communicating with MQTT publisher / subscriber using an API

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I have an MQTT publisher and subscriber written in Node JS.

I was wondering if it is possible to have it in the form of an API, that we can connect to and publish messages to using PostMan.

Here is my code for the publisher:

Publisher.js:

const mqtt = require('mqtt');
let client = mqtt.connect('mqtt://broker.hivemq.com');


client.on('connect', () =>{
    console.log(`MQTT Client Connected Successfully!`);
    client.publish('connected', `${true}`);
});

Here is my code for the Subscriber: Subscriber.js:

const mqtt = require('mqtt');
let client = mqtt.connect('mqtt://broker.hivemq.com');

let connected = false;


client.on('connect', () =>{
    console.log(`MQTT Client Connected Successfully!`);
    client.subscribe('connected');
});



client.on('message', (topic, message) =>{
    if(topic === "connected"){
      return handleGarageConnected(message);
    }

    console.log("No Handler for Topic %s", topic);

});

I want to be able to communicate with the Publisher / Subscriber over the internet using an API that I create.

Thank you.

iot paho mqtt postman
2 Answers

MQTT is a asynchronous protocol, HTTP is synchronous.

Combining them is possible but it requires a good understanding of both.

E.g. Messages for a subscription can arrive at any time, so suppose you map that to a GET HTTP request, what should it return?

  • The last message
  • Block until the next message (with suitable timeout)
  • All the previous messages
user_5045540

You can make a function which publishes on the desired topic in publisher.js and export it. This way you can use in any other module.

Publisher.js

const mqtt = require('mqtt');
let client = mqtt.connect('mqtt://broker.hivemq.com');


client.on('connect', () =>{
    console.log(`MQTT Client Connected Successfully!`);
    client.publish('connected', `${true}`);
});

module.exports = {

    publishTopic : function(payload){
      client.publish('randomTopic');
    }
}

You can make another file for your APIS, where you can import the exported function like so,

const mqttWrapper = require('./Publisher.js');

module.exports = {
    randomApi : function (req, res) {
        mqttWrapper.publishTopic("message");   
    }    
}
user_132561980
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