io-ts-serverless-handler

A simple wrapper for Serverless Framework HTTP handlers to remove the boilerplate of using io-ts codecs to validate and extract request parameters.

Usage

Install with npm/yarn:

$ yarn add io-ts-serverless-handler
# or npm i --save io-ts-serverless-handler

Create a file where you configure the wrapper function and export it:

// codec-handler.ts

import { configureWrapper } from "io-ts-serverless-handler";

export const codecHandler = configureWrapper({
  // Add optional config here
});

Wrap your handler functions with the wrapper function:

import { codecHandler } from "./codec-handler.ts";
import { NumberFromString } from "io-ts-types/lib/NumberFromString";

export const getUsers = codecHandler(
  {
    queryParameters: t.partial({
      pageSize: NumberFromString,
      pageNumber: NumberFromString
    }),
    pathParameters: t.type({
      userId: NumberFromString
    })
  },
  async ({
    queryParameters: { pageSize, pageNumber },
    pathParameters: { userId }
  }) => {
    // At this point, all the parameters have been validated by io-ts
    // If a validation error occurred, a 400 would have been returned before this point
    return userService.getUser(userId, pageNumber, pageSize);
  }
);

The request body will parsed as JSON and then passed to your codec.

All the other parameters from API Gateway will come through as strings so if you want to decode a non-string type you will have to use a codec that accepts a string, converts it to the type you want and than validates that.

There are a lot of types in the io-ts-types library that can do this for you such as NumberFromString or BooleanFromString.

Example Project

There is a sample Serverless project provided in this repo in the packages/example directory.

Running locally

You can run it locally:

cd packages/example
yarn start

and make some requests to it:

# Get a list of products
$ curl localhost:3000/products/
# Get a list of products with filters
$ curl localhost:3000/products/?pageNumber=2&pageSize=2
# Get the product with ID 0
$ curl localhost:3000/products/0

Deploying to AWS

You can also deploy the example project to an AWS environment:

cd packages/example
yarn sls deploy -s my-stage --verbose

After deployment, the URL of the API endpoint will be logged and you can use it to make requests as outlined above. For example:

# Get a list of products
$ curl https://dlda9fab1c.execute-api.us-east-1.amazonaws.com/my-stage/products/
# Get a list of products with filters
$ curl https://dlda9fab1c.execute-api.us-east-1.amazonaws.com/my-stage/products/?pageNumber=2&pageSize=2
# Get the product with ID 0
$ curl https://dlda9fab1c.execute-api.us-east-1.amazonaws.com/my-stage/products/0

Automated Integration Test

There is also a script which will deploy the example project to AWS, run some tests against it, and then tear it down again.

It is run by the CI pipeline automatically, but you can run it locally:

cd packages/example
yarn integration-test

Development

Project Structure

This project uses yarn workspaces to separate the core package and the example project.

To install the dependencies for all the packages, you run yarn install at the root of the project, and yarn will resolve all the inter-package dependencies.

$ yarn install

After the dependencies are resolved, you can work in each project individually.

You can also run commands across every project simultaniously. For example, to test every package, run the following:

yarn workspaces run test

Releases

This project uses semantic-release to automatically deploy to NPM when needed after changes are merged to the master branch.

Commit messages must be formatted using conventional commits. This allows semantic-release to determine how to increment versions.

A tool is provided to help write these commits. Simply use yarn commit instead of git commit and a wizard will guide you through the commit message writing process.

Roadmap

Extend example project to ensure all AWS API Gateway event types are covered
Support for serverless handlers for providers other than AWS

NoxHarmonium/io-ts-serverless-handler