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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"
}
}
Answer
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 the updated slides are here.