PyPubSub vs MQTT vs others

[danic85]

Something that I'd like to improve is the use of PyPubSub within the project and the posibility of building a wrapper to allow the library or protocol to be changed depending on requirements.

There is an option to, rather than directly utilise pypubsub in each module, reference a local module that changes the protocol used depending on the configuration. For example, MQTT could be used to interface other frameworks more easily, or for async processing of topic messages etc.

I'd be interested to find out more about the options available and the advantages of each.

[danic85]

The branch https://github.com/makerforgetech/modular-biped/tree/feature/messaging_service has been created for this change. A messaging_service is present in each module (loaded via parent class). The protocol used (pubsub or mqtt) can be chosen in the config file for messaging_service.

Currently the pubsub functionality works, but mqtt still needs some work.

The only real changes are that the subscribe calls must be outside of init methods, and that the names of the calls and arg positions have changed slightly to support both protocols.

• The module must extend BaseModule (from modules.base_module import BaseModule)
• Any subscribes must be set in setup_messaging() which is called after init as part of the module loader functionality.
• self.subscribe(topic, callback) is used to subscribe to a topic
• self.publish(topic, **kwargs) or self.publish(topic, message) can be used to publish.

class MyModule(BaseModule):
  def __init__(self):
      # Don't subscribe here
      pass
  
  def setup_messaging(self):
      """Subscribe to necessary topics."""
      self.subscribe('my_topic', self.my_callback)
      
  def my_callback(self, message):
      print(f'Received message: {message}')
      self.publish('my_response_topic', 'Hello from MyModule!')
      self.publish('log', type='info', message='MyModule received a message!')

[danic85]

This has been merged into the feature/cm5 branch https://github.com/makerforgetech/modular-biped/tree/feature/cm5. The MQTT functionality is still TODO, but the service class and implementation is in place to make that easier.
I also improved the logging because these changes made that much easier. See the README.md for more info.