YOUR DOMAIN.
NEXT BACKEND.

In your Next.js application, install the adapter, handler libraries and the validator used below.

npm i @domain-first/handlers-next @domain-first/handlers-rest @domain-first/handlers zod

This example adds two numbers. The application function receives validated values and returns its result.

import { defineHandler } from '@domain-first/handlers';
import { z } from 'zod';

export const sum = defineHandler({
  inputSchema: z.object({ a: z.number(), b: z.number() }),
  outputSchema: z.number(),
  handler: async ({ a, b }) => a + b,
});

Use nextAdapter with createEndpoint. Reuse the handler schema for the request body and map the validated body into its input.

import { createEndpoint } from '@domain-first/handlers-rest';
import { nextAdapter } from '@domain-first/handlers-next';
import { sum } from '../application/sum';

const endpoint = createEndpoint()(nextAdapter);

export const sumPOST = endpoint(sum, {
  route: { method: 'post', path: ['sum'] },
})
  .input((schema) => ({ body: schema }))
  .mapInput(({ body }) => body);

Import the full REST endpoint array from your presentation layer. Pass it to nextEndpoints once, then export the same handler for every HTTP method. One App Router entry point serves the whole collection.

import { nextEndpoints } from '@domain-first/handlers-next';
import { restHandlers } from '@/presentation/rest';

const handler = nextEndpoints(restHandlers);

export const GET = handler;
export const POST = handler;
export const PUT = handler;
export const PATCH = handler;
export const DELETE = handler;

The scaffolder automatically registers each new REST endpoint in @/presentation/rest. Import restHandlers and pass it to nextEndpoints — the collection is already maintained for you.

curl -X POST http://localhost:3000/api/sum \
  -H 'Content-Type: application/json' \
  -d '{"a":10,"b":30}'
# Result: 40