How to connect to a digitransit broker with a specific topic using paho mqtt client

I am pretty new to MQTT and I would like to establish a connection to a digitransit mqtt broker to receive public transportation data using python paho mqtt client. To connect to a broker the port and the topic is needed.

Regarding the information provided in the broker source I guess I need at least two pieces of information but I am not sure if something is missing. Please not that the script is executed via browser based jupyter notebook.

Broker source: https://digitransit.fi/en/developers/apis/4-realtime-api/vehicle-positions/ Paho documentation: https://www.eclipse.org/paho/index.php?page=clients/python/index.php

Port: 8883
Topic: /hfp/v2/journey/#
Broker: mqtt.hsl.fi

When running via command line the data can be received, e.g.

/hfp/v2/journey/ongoing/vp/bus/0022/01281/1040/2/Elielinaukio/14:29/1140118/0//// {"VP":{"desi":"40","dir":"2","oper":22,"veh":1281,"tst":"2022-07-06T11:56:53.417Z","tsi":1657108613,"spd":null,"hdg":null,"lat":null,"long":null,"acc":null,"dl":-101,"odo":8530,"drst":0,"oday":"2022-07-06","jrn":2646,"line":62,"start":"14:29","loc":"ODO","stop":null,"route":"1040","occu":0}}

You can try this out simply using two commands:

npm install -g mqtt

mqtt subscribe -h mqtt.hsl.fi -p 8883 -l mqtts -v -t "/hfp/v2/journey/#"

When running on a jupyter notebook or python script I only see the output that is defined on_connectmethod but no data shows up.

My code snippet is:

# pip install paho-mqtt

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+ str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("/hfp/v2/journey/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.tls_set()
client.connect("mqtt.hsl.fi", 8883, 60)

client.loop_forever()

Does anyone know what kind of detail is wrong or missing?

UPDATE: The accepted solution works for python scripts executed via python IDE like Pycharm or Visual Studio Code but not with browser based IDEs like Jupyter Notebook.

Answer

The problem is you have not told the Python Paho Client it needs to connect using TLS.

Add the client.tls_set() before the call to connect()

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.tls_set()
client.connect("mqtt.hsl.fi", 8883, 60)

client.loop_forever()

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Answer