ws.js

_init() {
  if (this._server) throw new Error('Server already initialized');

  this._server = http.createServer((req, res) => {
    const UPGRADE_REQUIRED = 426;
    const body = http.STATUS_CODES[UPGRADE_REQUIRED];
    res.writeHead(UPGRADE_REQUIRED, {
      'Content-Type': 'text/plain',
      'Upgrade': 'WebSocket',
    });
    res.end(body);
  });

  this._server.on('upgrade', (req, socket) => {
    this.emit('headers', req);

    if (req.headers.upgrade !== 'websocket') {
      socket.end('HTTP/1.1 400 Bad Request');
      return;
    }
  
    const acceptKey = req.headers['sec-websocket-key'];
    const acceptValue = this._generateAcceptValue(acceptKey);
  
    const responseHeaders = [
      'HTTP/1.1 101 Switching Protocols',
      'Upgrade: websocket',
      'Connection: Upgrade',
      `Sec-WebSocket-Accept: ${acceptValue}`,
    ];

    socket.write(responseHeaders.concat('\r\n').join('\r\n'));
  });
}