Javascript :: Returning A Byte String To ExternalInterface.call Throws An Error?

I am working on my open source project Downloadify, and up until now it simply handles returning Strings in response to ExternalInterface.call commands.

I am trying to put together a test case using JSZip and Downloadify together, the end result being that a Zip file is created dynamically in the browser, then saved to the disk using FileReference.save. However, this is my problem:

The JSZip library can return either a base64 encoded string of the Zip, or the raw byte string. The problem is, if I return that byte string in response to the ExternalInterface.call command, I get this error:

Error #1085: The element type "string" must be terminated by the matching end-tag "</string>"

ActionScript 3:

var theData:* = ExternalInterface.call('Downloadify.getTextForSave',queue_name);

Where queue_name is just a string used to identify the correct instance in JS.

JavaScript:

var zip = new JSZip();
zip.add("test.txt", "Hello world!
");
var content = zip.generate(true);
return content;

If I instead return a normal string instead of the byte string, the call works correctly.I would like to avoid using base64 as I would have to include a base64 decoder in my swf which will increase its size.

Finally: I am not looking for a AS3 Zip generator. It is imperative to my project to have that part run in JavaScript