serverless-request-handler

Wrapper for AWS Lambda functions with API Gateway creating unified response for error states.

By default the handler adds 'Access-Control-Allow-Origin': '*' and 'Content-Type': 'application/json; charset=utf-8' headers to the response.

Installation

1. Install npm package: yarn add @keboola/serverless-request-handler
2. Wrap each of your lambda handlers with this code:

const { RequestHandler } = require('@keboola/serverless-request-handler');

module.exports.handler = (event, context, callback) => RequestHandler.handler(() => {
  const promise = new Promise(res => res());
  const code = 204;
  return RequestHandler.responsePromise(promise, event, context, callback, code);
}, event, context, callback);

• RequestHandler.handler() catches uncaught exceptions
• RequestHandler.responsePromise() catches rejected promises and formats output for resolved promise chain

You can also return status code and headers in the resolved promise:

module.exports.handler = (event, context, callback) => RequestHandler.handler(() => {
  const promise = new Promise((res) => {
    // ...
    res({
      headers: { 'Access-Control-Allow-Headers': 'Token' },
      body: {
        message: 'Resource was created',
      },
      statusCode: 201,
    });
  });
  return RequestHandler.responsePromise(promise, event, context, callback);
}, event, context, callback);

Request logging

Each request is logged to Cloudwatch in this json format:

{
  "event": {
    "requestId": "4d4f1e1e-ca29-11e7-87c4-2fcc57c44b2d",
    "apiRequestId": "369391fb-ca29-11e7-90b1-95afd12f3597",
    "function": "developer-portal-prod-users",
    "httpMethod": "GET",
    "path": "/users/[email protected]"
  },
  "statusCode": 200
}

User Errors

If you want to return a user error, use UserError class which is handled by the handler automatically and the output is formatted in appropriate way. The class offer several static functions as shortcuts for most common user errors:

• badRequest(msg = 'Bad Request') - for 400 errors
• unauthorized(msg = 'Unauthorized') - for 401 errors
• notFound(msg = 'Not Found') - for 404 errors
• unauthorized(msg = 'Unauthorized') - for 401 errors
• unprocessable(msg = 'Unprocessable') - for 422 errors
• error(msg = 'Error', code = 400) - for other errors

Example:

const { UserError } = require('@keboola/serverless-request-handler');

if (!token) {
  throw UserError.unauthorized('Token is missing');
}

User then gets such response with status code 401:

{
  "errorMessage": "Token is missing",
  "errorType": "Unauthorized",
  "requestId": "4d4f1e1e-ca29-11e7-87c4-2fcc57c44b2d"
}

And CloudWatch log of the request is enriched with error field containing the error message.