public function BaseFileDownload($file_id)
 {
     // $file_id : IDType (string := integer) and no array
     $this->CheckAndSetHeader(__FUNCTION__);
     $reg_args["file_id"] = $file_id;
     $this->encodeString($reg_args);
     $results = parent::BaseFileDownload($reg_args);
     $this->methodClose();
     return $results->file->content;
     // returns file body (already base64decode)
 }