Post binary data cross domain in javascript

I'm writing a Chrome browser extension that takes a snapshot of the current tab's view and uploads it to a web service API that I don't control. The Chrome extension library has a function (chrome.tabs.captureVisibleTab. see http://code.google.com/chrome/extensions/tabs.html) that takes a snapshot and returns the data in a data url. I'm at an impasse as to how to get that data uploaded.

I've tried to write my own multipart-form request and use an ajax request to POST the data. But, ajax insists on UTF-8 encoding the data and the API insists on 8开发者_开发知识库-bit encoded binary. I thought maybe using a file uploader plugin like http://malsup.com/jquery/form/ would work, but I can't seem to get the data from the JS variable into a form the uploader will take.

Any ideas for at least a new path of investigation would be highly appreciated.

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Turns out that you can do this.

Chrome has a way to send a blob via XMLHTTPRequest.

Here's a link to example code from the Chromium issue tracker:

http://code.google.com/p/chromium/issues/detail?id=35705#c34

XMLHttpRequest.prototype.sendAsBinary = function(datastr,contentType) {
    var bb = new BlobBuilder();
    var len = datastr.length;
    var data = new Uint8Array(len);
    for (var i=0; i<len; i++) {
            data[i] = datastr.charCodeAt(i);
    }
    bb.append(data.buffer);
    this.send(bb.getBlob(contentType));
}