public function get_object_group($bucket, $object_group, $options = null)
{
//options
$this->validate_options($options);
//bucket
$this->is_empty($bucket, OSS_BUCKET_IS_NOT_ALLOWED_EMPTY);
//object group
$this->is_empty($object_group, OSS_OBJECT_GROUP_IS_NOT_ALLOWED_EMPTY);
$options[self::OSS_BUCKET] = $bucket;
$options[self::OSS_METHOD] = 'GET';
$options[self::OSS_OBJECT] = $object_group;
//$options[self::OSS_OBJECT_GROUP] = true; //设置?group
//$options[self::OSS_CONTENT_TYPE] = 'txt/xml'; //重设Content-Type
$options[self::OSS_HEADERS] = array(self::OSS_OBJECT_GROUP => self::OSS_OBJECT_GROUP);
//header中的x-oss-file-group不能为空,否则返回值错误
$response = $this->auth($options);
return $response;
}