PHP检测文件能否下载

用php代码检测一个文件是否可以下载，网上没有找到合适的代码，自己实现了一个还挺好用的，分享给有需要的朋友。

基本原理：使用http的HEAD方法，检测报文的头里httpcode是否为200。

 public static function curlDetectFileExists($url)
 {
     $ch = curl_init($url);
     curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
     curl_setopt($ch, CURLOPT_HEADER, true);
     curl_setopt($ch, CURLOPT_NOBODY, true);
     curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 5);
     $result = curl_exec($ch);
     $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
     $httpInfo = curl_getinfo($ch);
     $httpInfoString = json_encode($httpInfo);
     $errMsg = null;
     $errCode = null;
     if ($httpCode !== 200)
     {
         $errMsg = $httpInfoString;
         $errCode = false;
     }
     else
     {
         $errMsg = "OK";
         $errCode = true;
     }
     $obj = array(
         'code' => $errCode,
         'HttpCode' => $httpCode,
         'HttpInfo' => $httpInfoString,
     );
     return $obj;
 }