public function getHeaders(ResponseBag $bag)
{
if (!$bag->has(self::FILENAME)) {
throw new \Exception('Missing filename for streamed response');
}
$bag->addHeader('X-Sendfile', $bag->get(self::FILENAME));
$bag->addHeader('X-Accel-Buffering', 'no');
$bag->addHeader('Transfer-Encoding', 'chunked');
$bag->addHeader('Content-Type', 'application/force-download');
$bag->addHeader('Content-Disposition', sprintf('%s; filename="%s"', $bag->get(self::ATTACHMENT_DISPOSITION, 'attachment'), $bag->get(self::FILENAME)));
return $bag->getHeaders();
}