mqtt - How can I publish a file using Mosquitto in python?

Question

I am using python-mosquitto to subscribe to my MQTT broker which support file type uploads. I can use it just fine using the -f flag when going from Mosquitto on the command line. However, I can't figure out how to use the client.publish(topic, payload) to specify a file to publish when doing it from within my python script.

Python mosquitto gives me the error TypeError: payload must be a string, bytearray, int, float or None. when I try to throw something weird at it. I have a file stored in local directory already which I want to specify as the payload of the publish.

I'm experienced with MQTT but my python is very rusty, I am assuming I need to do some type of file stream function here, but not sure how to do it.

I want to specify the image here: mqttc.publish("/v3/device/file", NEED_TO_SPECIFY_HERE)

I have tried opening the image by doing:

    f = open("/home/pi/mosq/imagecap/imagefile.jpg", "rb")
    imagebin = f.read()
    mqttc.publish("/v3/device/file", imagebin)

But that didn't work and neither did mqttc.publish("/v3/device/file", bytearray(open('/tmp/test.png', 'r').read()))

The client.publish doesnt throw an error with those, but the file is not received properly by the broker. Any ideas?

Thanks!!

Answer 1

The publish has to be the whole file at once, so you will need to read the whole file in and publish it in one go.

The following code works

#!/usr/bin/python

import mosquitto

client = mosquitto.Mosquitto("image-send")
client.connect("127.0.0.1")

f = open("data")
imagestring = f.read()
byteArray = bytes(imagestring)
client.publish("photo", byteArray ,0)

And can be received with

#!/usr/bin/python

import time
import mosquitto

def on_message(mosq, obj, msg):
  with open('iris.jpg', 'wb') as fd:
    fd.write(msg.payload)


client = mosquitto.Mosquitto("image-rec")
client.connect("127.0.0.1")
client.subscribe("photo",0)
client.on_message = on_message

while True:
   client.loop(15)
   time.sleep(2)