QUESTION / PROBLEM

Link to question: https://stackoverflow.com/questions/50043605/how-to-send-a-response-back-over-a-established-tcp-connection-in-async-mode-usin

How to send a response back over a established TCP connection in async mode using Apache Camel Netty4?

I'm building a micro-service that has an Apache Camel route using Netty4 Component (http://camel.apache.org/netty4.html) in consumer mode. So, in my micro-service, this route that I'm building, will receive messages over a a TCP connection. To do that, I did this:

@Override
public void configure() throws Exception {
 this.from("netty4:tcp://localhost:7000?textline=true&encoding=utf8")
   .process(new Processor() {
      @Override
      public void process(final Exchange exchange) throws Exception {
        log.info("[Processor] - Incoming Message -> {}", exchange.getIn().getBody(String.class));
      }
   }).to("bean:messageService");
}

Well, I'm receiving the messages normally. To test, I use telnet:

$ telnet localhost 7000
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
TheMessage

The problem is when I want to send back a message to the same TCP channel established in that route. In synchronous mode, I can do that easily using the Exchange object. However, in asynchronous mode, I don't know how to send back a message to the producer.

The Spring Service that receive and should send the messages, is this:

@Service
public class MessageService {
  
  private static final Logger log = LoggerFactory.getLogger(MessageService.class);

  private List<String> messageStore = new LinkedList<>();
  
  public void sendToTCP(final String message) {
    log.info("[Service] - Sending Message over TCP Channel --> {}", message);
  }

  @Handler
  public void receiveFromTCP(final Exchange exchange) {
    final String messageFromTcp = exchange.getIn().getBody(String.class);
    log.info("[Service] - Message Received from TCP Channel --> {}", messageFromTcp);
    this.messageStore.add(messageFromTcp);
  }

  public List<String> getReceivedMessages() {
    return messageStore;
  }
}

In resume, what I need is to put some code in this method, something like that:

public void sendToTCP(final String message) {
  log.info("[Service] - Sending Message over TCP Channel --> {}", message);
  // Send message to producer here
  camelContext.createProducerTemplate.send....
}

I cannot create another route to producer because I don't know the producer IP. I really need to use the already established TCP channel between the producer and my application. The communication needs to be over TCP, other tools, like Queues, are not an option.

---

GitHub Sample Project

I uploaded a sample project on GitHub: https://github.com/rgiaviti/so-camel-netty4-tcp

Draw

I'm using:

• Spring Boot 1.5.12;
• Apache Camel 2.21.0;