akka-ws-client.scala

  val req = WebSocketRequest(uri = "ws://127.0.0.1/ws")
  val webSocketFlow = Http().webSocketClientFlow(req)

  val messageSource: Source[Message, ActorRef] =
    Source.actorRef[TextMessage.Strict](bufferSize = 10, OverflowStrategy.fail)

  val messageSink: Sink[Message, NotUsed] =
    Flow[Message]
      .map(message => println(s"Received text message: [$message]"))
      .to(Sink.ignore)

  val ((ws, upgradeResponse), closed) =
    messageSource
      .viaMat(webSocketFlow)(Keep.both)
      .toMat(messageSink)(Keep.both)
      .run()

  val connected = upgradeResponse.flatMap { upgrade =>
    if (upgrade.response.status == StatusCodes.SwitchingProtocols) {
      Future.successful(Done)
    } else {
      throw new RuntimeException(s"Connection failed: ${upgrade.response.status}")
    }
  }

  ws ! TextMessage.Strict("Hello World")
  ws ! TextMessage.Strict("Hi")
  ws ! TextMessage.Strict("Yay!")