MQTT client examples

Overview

In this section, Hello MQTT provides an easy introduction to the Cumulocity IoT MQTT protocol using a MQTT cross platform application.

It also contains examples on how to use the MQTT client with Cumulocity IoT employing pre-defined messages (called “static templates”) using C, Java, JavaScript and Python.

All the examples can be downloaded from the GitHub repository.

Hello MQTT

In this tutorial, you will learn how to use MQTT with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

Info
The screenshots in the tutorial use MQTTBox. Other tools may look different.
Info
If you are using a trial tenant, the default user will not work with this tutorial. Create an additional user instead. The tenant ID and URL data will also differ from trial tenant information.

Talking MQTT

Configuring the MQTT connection

To configure the MQTT connection, you must pass the following connection parameters (see the screenshot below).

Cumulocity IoT supports MQTT both via TCP and WebSockets. As URL you can use your tenant domain (for example mytenant.cumulocity.com/mqtt) or the domain of the instance in the format mqtt.<instance_domain> (for example mqtt.cumulocity.com).

Example MQTTBox Configuration

Info
You may review Tenants > Tenant ID and tenant domain in the Cumulocity IoT OpenAPI Specification to get a better understanding between tenant ID and tenant domain.

Other configurations like “clean session” are not important for this example. You can change them to your needs. After clicking Save, you will see a screen similar to the following screenshot.

MQTTBox Established Connection

If there is a blue button on the top bar with a label Not Connected, verify your configuration (especially username and password). If the button is green, you successfully established an MQTT connection to Cumulocity IoT.

Sending data

All MQTT publish messages in this tutorial will be sent to the topic s/us. This is the topic used for Cumulocity IoT’s pre-provided static templates.

MQTTBox Publish Message

Creating the device

The first message sent will create our device. Although the static templates support automatic device creation, in this example we will create the device manually. The template 100 will create a new device. It can be used with two optional parameters (deviceName, deviceType).

100,My first MQTT device,c8y_MQTTdevice

Afterwards, you will find this device in the Device management application as a new device. If you switch to the Identity tab of the device you will notice that there was an identity created automatically to link the device to the MQTT ClientId.

Besides the name and the type, the device does not have more information, so master data needs to be added.

You can use multiple static templates per publishing separated by a line break (one template per row). This feature is used to set the hardware and the required interval for the device in a single published message.

The hardware can be set with the template 110. It can take 3 parameters (serialNumber, model, revision). Optional parameters in static templates can be left empty if you don’t want to set them. For the hardware all parameters are optional.

The required interval can be set with the template 117 and just takes a single parameter (the interval in minutes).

110,,MQTT test model,1.2.3
117,10

After a reload of the Info page of your device in the Device management application, you should see the information we just added.

Creating measurements

Now the device has some master data and we can start sending some measurements. There are a couple of measurements that can be created directly by using a static template:

The temperature and battery measurement just take the value and time as parameters. For the signal strength, you can pass two values (RSSI and BER).

Passing timestamps in the Cumulocity IoT MQTT implementation is always optional. If you don’t pass them along, the server will automatically create a timestamp with the current server time.

We will make use of this feature in this example. Also, if you don’t set the last parameters, you do not need to enter the remaining commas.

210,-87
211,24
212,95

Besides the measurements above, we can also use the template 200 to create a more custom measurement. It will take the measurement fragment, series, value, unit and time as its parameters.

200,myCustomTemperatureMeasurement,fahrenheit,75.2,F

After a reload in the Device management application, you should see 4 graphs with the newly added measurements in the Measurements tab of your device.

Creating alarms

Now we will create some alarms for this device. There are templates to create alarms for the 4 alarm severities:

Each of them note a type (which is mandatory), a text and a time (both optional).

301,gpio_critical,There is a GPIO alarm
304,simple_warning

The alarm list of your device should now contain one critical alarm and one warning.

Note that we did not set any text for the warning, so it was created with a default alarm text.

Now we will clear the critical alarm again. To achieve this, we use the template 306 which refers to the type of the alarm that should be cleared.

306,gpio_critical

The critical alarm should be cleared afterwards.

Note that you did not have to handle any alarm IDs with the MQTT implementation. Cumulocity IoT will take over this part so that the device communication can be as easy as possible.

Creating events

Next, we will create some location events for the device. If you wish, you may use the LatLong website to get the latitude and longitude of your city.

The template 401 lets you create location events and takes latitude, longitude, altitude, accuracy and the time as parameters, but for now we will just use the first two.

401,51.227741,6.773456

In the Device management application, you can see one event in the event list but the location has not been updated. This is because on REST these are different requests. Instead of the template 401, you can use the template 402 in MQTT. It works exactly the same as 401 but additionally it also updates the position of the device itself.

402,51.227741,6.773456

Now you should see both the Location and the Tracking tab in the device with the Location tab having the same latitude and longitude as the last location event.

Receiving data

So far we have only used MQTT to send data from the client to the server. Now we will send data from the server to the client.

To achieve this, we must first subscribe to the responsible topic. We will do two subscriptions:

You can enter both topics after another in the Subscribe field and click Subscribe. The QoS selection does not matter for this example.

Afterwards, your MQTTBox should look like this:

MQTTBox Subscribed Topics

Receiving operations

At the current state, the UI does not show any tabs for operations. Up to this point, it was unknown what exactly the device supports, but the list of supported operations can be modified with the template 114. A list of supported operations can be added here.

We will add support for the configuration and shell.

114,c8y_Command,c8y_Configuration

After reloading the UI, the two new tabs will appear (Configuration and Shell).

We can now create a shell command from the UI and click Execute.

In the MQTTBox, you should now have received a new message for the s/ds subscription.

MQTTBox Received Operation

The 511 is indicating what kind of operation we received (in this case c8y_Command). This will be followed by the deviceIdentifier to locate the device with the dedicated operation. This is required if you have a hierarchy with multiple children. In such case, you must know for which of the children the operation was dedicated. Finally, you have the operation specific parameters, which in the case of c8y_Command is only the command text.

After receiving the operation, we can start executing it to initiate the client’s handling the operation. Similar to changing the status of an alarm, you can add the type of operation to the template.

501,c8y_Command

After completing the handling, the operation can be set to successful with the template 503.

Besides the operation type, this operation can also take additional parameters based on what kind of operation it was. We can return a result for the c8y_Command.

503,c8y_Command,Everything went fine
Learning from errors

The topic s/e can help you debugging in case something went wrong. For instance, if we try to send

999,I made this up

we can see a message on the topic because the template 999 is unknown.

40,999,No static template for this message id

Hello MQTT C

In this tutorial, you will learn how to use MQTT client in C with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Developing the “Hello, MQTT world!” client

To develop a very simple “Hello, world!” MQTT client for Cumulocity IoT, you must

Creating the application

Create a source file (for example hello_mqtt.c) with the following content:

#include "stdlib.h"
#include "string.h"
#include "unistd.h"
#include "MQTTClient.h"

#define ADDRESS     "<<serverUrl>>"
#define CLIENTID    "<<clientId>>"

void publish(MQTTClient client, char* topic, char* payload) {
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    pubmsg.payload = payload;
    pubmsg.payloadlen = strlen(pubmsg.payload);
    pubmsg.qos = 2;
    pubmsg.retained = 0;
    MQTTClient_deliveryToken token;
    MQTTClient_publishMessage(client, topic, &pubmsg, &token);
    MQTTClient_waitForCompletion(client, token, 1000L);
    printf("Message '%s' with delivery token %d delivered\n", payload, token);
}

int on_message(void *context, char *topicName, int topicLen, MQTTClient_message *message) {
    char* payload = message->payload;
    printf("Received operation %s\n", payload);
    MQTTClient_freeMessage(&message);
    MQTTClient_free(topicName);
    return 1;
}

int main(int argc, char* argv[]) {
    MQTTClient client;
    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    conn_opts.username = "<<tenant_ID>>/<<username>>";
    conn_opts.password = "<<password>>";

    MQTTClient_setCallbacks(client, NULL, NULL, on_message, NULL);

    int rc;
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to connect, return code %d\n", rc);
        exit(-1);
    }
    //create device
    publish(client, "s/us", "100,C MQTT,c8y_MQTTDevice");
    //set hardware information
    publish(client, "s/us", "110,S123456789,MQTT test model,Rev0.1");
    //listen for operation
    MQTTClient_subscribe(client, "s/ds", 0);

    for (;;) {
        //send temperature measurement
        publish(client, "s/us", "211,25");
        sleep(3);
    }
    MQTTClient_disconnect(client, 1000);
    MQTTClient_destroy(&client);
    return rc;
}

Replace <<clientId>>, <<serverUrl>>, <<tenant_ID>>, <<username>> and <<password>> with your data.

The Cumulocity IoT MQTT protocol supports both unsecured TCP and secured SSL connections (for example tcp://mqtt.cumulocity.com:1883 or ssl://mqtt.cumulocity.com:8883), so as the <<serverUrl>> you can pick the one which fits for you. When using SSL remember to configure MQTTClient_SSLOptions and set it in the MQTTClient_connectOptions.

What does the code in main do?

What does the code in publish do?

Note that the subscription is established after the device creation, otherwise if there is no device for a given clientId the server will not accept it.

Building and running the application

To build the application, enter

$ gcc hello_mqtt.c -o hello_mqtt -lpaho-mqtt3c

To run the application, enter

$ ./hello_mqtt
Message '100,C MQTT,c8y_MQTTDevice' with delivery token 1 delivered
...

After starting the application, you should see a new device in the Device management application, listed in All devices.

Additionally, if there will be a new operation created for this device (for example c8y_Restart), information about it will be printed to the console.

Improving the agent

Now that you have done your first step, check out the section Hello MQTT to learn more about Cumulocity IoT MQTT and improve your application.

Hello MQTT Java

In this tutorial, you will learn how to use the Java MQTT client with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

$ mvn -v
Maven home: /Library/Maven/apache-maven-3.6.0
Java version: 1.8.0_201, vendor: Oracle Corporation, runtime: /Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home/jre
Default locale: en_GB, platform encoding: UTF-8
OS name: "mac os x", version: "10.14.2", arch: "x86_64", family: "mac"

Maven can be downloaded from the Maven website.

Developing the “Hello, MQTT world!” client

To develop a very simple “Hello, world!” MQTT client for Cumulocity IoT, you must

Create a Maven project

To create a plain Java project with Maven, execute the following command:

$ mvn archetype:generate -DgroupId=c8y.example -DartifactId=hello-mqtt-java -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

This will create a folder hello-mqtt-java in the current directory with a skeleton structure for your project.

Add the MQTT Java client library

Edit the pom.xml in the hello-mqtt-java folder. Add a dependency to the MQTT Paho Java Client.

<dependency>
    <groupId>org.eclipse.paho</groupId>
    <artifactId>org.eclipse.paho.client.mqttv3</artifactId>
    <version>[1.2.1,)</version>
</dependency>

If you are using Java 9 or later, you must set the source and target as described at the Apache Maven Compiler Plugin page, adding the following code:

<properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

Create a Java application

Edit the App.java file located in the folder hello-mqtt-java/src/main/java/c8y/example with the following content:

package c8y.example;

import org.eclipse.paho.client.mqttv3.*;
import java.util.concurrent.*;

public class App {

    public static void main(String[] args) throws Exception {

        // client, user and device details
        final String serverUrl   = "tcp://mqtt.cumulocity.com";     /* ssl://mqtt.cumulocity.com:8883 for a secure connection */
        final String clientId    = "my_mqtt_java_client";
        final String device_name = "My Java MQTT device";
        final String tenant      = "<<tenant_ID>>";
        final String username    = "<<username>>";
        final String password    = "<<password>>";

        // MQTT connection options
        final MqttConnectOptions options = new MqttConnectOptions();
        options.setUserName(tenant + "/" + username);
        options.setPassword(password.toCharArray());

        // connect the client to Cumulocity IoT
        final MqttClient client = new MqttClient(serverUrl, clientId, null);
        client.connect(options);

        // register a new device
        client.publish("s/us", ("100," + device_name + ",c8y_MQTTDevice").getBytes(), 2, false);

        // set device's hardware information
        client.publish("s/us", "110,S123456789,MQTT test model,Rev0.1".getBytes(), 2, false);

        // add restart operation
        client.publish("s/us", "114,c8y_Restart".getBytes(), 2, false);

        System.out.println("The device \"" + device_name + "\" has been registered successfully!");

        // listen for operations
        client.subscribe("s/ds", new IMqttMessageListener() {
            public void messageArrived (final String topic, final MqttMessage message) throws Exception {
                final String payload = new String(message.getPayload());

                System.out.println("Received operation " + payload);
                if (payload.startsWith("510")) {
                    // execute the operation in another thread to allow the MQTT client to
                    // finish processing this message and acknowledge receipt to the server
                    Executors.newSingleThreadScheduledExecutor().execute(new Runnable() {
                        public void run() {
                            try {
                                System.out.println("Simulating device restart...");
                                client.publish("s/us", "501,c8y_Restart".getBytes(), 2, false);
                                System.out.println("...restarting...");
                                Thread.sleep(TimeUnit.SECONDS.toMillis(5));
                                client.publish("s/us", "503,c8y_Restart".getBytes(), 2, false);
                                System.out.println("...done...");
                            } catch (MqttException e) {
                                e.printStackTrace();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    });
                }
            }
        });

        // generate a random temperature (10º-20º) measurement and send it every 7 seconds
        Executors.newSingleThreadScheduledExecutor().scheduleWithFixedDelay(new Runnable() {
            public void run () {
                try {
                    int temp = (int) (Math.random() * 10 + 10);

                    System.out.println("Sending temperature measurement (" + temp + "º) ...");
                    client.publish("s/us", new MqttMessage(("211," + temp).getBytes()));
                } catch (MqttException e) {
                    e.printStackTrace();
                }
            }
        }, 1, 7, TimeUnit.SECONDS);
    }
}

Replace serverUrl, clientId and device_name as needed. Do not forget to specify the user credentials setting values for tenant_ID, username and password.

Cumulocity IoT MQTT protocol supports both unsecured TCP and secured SSL connections (that is, tcp://mqtt.cumulocity.com:1883 or ssl://mqtt.cumulocity.com:8883), so you can pick the one which fits for you and use it in serverUrl.

What does the code in main do?

Note that the subscription is established after the device creation, otherwise if there is no device for a given clientId, the server will not accept it.

Build and run the application

Use the following commands to build the application:

$ cd hello-mqtt-java
$ mvn clean install
...
[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ hello-mqtt-java ---
[INFO] Building jar: /home/schm/Pulpit/hello-mqtt-java/target/hello-mqtt-java-1.0-SNAPSHOT.jar
[INFO]
[INFO] --- maven-install-plugin:2.4:install (default-install) @ hello-mqtt-java ---
[INFO] Installing /home/schm/Pulpit/hello-mqtt-java/target/hello-mqtt-java-1.0-SNAPSHOT.jar to /home/schm/.m2/repository/c8y/example/hello-mqtt-java/1.0-SNAPSHOT/hello-mqtt-java-1.0-SNAPSHOT.jar
[INFO] Installing /home/schm/Pulpit/hello-mqtt-java/pom.xml to /home/schm/.m2/repository/c8y/example/hello-mqtt-java/1.0-SNAPSHOT/hello-mqtt-java-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.642 s
[INFO] Finished at: 2017-03-14T09:16:25+01:00
[INFO] Final Memory: 14M/301M
[INFO] ------------------------------------------------------------------------

and this command to run it:

$ mvn exec:java -Dexec.mainClass="c8y.example.App"
...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building hello-mqtt-java 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- exec-maven-plugin:1.6.0:java (default-cli) @ hello-mqtt-java ---
Received operation 510,123456789

After starting the application, you should see a new registered device in the Device management application, listed in All devices. In the Measurements tab, you will see the temperature measurements being sent by your client.

Additionally, if there will be a new operation created for this device (for example c8y_Restart), information about it will be printed to the console.

Improving the agent

Now that you have done your first step, check out the Section Hello MQTT to learn more about Cumulocity IoT MQTT and improve your application.

Hello MQTT Java with certificates

In this tutorial, you will learn how to use the Java MQTT client with Cumulocity IoT using X.509 certificates for authentication.

In the GitHub repository cumulocity-examples, you can find a sample Java MQTT client using X.509 certificates and all necessary scripts used in this tutorial.

Prerequisites

In order to follow this tutorial, check the following prerequisites:

To generate a valid certificate

If you don’t have a valid certificate, you can generate one for testing purposes, following the instructions below.

  1. Download the scripts from the cumulocity-examples repository.
  2. Create a root self-signed certificate (execute the script 00createRootSelfSignedCertificate.sh) and upload it to your tenant. You can do it via the Device management application in the UI or via REST.
  3. Create and sign the certificate (execute the script 01createSignedCertificate.sh).
  4. Move the certificates to keystore (execute the script 02moveCertificatesToKeystore.sh).
  5. Finally, import the trusted certificate into keystore running the following command:
$ keytool -importcert -file c8y-mqtt-server.cer -keystore chain-with-private-key-iot-device-0001.jks -alias "Alias"

Developing the “Hello, MQTT world!” client with certificates

To develop a “Hello, world!” MQTT client for Cumulocity IoT with certificates, you must

To copy and upload the certificate

Copy the certificate from the file chain-iot-device-0001.pem and upload it to the platform employing a POST request:

Endpoint: /tenant/tenants/{tenantId}/trusted-certificates
Authorization: Basic
Content-Type: application/json
Request body:

{
    "status" :  "ENABLED",
    "name" : "sampleName",
    "autoRegistrationEnabled" : "true",
    "certInPemFormat" : "<<certificate in pem format>>"
}

To change the configuration

To change the configuration in the MQTT client, copy the file chain-with-private-key-iot-device-0001.jks into the resource folder and set the configuration. Note that the script employed (Step 4.) uses the password changeit. If you changed the value in the script, also do it for KEYSTORE_PASSWORD and TRUSTSTORE_PASSWORD in the following example.

// Configuration
private static final String KEYSTORE_NAME = "chain-with-private-key-iot-device-0001.jks";
private static final String KEYSTORE_PASSWORD = "changeit";
private static final String KEYSTORE_FORMAT = "jks";

private static final String TRUSTSTORE_NAME = "chain-with-private-key-iot-device-0001.jks";
private static final String TRUSTSTORE_PASSWORD = "changeit";
private static final String TRUSTSTORE_FORMAT = "jks";

private static final String CLIENT_ID = "iotdevice0001";
private static final String BROKER_URL = "<SSL URL of the platform>";

private MqttClient connect() throws MqttException {
    MqttClient mqttClient = new MqttClient(BROKER_URL, "d:" + CLIENT_ID, new MemoryPersistence());
    MqttConnectOptions options = new MqttConnectOptions();

    options.setCleanSession(true);

    Properties sslProperties = new Properties();
    sslProperties.put(SSLSocketFactoryFactory.KEYSTORE, getClass().getClassLoader().getResource(KEYSTORE_NAME).getPath());
    sslProperties.put(SSLSocketFactoryFactory.KEYSTOREPWD, KEYSTORE_PASSWORD);
    sslProperties.put(SSLSocketFactoryFactory.KEYSTORETYPE, KEYSTORE_FORMAT);
    sslProperties.put(SSLSocketFactoryFactory.TRUSTSTORE, getClass().getClassLoader().getResource(TRUSTSTORE_NAME).getPath());
    sslProperties.put(SSLSocketFactoryFactory.TRUSTSTOREPWD, TRUSTSTORE_PASSWORD);
    sslProperties.put(SSLSocketFactoryFactory.TRUSTSTORETYPE, TRUSTSTORE_FORMAT);
    sslProperties.put(SSLSocketFactoryFactory.CLIENTAUTH, true);

    options.setSSLProperties(sslProperties);
    mqttClient.setCallback(this);
    System.out.println("Connecting to the broker at " + BROKER_URL);
    mqttClient.connect(options);

    return mqttClient;
}

The device can now publish and subscribe as a standard device. Note that before the first connect no other actions are required, for example, creating a user. The user is created during the auto registration process.

Info
You do not need to set a password, user or tenant for the MQTT client connecting using certificates. Cumulocity IoT will recognize the tenant and the user by the provided certificate.

Hello MQTT browser-based

In this tutorial, you will learn how to use the browser-based MQTT client with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

Developing the “Hello, MQTT world!” client

To develop a very simple “Hello, world!” MQTT client for Cumulocity IoT, you must

Creating a JavaScript application

Create an HTML file (for example hello_mqtt_js.html) with the following content:

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Hello MQTT World</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="https://cdnjs.cloudflare.com/ajax/libs/paho-mqtt/1.0.1/mqttws31.min.js"></script>
    <script src="main.js" defer></script>
</head>
<body>
    <div id="logger"></div>
</body>
</html>

Create a JavaScript file main.js with the following content:

// client, user and device details
var serverUrl   = "ws://mqtt.cumulocity.com/mqtt";     /* wss://mqtt.cumulocity.com/mqtt for a secure connection */
var clientId    = "my_mqtt_js_client";
var device_name = "My JS MQTT device";
var tenant      = "<<tenant_ID>>";
var username    = "<<username>>";
var password    = "<<password>>";

var undeliveredMessages = [];
var temperature = 25;

// configure the client to Cumulocity IoT
var client = new Paho.MQTT.Client(serverUrl, clientId);

// display all incoming messages
client.onMessageArrived = function (message) {
    log('Received operation "' + message.payloadString + '"');
    if (message.payloadString.indexOf("510") == 0) {
        log("Simulating device restart...");
        publish("s/us", "501,c8y_Restart");
        log("...restarting...");
        setTimeout(function() {
            publish("s/us", "503,c8y_Restart");
            log("...done...");
        }, 1000);
    }
};

// display all delivered messages
client.onMessageDelivered = function onMessageDelivered (message) {
    log('Message "' + message.payloadString + '" delivered');
    var undeliveredMessage = undeliveredMessages.pop();
    if (undeliveredMessage.onMessageDeliveredCallback) {
        undeliveredMessage.onMessageDeliveredCallback();
    }
};

function createDevice () {
    // register a new device
    publish("s/us", "100," + device_name + ",c8y_MQTTDevice", function() {
        // set hardware information
        publish("s/us", "110,S123456789,MQTT test model,Rev0.1", function() {
            publish('s/us', '114,c8y_Restart', function() {
                log('Enable restart operation support');
                //listen for operation
                client.subscribe("s/ds");
            })

            // send temperature measurement
            setInterval(function() {
                publish("s/us", '211,'+temperature);
                temperature += 0.5 - Math.random();
            }, 3000);
        });
    });
}

// send a message
function publish (topic, message, onMessageDeliveredCallback) {
    message = new Paho.MQTT.Message(message);
    message.destinationName = topic;
    message.qos = 2;
    undeliveredMessages.push({
        message: message,
        onMessageDeliveredCallback: onMessageDeliveredCallback
    });
    client.send(message);
}

// connect the client to Cumulocity IoT
function init () {
    client.connect({
        userName: tenant + "/" + username,
        password: password,
        onSuccess: createDevice
    });
}

// display all messages on the page
function log (message) {
    document.getElementById('logger').insertAdjacentHTML('beforeend', '<div>' + message + '</div>');
}

init();

Replace serverUrl, clientId and device_name as needed. Do not forget to specify the user credentials setting values for tenant_ID, username and password.

The Cumulocity IoT MQTT protocol supports both unsecured TCP and also secured SSL connections (that is, ws://mqtt.cumulocity.com/mqtt or wss://mqtt.cumulocity.com/mqtt), so you can pick the one which fits for you and use it in serverUrl.

What does the code do?

Note that the subscription is established after the device creation, otherwise if there is no device for a given clientId, the server will not accept it.

Running the application

Open the hello_mqtt_js.html file in a browser. You should see a new registered device in the Device management application, listed in All devices. In the Measurements tab, you will see the temperature measurements being sent by your client.

Additionally, if there will be a new operation created for this device (for example c8y_Restart), related information will be displayed in the browser page.

Improving the agent

Now that you have done your first step, check out the section Hello MQTT to learn more about Cumulocity IoT MQTT and improve your application.

Hello MQTT Node.js

In this tutorial, you will learn how to use the Node.js MQTT client with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

Developing the “Hello, MQTT world!” client

To develop a very simple “Hello, world!” MQTT client for Cumulocity IoT, you must

Creating a Node.js application

Create the package.json file to list down the dependencies and other basic information about your application.

{
  "dependencies": {
    "mqtt": "*"
  },
  "scripts": {
    "start": "node app.js"
  }
}

Create the start script (app.js) specified in the package.json file with the following content:

// MQTT dependency https://github.com/mqttjs/MQTT.js
const mqtt = require("mqtt");

// client, user and device details
const serverUrl   = "tcp://mqtt.cumulocity.com";
const clientId    = "my_mqtt_nodejs_client";
const device_name = "My Node.js MQTT device";
const tenant      = "<<tenant_ID>>";
const username    = "<<username>>";
const password    = "<<password>>";

var temperature   = 25;

// connect the client to Cumulocity IoT
const client = mqtt.connect(serverUrl, {
    username: tenant + "/" + username,
    password: password,
    clientId: clientId
});

// once connected...
client.on("connect", function () {
    // ...register a new device with restart operation
    client.publish("s/us", "100," + device_name + ",c8y_MQTTDevice", function() {
        client.publish("s/us", "114,c8y_Restart", function() {
            console.log("Device registered with restart operation support");
        });

        // listen for operations
        client.subscribe("s/ds");

        // send a temperature measurement every 3 seconds
        setInterval(function() {
            console.log("Sending temperature measurement: " + temperature + "º");
            client.publish("s/us", "211," + temperature);
            temperature += 0.5 - Math.random();
        }, 3000);
    });

    console.log("\nUpdating hardware information...");
    client.publish("s/us", "110,S123456789,MQTT test model,Rev0.1");
});

// display all incoming messages
client.on("message", function (topic, message) {
    console.log('Received operation "' + message + '"');
    if (message.toString().indexOf("510") == 0) {
        console.log("Simulating device restart...");
        client.publish("s/us", "501,c8y_Restart");
        console.log("...restarting...");
        setTimeout(function() {
            client.publish("s/us", "503,c8y_Restart");
            console.log("...done...");
        }, 1000);
    }
});

Replace serverUrl, clientId and device_name as needed. Do not forget to specify the user credentials setting values for tenant_ID, username and password.

The Cumulocity IoT MQTT protocol supports both unsecured TCP and secured SSL connections. No matter which connection type you select, your serverUrl should stay the same (like mqtt.cumulocity.com).

What does the code do?

Note that the subscription is established after the device creation, otherwise if there is no device for a given clientId, the server will not accept it.

Running the application

Before running the application, the MQTT middleware must be installed. To achieve this, execute the following command:

$ npm install

Installation needs to be done only once. Afterwards, you only need to execute the following command:

$ npm start

You should see a new registered device in the Device management application, listed in All devices. In the Measurements tab, you will see the temperature measurements being sent by your client.

Additionally, if there will be a new operation created for this device (for example c8y_Restart), related information about it will be printed to the console.

Improving the agent

Now that you have done your first step, check out the section Hello MQTT to learn more about Cumulocity IoT MQTT and improve your application.

Hello MQTT Python

In this tutorial, you will learn how to use the Python MQTT client with Cumulocity IoT using pre-defined messages (called “static templates”).

Prerequisites

In order to follow this tutorial, check the following prerequisites:

$ python3 --version
Python 3.8.5

Python can be downloaded from www.python.org.

$ pip install paho-mqtt
Info
The above command installs Paho on your system. You may want to use virtualenv to install it only for this example.
Info
On macOS you may need to execute sudo easy_install pip in case the pip command is not found.

Developing the “Hello, MQTT world!” client

To develop a very simple “Hello, world!” MQTT client for Cumulocity IoT, you must

Create a Python script

Create a script file (for example hello_mqtt.py) with the following content:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import paho.mqtt.client as mqtt
import time, random, threading
import multiprocessing as mp

# client, user and device details
serverUrl   = "mqtt.cumulocity.com"
clientId    = "my_mqtt_python_client"
device_name = "My Python MQTT device"
tenant      = "<<tenant_ID>>"
username    = "<<username>>"
password    = "<<password>>"

# task queue to overcome issue with paho when using multiple threads:
#   https://github.com/eclipse/paho.mqtt.python/issues/354
task_queue = mp.Queue()

# display all incoming messages
def on_message(client, userdata, message):
    payload = message.payload.decode("utf-8")
    print(" < received message " + payload)
    if payload.startswith("510"):
        task_queue.put(perform_restart)

# simulate restart
def perform_restart():
    print("Simulating device restart...")
    publish("s/us", "501,c8y_Restart", wait_for_ack = True);

    print("...restarting...")
    time.sleep(1)

    publish("s/us", "503,c8y_Restart", wait_for_ack = True);
    print("...restart completed")

# send temperature measurement
def send_measurement():
    print("Sending temperature measurement...")
    temperature = random.randint(10, 20)
    publish("s/us", "211,{}".format(temperature))

# publish a message
def publish(topic, message, wait_for_ack = False):
    QoS = 2 if wait_for_ack else 0
    message_info = client.publish(topic, message, QoS)
    if wait_for_ack:
        print(" > awaiting ACK for {}".format(message_info.mid))
        message_info.wait_for_publish()
        print(" < received ACK for {}".format(message_info.mid))

# display all outgoing messages
def on_publish(client, userdata, mid):
    print(" > published message: {}".format(mid))

# main device loop
def device_loop():
    while True:
        task_queue.put(send_measurement)
        time.sleep(7)

# connect the client to Cumulocity IoT and register a device
client = mqtt.Client(clientId)
client.username_pw_set(tenant + "/" + username, password)
client.on_message = on_message
client.on_publish = on_publish

client.connect(serverUrl)
client.loop_start()
publish("s/us", "100," + device_name + ",c8y_MQTTDevice", wait_for_ack = True)
publish("s/us", "110,S123456789,MQTT test model,Rev0.1")
publish("s/us", "114,c8y_Restart")
print("Device registered successfully!")

client.subscribe("s/ds")

device_loop_thread = threading.Thread(target = device_loop)
device_loop_thread.daemon = True
device_loop_thread.start()

# process all tasks on queue
try:
    while True:
        task = task_queue.get()
        task()
except (KeyboardInterrupt, SystemExit):
    print("Received keyboard interrupt, quitting ...")
    exit(0)

Replace serverUrl, clientId and device_name as needed. Do not forget to specify the user credentials setting values for tenant_ID, username and password.

Cumulocity IoT MQTT protocol supports both unsecured TCP and secured SSL connections, so when configuring a port remember to use the correct one. No matter which connection type you select, your serverUrl should stay the same (like mqtt.cumulocity.com).

The above example uses a TCP connection. If you would like to use an SSL connection, remember to use the proper configuration from the Paho MQTT client. Further information can be found at www.eclipse.org.

What does the script do?

What does the publish message do?

Note that the subscription is established after the device creation, otherwise if there is no device for a given clientId, the server will not accept it.

Run the script

To run the script just use the command:

$ python3 hello_mqtt.py

After starting the application you should see a new registered device in the Device management application, listed in All devices. In the Measurements tab, you will see the temperature measurements being sent by your client.

Additionally, if there will be a new operation created for this device (for example c8y_Restart), information about it will be printed to the console.

Improving the agent

Now that you have done your first step, check out the section Hello MQTT to learn more about Cumulocity IoT MQTT and improve your application.