Skip to content
pipefail
GitHubTwitter

Logging LoopBack Requests to Keen.io

— loopback, keen.io, node.js, javascript — 1 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");
2
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      });
12
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      };
26
27      client.addEvent("queries", queryEvent, function (err, res) {
28        if (err) {
29          console.log(err);
30        } else {
31          console.log(res);
32        }
33      });
34    });
35
36    // Don't forget to call next
37    next();
38  });
39};