Loopback Logging - intercept all HTTP responses, regardless of which middleware/route produced it

server.js

// Title:
//   Loopback Logging - intercept all HTTP responses,
//   regardless of which middleware/route produced it

// References:
//   https://apidocs.strongloop.com/loopback/#app-middleware
//   https://apidocs.strongloop.com/loopback/#app-middlewarefromconfig
//   https://apidocs.strongloop.com/loopback/#app-definemiddlewarephases

//Sample # 1 - super simple
// If you would rather use middleware.json ... make sure to
// install this middleware among the first middleware,
// as it needs to hook into the response object before
// any other middleware sends back the response.
app.middleware('initial', function logResponse(req, res, next) {
  // install a listener for when the response is finished
  res.on('finish', function() {
    // the request was handled, print the log entry
    log(req.method, req.originalUrl, res.statusCode);
  });

  // resume the routing pipeline,
  // let other middleware to actually handle the request
  next();
});


//Sample # 2 - bit more advanced
// Also helps track reponse time for all URLs
app.middleware('initial', function logResponse(req, res, next) {
  // http://www.senchalabs.org/connect/responseTime.html
  var start = new Date;
  if (res._responseTime) {
    return next();
  }
  res._responseTime = true;

  // install a listener for when the response is finished
  res.on('finish', function() { // the request was handled, print the log entry
    var duration = new Date - start;
    log(req.method, req.originalUrl, res.statusCode, duration + 'ms', {
      lbHttpMethod:req.method,
      lbUrl:req.originalUrl,
      lbStatusCode:res.statusCode,
      lbResponseTime:duration
    });
  });

  // resume the routing pipeline,
  // let other middleware to actually handle the request
  next();
});

//Sample # 3 - bit more focused
// Does work only for the API related URLs
app.middleware('initial', '/api/*', function logResponse(req, res, next) {
  // same code as sample # 2 
});