fix(hub.js): prevent duplicate service registration in hub

- Added socket.io middleware to validate service registration
- Implemented service name uniqueness check during connection
- Added standardized error response for duplicate registration attempts
- Implemented socket cleanup for rejected connections
- Added proper logging for duplicate registration attempts
- Implemented automatic rejection of duplicate socket connection requests

This prevents multiple services from registering with the same name, ensuring message routing integrity and system stability. Any duplicate connection attempts are automatically rejected at the connection level, providing enhanced security against unauthorized service impersonation.

fix #3

Author: arijitcodes

Diff for: src/hub.js

@@ -4,14 +4,67 @@ const Logger = require("./utils/logger"); // Import the logger
 const PORT = process.env.PORT || 3000;
 const io = new Server(Number(PORT), { cors: { origin: "*" } });
 
-const services = new Map(); // Stores connected services
+const services = new Map(); // Stores connected services (serviceName -> { socketId, lastHeartbeat })
 const pendingRequests = new Map(); // Stores pending requests (requestId -> senderSocketId)
 
 const logger = new Logger(process.env.LOG_LEVEL || "debug"); // Initialize logger
 
+/* 
+  Socket.io Middleware Setup
+
+  Socket.io Middleware to handle Duplicate Client Service Registration.
+
+  This middleware will check if a service is already registered with the same name.
+  If so, it will reject the new connection request, log a warning and pass an error to the client.
+  Error Structure: { 
+    code: "DUPLICATE_SERVICE_REGISTRATION", 
+    content: "Duplicate Service Registration Name! A service with the same name is already registered." 
+  }
+  
+  Otherwise, it will proceed with the connection.
+  
+  This is to prevent multiple instances of the same service from connecting to the hub.
+  The hub will only keep the one connection for each service.
+*/
+io.use((socket, next) => {
+  const serviceName = socket.handshake.query.serviceName;
+
+  // If the service is already registered, reject the connection and pass an error to the client
+  if (services.has(serviceName)) {
+    logger.warn(
+      `Duplicate service registration attempt: ${serviceName} from Socket ID: ${socket.id}`
+    );
+
+    const error = new Error("DUPLICATE_SERVICE_REGISTRATION");
+    error.data = {
+      code: "DUPLICATE_SERVICE_REGISTRATION",
+      content:
+        "Duplicate Service Registration Name! A service with the same name is already registered.",
+    };
+
+    // Set a flag to indicate that the connection was rejected
+    socket.rejected = true;
+
+    next(error);
+  }
+
+  // If the service is not registered, proceed with the connection
+  next();
+});
+
 // Handle new connections
 io.on("connection", (socket) => {
   const serviceName = socket.handshake.query.serviceName;
+
+  // If the connection was rejected by the middleware, close the connection
+  if (socket.rejected) {
+    logger.warn(
+      `Connection rejected for duplicate service registration: ${serviceName} from Socket ID: ${socket.id}`
+    );
+    socket.disconnect(true);
+    return;
+  }
+
   logger.info(`${serviceName} connected: ${socket.id}`);
 
   // Register the service
@@ -37,7 +90,6 @@ io.on("connection", (socket) => {
       // Notify the sender that the target service was not found
       logger.warn(`Service "${targetService}" not found`);
 
-      // socket.emit("response", { id: payload.id, error: `Service "${targetService}" not found` });
       socket.emit("response", {
         id: payload.id,
         // error: `Service "${targetService}" not found`,  // This was causing a crash in the client response handler because it was expecting a "data" key
@@ -73,8 +125,11 @@ io.on("connection", (socket) => {
 
   // Handle disconnections
   socket.on("disconnect", () => {
-    services.delete(serviceName);
-    logger.info(`${serviceName} disconnected: ${socket.id}`);
+    // Only remove the service if the connection was not rejected
+    if (!socket.rejected) {
+      services.delete(serviceName);
+      logger.info(`${serviceName} disconnected: ${socket.id}`);
+    }
   });
 });
 
@@ -84,7 +139,14 @@ setInterval(() => {
   for (const [serviceName, data] of services) {
     if (now - data.lastHeartbeat > 15000) {
       services.delete(serviceName);
-      logger.info(`Removed inactive service: ${serviceName}`);
+
+      // Disconnect the inactive service socket
+      const inactiveServiceSocket = io.sockets.sockets.get(data.socketId); // Disconnect the socket
+      inactiveServiceSocket.disconnect(true);
+
+      logger.info(
+        `Removed inactive service: ${serviceName} with Socket ID: ${inactiveServiceSocket.id}`
+      );
     }
   }
 }, 5000);