PHP curl反回远程数据大小

function remote_filesize($uri) {
ob_start();
$ch = curl_init($uri);
curl_setopt($ch, CURLOPT_HEADER, 1);
curl_setopt($ch, CURLOPT_NOBODY, 1);// remove body
curl_setopt($ch, CURLOPT_FOLLOWLOCATION,1); // follow redirects recursively
curl_exec($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';
}