Add intentional latency in express - node.js

Question

Im using express with node.js, and testing certain routes. I'm doing this tute at http://coenraets.org/blog/2012/10/creating-a-rest-api-using-node-js-express-and-mongodb/
Im calling the http://localhost:3000/wines via ajax (the content doesn't matter). But I want to test latency. Can I do something like make express respond after 2 seconds? (I want to simulate the ajax loader and I'm running on localhost so my latency is pretty much nil)

Answer 1

Use as middleware, for all your requests
app.use(function(req,res,next){setTimeout(next,1000)});

Answer 2

Just call res.send inside of a setTimeout:
setTimeout((() => {
res.send(items)
}), 2000)

Answer 3

To apply it globaly on all requests you can use the following code:
app.use( ( req, res, next ) => {
setTimeout(next, Math.floor( ( Math.random() * 2000 ) + 100 ) );
});
Time values are:
Max = 2000 (sort of.... min value is added so in reality its 2100)
Min = 100

Answer 4

Try connect-pause module. It adds delay to all or only some routes in your app.

Answer 5

app.get('/fakeDelay', function(req,res){
let ms = req.query.t;
ms = (ms>5000 || isNaN(ms)) ? 1000 : parseInt(ms);
setTimeout((()=> res.status(200).send({delay:ms})), ms);
})
Then request the URL as: http://localhost/fakeDelay/?t=2000
(max 5000ms and default of 1000ms on this example)
Update:
Using a Promise. The function 'sleep' can be used for delaying any Express response or other async function.
const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));
app.get('/fakeDelay', async (req, res) => {
await sleep(500);
res.send([])
})

Answer 6

just add a comment on top of the solution of #maggocnx : put this middleware early (before your route handler)
app.use(function(req,res,next){setTimeout(next,1000)});

Answer 7

You could also just write your own generic delay handler using a Promise or callback (using a q promise in this case):
pause.js:
var q = require('q');
function pause(time) {
var deferred = q.defer();
// if the supplied time value is not a number,
// set it to 0,
// else use supplied value
time = isNaN(time) ? 0 : time;
// Logging that this function has been called,
// just in case you forgot about a pause() you added somewhere,
// and you think your code is just running super-slow :)
console.log('pause()-ing for ' + time + ' milliseconds');
setTimeout(function () {
deferred.resolve();
}, time);
return deferred.promise;
}
module.exports = pause;
then use it however you'd like:
server.js:
var pause = require('./pause');
router.get('/items', function (req, res) {
var items = [];
pause(2000)
.then(function () {
res.send(items)
});
});

Answer 8

You can use the express-delay package.
The code below will delay all incoming requests by one second.
const app = require('express')();
const delay = require('express-delay');
app.use(delay(1000));
The package also offers the possibility to introduce a random delay within specified boundaries, e.g. by calling delay(1000, 2000) for a delay between one and two seconds.

Answer 9

In my case I wanted a way to have the same processing time for all of my endpoints.
The solution I found is to override one of the Response methods :
/* MINIMUM DELAY */
const minDelay = 200; /* ms */
app.use((req, res, next) => {
const tmp = res.json;
const start = new Date().getTime();
(res.json as any) = async (body: any) => {
await new Promise((re) => setTimeout(re, minDelay - new Date().getTime() + start));
tmp.apply(res, [body]);
};
next();
});
This way an attacker would not be able to differentiate failed login requests from OK requests just by looking at the response time :)