websocket-server.js

var http   = require('http');
var crypto = require('crypto');

var PORT = process.env.PORT || 8888;
var MAGIC_STRING = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11';

function Frame(buffer){
  
  this.buffer = buffer;
  
  // header
  // 128 = text-message
  // 1   = end-frame
  // 128 + 1 = complete text frame
  this.buffer.writeUInt8(129,0);
  
  this.length = 0;
  
}

Frame.prototype.prepare = function(msg){
  
  this.length = msg.length;
  
  // write the message to the data section
  // of the frame, utf-8 encoded
  this.buffer.write(msg,2);
  
  // encode message length,
  // if this is over 127, we need to use the
  // extended protocol, which we don't support
  this.buffer.writeUInt8(this.length,1);
  
}

Frame.prototype.write = function(){
  return this.buffer.slice(0,this.length + 2);
}

// send buffer
var frame = new Frame(
  // create a large buffer to handle all 
  // outgoing messages, it will be re-used
  new Buffer(Array(150))
);

http.createServer()
.on('upgrade', function(req, socket) {
  
  console.log('Upgrading to WebSocket Connection');
  
  socket.on('close',function(){
    console.log('socket closed');
  });
  
  socket.on('data',function(data){
    
    // mask octets
    // these are random, and set by the client
    var mask = [
      data.readUInt8(2),
      data.readUInt8(3),
      data.readUInt8(4),
      data.readUInt8(5)
    ];
    
    // we assume all messages are of length
    // of <127 otherwise our protocol needs to be
    // smarter
    
    // decode incoming data
    for(var i=0; i<data.length-6; i++){
      // data is overwritten with decoded message
      var msg  = data.readUInt8( i + 6 );
      data.writeUInt8( 
        // XOR the incomign message with the 
        // appropriate bit mask
        msg^mask[i % 4], i + 6 
      );
    }
    
    // Capture the string portion of the message
    var reply = data.slice(6).toString('utf-8');
    
    console.log(reply);
    
    // Write the reply back to the socket
    frame.prepare('PONG:' + reply);
    socket.write( frame.write() );
    
  });
  
  // Server Handshake
  // there is no error handling
  
  // Calculate server response key
  var key = req.headers['sec-websocket-key'];
  var shasum = crypto.createHash('sha1');
  shasum.update(key);
  shasum.update(MAGIC_STRING);
  var dig = shasum.digest('base64');
  
  out = [
    'HTTP/1.1 101 Switching Protocols',
    'Upgrade: WebSocket',
    'Connection: Upgrade',
    'Sec-WebSocket-Accept: ' + dig,
    ''
  ];
  
  for( i in out ){
    socket.write(out[i]);
    socket.write('\r\n')
  }
  
})
.listen(PORT);

console.log("WebSocket Server Listening on Port %d",PORT);