How to send message from mosca broker to mqtt.js client

we are setting up an MQTT client using MQTT.js (either on a desktop pc or an actual board, same thing) and the MQTT Broker runs on mosca which runs on the desktop pc.

We can successfully send a message with a specific topic from client to broker, but now we are stuck in the opposite: send a message from broker to client .

We follow the code samples provided in both project docs but no luck. The client can register correctly for the topic, but does not respond in any way to sending the message. The broker can send the message correctly as well as listen to his own message, since he is listening for all messages anyway.

Excerpt from MQTT Broker:

broker.on('published', function(packet, client) {
  console.log('MQTT broker received message');  // it passes by here
  console.log(' - packet:', packet);
  console.log(' - packet payload:', packet.payload.toString());
});

// ...

var packet = {
  topic: 'our_custom_topic',
  payload: ourCustomPayload,
  qos: 1,
  retain: false,  
};

console.log('MQTT broker sending message to client ...');

broker.publish(packet, function() {
  console.log('Message sent');  // it passes by here
});

      

        
        
        
      

    

Excerpt from MQTT client:

client.on('connect', function () {
  console.log('MQTT client connected');

  client.subscribe('our_custom_topic', { qos: 1 }, function onSubscribe(err, granted) {
    if (err) {
      console.log('subscribe errors:', err);  // no error shown
    }

    if (granted) {
      console.log('subscribe granted:', granted);  // it passes by here
    }
  });
});

// ...

client.on('message', function (topic, message, packet) {
  console.log('MQTT client received message');  // it DOESN'T pass by here
  console.log(' - topic', topic);
  console.log(' - message', JSON.stringify(message));
  console.log(' - packet', JSON.stringify(packet));
});

      

        
        
        
      

    

Update

The problem seems to come up when persistence is based on mongoDb. Instead, messages are correctly sent to subscribers when the save is memory-based. Here are our pub-sub settings when you rely on persisting to mongoDb. In fact, this is a development instance running at mongolab.com:

var mongoDbSettings = {
  // remote MongoLab mongodb instance
  url: 'mongodb://mqtt-db-user:<OUR-USER-CODE>@<THEIR-INSTANCE-SUBDOMAIN>.mongolab.com:39291/sample-mqtt-datastore',
  pubsubCollection: 'myCollections',
};

var mongoDbBrokerSettings = {
  port: 1883,  // mosca (mqtt) port

  // using ascoltatore over MongoDB
  backend: {
    type: 'mongo',
    url: mongoDbSettings.url,
    pubsubCollection: mongoDbSettings.pubsubCollection,
    mongo: {},
  },
  persistence: {
    factory: mosca.persistence.Mongo,
    url: mongoDbSettings.url,
  }
};

var broker = new mosca.Server(mongoDbBrokerSettings, function onCreated(err, broker) {
  // assume no errors

  console.log('MQTT broker is up and running');
});

      

        
        
        
      

    

can anyone detect something wrong with this?