MD5 in XULRunner (or Firefox extensions) 2007/11/15

Rather than including an outside JavaScript library just to do MD5 sums, how about using Mozilla's nsICryptoHash interface?  For the Flickr API, this took slightly more effort than expected because it only returns data in base64-encoded ASCII or binary.  Fortunately for me, the binary format was packed as a string, so making this usable was a matter of a little bin2hex function.  Behold:

var _md5 = null;
try {
	_md5 = Cc['@mozilla.org/security/hash;1'].createInstance(Ci.nsICryptoHash);
} catch (err) {
	Components.utils.reportError(err);
}
var md5 = function(str) {
	if (null == _md5) {
		return '';
	}

	// Build array of character codes to MD5
	var arr = [];
	var ii = str.length;
	for (var i = 0; i < ii; ++i) {
		arr.push(str.charCodeAt(i));
	}
	_md5.init(Ci.nsICryptoHash.MD5);
	_md5.update(arr, arr.length);
	var hash = _md5.finish(false);

	// Unpack the binary data bin2hex style
	var ascii = [];
	ii = hash.length;
	for (var i = 0; i < ii; ++i) {
		var c = hash.charCodeAt(i);
		var ones = c % 16;
		var tens = c >> 4;
		ascii.push(String.fromCharCode(tens + (tens > 9 ? 87 : 48)) +
			String.fromCharCode(ones + (ones > 9 ? 87 : 48)));
	}

	return ascii.join('');
};