Need Help in Publishing to a Client when it subscribes to a topic

[aqibamir]

Whenever a client subscribes to a topic , I have to deliver the latest data of the device to the subscribing client. In the following code whenever I use aedes.publish(), immediately after publishing the client gets disconnected. Is there something wrong with my approach ?

` aedes.authorizeSubscribe = async function (client, subscription, callback) {
try {
const splitted = subscription.topic.split('/');

if (splitted.length < 4)
  callback(null, null);

const projectDocument = await auth.verifyApiKey(fusionClient, splitted[0]);

if (projectDocument == null) {
  return callback(new Error('Invlaid topic string'), null);
}

const res = await fusionClient.run('device', 'getDeviceData', [splitted[2], splitted[3], projectDocument.project._id]);

if (res) {
  const returnPacket = {
    topic: subscription.topic,
    payload: Buffer.from(res.data),
    messageId: cuid(),
    qos: 2
  }
  aedes.publish(returnPacket, null);
}
return callback(new Error('DeviceID invalid'));

}
catch (err) {
console.log(err);
return callback(new Error(err));
}
}
`

[robertsLando]

You should use retain flag for such purposes. What I suggest is to give a look at MQTT foundamentals first

About your code you don't have to add messageId to the packet, just topic, payload, qos and retain flag