Chat implementation in Node.js using a Duplex

nodejs-duplex-chat.js

import net from "net";
import { Duplex } from "stream";

function createClient(socket) {
  return new Duplex({
    read(size) {
      // This function is called when the stream wants to pull more data in.
      // In this chat application example, data reading is handled by the socket's 'data' event,
      // so you might not need to implement anything here.
    },

    write(chunk, encoding, callback) {
      // This function is called when there is data to write to the stream.
      // Write the chunk of data to the socket.
      socket.write(chunk, encoding, callback);
    },

    // It's important to handle the end-of-stream condition properly.
    final(callback) {
      socket.end(callback);
    },
  });
}

const clients = [];

// Create a server
const server = net.createServer((socket) => {
  const client = createClient(socket);
  clients.push(client);

  socket.on("data", (data) => {
    // Broadcast message to all clients
    clients.forEach((c) => {
      if (c !== client) {
        c.write(`Someone says: ${data}`);
      }
    });
  });

  socket.on("end", () => {
    // Remove client from list when they disconnect
    const index = clients.indexOf(client);
    if (index !== -1) {
      clients.splice(index, 1);
    }
  });
});

server.listen(3000, () => {
  console.log("Chat server running on port 3000");
});

// To run:
// Start the server in one terminal window:
// $ node 5-duplex-chat.js
// Connect to the server in another terminal window:
// $ telnet localhost 3000
// Type messages in the telnet window and press enter to send.
// Messages will be broadcast to all connected clients.
// ---
// Can also use Node itself to connect to the server and send messages:
// $ node -e 'const net = require("net"); const client = net.createConnection({ port: 3000 }, () => { console.log("Connected to server!"); process.stdin.resume(); process.stdin.on("data", (data) => client.write(data)); }); client.on("data", (data) => console.log("Server:", data.toString()))'