docs: def recover_db(self, src_file):
          """
          " Recover DB from xxxxx.backup.json or xxxxx.json.factory to xxxxx.json
          " [src_file]: copy from src_file to xxxxx.json
          """
          with self.db_mutex:
              try:
                  shutil.copy2(src_file, self.json_db_path)
              except IOError as e:
                  _logger.debug("*** NO: %s file." % src_file)
                  raise e