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Re: [XHR][XHR2] HTTP redirects / XHR Version detection

From: Anne van Kesteren <annevk@opera.com>
Date: Sat, 30 Jan 2010 13:41:47 +0100
To: "David Bruant" <dbruant@ucsd.edu>, public-webapps@w3.org
Message-ID: <op.u7civxs964w2qv@annevk-t60>
On Sat, 23 Jan 2010 23:05:50 +0100, David Bruant <dbruant@ucsd.edu> wrote:
> My comments and questions are based on the editor's drafts  
> (http://dev.w3.org/2006/webapi/XMLHttpRequest/ and  
> http://dev.w3.org/2006/webapi/XMLHttpRequest-2).
>
> Between the two versions of the same-origin request event rules  
> (#same-origin-request-event-rules), for the "If the response is an HTTP  
> redirect" rule, the word "transparently" has disappeared. I understood  
> the word "transparently" as "don't consider any other step of the  
> algorithm" (like switching to the HEADERS_RECEIVED state, because if a  
> redirect has been detected, it means that the headers has been received  
> at least the location header).
> The absence of this word in XHR2 suggests that the state should be  
> switched to HEADERS_RECEIVED even if it is a redirect.
>
> So, more generally, my question is : for HTTP redirects, should the  
> implementations of XHR and XHR2 switch the state to HEADERS_RECIEVED ? I  
> don't know how it is currently implemented by the current browsers, but  
> I would be in favor of switching the state (and thus dispatch an event)  
> so that authors could write tools allowing them to have an idea of the  
> number of redirects generated by some URL and then do an analysis of  
> their websites (for instance all the links within a HTML page) "from the  
> client side".

The idea is actually that a redirect does not involve a "state"  
transition. I have suggested on this mailing list a way to control whether  
redirects are followed but due to lack of response I have not done  
anything with it so far.

Would it be clearer if after "Once all HTTP headers have been received and  
the asynchronous flag is true" I added "(and this is not an HTTP  
redirect)"?


> My next question should find its answer thanks to the previous one, but  
> juste to be sure : Is it possible that the state be to DONE and the  
> status be a redirect (300 <= status < 400) ?

If there is no Location header this is possible. (Have not tested whether  
this is correctly implemented.)


> If the behavior has changed between XHR and XHR2, how authors can know  
> what version is implemented by user agents ? In other words, is there a  
> way defined by the spec to make the difference between a XHR "conforming  
> user agent" and a XHR2 "conforming user agent" since the interface has  
> the same name (XMLHttpRequest) ?

No, because in general user agents do not implement everything from one or  
the other. E.g. a couple of user agents implemented features from XHR2 but  
are not at all conforming to XHR1 requirements that did not change in  
XHR2. Implementations evolve organically, not in concrete steps.


-- 
Anne van Kesteren
http://annevankesteren.nl/
Received on Saturday, 30 January 2010 12:42:25 GMT

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