Add cache-control for assets served via registerStaticDir (#102756)

* Add cache-control for assets served via `registerStaticDir`

* fix case

* add test for 'dynamic' file content

src/core/server/http/http_server.test.ts

@@ -7,9 +7,10 @@
  */
 
 import { Server } from 'http';
-import { readFileSync } from 'fs';
+import { rmdir, mkdtemp, readFile, writeFile } from 'fs/promises';
 import supertest from 'supertest';
 import { omit } from 'lodash';
+import { join } from 'path';
 
 import { ByteSizeValue, schema } from '@kbn/config-schema';
 import { HttpConfig } from './http_config';
@@ -47,9 +48,9 @@ const enhanceWithContext = (fn: (...args: any[]) => any) => fn.bind(null, {});
 let certificate: string;
 let key: string;
 
-beforeAll(() => {
-  certificate = readFileSync(KBN_CERT_PATH, 'utf8');
-  key = readFileSync(KBN_KEY_PATH, 'utf8');
+beforeAll(async () => {
+  certificate = await readFile(KBN_CERT_PATH, 'utf8');
+  key = await readFile(KBN_KEY_PATH, 'utf8');
 });
 
 beforeEach(() => {
@@ -1409,13 +1410,131 @@ describe('setup contract', () => {
   });
 
   describe('#registerStaticDir', () => {
+    const assetFolder = join(__dirname, 'integration_tests', 'fixtures', 'static');
+    let tempDir: string;
+
+    beforeAll(async () => {
+      tempDir = await mkdtemp('cache-test');
+    });
+
+    afterAll(async () => {
+      if (tempDir) {
+        await rmdir(tempDir, { recursive: true });
+      }
+    });
+
     test('does not throw if called after stop', async () => {
       const { registerStaticDir } = await server.setup(config);
       await server.stop();
       expect(() => {
         registerStaticDir('/path1/{path*}', '/path/to/resource');
       }).not.toThrow();
     });
+
+    test('returns correct headers for static assets', async () => {
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+
+      registerStaticDir('/static/{path*}', assetFolder);
+
+      await server.start();
+      const response = await supertest(innerServer.listener)
+        .get('/static/some_json.json')
+        .expect(200);
+
+      expect(response.get('cache-control')).toEqual('must-revalidate');
+      expect(response.get('etag')).not.toBeUndefined();
+    });
+
+    test('returns compressed version if present', async () => {
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+
+      registerStaticDir('/static/{path*}', assetFolder);
+
+      await server.start();
+      const response = await supertest(innerServer.listener)
+        .get('/static/compression_available.json')
+        .set('accept-encoding', 'gzip')
+        .expect(200);
+
+      expect(response.get('cache-control')).toEqual('must-revalidate');
+      expect(response.get('etag')).not.toBeUndefined();
+      expect(response.get('content-encoding')).toEqual('gzip');
+    });
+
+    test('returns uncompressed version if compressed asset is not available', async () => {
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+
+      registerStaticDir('/static/{path*}', assetFolder);
+
+      await server.start();
+      const response = await supertest(innerServer.listener)
+        .get('/static/some_json.json')
+        .set('accept-encoding', 'gzip')
+        .expect(200);
+
+      expect(response.get('cache-control')).toEqual('must-revalidate');
+      expect(response.get('etag')).not.toBeUndefined();
+      expect(response.get('content-encoding')).toBeUndefined();
+    });
+
+    test('returns a 304 if etag value matches', async () => {
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+
+      registerStaticDir('/static/{path*}', assetFolder);
+
+      await server.start();
+      const response = await supertest(innerServer.listener)
+        .get('/static/some_json.json')
+        .expect(200);
+
+      const etag = response.get('etag');
+      expect(etag).not.toBeUndefined();
+
+      await supertest(innerServer.listener)
+        .get('/static/some_json.json')
+        .set('If-None-Match', etag)
+        .expect(304);
+    });
+
+    test('serves content if etag values does not match', async () => {
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+
+      registerStaticDir('/static/{path*}', assetFolder);
+
+      await server.start();
+
+      await supertest(innerServer.listener)
+        .get('/static/some_json.json')
+        .set('If-None-Match', `"definitely not a valid etag"`)
+        .expect(200);
+    });
+
+    test('dynamically updates depending on the content of the file', async () => {
+      const tempFile = join(tempDir, 'some_file.json');
+
+      const { registerStaticDir, server: innerServer } = await server.setup(config);
+      registerStaticDir('/static/{path*}', tempDir);
+
+      await server.start();
+
+      await supertest(innerServer.listener).get('/static/some_file.json').expect(404);
+
+      await writeFile(tempFile, `{ "over": 9000 }`);
+
+      let response = await supertest(innerServer.listener)
+        .get('/static/some_file.json')
+        .expect(200);
+
+      const etag1 = response.get('etag');
+
+      await writeFile(tempFile, `{ "over": 42 }`);
+
+      response = await supertest(innerServer.listener).get('/static/some_file.json').expect(200);
+
+      const etag2 = response.get('etag');
+
+      expect(etag1).not.toEqual(etag2);
+    });
   });
 
   describe('#registerOnPreRouting', () => {

src/core/server/http/http_server.ts

@@ -465,7 +465,13 @@ export class HttpServer {
           lookupCompressed: true,
         },
       },
-      options: { auth: false },
+      options: {
+        auth: false,
+        cache: {
+          privacy: 'public',
+          otherwise: 'must-revalidate',
+        },
+      },
     });
   }
 

src/core/server/http/integration_tests/fixtures/static/compression_available.json

@@ -0,0 +1,3 @@
+{
+  "hello": "dolly"
+}

src/core/server/http/integration_tests/fixtures/static/some_json.json

@@ -0,0 +1,3 @@
+{
+  "foo": "bar"
+}