Base64URL decoding via JavaScript?

Question

So I'm stumped. I know there's lots of Base64 encoders/decoders for JS, but not for the modified (and Facebook-favored) Base64URL variation. So far searching across stackoverflow has come up dry.

Yes, I could use PHP or another server-side library to decode this, but I'm trying to keep this universal regardless of what platform I'm using... for example, if I were to host a HTML-only Facebook app on Amazon S3/CloudFront and only use their JS SDK and jQuery to take care of processing forms and getting data.

That said, does anyone know of any Base64URL-specific decoders for JavaScript?

Thanks in advance!

Answer 1

Use this before decoding :

var decode = function(input) {
        // Replace non-url compatible chars with base64 standard chars
        input = input
            .replace(/-/g, '+')
            .replace(/_/g, '/');

        // Pad out with standard base64 required padding characters
        var pad = input.length % 4;
        if(pad) {
          if(pad === 1) {
            throw new Error('InvalidLengthError: Input base64url string is the wrong length to determine padding');
          }
          input += new Array(5-pad).join('=');
        }

        return input;
    }

After using this function you can use any base64 decoder

Answer 2

Solution:

var b64str = base64.encode('foo bar');

// fix padding according to the new format
b64str = b64str.padRight(b64str.length + (4 - b64str.length % 4) % 4, '=');

Using this great base64 encode/decode: http://code.google.com/p/stringencoders/source/browse/trunk/javascript/base64.js

Also depends on the padRight method:

String.prototype.padRight = function(n, pad){
    t = this;
    if(n > this.length)
        for(i = 0; i < n-this.length; i++)
            t += pad;
    return t;
}