index.js

var Emitter = require('component-emitter');

exports.protocol = 5;

/**
 * Packet types (see https://github.com/socketio/socket.io-protocol)
 */

var PacketType = (exports.PacketType = {
  CONNECT: 0,
  DISCONNECT: 1,
  EVENT: 2,
  ACK: 3,
  CONNECT_ERROR: 4
});

var isInteger = Number.isInteger || function (value) {
  return typeof value === 'number' &&
    isFinite(value) &&
    Math.floor(value) === value;
};

var isString = function (value) { return typeof value === 'string'; };

var isObject = function (value) {
  return Object.prototype.toString.call(value) === '[object Object]';
};

function Encoder () {}

Encoder.prototype.encode = function (packet) {
  return [ JSON.stringify(packet) ];
};

function Decoder () {}

Emitter(Decoder.prototype);

function isDataValid (decoded) {
  switch (decoded.type) {
    case PacketType.CONNECT:
      return decoded.data === undefined || isObject(decoded.data);
    case PacketType.DISCONNECT:
      return decoded.data === undefined;
    case PacketType.CONNECT_ERROR:
      return isObject(decoded.data);
    default:
      return Array.isArray(decoded.data);
  }
}

Decoder.prototype.add = function (obj) {
  var decoded = JSON.parse(obj);

  var isTypeValid = isInteger(decoded.type) && decoded.type >= PacketType.CONNECT && decoded.type <= PacketType.CONNECT_ERROR;
  if (!isTypeValid) {
    throw new Error('invalid packet type');
  }

  if (!isString(decoded.nsp)) {
    throw new Error('invalid namespace');
  }

  if (!isDataValid(decoded)) {
    throw new Error('invalid payload');
  }

  var isAckValid = decoded.id === undefined || isInteger(decoded.id);
  if (!isAckValid) {
    throw new Error('invalid packet id');
  }

  this.emit('decoded', decoded);
};

Decoder.prototype.destroy = function () {};

exports.Encoder = Encoder;
exports.Decoder = Decoder;