Re: XHR.responseBlob and BlobWriter [nee FileWriter]

On Mon, Jun 28, 2010 at 6:58 PM, Eric Uhrhane <ericu@google.com> wrote:

> The discussion at [1] got tangled up with the debate of .URL vs. .url,
> so I'm starting a new thread to pick back up the original topic: how
> do we save binary data from XMLHttpRequest?  Here's my proposal [built
> mainly from the good ideas other folks posted in the original thread].
>
> Use case 1: the developer wants to download a Blob of data, use it for
> a while [e.g. slicing out sub-Blobs and displaying them as images],
> then have it go away automatically.
> Use case 2: the developer wants to download a Blob of data, saving it
> in a location of the user's choice outside the sandbox.
> Use case 3: the developer wants to download a Blob of data, save it in
> the sandboxed FileSystem, and access it again later.
>
> XHR will have a responseBlob property.
> In order to signal the XHR that it should spool to disk and supply
> responseBlob, a flag must be set before send() is called.  Call this
> wantBlob for now, although a better name would be appreciated.
> If wantBlob is set, responseBlob will be valid when the XHR completes,
> and responseText and responseXML will be null.
> If wantBlob is not set, responseBlob will be null, and the XHR will
> function as it does now.
>
> When wantBlob is set, on all progress events before the XHR is
> complete, responseBlob will be null.  As of completion, it will return
> a Blob containing the full contents of the download.  [We could later
> add incremental Blobs in progress events, but let's keep this simple
> to start with.]
>
> This satisfies use case 1 as-is.
> With the BlobWriter spec [2], as currently written [assuming we agree
> on how to get our hands on a BlobWriter], it takes care of use case 2.
> With the FileSystem spec [3], as currently written, it takes care of use
> case 3.
>
> I think this takes care of the major use cases, doesn't force anyone
> to implement FileSystem to solve the cases that don't really require
> it, removes any need for synchronous IO, and is pretty simple for
> developers to understand and use.  What do you think?
>

SGTM


>
>       Eric
>
> [1]
> http://lists.w3.org/Archives/Public/public-webapps/2010AprJun/0313.html
> [2] http://dev.w3.org/2009/dap/file-system/file-writer.html
> [3] http://dev.w3.org/2009/dap/file-system/file-dir-sys.html
>