Sending Data between components of SUSI MagicMirror Module

SUSI MagicMirror module is a module to add SUSI assistant right on your MagicMirror. The software for MagicMirror constitutes of an Electron app to which modules can be added easily. Since there are many modules, there might be functionalities that need interaction between various modules by transfer of information. MagicMirror also provides a node_helper script that facilitates a module to perform some background tasks. Therefore, a mechanism to transfer information from node_helper to various components of module is also needed.

MagicMirror provides an inbuilt module notification system that can be used to send notification across the modules and a socket notification system to send information between node_helper and various components of the system.

Our codebase for SUSI MagicMirror is divided mainly into two parts. A Main module that handles all the process of hotword detection, speech recognition, calling SUSI API and saving audio after Text to Speech and a Renderer module which performs the task of managing the display of content on the Mirror Screen and playing back the file obtained by Speech Synthesis. Plainly put, Main module mainly handles the backend logic of the application and the Renderer handles the frontend. Main and Renderer module work on different layers of the application and to facilitate communication between them, we need to make a mechanism. A schematic of flow that is needed to be maintained can be highlighted as:

As you can see in the above diagram, we need to transfer a lot of information between the components. We display animation and text based on the current state of recognition in the  module, thus we need to transfer this information frequently. This task is accomplished by utilizing the inbuilt socket notification system in the MagicMirror. For every event like when system enters into listening , busy or recognized speech state, we need to pass message to renderer. To achieve this, we made a rendererSend function to send notification to renderer.

const rendererSend =  (event: NotificationType , payload: any) => {
   this.sendSocketNotification(event, payload);

This function takes an event and a payload as arguments. Event tells which event occurred and payload is any data that we wish to send. This method in turn calls the method provided by MagicMirror module to send socket notifications within the module.

When certain events occur like when system enters busy state or listening state, we trigger the rendererSend call to send a socket notification to the module. The rendererSend method is supplied in the State Machine Components available to every state. The task of sending notifications can be done using the code snippet as follows:

// system enters busy state
this.components.rendererSend("busy", {});
// send speech recognition hypothesis text to renderer
this.components.rendererSend("recognized", {text: recognizedText});
// send susi api output json to renderer to display interactive results while Speech Output is performed
this.components.rendererSend("speak", {data: susiResponse});

The socket notification sent via the above method is received in SUSI Module via a callback called socketNotificationReceived . We need to define this callback with implementation while registering module to MagicMirror. So, we register the MMM-SUSI-AI module by adding the definition for socketNotificationReceived method.

Module.register("MMM-SUSI-AI", {
//other function definitions
   // define socketNotificationReceived function
   socketNotificationReceived: function (notification, payload) {
       susiMirror.receivedNotification(notification, payload);

In this way, we send all the notification received to susiMirror object in the renderer module by calling the receivedNotification method of susiMirror object

We can now receive all the notifications in the SusiMirror and update UI. To handle notifications, we define receivedNotification method as follows:

public receivedNotification(type: NotificationType, payload: any): void {

   switch (type) {
       case "idle":
            // handle idle state
       case "listening":
           // handle listening state
       case "busy":
           // handle busy state
       case "recognized":
           // handle recognized state. This notification also contains a payload about the hypothesis text           
       case "speak":
           // handle speaking state. We need to play back audio file and display text on screen for SUSI Output. Notification Payload contains SUSI Response

In this way, we utilize the Socket Notification System provided by the MagicMirror Electron Application to send data across the components of Magic Mirror module for SUSI AI.


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GSoC Student Developer at FOSSASIA