A compose function for functional lambda middleware.
npm install @lambda-middleware/compose
A compose function for lambda middleware. This is a pure convenience copy of ramda's compose, using it directly or using other compose functions works as well.
This middleware is part of the lambda middleware series. It can be used independently.
``typescript
import { compose } from "@lambda-middleware/compose";
import { PromiseHandler } from "@lambda-middleware/utils";
import { Context, ProxyHandler, APIGatewayEvent } from "aws-lambda";
// This is your AWS handler
async function helloWorld(): Promise
// Write your own middleware
const stringifyToBody = () => (
handle: PromiseHandler
) => async (event: APIGatewayEvent, context: Context) => {
const response = await handle(event, context);
return {
body: JSON.stringify(response),
};
};
const addStatusCode = (statusCode: number) => (
handle: PromiseHandler
) => async (event: APIGatewayEvent, context: Context) => {
const response = await handle(event, context);
return {
...response,
statusCode,
};
};
// Wrap the handler with the middleware.
// With compose you can wrap multiple middlewares around one handler.
export const handler: ProxyHandler = compose(
addStatusCode(200),
stringifyToBody()
)(helloWorld);
`
There's a known issue with TypeScript that pipe and compose functions cannot
infer types correctly if the innermost function is generic (in this case the last argument to compose).composeHandler
To get around it, this package also exports :
`ts
import "reflect-metadata";
import { classValidator } from "@lambda-middleware/class-validator";
import { compose } from "@lambda-middleware/compose";
import { errorHandler } from "@lambda-middleware/http-error-handler";
import { IsString } from "class-validator";
import { APIGatewayProxyResult } from "aws-lambda";
class NameBody {
constructor(firstName: string, lastName: string) {
this.firstName = firstName;
this.lastName = lastName;
}
@IsString()
public firstName: string;
@IsString()
public lastName: string;
}
async function helloWorld(event: {
body: NameBody;
}): Promise
return {
body: Hello ${event.body.firstName} ${event.body.lastName},
headers: {
"content-type": "text",
},
statusCode: 200,
};
}
export const handler = composeHandler(
errorHandler(),
classValidator({
bodyType: NameBody,
}),
// The following function solves the type trouble:
helloWorld
);
``