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
+--- venus-gui-v2.html	2024-12-19 11:52:03.677046276 +1000
++++ index.html	2024-12-19 13:54:58.232268241 +1000
 @@ -12,15 +12,18 @@
      <title>venus-gui-v2</title>
      <style>
@@ -63,3 +62,26 @@ diff -u index.html venus-gui-v2.html
                      qt: {
                          onLoaded: () => showUi(screen),
                          onExit: exitData =>
+@@ -70,5 +99,22 @@
+     </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 via BackendConnection::hitWatchdog()
++        console.log("starting watchdog timer")
++        setTimeout(function(){ // wait 2 minutes for the page to load, then set a 10 second watchdog timer
++            checkWatchdog()
++            setInterval(checkWatchdog, 10000)
++        }, 120000)
++
++        function checkWatchdog()
++        {
++            if (!watchdogHit) {
++                console.error("Watchdog timer expired - reloading page")
++                location.reload()
++            }
++            watchdogHit = false
++        }
++    </script>
+   </body>
+ </html>

ApplicationContent.qml

@@ -156,4 +156,12 @@ Item {
 				? "qrc:/qt/qml/Victron/VenusOS/components/InputPanel.qml"
 				: "qrc:/qt/qml/Victron/VenusOS/components/WasmVirtualKeyboardHandler.qml"
 	}
+
+	// Sometimes, the wasm code may crash. Use a watchdog to detect this and reload the page when necessary.
+	Timer {
+		running: Qt.platform.os === "wasm" && BackendConnection.state === BackendConnection.Ready
+		repeat: true
+		interval: 1000
+		onTriggered: BackendConnection.hitWatchdog()
+	}
 }

src/backendconnection.cpp

@@ -222,6 +222,11 @@ void BackendConnection::openUrl(const QString &url)
 	emscripten_run_script(ba.constData());
 }
 
+void BackendConnection::hitWatchdog()
+{
+	emscripten_run_script("watchdogHit = true"); // 'watchdogHit' is defined in index.html, which checks it periodically and reloads the page if not hit regularly.
+}
+
 #else
 
 void BackendConnection::onNetworkConfigChanged(const QVariant var) { Q_UNUSED(var); }

src/backendconnection.h

@@ -139,6 +139,9 @@ class BackendConnection : public QObject
 	// Move this to some mock data manager when available
 	Q_INVOKABLE void setMockValue(const QString &uid, const QVariant &value);
 	Q_INVOKABLE QVariant mockValue(const QString &uid) const;
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	Q_INVOKABLE void hitWatchdog();
+#endif
 
 Q_SIGNALS:
 	void stateChanged();