import { createServer } from 'node:net';

/** A TCP port free right now on the loopback interface. */
export async function freePort(): Promise<number> {
	const server = createServer();
	await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
	const address = server.address();
	await new Promise((resolve) => server.close(resolve));

	if (address === null || typeof address === 'string') {
		throw new Error('no TCP address');
	}

	return address.port;
}