socket.sink.timeout().timeout(writeTimeoutMillis.toLong(), TimeUnit.MILLISECONDS)
      tunnelCodec.writeRequest(nextRequest.headers, requestLine)
      tunnelCodec.finishRequest()
      val response =
        tunnelCodec
          .readResponseHeaders(false)!!
          .request(nextRequest)
          .build()
      tunnelCodec.skipConnectBody(response)

      "Trailers cannot be read because the state is $state"
    }
    return trailers
  }

  override fun flushRequest() {
    socket.sink.flush()
  }

  override fun finishRequest() {
    socket.sink.flush()
  }

  /** Returns bytes of a request header for sending on an HTTP transport. */
  fun writeRequest(
    headers: Headers,
    requestLine: String,
  ) {