[wptrunner] Transmit test results via postMessage

tools/wptrunner/wptrunner/executors/runner.js

@@ -1,42 +1,44 @@
 document.title = '%(title)s';
 
-window.addEventListener(
-  "message",
-  function(event) {
-    window.message_queue.push(event);
-    window.process_next_event();
-  },
-  false
-);
-
-
-window.process_next_event = function() {
-  /* This function handles the next testdriver event. The presence of
-     window.testdriver_callback is used as a switch; when that function
-     is present we are able to handle the next event and when is is not
-     present we must wait. Therefore to drive the event processing, this
-     function must be called in two circumstances:
-       * Every time there is a new event that we may be able to handle
-       * Every time we set the callback function
-     This function unsets the callback, so no further testdriver actions
-     will be run until it is reset, which wptrunner does after it has
-     completed handling the current action.
-   */
-  if (!window.testdriver_callback) {
+var message_queue = [];
+var source = null;
+
+/**
+ * In preparation to execute a test, testdriver issues a number of messages
+ * which should be queued until execution time. During execution, testdriver
+ * consumes the queued messages by repeatedly "resuming" via `do_testharness`.
+ * The sequence of these events is variable, so the handler must account for
+ * cases where "resume" requests arrive before any messages are available (by
+ * caching the request's source) and where messages arrive before "resume"
+ * requests (by queuing the messages).
+ */
+window.addEventListener("message", function(event) {
+  if (!event.data) {
     return;
   }
-  var event = window.message_queue.shift();
-  if (!event) {
+
+  if (event.data.type === "testdriver-resume") {
+    source = event.source;
+  } else {
+    message_queue.push(event.data);
+  }
+
+  if (!source || !message_queue.length) {
     return;
   }
-  var data = event.data;
 
+  reply(source, message_queue[0]);
+  source = null;
+  message_queue.shift();
+}, false);
+
+function reply(source, data) {
   var payload = undefined;
 
   switch(data.type) {
   case "complete":
-    var tests = event.data.tests;
-    var status = event.data.status;
+    var tests = data.tests;
+    var status = data.status;
 
     var subtest_results = tests.map(function(x) {
       return [x.name, x.status, x.message, x.stack];
@@ -53,7 +55,11 @@ window.process_next_event = function() {
   default:
     return;
   }
-  var callback = window.testdriver_callback;
-  window.testdriver_callback = null;
-  callback([window.url, data.type, payload]);
-};
+
+  source.postMessage({
+      type: "testdriver-next message",
+      message: [window.url, data.type, payload]
+    },
+    "*"
+  );
+}

tools/wptrunner/wptrunner/executors/testharness_webdriver.js

@@ -8,10 +8,6 @@ window.win.addEventListener('DOMContentLoaded', (e) => {
   callback();
 });
 
-
-window.message_queue = [];
-window.testdriver_callback = null;
-
 if (%(timeout)s != null) {
   window.timer = setTimeout(function() {
     window.win.timeout();

tools/wptrunner/wptrunner/executors/testharness_webdriver_resume.js

@@ -1,3 +1,24 @@
 var callback = arguments[arguments.length - 1];
-window.opener.testdriver_callback = callback;
-window.opener.process_next_event();
+
+window.addEventListener("message", function handle(event) {
+  if (!event.data || event.data.type !== "testdriver-next message") {
+    return;
+  }
+
+  window.removeEventListener("message", handle);
+
+  callback(event.data.message);
+});
+
+/**
+ * The current window and its opener belong to the same domain, making it
+ * technically possible for data structures to be shared directly. Some
+ * browser/WebDriver implementations [1] do not correctly serialize Arrays from
+ * a foreign realm. Transmitting data structures via the `postMessage` API
+ * avoids this issue because doing so involves de-serializing values in the
+ * local realm.
+ *
+ * [1] This has been observed in Edge version 17 and/or the corresponding
+ *     release of Edgedriver
+ */
+window.opener.postMessage({ type: "testdriver-resume" }, "*");