php怎么将数据写入指定url的txt中，然后并返回保存地址提供下载？

/**

* 写入日志

* @param [type] $data [description]

* @param string $url [description]

* @return [type] [description]

*/

function writeLogs($data,$file_name=""){

$contents = "";

foreach ($data as $k => $v) {

$contents .=$v.";\r\n";

}

$file_url = "./upload/log";

if(!is_dir($file_url))mkdir($file_url,0777,true);

file_put_contents($file_url.$file_name,$contents);

return $url = $file_url.$file_name;

}