[core] Modernized Link Format

[Klaus Hartke <[e-mail]>]

I've done a quick review of appendix D of the Resource Directory draft
[1]. If I understand correctly, the section obsoletes Section 2.1 of
RFC 6690 [2]...

   Each link conveys one target URI as a URI-reference inside angle
   brackets ("<>").  The context URI of a link (also called the base URI
   in [RFC3986]) is determined by the following rules in this
   specification:

   (a)  The context URI is set to the anchor parameter, when specified.

   (b)  Origin of the target URI, when specified.

   (c)  Origin of the link format resource's base URI.

...and replaces it with the following new rules:

   o  The URI-reference inside angle brackets ("<>") describes the
      target URI of the link.

   o  The context of the link is expressed by the "anchor" parameter.
      If the anchor attribute is absent, it defaults to the empty
      reference ("").

   o  Both these references are resolved according to Section 5 of
      [RFC3986].

The resolution of the anchor URI in the final step is presumably
performed against the URI used to retrieve the Link Format document.

This means that the link in the following Link Format document located
at <coap://example.com:1234/.well-known/core>...

    <foo/bar>

...would resolve to the following URI under the old rules...

    coap://example.com:1234/foo/bar

...and  to the following URI under the new rules...

    coap://example.com:1234/.well-known/foo/bar

...regardless of whether "rel" is the implicit "hosts" relation type
as in this example or any other relation type.

Is that correct?

While the impact of this change on existing deployments might be low,
it's a breaking change and as such IMO requires an RFC that updates or
obsoletes RFC 6609.

Klaus

[1] https://tools.ietf.org/html/draft-ietf-core-resource-directory-15#appendix-D
[2] https://tools.ietf.org/html/rfc6690#section-2.1