DefaultFormatTestController.php in Drupal 10        
                          
                  
                        
  
  
  
  
File
  core/modules/system/tests/modules/default_format_test/src/DefaultFormatTestController.php
  
    View source  
  <?php
namespace Drupal\default_format_test;
use Drupal\Core\Cache\CacheableResponse;
use Symfony\Component\HttpFoundation\Request;
class DefaultFormatTestController {
  public function content(Request $request) {
    $format = $request
      ->getRequestFormat();
    return new CacheableResponse('format:' . $format, 200, [
      'Content-Type' => $request
        ->getMimeType($format),
    ]);
  }
}