public function setMagicFile($file)
    {
        if (empty($file)) {
            $this->_magicfile = null;
        } else if (!is_readable($file)) {
            require_once 'Zend/Validate/Exception.php';
            throw new Zend_Validate_Exception('The given magicfile can not be read');
        } else {
            $this->_magicfile = (string) $file;
        }

        return $this;
    }