Network Working GroupM. Nottingham
Internet-DraftMarch 14, 2008
Intended status: Informational
Expires: September 15, 2008

HTTP Header Linking

draft-nottingham-http-link-header-01

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Abstract

This document clarifies the status of the Link HTTP header and attempts to consolidate link relations in a single registry.


1. Introduction

A means of indicating the relationships between documents on the Web has been available for some time in HTML, and was considered as a HTTP header in [RFC2068], but removed from [RFC2616], due to a lack of implementation experience.

There have since surfaced many cases where a means of including this information in HTTP headers has proved useful. However, because it was removed, the status of the Link header is unclear, leading some to consider minting new application-specific HTTP headers instead of reusing it.

This document seeks to address these shortcomings.

Additionally, formats other than HTML -- namely, Atom [RFC4287] -- have also defined generic linking mechanisms that are similar to those in HTML, but not identical. This document aims to reconcile these differences when such links are expressed as headers.

This document does not attempt to specify how an XLink [W3C.REC-xlink-20010627] might be mapped into the Link header, but does not prohibit this from being done.

[[ NOTE: This is a straw-man draft that is intended to give a ROUGH idea of what it would take to align and consolidate the HTML and Atom link relations into a single registry with reasonable extensibility rules. In particular; a) it changes the registry for Atom link relations, and the process for registration; b) it assigns more generic semantics to several existing link relations, both Atom and HTML; c) it changes the syntax of the Link header (in the case where extensions are present). Feedback is welcome on the ietf-http-wg@w3.org mailing list, although this is NOT a work item of the HTTPBIS WG. ]]

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 BCP 14, [RFC2119], as scoped to those conformance targets.

This document uses the Augmented Backus-Naur Form (ABNF) notation of [RFC2616], and explicitly includes the following rules from it: quoted-string, token, SP (space). Additionally, the following rules are included from [RFC3986]: URI-Reference.

4. IANA Considerations

5. Security Considerations

The content the Link headers is not secure, private or integrity-guaranteed, and due caution should be excercised when using it.

Applications that take advantage of these mechanisms should consider the attack vectors opened by automatically following, trusting, or otherwise using links gathered from HTTP headers.

6. References

6.1. 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.
[RFC3986]
Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax”, STD 66, RFC 3986, January 2005.

6.2. Informative References

[RFC2068]
Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1”, RFC 2068, January 1997.
[RFC4287]
Nottingham, M. and R. Sayre, “The Atom Syndication Format”, RFC 4287, December 2005.
[RFC4685]
Snell, J., “Atom Threading Extensions”, RFC 4685, September 2006.
[RFC4946]
Snell, J., “Atom License Extension”, RFC 4946, July 2007.
[RFC5005]
Nottingham, M., “Feed Paging and Archiving”, RFC 5005, September 2007.
[RFC5023]
Gregorio, J. and B. de hOra, “The Atom Publishing Protocol”, RFC 5023, October 2007.
[W3C.REC-html401-19991224]
Jacobs, I., Raggett, D., and A. Hors, “HTML 4.01 Specification”, World Wide Web Consortium Recommendation REC-html401-19991224, December 1999, <http://www.w3.org/TR/1999/REC-html401-19991224>.
DeRose, S., Maler, E., and D. Orchard, “XML Linking Language (XLink) Version 1.0”, W3C REC REC-xlink-20010627, June 2001.

C. Acknowledgements

This specification lifts the definition of the Link header from RFC2068; credit for it belongs entirely to the authors of and contributors to that document. The link relation registrations themselves are sourced from several documents; see the applicable references.

D. Document history

-01

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Author's Address

Mark Nottingham
EMail: mnot@mnot.net
URI: http://www.mnot.net/

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