Bolt: Extending the upload handler with custom sanitiser

uploadSanitiser.php

        $app['upload'] = $app->share(
            $app->extend(
                'upload',
                function ($uploadHandler) {

                    // Set max file size
                    $uploadHandler->addRule('size', ['max' => '2M'])

                    // Sanitize filename
                    $uploadHandler->setSanitizerCallback(
                        function ($filename) {
                            // Do things with filename string here.
                            return $filename;
                        }
                    );
                    
                    return $uploadHandler;
                }
            )
        );