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Re: XML base after redirection

From: Nathan <nathan@webr3.org>
Date: Tue, 26 Oct 2010 12:54:29 +0100
Message-ID: <4CC6C175.406@webr3.org>
To: Tim Berners-Lee <timbl@w3.org>
CC: TAG List <www-tag@w3.org>
Tim Berners-Lee wrote:
> Looking at my action item to characterize the deductions made from HTTP responses in the tabulator library, I found these related questions:
> 
> 1) If A redirects 301 "Moved" to B, what should be the XML base which is used to parse the representation returned from B?
> 
> 2) If A redirects 302 "Found" to B, what should be the XML base which is used to parse the representation returned from B?
> 
> I assume everybody parses with B as the base.
> 
> One could make an argument that in the Found case, the original URI is the one everyone should use for the document, and so any self-reference ought also to apply to A, which is best served by 
> Example:  a canonical place for an ontology is redirected Found to a SVN store where the current 
> version of the ontology file is. That file says    in N3  <> dc:title "This is an ontology which...".
> 
> What do people thing about (a) logic and (b) current practice?

Regarding (b):

The short version is that most of the time only URI A is known, and any 
redirected-to URIs are hidden within blackbox client libs; the common 
approach is:

   uri = 'http://...';
   doc = get(uri);
   dom = parse(doc,uri);

Where get is a method which follows redirects, thus the true Location of 
the document is often unconsidered and the URI used as base is that 
which was requested.

I've checked XMLHttpRequest by setting xhr.followRedirects = true;

The results for 1) /foo => 301 /nathan are:

  xhr.responseXML.URL = "http://webr3.org/foo";
  xhr.responseXML.baseURI = "http://webr3.org/foo";
  xhr.responseXML.documentURI = "http://webr3.org/foo";

The results for 2) /bar => 302 /nathan are:

  xhr.responseXML.URL = "http://webr3.org/bar";
  xhr.responseXML.baseURI = "http://webr3.org/bar";
  xhr.responseXML.documentURI = "http://webr3.org/bar";

In fact it goes one further, I actually couldn't find any way to get the 
redirected-to URI (/nathan) back out from XHR - it's completely hidden.

This is also the case for many (most) server side HTTP clients which 
follow redirects.

Thus in most cases, the only URI known is that which was originally 
requested.

The only common exception I know is that for 2xx responses which have 
been conneg'd, then the Content-Location header is exposed on request, 
but again it isn't used at all.

Best,

Nathan
Received on Tuesday, 26 October 2010 11:55:27 GMT

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