CODEWITHSUNDEEP
javascriptnode.jsmqtt
Thor
Thor

Reputation: 340

Troubles with offline messages using mqtt.js and Mosca

I'm trying to learn how to send offline messages using mqtt.js and Mosca based on the author's demo and other instructions. Below is what I attempted, but I'm not sure why my listening client works online, but not when the subscription process includes offline configuration (QoS, clientId, clean).

1.Start a standalone Mosca broker using:

npm install mosca bunyan -g
mosca -v | bunyan

2.Run the following scripts (listed below) sequentially:

node subscribe.js   // User8 subscribes to topic called Channel-01 with QoS=1, then closes connection
node send.js        // TxUser sends a message on Channel-01
node listen.js      // User8 reconnects and should see TxUser's message

3.Attempt to identify why listen.js does not receive TxUser's message.

Here are my scripts:

subscribe.js User8 subscribes to a topic called Channel-01 with QoS=1, then closes connection.

var mqtt = require('mqtt');

var client = mqtt.connect({
    servers: [{ host: 'localhost', port: 1883 }]
    , clientId:"User8"
    , clean:false
});

client.subscribe('Channel-01', {qos:1} , function(){
  console.log("Subscriber Client: subscribed and closing connection.");
  client.end();
});

send.js TxUser sends a message on Channel-01

var mqtt = require('mqtt');

var client = mqtt.connect({
  servers: [{ host: 'localhost', port: 1883 }]
  , clientId:"TxUser"
  , clean:false
});

client.on('connect', function(){
  client.publish('Channel-01', '* * * IMPORTANT msg ' + Date() + ' * * *' , function() {
    client.end( function (){
      console.log('Sender Client: published message and closed connection');
    });
  });
});

listen.js User8 reconnects and should see TxUser's message

var mqtt = require('mqtt');

var client = mqtt.connect({
  servers: [{ host: 'localhost', port: 1883 }]
  , clientId:"User8"
  , clean:false
});

client.subscribe('Channel-01');

client.on('message', function(topic, message) {
  // this is never fired when offline options (QoS, clientId, clean) 
  // are configured in subscribe.js 
  console.log('Listener Client: Message Received = ',message.toString());
});

setTimeout(function() {
  console.log('Listener Client: Exiting');
  client.end();
},10*1000);

package.js

{
  "name": "MQTT-Test-System",
  "version": "0.0.1",
  "dependencies": {
    "mosca": "1.0.1",
    "mqtt": "1.6.3"
  }
}

Upvotes: 0

Views: 1497

Answers (1)

Thor
Thor

Reputation: 340

OK I figured this out. Apparently, I just needed to add {qos:1} in the publish statement within the send.js script. So it should look like:

client.publish('Channel-01', '* * * IMPORTANT msg ' + Date() + ' * * *' , {qos:1}, function() {...etc

To clarify the MQTT.js introduction/demo slides, I submitted a PR to the author and the updated slides are here.

Upvotes: 1

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