docs: function(opts) {
    opts = opts || {};
    this.heartbeat = null;
    this.timeout = null;
    this.disconnectOnTimeout = opts.disconnectOnTimeout;
  
    if(opts.heartbeat) {
      this.heartbeat = opts.heartbeat * 1000; // heartbeat interval
      this.timeout = opts.timeout * 1000 || this.heartbeat * 2;      // max heartbeat message timeout
      this.disconnectOnTimeout = true;
    }
  
    this.timeouts = {};
    this.clients = {};
  }