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;
}