How to write an RSocket client in JavaScript

Question

I try to implement an RSocket server in Java and a client in JavaScript, but I can't call any of the methods in my backend.

Java server

public final class RawServer {
    public static void main(String[] args) {
        RSocketFactory.receive()
                .acceptor((setup, sendingSocket) -> Mono.just(new DefaultSimpleService()))
                .transport(WebsocketServerTransport.create("localhost", 8801))
                .start()
                .block()
                .onClose()
                .block();
    }

    private static final class DefaultSimpleService extends AbstractRSocket {
        private ObjectMapper jsonMapper = new ObjectMapper();

        @Override
        public Flux<Payload> requestStream(Payload payload) {
            return Mono.just(payload.getDataUtf8())
                    .map(json -> {
                        try {
                            return jsonMapper.readValue(json, Message.class);
                        } catch (IOException e) {
                            e.printStackTrace();
                            return null;
                        }
                    })
                    .doOnNext(msg -> System.out.println("got message " + msg.message))
                    .flatMapMany(msg -> Flux.range(0, 5)
                            .map(count -> msg.message + " #" + count))
                    .map(message -> DefaultPayload.create(message));
        }
    }
}

public class Message {

    public final String message;

    @JsonCreator
    public Message(@JsonProperty("message") String message) {
        this.message = message;
    }
}

JavaScript client

    import { RSocketClient, JsonSerializers } from "rsocket-core";
    import RSocketWebSocketClient from "rsocket-websocket-client";

    const transport = new RSocketWebSocketClient({
        url: "ws://localhost:8801"
      });

      const client = new RSocketClient({
        // send/receive JSON objects instead of strings/buffers
        serializers: JsonSerializers,
        setup: {
          // ms btw sending keepalive to server
          keepAlive: 60000,
          // ms timeout if no keepalive response
          lifetime: 180000,
          // format of `data`
          dataMimeType: "application/json",
          // format of `metadata`
          metadataMimeType: "application/json"
        },
        transport
      });
      client.connect().subscribe({
        onComplete: socket => {
          socket.requestStream({
            data: { message: "hello from javascript!" },
            metadata: null
          });
        },
        onError: error => {
          console.log("got error");
          console.error(error);
        },
        onSubscribe: cancel => {
          /* call cancel() to abort */
          console.log("subscribe!");
          console.log(cancel);
          // cancel.cancel();
        }
      });

It seems like the WebSocket connection is established, but no message is pushed to the server. How can I do this?

I also implemented the client side in Java and it work's fine. The JavaScript example I found is https://github.com/rsocket/rsocket-js/blob/master/docs/01-client-configuration.md, but I can't make it work.