* return the value but instead throw an exception.
   */
  private var trailers: Headers? = null

  override val isResponseComplete: Boolean
    get() = state == STATE_CLOSED

  override fun createRequestBody(
    request: Request,
    contentLength: Long,
  ): Sink =
    when {
      request.body?.isDuplex() == true -> throw ProtocolException(
        "Duplex connections are not supported for HTTP/1",
      )