Subject: NEW ISSUE (?): LINK header

From: Julian Reschke <[email-masked]>
Date: Sun, 02 Sep 2007 20:55:52 +0200

Hi,

the current editor's draft of HTML5 requires User-Agents to respect the 
HTTP Link header (as specified in RFC2068, and dropped from RFC2616) -- 
see <http://www.w3.org/html/wg/html5/#the-link>:

"Some versions of HTTP defined a Link: header, to be processed like a 
series of link  elements. When processing links, those must be taken 
into consideration as well. For the purposes of ordering, links defined 
by HTTP headers must be assumed to come before any links in the 
document, in the order that they were given in the HTTP entity header. 
Relative URIs in these headers must be resolved according to the rules 
given in HTTP, not relative to base URIs set by the document (e.g. using 
a base element or xml:base attributes). [RFC2616] [RFC2068]"

So either this is just wishful thinking, or implementation support for 
the Link header has indeed improved lately (I'll guess in FF and Opera). 
In the latter case, we may want to re-add it in RFC2616bis.

Best regards, Julian

---

From: "Anne van Kesteren" <[email-masked]>
Date: Mon, 03 Sep 2007 17:36:21 +0200

> In the latter case, we may want to re-add it in RFC2616bis.

There's also a Default-Style header. For both it's not really to me though  
what RFC 2616 would say about them though, other than maybe register the  
names.

-- 
Anne van Kesteren
<http://annevankesteren.nl/>
<http://www.opera.com/>

---

From: Julian Reschke <[email-masked]>
Date: Mon, 03 Sep 2007 17:48:02 +0200

Anne van Kesteren wrote:
> 
> On Sun, 02 Sep 2007 20:55:52 +0200, Julian Reschke 
> <[email-masked]> wrote:
>> the current editor's draft of HTML5 requires User-Agents to respect 
>> the HTTP Link header (as specified in RFC2068, and dropped from 
>> RFC2616) -- see <http://www.w3.org/html/wg/html5/#the-link>:
>>
>> into consideration as well. For the purposes of ordering, links 
>> defined by HTTP headers must be assumed to come before any links in 
>> the document, in the order that they were given in the HTTP entity 
>> header. Relative URIs in these headers must be resolved according to 
>> the rules given in HTTP, not relative to base URIs set by the document 
>> (e.g. using a base element or xml:base attributes). [RFC2616] [RFC2068]"
>>
>> the Link header has indeed improved lately (I'll guess in FF and 
>> Opera). In the latter case, we may want to re-add it in RFC2616bis.
> 
> There's also a Default-Style header. For both it's not really to me 
> though what RFC 2616 would say about them though, other than maybe 
> register the names.

One difference is that "Default-Style" is defined by HTML4, not an HTTP 
spec.

The "Link" header on the other hand is only defined by RFC2068, which 
has been obsoleted by RFC2616; so it's not defined by a "current" IETF 
spec. Furthermore, it defines something of universal use (for non-HTML 
documents as well), so it seems unwise to define it inside HTML.

Best regards, Julian

---

From: Mark Nottingham <[email-masked]>
Date: Tue, 4 Sep 2007 15:37:52 +1000

See:
   http://ietfreport.isoc.org/idref/draft-nottingham-http-link-header/

I still regularly get queries about the status of this; there are a  
fair number of interested people, so I think it's a good idea.

The blocking issue is 'rel', as discussed earlier; in a nutshell,  
HTML and Atom both have the concept of a link relation, but they have  
different syntax and possibly different semantics.

I've been thinking of writing up an I-D describing the problem, but  
as of yet haven't had time.

Cheers,

On 2007/09/03, at 4:55 AM, Julian Reschke wrote:

> "Some versions of HTTP defined a Link: header, to be processed like  
> a series of link  elements. When processing links, those must be  
> taken into consideration as well. For the purposes of ordering,  
> links defined by HTTP headers must be assumed to come before any  
> links in the document, in the order that they were given in the  
> HTTP entity header. Relative URIs in these headers must be resolved  
> according to the rules given in HTTP, not relative to base URIs set  
> by the document (e.g. using a base element or xml:base attributes).  
> [RFC2616] [RFC2068]"
>
> So either this is just wishful thinking, or implementation support  
> for the Link header has indeed improved lately (I'll guess in FF  
> and Opera). In the latter case, we may want to re-add it in  
> RFC2616bis.
>
> Best regards, Julian
>

--
Mark Nottingham       [email-masked]

---

From: Julian Reschke <[email-masked]>
Date: Tue, 04 Sep 2007 12:21:46 +0200

>   http://ietfreport.isoc.org/idref/draft-nottingham-http-link-header/

Yup. And: 
<http://greenbytes.de/tech/webdav/#draft-nottingham-http-link-header> :-)

> I still regularly get queries about the status of this; there are a fair 
> number of interested people, so I think it's a good idea.

Definitively; either stand-alone, or as part of RFC2616bis.

> The blocking issue is 'rel', as discussed earlier; in a nutshell, HTML 
> and Atom both have the concept of a link relation, but they have 

The current state of things is confusing. We have:

- HTML4 defining a LINK element, corresponding to the RFC2068-defined 
header (or the other way around)

- no link relation registry

- the HTML5 draft (<http://www.w3.org/html/wg/html5/#linkTypes>) 
stepping in and claiming the registry (currently a Wiki (!) at 
<http://wiki.whatwg.org/wiki/RelExtensions>)

- Atom (RFC4287) defining a registry 
<http://greenbytes.de/tech/webdav/rfc4287.html#rfc.section.7.1> for Atom 
links elements.

> I've been thinking of writing up an I-D describing the problem, but as 
> of yet haven't had time.

Let's try start by agreeing on the problem then.

IMHO...:

- The HTTP Link header allows to express relations between resources. 
The type of the relation is specified by the "rel" and "rev" parameters.

- The type of link relations in general is orthogonal to the type of 
document it occurs in. So it's not limited to (X)HTML and Atom feeds. 
Thus, a generic registry seems to make most sense.

- For experimentation, it might be a good idea to be able to mint 
relation identifiers without registering them centrally.

Finally, I'm not convinced that we have a syntax issue between HTML4 and 
Atom; I think we discussed this some time ago over on the mailing list 
(can you remind us what you think the problem is?). Right now, 
<http://www.iana.org/assignments/link-relations.html> doesn't seem to 
list anything problematic, and if there is a syntax conflict, we 
probably can have a small document updating that part of Atom.

Best regards, Julian

---

From: Julian Reschke <[email-masked]>
Date: Tue, 04 Sep 2007 13:09:04 +0200

Julian Reschke wrote:
> ...
> ...

OK, here's the whole thread: 
<http://lists.w3.org/Archives/Public/ietf-http-wg/2007JanMar/0129.html>.

Best regards, Julian