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Nicholas Duffy

Logging LoopBack Requests to

loopback,, node.js, javascript1 min read

I've been experimenting with LoopBack recently, using it to prototype an API. It really is quite amazing how quickly you can get a full-fledged API up and running with LoopBack. Just follow the getting started guide and you’ll see what I mean.

After getting a pretty decent API up and running, I began testing a few different ways of logging API requests. I still haven't quite settled on the way that I want to do this yet, but one issue that I did encounter was trying to get the response time of the call from expressjs/response-time.

Response-time is a great, little Node.js module that automatically adds an X-Response-Time header to your responses to indicate the time in milliseconds that the request took.

The issue that I was running into was that I could not figure out how to properly get to that header in the LoopBack afterRemote method that I was using to log requests. Thanks to an SO user, however, I was able to eventually get to what I wanted. The key was that the response wasn't available when I was trying to log the query -I needed to use the res.on('finish') event to get the response headers.

1var Keen = require("keen-js");
3module.exports = function (myModel) {
4 myModel.afterRemote("*", function (ctx, affectedModelInstance, next) {
5 // Listen to the finish event of the response to wait
6 // for the response to be available
7 ctx.res.on("finish", function () {
8 var client = new Keen({
9 projectId: "keenprojectid",
10 writeKey: "keenwritekey",
11 });
13 var queryEvent = {
14 ip: ctx.req.ip,
15 baseUrl: ctx.req.baseUrl,
16 url: ctx.req.url,
17 route: ctx.req.route,
18 query: ctx.req.query,
19 method: ctx.methodString,
20 // Here's the header that I wanted to grab
21 responseTime: Number(ctx.res._headers["x-response-time"]),
22 keen: {
23 timestamp: new Date().toISOString(),
24 },
25 };
27 client.addEvent("queries", queryEvent, function (err, res) {
28 if (err) {
29 console.log(err);
30 } else {
31 console.log(res);
32 }
33 });
34 });
36 // Don't forget to call next
37 next();
38 });