Individual Submission J. Snell
Internet-Draft February 15, 2008
Expires: August 18, 2008
Prefer Header for HTTP
draft-snell-http-prefer-02
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Copyright Notice
Copyright (C) The IETF Trust (2008).
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
while processing a request.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Prefer Request Header . . . . . . . . . . . . . . . . . . . 3
3. The Preference-Applied Response Header . . . . . . . . . . . . 3
4. The "return-no-content" Preference . . . . . . . . . . . . . . 4
5. The "return-content" Preference . . . . . . . . . . . . . . . . 4
6. The "return-status" Preference . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7.1. The Registry of Preferences . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 5
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 5
Appendix C. Notes to RFC Editor . . . . . . . . . . . . . . . . . 6
Appendix D. Editorial Notes . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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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
while 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 = "return-no-content" |
"return-content" |
"return-status" |
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
values included in the Registry of Preferences (see Section 7.1). A
server that does not recognize or is unable to comply with particular
preference values in the Prefer header 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.
An HTTP proxy MAY choose to honor a preference even if the origin
server does not. The Prefer request-header MUST be forwarded by the
proxy if the request is forwarded.
3. The Preference-Applied Response Header
The Preference-Applied response header MAY be included in the
response message to indicate which Prefer request header values were
honored by the server and applied to the request.
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Prefer = "Preference-Applied" ":" 1#preference
4. 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
status codes can be used as appropriate.
5. The "return-content" Preference
The "return-content" token indicates that the client prefers that the
server include an entity representing the current state of the
resource in the response to a successful request.
6. The "return-status" Preference
The "return-status" token indicates that the client prefers that the
server include an entity describing the status of the request in the
response to a successful request.
7. 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
7.1. The Registry of Preferences
This registry is maintained by IANA and initially contains three
values: "return-no-content", "return-content" and "return-status".
New assignments are subjects to IESG approval, as outlined in
[RFC2434]. Requests should be made by email to IANA, which will then
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forward the request to the IESG, requesting approval. The request
should use the following template:
o Preference: (A value for the Prefer request header that conforms
to the syntax rule given in Section 2)
o Description:
o Expected server behavior:
o Security considerations:
8. 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.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[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.
Appendix B. Changes
TODO
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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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