Let's get the MQTT client from the official GCP GitHub repository. In this simple example, we are going to use Node.js:

1. First, we need to clone the Node.js client from the official repository. From the root path where we have stored our certificate, enter the following command:

$ mkdir my-iiot-device
$ cd my-iiot-device
$ git clone https://github.com/GoogleCloudPlatform/nodejs-docs-samples
$ cd nodejs-docs-samples/iot/mqtt_example/
$ npm install

2. We can then start publishing. The following code sends an MQTTS payload to the IoT core that was just configured on europe-west1, identifying itself as my-iiot-device:

$ node cloudiot_mqtt_example_nodejs.js 
    --projectId=iiot-book 
    --cloudRegion=europe-west1 
    --registryId=iiot-book-registry 
    --deviceId=my-iiot-device 
    --privateKeyFile=../../../../../certificates/device_private.pem 
    --algorithm=RS256

3. Finally, we can check the reception status on the Registry details page, as shown in the following screenshot:

4. We now need to change the payload so that it is compliant with our CSV format. On line 161 of the cloudiot_mqtt_example_nodejs.js file located in the nodejs-docs-samples/iot/mqtt_example/ directory, we need to replace the payload with the following:

… 
setTimeout(function () {
    //const payload = `${argv.registryId}/${argv.deviceId}-payload-${messagesSent}`;
    const ts = new Date().getTime();
    const payload = 
 `${argv.registryId}.${argv.deviceId}.signal1,${messagesSent},${ts},GOOD`;
…

The expected output is as follows: