From 2879166426208f073263d29008c1a5223df36c77 Mon Sep 17 00:00:00 2001
From: Kostas Pelelis <13784424+kpelelis@users.noreply.github.com>
Date: Mon, 16 Dec 2024 17:27:29 +0200
Subject: [PATCH] Faro: Improve performance of TRACKING_URLS regex (#98022)

There have been reports of faro performing poorly when the URLs
generated are long (there was a 39KB one). The TRACKING_URLS we are
using leading wildcard characters, leading to excessive backtracking.

This commit uses a simpler regular expression, that ensures we are
blocking the appropriate URLs without the performance hit. To prevent
that from happening, a timed test is introduced. The timeout threshold
is long enough to be hardware independent.
---
 .../GrafanaJavascriptAgentBackend.test.ts     | 20 ++++++++++++++++---
 .../GrafanaJavascriptAgentBackend.ts          |  5 ++---
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.test.ts b/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.test.ts
index ca7d940b2fc..5ee5b184736 100644
--- a/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.test.ts
+++ b/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.test.ts
@@ -5,7 +5,11 @@ import * as faroWebSdkModule from '@grafana/faro-web-sdk';
 import { BrowserConfig, FetchTransport } from '@grafana/faro-web-sdk';
 
 import { EchoSrvTransport } from './EchoSrvTransport';
-import { GrafanaJavascriptAgentBackend, GrafanaJavascriptAgentBackendOptions } from './GrafanaJavascriptAgentBackend';
+import {
+  GrafanaJavascriptAgentBackend,
+  GrafanaJavascriptAgentBackendOptions,
+  TRACKING_URLS,
+} from './GrafanaJavascriptAgentBackend';
 
 describe('GrafanaJavascriptAgentEchoBackend', () => {
   let mockedSetUser: jest.Mock;
@@ -93,8 +97,7 @@ describe('GrafanaJavascriptAgentEchoBackend', () => {
     expect(initializeFaroMock.mock.calls[0][0].transports?.[0]).toBeInstanceOf(EchoSrvTransport);
     expect(initializeFaroMock.mock.calls[0][0].transports?.[0].getIgnoreUrls()).toEqual([
       /.*\/log-grafana-javascript-agent.*/,
-      /.*.google-analytics.com*.*/,
-      /.*.googletagmanager.com*.*/,
+      /\.(google-analytics|googletagmanager)\.com/,
       /frontend-metrics/,
       /\/collect(?:\/[\w]*)?$/,
     ]);
@@ -116,6 +119,17 @@ describe('GrafanaJavascriptAgentEchoBackend', () => {
     });
   });
 
+  test('will ensure the performance of TRACKING_URLS', async () => {
+    // 10e6 is based on true events
+    const longString = Array.from({ length: 10e6 }, () => Math.random().toString(36)[2]).join('');
+    const maxExecutionTime = 500;
+
+    const start = performance.now();
+    TRACKING_URLS.some((u) => u && longString.match(u) !== null);
+    const end = performance.now();
+    expect(end - start).toBeLessThanOrEqual(maxExecutionTime);
+  });
+
   //@FIXME - make integration test work
 
   // it('integration test with EchoSrv and  GrafanaJavascriptAgent', async () => {
diff --git a/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.ts b/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.ts
index 4ea54e38053..2aa81fb11fc 100644
--- a/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.ts
+++ b/public/app/core/services/echo/backends/grafana-javascript-agent/GrafanaJavascriptAgentBackend.ts
@@ -37,9 +37,8 @@ export interface GrafanaJavascriptAgentBackendOptions extends BrowserConfig {
   ignoreUrls: RegExp[];
 }
 
-const TRACKING_URLS = [
-  /.*.google-analytics.com*.*/,
-  /.*.googletagmanager.com*.*/,
+export const TRACKING_URLS = [
+  /\.(google-analytics|googletagmanager)\.com/,
   /frontend-metrics/,
   /\/collect(?:\/[\w]*)?$/,
 ];