Express + MQTT from POST request to publish in topic - node.js

Question

I need a Node.js web service that accept a specific POST request that will trigger a publishing in a specific MQTT topic.
I use Express to listen for the request and this part of the script works fine.
The problem is when I it should trigger the publish in topic to perform a downlink.
The code without the Express part works fine. So It seems like Express interfere with MQTT. But the connection to the Broker works fine. Only the publish procedure doesn't work.
var express = require('express');
var bodyParser = require('body-parser');
var mqtt = require('mqtt')
var fs = require('fs')
var path = require('path')
const util = require('util')
var app = express();
var CERT = //certificate
var PORT = //port
var HOST = // host
var options = {
port: PORT,
host: HOST,
clientId: //client_id
username: //uname
password: //pswd
cert: CERT,
rejectUnauthorized: false,
protocol: 'mqtts'
}
var client;
var jsonParser = bodyParser.json();
var port = process.env.PORT || 8080;
app.use(express.static('public'));
app.get('/', function (req, res) {
res.render(__dirname + "/public/index.html");
})
client = mqtt.connect(options);
client.on("connect", () => {
console.log("MQTT connected");
})
client.on('message', function (topic, message) {
var msg = JSON.parse(message)
console.log("topic: " + topic + " msg:" + util.inspect(msg))
});
app.post('/', jsonParser, function (req, res) {
// Prepare output in JSON format
data = {
dev_id: req.body.dev_id,
pswd: req.body.password,
tx_cycle: req.body.tx_cycle
};
if (data.pswd != "password") {
console.log("Wrong password")
}
else {
console.log(data);
var topic = 'publish_topic';
var tx_cy = data.tx_cycle;
var msg = '{"port":"222","payload":"' + tx_cy + '","confirmed": false,"window":"BOTH","priority":0}';
console.log('Try to send downlink message, for ' + data.dev_id + ' set to ' + data.tx_cycle + ' min -> hex ' + tx_cy);
client.subscribe('reply/+/id/+');
client.publish(topic, msg);
res.status(200).send(msg + " sent to broker");
}
});
var server = app.listen(port, function () {
var host = server.address().address
var port = server.address().port
console.log("App listening at http://%s:%s", host, port)
})

Answer 1

I solve the problem. The client id was refused by the broker because was not unique. Changing it solved the issue.