First Working Group draft; updated boilerplate accordingly.
A.4. Since draft-ietf-httpbis-cice-00
Apply editorial improvements suggested by Mark Nottingham.
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A.5. Since draft-ietf-httpbis-cice-01
Clarify that we're also extending the definition of status code 415
(so update that IANA registry entry as well).
A.6. Since draft-ietf-httpbis-cice-02
Removed normative language that required used of Accept-Encoding in
responses (which would have made existing servers non-compliant).
Add BREACH like attacks to security considerations
(<https://github.com/httpwg/http-extensions/issues/94>).
Appendix B. Acknowledgements
Thanks go to the members of the and HTTPbis Working Group, namely
Amos Jeffries, Ben Campbell, Mark Nottingham, Pete Resnick, Stephen
Farrell, and Ted Hardie.
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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