// what we did get (such as a 4xx response) without ever transmitting the request body.
        if ("100-continue".equals(request.header("Expect"), ignoreCase = true)) {
          exchange.flushRequest()
          responseBuilder = exchange.readResponseHeaders(expectContinue = true)
          exchange.responseHeadersStart()
          invokeStartEvent = false
        }
        if (responseBuilder == null) {

    return RequestBodySink(
      delegate = rawRequestBody,
      contentLength = contentLength,
      isSocket = false,
    )
  }

  @Throws(IOException::class)
  fun flushRequest() {
    try {
      codec.flushRequest()
    } catch (e: IOException) {
      call.eventListener.requestFailed(call, e)
      trackFailure(e)
      throw e
    }
  }

  @Throws(IOException::class)
  fun finishRequest() {