Express on vnykmshr

The middleware chain

Wed, 20 Aug 2014 00:00:00 +0000

I wrote about Express middleware chains last year as a pattern for keeping route handlers flat. That was a toy example. This is what it looks like in a real application.

We’re two people building a platform. The home page needs to show the user’s feed, friend recommendations, today’s happenings, friend request count, and unread notifications. That’s five data sources, each requiring its own database query, each needing the user to be authenticated first.

Express middleware chains

Tue, 15 Oct 2013 00:00:00 +0000

A typical Express route handler fetches some data and renders a template:

app.get('/book/:book', function(req, res, next) {
 Book.fetch(req.param('book'), function(err, book) {
 if (err) return next(err);
 Author.fetch(book.author, function(err, author) {
 if (err) return next(err);
 res.render('book', { book: book, author: author });
 });
 });
});

Two async calls, three levels of nesting. Add authentication, input validation, permission checks – and you’re five levels deep in a single route definition. The callback alignment pattern helps with formatting, but the nesting is structural. The route handler is doing too many things.

Middleware as steps

Express lets you pass multiple handler functions to a route. Each one gets req, res, and next. Do your work, attach results to req, call next() to pass control to the next handler. Bail out early if something fails.

A fifty-line rate limiter

Wed, 05 Sep 2012 00:00:00 +0000

I needed rate limiting. Not a sophisticated system – something that stops a single IP from hammering the app. The options were a Redis-backed solution or an npm module I hadn’t vetted. I wrote one instead.

var hits = {};
var timers = {};

function ratelimit(max, mins) {
 max = max || 600;
 mins = mins || 1;
 var window = 60 * mins * 1000;

 return function(req, res, next) {
 var ip = req.headers['x-real-ip'] || req.socket.remoteAddress;
 var key = 'rl:' + ip;
 var n = hits[key] || 0;

 res.setHeader('X-Ratelimit-Limit', max);
 res.setHeader('X-Ratelimit-Remaining', max - n);

 if (n >= max) {
 var retry = Math.ceil(
 (timers[key]._idleStart.getTime() + timers[key]._idleTimeout - Date.now()) / 1000
 );
 res.setHeader('X-Ratelimit-Message', 'Enhance Your Calm');
 res.setHeader('X-Ratelimit-Retry-After', retry + 's');
 res.statusCode = 420;
 return res.end('Rate limit exceeded. Try again in ~' + retry + 's.');
 }

 hits[key] = n + 1;
 if (!timers[key]) {
 timers[key] = setTimeout(function() {
 delete hits[key];
 delete timers[key];
 }, window);
 }
 next();
 };
}

That’s it. Wire it into Express as middleware:

URL mapping in Redis

Sun, 10 Jun 2012 00:00:00 +0000

I’m working on an e-commerce app in Node.js. The store has SEO-friendly URLs – /blue-widget/SKU12345/p/ for products, /category-name.html for categories, /brand-name/ for brands. Those URLs are indexed, bookmarked, linked from everywhere. They can’t change.

Express routes are defined in code. The catalog has enough products, categories, and brands that I’m not writing a route for each one. I need a way to map the friendly URL to an internal route at runtime.