MQTT

Congatudo supports publishing status data and receiving commands from MQTT.

The following autodiscovery protocols are supported:

• Home Assistant
• Homie

They are both optional and mutually compatible: you can enable both at the same time or none at all.

Main concepts

Since the MQTT code is heavily based on the capabilities system you may want to first give a look to how capabilities, status attributes, and the robot object work.

The MQTT OOP structure is heavily influenced by the Homie convention. This page will also contain lots of references to it, so make sure you grasp the fundamental concepts of the convention before proceeding further:

• Overview: https://homieiot.github.io/
• Specification: https://homieiot.github.io/specification/spec-core-v4_0_0/

Responsibilities

To keep the codebase maintainable and prevent entire classes of potential issues, the code tries to define and restrict the responsibilities of each component as follows:

• MqttHandle and subclasses
  • Provide infrastructure to receive events from status attributes and send commands to capabilities
  • Manage Homie attributes
  • Parse and validate incoming and outgoing payloads
• HassComponent and subclasses
  • Provide infrastructure to allow sharing as much data as possible with MqttHandles
  • Manage Hass autoconfiguration payloads
• MqttController
  • Handle the MQTT configuration
  • Handle all aspects of the MQTT communication, such as connection, disconnection, publication, subscriptions
  • Enforce a well-defined procedure for Homie state changes and reconfiguration
  • Handle and dispatch events that can’t be handled by handles directly
• HassController
  • Act as a middleware between MqttController and HassComponents

Handles

Handles are subclasses of MqttHandle. They are designed to map exactly to the levels of the Homie convention topology. Specifically:

• RobotMqttHandle ⇒ Homie device
• NodeMqttHandle ⇒ Homie node
• PropertyMqttHandle ⇒ Homie property

Two more classes are present that further extend from these and bridge the handles to Congatudo’s internals:

• RobotStateNodeMqttHandle maps to StatusStateAttribute
• CapabilityMqttHandle maps to Capability
• (RobotMqttHandle maps to CecotecCongaRobot)

Handle tree and data publication

Handles are assigned into a tree structure:

• RobotMqttHandle, being the root handle, registers to the MqttController
• NodeMqttHandles register to RobotMqttHandle
• PropertyMqttHandles register to NodeMqttHandle

This structure simplifies and unifies publication to the MQTT broker, Instead of publishing data directly, any handle may “refresh” itself.

When a handle is refreshed it will ask the MqttController to retrieve a fresh payload from it and publish it to its designated topic.

Refreshing is recursive: whenever a handle is refreshed all children are refreshed as well. Attached Home Assistant components will also be refreshed, but we will discuss this later.

The robot handle

RobotMqttHandle is special since it is the root handle. It maps to a Homie device. It is mainly responsible for checking which capabilities the robot supports and registering the corresponding handles.

It will also subscribe to the robot status and register matching handles as soon as the corresponding attributes are added (therefore it’s normal if they don’t show up until the robot is fully connected and the status is polled).

Finally, it handles the registration of MapNodeMqttHandle, which as the name suggests provides map data.

The state handles

RobotStateNodeMqttHandle children all map to Homie nodes. Their peculiarity is that they provide infrastructure to subscribe to the robot state.

This is accomplished by providing a list of status attribute matchers, which the handle will subscribe to.

When a status event occurs, the handle and all its children are refreshed.

The capability handles

CapabilityMqttHAndle children also map to Homie nodes. The class itself inherits from RobotStateNodeMqttHandle, therefore it is as well able to subscribe to robot status events.

It is encouraged, whenever possible, to handle status data in a capability handle as opposed to a status handle whenever actions performed on the capability will be reflected into and match exactly to a status attribute event.

This is true, for example, for both PresetSelectionCapabilitys, since setting a preset will usually result in the same value being reflected back to the status attribute: you send low and you get back low.

This is NOT true, for example, for BasicControlCapability. While actions performed on it will directly affect StatusStateAttribute, the status event won’t match exactly: you perform START but you get back CLEANING.

The property handles

PropertyMqttHandle, as the name suggests, maps to Homie properties. However, unlike the previously discussed handles, property handles do not have subclasses and should not be subclassed.

Property handles are in fact defined and registered in-line in the capability/status handle constructors. All data is provided as parameters to the constructor.

These handles handle the actual data to be published and receive commands. However, they never interact directly with the MQTT client. They instead must be provided with at least one of the following callbacks: a getter to retrieve fresh data to be published; a setter to perform operations with the data received from MQTT.

When a setter callback is provided, property handles will be subscribed to a /set topic.

When a setter is provided but a getter is not provided, the property will act as a command property according to the Homie convention: the data received in the /set topic will automatically be reflected back to the main topic to acknowledge the command.

Home Assistant components

Home Assistant uses a very different workflow. Instead of defining a structure, it defines components which may or may not map to some capabilities’ behavior.

In some instances it will try to adapt to an existing MQTT structure and allow you to provide topics and payloads for accomplishing different tasks. In some other cases it will try to impose its own structure.

This makes it difficult to share data with the previously defined structure. However, Congatudo provides enough abstraction to make this easier: HassComponent.

Home Assistant components may subscribe to topics. However, this should be avoided when possible: most features can and should be implemented by providing Hass with the handle topics.

Components and the handle tree

Components are not handles, they are a separate entity. However, in order to share data with handles, they are attached to and managed by the handle they share information with.

Components may be attached to any type of handle, from the robot handle to the property handle. For instance, the map component is attached to the map handle.

Whenever an handle is refreshed, the attached Hass components are refreshed as well.

Sharing topics and data through anchors

Some components are trickier. For example, the VacuumHassComponent is attached to the robot handle since that’s what it shares most data with. However, it also needs access to the fan speed and a reference to the BasicControlCapability command topic in order to send cleaning control commands.

This is accomplished using HassAnchor.

HassAnchor is a utility to share data from the handle that manages some type of information to the hass component that needs it.

There are two types of HassAnchor: plain anchors and topic references. The implementation is exactly the same, the distinction has been put in place, once again, to separate responsibilities: “plain” anchors may only be used in payloads, topic references may only be used in autoconfiguration payloads.

HassAnchors can be thought of as fancy “template variables”. Hass component payloads are in fact provided as regular JavaScript objects. For any value that is not immediately available, an HassAnchor may be retrieved and used in its place.

Of course, the value isn’t going to jump into existence on its own: some other component needs to provide it. This is a responsibility of handles: whenever they share some value with a hass component, they should also post() it into the anchor every time they retrieve it for their own needs.

HassAnchors are eventful: whenever a handle posts a value into an anchor, the hass component that uses it is automatically refreshed and its payload published to MQTT.

If for whatever reason an anchor doesn’t hold any value when the hass component payload is requested for publication, the publication will be delayed. This means that you should only use anchors if you are sure they will be populated, otherwise the hass component will stay in a limbo forever.

Dos and don’ts

Here’s a bunch of things to keep in mind when adding new MQTT handles and Home Assistant components.

• Don’t try to bypass the API restrictions: if you find it hard to get something done you’re probably not doing it correctly
• Do suggest and discuss API changes that accommodate your use case

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• Don’t implement something only for Homie or for Home Assistant
• Do take your time and do things properly

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• Don’t abuse HassAnchor
• Do try to define your hass component close to its handle, so that most data you need will be in the same scope

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• Don’t link Home Assistant fields to Homie $attributes - they won’t be available if Homie is disabled
• Do define a payload for the Home Assistant component with all the data you need, using anchors if needed

Troubleshooting

This section does not describe general MQTT troubleshooting, but rather troubleshooting of problems that can occur when writing new code.

A status/capability handle does not get published

Status handles are only published once the StatusAttribute they subscribe to first appears. If it does appear, but the handle isn’t published, you may have an incorrect attribute matcher.

Both status and capability handles have to be registered into the designated lists inside the HandleMappings.js file for them to be loaded.

Anchors are not updating but handles are

You can enable debug.debugHassAnchors in the configuration and set the log level to trace. It will print a report whenever an anchor is blocking publication for a Hass component.