Add Google Tag Manager first-party integration

crates/common/src/integrations/mod.rs

@@ -6,6 +6,7 @@ pub mod adserver_mock;
 pub mod aps;
 pub mod datadome;
 pub mod didomi;
+pub mod google_tag_manager;
 pub mod lockr;
 pub mod nextjs;
 pub mod permutive;
@@ -31,6 +32,7 @@ pub(crate) fn builders() -> &'static [IntegrationBuilder] {
         permutive::register,
         lockr::register,
         didomi::register,
+        google_tag_manager::register,
         datadome::register,
     ]
 }

crates/js/lib/src/integrations/google_tag_manager/index.ts

@@ -0,0 +1,31 @@
+import { log } from '../../core/log';
+
+import { installGtmBeaconGuard } from './script_guard';
+import { installGtmGuard } from './script_guard';
+
+/**
+ * Google Tag Manager integration for tsjs
+ *
+ * Installs guards to intercept GTM and Google Analytics traffic:
+ *
+ * 1. **Script guard** — intercepts dynamically inserted `<script>` and
+ *    `<link>` elements and rewrites their URLs to the first-party proxy.
+ *
+ * 2. **Beacon guard** — intercepts `navigator.sendBeacon()` and `fetch()`
+ *    calls to Google Analytics domains (www.google-analytics.com,
+ *    analytics.google.com) and rewrites them to the first-party proxy.
+ *    This is necessary because gtag.js constructs beacon URLs dynamically
+ *    from bare domain strings, which can't be safely rewritten at the
+ *    script level.
+ *
+ * URLs are rewritten to preserve the original path:
+ * - https://www.googletagmanager.com/gtm.js?id=GTM-XXXX -> /integrations/google_tag_manager/gtm.js?id=GTM-XXXX
+ * - https://www.google-analytics.com/g/collect -> /integrations/google_tag_manager/g/collect
+ * - https://analytics.google.com/g/collect -> /integrations/google_tag_manager/g/collect
+ */
+
+if (typeof window !== 'undefined') {
+  installGtmGuard();
+  installGtmBeaconGuard();
+  log.info('Google Tag Manager integration initialized');
+}

crates/js/lib/src/integrations/google_tag_manager/script_guard.ts

@@ -0,0 +1,91 @@
+import { createBeaconGuard } from '../../shared/beacon_guard';
+import { createScriptGuard } from '../../shared/script_guard';
+
+/**
+ * Google Tag Manager Script Interception Guard
+ *
+ * Intercepts dynamically inserted script tags that load GTM or Google Analytics
+ * and rewrites their URLs to use the first-party proxy endpoint. This catches
+ * scripts inserted via appendChild, insertBefore, or any other dynamic DOM
+ * manipulation (e.g. Next.js dynamic imports).
+ *
+ * Built on the shared script_guard factory with custom URL rewriting to preserve
+ * the original path and query string.
+ */
+
+/** Regex to match GTM/GA domains: www.googletagmanager.com, www.google-analytics.com, analytics.google.com */
+const GTM_URL_PATTERN =
+  /^(?:https?:)?(?:\/\/)?(www\.(googletagmanager|google-analytics)\.com|analytics\.google\.com)(?:\/|$)/i;
+
+/**
+ * Check if a URL is a GTM or Google Analytics URL.
+ * Matches the logic from google_tag_manager.rs GTM_URL_PATTERN.
+ *
+ * Valid patterns:
+ * - https://www.googletagmanager.com/gtm.js?id=GTM-XXXX
+ * - https://www.google-analytics.com/g/collect
+ * - https://analytics.google.com/g/collect
+ * - //www.googletagmanager.com/gtm.js?id=GTM-XXXX
+ *
+ * Invalid:
+ * - https://googletagmanager.com/gtm.js (missing www.)
+ * - https://example.com/www.googletagmanager.com (domain mismatch)
+ */
+function isGtmUrl(url: string): boolean {
+  return !!url && GTM_URL_PATTERN.test(url);
+}
+
+/**
+ * Extract the path and query string from a GTM/GA URL.
+ * e.g., "https://www.googletagmanager.com/gtm.js?id=GTM-XXXX" -> "/gtm.js?id=GTM-XXXX"
+ *       "https://www.google-analytics.com/g/collect?v=2" -> "/g/collect?v=2"
+ */
+function extractGtmPath(url: string): string {
+  try {
+    const normalizedUrl = url.startsWith('//')
+      ? `https:${url}`
+      : url.startsWith('http')
+        ? url
+        : `https://${url}`;
+
+    const parsed = new URL(normalizedUrl);
+    return parsed.pathname + parsed.search;
+  } catch {
+    // Fallback: extract path after the domain
+    console.debug('[GTM Guard] URL parsing failed, using fallback for:', url);
+    const match = url.match(
+      /(?:www\.(?:googletagmanager|google-analytics)\.com|analytics\.google\.com)(\/[^'"\s]*)/i
+    );
+    return match?.[1] || '/gtm.js';
+  }
+}
+
+/**
+ * Rewrite a GTM/GA URL to the first-party proxy path.
+ */
+function rewriteGtmUrl(originalUrl: string): string {
+  return `${window.location.origin}/integrations/google_tag_manager${extractGtmPath(originalUrl)}`;
+}
+
+const guard = createScriptGuard({
+  name: 'GTM',
+  isTargetUrl: isGtmUrl,
+  rewriteUrl: rewriteGtmUrl,
+});
+
+const beaconGuard = createBeaconGuard({
+  name: 'GTM',
+  isTargetUrl: isGtmUrl,
+  rewriteUrl: rewriteGtmUrl,
+});
+
+export const installGtmGuard = guard.install;
+export const isGuardInstalled = guard.isInstalled;
+export const resetGuardState = guard.reset;
+
+export const installGtmBeaconGuard = beaconGuard.install;
+export const isBeaconGuardInstalled = beaconGuard.isInstalled;
+export const resetBeaconGuardState = beaconGuard.reset;
+
+// Export for testing
+export { isGtmUrl, extractGtmPath, rewriteGtmUrl };

crates/js/lib/src/shared/beacon_guard.ts

@@ -0,0 +1,123 @@
+import { log } from '../core/log';
+
+/**
+ * Shared Beacon Guard Factory
+ *
+ * Creates a network interception guard that patches `navigator.sendBeacon`
+ * and `window.fetch` to intercept outgoing beacon/analytics requests whose
+ * URLs match an integration's target domains. Matched URLs are rewritten to
+ * a first-party proxy endpoint.
+ *
+ * This complements the script_guard (which intercepts DOM insertions) by
+ * handling the _runtime_ network calls that analytics SDKs use to send data.
+ *
+ * Each call to createBeaconGuard() produces an independent guard with its
+ * own installation state, so multiple integrations can coexist.
+ */
+
+export interface BeaconGuardConfig {
+  /** Integration name used in log messages (e.g. "GTM"). */
+  name: string;
+  /** Return true if the URL belongs to this integration's analytics domain. */
+  isTargetUrl: (url: string) => boolean;
+  /** Rewrite the original URL to a first-party proxy URL. */
+  rewriteUrl: (url: string) => string;
+}
+
+export interface BeaconGuard {
+  /** Patch sendBeacon/fetch to intercept matching beacon requests. */
+  install: () => void;
+  /** Whether the guard has already been installed. */
+  isInstalled: () => boolean;
+  /** Reset installation state (primarily for testing). */
+  reset: () => void;
+}
+
+/**
+ * Extract a URL string from the various input types that fetch() accepts.
+ * Returns null if the input can't be resolved to a URL string.
+ */
+function extractUrl(input: RequestInfo | URL): string | null {
+  if (typeof input === 'string') {
+    return input;
+  }
+  if (input instanceof URL) {
+    return input.href;
+  }
+  if (input instanceof Request) {
+    return input.url;
+  }
+  return null;
+}
+
+/**
+ * Create an independent beacon guard for a specific integration.
+ */
+export function createBeaconGuard(config: BeaconGuardConfig): BeaconGuard {
+  let installed = false;
+  const prefix = `${config.name} beacon guard`;
+
+  function install(): void {
+    if (installed) {
+      log.debug(`${prefix}: already installed, skipping`);
+      return;
+    }
+
+    if (typeof window === 'undefined') {
+      log.debug(`${prefix}: not in browser environment, skipping`);
+      return;
+    }
+
+    log.info(`${prefix}: installing network interception`);
+
+    // --- Patch navigator.sendBeacon ---
+    if (typeof navigator !== 'undefined' && typeof navigator.sendBeacon === 'function') {
+      const originalSendBeacon = navigator.sendBeacon.bind(navigator);
+
+      navigator.sendBeacon = function (url: string, data?: BodyInit | null): boolean {
+        if (config.isTargetUrl(url)) {
+          const rewritten = config.rewriteUrl(url);
+          log.info(`${prefix}: rewriting sendBeacon`, { original: url, rewritten });
+          return originalSendBeacon(rewritten, data);
+        }
+        return originalSendBeacon(url, data);
+      };
+    }
+
+    // --- Patch window.fetch ---
+    if (typeof window.fetch === 'function') {
+      const originalFetch = window.fetch.bind(window);
+
+      window.fetch = function (input: RequestInfo | URL, init?: RequestInit): Promise<Response> {
+        const url = extractUrl(input);
+
+        if (url && config.isTargetUrl(url)) {
+          const rewritten = config.rewriteUrl(url);
+          log.info(`${prefix}: rewriting fetch`, { original: url, rewritten });
+
+          // If the input was a Request, create a new one with the rewritten URL
+          if (input instanceof Request) {
+            const newRequest = new Request(rewritten, input);
+            return originalFetch(newRequest, init);
+          }
+          return originalFetch(rewritten, init);
+        }
+
+        return originalFetch(input, init);
+      };
+    }
+
+    installed = true;
+    log.info(`${prefix}: network interception installed successfully`);
+  }
+
+  function isInstalled(): boolean {
+    return installed;
+  }
+
+  function reset(): void {
+    installed = false;
+  }
+
+  return { install, isInstalled, reset };
+}