Fastify server with payload validation, using TypeBox and Ajv.

fastify-server-with-payload-validation.ts

import Ajv from "ajv"
import Fastify from "fastify"
import type { TypeBoxTypeProvider } from "@fastify/type-provider-typebox"
import type { Static } from "@sinclair/typebox"
import { Type } from "@sinclair/typebox"

export const payloadSchema = Type.Object({
    message: Type.String(),
})

export type Payload = Static<typeof payloadSchema>

export const reqBodySchema = Type.Object({
    name: Type.String(),
    payload: Type.Object({}), // we will validate this part programatically
})

export type ReqBody = Static<typeof reqBodySchema>

const server = Fastify({ logger: true }).withTypeProvider<TypeBoxTypeProvider>()

server.addHook("preValidation", async (req) => {
    req.log.warn({ body: req.body }, "[preValidation] body") // useful to troubleshoot validation errors, inspired by https://www.fastify.io/docs/latest/Reference/Logging/#usage
})

server.post<{ Body: ReqBody }>(
    "/",
    { schema: { body: reqBodySchema } },
    async ({ body }, reply) => {
        const ajv = new Ajv()
        if (!ajv.validate(payloadSchema, body.payload)) {
            const errMessage = ajv.errorsText()
            server.log.warn(`validation error: ${errMessage}`)
            reply.statusCode = 400
            return { error: err.message }
        }
        // TODO: process the request
        return { ok: true }
    }
)

createServer()
    .listen({
        port: process.env.PORT,
        host: "0.0.0.0", // makes the server reachable to all interfaces, when running from from a Docker container
    })
    .catch((err) => {
        server.log.error(err)
        process.exit(1)
    })