WebView URL filtering #3442

t-arn · 2025-05-13T11:45:37Z

This PR aims to implement URL filtering for WebView on Windows and Android.
Possible use cases are:

preventing users from navigating off the site intended to be handled by your application's WebView
preventing users from navigating to known malicious web sites

PR Checklist:

All new features have been tested
All new features have been documented
I have read the CONTRIBUTING.md file
I will abide by the code of conduct

* implented on_navigation_started for android * extended the webview example

* applied black

freakboy3742

Thanks for the PR; I've flagged a few issues inline, and the test suite is obviously failing on most platforms (although it looks like the reason for the failure is something that won't be an issue once you've addressed one of the comments inline).

freakboy3742 · 2025-05-13T12:25:44Z

android/src/toga_android/widgets/webview.py

+    @Override(jboolean, [A_WebView, WebResourceRequest])
+    def shouldOverrideUrlLoading(self, webview, webresourcerequest):
+        if self.webview_impl.interface.on_navigation_starting:
+            event = TogaNavigationEvent(webresourcerequest)


I'm a little confused about what is going on here. TogaNavigationEvent is a Python class, wrapping a request and a cancel attribute. It's never assigned to anything, or passed as an argument to anything - then it's cleared. Why is it required at all?

freakboy3742 · 2025-05-13T12:26:44Z

android/src/toga_android/widgets/webview.py

@@ -86,3 +117,7 @@ def evaluate_javascript(self, javascript, on_result=None):

        self.native.evaluateJavascript(javascript, ReceiveString(result))
        return result
+
+    def set_on_navigation_starting(self, handler):


At this point, I'm pretty sure we've removed all the "set_on_..." methods; unless there's a specific use case (and it doesn't look like there is), this can be removed.

freakboy3742 · 2025-05-13T12:27:13Z

core/src/toga/widgets/webview.py

@@ -33,6 +33,7 @@ def __init__(
        url: str | None = None,
        content: str | None = None,
        user_agent: str | None = None,
+        on_navigation_starting=None,


This needs a type declaration (if only for documentation purposes)

freakboy3742 · 2025-05-13T12:29:23Z

examples/webview/pyproject.toml

@@ -53,6 +53,10 @@ build_gradle_dependencies = [
    "com.google.android.material:material:1.12.0",
 ]

+build_gradle_extra_content="""
+chaquopy.defaultConfig.staticProxy("toga_android.widgets.webview")
+"""


Hrm... Requiring users to manually inject an "extra content" block to make a feature work is a problematic requirement. I understand why it's needed - but we possibly need to solve the bigger problem of allowing toga to declare a list of "classes that need a static proxy".

I agree. But this probably means that this PR cannot be merged any time soon, right?

It depends how essential the change is.

If a WebView will continue to work on Android, but this feature won't work without the extra content declaration, we can probably merge it. We will need to add a set of platform notes in the docs, and we'll need to prioritise finding a better fix - but I don't think it needs to be a complete blocker.

However, if Webview (or the whole Android backend) won't work at all if this addition isn't in place, then we'll need to solve that problem first.

freakboy3742 · 2025-05-13T12:30:20Z

examples/webview/webview/app.py

+            allow = False
+            message = f"Navigation not allowed to: {url}"
+            dialog = toga.InfoDialog("on_navigation_starting()", message)
+            asyncio.create_task(self.dialog(dialog))


It might be easier to make on_navigation_starting an async callback, and then await the response.

freakboy3742 · 2025-05-13T12:32:40Z

android/src/toga_android/widgets/webview.py

+            event = TogaNavigationEvent(webresourcerequest)
+            allow = self.webview_impl.interface.on_navigation_starting(
+                webresourcerequest.getUrl().toString()
+            )


I haven't checked, but this could be a problem if on_navigation_starting is an async callback, because the returned value will be a future.

freakboy3742 · 2025-05-13T12:33:49Z

examples/webview/webview/app.py

@@ -92,6 +106,9 @@ def startup(self):
            on_webview_load=self.on_webview_load,
            style=Pack(flex=1),
        )
+        # activate web navigation filtering on supported platforms
+        if getattr(self.webview._impl, "SUPPORTS_ON_NAVIGATION_STARTING", True):


Good instinct, but it's fine for the example to raise a warning if a feature isn't available.

freakboy3742 · 2025-05-13T12:34:44Z

winforms/src/toga_winforms/widgets/webview.py

@@ -136,6 +135,10 @@ def winforms_initialization_completed(self, sender, args):
            settings.IsSwipeNavigationEnabled = False
            settings.IsZoomControlEnabled = True

+            self.native.CoreWebView2.NavigationStarting += (
+                self.winforms_navigation_starting


This almost certainly needs a WeakrefCallable wrapper.

You mean like the winforms_FormClosing in the winforms dialogs module?

Yes - you can see the same handling in NavigationCompleted and CoreWebView2InitializationCompleted in the WebView widget.

freakboy3742 · 2025-05-13T12:35:01Z

winforms/src/toga_winforms/widgets/webview.py

+    def winforms_navigation_starting(self, sender, event):
+        # print(f"winforms_navigation_starting: {event.Uri}")
+        if self.interface.on_navigation_starting:
+            allow = self.interface.on_navigation_starting(event.Uri)


As with the Android version, this needs to handle a Future being returned.

t-arn · 2025-05-13T13:16:11Z

@freakboy3742 I wonder if it is possible to make the on_navigation_starting handler async when it is being called by a native event. Aren't those native events always synchronous?

freakboy3742 · 2025-05-13T13:19:36Z

@freakboy3742 I wonder if it is possible to make the on_navigation_starting handler async when it is being called by a native event. Aren't those native events always synchronous?

Yes, native event handlers are always synchronous - but Toga events must be able to be defined asynchronously. That's why they return a future; we need to make sure that if a future is returned, we wait for that future.

t-arn added 4 commits May 13, 2025 07:34

* implented on_navigation_started for winforms

a476f73

* implented on_navigation_started for android * extended the webview example

* fixed some issues

23e2747

* added change note

4c6777d

* applied black

fixed pre-commit issue

4849755

freakboy3742 requested changes May 13, 2025

View reviewed changes

removed unnecessary set_on_navigation_starting() method

7f335d6

Uh oh!

WebView URL filtering #3442

Are you sure you want to change the base?

WebView URL filtering #3442

Uh oh!

Conversation

t-arn commented May 13, 2025

PR Checklist:

Uh oh!

freakboy3742 left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

t-arn May 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

t-arn commented May 13, 2025

Uh oh!

freakboy3742 commented May 13, 2025

Uh oh!

Uh oh!

t-arn May 13, 2025 •

edited

Loading