WebSockets & Real-Time Communication

1// WebSockets with Socket.IO — Real-Time Chat
2
3const express = require("express");
4const { createServer } = require("http");
5const { Server } = require("socket.io");
6
7const app = express();
8const httpServer = createServer(app);
9const io = new Server(httpServer, {
10  cors: { origin: "*", methods: ["GET", "POST"] },
11  pingTimeout: 60000,
12  pingInterval: 25000,
13});
14
15app.use(express.static("public"));
16
17// Track online users
18const onlineUsers = new Map();
19
20// 1. Connection handling
21io.on("connection", (socket) => {
22  console.log(`User connected: ${socket.id}`);
23
24  // 2. User joins with username
25  socket.on("user:join", (username) => {
26    onlineUsers.set(socket.id, { username, joinedAt: Date.now() });
27    socket.username = username;
28
29    // Broadcast to all clients
30    io.emit("user:online", {
31      users: Array.from(onlineUsers.values()),
32      count: onlineUsers.size,
33    });
34
35    // Notify others
36    socket.broadcast.emit("system:message", {
37      text: `${username} joined the chat`,
38      timestamp: Date.now(),
39    });
40  });
41
42  // 3. Chat messages
43  socket.on("chat:message", (data) => {
44    const message = {
45      id: Date.now().toString(),
46      text: data.text,
47      username: socket.username,
48      timestamp: Date.now(),
49    };
50
51    // Send to everyone (including sender)
52    io.emit("chat:message", message);
53  });
54
55  // 4. Rooms (channels)
56  socket.on("room:join", (roomName) => {
57    socket.join(roomName);
58    socket.to(roomName).emit("system:message", {
59      text: `${socket.username} joined #${roomName}`,
60      room: roomName,
61    });
62  });
63
64  socket.on("room:message", ({ room, text }) => {
65    io.to(room).emit("chat:message", {
66      id: Date.now().toString(),
67      text,
68      username: socket.username,
69      room,
70      timestamp: Date.now(),
71    });
72  });
73
74  socket.on("room:leave", (roomName) => {
75    socket.leave(roomName);
76  });
77
78  // 5. Typing indicator
79  socket.on("user:typing", (data) => {
80    socket.broadcast.emit("user:typing", {
81      username: socket.username,
82      isTyping: data.isTyping,
83    });
84  });
85
86  // 6. Acknowledgements (delivery confirmation)
87  socket.on("chat:private", (data, callback) => {
88    const { to, text } = data;
89    const targetSocket = [...io.sockets.sockets.values()].find(
90      (s) => s.username === to
91    );
92
93    if (targetSocket) {
94      targetSocket.emit("chat:private", {
95        from: socket.username,
96        text,
97        timestamp: Date.now(),
98      });
99      callback({ delivered: true });
100    } else {
101      callback({ delivered: false, reason: "User not online" });
102    }
103  });
104
105  // 7. Disconnection
106  socket.on("disconnect", (reason) => {
107    console.log(`User disconnected: ${socket.username} (${reason})`);
108    onlineUsers.delete(socket.id);
109
110    io.emit("user:online", {
111      users: Array.from(onlineUsers.values()),
112      count: onlineUsers.size,
113    });
114
115    if (socket.username) {
116      io.emit("system:message", {
117        text: `${socket.username} left the chat`,
118        timestamp: Date.now(),
119      });
120    }
121  });
122});
123
124// 8. Server-Sent Events (SSE) endpoint — simpler alternative
125app.get("/api/events", (req, res) => {
126  res.writeHead(200, {
127    "Content-Type": "text/event-stream",
128    "Cache-Control": "no-cache",
129    Connection: "keep-alive",
130  });
131
132  const intervalId = setInterval(() => {
133    const data = JSON.stringify({ timestamp: Date.now(), message: "heartbeat" });
134    res.write(`data: ${data}\n\n`);
135  }, 5000);
136
137  req.on("close", () => {
138    clearInterval(intervalId);
139  });
140});
141
142const PORT = process.env.PORT || 3000;
143httpServer.listen(PORT, () => {
144  console.log(`Server running on http://localhost:${PORT}`);
145});