AWS Lambda handler to express

express-handler.ts

import { Request, Response } from "express";
import { Lambdas, LambdaMap } from "./types";

/**
 * Converts an uri with colon-based parameters to brackets-based parameters
 * - i.e (:username to {username})
 * @param path The url to map
 */
const mapPathToApiGateway = (path: string) => path.replace(/:(.+?)\b/g, "{$1}");

const mapExpressRequestToLambdaRequest = (request: Request) => ({
  resource: mapPathToApiGateway(request.route.path),
  pathParameters: request.params,
  queryStringParameters: request.query,
  headers: request.headers,
  body: request.body,
  httpMethod: request.method
});


/**
 * Calls respective api handler and sends a express response on lambda done callback.
 * @param request Express request object
 * @param response Express response object
 */
const expressHandler = (
  lambda: Lambdas,
  request: Request,
  response: Response
) => {
  const map: Partial<LambdaMap> = {
    users: usersHandler,
  };
  const lambdaRequest = mapExpressRequestToLambdaRequest(request);
  const lambdaFn = map[lambda];
  lambdaFn(lambdaRequest, {}, (error, result) =>
    response
      .set(result?.headers ?? {}) // sets the express response headers if available
      .status(result.statusCode)
      .send(result.body)
  );
};
    
/**
 * Calls the express handler with the documents param
 * - This method is the one used as the `operationId` 
 */
export const expressUsersHandler = (request: Request, response: Response) => {
  expressHandler("users", request, response);
};