By dawehner on
Change record status: 
Published (View all published change records)
Project: 
Drupal core
Introduced in branch: 
8.x
Issue links: 
https://www.drupal.org/node/1987712
Description: 

Instead of calling file_download to serve a downloaded file you should use the file download controller Drupal\system\FileDownloadController, which itself gets the module handler Drupal::moduleHandler() injected.
Before

return file_download('temporary', 'config.tar.gz');

Now

use Drupal\system\FileDownloadController;

$this->fileDownloadController = new FileDownloadController($module_handler);
$request = new Request(array('file' => 'config.tar.gz'));
return $this->fileDownloadController->download($request, 'temporary');