[webview_flutter] handle onWebResourceError in onReceivedSslError on Android

[ycherniavskyi]

Description

Currently, on Android, there is no possibility to get a notification in Flutter that an SSL error occurred while loading a resource.
The user sees a white screen, and the developer doesn't receive any error callbacks from WebView. Only in log developer can see some error:

[ERROR:ssl_client_socket_impl.cc(962)] handshake failed; returned -1, SSL error code 1, net_error -200

By the way, on iOS, the developer receives onWebResourceError callbacks with an appropriate error.

The reason that Android implementation doesn't implement/provide onReceivedSslError notifier.

My proposal is to left the default behavior of this notifier (call SslErrorHandler#cancel), but handle onWebResourceError callback from WebView, so the developer can see this error and provide some actions.

Related Issues & Pull requests

• [webview_flutter] Ignore SSL certificate errors plugins#2285

[timukasr]

We'd like to show custom SSL error to users in our app and this feature would be really helpful.
Browsing the code, it seems that adding something like this to WebViewClientHostApiImpl.java could be simple fix:

@Override
public void onReceivedSslError(WebView view, SslErrorHandler handler, SslError error) {
	if (flutterApi != null) {
		flutterApi.onReceivedError(
			this,
			view,
			(long) WebViewClient.ERROR_FAILED_SSL_HANDSHAKE,
			"Failed to perform SSL handshake",
			error.getUrl(),
			reply -> {}
		);
	}
	handler.cancel();
}