public function prefetch($bucket, $key)
{
$resource = \Qiniu\entry($bucket, $key);
$path = '/prefetch/' . $resource;
$ak = $this->auth->getAccessKey();
$ioHost = $this->zone->getIoHost($ak, $bucket);
$url = $ioHost . $path;
list(, $error) = $this->post($url, null);
return $error;
}