Drupal 8 - sending files to browser via route module - file

Question

I have a module, and inside this module, there should be a new route in the .routing.yml with:
path: '/file_exporter/{filename}'
defaults:
_controller: '\Drupal\file_exporter\Controller\ExportController::file_export'
Inside the ExportController, there is happening a bit magic, where a file is created depending on the user and other circumstances, and this works fine, and i have this file in a temp folder inside the module.
But how could i send it to the browser with drupal?
Target ist, that i have a link on another site to /fileexporter/file_123.xyz and a click on this link lets the browser directly download the new generated file_123.xyz
Is there a class which i could extend, or a function that i could use in Drupal 8 to send files direct to browsers via a Route and a Controller?

Answer 1

The trick is in using BinaryFileResponse.
Here's an example function that handles setting up the HTTP headers and content type and returns a BinaryFileResponse:
<?php
// $uri: the file you want to send, as a URI (e.g. private://somefile.txt)
// $ofilename: the output filename, this will be displayed in the browser.
// $contenttype: the mime content type for the browser
// $delete_after_send: delete the file once it's been sent to the browser
function mymodule_transfer_file($uri, $ofilename, $contenttype = NULL, $delete_after_send = FALSE) {
$mime = \Drupal::service('file.mime_type.guesser')->guess($uri);
$headers = array(
'Content-Type' => $mime . '; name="' . Unicode::mimeHeaderEncode(basename($uri)) . '"',
'Content-Length' => filesize($uri),
'Content-Disposition' => 'attachment; filename="' . Unicode::mimeHeaderEncode($ofilename) . '"',
'Cache-Control' => 'private',
);
if (isset($contenttype)) {
$headers['Content-Type'] = $contenttype;
}
if ($delete_after_send) {
// Delete after end of script.
drupal_register_shutdown_function('file_unmanaged_delete', $uri);
}
$uri_obj = new Uri($uri);
return new BinaryFileResponse($uri, 200, $headers, $uri_obj->getScheme() !== 'private');
}