mqtt mbox example

mbox_receiver.py

# An example of a mailbox client that wakes up every
# few seconds and checks for messages and then goes
# back to sleep.
#
# License: This code has been donated to the public domain
#
# Dov Grobgeld <dov.grobgeld@gmail.com>
# 2020-08-08 Sat

import paho.mqtt.client as mqtt #import the client1
import time

############
def on_message(client, userdata, message):
    print("message:", message.topic + ': ' + str(message.payload.decode("utf-8")))

########################################
print('I\'m listening for mbox messages !')
broker_address="127.0.0.1"
client_name='mbox'
is_first=True
while 1:
  client = mqtt.Client(client_name, clean_session=is_first)
  is_first=False
  print("polling")
  client.on_message=on_message #attach function to callback
  client.connect(broker_address) #connect to broker
  client.subscribe('mbox/#',qos=1)
  client.loop_start()
  time.sleep(0.1) # How long should this time be?
  client.loop_stop()
#  client.loop(0.1) # why doesn't this do the same as the previous three lines?
  client.disconnect()
  time.sleep(5)

mbox_sender.py

#!/usr/bin/python3
# send a message to a mbox through mqtt

import paho.mqtt.client as mqtt #import the client1
import time
    
broker_address='127.0.0.1'

client = mqtt.Client('MBoxClient') 

client.connect(broker_address)

counter = 1
while True:
  print('Press Enter to send msg #'+str(counter)+': ', end='')
  a=input()
  if a.startswith('q'):
    break
  client.publish("mbox/mail","Hello "+str(counter), qos=1)
  counter += 1
client.disconnect()
print('done!')

This example shows how to create a "Mail Box" service through mqtt. The mbox_receive does the following loop:

1. Connects to broker
2. Receive new mail
3. Goes to sleep

A real application of this would be a battery powered ESP8266 chip that e.g. controls an IR LED. By sleeping most of the time, we can draw very little power from the battery.