Add a watchdog to detect crashed wasm builds and reload the page

Fixes #1803

.github/patches/index.html.patch

@@ -1,6 +1,5 @@
-diff -u index.html venus-gui-v2.html
---- index.html	2024-05-16 22:12:44.106129598 +0300
-+++ venus-gui-v2.html	2024-07-05 12:44:44.396192697 +0200
+--- index.html	2024-12-17 17:13:52.442569994 +1000
++++ venus-gui-v2.html	2024-12-17 17:08:58.496874189 +1000
 @@ -12,15 +12,18 @@
      <title>venus-gui-v2</title>
      <style>
@@ -63,3 +62,19 @@ diff -u index.html venus-gui-v2.html
                      qt: {
                          onLoaded: () => showUi(screen),
                          onExit: exitData =>
+@@ -70,5 +99,15 @@
+     </script>
+     <script src="venus-gui-v2.js"></script>
+     <script type="text/javascript" src="qtloader.js"></script>
++    <script type="text/javascript">
++        var watchdogHit = false // this gets set to 'true' by a timer in BackendConnection::onWatchdogTimerExpired()
++        setInterval(function() {
++            if (!watchdogHit) {
++                console.error("Watchdog timer expired - reloading page")
++                location.reload()
++            }
++            watchdogHit = false
++        }, 20000);
++    </script>
+   </body>
+ </html>

Main.qml

@@ -8,6 +8,7 @@ import QtQuick.Window
 
 // *** This file cannot be edited directly on the cerbo filesystem. It is loaded from the binary ***
 
+
 Window {
 	id: root
 

src/backendconnection.cpp

@@ -193,6 +193,12 @@ void BackendConnection::onReloadPageTimerExpired()
 	reloadPage();
 }
 
+// Sometimes, the wasm code may crash. Use a watchdog to detect this and reload the page when necessary.
+void BackendConnection::onWatchdogTimerExpired()
+{
+	emscripten_run_script("watchdogHit = true"); // 'watchdogHit' is defined in venus-gui-v2.html, which checks it periodically and reloads the page if not hit regularly.
+}
+
 // If the wasm itself changed the Security Profile, it should normally be notified
 // that it is accepted by receiving a Network Config change. Since that event is send
 // over a connection which is going to be disconnected, this acts as a fallback if
@@ -272,6 +278,9 @@ void BackendConnection::initMqttConnection(const QString &address)
 
 	VeQItem *item = mqttProducer->services()->itemGetOrCreate("/platform/0/Network/ConfigChanged");
 	connect(item, &VeQItem::valueChanged, this, &BackendConnection::onNetworkConfigChanged);
+
+	connect(&mWatchdogTimer, &QTimer::timeout, this, &BackendConnection::onWatchdogTimerExpired);
+	mWatchdogTimer.start(1000);
 #else
 	const QStringList parts = address.split(':');
 	if (parts.size() >= 2) {

src/backendconnection.h

@@ -157,6 +157,9 @@ class BackendConnection : public QObject
 private Q_SLOTS:
 	void onNetworkConfigChanged(const QVariant var);
 	void onReloadPageTimerExpired();
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	void onWatchdogTimerExpired();
+#endif
 
 private:
 	explicit BackendConnection(QObject *parent = nullptr);
@@ -195,6 +198,10 @@ private Q_SLOTS:
 	AlarmBusitem *m_alarmBusItem = nullptr;
 #endif
 	QNetworkAccessManager *m_network = nullptr;
+
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	QTimer mWatchdogTimer;
+#endif
 };
 
 class BackendConnectionTester : public QObject