@lambda-middleware/middy-adaptor

An adaptor to use middy middleware as functional middleware. Please note that this will limit type safety. If you the middleware returns a Promise, calls the next function and calls instance.callback (or any two of these), no specific behavior of this adaptor is guaranteed.

Lambda middleware

This middleware is part of the lambda middleware series. It can be used independently.

Usage

import {
  middyAdaptor,
  MiddlewareObject,
} from "@lambda-middleware/middy-adaptor";
import { APIGatewayProxyEvent, APIGatewayProxyResult } from "aws-lambda";

// This is your AWS handler
async function helloWorld(
  event: APIGatewayProxyEvent
): Promise<APIGatewayProxyResult> {
  if (event.headers["before-middleware-ran"] === undefined) {
    throw new Error("Before middleware never ran");
  }
  if (event.headers["throw-error"] !== undefined) {
    throw new Error("Throw-error header is set");
  }
  return {
    statusCode: 200,
    body: JSON.stringify({ msg: "Hello World" }),
  };
}

// Import an existing middy middleware or write your own
function customMiddyMiddleware(): MiddlewareObject<any, any> {
  function createCustomHeaderAdder(headerName: string, headerValue: string) {
    return (
      instance: { response: any; error: Error | null },
      next: (error?: any) => void
    ): void => {
      instance.response = instance.response ?? { statusCode: 200 };
      instance.response.headers = instance.response.headers ?? {};
      instance.response.headers[headerName] = headerValue;
      next();
    };
  }

  return {
    before: async (instance: { event: any }): Promise<void> => {
      instance.event.headers = {
        ...instance.event.headers,
        "before-middleware-ran": "true",
      };
    },
    after: createCustomHeaderAdder("Custom-Test-After-Header", "set"),
    onError: createCustomHeaderAdder("Custom-Test-On-Error-Header", "set"),
  };
}

// Wrap the handler with the middleware
export const handler = middyAdaptor(customMiddyMiddleware())(helloWorld);