Bug 1923899 - [bidi] Wait for currentWindowGlobal when sending commands to window global message handlers r=webdriver-reviewers,Sasha

When attempting to send commands on a very early browsing context, the command might fail
due to a missing currentWindowGlobal.
This patch adds a helper to wait for the currentWindowGlobal property to be set and uses it from
RootTransport in order to avoid this issue.
A browser mochitest is added to cover this scenario.

Differential Revision: https://phabricator.services.mozilla.com/D225281

remote/shared/messagehandler/test/browser/browser_handle_simple_command.js

@@ -79,6 +79,53 @@ add_task(async function test_windowglobalModule_command() {
   rootMessageHandler.destroy();
 });
 
+// Test calling a windowglobal module as soon as possible.
+add_task(async function test_windowglobalModule_early_command() {
+  const rootMessageHandler = createRootMessageHandler(
+    "session-id-windowglobalModule-early"
+  );
+
+  info("Setup an observer to send a command as soon as the context is created");
+  const onContext = new Promise((resolve, reject) => {
+    const onContextAttached = async browsingContext => {
+      try {
+        const result = await rootMessageHandler.handleCommand({
+          moduleName: "command",
+          commandName: "testWindowGlobalModule",
+          destination: {
+            type: WindowGlobalMessageHandler.type,
+            id: browsingContext.id,
+          },
+        });
+        info("Early command succeeded, resolve the retrieved value");
+        resolve(result);
+      } catch (e) {
+        info("Early command failed, reject");
+        reject(e);
+      } finally {
+        Services.obs.removeObserver(
+          onContextAttached,
+          "browsing-context-attached"
+        );
+      }
+    };
+    Services.obs.addObserver(onContextAttached, "browsing-context-attached");
+  });
+
+  const tab = await addTab("https://example.com/document-builder.sjs?html=tab");
+
+  const windowGlobalValue = await onContext;
+  is(
+    windowGlobalValue,
+    "windowglobal-value",
+    "Retrieved the expected value from testWindowGlobalModule"
+  );
+
+  rootMessageHandler.destroy();
+
+  gBrowser.removeTab(tab);
+});
+
 // Test calling a method on a module which is only available in the "windowglobal"
 // folder. This will check that the MessageHandler/ModuleCache correctly moves
 // on to the next layer when no implementation can be found in the root layer.

remote/shared/messagehandler/transports/BrowsingContextUtils.sys.mjs

@@ -2,6 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  PollPromise: "chrome://remote/content/shared/Sync.sys.mjs",
+});
+
 function isExtensionContext(browsingContext) {
   let principal;
   try {
@@ -93,3 +99,31 @@ export function isBrowsingContextCompatible(browsingContext, options = {}) {
     !isExtensionContext(browsingContext) && !isParentProcess(browsingContext)
   );
 }
+
+/**
+ * Wait until `currentWindowGlobal` is available on a browsing context. When a
+ * browsing context has just been created, the `currentWindowGlobal` might not
+ * be attached yet.
+ *
+ * @param {CanonicalBrowsingContext} browsingContext
+ *     The browsing context to wait for.
+ *
+ * @returns {Promise}
+ *     Promise which resolves when `currentWindowGlobal` is set on the browsing
+ *     context or throws after 100ms.
+ */
+export async function waitForCurrentWindowGlobal(browsingContext) {
+  await lazy.PollPromise(
+    (resolve, reject) => {
+      if (browsingContext.currentWindowGlobal) {
+        resolve();
+      } else {
+        reject();
+      }
+    },
+    {
+      errorMessage: `currentWindowGlobal was not available for Browsing Context with id: ${browsingContext.id}`,
+      timeout: 100,
+    }
+  );
+}

remote/shared/messagehandler/transports/RootTransport.sys.mjs

@@ -15,6 +15,8 @@ ChromeUtils.defineESModuleGetters(lazy, {
   MessageHandlerFrameActor:
     "chrome://remote/content/shared/messagehandler/transports/js-window-actors/MessageHandlerFrameActor.sys.mjs",
   TabManager: "chrome://remote/content/shared/TabManager.sys.mjs",
+  waitForCurrentWindowGlobal:
+    "chrome://remote/content/shared/messagehandler/transports/BrowsingContextUtils.sys.mjs",
 });
 
 ChromeUtils.defineLazyGetter(lazy, "logger", () => lazy.Log.get());
@@ -124,6 +126,9 @@ export class RootTransport {
     let attempts = 0;
     while (true) {
       try {
+        if (!webProgress.browsingContext.currentWindowGlobal) {
+          await lazy.waitForCurrentWindowGlobal(webProgress.browsingContext);
+        }
         return await webProgress.browsingContext.currentWindowGlobal
           .getActor("MessageHandlerFrame")
           .sendCommand(command, this._messageHandler.sessionId);