How do I do base64 encoding in LibSass?

Question

I have a bunch of SVGs that get color and parameter adaptations in Sass and then when called to be background-image. That's done using something like:

this @function(@params) dostuff..
    @return url('data:image/svg+xml;base64,'+ base64_encode($svg));

The base64_encode function is ruby but with ever growing Sass we're looking at switching to LibSass but i have so far been unable to get base64 encoding to work with LibSass. How do i get base64 encoding in LibSass?