Re: File API - Progress - Question about Partial Blob data

Le 21/08/2013 16:16, Arun Ranganathan a écrit :
> On Aug 20, 2013, at 7:13 PM, Aymeric Vitte wrote:
>
>> The specs says :
>>
>> " It can also return /partial Blob data/. Partial Blob data is the 
>> part of the |File| <http://www.w3.org/TR/FileAPI/#dfn-file> or |Blob| 
>> <http://www.w3.org/TR/FileAPI/#dfn-Blob> that has been read into 
>> memory /currently/; when processing the read method 
>> <http://www.w3.org/TR/FileAPI/#read-methods> |readAsText| 
>> <http://www.w3.org/TR/FileAPI/#dfn-readAsText>, partial Blob data is 
>> a |DOMString| that is incremented as more bytes are |loaded| (a 
>> portion of the |total|) [ProgressEvents 
>> <http://www.w3.org/TR/FileAPI/#ProgressEvents>], and when processing 
>> |readAsArrayBuffer| 
>> <http://www.w3.org/TR/FileAPI/#dfn-readAsArrayBuffer> partial Blob 
>> data is an |ArrayBuffer| [TypedArrays 
>> <http://www.w3.org/TR/FileAPI/#TypedArrays>] object consisting of the 
>> bytes |loaded| so far (a portion of the |total|)[ProgressEvents 
>> <http://www.w3.org/TR/FileAPI/#ProgressEvents>]. The list below is 
>> normative for the |result| attribute and is the conformance criteria 
>> for this attribute"
>>
>> What is the rationale for that? The result attribute should better 
>> contain for progress events the latest data read and not the data 
>> read from the begining that you could easily reconstitute while the 
>> contrary requires more work.
>>
>> Use case: calculate the hash of a file while you are reading it.
>
>
> The ask for "deltas" to be sent with progress notifications came up on 
> this listserv before -- see the thread starting at 
> http://lists.w3.org/Archives/Public/public-webapps/2013JanMar/0069.html
>
> I agree that the deltas model is also useful, but you can see there's 
> some implementation history with XHR here as well.  The use case is to 
> receive the file bits as they are constituted from the read (just as 
> with an HTTP request, where you get the bits "so far" till the rest 
> are constituted).
>
> A good way to solve the use case of meaningful deltas might be with 
> the Streams API, still TBD.
>
>
>> PS: I did not test it in all browsers, but unless I am using it 
>> wrongly, the result attribute is always null for progress events.
>
>
> But not null for the onload ?  In many cases, a progress might not 
> fire, depending on file size.

No, only for progress, which does fire for files of several MB.

I don't know about the XHR history but what is the use case of 
incremented data (which is not implemented currently)?

>
> -- A*

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