Web socket notification receiver per user and backend server on golang

backend.go

package main

import (
    "log"
    "net/http"
    "time"

    "github.com/gin-gonic/gin"
    "github.com/gorilla/websocket"
)

type Message struct {
    UserID      string    `json:"userId"`
    Notification string    `json:"notification"`
    Timestamp   time.Time `json:"timestamp"`
}

var (
    upgrader = websocket.Upgrader{
        ReadBufferSize:  1024,
        WriteBufferSize: 1024,
    }
    clients = make(map[string]*websocket.Conn)
)

func main() {
    router := gin.Default()

    router.GET("/ws", func(c *gin.Context) {
        conn, err := upgrader.Upgrade(c.Writer, c.Request, nil)
        if err != nil {
            log.Println("Failed to upgrade to WebSocket:", err)
            return
        }

        userId := c.Query("userId")
        clients[userId] = conn

        log.Println("WebSocket connection established for user:", userId)

        for {
            // Read message from client
            _, msg, err := conn.ReadMessage()
            if err != nil {
                log.Println("Failed to read message from WebSocket:", err)
                delete(clients, userId)
                break
            }

            log.Printf("Received message from user %s: %s\n", userId, msg)
        }
    })

    router.GET("/send-notification", func(c *gin.Context) {
        userId := c.Query("userId")
        notification := c.Query("notification")

        if conn, ok := clients[userId]; ok {
            message := Message{
                UserID:      userId,
                Notification: notification,
                Timestamp:   time.Now(),
            }

            err := conn.WriteJSON(message)
            if err != nil {
                log.Println("Failed to send notification to WebSocket:", err)
            }
        }

        c.String(http.StatusOK, "Notification sent to user %s", userId)
    })

    log.Println("Backend server is running on port 8080")
    router.Run(":8080")
}

notifycation_receiver.js

let socket;

function connectWebSocket(userId) {
  const url = `ws://localhost:8080/ws?userId=${userId}`;
  socket = new WebSocket(url);

  // Connection opened
  socket.addEventListener('open', (event) => {
    console.log('WebSocket connection established');
  });

  // Listen for messages
  socket.addEventListener('message', (event) => {
    const notification = JSON.parse(event.data);
    console.log('Received notification:', notification);
    // Do something with the notification data
  });

  // Connection closed
  socket.addEventListener('close', (event) => {
    console.log('WebSocket connection closed');
  });

  // Error occurred
  socket.addEventListener('error', (event) => {
    console.error('WebSocket error:', event);
  });
}

function disconnectWebSocket() {
  if (socket) {
    socket.close();
    socket = null;
    console.log('WebSocket connection disconnected');
  }
}

// Subscribe to notifications for a specific user
function subscribe(userId) {
  if (!socket) {
    connectWebSocket(userId);
  } else {
    console.log('WebSocket connection already established');
  }
}

// Unsubscribe from notifications
function unsubscribe() {
  disconnectWebSocket();
}

// Update WebSocket connection for a different user
function updateUser(userId) {
  disconnectWebSocket();
  connectWebSocket(userId);
}