Send JSON documents with the pubsub.py sample app - MQTT Test Client displays string not json

Question

Hi, I am new to AWS IoT and working through the SDK tutorials. Using RPi3B and python. https://docs.aws.amazon.com/iot/latest/developerguide/sdk-tutorials.html - I am @ "publish JSON documents in the message payload". I created pubsub3.py & changed the line of code: ...message = "{}".format(message_string). Tutorial says to 'change this line of code' to... message = "{}".format(args.message) BUT my pubsub.py has .format(message_string) var instead.
The MQTT Test client is displaying as string literal and not interpreting/formatting correctly in json format.
I have tried all sorts of combinations of quotes and breaks and brackets (" \ ' { ] ). From what I see it should be sending the payload as a json string...

Command line:
pi3@raspberrypi:~ $ python3 aws-iot-device-sdk-python-v2/samples/pubsub3.py --message '{"temperature":40}' --count 1 --topic pi3/battery1/data --endpoint...
_______________
pubsub3.py:
message = "{}".format(message_string)
            print("Publishing message to topic '{}': {}".format(message_topic, message))
            message_json = json.dumps(message)
            mqtt_connection.publish(
                topic=message_topic,
                payload=message_json,
                qos=mqtt.QoS.AT_LEAST_ONCE)
            time.sleep(1)
__________________
Terminal:
Sending 1 message(s)
Publishing message to topic 'pi3/battery1/data': {"temperature":40}
Received message from topic 'pi3/battery1/data': b'"{\"temperature\":40}"'
____________________
MQTT Test Client:
pi3/battery1/data     December 01, 2022, 11:59:52 (UTC-0500)

"{temperature: 40}"

If someone could offer me some assistance I would be very grateful!

Accepted Answer

Hi,

Your `message` is already a string encoded JSON which is what the `publish()` methods expects.

Try replacing the line
```
message_json = json.dumps(message) 
```

with

```
message_json = message
```

Cheers,

Massimiliano

Send JSON documents with the pubsub.py sample app - MQTT Test Client displays string not json

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