php获取远程文件的大小

function remote_filesize($url, $user = "", $pw = "")
{
    ob_start();
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_HEADER, 1);
    curl_setopt($ch, CURLOPT_NOBODY, 1);
    if(!empty($user) && !empty($pw))
    {
        $headers = array('Authorization: Basic ' .  base64_encode("$user:$pw"));
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    }
    $ok = curl_exec($ch);
    curl_close($ch);
    $head = ob_get_contents();
    ob_end_clean();
    $regex = '/Content-Length:\s([0-9].+?)\s/';
    $count = preg_match($regex, $head, $matches);
    return isset($matches[1]) ? $matches[1] : "unknown";
}

语法：

$file = "http://www.dmaku.com/static/index/images/logo.png";
$size = remote_filesize($url);
echo $size;