Openapi-typescript-aws-handler NPM

This library extends upon the awesome openapi-typescript library to create AWS lambda bindings for handling requests that are made to an OpenAPI API. The intention is to make it as easy as possible to create a typescript handler that will accept requests from somewhere else (presumably an (API gateway)) and will execute some type safe(ish) code to process that request. It assumes that all validation has already been performed by an upstream

This library does no code-generation of its own. It depends on openapi-typescript for that. Instead, it just provides some typescript type magic to provide a type-safe way of defining your handlers, and a simple wrapper that will take input and call your function.

🚧 NOTE
This library does not currently vend or return AWS API Gateway proxy objects (as served by API Gateway) - This is because I have another wrapper around these objects, but I will add in another version of the wrapper that does work directly with Proxy request. You could write a trivial wrapper around this to do it yourself in the mean time.
This library also assumes that you are transmitting and receiving JSON only. Some APIs may use different content types. Its unclear to me whether my API adapter should auto-transform, or whether the API desginer should be given control - probably a mixture of both. Transforming between YAML and JSON is trivial, and could easily be handled by the wrapper.

Usage

To use this library there are a couple of steps

Generate bindings for your application using openapi-typescript

Create a lambda handler using the makeOpenApiLambdaHandler call from this package. For example

import { OperationHandler, makeOpenApiLambdaHandler, Non2xxResult } from "openapi-typescript-aws-handler"
import { operations, components,  } from "./api"  // This is the file you generated using openapi-typescript

/**
* Makes it easier to throw the API specific ApiError.
*/
class ApiError extends Non2xxResult<components['schemas']['ApiError']> {
    constructor(message: string, code: number = 500) {
        super({ message }, code)
    }
}

/**
*  Handler for the *echoInput* operation
*/
const echoInput: OperationHandler<operations["echoInput"]> = async ({ body, params }) => {

    // For demo purposes, we execute differently based upon a mock query parameter passed in
    const mockParam = params?.query?.mock;
    if (mockParam) {
        switch (mockParam) {
            case 'fail':
                throw new ApiError("you told me to fail", 500);
            case 'not_found':
                throw new ApiError("Not Found", 404);
        }
    }

    if (!body) {
        throw new ApiError("No body supplied");
    }

    return {
        status: 200,
        content: {
            response: body.input
        }
    };
}

export const handler = makeOpenApiLambdaHandler<operations>({
    echoInput,
});