protected function getDefaultHeaders()
    {
        $headers = array();

        $mimeType = $this->calendar->getContentType();
        $headers['Content-Type'] = sprintf('%s; charset=utf-8', $mimeType);

        $filename = $this->calendar->getFilename();
        $headers['Content-Disposition'] = sprintf('attachment; filename="%s', $filename);

        return $headers;
    }