nodejs - why mosca server publish back a message client just published

Question

I'm making an IoT project that using mosca server, mqtt.js and express and jQuery for making a web. My purpose is making a website that can communicate with some embeded board such as Arduino, esp,...

I want the server publish back 'Hello World' when I publish some message to server. But the problem is when I do it, server sent back 'Hello World' and the message I just published.

Here is the example code:

server mosca

var mosca = require("mosca");

var settings = {
    http: {
        port: 8080,
        bundle: true,
        static: './'
    }
};

var server = new mosca.Server(settings);

server.on('clientConnected', function(client) {
    console.log('client ' +  client.id+ ' connect');
});

server.on('clientDisconnected', function(client) {
    console.log('client ' +  client.id+ ' disconnect');
});

// fired when a packet is send from server and is received from client
server.on('published', function(packet, client) {
    // console.log('Published', packet);
    if(typeof packet.payload == "object"){
            console.log(packet);
            console.log("From Client(Buffer) : "+ packet.payload.toString());
            var mesFromServer = {
                        topic:packet.topic,
                        payload:"Hello World",
                        qos:0,
                        retain:false
                    };
            server.publish(mesFromServer,client);
    }
});

server.on('ready', setup);

// fired when the mqtt server is ready
function setup() {
    console.log('Mosca server is up and running');
}

client.js using mqtt.js

$(document).ready(function(){
    $("#btnConnect").click(function(){

        $("#Connect-loader").css("display","inline");
        var client  = mqtt.connect({ host: 'localhost', port:8080 });
    
        client.on('connect', function () {
            if(client.connected)
            {
                $("#Connect-loader").css("display","none");
                $("#btnConnect").prop("disabled",true);
                $("#btnDisconnect").prop("disabled",false);
                $("#connect-notification").html("Server connected");
                $("#connect-notification").css("color","green");
            }
        });
        
        client.on('message', function (topic, message,packet) {
            // message is Buffer
            console.log(packet);
            $("#txtDataFromServer").val($("#txtDataFromServer").val()+"From Server: " + message.toString()+"\n");
        });

        client.on('close',function(){
            $("#btnConnect").prop("disabled",false);
            $("#btnDisconnect").prop("disabled",true);

            $("#connect-notification").html("Server disconnected");
            $("#connect-notification").css("color","red");
        });

        $("#btnSend").click(function(){
            var topic = $("#txtTopic").val();
            var mess = $("#txtMessage").val();
            
            if(topic != "" && mess !=""){
                client.subscribe(topic);
                client.publish(topic,mess,{qos:0,retain:false});
            }
        });
        
        $("#btnDisconnect").click(function(){
           client.end(); 
        });
    });
});

index.js using express

var express = require("express");
var app = express();

app.use(express.static("public")); 
app.use(express.static("node_modules"));

app.set("view engine","ejs");
app.set("views","./views");
var server = require("http").createServer(app);

server.listen(8000);

app.get("/",function(req,res){
    res.render("home");
});

I start the server mosca and index.js:

node server.js

node index.js

then I hit a button in my web to connect to mosca and then sent a message 'hello mqtt + mosca' to it but it sent back to me 2 messages.

From Server: hello mqtt + mosca

From Server: Hello World

And I don't expect the result 'hello mqtt + mosca'. How can I prevent the server publish back to me the message I publish to it ?

Answer 1

There is user data option to set while connecting to the server, add some unique data for each client, you will get this data in on message event handler, set condition base on this data.

Answer 2

The short answer is you don't.

If the client subscribes to a topic it will receive ALL messages published on that topic regardless of who published it.

This is just how MQTT works.