feat: add long-term caching for immutable assets

src/hooks.server.test.ts

@@ -0,0 +1,145 @@
+import type { RequestEvent } from '@sveltejs/kit';
+import { describe, expect, it, vi } from 'vitest';
+
+import { handle } from './hooks.server';
+
+describe('hooks.server', () => {
+  describe('handle', () => {
+    const createMockEvent = (pathname: string): RequestEvent => {
+      return {
+        url: new URL(`http://localhost${pathname}`),
+      } as RequestEvent;
+    };
+
+    const createMockResolve = (
+      headers?: Record<string, string>,
+      status = 200,
+    ) => {
+      const responseHeaders = new Headers(headers);
+      return vi.fn().mockResolvedValue(
+        new Response('test', {
+          headers: responseHeaders,
+          status,
+        }),
+      );
+    };
+
+    it('should set Cache-Control header for /_app/immutable/ paths', async () => {
+      const event = createMockEvent('/_app/immutable/chunks/index.js');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe(
+        'public, max-age=31536000, immutable',
+      );
+    });
+
+    it('should set Cache-Control header for nested /_app/immutable/ paths', async () => {
+      const event = createMockEvent('/_app/immutable/assets/styles.css');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe(
+        'public, max-age=31536000, immutable',
+      );
+    });
+
+    it('should set Cache-Control header for /_app/immutable/nodes/ paths', async () => {
+      const event = createMockEvent('/_app/immutable/nodes/0.abc123.js');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe(
+        'public, max-age=31536000, immutable',
+      );
+    });
+
+    it('should set Cache-Control header for /_app/immutable/entry/ paths', async () => {
+      const event = createMockEvent('/_app/immutable/entry/app.abc123.js');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe(
+        'public, max-age=31536000, immutable',
+      );
+    });
+
+    it('should not set Cache-Control header for non-immutable /_app/ paths', async () => {
+      const event = createMockEvent('/_app/version.json');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBeNull();
+    });
+
+    it('should not set Cache-Control header for regular routes', async () => {
+      const event = createMockEvent('/namespaces/default/workflows');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBeNull();
+    });
+
+    it('should not set Cache-Control header for root path', async () => {
+      const event = createMockEvent('/');
+      const resolve = createMockResolve();
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBeNull();
+    });
+
+    it('should not set Cache-Control header for error responses on immutable paths', async () => {
+      const event = createMockEvent('/_app/immutable/chunks/index.js');
+      const resolve = createMockResolve({}, 404);
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBeNull();
+    });
+
+    it('should not set Cache-Control header for 500 responses on immutable paths', async () => {
+      const event = createMockEvent('/_app/immutable/chunks/index.js');
+      const resolve = createMockResolve({}, 500);
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBeNull();
+    });
+
+    it('should not override existing Cache-Control headers for non-immutable paths', async () => {
+      const event = createMockEvent('/api/some-endpoint');
+      const resolve = createMockResolve({
+        'Cache-Control': 'no-cache',
+      });
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe('no-cache');
+    });
+
+    it('should preserve other headers while setting Cache-Control', async () => {
+      const event = createMockEvent('/_app/immutable/chunks/index.js');
+      const resolve = createMockResolve({
+        'Content-Type': 'application/javascript',
+        'X-Custom-Header': 'test-value',
+      });
+
+      const response = await handle({ event, resolve });
+
+      expect(response.headers.get('Cache-Control')).toBe(
+        'public, max-age=31536000, immutable',
+      );
+      expect(response.headers.get('Content-Type')).toBe(
+        'application/javascript',
+      );
+      expect(response.headers.get('X-Custom-Header')).toBe('test-value');
+    });
+  });
+});

src/hooks.server.ts

@@ -1,8 +1,17 @@
 import type { Handle } from '@sveltejs/kit';
 
+const ONE_YEAR = 31536000; // 365 days in seconds
+
 export const handle: Handle = async ({ event, resolve }) => {
   const response = await resolve(event, {});
 
+  if (response.ok && event.url.pathname.startsWith('/_app/immutable/')) {
+    response.headers.set(
+      'Cache-Control',
+      `public, max-age=${ONE_YEAR}, immutable`,
+    );
+  }
+
   return response;
 };