Fastify + TypeBox fully typed

app.ts

import { Static, Type } from '@sinclair/typebox'
import fastify, { FastifyInstance, FastifyPluginAsync } from 'fastify'
import type { RouteGenericInterface, RouteHandler } from 'fastify/types/route'

const port = 8080

const requestBodySchema = Type.Object({
  email: Type.Readonly(Type.String({ format: 'email' })),
})

const responseBodySchema = Type.Object({
  ok: Type.Boolean(),
})

const queryStringSchema = Type.Object({
  test: Type.ReadonlyOptional(Type.Number({ minimum: 200 })),
})

type RequestBody = Static<typeof requestBodySchema>
type ResponseBody = Static<typeof responseBodySchema>
type QueryString = Static<typeof queryStringSchema>

interface DummyRoute extends RouteGenericInterface {
  Body: RequestBody
  Querystring: QueryString
  Reply: ResponseBody
}

const handler: RouteHandler<DummyRoute> = async (req, res) => {
  console.log('Caller email', req.body.email)
  console.log('Test', req.query.test)

  return res.send({ ok: true })
}

const routes: FastifyPluginAsync = (instance) => {
  instance.route<DummyRoute>({
    method: 'POST',
    url: '/dummy',
    handler: handler,
    schema: {
      body: requestBodySchema,
      querystring: queryStringSchema,
      response: {
        200: responseBodySchema,
      },
    },
  })

  return Promise.resolve()
}

const initApp = async (): Promise<FastifyInstance> => {
  const app = fastify()

  await app.register(routes, { prefix: '/api' })

  return app
}

initApp()
  .then((app) => {
    app.listen(port, () => {
      console.log('App listening on port', port)
    })
  })
  .catch((err) => {
    console.error('Failed to start', err)
  })

responses.md

Fastify + TypeBox

Just a reminder for self -type of gist, and overly verbose on purpose.

Example returns

Body missing

{
  "statusCode": 400,
  "error": "Bad Request",
  "message": "body should be object"
}

Body not valid

With payload { "lol": "kissa" }, returns

{ 
  "statusCode": 400,
  "error": "Bad Request",
  "message": "body should have required property 'email'"
 }

and with payload { "email": "kaunis kissa" } returns

{
  "statusCode": 400,
  "error": "Bad Request",
  "message": "body.email should match format \"email\""
}

Query string number too small

Eg. ?test=2 in query string returns

{ 
  "statusCode": 400,
  "error": "Bad Request",
  "message": "querystring.test should be >= 200"
}

Invalid response

Typings prevent returning invalid responses, but had we managed to return { "nok": true } the response to the caller would be

{
  "statusCode": 500,
  "error": "Internal Server Error",
  "message": "\"ok\" is required!"
}