Unfortunately, groovr appears to circumvent internal copyright protections for content hosted at Grooveshark. The groovr library offered a way to get, and subsequently allow you to easily download, song mp3s via a call (groovr.getSongFile). It was able to provide these services by using our internal authentication methods and internal API.
Grooveshark offers a public API (http://developers.grooveshark.com/) which allows you to search for content, authenticate users, view popular music, and more, all for free. Developers are encouraged to register for a key and use our content for their applications.