next/dist/server/lib/types.d.ts

The React Framework

import type { IncomingMessage, ServerResponse } from 'http';
import type { Duplex } from 'stream';
export type WorkerRequestHandler = (req: IncomingMessage, res: ServerResponse) => Promise<any>;
export type WorkerUpgradeHandler = (req: IncomingMessage, socket: Duplex, head: Buffer) => any;