Tutorial for using the Node.js MQTT client with FairCom's MQTT broker engine

node publish.js -t topic -f fileName -q qos -c clientid -s hostname:port -u username -p password

Options may be present in any order, and if absent, default values will be used.

node publish.js -t testTopic -f /Users/username/myjsonfiles/data.json

connecting to client at: mqtt://127.0.0.1:1883

connected to client at: mqtt://127.0.0.1:1883

publishing to topic testTopic

Connection closed by client

// Variable declarations and initialization
const argv            = require('yargs').argv,
      mqtt            = require('mqtt'),
      process         = require('process'),
      validation      = require('./validation')
const fs              = require('fs')
let client            = null,
    hasHelpParam      = validation.hasHelpParam(argv),
    hasRequiredParams = validation.hasRequiredParams(argv)
// Default settings used to configure MQTT client
var settings          = {
    brokerAddress: '127.0.0.1:1883',
    clientID     : 'testPubClientID',
    fileName     : null,
    qos          : 1,
    topic        : 'testTopic',
    username     : null,
    password     : null
}

if (hasHelpParam) {
    validation.usage()
}
/* Parameter exit conditions
      1 - User passed the 'help' parameter
      2 - User didn't pass required parameters
      3 - User pressed Ctrl + C */
if (hasHelpParam || !hasRequiredParams) {
    process.exit()
}
process.on('SIGINT', function () {
    console.log('\nshutting down MQTT client after Ctrl C')
    process.exit()
})

// Override default 'settings' object properties using params passed by user.
Object.keys(argv).forEach((key) => {
    let property = validation.getArgProperty(key)

    if (property != null) {
        settings[property] = argv[key]
    }
})

// Connect to client connection.
console.log(`connecting to client at: ${settings.brokerAddress}`)
client = mqtt.connect(`mqtt://${settings.brokerAddress}`, {
    clientId       : settings.clientID,
    connectTimeout : 30 * 1000,
    reconnectPeriod: 1000,
    protocolId     : 'MQIsdp',
    protocolVersion: 3,
    ...((settings.username !== null) && { username: settings.username }),
    ...((settings.password !== null) && { password: settings.password })
})

// Add mqtt client event listeners
client.on('connect', function () {
        console.log(`connected to broker at: ${settings.brokerAddress}`)

        // read in file from fileName path passed in by user.
        console.log(`reading file at ${settings.fileName}`)
        try {
            const fs = require('fs'),
                  msgData = fs.readFileSync(settings.fileName);
            publishMsg(msgData)
        } catch (e) {
            if (e.code !== 'MODULE_NOT_FOUND') {
                client.end()
                throw e
            }
        }
    },
)

client.on('error', function (err) {
    console.log('Error: ' + err)
    if (err.code === 'ENOTFOUND') {
        console.log(
            'Network error: Verify the passed hostname:port and that ' +
            'your MQTT server is running.')
    }
})

client.on('close', function () {
    console.log('connection closed by client')
    if (client.isConnected) {
        client.end()
    }
    process.exit()
})

function publishMsg (msgData) {
    console.log(`publishing to topic ${settings.topic}`)
    client.publish(settings.topic,
        JSON.stringify(msgData),
        { qos: settings.qos })
    client.end()
}

node subscribe.js -t topic -d directory -q QoS -c clientID -s hostname:port -u username -p password

Options may be present in any order, and if absent, default values will be used.

node subscribe.js -t testTopic -d testDir -c testSubClientID

connecting to broker at: 127.0.0.1:1883

connected to broker at: 127.0.0.1:1883

subscribing to topic: testTopic

 

Messages that arrive will be printed to the screen.

received message: {

       "property":    "value",

       "string":      "string",

       "number":      1,

       "boolean":     true,

       "null...

When a directory is specified, the utility writes the payload of each received message to a file. The name of the file is the name of the topic you specified followed by an underscore plus a sequential number. Topic names are case-sensitive. The file has no extension because an MQTT payload can be anything.

module.exports         = {
    getArgProperty: function (arg) {
        let property = null
        switch (arg.toLowerCase()) {
            case 's':
            case 'server':
            case 'broker':
            case 'brokeraddress':
                property = 'brokerAddress'
                break
            case 't':
            case 'topic':
                property = 'topic'
                break
            case 'c':
            case 'client':
            case 'clientid':
                property = 'clientID'
                break
            case 'f':
            case 'file':
            case 'filename':
                property = 'fileName'
                break
            case 'u':
            case 'user':
            case 'username':
                property = 'username'
                break
            case 'p':
            case 'pass':
            case 'password':
                property = 'password'
                break
            case 'q':
            case 'qos':
                property = 'qos'
                break
        }

        return property
    },

    hasHelpParam: function(argv) {
        return Object.keys(argv).some(k => (k === 'h')) || Object.keys(argv).some(k => k.startsWith('help') );
    },

    hasRequiredParams: function(argv) {
        let hasFileNameProperty = Object.keys(argv).some(k => (k === 'f')) || Object.keys(argv).some(k => k.startsWith('file') )

        if (!hasFileNameProperty && !this.hasHelpParam(argv)) {
            console.log(`The fileName (-f) parameter is required.`)
            return false;
        }

        return true;
    },

    usage: function () {
        console.log(`
            Usage: node publish.js -f /pathtofile/sample.json
            Publish the contents of a file to a broker using the specified topic.
            
            Options:
               -s server     Server address.  Defaults to \"127.0.0.1:1883\"
               -t topic      The topic to publish to.  Defaults to \"testTopic\".
               -c clientID   The unique ID to use when connecting to the broker.  
                             Defaults to \"testPubClientID\".
               -f fileName   The file to use as a payload to publish.
               -u username   An optional username to authenticate with when 
                             connecting to the broker.  If absent, a connection 
                             without credentials will be attempted.
               -p password   The password to use with the username provided 
                             above.  Ignored if the username is absent.
               -q qos        The Quality Of Service to publish with.  
                             Defaults to 1.
               -h help       Print the usage and exit.
               
            Options may be present in any order, and if absent, default values 
            will be used. Invalid options will be ignored.
        `)
    },
}