GPT 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 gpt;
 pub mod lockr;
 pub mod nextjs;
 pub mod permutive;
@@ -32,5 +33,6 @@ pub(crate) fn builders() -> &'static [IntegrationBuilder] {
         lockr::register,
         didomi::register,
         datadome::register,
+        gpt::register,
     ]
 }

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

@@ -0,0 +1,167 @@
+import { log } from '../../core/log';
+
+import { installGptGuard } from './script_guard';
+
+/**
+ * Google Publisher Tags (GPT) Integration Shim
+ *
+ * Hooks into the googletag.cmd command queue so the Trusted Server can
+ * observe and augment ad-slot definitions before GPT processes them.
+ * The shim ensures the googletag stub exists early (matching GPT's own
+ * bootstrap pattern) and patches `cmd.push` to wrap queued callbacks.
+ *
+ * Current capabilities:
+ *   - Installs a script guard that rewrites dynamically inserted GPT
+ *     `<script>` elements to the first-party proxy endpoint.
+ *   - Takes over the `googletag.cmd` array so that every callback runs
+ *     through a wrapper that can inject targeting, logging, or consent
+ *     signals before the real GPT processes the command.
+ *
+ * Future enhancements (driven by config or tsjs API):
+ *   - Inject synthetic ID as page-level key-value targeting.
+ *   - Gate ad requests on consent status.
+ *   - Rewrite ad-unit paths for A/B testing.
+ */
+
+// ------------------------------------------------------------------
+// googletag type stubs (minimal surface needed by the shim)
+// ------------------------------------------------------------------
+
+interface GoogleTagSlot {
+  getAdUnitPath(): string;
+  getSlotElementId(): string;
+  setTargeting(key: string, value: string | string[]): GoogleTagSlot;
+}
+
+interface GoogleTagPubAdsService {
+  setTargeting(key: string, value: string | string[]): GoogleTagPubAdsService;
+  getTargeting(key: string): string[];
+  enableSingleRequest(): void;
+}
+
+interface GoogleTag {
+  cmd: Array<() => void>;
+  pubads(): GoogleTagPubAdsService;
+  defineSlot(
+    adUnitPath: string,
+    size: Array<number | number[]>,
+    elementId: string
+  ): GoogleTagSlot | null;
+  enableServices(): void;
+  display(elementId: string): void;
+  _loaded_?: boolean;
+}
+
+type GptWindow = Window & {
+  googletag?: Partial<GoogleTag>;
+};
+
+// ------------------------------------------------------------------
+// Shim implementation
+// ------------------------------------------------------------------
+
+/**
+ * Ensure the `googletag` stub exists on `window`.
+ *
+ * This mirrors the official GPT bootstrap snippet:
+ * ```js
+ * window.googletag = window.googletag || {};
+ * googletag.cmd = googletag.cmd || [];
+ * ```
+ * By running before the publisher's own snippet we can patch `cmd` early.
+ */
+function ensureGoogleTagStub(win: GptWindow): Partial<GoogleTag> {
+  const tag = (win.googletag = win.googletag ?? {});
+  tag.cmd = tag.cmd ?? [];
+  return tag;
+}
+
+/**
+ * Wrap a queued GPT callback to add instrumentation and future hook points.
+ *
+ * Today the wrapper only logs; as the integration matures it will inject
+ * synthetic ID targeting and consent gates.
+ */
+function wrapCommand(fn: () => void): () => void {
+  return () => {
+    try {
+      fn();
+    } catch (err) {
+      log.error('GPT shim: queued command threw', err);
+    }
+  };
+}
+
+/**
+ * Patch `googletag.cmd` so every pushed callback runs through [`wrapCommand`].
+ *
+ * Preserves the existing `tag.cmd` array identity so that GPT's own custom
+ * `cmd.push` behaviour (immediate execution when the library is already
+ * loaded) is not lost. The original `push` is saved and delegated to after
+ * wrapping each callback.
+ *
+ * Already-queued callbacks are re-wrapped in place so GPT processes them
+ * through our wrapper when it drains the queue.
+ */
+function patchCommandQueue(tag: Partial<GoogleTag>): void {
+  // Ensure the queue exists.
+  if (!Array.isArray(tag.cmd)) {
+    tag.cmd = [];
+  }
+
+  const queue = tag.cmd;
+
+  // Guard against double-patching (idempotent install).
+  if ((queue as { __tsPushed?: boolean }).__tsPushed) {
+    log.debug('GPT shim: command queue already patched, skipping');
+    return;
+  }
+
+  const originalPush = queue.push.bind(queue);
+
+  // Override push on the *existing* array — preserves object identity so
+  // GPT (if already loaded) keeps its reference.
+  queue.push = function (...callbacks: Array<() => void>): number {
+    const wrapped = callbacks.map(wrapCommand);
+    return originalPush(...wrapped);
+  };
+
+  // Mark as patched to prevent double-wrapping.
+  (queue as { __tsPushed?: boolean }).__tsPushed = true;
+
+  // Re-wrap any callbacks that were queued before we patched.
+  for (let i = 0; i < queue.length; i++) {
+    queue[i] = wrapCommand(queue[i]);
+  }
+
+  log.debug('GPT shim: command queue patched', { pendingCommands: queue.length });
+}
+
+/**
+ * Install the GPT integration shim.
+ *
+ * Sets up the script guard for dynamic script interception and patches the
+ * `googletag.cmd` command queue.
+ */
+export function installGptShim(): boolean {
+  if (typeof window === 'undefined') {
+    return false;
+  }
+
+  const win = window as GptWindow;
+
+  // Install DOM interception guard first so any dynamic GPT script insertions
+  // are rewritten before the browser fetches them.
+  installGptGuard();
+
+  const tag = ensureGoogleTagStub(win);
+  patchCommandQueue(tag);
+
+  log.info('GPT shim installed');
+  return true;
+}
+
+// Self-initialise on import (guarded for SSR safety)
+if (typeof window !== 'undefined') {
+  installGptShim();
+}