No response compression when there is a referer (elastic#47751)

* Hacking it in there, this is obviously not where this belongs

* Moving implementation to a private method

* Adding unit tests, I don't like the way I had to write these

* Adding integration tests

* Test not relying on implementation details...

* No longer using .inject, thanks Mikhail!!!

* Adding comment explaining the long body

* Fixing nesting of describes for api integration tests

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

@@ -577,6 +577,45 @@ test('exposes route details of incoming request to a route handler', async () =>
     });
 });
 
+describe('conditional compression', () => {
+  test('disables compression when there is a referer', async () => {
+    const { registerRouter, server: innerServer } = await server.setup(config);
+
+    const router = new Router('', logger, enhanceWithContext);
+    router.get({ path: '/', validate: false }, (context, req, res) =>
+      // we need the large body here so that compression would normally be used
+      res.ok({ body: 'hello'.repeat(500), headers: { 'Content-Type': 'text/html; charset=UTF-8' } })
+    );
+    registerRouter(router);
+
+    await server.start();
+    const response = await supertest(innerServer.listener)
+      .get('/')
+      .set('accept-encoding', 'gzip')
+      .set('referer', 'http://some-other-site/');
+
+    expect(response.header).not.toHaveProperty('content-encoding');
+  });
+
+  test(`enables compression when there isn't a referer`, async () => {
+    const { registerRouter, server: innerServer } = await server.setup(config);
+
+    const router = new Router('', logger, enhanceWithContext);
+    router.get({ path: '/', validate: false }, (context, req, res) =>
+      // we need the large body here so that compression will be used
+      res.ok({ body: 'hello'.repeat(500), headers: { 'Content-Type': 'text/html; charset=UTF-8' } })
+    );
+    registerRouter(router);
+
+    await server.start();
+    const response = await supertest(innerServer.listener)
+      .get('/')
+      .set('accept-encoding', 'gzip');
+
+    expect(response.header).toHaveProperty('content-encoding', 'gzip');
+  });
+});
+
 describe('setup contract', () => {
   describe('#createSessionStorage', () => {
     it('creates session storage factory', async () => {

src/core/server/http/http_server.ts

@@ -96,6 +96,7 @@ export class HttpServer {
 
     const basePathService = new BasePath(config.basePath);
     this.setupBasePathRewrite(config, basePathService);
+    this.setupConditionalCompression();
 
     return {
       registerRouter: this.registerRouter.bind(this),
@@ -175,6 +176,23 @@ export class HttpServer {
     });
   }
 
+  private setupConditionalCompression() {
+    if (this.server === undefined) {
+      throw new Error('Server is not created yet');
+    }
+
+    this.server.ext('onRequest', (request, h) => {
+      // whenever there is a referrer, don't use compression even if the client supports it
+      if (request.info.referrer !== '') {
+        this.log.debug(
+          `Not using compression because there is a referer: ${request.info.referrer}`
+        );
+        request.info.acceptEncoding = '';
+      }
+      return h.continue;
+    });
+  }
+
   private registerOnPostAuth(fn: OnPostAuthHandler) {
     if (this.server === undefined) {
       throw new Error('Server is not created yet');

test/api_integration/apis/core/index.js

@@ -16,21 +16,45 @@
  * specific language governing permissions and limitations
  * under the License.
  */
+import expect from '@kbn/expect';
 
 export default function ({ getService }) {
   const supertest = getService('supertest');
 
-  describe('core request context', () => {
-    it('provides access to elasticsearch', async () => (
-      await supertest
-        .get('/requestcontext/elasticsearch')
-        .expect(200, 'Elasticsearch: true')
-    ));
+  describe('core', () => {
+    describe('request context', () => {
+      it('provides access to elasticsearch', async () => (
+        await supertest
+          .get('/requestcontext/elasticsearch')
+          .expect(200, 'Elasticsearch: true')
+      ));
 
-    it('provides access to SavedObjects client', async () => (
-      await supertest
-        .get('/requestcontext/savedobjectsclient')
-        .expect(200, 'SavedObjects client: {"page":1,"per_page":20,"total":0,"saved_objects":[]}')
-    ));
+      it('provides access to SavedObjects client', async () => (
+        await supertest
+          .get('/requestcontext/savedobjectsclient')
+          .expect(200, 'SavedObjects client: {"page":1,"per_page":20,"total":0,"saved_objects":[]}')
+      ));
+    });
+
+    describe('compression', () => {
+      it(`uses compression when there isn't a referer`, async () => {
+        await supertest
+          .get('/app/kibana')
+          .set('accept-encoding', 'gzip')
+          .then(response => {
+            expect(response.headers).to.have.property('content-encoding', 'gzip');
+          });
+      });
+
+      it(`doesn't use compression when there is a referer`, async () => {
+        await supertest
+          .get('/app/kibana')
+          .set('accept-encoding', 'gzip')
+          .set('referer', 'https://www.google.com')
+          .then(response => {
+            expect(response.headers).not.to.have.property('content-encoding');
+          });
+      });
+    });
   });
 }

test/api_integration/apis/index.js

@@ -34,5 +34,6 @@ export default function ({ loadTestFile }) {
     loadTestFile(require.resolve('./status'));
     loadTestFile(require.resolve('./stats'));
     loadTestFile(require.resolve('./ui_metric'));
+    loadTestFile(require.resolve('./core'));
   });
 }