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Versions: 00 01 02 draft-ietf-httpbis-cice

Network Working Group                                         J. Reschke
Internet-Draft                                                greenbytes
Intended status: Standards Track                            July 2, 2014
Expires: January 3, 2015


  Hypertext Transfer Protocol (HTTP) Client-Initiated Content-Encoding
                       draft-reschke-http-cice-01

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>.

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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   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."




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   This Internet-Draft will expire on January 3, 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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  Extensions to 'Accept-Encoding' Header Field  . . . . . . . . . 3
   4.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Deployment Considerations . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . . . 6
     A.1.  draft-reschke-http-cice-00  . . . . . . . . . . . . . . . . 6



















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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 is willing to accept in future requests.
   A field value that only contains "identity" implies that no content
   codings are supported.

   Note that this information is specific to the requested resource.
   The set of supported encodings might be different for resources on
   the same server, and could also change depending 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
   SHOULD respond with a 415 status and SHOULD include an "Accept-
   Encoding" header in that response, allowing clients to distinguish
   between content coding related issues and media type related issues.





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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.

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



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   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.  References

8.1.  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.





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8.2.  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.

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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