1 files changed, 74 insertions, 0 deletions
diff --git a/testing/web-platform/tests/speculation-rules/prerender/resources/deferred-promise-utils.js b/testing/web-platform/tests/speculation-rules/prerender/resources/deferred-promise-utils.js
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+++ b/testing/web-platform/tests/speculation-rules/prerender/resources/deferred-promise-utils.js
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+/**
+ * This file co-works with a html file and utils.js to test a promise that
+ * should be deferred during prerendering.
+ *
+ * Usage example:
+ *  Suppose the html is "prerender-promise-test.html"
+ *  On prerendering page, prerender-promise-test.html?prerendering:
+ *    const prerenderEventCollector = new PrerenderEventCollector();
+ *    const promise = {a promise that should be deferred during prerendering};
+ *    prerenderEventCollector.start(promise, {promise name});
+ *
+ *  On the initiator page, prerender-promise-test.html:
+ *   execute
+ *    `loadInitiatorPage();`
+ */
+
+// Collects events that happen relevant to a prerendering page.
+// An event is added when:
+// 1. start() is called.
+// 2. a prerenderingchange event is dispatched on this document.
+// 3. the promise passed to start() is resolved.
+// 4. addEvent() is called manually.
+class PrerenderEventCollector {
+  constructor() {
+    this.eventsSeen_ = [];
+    new PrerenderChannel('close').addEventListener('message', () => {
+      window.close();
+    });
+  }
+
+  // Adds an event to `eventsSeen_` along with the prerendering state of the
+  // page.
+  addEvent(eventMessage) {
+    this.eventsSeen_.push(
+        {event: eventMessage, prerendering: document.prerendering});
+  }
+
+  // Starts collecting events until the promise resolves. Triggers activation by
+  // telling the initiator page that it is ready for activation.
+  async start(promise, promiseName) {
+    assert_true(document.prerendering);
+    this.addEvent(`started waiting ${promiseName}`);
+    promise
+        .then(
+            () => {
+              this.addEvent(`finished waiting ${promiseName}`);
+            },
+            (error) => {
+              if (error instanceof Error)
+                error = error.name;
+              this.addEvent(`${promiseName} rejected: ${error}`);
+            })
+        .finally(() => {
+          // Used to communicate with the main test page.
+          const testChannel = new PrerenderChannel('test-channel');
+          // Send the observed events back to the main test page.
+          testChannel.postMessage(this.eventsSeen_);
+          testChannel.close();
+        });
+    document.addEventListener('prerenderingchange', () => {
+      this.addEvent('prerendering change');
+    });
+
+    // Post a task to give the implementation a chance to fail in case it
+    // resolves a promise without waiting for activation.
+    setTimeout(() => {
+      // Used to communicate with the initiator page.
+      const prerenderChannel = new PrerenderChannel('prerender-channel');
+      // Inform the initiator page that this page is ready to be activated.
+      prerenderChannel.postMessage('readyToActivate');
+      prerenderChannel.close();
+    }, 0);
+  }
+}