apigateway-ts

A simple way to create routes and routers for HTTP request from API Gateway for AWS Lambda.

Get Started

Create an AWS Lambda with a simple route matching GET /hello returning HTTP 200 world and HTTP 404 for anything else

export const handler = router([
  route('/hello', HttpMethod.GET, async () => ({statusCode: 200, body: 'world'}))
]);

Handlers

type Handler = (event: APIGatewayProxyEvent) => Promise<APIGatewayProxyResult>

A function that takes an API Gateway Proxy event and returns an API Gateway Proxy Result these types come from @types/aws-lambda and describe the request and response types for an AWS Lambda when triggered from API Gateway. For example:

const helloWorldHandler: Handler = async event => ({
  statusCode: 200,
  body: '{"msg": "hello world"}'
})

Handlers are passed to routers shown below.

Routers

Routers provide a way to route requests to a particular handler based on resources like /a/b/1 and http methods like GET, PUT, POST

function router(routes: RoutingHttpHandler[], notFoundResponse: APIGatewayProxyResult = { statusCode: 404, body: '' }): Handler

RoutingHttpHandlers can be created using one of the following methods and can be nested:

function route(resource: string, method: HttpMethod | undefined, handler: Handler, filter?: Filter): RoutingHttpHandler {

function bind(resourceInfo: resourceInfo, handler: Handler, ...filters: Filter[]): RoutingHttpHandler {

HTTP Methods and paths are used by the router to find the appropriate handler to use

 const router: Handler = router([
    bind(["/", HttpMethod.GET], fetchAllHandler),
    bind(["/{id}", HttpMethod.GET], fetchOneHandler),
    bind(["/{id}", HttpMethod.PATCH], updateHandler),
    bind(["/{id}", HttpMethod.DELETE], deleteHander)
  ], 
  notFoundResponse // optional
  ) 

Routers can be nested to form more complex routers

 const idRoute: Handler = router([
      bind(HttpMethod.GET, fetchOneHandler),
      bind(HttpMethod.PATCH, updateHandler),
      bind(HttpMethod.DELETE, deleteHandler)
    ]);

 const routes: Handler = router([
      bind(HttpMethod.GET, fetchAllHandler),
      bind("/{id}",idRoute )], 
    notFoundResponse // optional
    ); 

Filters

Filters can be attached to any Handler to intercept the Request or Response from the handler. The filter Type signature is defined as

export type Filter = (handler: Handler) => Handler;

A filter to measure time taken by a Handler could be written as

const timingFilter: Filter =
  nextHandler => async event => {
    const before = new Date().getTime();
    const result = await nextHandler(event);
    const after = new Date().getTime();
    console.log(`handler time ${after - before}`);
    return result;
  };

Filters can also combined and attached to a handler using

export function withFilters<T extends Handler>(handler: T, ...filters: Filter[]): T

For example

const helloWorldHandler: Handler = ...
const timingFilter: Filter = ...
const authFilter: Filter = ...
const handlerWithFilters: Handler = 
  withFilters(helloWorldHandler, authFilter, timingFilter) 

Included Filters

Apigateway-ts includes some useful filters as part of the library

• corsFilter : Filter for CORS headers
• loggingFilter: Logs basic Request and Response info
• httpErrorFilter: Catches errors thrown by the handler returning 500 with the thrown error message
• contentType : Sets the content type to whatever you want it to be
• versionFilter: Takes a version argument and logs warnings if header (default X-API-VERSION) does not match