点击下载图片、文档等文件（不打开不预览）

public function downloadOne()
    {
        $file_name = input('file_name'); //远程地址或本地都可以
        $mime = 'application/force-download';
        header('Pragma: public'); // required
        header('Expires: 0'); // no cache
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Cache-Control: private',false);
        header('Content-Type: '.$mime);
        header('Content-Disposition: attachment; filename="'.basename($file_name).'"');
        header('Content-Transfer-Encoding: binary');
        header('Connection: close');
        readfile($file_name); // push it out
        exit();
    }