aws-lambda-res

is a tiny helper to create a response object for AWS Lambda with Proxy integration

Usage | Annotated source | License

Usage

Suppose you have an API Gateway resource with a method configured with Lambda Proxy integration.

Suppose you have a dummy endpoint which returns JSON { "ok": true }, then the following code will be a working implementation.

const response = require('aws-lambda-res')

function handler (event, context, callback) {
  callback(null, response(200)({ ok: true }))
}

exports.handler = handler

You can pass headers as second argument, body can be null: for example to logout and redirect to homepage you can use something like

function handler (event, context, callback) {
  const Expires = 'Sat, 01 Jan 2000 00:00:00 GMT' // Some day in the past.

  callback(null, response(302)(null, {
    'Location': 'https://example.org',
    'set-cookie': `user_authenticated=; Domain=example.com; Expires=${Expires}`
  }))
}

exports.handler = handler

Let me write few tips I want to remember. When a method on API Gateway is configured with Lambda Proxy integration no additional mapping is needed. Everything you need will be available in event argument.

To get a JSON payload, just parse it from body.

function handler (event, context, callback) {
  const { id, name } = JSON.parse(event.body)

  // Follows your code...
}

To extract form parameters, or from any POST or PUT method, use querystring package.

const querystring = require('querystring')

function handler (event, context, callback) {
  const { email, password } = querystring.parse(event.body)

  // Follows your code...
}

To access query string parameters in a GET do

function handler (event, context, callback) {
  const { param1, param2 } = event.queryStringParameters

  // Follows your code...
}

To get cookies, parse event.cookie.

function handler (event, context, callback) {
  const cookies = event.cookie.split(';')

  let session

  cookies.forEach(cookie => {
    if (cookie.indexOf('session=') === 0) {
      session = cookie.split('=')[1]
    }
  })

  // Follows your code...
}

To get headers, look into event.headers. For example, you can get a JWT header with the following snippet.

function handler (event, context, callback) {
  const auth = event.headers.Authorization

  const token = (auth && auth.startsWith('BEARER ')) ? auth.substring(7) : null

  // Follows your code...
}

For route placeholders, for example suppose you want to handle an enpoint like GET /user/{id}, go to API Gateway and create first a resource with path /user. Then create a child resource with path /{id} and add a GET method. The code of associated Lambda function will be something like the following.

function handler (event, context, callback) {
  const { id } = event.pathParameters

  // Follows your code...
}

Annotated source

// This code is generated by command: npm run markdown2code

Lambda Proxy integration needs a response with the following properties:

• isBase64Encoded
• statusCode
• headers
• body

/**
 * Create a response helper.
 *
 * @params {Number} statusCode
 * @returns {Function} awsLambdaResponse helper
 */

function response (statusCode) {

The exported response function, requires statusCode argument and returns an helper function which accepts parameters:

1. body: can be any data, even null.
2. headers, defaults to { 'Content-type': 'application/json' }.

  /**
   * AWS Lambda response helper.
   *
   * @params {Object|null} body
   * @params {Object} [headers]
   * @returns {Object} responseObj required by AWS Lambda Proxy integration
   */

  function awsLambdaResponse (
    body,
    headers = { 'Content-Type': 'application/json' }
  ) {
    const responseObj = {
      isBase64Encoded: false,
      headers,
      statusCode,
      body: body === null ? null : JSON.stringify(body)
    }

    return responseObj
  }

Return helper and export function

  return awsLambdaResponse
}

module.exports = response

License

MIT