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Re: using BlobBuilder append method with generated binary data

From: Toni Ruottu <toni.ruottu@iki.fi>
Date: Mon, 6 Dec 2010 22:34:43 +0200
Message-ID: <AANLkTi=betDdbiegTSB4ERUC1Bb=CwjQfdwqrYGvF_1D@mail.gmail.com>
To: Paul Kinlan <paulkinlan@google.com>
Cc: Eric Uhrhane <ericu@google.com>, "public-webapps@w3.org" <public-webapps@w3.org>
I do not think UInt8Array has any data. It is just a view for
accessing the buffer.


On Sat, Dec 4, 2010 at 1:12 AM, Paul Kinlan <paulkinlan@google.com> wrote:
> I might have missed something but for appending client-side generated
> data to a blob can't you just append a UInt8Array as that is based off
> ArrayBuffer?
> I use it to generate zip files client side and attach them to an
> iframe so they are downloaded.
> P
> On Thursday, December 2, 2010, Toni Ruottu <toni.ruottu@iki.fi> wrote:
>> My code had a bug in it. The APIs seem to be working ok for my purposes.
>> Using the APIs, I was able to write Firefox's sendAsBinary method for chrome.
>> It is available from http://javascript0.org/wiki/Portable_sendAsBinary
>>   --Toni
>> On Tue, Nov 16, 2010 at 5:25 PM, Toni Ruottu <toni.ruottu@iki.fi> wrote:
>>> Sorry for slow answer. Took me a while to get on top of this. I think
>>> they just might answer my problem. However, I can not really tell
>>> before I see a working implementation. I wrote a test. See
>>> http://www.cs.helsinki.fi/u/twruottu/testi/bpost3.html It does not
>>> currently work with the latest development version of Chrome. I
>>> wonder, if I am doing something wrong.
>>>  --Toni
>>> On Wed, Oct 20, 2010 at 6:17 PM, Eric Uhrhane <ericu@google.com> wrote:
>>>> Toni:
>>>>    BlobBuilder now has an append() method that takes an ArrayBuffer,
>>>> and FileReader has readAsArrayBuffer.  Do these together satisfy your
>>>> needs?
>>>>        Eric
>>>> On Wed, Oct 20, 2010 at 3:39 AM, Toni Ruottu <toni.ruottu@iki.fi> wrote:
>>>>> I have discussed the topic before on some Chromium bug threads. I
>>>>> searched the archives of this mailing list for blobs and generated
>>>>> content, but was not too successful. There may be multiple different
>>>>> reasons why one would need to build blobs from generated data. The one
>>>>> that concerns me, is being able to do binary POSTs with XmlHTTPRequest
>>>>> in a standard manner. To send binary data over XHR one is required to
>>>>> send out a blob, but first the blob needs to be constructed with
>>>>> BlobBuilder. Let me fill you in on how I see the current situation.
>>>>> Maybe someone can spot an error in my line of thought.
>>>>> A new (empty) BlobBuilder is created by stating...
>>>>> var bb = new BlobBuilder();
>>>>> After creating a BlobBuilder, the user appends some data into the blob
>>>>> being generated by using the append function. The append function is
>>>>> overloaded and can be used to append multiple different types of data
>>>>> into the blob. Currently only existing blobs, and utf-8 text are
>>>>> supported.
>>>>> One can add an existing blob into the new one by doing...
>>>>> bb.append(existingBlob);
>>>>> One can add a text string in utf-8 format by doing...
>>>>> bb.append(aTextString);
>>>>> Once the data is in there, it is possible to construct the new blob with...
>>>>> var blob = bb.getBlob()
>>>>> A blob has a slice method which makes it possible to turn a large blob
>>>>> into smaller ones. It is thus possible to cut out single bytes from a
>>>>> blob and use them construct new blobs by appending copies of these
>>>>> sample bytes together with the BlobBuilder.
>>>>> As sample bytes can only be generated by writing text into the blob as
>>>>> utf-8, it is not possible to generate all 8-bit patterns. More
>>>>> specifically, the bit patterns that are illegal in any given utf-8
>>>>> string, are not possible to generate using the current API. This leads
>>>>> developers into using various hacks to overcome the issue.
>>>>> For example one could ask the user to provide a file with sample
>>>>> bytes. Methods for reading a file into a blob are available, so there
>>>>> is no need to generate the sample bytes. There is however no way to
>>>>> make sure that the user provided a file with correct bit-patterns as
>>>>> the blob interface is to a large degree a read-only interface. A
>>>>> demonstration of using a file to overcome the issue is available at
>>>>> http://www.cs.helsinki.fi/u/twruottu/testi/bpost.html
>>>>> To solve the problem a third append function which accepts a list of
>>>>> integers, and adds the corresponding bytes into the blob is needed.
>>>>> Once such method has been introduced it should be possible to write
>>>>> the 7-bit ascii string "foo" into a BlobBuilder by doing...
>>>>> bb.append([102,111,111]);
>>>>> It should also be possible to add bytes 0x00 a
> --
> Paul Kinlan
> Developer Advocate @ Google for Chrome and HTML5
> t: +447730517944
> tw: @Paul_Kinlan <http://twitter.com/paul_kinlan>
> LinkedIn: http://uk.linkedin.com/in/paulkinlan
> Blog: http://paul.kinlan.me
> Skype: paul.kinlan
Received on Monday, 6 December 2010 20:35:16 UTC

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