Function callback

lib/agent.js:365–367

(err, message)

    var request = {data: chunk};
    agent.backend.trigger(agent.backend.MIDDLEWARE_ACTIONS.receive, agent, request, function(err) {
      var callback = function(err, message) {
        agent._reply(request.data, err, message);
      };
      if (err) return callback(err);
      agent._handleMessage(request.data, callback);
    });