* lifted. Such writes occur on an application-provided thread and may occur concurrently with
   * reads of the [ResponseBody]. For duplex request bodies, [writeTo] should return
   * quickly, possibly by handing off the provided request body to another thread to perform
   * writing.
   *
   * [grpc]: https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
   */
  open fun isDuplex(): Boolean = commonIsDuplex()

  /**