//网上找到的资源感谢分享

function getsize($url,$user='',$pw='')
{
            
                // start output buffering
                ob_start();
                // initialize curl with given uri
                $ch = curl_init($url); // make sure we get the header
                curl_setopt($ch, CURLOPT_HEADER, 1); // make it a http HEAD request
                curl_setopt($ch, CURLOPT_NOBODY, 1); // if auth is needed, do it here
                if (!empty($user) && !empty($pw))
                {
                    $headers = array('Authorization: Basic ' . base64_encode($user.':'.$pw));
                    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
                }
                $okay = curl_exec($ch);
                curl_close($ch); // get the output buffer
                $head = ob_get_contents(); // clean the output buffer and return to previous // buffer settings
                ob_end_clean();  // gets you the numeric value from the Content-Length // field in the http header
                $regex = '/Content-Length:\s([0-9].+?)\s/';
                $count = preg_match($regex, $head, $matches);  // if there was a Content-Length field, its value // will now be in $matches[1]
                if (isset($matches[1]))
                {
                    $size = $matches[1];
                }
                else
                {
                    $size = 'unknown';
                }
                $last_mb = round($size/(1024*1024),3);
                $last_kb = round($size/1024,3);
                return $last_kb . 'KB / ' . $last_mb.' MB';
}

echo  getsize('xxx.png',$user='',$pw='');