code: function send(id) {
          if (msg.ack) { server._rememberAck(msg.ack, ws.broker_uuid); }
  
          var destWs = server.id2ws[id];
          if (destWs) {
              if (destWs.readyState === WebSocket.OPEN) {
                  destWs.send(JSON.stringify({
                      action: 'message',
                      message: msg.message,
                      ack: msg.ack,
                      from: server.ws2id[ws.broker_uuid]
                  }));
              } else {
                  err = new Error('Unable to send message. Client "'+id+'" disconnected');
                  server.emit('error', err);
              }
          } else {
              server.emit('warn', new Error('Unable to send message. Client "'+id+'" unknown'));
          }
      }
docs: Re-wraps incoming 'send' message into a 'message' message to the specified destination
  @param id