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validator

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/validator

Options

  • eventSchema (object|function) (default undefined): The JSON schema object or compiled ajv validator that will be used to validate the input (request.event) of the Lambda handler. Supports alias inputSchema
  • contextSchema (object|function) (default undefined): The JSON schema object or compiled ajv validator that will be used to validate the input (request.context) of the Lambda handler. Has additional support for typeof keyword to allow validation of "typeof":"function".
  • responseSchema (object|function) (default undefined): The JSON schema object or compiled ajv validator that will be used to validate the output (request.response) of the Lambda handler. Supports alias inputSchema
  • ajvOptions (object) (default undefined): Options to pass to ajv class constructor. Defaults are { strict: true, coerceTypes: 'array', allErrors: true, useDefaults: 'empty', messages: false, defaultLanguage: 'en' }.
  • i18nEnabled (boolean) (default true): Option to disable i18n default package.

NOTES:

  • At least one of eventSchema or responseSchema is required.
  • Important Compiling schemas on the fly will cause a 50-100ms performance hit during cold start for simple JSON Schemas. Precompiling is highly recommended.
  • Default ajv plugins used: ajv-i18n, ajv-formats, ajv-formats-draft2019
  • If you'd like to have the error details as part of the response, it will need to be handled separately. You can access them from request.error.details, the original response can be found at request.error.response.

Sample usage

Example for input validation:

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

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

const schema = {
required: ['body', 'foo'],
properties: {
// this will pass validation
body: {
type: 'string'
},
// this won't as it won't be in the event
foo: {
type: 'string'
}
}
}

handler.use(validator({
inputSchema: schema
}))

// 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 output validation:

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

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

const responseSchema = {
required: ['body', 'statusCode'],
properties: {
body: {
type: 'object'
},
statusCode: {
type: 'number'
}
}
}

handler.use(validator({responseSchema}))

handler({}, {}, (err, response) => {
t.not(err, null)
t.is(err.message,'Response object failed validation')
expect(response).not.toBe(null)
// it doesn't destroy the response so it can be used by other middlewares
})