fix: express and socket share same server

backend/src/chat-server.ts

@@ -1,40 +1,28 @@
 import express, { Request, Response } from 'express';
 import { Logger } from "pino";
 import { Server, Socket } from "socket.io";
-import { createServer } from "http";
 
 export class ChatServer {
     port: number;
     app: express.Application;
     logger: Logger;
-    io: Server;
 
     constructor(logger: Logger, port: number = 3000) {
         this.port = port;
         this.logger = logger;
         this.app = express();
-        // ref: https://socket.io/docs/v4/server-initialization/#with-express
-        this.io = new Server(createServer(this.app), {
-            cors: {
-                origin: '*',
-            }
-        });
         this.setupAppRoutes();
-        this.setupSocketHandler();
     }
-    setupAppRoutes() {
+    private setupAppRoutes() {
         // health check
         // ref: https://kubernetes.io/docs/reference/using-api/health-checks/
         this.app.get('/livez', (req: Request, res: Response) => {
             res.send('OK');
         });
     }
 
-    setupSocketHandler() {
-        this.io.on("listening", () => {
-            this.logger.info(`Server running at http://localhost:${this.port}`);
-        });
-        this.io.on('connection', (socket: Socket) => {
+    private setupSocketHandler(io: Server) {
+        io.on('connection', (socket: Socket) => {
             const sessionLogger = this.logger.child({ session: socket.id });
             sessionLogger.info(`Connected client session ${socket.id} on port ${this.port}`);
             socket.on('disconnect', () => {
@@ -43,7 +31,17 @@ export class ChatServer {
         });
     }
 
-    listen() {
-        this.io.listen(this.port);
+    public listen() {
+        const httpServer = this.app.listen(this.port,
+            () => { console.log(`Server listening on port ${this.port}`) }
+        );
+
+        // Express server and socket.io server is sharing the same http server
+        const io = new Server(httpServer, {
+            cors: {
+                origin: '*',
+            }
+        });
+        this.setupSocketHandler(io);
     }
 }