## MQTT 101
miroslav.binas@tuke.sk / [**IT Akadémia**](http://linka.na.stranku/)
## What is MQTT?
* [MQTT](https://en.wikipedia.org/wiki/MQTT) (Message Queue Telemetry Transport)
* lightweight publish-subscribe protocol that is used on top of TCP/IP
* designed to _M2M_ communications
* uses _publisher/subscriber pattern_ and _MQ model_
* becoming one of the main protocols for _IoT_
Notes:
* https://pagefault.blog/2017/03/02/using-local-mqtt-broker-for-cloud-and-interprocess-communication/
* https://www.youtube.com/watch?v=eS4nx6tLSLs
* http://www.steves-internet-guide.com/mqtt/
Notes:
* https://blog.securitycompass.com/publish-subscribe-threat-modeling-11add54f1d07
## The Basics
* broker
* topics
* publisher
* subscriber
* message
IoT Example
[](https://mosquitto.org/)
## [Eclipse Mosquitto™](https://mosquitto.org/)
* an open source lightweight MQTT broker
* implements the MQTT protocol versions 3.1 and 3.1.1
* install with
`sudo apt install mosquitto`
`sudo apt install mosquitto-clients`
## `mosquitto_pub`
* client for publishing simple messages
* syntax:
`mosquitto_pub -h host -t topic -m message`
Notes:
* man mosquitto_pub
## `mosquitto_sub`
* client for subscribing to topics
* syntax:
`mosquitto_sub -h host -t topic [-F format]`
* example:
`mosquitto_sub -h localhost -t '#' -F "%t: %p"`
Notes:
* man mosquitto_sub
## Topics
* string used by broker to filter messages
* consist of one/more topic levels
* topic level separator is '`/`'
* topics don't need to be initialized first
* cAsE sEnsItIvE
* allows to use wildcards when subscribing:
* '`#`' - multi level
* '`+'` - single level
Notes:
* https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices
Slovensko/Košice/Letná 9/IoT Lab
home/ground/livingroom/temperature
## Paho MQTT
* [Eclipse Paho](http://eclipse.org/paho/)
* Python support for MQTT _3.1_ and _3.1.1_
* [documentation](https://pypi.org/project/paho-mqtt/)
* install:
`pip3 install paho-mqtt`
Notes:
* http://www.steves-internet-guide.com/mqtt/
* https://pypi.org/project/paho-mqtt/
### Hello World with Paho
```python
import paho.mqtt.client as mqtt
client = mqtt.Client()
client.connect('localhost', port=1883)
client.publish('general', 'hello world')
```
### Paho: Subscribing to Topics
```python
import paho.mqtt.client as mqtt
client = mqtt.Client()
client.connect('localhost', port=1883)
client.publish('general', 'hello world')
client.subscribe('general')
# EOF
```
### Paho `on_message()` Callback
* called when a message has been received on a subscribed topic
* example:
```python
def on_message(client, userdata, message):
print('Message "{}" on topic "{}" with QoS {}'.format(
str(message.payload.decode('utf-8')),
message.topic,
str(message.qos)
)
)
client.on_message = on_message
...
```
Notes:
* https://pypi.org/project/paho-mqtt/#callbacks
### Paho: Complete Example
```python
import paho.mqtt.client as mqtt
from time import sleep
def on_message(client, userdata, message):
text = str(message.payload.decode("utf-8"))
print('Received message "{}" in topic "{}"'.format(
text, message.topic))
if __name__ == '__main__':
client = mqtt.Client()
client.connect('localhost', port=1883)
client.subscribe('general')
client.on_message = on_message
client.loop_start() # non blocking call
# or client.loop_forever() - blocking call (no need the rest of code)
while True:
# your job goes here
sleep(1)
client.loop_stop()
```
(**http://bit.ly/2wKbheb**)