users online with redis

app.js

var express = require('express');
var redis = require('redis');
var db = redis.createClient();
var app = express();

// track users online (replace UA string with user id)

app.use(function(req, res, next){
  var ua = req.headers['user-agent'];
  db.zadd('online', Date.now(), ua, next);
});

// fetch the users online in the last minute

app.use(function(req, res, next){
  var min = 60 * 1000;
  var ago = Date.now() - min;
  db.zrevrangebyscore('online', '+inf', ago, function(err, users){
    if (err) return next(err);
    req.online = users;
    next();
  });
});

// route

app.get('/', function(req, res){
  res.send(req.online.length + ' users online');
});

app.listen(3000);

package.json

{
  "name": "app",
  "version": "0.0.1",
  "dependencies": {
    "express": "3.x",
    "redis": "*"
  }
}