detection of the window.postMessage() transfer parameter improved

rbri · rbri · commit 4dd9d6a2b787 · 2025-10-03T15:52:50.000+02:00
diff --git a/src/changes/changes.xml b/src/changes/changes.xml
@@ -8,6 +8,9 @@
 
     <body>
         <release version="4.17.0" date="October xx, 2025" description="Chrome/Edge 140, Firefox 142, css :has(), :is(), :where(), BroadcastChannel, Bugfixes">
+            <action type="fix" dev="rbri">
+                Detection of the window.postMessage() transfer parameter improved.
+            </action>
             <action type="remove" dev="rbri">
                 Deprecated methods HTMLParser.parse(WebResponse, HtmlPage, boolean, boolean),
                 HTMLParser.parseFragment(DomNode, DomNode, String, boolean),
diff --git a/src/main/java/org/htmlunit/javascript/JavaScriptEngine.java b/src/main/java/org/htmlunit/javascript/JavaScriptEngine.java
@@ -1394,6 +1394,15 @@ public static boolean isNaN(final Object obj) {
         return ScriptRuntime.isNaN(obj);
     }
 
+    /**
+     * @param obj the value to check
+     * @return whether obj is an Array
+     */
+    public static boolean isArray(final Object obj) {
+        return (obj instanceof Scriptable)
+                    && "Array".equals(((Scriptable) obj).getClassName());
+    }
+
     /**
      * @return the top call scope
      */
diff --git a/src/main/java/org/htmlunit/javascript/host/Window.java b/src/main/java/org/htmlunit/javascript/host/Window.java
@@ -1969,13 +1969,21 @@ public static void postMessage(final Context context, final Scriptable scope,
         final Object message = args[0];
 
         String targetOrigin = "*";
+        Object transfer = JavaScriptEngine.UNDEFINED;
+
         if (args.length > 1) {
-            targetOrigin = JavaScriptEngine.toString(args[1]);
+            if (JavaScriptEngine.isArray(args[1])) {
+                transfer = args[1];
+            }
+            else {
+                targetOrigin = JavaScriptEngine.toString(args[1]);
+            }
         }
 
-        Object transfer = JavaScriptEngine.UNDEFINED;
         if (args.length > 2) {
-            transfer = args[2];
+            if (JavaScriptEngine.isArray(args[2])) {
+                transfer = args[2];
+            }
         }
 
         final Window sender = (Window) scope;
diff --git a/src/test/java/org/htmlunit/javascript/host/WindowPostMessageTest.java b/src/test/java/org/htmlunit/javascript/host/WindowPostMessageTest.java
@@ -182,6 +182,51 @@ public void postMessageWithoutTargetOrigin() throws Exception {
         loadPageVerifyTitle2(html);
     }
 
+    /**
+     * @throws Exception if the test fails
+     */
+    @Test
+    @Alerts({"type: message", "bubbles: false", "cancelable: false", "data: hello",
+             "origin: ", "source: false true", "lastEventId: "})
+    public void postMessageWithTransferableOnly() throws Exception {
+        final String[] expectedAlerts = getExpectedAlerts();
+        expectedAlerts[4] += "http://localhost:" + PORT;
+        setExpectedAlerts(expectedAlerts);
+
+        final String html = DOCTYPE_HTML
+            + "<html>\n"
+            + "<head></head>\n"
+            + "<body>\n"
+            + "  <iframe id='myFrame' src='" + URL_THIRD + "'></iframe>\n"
+
+            + "<script>\n"
+            + LOG_TITLE_FUNCTION
+            + "  var win = document.getElementById('myFrame').contentWindow;\n"
+
+            + "  function receiveMessage(event) {\n"
+            + "    log('type: ' + event.type);\n"
+            + "    log('bubbles: ' + event.bubbles);\n"
+            + "    log('cancelable: ' + event.cancelable);\n"
+            + "    log('data: ' + event.data);\n"
+            + "    log('origin: ' + event.origin);\n"
+            + "    log('source: ' + (event.source === win) + ' ' + (event.source === window));\n"
+            + "    log('lastEventId: ' + event.lastEventId);\n"
+            + "  }\n"
+
+            + "  win.addEventListener('message', receiveMessage, false);\n"
+
+            + "  uInt8Array = new Uint8Array(1);\n"
+            + "  win.postMessage('hello', [uInt8Array.buffer]);\n"
+            + "</script>\n"
+            + "</body></html>";
+
+        final String iframe = DOCTYPE_HTML
+                + "<html><body><p>inside frame</p></body></html>";
+
+        getMockWebConnection().setResponse(URL_THIRD, iframe);
+        loadPageVerifyTitle2(html);
+    }
+
     /**
      * Test for #1589 NullPointerException because of missing context.
      *
