Middy AJV

This middleware automatically validates incoming events and outgoing responses against custom schemas defined with the JSON schema syntax.

If an incoming event fails validation a BadRequest error is raised. If an outgoing response fails validation a InternalServerError error is raised.

This middleware can be used in combination with httpErrorHandler to automatically return the right response to the user.

It can also be used in combination with httpcontentnegotiation to load localised translations for the error messages (based on the currently requested language). This feature uses internally ajv-i18n module, so reference to this module for options and more advanced use cases. By default the language used will be English (en), but you can redefine the default language by passing it in the ajvOptions options with the key defaultLanguage and specifying as value one of the supported locales.

Also, this middleware accepts an object with plugins to be applied to customize the internal ajv instance. Out-of-the-box ajv-i18n and ajv-formats are being used.

Install

To install this middleware you can use NPM:

npm install --save middy-ajv

Requires: @middy/core:>=2.0.0

Options

• inputSchema (object) (optional): The JSON schema compiled ajv validator that will be used to validate the input (request.event) of the Lambda handler.
• outputSchema (object) (optional): The JSON schema compiled ajv validator that will be used to validate the output (request.response) of the Lambda handler.
• availableLanguages (object) (optional): Error messages can be returned in multiple languages using ajv-i18n. Language is selected based on event.preferredLanguage set by @middy/http-content-negotiation. Should be in the format: { 'en': require('ajv-i18n/localize/en') }.
• defaultLanguage (string) (default: en): The default language to use when availableLanguages is provided and event.preferredLanguage is not supported.

NOTES:

• At least one of inputSchema or outputSchema is required.

Sample usage

Example for validation using precompiled schema:

import middy from '@middy/core'
import validator from 'middyajv'

const handler = middy((event, context) => {
  return {}
})

const inputSchema = require('schema.js')

handler.use(validator({ inputSchema }))

// invokes the handler, note that property foo is missing
const event = {
  body: JSON.stringify({something: 'somethingelse'})
}
handler(event, {}, (err, res) => {
  t.is(err.message,'Event object failed validation')
})

Example for validation that will compile the schema before deploying:

import middy from '@middy/core'
import validator from '@middy/validator' // We use the more developer friendly middeware, with place of replacing during build

const handler = middy((event, context) => {
  return {}
})

const schema = require('schema.json')

handler.use(validator({ inputSchema }))

// invokes the handler, note that property foo is missing
const event = {
  body: JSON.stringify({something: 'somethingelse'})
}
handler(event, {}, (err, res) => {
  t.is(err.message,'Event object failed validation')
})

Build step

Folder Structure

{project}
|-- handlers
| |-- {enpoint}
| | |-- index.mjs
| | |-- schema.json

After the build scripts have been run the endpoint folder will contain schema.js and index.js. The later of which you need to upload to AWS.

Install

$ npm install -D ajv-cli rollup @rollup/plugin-commonjs @rollup/plugin-json @rollup/plugin-node-resolve @rollup/plugin-replace rollup-plugin-esbuild esbuild

rollup.config.js

import { readdirSync } from 'fs'
import commonjs from '@rollup/plugin-commonjs'
import json from '@rollup/plugin-json'
import resolve from '@rollup/plugin-node-resolve'
import replace from '@rollup/plugin-replace'
import esbuild from 'rollup-plugin-esbuild'

function onwarn (warning, warn) {
  if (warning.code === 'CIRCULAR_DEPENDENCY') return
  warn(warning)
}

import {dirname, join} from 'path'
const handlers = readdirSync('./handlers').filter((dir) => dir !=='.DS_Store')
export default handlers.map((input) => ({
  input: 'handlers/' + input + '/index.mjs',
  output: {
    file: 'handlers/' + input + '/index.js',
    format: 'cjs',
  },
  plugins: [
    replace({
      preventAssignment: false,  // remove warning, will be default in future version
      delimiters: ['',''],
      include: ['./**/index.mjs'],
      values: {
        // use leaner version of `@middy/validator`
        'require(\'@middy/validator\')': 'require(\'middy-ajv\')',
        'from \'@middy/validator\'': 'from \'middy-ajv\'',

        // use compiled schemas for `middy-ajv`
        'require(\'./schema.json\')': 'require(\'./schema.js\').default',
        'inputSchema from \'./schema.json\'': 'inputSchema from \'./schema.js\'',
      }
    }),
    json(),
    resolve({ preferBuiltins: true }),
    commonjs(),
    esbuild({
      minify: true,
      target: 'es2020'
    })
  ],
  external: [
    'aws-sdk',
    'aws-sdk/clients/cloudfront', 'aws-sdk/clients/waf', 'aws-sdk/clients/s3',
    'aws-sdk/clients/ssm', 'aws-sdk/clients/sns', 'aws-sdk/clients/sqs', 'aws-sdk/clients/stepfunctions',
    'aws-sdk/clients/dynamodb', 'aws-sdk/clients/rds'
  ],
  onwarn,
}))

Run

# Compile JSON Schemas
$ for dir in handlers/*/; do node ./node_modules/ajv-cli/dist/index.js compile -c ajv-formats -c ajv-formats-draft2019 --strict=true --coerce-types=array --all-errors=true --use-defaults=empty --messages=false -s $dir'schema.json' -o $dir'schema.js'; done
# Bundle
$ rollup --config rollup.config.js --environment INCLUDE_DEPS,BUILD:production

Middy documentation and examples

For more documentation and examples, refers to the main Middy monorepo on GitHub or Middy official website.

Contributing

Everyone is very welcome to contribute to this repository. Feel free to raise issues or to submit Pull Requests.

License

Licensed under MIT License. Copyright (c) 2017-2021 will Farrell and the Middy team.