composeResponse = function(msgId, route, msgBody) {
  return {
    id: msgId,
    body: msgBody
  };
}
Decode client message package.

Package format:
  message id: 4bytes big-endian integer
  route length: 1byte
  route: route length bytes
  body: the rest bytes

@param  {String} data socket.io package from client
@return {Object}      message object