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Re: [dxwg] Registration of target attribute "profile" for the Link-Header (#501)

From: Lars G. Svensson via GitHub <sysbot+gh@w3.org>
Date: Fri, 30 Aug 2019 07:43:35 +0000
To: public-dxwg-wg@w3.org
Message-ID: <issue_comment.created-526496234-1567151014-sysbot+gh@w3.org>
The discussion over in #290 (unfortunately) has implications for this issue, too.
The preferred way of publishing URI/token mappings discussed there is to use the `Link` header and the target attribute `profile` discussed here. That way a host could declare that for the resource `https://example.org/some/resource` the URI `urn:example:foo` is mapped to the token `bar` by adding the following `Link` header to the http response:
```
Link: <https://example.org/some/resource>
    profile="urn:example:foo token=bar"
```
Currently, the I-D defines the value of the `profile` parameter as `absolute-URI`. That means that **if** we want to support tokens, we need to extend the syntax of the `profile` attribute to something like
`absolute-URI[<delimiting-character>"token"=token]` (where the first "token" is the string "token" and the second "token" is a `token` defined as in [RFC 7230 §3.2.6](https://tools.ietf.org/html/rfc7230#section-3.2.6)) which would allow
```
profile="urn:example:foo|token=bar"
```
My personal feeling is that defining an extension to the `profile` attribute only to map tokens to URIs is a Bad Idea (TM), particularly since we might not need it (depending on #290). In order to future-proof the syntax, however, it could make sense to define a generic extension syntax, à la
`absolute-URI[<delimiting-character>token=token]` which would also allow
```
profile="urn:example:foo|bar=baz"
```

As `<delimiting-character>` we need something not allowed in `absolute-URI`. Blank (U+0020) or pipe (U+007C) come to mind. If we use blank, we also must mandate the use of quotation marks on the right hand side of `profile="bla"`.
See also https://github.com/ProfileNegotiation/I-D-Profile-Negotiation/issues/12 and https://github.com/ProfileNegotiation/I-D-Profile-Negotiation/issues/8.
@nicholascar, @rob-metalinkage, @RubenVerborgh: What do you think?
And ACTION-290

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