06. MQTT

The mqtt object is a built-in object that provides MQTT client functionality.

Functional overview:

• Provides the MQTT client function.
• Supports MQTT v3.1.1 and v3.1.
• Supports TLS.
• Supports server and client authentication.

Limitations:

• The number of MQTT session resources that can be used is 1.

---

mqtt Global Object

Methods()/Properties	Summary	Version	Note
mqtt.connect()	Starts an MQTT connection.	01.00.00+	A {Client} instance is generated.
mqtt.set()	Sets the information used for the connection.	01.00.00+

---

Details

mqtt.connect(url[,options])

Starts an MQTT connection.
Generates a {Client} instance.

Name	Type	M/O	Summary	Note
url	string	mandatory	Broker URL URL is specified in [protocol]://[hostname]:[port] format. The maximum number of characters is 255 bytes. protocol Specify ’mqtt’ or ’mqtts’. hostname Domain name or IP address of the MQTT Broker port Port number Specify a decimal digit string. The default value is 1883. The TLS CA certificate can be set with mqtt.set().
options	Object	optional	MQTT connection options Refer to options for details.
return	{Client}, undefined	-	{Client} : Generated {Client} undefined : {Client} generate failed due to invalid arguments or insufficient resources.

options

Name	Type	M/O	Summary	Note
keepalive	number	optional	Keep-alive time [s] 0: Invalid Range: 0 - 2,147,483,647 Default: 60
clientId	string	optional	MQTT client id Range: 1 - 127 bytes of single-byte alphanumeric characters Default: 'mqttjs_' + 8 random decimal digits
protocolId	string	optional	Protocol id Default: MQTT
protocolVersion	number	optional	MQTT protocol version 4: MQTT v3.1.1 3: MQTT v3.1 When setting to 3, set protocolId to ’MQIsdp’. Default: 4
reconnectPeriod	number	optional	Time to wait to reconnect when disconnected [ms] Range: 0 - 10000 Default: 1000
connectTimeout	number	optional	Connection timeout (wait for CONNACK) [ms] Range: 0 - 2,147,483,647 Default: 30000
username	string	optional	Username Set if broker requires username. Range: 1 - 511 bytes of single-byte alphanumeric characters (Version 01.00.00+) Range: 1 - 127 bytes of single-byte alphanumeric characters (Previous Versions) Default: None
password	string	optional	Password Set if broker requires password. Range: 1 - 511 bytes of single-byte alphanumeric characters (Version 01.00.00+) Range: 1 - 159 bytes of single-byte alphanumeric characters (Previous Versions) Default: None
reconnectCount	number	optional	Number of automatic reconnection retries If set to 0, automatic reconnection is disabled. 0: Invalid 1855: Infinite times Range: 0 - 999, 1855 Default: 0

This is a sample that specifies a user name and password and starts a connection to foo.bar.

var mqttOpt = {
    clientId: 'testClientId',
    username: 'foo',
    password: 'bar',
    keepalive: 300
};
var client = mqtt.connect('mqtt://foo.bar',mqttOpt);

mqtt.set(name[,arg])

Sets the information used for a connection.

Name	Type	M/O	Summary	Note
name	string	mandatory	Setting name Names that can be used are: ssl.ca, ssl.cert, ssl.key
arg	string	optional	Setting information
return	undefined	-	-

mqtt.set(’ssl.ca’,certificate);

Sets the CA certificate used for the MQTTS connection.

Name	Type	M/O	Summary	Note
’ssl.ca’	string	mandatory	Name for setting CA certificate
certificate	string	optional	Set the CA certificate used for the MQTTS connection. If omitted, the CA certificate settings are released.
return	undefined	-	-

Set as follows:
Use \n for line feed code.

var sslCa = '-----BEGIN CERTIFICATE-----\n' + 
'(...ContentOmission...)\n' + 
//...Omit...
'(...ContentOmission...)\n' + 
'-----END CERTIFICATE-----';

mqtt.set('ssl.ca', sslCa);

mqtt.set(’ssl.cert’,certificate);

Sets the client certificate used for the MQTTS connection.
If not set, client authentication is disabled.

Name	Type	M/O	Summary	Note
’ssl.cert’	string	mandatory	Name for setting client certificate
certificate	string	optional	Set the client certificate used for the MQTTS connection. If omitted, the client certificate settings are released.
return	undefined	-	-

mqtt.set(’ssl.key’,clientkey);

Sets the client private key used for the MQTTS connection.
If not set, client authentication is disabled.

Name	Type	M/O	Summary	Note
’ssl.key’	string	mandatory	Name for setting client private key
clientkey	string	optional	Set the client private key used for the MQTTS connection. If omitted, the client private key settings are released.
return	undefined	-	-

If you want to connect MQTTS using client authentication, set as follows:

var sslCa = '-----BEGIN CERTIFICATE-----\n(...ContentOmission...)\n-----END CERTIFICATE-----';
var sslClientCa  = '-----BEGIN CERTIFICATE-----\n(...ContentOmission...)\n-----END CERTIFICATE-----';
var sslClientKey = '-----BEGIN PRIVATE KEY-----\n(...ContentOmission...)\n-----END PRIVATE KEY-----';
mqtt.set('ssl.ca', sslCa);
mqtt.set('ssl.cert', sslClientCa);
mqtt.set('ssl.key', sslClientKey);

---

{Client}

Methods()/Properties	Summary	Version	Note
.on()	Registers an event handler.	01.00.00+
.publish()	Publishes a message to a topic.	01.00.00+
.subscribe()	Subscribes to a topic.	01.00.00+
.unsubscribe()	Unsubscribes from a topic.	01.00.00+
.end()	Disconnects MQTT and exit.	01.00.00+
.reconnect()	Initiates an MQTT reconnection.	01.00.00+
.isConnected()	Gets MQTT connection status.	01.00.00+
.isReconnecting()	Gets the status of MQTT when reconnecting.	01.00.00+
.canPublish()	Gets the status of whether the MQTT message can be published.	01.00.00+
.get()	Gets information related to the given argument.	01.00.00+

---

Details

.on(event,callback)

Registers an event handler.

Name	Type	M/O	Summary	Note
event	string	mandatory	Event name Names that can be used are: connect, reconnect, close, error, end, message
callback()	function	mandatory	Executes callback processing when an event occurs.
return	undefined	-	-

event : ’connect’

Executes callback when MQTT connection and reconnection are successful.
The arguments for the callback are as follows:

Arguments	Type	Summary	Note
connack	Object	connack is the content of the recieved connack packet. This argument is not mandatory.

event : ’reconnect’

Executes callback when MQTT reconnection is started.

event : ’close’

Executes callback when MQTT is disconnected.

event : ’error’

Executes callback when an error occurs or the MQTT connection fails.
The arguments for the callback are as follows:

Arguments	Type	Summary	Note
err	{MqttError}	Error information

event : ’end’

Executes callback processing when .end() processing is started.

event : ’message’

Executes callback when a publish message received.
The arguments for the callback are as follows:

Arguments	Type	Summary	Note
topic	string	The topic of the received publish
message	string, ArrayBuffer	The message of the received publish A string of up to 380 bytes. If the maximum number of bytes is exceeded, the message is discarded.	The ArrayBuffer type is supported from Version 01.03.00 or later. Specify the type with the bin option of .subscribe().

.publish(topic,message[,options][,callback])

Publishes a message to a topic.

Name	Type	M/O	Summary	Note
topic	string	mandatory	Topic name Topic name can be up to 127 bytes of alphanumeric characters and the symbols /, *, and #.
message	string, ArrayBuffer	mandatory	The message to publish If the message to be published is more than 2500 bytes, an argument error occurs and the callback process of .on('error') is executed.	The ArrayBuffer type is supported from Version 01.03.00 or later.
options	Object	optional	Publish options qos : {number} QoS level Range: 0, 1, 2 Default: 0 retain : {boolean} Retain flag Default: false dup : {boolean} Duplicate flag Default: false Refer to the MQTT specifications for details such as QoS parameters. (http://mqtt.org/)
callback(err)	function	optional	Execute the callback process when the publish process is completed. err : {MqttError} Error information When err.code is 0, it means success.
return	undefined, {MqttError}	-	{MqttError} : If the request is not accepted due to an illegal argument error, disconnection, etc., {MqttError} is returned. (Version 02.00.00+)

Note: If the next .publish() is performed before the current .publish() callback, the latter .publish() may be discarded. Before performing a .publish(), it is recommended to check whether the callback of the previous .publish() has been executed, or check whether publishing is possible with .canPublish().

.subscribe(topic[,options][,callback])

Subscribes to a topic.
Up to 5 topics can be subscribed to.

Name	Type	M/O	Summary	Note
topic	string	mandatory	Topic name Topic name can be up to 127 bytes of alphanumeric characters and the symbols /, *, and #.
options	Object	optional	Subscribe options qos : {number} QoS level Range: 0, 1, 2 Default: 0 bin : {boolean} (Version 01.03.00+) Specifies the type of the 'message' argument of message event. true: ArrayBuffer false: string Default: false
callback(err)	function	optional	Execute the callback process when the subscribe process is completed. err : {MqttError} Error information An err.code value of 0 means success.
return	undefined, {MqttError}	-	{MqttError} : If the request is not accepted due to an illegal argument error, disconnection, etc., {MqttError} is returned. (Version 02.00.00+)

.unsubscribe(topic[,callback])

Unsubscribes from a topic.

Name	Type	M/O	Summary	Note
topic	string	mandatory	Topic name Topic name can be up to 127 bytes of alphanumeric characters and the symbols /, *, and #.
callback(err)	function	optional	Execute the callback process when the unsubscribe process is completed. err : {MqttError} Error information An err.code value of 0 means success.
return	undefined, {MqttError}	-	{MqttError} : If the request is not accepted due to an illegal argument error, disconnection, etc., {MqttError} is returned. (Version 02.00.00+)

.end([,callback])

Disconnects MQTT and exit.
It may take some time before the MQTT session resource is released.
If you want to connect MQTT again, you need to wait until MQTT session resource is released.
Please refer to Sample Code.

Name	Type	M/O	Summary	Note
callback()	function	optional	Executes callback processing when releasing MQTT session resources.
return	undefined	-	-

.reconnect()

Initiates an MQTT reconnection.

Name	Type	M/O	Summary	Note
return	undefined	-	-

.isConnected()

Gets MQTT connection status.

Name	Type	M/O	Summary	Note
return	boolean	-	MQTT connection status true: MQTT connected false: Not connected

.isReconnecting()

Gets the status of MQTT when reconnecting.

Name	Type	M/O	Summary	Note
return	boolean	-	MQTT reconnecting status true: MQTT reconnecting false: Not reconnecting

.canPublish()

Gets the status of whether the MQTT message can be published.

Name	Type	M/O	Summary	Note
return	boolean	-	Whether the MQTT message can be published true: Can publish false: Cannot publish

.get(name)

Gets information related to the given argument.

Name	Type	M/O	Summary	Note
name	string	mandatory	The name of the information to be obtained The name that can be used is errnoConnect.
return	number, undefined	-	number : Acquired information undefined : When information cannot be obtained

.get(’errnoConnect’)

Gets the connection error number.

Name	Type	M/O	Summary	Note
’errnoConnect’	string	mandatory	Name to get connection error number
return	number	-	Refer to errnoConnect table for connection error number details.

---

Appendix

{MqttError}

Methods()/Properties	Type	Summary	Note
.code	number	Error code Refer to mqtt errors table for error code details.
.message	string	Error contents Refer to mqtt errors table for error content details.

mqtt errors table

The following is the error code table.
"✓" indicates the callback to be notified. (xx.xx.xx) is the supported FW version.

.code	.message	Note	.on('error',cb)	.publish(cb)	.subscribe(cb)	.unsubscribe(cb)
0	OK	No error		✓	✓	✓
1	Connection failed	Connection (reconnection) failure	✓
10	Illegal argument	Invalid argument error	✓	✓ (02.00.00+)	✓ (02.00.00+)	✓ (02.00.00+)
11	Disconnected *	Disconnect error		✓	✓	✓
12	Publish failed	Publish failed	✓ (02.00.00+)	✓
13	Subscribe failed	Subscribe failed	✓ (02.00.00+)		✓
14	Unsubscribe failed	Unsubscribe failed	✓ (02.00.00+)			✓
255	Other error	Other errors	✓

* Notified when publish()/subscribe()/unsubscribe() is executed while unconnected.

errnoConnect table

The following is the connection error code table.

errnoConnect	Summary	Note
0	OK	No error
1	Unacceptable protocol version	Protocol version not supported
2	Identifier rejected	Identifier rejection
3	Server unavailable	Server unavailable
4	Bad user name or password	Invalid username or password
5	Not authorized	Permission error
6	Connection failed	Other errors (mainly network errors)
7	SSL/TLS error	TLS related errors
Others	Reserved	Reserved

---

Object Usage Examples

Sample 1

This is a sample MQTT connection.
Starts a 10-second period timer, transmits and receives.

var client = mqtt.connect('mqtt://foo.bar');
if(!client) {
    print('Failed to create mqtt instance');
} else {
    client.on('connect', function(connack) {
        print('CONNECTED');
        client.subscribe('foo_topic/device01');
    });
    client.on('error', function(err) {
        print('ERROR: ' + err.code + ' ERRNO: ' + client.get('errnoConnect'));
        if(1 == err.code) { //Connection failed
            client.reconnect();
        }
        //TODO: Error handling
    });
    client.on('close', function() {
        print("DISCONNECTED");
        client.reconnect();
    });
    client.on('message', function(topic, message) {
        print('TOPIC: ' + topic + ' MESSAGE: ' + message);
        //TODO: Message handling
    });
}
var tmobj = setInterval(function() {
    if(!client) {
    } else {
        if(client.isConnected()) {
            var dummyBatteryLevel = 10;
            if(10 >= dummyBatteryLevel) {
                client.publish( 'bar_topic/device01',
                                'Battery level : '
                                 + dummyBatteryLevel.toString()
                                 + '%');
            }
        } else {
            print('Skipped');
        }
    }
}, 10000);

Sample 2

This is a sample MQTTS connection.
Starts a 10-second period timer, transmits and receives.

var sslCa = '-----BEGIN CERTIFICATE-----\n(...ContentOmission...)\n-----END CERTIFICATE-----';
mqtt.set('ssl.ca', sslCa);

var client = mqtt.connect('mqtts://foo.bar:8883');
if(!client) {
    print('Failed to create mqtt instance');
} else {
    client.on('connect', function(connack) {
        print('CONNECTED');
        client.subscribe('foo_topic/device01');
    });
    client.on('error', function(err) {
        print('ERROR: ' + err.code + ' ERRNO: ' + client.get('errnoConnect'));
        if(1 == err.code) { //Connection failed
            client.reconnect();
        }
        //TODO: Error handling
    });
    client.on('close', function() {
        print("DISCONNECTED");
        client.reconnect();
    });
    client.on('message', function(topic, message) {
        print('TOPIC: ' + topic + ' MESSAGE: ' + message);
        //TODO: Message handling
    });
}
var tmobj = setInterval(function() {
    if(!client) {
    } else {
        if(client.isConnected()) {
            var dummyBatteryLevel = 10;
            if(10 >= dummyBatteryLevel) {
                client.publish( 'bar_topic/device01',
                                'Battery level : '
                                 + dummyBatteryLevel.toString()
                                 + '%');
            }
        } else {
            print('Skipped');
        }
    }
}, 10000);

Sample 3

This is a sample MQTTS connection using client authentication.
Starts a 10-second period timer, transmits and receives.

var sslCa = '-----BEGIN CERTIFICATE-----\n(...ContentOmission...)\n-----END CERTIFICATE-----';
var sslClientCert = '-----BEGIN CERTIFICATE-----\n(...ContentOmission...)\n-----END CERTIFICATE-----';
var sslClientKey = '-----BEGIN PRIVATE KEY-----\n(...ContentOmission...)\n-----END PRIVATE KEY-----';
mqtt.set('ssl.ca', sslCa);
mqtt.set('ssl.cert', sslClientCert);
mqtt.set('ssl.key', sslClientKey);

var mqttClientId = 'foo';
var mqttUser = 'foo';
var mqttPass = 'foobar';
var mqttOpt = {clientId:mqttClientId, username:mqttUser, password:mqttPass, reconnectCount:1855};

var client = mqtt.connect('mqtts://foo.bar:8883', mqttOpt);
if(!client) {
    print('Failed to create mqtt instance');
} else {
    client.on('connect', function(connack) {
        print('CONNECTED');
        client.subscribe('foo_topic/device01');
    });
    client.on('error', function(err) {
        print('ERROR: ' + err.code + ' ERRNO: ' + client.get('errnoConnect'));
        if(1 == err.code) { //Connection failed
            client.reconnect();
        }
        //TODO: Error handling
    });
    client.on('close', function() {
        print("DISCONNECTED");
        client.reconnect();
    });
    client.on('message', function(topic, message) {
        print('TOPIC: ' + topic + ' MESSAGE: ' + message);
        //TODO: Message handling
    });
}
var tmobj = setInterval(function() {
    if(!client) {
    } else {
        if(client.isConnected()) {
            var dummyBatteryLevel = 10;
            if(10 >= dummyBatteryLevel) {
                client.publish( 'bar_topic/device01',
                                'Battery level : '
                                 + dummyBatteryLevel.toString()
                                 + '%');
            }
        } else {
            print('Skipped');
        }
    }
}, 10000);

Sample 4

This sample repeats the start and end of MQTT connection.
If you do mqtt.connect() immediately after exiting with .end(), mqtt.connect() may fail because MQTT resources have not been released yet. In that case, wait a while and try the connection again.

var mqttUrl = 'mqtt://foo.bar:1883';
var mqttc = undefined;
var endEv = 0;

var to = setInterval(function() {
    print('end event');
    endEv = 1;
}, 30000);

while(1) {
    if(!mqttc) {
        mqttc = mqtt.connect(mqttUrl, {reconnectCount:1855});
        if(!mqttc) {
            print('Waiting for mqtt resource release');
            setTimeout(200).wait();
            continue;
        }
        mqttc.on('connect', function(connack) {
            print('CONNECTED');
        });
        //  ...Omitted: Registers an event handler.
    }
    //  ...Omitted: mqtt communication processing.
    if(1 == endEv) {
        endEv = 0;
        print('ABORT');
        mqttc.end();
        mqttc = undefined;
        continue;
    }
}

Sample 5

This is a sample to connect MQTT with automatic reconnection enabled.
After connection, loopback test of transmission and reception is performed.

var client = mqtt.connect('mqtt://foo.bar:1883', {reconnectCount: 1855});
if(!client) {
    throw 'Failed to create mqtt instance';
}

client.on('error', function(err) {
    print('ERROR: ' + err.code + ' ERRNO: ' + client.get('errnoConnect'));
    //TODO: Error handling
});
client.on('message', function(topic, message) {
    print('TOPIC: ' + topic + ' MESSAGE: ' + message);
    //TODO: Message handling
});
client.on('connect', function() {
    print('CONNECTED');
    client.subscribe('testtopic/subtopic/#', { qos: 1 }, function(err) {
        if(err.code > 0) {
            print('MQTT SUBSCRIBE ERROR', err.code);
            //TODO: Error handling
        }
    });
    client.subscribe('shadowtopic/#', { qos: 1 }, function(err) {
        if(err.code > 0) {
            print('MQTT SUBSCRIBE ERROR', err.code);
            //TODO: Error handling
        }
    });
});

setInterval(function() {
    if (client.canPublish()) {
        var body = JSON.stringify({ "message" : "dummy" });
        client.publish('testtopic/subtopic/dummy', body, { qos: 1 }, function(err) {
            if(err.code == 0) {
                print('Publish OK');
            } else {
                print('Publish failed');
                //TODO: Error handling
            }
        });
    } else {
        print('Cannot publish');
    }
}, 15000);

Sample 6

This is a sample to manually reconnect MQTT.
If the reconnects fail consecutively, release the instance and recreate it.

var mqttUrl = 'mqtt://foo.bar:1883';
var reconnectAttempts = 0;
var maxReconnectAttempts = 24;

var registerEventHandlers = function() {
    if(!client) {
        return;
    }
    client.on('error', function(err) {
        print('ERROR: ' + err.code + ' ERRNO: ' + client.get('errnoConnect'));
        if (err.code == 1) { //Connection failed
            if (reconnectAttempts++ < maxReconnectAttempts) {
                print('reconnectAttempts:', reconnectAttempts);
                client.reconnect();
            } else {
                print('ABORT');
                reconnectAttempts = 0;
                client.end(); //Release mqtt instance
                client = undefined;
            }
        }
    });
    client.on('message', function(topic, message) {
        print('TOPIC: ' + topic + ' MESSAGE: ' + message);
        //TODO: Message handling
    });
    client.on('close', function() {
        print("DISCONNECTED");
        client.reconnect();
    });
    client.on('connect', function() {
        reconnectAttempts = 0;
        print("CONNECTED");
        client.subscribe("foo_topic/device01/#", { qos: 1 }, function(err) {
            if(err.code > 0) {
                print("MQTT SUBSCRIBE ERROR", err.code);
                //TODO: Error handling
            }
        });
    });
}

var client = mqtt.connect(mqttUrl);
if(!client) {
    throw 'Failed to create mqtt instance';
}

registerEventHandlers();

setInterval(function() {
    if(!client) {
        print('mqtt instance recreate');
        client = mqtt.connect(mqttUrl);
        registerEventHandlers();
    }
    if(client && client.canPublish()) {
        var body = JSON.stringify({ "message" : "dummy" });
        client.publish("foo_topic/device01/dummy", body, { qos: 1 }, function(err) {
            if(err.code == 0) {
                print('Publish OK');
            } else {
                print('Publish failed');
                //TODO: Error handling
            }
        });
    }
}, 15000);

---

Updated: 2022-06-03