Classmethod that applies conditional encoding based on
        mime-type. Given an entry as returned by __call__ return the
        data in the appropriate encoding.

def encode(cls, entry):
        """
        Classmethod that applies conditional encoding based on
        mime-type. Given an entry as returned by __call__ return the
        data in the appropriate encoding.
        """
        (data, info) = entry
        if info['mime_type'] in cls.utf8_mime_types:
            return data.encode('utf-8')
        else:
            return data