code: def __GetChunk(self, start, end, additional_headers=None):
          
          self.EnsureInitialized()
          request = http_wrapper.Request(url=self.url)
          self.__SetRangeHeader(request, start, end=end)
          if additional_headers is not None:
              request.headers.update(additional_headers)
          return http_wrapper.MakeRequest(
              self.bytes_http, request, retry_func=self.retry_func,
              retries=self.num_retries)
docs: Retrieve a chunk, and return the full response.