I should set up a simple download manager and I don't understand whay this code doesn't work:

protected function doDownload($filename){
        //$this->_helper->layout()->disableLayout();
        //$this->_helper->viewRenderer->setNoRender(true);
        $dir = Zend_Registry::get('dir');
        $file = $dir->assets.$filename;
        if(file_exists($file)){
            $response = $this->getResponse();
            $response->setHeader('Content-Description','File Transfer', true);
            $response->setHeader('Content-Type','application/octet-stream', true);
            $response->setHeader('Content-Disposition','attachment; filename='.basename($file), true);
            $response->setHeader('Content-Transfer-Encoding','binary', true);
            $response->setHeader('Expires','0', true);
            $response->setHeader('Cache-Control','must-revalidate, post-check=0, pre-check=0', true);
            $response->setHeader('Pragma','public', true);
            $response->setHeader('Content-Length: ' , filesize($file),true);
            ob_clean();
            flush();
            readfile($file);
            exit(0);
          /*header('Content-Description: File Transfer');
            header('Content-Type: application/octet-stream');
            header('Content-Disposition: attachment; filename='.basename($file));
            header('Content-Transfer-Encoding: binary');
            header('Expires: 0');
            header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
            header('Pragma: public');
            header('Content-Length: ' . filesize($file));
            ob_clean();
            flush();
            readfile($file);
            exit(0);*/

         }


    }

yorumladı kodu ile script çalışıyor ise.