server-only

/* src/lib/server-utils.ts */ // This directive ensures that this entire file can only be imported in Server Components. import 'server-only'; import { promises as fs } from 'fs'; export async function getSecretData() { // This code will only run on the server. // Accessing process.env directly is safe here. const apiKey = process.env.DATABASE_API_KEY ?? 'default_api_key'; console.log('Fetching secret data on the server...'); // Simulate reading from a server-side file system const fileContent = await fs.readFile(process.cwd() + '/src/lib/server-config.txt', 'utf-8'); return { message: `Hello from the server! Key used: ${apiKey.substring(0, 5)}...`, config: fileContent }; } /* src/app/page.tsx (Server Component) */ // This is a Server Component, so it can safely import 'server-utils.ts' import { getSecretData } from '../lib/server-utils'; export default async function HomePage() { const data = await getSecretData(); return ( <div> <h1>Welcome to the Server Component App</h1> <p>{data.message}</p> <p>Server config snippet: {data.config.substring(0, 20)}...</p> {/* You cannot import 'use client' components here that directly use getSecretData */} </div> ); } // Example of how to prevent client-side usage, if you tried to import getSecretData in a 'use client' component: // /* src/components/ClientComponent.tsx */ // 'use client'; // import { getSecretData } from '../lib/server-utils'; // This line would cause a build error // export default function ClientComponent() { return <div>Client component</div>; }