polyglot: introduce an abstraction level between the main and brokers' clients

[stefanoterna]

Architecture

Iottly BackendBrokerClients

Each client is basically a wrapper for the specific third party client (sleekxmpp or paho)

Currently we implement:

• BackendBrokerClientXmpp
• BackendBrokerClientMqtt

Each broker client is implemented as a class with the same interface:

• __init__(params): a constructor taking the necessary parameters to let the inner third party client to connect to the broker
• send_command(cmd): a method to send commands over the protocol

Each BackendBrokerClient

Iottly Polyglot

The Polyglot class abstracts the interaction with each BackendBrokerClient:

• once instantiated it knows the lisk of currently running BackendBrokerClient
• it knows how to route the requests to abstract methods towards the corresponding methods of each BackendBrokerClient

Polyglot structure

Globals

A dictionary of currently loaded BackendBrokerClients

Constructor

__init__(backendbrokerclientconf: dict)
Accepts a dict of parameters, grouped in a sub-dict for each of the required BackendBrokerClients:

backendbrokerclientconf = {
  'BackendBrokerClientXmpp': {
  # place here IOTTLY_XMPP_<...> settings needed by BackendBrokerClientXmpp
  },
  'BackendBrokerClientMqtt': {
  # place here IOTTLY_MQTT_<...> settings needed by BackendBrokerClientMqtt
  }
}

The constructor performs the following actions:

• dinamically loads (with reflection) each module defined in the list of keys of the dict backendbrokerclientconf
• dinamically instantes (with reflection) each BackendBrokerClient class
• sets the reference to each instance into the inner dictionary for later retrieval

Methods

• send_command(cmd, brokerclientname): a method responsible for routing the request to send a command to the proper BackendBrokerClient instance, looking it up in the dictionary by means of the brokerclientname parameter

Main

The Main module must interact with each BackendBrokerClient solely via Polyglot.
It knows:

• the list of BackendBrokerClient that must be run
• the dict of conf parameters needed by each BackendBrokerClient to be started
• the brokerclientname (or protocol) of each device (to ask polyglot to properly route the requests)

[stefanoterna]

TODO

• implement the interface (the mocks) of BackendBrokerClientXmpp and BackendBrokerClientMqtt (with pass methods)
• implement Polyglot
  • test it passing in the constructor the correct configuration dict and printing logs from the constructor of each BackendBrokerClient mock
• implement BackendBrokerClientXmpp porting the current commander module
  • note that currently init and send_command are module methods, they must become instance (class) methods
• refactor main:
  • refactor imports
  • substitute commanded.init with the instantiation of the Polyglot class, passing in the correct config dict as defined previously
  • everywhere a commander.send_command is referred, substitute with the polyglot.send_command method
    • temporarily set brokerclientname='BackendBrokerClientXmpp' since the BackendBrokerClientMqtt is not yet implemented
• regression test of the xmpp protocol
  • apply this same checklist: xmpp regression test after introduction of mqtt iottly-device-agent-py#10
• implement BackendBrokerClientMqtt
• test the mqtt implementation,
  • changing the temporary setting brokerclientname='BackendBrokerClientMqtt' in main
  • run the device in interactive mode, with settings.json customized to use mqtt
  • test sending a command from the iottly front-end
    • NB: the response message will not be available in the console, since subscription is not yet implemented