$ npm install kr

var koa = require('koa');
var kr = require('kr');
var app = koa();
var db = {
  tobi: { name: 'tobi', species: 'ferret' },
  loki: { name: 'loki', species: 'ferret' },
  jane: { name: 'jane', species: 'ferret' }
};
function *authenticate(next) {
  // authenticate or redirect
  yield next;
}
var pets = {
  list: function *(){
    var names = Object.keys(db);
    this.body = 'pets: ' + names.join(', ');
  },
  show: function *(){
    var name = this.params.name;
    var pet = db[name];
    if (!pet) return this.throw('cannot find that pet', 404);
    this.body = pet.name + ' is a ' + pet.species;
  }
};
app.use(kr.get('/pets', authenticate, pets.list));
app.use(kr.get('/pets/:name', authenticate, pets.show));
app.listen(3000);
console.log('listening on port 3000');