fastify-zod-plugin.ts

import type { FastifyInstance } from 'fastify'
import fp from 'fastify-plugin'
import type { ZodAny, ZodError, ZodTypeAny } from 'zod'
import { z } from 'zod'
import { fromZodError } from 'zod-validation-error'

declare module 'fastify' {
  // TODO: Copy ZodTypeProvider here (output)
  interface FastifyTypeProviderDefault {
    output: this['input'] extends ZodTypeAny ? z.infer<this['input']> : unknown
  }
}

function asError(zodError: ZodError) {
  return fromZodError(zodError, { prefix: null, issueSeparator: '\n' })
}

async function plugin(server: FastifyInstance) {
  server.setValidatorCompiler<ZodAny>(({ schema }) => data => {
    const result = schema.safeParse(data)
    if (result.success) return { value: result.data }
    return { error: asError(result.error) }
  })
  server.setSerializerCompiler<ZodAny>(({ schema }) => data => {
    const result = schema.safeParse(data)
    if (result.success) return JSON.stringify(result.data)
    throw asError(result.error)
  })
}

export default fp(plugin)