code: def _query_server_state(self, conn, file_length):
          
          # Send an empty PUT so that server replies with this resumable
          # transfer's state.
          put_headers = {}
          put_headers['Content-Range'] = (
              self._build_content_range_header('*', file_length))
          put_headers['Content-Length'] = '0'
          return AWSAuthConnection.make_request(conn, 'PUT',
                                                path=self.tracker_uri_path,
                                                auth_path=self.tracker_uri_path,
                                                headers=put_headers,
                                                host=self.tracker_uri_host)
docs: Queries server to find out state of given upload.
  
          Note that this method really just makes special case use of the
          fact that the upload server always returns the current start/end
          state whenever a PUT doesn't complete.
  
          Returns HTTP response from sending request.
  
          Raises ResumableUploadException if problem querying server.