koa2-router

koa2-router

An express-liked router component for koa2

Features

Getting Started

You can follow the instructions below to setup a router component in koa@2 environment.

Prerequisties

• node version > 8.10
• depends on koa@2.0

Installing

• If you use npm to manage your dependencies, run

npm install koa2-router

Usage

• Import component

const Router = require('koa2-router');

• Create a router

const router = new Router(opts);

• Mount a router to a koa application

const app = new Koa();
app.use(router);

• Mount a router to another router

const router2 = new Router();
router2.use(...);
router.use('/users', router2);

• Use http method to handle request

router2.get('/:userId', ctx => ctx.body = `hello user ${ctx.params.userId}`);

• Use params middleware like express

const router3 = Router();
router3.params('userName', (ctx, next, userName, key) => (ctx[key] = userName, next()))
  .get('/:userName', async ctx => ctx.body = await ctx.db.getStaffFromName(ctx.userName));
router.use('/staff', router3);

• Use route to make a rest api

const route = router3.route('/:id');
route
  .get(async ctx => ctx.body = await ctx.db.getStaffFromId(ctx.params.id));

• exit route or router without exception

route
  .all(async (ctx, next) => {
     if (ctx.authenticate.userId === ctx.params.id) return next();
     else throw 'route'; // exit this route without any exception
  })   
  .put(async ctx => ctx.body = await ctx.db.updateStaff(ctx.params.id, ctx.request.body))
  .del(async ctx => ctx.body = await ctx.db.deleteStaff(ctx.params.id));
  
route3.use('/admin', (ctx, next) => {
    if (ctx.authenticate.userRoles.includes('admin')) return next();
    else throw 'router'; // exit this router3 without any exception
  })
  .post('/posts', async ctx => ctx.body = await ctx.db.createPost(ctx.request.body, ctx.authenticate.userId));

• implement Method Not Allowed and Not Implemented

router.use('/api', router3, router3.allowMethods(opts))

opts the allowMethods options

opts.throw [boolean] default false, set to true to throw errors

opts.methodNotAllowed [function(ctx, methods)] set if throw a custom 405 error

opts.notImplemented [function(ctx)] set if throw a custom 501 error

Nested Router Stacks

In this module, router is a specific function instance which can be constructed via router = new Router(opts) or router = Router(opts), and can be directly used as a Koa.Middleware function - app.use(router).

We create a router model called Express Liked Router Model. The router constructed via this mechanism, implements everything that express.Router also dose, like Router.use(), Router[method|all]() Router.params() Router.route().

But there is an issue about that mode, how nested router stacks proceed for an asynchronized middleware system.

Nested routers are supported, but not behaves like in a single stack: enter -> enter -> enter <-> leave <- leave <- leave. Considering the entering and leaving order of the stack is relevant to the way they are mounted, we consulted and borrowed the algo from a Golang open source project gobwas/glob: within that a new Group midleware is introduced, and it can make a branching stack. So we borrowed this design and setup new rules in nested routers in order to constraint excuting stack orders:

1. Middleares using .use() in which path can just be / or *, insert middlewares to the original stack

in Router.use(middlewares), middlewares are inserted into the parent's middlewares, thus when the last one invokes next(), it will continue enter the next one of the parent router, until all things done, then it will leave from the bottom to the top of the parent router's stack

1. Middlewares using [method] .all .route or .use(path) makes a branching stack of route nested in the parent stack

in this situation, middlewares are handled via a mounted path or route if the one is matched both in path & route, calling next in the last middlewares of the nested router will leave the mounted router stack from bottom to the top first, and then if nothing is responded before that, it enters the next middleware of the parent stack

Let's see an example

var router = new Router('A')
var nested = new Router('B')
router.use(async (ctx, next) => {
  console.log('enter parent')
  await next()
  console.log('leave parent')
})
// use `.use so nested mw is bundled together with the parent`
router.use('/stuff', nested)
router.use(async (ctx, next) => {
  console.log('prepare')
  await next()
  console.log('post')
})
router.use(ctx => {
  console.log('output body')
  ctx.body = 'success'
})

nested.use(async (ctx, next) => {
  console.log('enter nested')
  await next()
  console.log('leave nested')
})

GET /stuff and watch the console

> enter parent
> enter nested
> leave nested
> prepare
> output body
> post
> leave parent

> HTTP/1.1 200 OK
> success

The order of entering/leaving differs between router and nested router. Because we make a branching stack nested in the router by mounting it to a path /stuff, and it will leave the branching stack before go over the next. It is just like the Group in the project gobwas/glob powered by golang

Running tests

You should clone thie repository down to your file system, and execute

npm run test

Acknowledgements

• Thanks to the expressjs/express project
• Thanks to the alexmingoia/koa-router project
• Thanks to the pillarjs/router project
• Thanks to the gobwas/glob project

License

MIT