@fastify/middie

@fastify/middie is the plugin that adds middleware support on steroids to Fastify.

The syntax style is the same as express/connect. Does not support the full syntax middleware(err, req, res, next), because error handling is done inside Fastify.

Install

npm i @fastify/middie

Usage

Register the plugin and start using your middleware.

const Fastify = require('fastify')

async function build () {
  const fastify = Fastify()
  await fastify.register(require('@fastify/middie'), {
    hook: 'onRequest' // default
  })
  // do you know we also have cors support?
  // https://github.com/fastify/fastify-cors
  fastify.use(require('cors')())
  return fastify
}

build()
  .then(fastify => fastify.listen({ port: 3000 }))
  .catch(console.log)

Encapsulation support

The encapsulation works as usual with Fastify, you can register the plugin in a subsystem and your code will work only inside there, or you can declare the middie plugin top level and register a middleware in a nested plugin, and the middleware will be executed only for the nested routes of the specific plugin.

Register the plugin in its own subsystem:

const fastify = require('fastify')()

fastify.register(subsystem)

async function subsystem (fastify, opts) {
  await fastify.register(require('@fastify/middie'))
  fastify.use(require('cors')())
}

Register a middleware in a specific plugin:

const fastify = require('fastify')()

fastify
  .register(require('@fastify/middie'))
  .register(subsystem)

async function subsystem (fastify, opts) {
  fastify.use(require('cors')())
}

Hooks and middleware

Every registered middleware will be run during the onRequest hook phase, so the registration order is important. Take a look at the Lifecycle documentation page to understand better how every request is executed.

const fastify = require('fastify')()

fastify
  .register(require('@fastify/middie'))
  .register(subsystem)

async function subsystem (fastify, opts) {
  fastify.addHook('onRequest', async (req, reply) => {
    console.log('first')
  })

  fastify.use((req, res, next) => {
    console.log('second')
    next()
  })

  fastify.addHook('onRequest', async (req, reply) => {
    console.log('third')
  })
}

It is possible to change the Fastify hook that the middleware will be attached to. Supported lifecycle hooks are:

• onRequest
• preParsing
• preValidation
• preHandler
• preSerialization
• onSend
• onResponse
• onError
• onTimeout

To change the hook, pass a hook option like so:

Note you can access req.body from the preParsing, onError, preSerialization and onSend lifecycle steps. Take a look at the Lifecycle documentation page to see the order of the steps.

const fastify = require('fastify')()

fastify
  .register(require('@fastify/middie'), { hook: 'preHandler' })
  .register(subsystem)

async function subsystem (fastify, opts) {
  fastify.addHook('onRequest', async (req, reply) => {
    console.log('first')
  })

  fastify.use((req, res, next) => {
    console.log('third')
    next()
  })

  fastify.addHook('onRequest', async (req, reply) => {
    console.log('second')
  })

  fastify.addHook('preHandler', async (req, reply) => {
    console.log('fourth')
  })
}

Restrict middleware execution to a certain path(s)

If you need to run a middleware only under certain path(s), just pass the path as first parameter to use and you are done!

const fastify = require('fastify')()
const path = require('node:path')
const serveStatic = require('serve-static')

fastify
  .register(require('@fastify/middie'))
  .register(subsystem)

async function subsystem (fastify, opts) {
  // Single path
  fastify.use('/css', serveStatic(path.join(__dirname, '/assets')))

  // Wildcard path
  fastify.use('/css/*', serveStatic(path.join(__dirname, '/assets')))

  // Multiple paths
  fastify.use(['/css', '/js'], serveStatic(path.join(__dirname, '/assets')))
}

⚠️ potential ReDoS attacks

Middie use path-to-regexp to convert paths to regular expressions. This might cause potential ReDoS attacks in your applications if certain patterns are used. Use it with care.

Middie Engine

You can also use the engine itself without the Fastify plugin system.

Usage

const Middie = require('@fastify/middie/engine')
const http = require('node:http')
const helmet = require('helmet')
const cors = require('cors')

const middie = Middie(_runMiddlewares)
middie.use(helmet())
middie.use(cors())

http
  .createServer(function handler (req, res) {
    middie.run(req, res)
  })
  .listen(3000)

function _runMiddlewares (err, req, res) {
  if (err) {
    console.log(err)
    res.end(err)
    return
  }

  // => routing function
}

Keep the context

If you need it you can also keep the context of the calling function by calling run with run(req, res, this), in this way you can avoid closures allocation.

http
  .createServer(function handler (req, res) {
    middie.run(req, res, { context: 'object' })
  })
  .listen(3000)

function _runMiddlewares (err, req, res, ctx) {
  if (err) {
    console.log(err)
    res.end(err)
    return
  }
  console.log(ctx)
}

Restrict middleware execution to a certain path(s)

If you need to run a middleware only under certains path(s), just pass the path as first parameter to use and you are done!

Note that this does support routes with parameters, e.g. /user/:id/comments, but all the matched parameters will be discarded

// Single path
middie.use('/public', staticFiles('/assets'))

// Multiple middleware
middie.use('/public', [cors(), staticFiles('/assets')])

// Multiple paths
middie.use(['/public', '/dist'], staticFiles('/assets'))

// Multiple paths and multiple middleware
middie.use(['/public', '/dist'], [cors(), staticFiles('/assets')])

To guarantee compatibility with Express, adding a prefix uses path-to-regexp to compute a RegExp, which is then used to math every request: it is significantly slower.

TypeScript support

To use this module with TypeScript, make sure to install @types/connect.

Middleware alternatives

Fastify offers some alternatives to the most commonly used Express middleware:

Express Middleware	Fastify Plugin
helmet	fastify-helmet
cors	fastify-cors
serve-static	fastify-static

Acknowledgements

This project is kindly sponsored by:

• nearForm

Past sponsors:

• LetzDoIt

License

Licensed under MIT.