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Re: Erratum on HTTP_RESPONSE-11 for mobileOK Basic Tests 1.0?

From: Francois Daoust <fd@w3.org>
Date: Thu, 20 May 2010 15:33:39 +0200
Message-ID: <4BF53A33.1010901@w3.org>
To: Jo Rabin <jo@linguafranca.org>
CC: Mobile Web Best Practices Working Group WG <public-bpwg@w3.org>
Following the group's resolution on Tuesday, I added the erratum to the 
errata document (linked from the top of the mobileOK Basic Tests 1.0 spec):
http://www.w3.org/2008/12/mobileok-errata.html#ed-1

Francois.

On 05/06/2010 03:56 PM, Jo Rabin wrote:
> I'm grateful to Francois for stepping me through the ins and outs of
> this rule (off line), and apologise to him for being opaque in my
> understanding - but I now see what he means and agree with his proposed
> erratum.
>
> I'd go further and say that the clause relating to HTTP_RESPONSE-11
> could be better clarified as:
>
> [[ If the HTTP status represents failure (4xx), other than *in any of
> the following cases: i)* the HTTP status is 404, *ii) the HTTP status
> represents* a request for authentication (e.g. 401) or *iii) the HTTP
> status is* 406 *for object elements (but not any other elements)* when
> carrying out the 3.15.1 Object Element Processing Rule, FAIL ]]
>
> Jo
>
> On 03/05/2010 14:49, Francois Daoust wrote:
>> Hi BPWG,
>>
>> This is proposal to clarify the application of the HTTP_RESPONSE-11
>> failure message on images in an erratum of the mobileOK Basic Tests 1.0
>> recommendation.
>>
>>
>> Context
>> -----
>> A bit less than two years ago, on our way to finalizing mobileOK, we
>> spent some time playing (sigh!) with a section in the spec entitled
>> "Object Element Processing Rule":
>> http://www.w3.org/TR/mobileOK-basic10-tests/#ObjectElementProcessingRule
>>
>> For objects that define a type "attribute" set to a content-type not
>> supported by the DDC, it is actually quite normal for a server to reply
>> with a 406 HTTP status code if the browser still tries to retrieve the
>> resource. Mobile browsers do not have to retrieve such objects in
>> theory, but the above-mentioned algorithm on object element processing
>> kind of ignores the "type" attribute for good reasons that are not the
>> topic of this email.
>>
>> As a consequence, not to trigger an HTTP_RESPONSE-11 on objects
>> retrieved by the Checker for testing purpose, one of the last changes we
>> made to the spec was to add an exception to the HTTP_RESPONSE-11 message
>> that says that 406 status codes received when carrying out the object
>> element processing rule should be ignored:
>> http://www.w3.org/TR/mobileOK-basic10-tests/#http_response-11
>> (I plead guilty for that change, but the change in itself is not the
>> problem anyway)
>>
>>
>> Problem
>> -----
>> The problem is that, in the absence of object elements, with the
>> following code, and supposing that the image is only available as a PNG
>> image and that the server returns a 406 status code when the mobileOK
>> Checker tries to retrieve the image (because of the Accept HTTP field
>> set by the mobileOK Checker):
>> <img src="bad.png" alt="The great BPWG group" />
>>
>> ... should HTTP_RESPONSE-11 be triggered?
>>
>> I would expect it to be the case, because the server cannot serve the
>> image in the appropriate format and fails to remove the img tag (as
>> opposed to object elements, it is not possible to indicate the type of
>> an image using a type attribute), thus requiring a useless HTTP exchange.
>>
>> Problem is the spec can be interpreted either way, IMO, because the 406
>> exception covers the whole object element processing rule which starts
>> with:
>> [[
>> For each img element that has no object element ancestor (other than the
>> context node) in this context:
>> Treat this image as an Included Resource (and carry out appropriate
>> tests).
>> ]]
>> In short, the 406 exception seems to apply to img elements as well or
>> not, depending on whether you treat images as regular included resources
>> before or after the retrieval.
>>
>>
>> Proposal
>> -----
>> I propose to clarify, in an erratum, that the HTTP_RESPONSE-11
>> description should rather read (added text between "*"):
>> [[ If the HTTP status represents failure (4xx), other than 404, a
>> request for authentication (e.g. 401) or a 406 *for object elements*
>> when carrying out the 3.15.1 Object Element Processing Rule, FAIL ]]
>>
>>
>> What do you think?
>>
>> Francois.
>>
>
Received on Thursday, 20 May 2010 13:34:17 UTC

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