TYPO3 ExtBase: Force download of a file from a controller action. Example will force download a file from a folder defined in the TypoScript settings for the extension

downloadAction.php

/**
 * @param string $fileName
 * @return void
 */  
public function downloadAction($fileName) {

    $file = $this->settings['uploadFolder'] . 'uploadedPhotos/' . $fileName;        

    if(is_file($file)) {

        $fileLen    = filesize($file);          
        $ext        = strtolower(substr(strrchr($fileName, '.'), 1));

        switch($ext) {
            case 'txt':
                $cType = 'text/plain'; 
            break;              
            case 'pdf':
                $cType = 'application/pdf'; 
            break;
            case 'exe':
                $cType = 'application/octet-stream';
            break;
            case 'zip':
                $cType = 'application/zip';
            break;
            case 'doc':
                $cType = 'application/msword';
            break;
            case 'xls':
                $cType = 'application/vnd.ms-excel';
            break;
            case 'ppt':
                $cType = 'application/vnd.ms-powerpoint';
            break;
            case 'gif':
                $cType = 'image/gif';
            break;
            case 'png':
                $cType = 'image/png';
            break;
            case 'jpeg':
            case 'jpg':
                $cType = 'image/jpg';
            break;
            case 'mp3':
                $cType = 'audio/mpeg';
            break;
            case 'wav':
                $cType = 'audio/x-wav';
            break;
            case 'mpeg':
            case 'mpg':
            case 'mpe':
                $cType = 'video/mpeg';
            break;
            case 'mov':
                $cType = 'video/quicktime';
            break;
            case 'avi':
                $cType = 'video/x-msvideo';
            break;

            //forbidden filetypes
            case 'inc':
            case 'conf':
            case 'sql':                 
            case 'cgi':
            case 'htaccess':
            case 'php':
            case 'php3':
            case 'php4':                        
            case 'php5':
            exit;

            default:
                $cType = 'application/force-download';
            break;
        }

        $headers = array(
            'Pragma'                    => 'public', 
            'Expires'                   => 0, 
            'Cache-Control'             => 'must-revalidate, post-check=0, pre-check=0',
            'Cache-Control'             => 'public',
            'Content-Description'       => 'File Transfer',
            'Content-Type'              => $cType,
            'Content-Disposition'       => 'attachment; filename="'. $fileName .'"',
            'Content-Transfer-Encoding' => 'binary', 
            'Content-Length'            => $fileLen         
        );

        foreach($headers as $header => $data)
            $this->response->setHeader($header, $data); 

        $this->response->sendHeaders();                 
        @readfile($file);   

    }   
    exit;   
}