Sf 1.4. send an Excel file to browser

gistfile1.txt

$this->getResponse()->clearHttpHeaders();
$this->getResponse()->setStatusCode(200);
$this->getResponse()->setContentType('application/vnd.ms-excel');
$this->getResponse()->setHttpHeader('Content-Disposition', "attachment; filename=filename.xls");
$this->getResponse()->setHttpHeader('Content-Transfer-Encoding', 'binary');
$this->getResponse()->setHttpHeader('Content-Length', $file_size); 

return $this->renderText($file_contents);