title: What's a valid @MessagePattern for NestJS MQTT microservice?
body: <p>I'm trying to setup a MQTT Microservice using NestJS according to <a href="https://docs.nestjs.com/microservices/mqtt" rel="nofollow noreferrer">the docs</a>.</p>
  
  <p>I've started a working Mosquitto Broker using Docker and verified it's operability using various MQTT clients. Now, when I start the NestJS service it seems to be connecting correctly (mqqt.fx shows new client), yet I am unable to receive any messages in my controllers.
  This is my bootstrapping, just like in the docs:</p>
  
  <p><strong>main.ts</strong></p>
  
  <pre><code>async function bootstrap() {
      const app = await NestFactory.createMicroservice(AppModule, {
          transport: Transport.MQTT,
          options: {
              host: 'localhost',
              port: 1883,
              protocol: 'tcp'
          }
      });
      app.listen(() =&gt; console.log('Microservice is listening'));
  }
  bootstrap();
  </code></pre>
  
  <p><strong>app.controller.ts</strong></p>
  
  <pre><code>@Controller()
  export class AppController {
  
      @MessagePattern('mytopic') // tried {cmd:'mytopic'} or {topic:'mytopic'}
      root(msg: Buffer) {
          console.log('received: ', msg)
      }
  }
  </code></pre>
  
  <p>Am I using the message-pattern decorator wrongly or is my concept wrong of what a NestJS MQTT microservice even is supposed to do? I thought it might subscribe to the topic I pass to the decorator. My only other source of information being the corresponding <a href="https://github.com/nestjs/nest/blob/master/packages/microservices/test/server/server-mqtt.spec.ts" rel="nofollow noreferrer">unit tests</a></p>