js server comments

server.js

@@ -1,13 +1,21 @@
+// Import dependencies
 const { WebSocket, WebSocketServer } = require("ws");
+const express = require("express");
 const dotenv = require("dotenv");
 dotenv.config();
 
-const express = require("express");
+// Setup Environmental Variables
-
 const PORT = process.env.PORT || 3000;
 const PREFIX = process.env.PREFIX || "";
 const PUBLIC = process.env.PUBLIC || "";
 
+// Setup Express Router
+// Create the routes of the application
+// Here are two pages and a wildcard:
+// at / there is the index.html page, where to draw
+// at /destination there is the destination.html page, where to receive the drawings
+// the wildcard /* serves the static files from the public folder
+
 const router = express.Router();
 const routes = (app) => {
 	app.get("/", (req, res) => {
@@ -26,6 +34,7 @@ const routes = (app) => {
 	return app;
 };
 
+// Setup the Express server
 const server = express()
 	.set("view engine", "html")
 	.engine("html", require("hbs").__express)
@@ -33,12 +42,19 @@ const server = express()
 	.use(express.static("public"))
 	.listen(PORT, () => console.log(`Listening on ${PORT}`));
 
+// Setup the Websocket server on top of the Express one
 const wss = new WebSocketServer({ server, clientTracking: true });
 
+// Global variables to manage the connected Destination and User clients
 let DESTINATIONS = new Set();
 let USERS = new Set();
 var theme = "";
 
+// The message processor defines which function is associated to every websocket message type.
+// It map a type to a function, passing some optional parameters such as the message itself and the websocket client that sent it.
+// for example an incoming message like {type: hello} will trigger the registerDest(ws, msg) function.
+// In this way to add message types and functionalities gets easier, and avoid long chain of if-else statements.
+
 const messageProcessor = {
 	default: (ws, msg) => unknownMsg(msg),
 	hello: (ws, msg) => registerDest(ws, msg),
@@ -46,11 +62,16 @@ const messageProcessor = {
 	theme: (ws, msg) => ((theme = msg.theme), broadcast(msg)),
 };
 
+// Message processor functions
+
+// Default function, to cactch unkown message types
 const unknownMsg = (msg) => {
 	console.log("Unknown message type...");
 	console.log(msg);
 };
 
+// Add the ws client in the destinations set
+// Removing it when it disconnets
 const registerDest = (ws, msg) => {
 	console.log("Destination client connected");
 	DESTINATIONS.add(ws);
@@ -59,14 +80,17 @@ const registerDest = (ws, msg) => {
 	});
 };
 
+// Send a message to all the connected Destinations
 const toDest = (msg) => {
+	let message = JSON.stringify(msg);
 	DESTINATIONS.forEach((DESTINATION) => {
 		if (DESTINATION?.readyState === WebSocket.OPEN) {
-			DESTINATION.send(JSON.stringify(msg));
+			DESTINATION.send(message);
 		}
 	});
 };
 
+// Send a message to all the connected Users
 const broadcast = (msg) => {
 	let message = JSON.stringify(msg);
 	for (const user of USERS.values()) {
@@ -76,18 +100,21 @@ const broadcast = (msg) => {
 	}
 };
 
+// Websocket events listener
 wss.on("connection", (ws) => {
 	USERS.add(ws);
 	ws.send(JSON.stringify({ type: "theme", theme: theme }));
 
 	ws.on("message", (data) => {
+		// Parse the incoming data safely
 		let message;
 		try {
 			message = JSON.parse(data);
 		} catch (e) {}
 
+		// Call the message processor, eventually falling back to use the default function if the type is not defined.
 		if (message) {
-			(messageProcessor[message.type] || messageProcessor.default)(ws, message);
+			(messageProcessor[message?.type] || messageProcessor.default)(ws, message);
 		}
 	});