API Caching

Add caching layer to API responses

Add caching layer to API responses.

Instructions

1. HTTP caching headers:

export async function GET(req: Request) {
  const data = await fetchData();
  const etag = crypto.createHash('md5').update(JSON.stringify(data)).digest('hex');

  // Check if client has current version
  if (req.headers.get('if-none-match') === etag) {
    return new Response(null, { status: 304 });
  }

  return Response.json({ data }, {
    headers: {
      'Cache-Control': 'public, max-age=60, stale-while-revalidate=300',
      'ETag': etag,
    },
  });
}

2. Server-side caching with Redis:

async function getCachedOrFetch<T>(key: string, ttlSeconds: number, fetcher: () => Promise<T>): Promise<T> {
  const cached = await redis.get(key);
  if (cached) return JSON.parse(cached);

  const data = await fetcher();
  await redis.setex(key, ttlSeconds, JSON.stringify(data));
  return data;
}

// Usage
const users = await getCachedOrFetch('users:list', 60, () => db.user.findMany());

Cache Invalidation

• Invalidate on write: after POST/PATCH/DELETE, delete related cache keys
• Use cache tags to invalidate groups: users:*
• Set reasonable TTLs: 60s for lists, 300s for rarely-changed data