Google Cloud IoT - How to connect and publish to specific topic with MQTT?

[Dalton Cezane]

Hello.

I am trying to connect a Python client to a pub/sub topic. I am using paho-mqtt. My code is below, based on examples of the Google IoT documentation, which is not so clear:

import paho.mqtt.client as mqtt 
import ssl, random, jwt_maker 
from time import sleep 

root_ca = './../roots.pem' 
public_crt = './../my_cert.pem' 
private_key = './../my_pr.pem' 

mqtt_url = "mqtt.googleapis.com" 
mqtt_port = 8883 
mqtt_topic = "/devices/sm1/events" 
project_id = "myprojectname" 
cloud_region = "us-central1" 
registry_id = "sm1" 
device_id = "sm1" 

connflag = False 

def on_connect(client, userdata, flags, response_code): 
    global connflag 
    connflag = True 
    print("Connected with status: {0}".format(response_code)) 

def on_publish(client, userdata, mid): 
    print("User data: {0} -- mid: {1}".format(userdata, mid)) 
    #client.disconnect() 

if __name__ == "__main__": 
    client = mqtt.Client("projects/{}/locations/{}/registries/{}/devices/{}".format( project_id, cloud_region, registry_id, device_id)) 
    client.username_pw_set(username='unused', password=jwt_maker.create_jwt(project_id, private_key, algorithm="RS256")) 
    client.tls_set(root_ca, certfile = public_crt, keyfile = private_key, cert_reqs = ssl.CERT_REQUIRED, tls_version = ssl.PROTOCOL_TLSv1_2, ciphers = None) 

    client.on_connect = on_connect 
    client.on_publish = on_publish 

    print("Connecting to Google IoT Broker...") 
    client.connect(mqtt_url, mqtt_port, keepalive=60) 
    client.loop() 
 
    while True: 
        sleep(0.5) 
        print connflag 
        if connflag == True: 
           print("Publishing...") 
           ap_measurement = random.uniform(25.0, 150.0) 
           #payload = "sm1/sm1-payload-{}".format(ap_measurement) 
           client.publish(mqtt_topic, ap_measurement, qos=1)
           print("Payload published: %.2f" % ap_measurement) 
        else: 
           print("Waiting for connection...")

When I run, this is the output:

Connecting to Google IoT Broker...
False
Waiting for connection...
False
Waiting for connection...

Any help? I already read the following documentation and code:

• https://cloud.google.com/iot/docs/how-tos/mqtt-bridge#iot-core-mqtt-auth-run-python
• https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/iot/api-client/mqtt_example/cloudiot_mqtt_example.py

This problem is also described at StackOverflow: https://stackoverflow.com/questions/49904705/google-cloud-iot-how-to-connect-and-publish-to-specific-topic-with-mqtt
Thank you in advance.

[Dalton Cézane]

I got success on the connect operation, just changing the "client.loop()" to "client.start_loop()". But now I am not able to publish to my specific topic, as described here:
https://stackoverflow.com/questions/49907529/google-cloud-iot-invalid-mqtt-publish-topic

The Google IoT Console presents the following message: "Invalid MQTT publish topic: projects/my_project/topics/sm1".

Any help?

Thank you.

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Dalton Cézane
Doutorando/Mestre/Especialista/Bacharel em Ciência da Computação (UFCG)

MBA em Gerenciamento de Projetos (Anglo Americano)
Técnico em Informática (ETER)

[Katayoon (Cloud Platform Support)]

I should note that Google Groups are reserved for general product discussions and are not for technical questions. For further technical support I recommend to work with the duplicate thread you have created in Stack Overflow.