Chat

index.js

// 1. Server
//    node index.js
//
// 2. Client
//   1) Start
//      telnet localhost 3001
//
//   2) Quit
//      Click Ctrl + ], then Ctrl + C

const net = require('net');

const clients = new Map();
const names = new Set();
const cache = [];

const server = net.createServer((socket) => {
  console.log('client connected');

  socket.write('Welcome to my chat server! What is your nickname?\n');
  clients.set(socket, null);
  let myName = null;
  let isNickname = true;

  socket.on('data', buffer => {
    const msg = buffer.toString();

    if (isNickname) {
      if (names.has(msg)) {
        socket.write('Please select new name\n');
      } else {
        // Connected with
        socket.write(`You are connected with ${names.size} other users: ${Array.from(names).toString()}\n`);

        // Print last 10 messages
        cache.forEach(m => {
          socket.write(m);
        });

        // Notify the rest of users you joined the chat
        myName = msg.trim();
        clients.forEach((name, s) => {
          if (socket !== s) {
            s.write(`*${myName} has joined the chat*\n`);
          }
        });

        clients.set(socket, msg);
        names.add(msg);
        isNickname = false;
      }
    } else {
      // Cache messages
      const time = new Date();
      const m = `[${time}] <${myName}> ${msg}`;
      if (cache.length < 10) {
        cache.push(m);
      } else {
        cache.shift();
        cache.push(m);
      }

      // Broadcast
      clients.forEach((name, s) => {
        if (socket !== s) {
          s.write(m);
        }
      });
    }
  });

  socket.on('end', () => {
    // Notify someone left the chat
    clients.forEach((name, s) => {
      if (socket !== s) {
        const time = new Date();
        s.write(`*${myName} has left the chat\n`);
      }
    });

    names.delete(clients.get(socket));
    clients.delete(socket);
    console.log('client disconnected');
  });

}).on('error', (err) => {
  throw err;
});

server.listen(3001, '127.0.0.1');