两次下载CSV文件

Question

我正在使用以下代码下载csv文件。

static function download(){

        $wooe_download = filter_input(INPUT_GET, 'woooe_download', FILTER_DEFAULT);
        $wooe_filename = filter_input(INPUT_GET, 'filename', FILTER_DEFAULT);

        if( !empty($wooe_filename) && !empty($wooe_download) && file_exists(path_join( self::upload_dir(), $wooe_filename.'.csv'))
            && wp_verify_nonce($wooe_download, 'woooe_download')
        )
        {
            $charset    =   get_option('blog_charset');
            $csv_file   =   path_join( self::upload_dir(), $wooe_filename.'.csv');

            header('Content-Description: File Transfer');
            header('Content-Type: application/octet-stream');
            header("Content-Disposition: attachment; filename=". self::filename());
            header("Expires: 0");
            header('Cache-Control: must-revalidate');
            header('Content-Encoding: '. $charset);
            header('Pragma: public');
            //header('Content-type: text/csv; charset='. $charset);
            header('Content-Length: ' . filesize($csv_file));
            //header("Pragma: public");
            readfile($csv_file);
            //unlink($csv_file);
            exit;
        }
    }

文件已在浏览器中下载了两次。我不确定如何将其限制为仅一次？