How Do You Use WebMessagePort As An Alternative to addJavascriptInterface()?

Question

Google\'s security guidelines for Android app developers has the following:

WebViews do not use addJavaScriptInterface() with untrusted cont

Answer 1

There's a test for it in CTS

// Create a message channel and make sure it can be used for data transfer to/from js.
public void testMessageChannel() throws Throwable {
    if (!NullWebViewUtils.isWebViewAvailable()) {
        return;
    }
    loadPage(CHANNEL_MESSAGE);
    final WebMessagePort[] channel = mOnUiThread.createWebMessageChannel();
    WebMessage message = new WebMessage(WEBVIEW_MESSAGE, new WebMessagePort[]{channel[1]});
    mOnUiThread.postWebMessage(message, Uri.parse(BASE_URI));
    final int messageCount = 3;
    final CountDownLatch latch = new CountDownLatch(messageCount);
    runTestOnUiThread(new Runnable() {
        @Override
        public void run() {
            for (int i = 0; i < messageCount; i++) {
                channel[0].postMessage(new WebMessage(WEBVIEW_MESSAGE + i));
            }
            channel[0].setWebMessageCallback(new WebMessagePort.WebMessageCallback() {
                @Override
                public void onMessage(WebMessagePort port, WebMessage message) {
                    int i = messageCount - (int)latch.getCount();
                    assertEquals(WEBVIEW_MESSAGE + i + i, message.getData());
                    latch.countDown();
                }
            });
        }
    });
    // Wait for all the responses to arrive.
    boolean ignore = latch.await(TIMEOUT, java.util.concurrent.TimeUnit.MILLISECONDS);
}

file: cts/tests/tests/webkit/src/android/webkit/cts/PostMessageTest.java. At least some starting point.