router

Simple middleware-style router

Installation

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install router

API

var finalhandler = require('finalhandler')
var http = require('http')
var Router = require('router')

var router = Router()
router.get('/', function (req, res) {
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')
  res.end('Hello World!')
})

var server = http.createServer(function (req, res) {
  router(req, res, finalhandler(req, res))
})

server.listen(3000)

This module is currently an extracted version from the Express project, but with the main change being it can be used with a plain http.createServer object or other web frameworks by removing Express-specific API calls.

Router(options)

Options

• strict - When false trailing slashes are optional (default: false)
• caseSensitive - When true the routing will be case sensitive. (default: false)
• mergeParams - When true any req.params passed to the router will be merged into the router's req.params. (default: false) (example)

Returns a function with the signature router(req, res, callback) where callback([err]) must be provided to handle errors and fall-through from not handling requests.

router.use([path], ...middleware)

Use the given middleware function for all http methods on the given path, defaulting to the root path.

router does not automatically see use as a handler. As such, it will not consider it one for handling OPTIONS requests.

• Note: If a path is specified, that path is stripped from the start of req.url.

router.use(function (req, res, next) {
  // do your things

  // continue to the next middleware
  // the request will stall if this is not called
  next()

  // note: you should NOT call `next` if you have begun writing to the response
})

Middleware can themselves use next('router') at any time to exit the current router instance completely, invoking the top-level callback.

router[method](path, ...[middleware], handler)

The http methods provide the routing functionality in router.

Method middleware and handlers follow usual middleware behavior, except they will only be called when the method and path match the request.

// handle a `GET` request
router.get('/', function (req, res) {
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')
  res.end('Hello World!')
})

Middleware given before the handler have one additional trick, they may invoke next('route'). Calling next('route') bypasses the remaining middleware and the handler mounted for this route, passing the request to the next route suitable for handling this request.

Route handlers and middleware can themselves use next('router') at any time to exit the current router instance completely, invoking the top-level callback.

router.param(name, param_middleware)

Maps the specified path parameter name to a specialized param-capturing middleware.

This function positions the middleware in the same stack as .use.

The function can optionally return a Promise object. If a Promise object is returned from the function, the router will attach an onRejected callback using .then. If the promise is rejected, next will be called with the rejected value, or an error if the value is falsy.

Parameter mapping is used to provide pre-conditions to routes which use normalized placeholders. For example a :user_id parameter could automatically load a user's information from the database without any additional code:

router.param('user_id', function (req, res, next, id) {
  User.find(id, function (err, user) {
    if (err) {
      return next(err)
    } else if (!user) {
      return next(new Error('failed to load user'))
    }
    req.user = user

    // continue processing the request
    next()
  })
})

router.route(path)

Creates an instance of a single Route for the given path. (See Router.Route below)

Routes can be used to handle http methods with their own, optional middleware.

Using router.route(path) is a recommended approach to avoiding duplicate route naming and thus typo errors.

var api = router.route('/api/')

Router.Route(path)

Represents a single route as an instance that can be used to handle http methods with it's own, optional middleware.

route[method](handler)

These are functions which you can directly call on a route to register a new handler for the method on the route.

// handle a `GET` request
var status = router.route('/status')

status.get(function (req, res) {
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')
  res.end('All Systems Green!')
})

route.all(handler)

Adds a handler for all HTTP methods to this route.

The handler can behave like middleware and call next to continue processing rather than responding.

router.route('/')
  .all(function (req, res, next) {
    next()
  })
  .all(checkSomething)
  .get(function (req, res) {
    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
    res.end('Hello World!')
  })

Middleware

Middleware (and method handlers) are functions that follow specific function parameters and have defined behavior when used with router. The most common format is with three parameters - "req", "res" and "next".

• req - This is a HTTP incoming message instance.
• res - This is a HTTP server response instance.
• next - Calling this function that tells router to proceed to the next matching middleware or method handler. It accepts an error as the first argument.

The function can optionally return a Promise object. If a Promise object is returned from the function, the router will attach an onRejected callback using .then. If the promise is rejected, next will be called with the rejected value, or an error if the value is falsy.

Middleware and method handlers can also be defined with four arguments. When the function has four parameters defined, the first argument is an error and subsequent arguments remain, becoming - "err", "req", "res", "next". These functions are "error handling middleware", and can be used for handling errors that occurred in previous handlers (E.g. from calling next(err)). This is most used when you want to define arbitrary rendering of errors.

router.get('/error_route', function (req, res, next) {
  return next(new Error('Bad Request'))
})

router.use(function (err, req, res, next) {
  res.end(err.message) //= > "Bad Request"
})

Error handling middleware will only be invoked when an error was given. As long as the error is in the pipeline, normal middleware and handlers will be bypassed - only error handling middleware will be invoked with an error.

Examples

// import our modules
var http = require('http')
var Router = require('router')
var finalhandler = require('finalhandler')
var compression = require('compression')
var bodyParser = require('body-parser')

// store our message to display
var message = 'Hello World!'

// initialize the router & server and add a final callback.
var router = Router()
var server = http.createServer(function onRequest (req, res) {
  router(req, res, finalhandler(req, res))
})

// use some middleware and compress all outgoing responses
router.use(compression())

// handle `GET` requests to `/message`
router.get('/message', function (req, res) {
  res.statusCode = 200
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')
  res.end(message + '\n')
})

// create and mount a new router for our API
var api = Router()
router.use('/api/', api)

// add a body parsing middleware to our API
api.use(bodyParser.json())

// handle `PATCH` requests to `/api/set-message`
api.patch('/set-message', function (req, res) {
  if (req.body.value) {
    message = req.body.value

    res.statusCode = 200
    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
    res.end(message + '\n')
  } else {
    res.statusCode = 400
    res.setHeader('Content-Type', 'text/plain; charset=utf-8')
    res.end('Invalid API Syntax\n')
  }
})

// make our http server listen to connections
server.listen(8080)

You can get the message by running this command in your terminal, or navigating to 127.0.0.1:8080 in a web browser.

curl http://127.0.0.1:8080

You can set the message by sending it a PATCH request via this command:

curl http://127.0.0.1:8080/api/set-message -X PATCH -H "Content-Type: application/json" -d '{"value":"Cats!"}'

Example using mergeParams

var http = require('http')
var Router = require('router')
var finalhandler = require('finalhandler')

// this example is about the mergeParams option
var opts = { mergeParams: true }

// make a router with out special options
var router = Router(opts)
var server = http.createServer(function onRequest (req, res) {
  // set something to be passed into the router
  req.params = { type: 'kitten' }

  router(req, res, finalhandler(req, res))
})

router.get('/', function (req, res) {
  res.statusCode = 200
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')

  // with respond with the the params that were passed in
  res.end(req.params.type + '\n')
})

// make another router with our options
var handler = Router(opts)

// mount our new router to a route that accepts a param
router.use('/:path', handler)

handler.get('/', function (req, res) {
  res.statusCode = 200
  res.setHeader('Content-Type', 'text/plain; charset=utf-8')

  // will respond with the param of the router's parent route
  res.end(req.params.path + '\n')
})

// make our http server listen to connections
server.listen(8080)

Now you can get the type, or what path you are requesting:

curl http://127.0.0.1:8080
> kitten
curl http://127.0.0.1:8080/such_path
> such_path

Example of advanced .route() usage

This example shows how to implement routes where there is a custom handler to execute when the path matched, but no methods matched. Without any special handling, this would be treated as just a generic non-match by router (which typically results in a 404), but with a custom handler, a 405 Method Not Allowed can be sent.

var http = require('http')
var finalhandler = require('finalhandler')
var Router = require('router')

// create the router and server
var router = new Router()
var server = http.createServer(function onRequest (req, res) {
  router(req, res, finalhandler(req, res))
})

// register a route and add all methods
router.route('/pet/:id')
  .get(function (req, res) {
    // this is GET /pet/:id
    res.setHeader('Content-Type', 'application/json')
    res.end(JSON.stringify({ name: 'tobi' }))
  })
  .delete(function (req, res) {
    // this is DELETE /pet/:id
    res.end()
  })
  .all(function (req, res) {
    // this is called for all other methods not
    // defined above for /pet/:id
    res.statusCode = 405
    res.end()
  })

// make our http server listen to connections
server.listen(8080)

License

MIT