1 files changed, 64 insertions, 0 deletions
diff --git a/testing/web-platform/tests/html/browsers/browsing-the-web/back-forward-cache/resources/executor.js b/testing/web-platform/tests/html/browsers/browsing-the-web/back-forward-cache/resources/executor.js
new file mode 100644
index 0000000000..67ce068130
--- /dev/null
+++ b/testing/web-platform/tests/html/browsers/browsing-the-web/back-forward-cache/resources/executor.js
@@ -0,0 +1,64 @@
+const params = new URLSearchParams(window.location.search);
+const uuid = params.get('uuid');
+
+// Executor and BFCache detection
+
+// When navigating out from this page, always call
+// `prepareNavigation(callback)` synchronously from the script injected by
+// `RemoteContext.execute_script()`, and trigger navigation on or after the
+// callback is called.
+// prepareNavigation() suspends task polling and avoid in-flight fetch
+// requests during navigation that might evict the page from BFCache.
+//
+// When we navigate to the page again, task polling is resumed, either
+// - (BFCache cases) when the pageshow event listener added by
+//   prepareNavigation() is executed, or
+// - (Non-BFCache cases) when `Executor.execute()` is called again during
+//   non-BFCache page loading.
+//
+// In such scenarios, `assert_bfcached()` etc. in `helper.sub.js` can determine
+// whether the page is restored from BFCache or not, by observing
+// - `isPageshowFired`: whether the pageshow event listener added by the
+//   prepareNavigation() before navigating out, and
+// - `loadCount`: whether this inline script is evaluated again.
+// - `isPageshowPersisted` is used to assert that `event.persisted` is true
+//   when restored from BFCache.
+
+window.isPageshowFired = false;
+window.isPageshowPersisted = null;
+window.loadCount = parseInt(localStorage.getItem(uuid + '.loadCount') || '0') + 1;
+localStorage.setItem(uuid + '.loadCount', loadCount);
+
+window.pageShowPromise = new Promise(resolve =>
+  window.addEventListener('pageshow', resolve, {once: true}));
+
+const executor = new Executor(uuid);
+
+window.prepareNavigation = function(callback) {
+  window.addEventListener(
+    'pageshow',
+    (event) => {
+      window.isPageshowFired = true;
+      window.isPageshowPersisted = event.persisted;
+      executor.resume();
+    },
+    {once: true});
+  executor.suspend(callback);
+}
+
+// Try to disable BFCache by acquiring and never releasing a Web Lock.
+// This requires HTTPS.
+// Note: This is a workaround depending on non-specified WebLock+BFCache
+// behavior, and doesn't work on Safari. We might want to introduce a
+// test-only BFCache-disabling API instead in the future.
+// https://github.com/web-platform-tests/wpt/issues/16359#issuecomment-795004780
+// https://crbug.com/1298336
+window.disableBFCache = () => {
+  return new Promise(resolve => {
+    // Use page's UUID as a unique lock name.
+    navigator.locks.request(uuid, () => {
+      resolve();
+      return new Promise(() => {});
+    });
+  });
+};