Individual Submission J. Snell
Internet-Draft September 17, 2007
Expires: March 20, 2008
Prefer Header for HTTP
draft-snell-http-prefer-00
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This specification defines a new HTTP header that can be used by a
client to request that certain behaviors be implemented by a server
during the processing a request.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Prefer Request Header . . . . . . . . . . . . . . . . . . . 3
3. The "return-no-content" Preference . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 4
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 5
Appendix C. Notes to RFC Editor . . . . . . . . . . . . . . . . . 5
Appendix D. Editorial Notes . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . . . 6
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1. Introduction
This specification defines a new HTTP header that can be used by a
client to request that certain behaviors be implemented by a server
during the processing a request.
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. The Prefer Request Header
The Prefer request-header is used to indicate that particular server
behaviors are preferred, but not required, by the client. Prefer is
similar in nature to the Expect header defined by [RFC2616] with the
exception that servers are allowed to ignore a clients stated
preferences.
Prefer = "Prefer" ":" 1#preference
preference = "no-content" | "content-returned" |
preference-extension
preference-extension = token [ "=" ( token | quoted-string )
*prefer-params ]
prefer-params = ";" token [ "=" ( token | quoted-string ) ]
This header is defined with an extensible syntax to allow for future
extensions. A server that does not understand or is unable to comply
with any of the preference values in the Prefer field of a request
MUST ignore those values and MUST NOT stop processing or signal an
error.
Comparison of preference values is case-insensitive for unquoted
tokens and is case-sensitive for quoted-string preference-extensions.
The Prefer mechanism is hop-by-hop: that is, an HTTP proxy MAY choose
to honor a preference even if the origin server does not. However,
the Prefer request-header itself is end-to-end; it MUST be forwarded
if the request is forwarded.
3. The "return-no-content" Preference
The "return-no-content" token indicates that the client prefers that
the server not include an entity in the response to a successful
request. Typically, such responses would use the 204 No Content
status code as defined in Section 10.2.5 of [RFC2616], but other
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status codes can be used as appropriate.
4. IANA Considerations
The 'Prefer' request header should be added to the permanent registry
(see [RFC3864]).
Header field name: Prefer
Applicable Protocol: HTTP
Status: standard
Author/Change controller: IETF
Specification document: this specification
5. Security Considerations
Specific preferences requested by a client can introduce security
considerations and concerns beyond those discussed in [RFC2616].
Implementors must refer to the specifications and descriptions of
those preferences to determine the security considerations relevant
to each.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
Appendix A. Acknowledgements
The author greatfully acknowledges the input from the IETF HTTP
mailing list on the development of this document.
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Appendix B. Changes
TODO
Appendix C. Notes to RFC Editor
The RFC Editor should remove this section and the Changes section.
Appendix D. Editorial Notes
We need to determine how new preference codes are created/registered
Author's Address
James M Snell
Phone:
Email: jasnell@gmail.com
URI: http://www.snellspace.com
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