docs: def _save_upload_state_to_file(self):
          """if create and create_file has execute, save upload state
          to file for next resume upload if current upload process is
          interrupted.
          """
          if os.access(self.file_dir, os.W_OK | os.R_OK | os.X_OK):
              save_file = self.file + '.upload'
              data = {
                  'upload_token': self.upload_token,
                  'upload_server_ip': self.upload_server_ip
              }
              with open(save_file, 'w') as f:
                  json.dump(data, f)