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

Answer 1

It's worth noting that this is one of the areas that can have differences between Python 2 and Python 3.

Python 2 file.read() returns a str whereas Python 3 is bytes. mosquitto.publish() handles both types so you should be ok in that case, but it is something to be aware of.

I've added what I consider some minor improvements to @hardillb 's code below. Please don't accept my answer in preference to his because he wrote it originally and got there first! I would have edited his answer, but I think it's useful to see the difference.

#!/usr/bin/python

import mosquitto

def on_publish(mosq, userdata, mid):
  # Disconnect after our message has been sent.
  mosq.disconnect()

# Specifying a client id here could lead to collisions if you have multiple
# clients sending. Either generate a random id, or use:
#client = mosquitto.Mosquitto()
client = mosquitto.Mosquitto("image-send")
client.on_publish = on_publish
client.connect("127.0.0.1")

f = open("data")
imagestring = f.read()
byteArray = bytes(imagestring)
client.publish("photo", byteArray ,0)
# If the image is large, just calling publish() won't guarantee that all 
# of the message is sent. You should call one of the mosquitto.loop*()
# functions to ensure that happens. loop_forever() does this for you in a
# blocking call. It will automatically reconnect if disconnected by accident
# and will return after we call disconnect() above.
client.loop_forever()

Answer 2

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)