Core NATS request reply supplies it's own reply-to address

[LLLLimbo]

I'm supplying the reply-to in the request, but when the replier responds, it never gets back to the requestor.

[LLLLimbo]

As shown in the code below, the NATS client cannot receive Reply messages from the MQTT client in this case:

public static void main(String[] args) throws IOException, InterruptedException {
    Options options = new Options.Builder()
        .server("nats://192.168.2.102:14222")
        .userInfo("seeiner", "seeiner")
        .build();

    Connection nc = Nats.connect(options);
    Message message = NatsMessage.builder().replyTo("replyto.123")
        .data("hello".getBytes(StandardCharsets.UTF_8))
        .subject("request.123")
        .build();

    Message res = nc.request(message, Duration.ofSeconds(10));
    System.out.println(new String(res.getData()));
  }

public static void main(String[] args) {
    String content = "Message from MQTT";

    MemoryPersistence persistence = new MemoryPersistence();
    try {
      MqttClient sampleClient = new MqttClient("tcp://192.168.2.102:11883", "sample_mqtt_client",
          persistence);
      MqttConnectOptions connOpts = new MqttConnectOptions();
      connOpts.setCleanSession(true);
      connOpts.setUserName("seeinerx");
      connOpts.setPassword("seeinerx".toCharArray());
      sampleClient.connect(connOpts);

      sampleClient.subscribe("request/123", 0, (s, mqttMessage) -> {
        System.out.println("Received mesage from nats: " + new String(mqttMessage.getPayload()));
        System.out.println("Publishing message: " + content);
        MqttMessage message = new MqttMessage(content.getBytes());
        message.setQos(0);
        sampleClient.publish("replyto/123", message);
        System.out.println("Message published");
      });

      Thread.sleep(30000L);
      sampleClient.disconnect();
      System.exit(0);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

[scottf]

The problem is that you are replying to the wrong subject. When you make the request in java, your replyTo("replyto.123") is ignored, the client makes a reply to that looks like this _INBOX.vqNUxbuYpUUHepWvptfH5M.vqNUxbuYpUUHepWvptfH8c
On the mqtt side, you must look at the exact replyTo that is with the message you receive and publish to it.

If you can't access the reply-to field on the mqtt side, then what I would do is used fixed subjects, have java just publish (not request) to request.123 and then be a subscriber to fixed subject reply.123

Also, in the case of a publish, the client will not provide it's own reply-to so you could use that to provide your own subject. You can also use headers to supply information.