Network Working GroupM. Nottingham
Internet-DraftJuly 3, 2008
Updates: 4287 (if approved)
Intended status: Standards Track
Expires: January 4, 2009

HTTP Header Linking

Status of this Memo

By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

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”.

The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html.

This Internet-Draft will expire on January 4, 2009.

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 [W3C.REC-html401-19991224], 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.

[[ 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, and from [RFC4288]: type-name.

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

6.2. 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>.

Appendix 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.

The author would like to thank the many people who commented upon, encouraged and gave feedback to this draft, especially including Frank Ellermann and Julian Reschke.

Appendix D. Document history

-02

-01

-00

Author's Address

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

Full Copyright Statement

Copyright © The IETF Trust (2008).

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

This document and the information contained herein are provided on an “AS IS” basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org.