qt: force mime type resolution by extension

Fixes BitBoxSwiss#2684 and hopefully BitBoxSwiss#3061.

Without this, on linux the local mimetype database (influenced by
various packages installed on the system) can mess with the mimetype
resolution of our .html/.js/.css files served locally, resulting in a
blank page.

This manually intercepts local requests and forces the correct
mimetype for a set of hardcoded extensions.

Author: benma

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+# 4.46.2
+- Fix Linux blank screen issue related to the local mimetype database
+
 # 4.46.1
 - Fix Android app crash on old Android versions
 

frontends/qt/main.cpp

@@ -20,6 +20,11 @@
 #include <QWebEnginePage>
 #include <QWebChannel>
 #include <QWebEngineUrlRequestInterceptor>
+#include <QWebEngineUrlScheme>
+#include <QWebEngineUrlSchemeHandler>
+#include <QWebEngineUrlRequestJob>
+#include <QMimeDatabase>
+#include <QFile>
 #include <QContextMenuEvent>
 #include <QMenu>
 #include <QRegularExpression>
@@ -52,6 +57,11 @@
 
 #define APPNAME "BitBoxApp"
 
+// Custom scheme so we can intercept and serve local files.
+// If you change this, MoonPay may break, as this scheme is whitelisted as a frame ancestor in
+// their CSP response headers.
+static const char* scheme = "bitboxapp";
+
 static QWebEngineView* view;
 static QWebEnginePage* mainPage;
 static QWebEnginePage* externalPage;
@@ -111,12 +121,60 @@ class WebEnginePage : public QWebEnginePage {
     }
 };
 
+// Custom scheme handler so we can force mime type resolution manually.
+// Without this, on linux the local mimetype database can mess with the mimetype resolution.
+// Programs like monodevelop or Steam/Proton install weird mime types making for example our
+// .js or .html files be served with the wrogn mimetype, resulting in the webengine displaying a
+// blank page only.
+class SchemeHandler : public QWebEngineUrlSchemeHandler {
+public:
+    // Similar like the built-in qrc scheme handler, but with hardcoded mime-types.
+    // https://github.com/qt/qtwebengine/blob/v6.2.4/src/core/net/qrc_url_scheme_handler.cpp
+    void requestStarted(QWebEngineUrlRequestJob *request) override {
+        QByteArray requestMethod = request->requestMethod();
+        if (requestMethod != "GET") {
+            request->fail(QWebEngineUrlRequestJob::RequestDenied);
+            return;
+        }
+        QUrl url = request->requestUrl();
+        QString path = url.path();
+
+        QMimeDatabase mimeDb;
+
+        QMimeType mimeType = mimeDb.mimeTypeForFile(path);
+
+        QString hardcodedMimeType;
+        if (path.endsWith(".html")) {
+            hardcodedMimeType = "text/html";
+        } else if (path.endsWith(".js")) {
+            hardcodedMimeType = "application/javascript";
+        } else if (path.endsWith(".css")) {
+            hardcodedMimeType = "text/css";
+        } else if (path.endsWith(".svg")) {
+            hardcodedMimeType = "image/svg+xml";
+        } else {
+            // Fallback to detected mimetype.
+            hardcodedMimeType = mimeType.name();
+        }
+
+        // Read resource from QRC (local static assets).
+        auto file = new QFile(":" + path);
+        if (file->open(QIODevice::ReadOnly)) {
+            request->reply(hardcodedMimeType.toUtf8(), file);
+            file->setParent(request);
+        } else {
+            delete file;
+            request->fail(QWebEngineUrlRequestJob::UrlNotFound);
+        }
+    }
+};
+
 class RequestInterceptor : public QWebEngineUrlRequestInterceptor {
 public:
     explicit RequestInterceptor() : QWebEngineUrlRequestInterceptor() { }
     void interceptRequest(QWebEngineUrlRequestInfo& info) override {
         // Do not block qrc:/ local pages or js blobs
-        if (info.requestUrl().scheme() == "qrc" || info.requestUrl().scheme() == "blob") {
+        if (info.requestUrl().scheme() == scheme || info.requestUrl().scheme() == "blob") {
             return;
         }
 
@@ -126,8 +184,8 @@ class RequestInterceptor : public QWebEngineUrlRequestInterceptor {
         // We treat the exchange pages specially because we need to allow exchange
         // widgets to load in an iframe as well as let them open external links
         // in a browser.
-        bool onExchangePage = currentUrl.contains(QRegularExpression("^qrc:/exchange/.*$"));
-        bool onBitsurancePage = currentUrl.contains(QRegularExpression("^qrc:/bitsurance/.*$"));
+        bool onExchangePage = currentUrl.contains(QRegularExpression(QString("^%1:/exchange/.*$").arg(scheme)));
+        bool onBitsurancePage = currentUrl.contains(QRegularExpression(QString("^%1:/bitsurance/.*$").arg(scheme)));
         if (onExchangePage || onBitsurancePage) {
             if (info.firstPartyUrl().toString() == info.requestUrl().toString()) {
                 // Ignore requests for certain file types (e.g., .js, .css) Somehow Moonpay loads
@@ -150,7 +208,7 @@ class RequestInterceptor : public QWebEngineUrlRequestInterceptor {
 
         // All the requests originated in the wallet-connect section are allowed, as they are needed to
         // load the Dapp logos and it is not easy to filter out non-images requests.
-        bool onWCPage = currentUrl.contains(QRegularExpression(R"(^qrc:/account/[^\/]+/wallet-connect/.*$)"));
+        bool onWCPage = currentUrl.contains(QRegularExpression(QString(R"(^%1:/account/[^\/]+/wallet-connect/.*$)").arg(scheme)));
         if (onWCPage) {
             return;
         }
@@ -280,6 +338,14 @@ int main(int argc, char *argv[])
         return 0;
     }
 
+    QWebEngineUrlScheme bbappScheme(scheme);
+    bbappScheme.setSyntax(QWebEngineUrlScheme::Syntax::HostAndPort);
+    bbappScheme.setFlags(
+        QWebEngineUrlScheme::LocalScheme |
+        QWebEngineUrlScheme::SecureScheme |
+        QWebEngineUrlScheme::LocalAccessAllowed);
+    QWebEngineUrlScheme::registerScheme(bbappScheme);
+
     view = new WebEngineView();
     view->setGeometry(0, 0, a.devicePixelRatio() * view->width(), a.devicePixelRatio() * view->height());
     view->setMinimumSize(360, 375);
@@ -369,6 +435,11 @@ int main(int argc, char *argv[])
 
     RequestInterceptor interceptor;
     view->page()->profile()->setUrlRequestInterceptor(&interceptor);
+
+    // For manual mimetype resolution.
+    SchemeHandler schemeHandler;
+    view->page()->profile()->installUrlSchemeHandler(scheme, &schemeHandler);
+
     QObject::connect(
         view->page(),
         &QWebEnginePage::featurePermissionRequested,
@@ -381,11 +452,12 @@ int main(int argc, char *argv[])
                     QWebEnginePage::PermissionGrantedByUser);
             }
         });
+
     QWebChannel channel;
     channel.registerObject("backend", webClass);
     view->page()->setWebChannel(&channel);
     view->show();
-    view->load(QUrl("qrc:/index.html"));
+    view->load(QUrl(QString("%1:/index.html").arg(scheme)));
 
     // Create TrayIcon
     {