From c28da40405f122a88fcd9cdf6aa44e0fc3298144 Mon Sep 17 00:00:00 2001
From: Marko Bencun <marko@shiftcrypto.ch>
Date: Thu, 21 Nov 2024 09:33:25 +0100
Subject: [PATCH] qt: force mime type resolution by filename extension only

Fixes #2684 and hopefully #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 mimetype resolution
by filename extension only, to avoid the system mimetype database from
breaking the app.
---
 CHANGELOG.md          |  1 +
 frontends/qt/main.cpp | 44 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 27997d447a..2003e279da 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 # 4.46.1
 - Fix Android app crash on old Android versions
+- Fix Linux blank screen issue related to the local mimetype database
 
 # 4.46.0
 - Android: enable export logs feature
diff --git a/frontends/qt/main.cpp b/frontends/qt/main.cpp
index 7a34a4d00b..dee2894886 100644
--- a/frontends/qt/main.cpp
+++ b/frontends/qt/main.cpp
@@ -20,6 +20,10 @@
 #include <QWebEnginePage>
 #include <QWebChannel>
 #include <QWebEngineUrlRequestInterceptor>
+#include <QWebEngineUrlSchemeHandler>
+#include <QWebEngineUrlRequestJob>
+#include <QMimeDatabase>
+#include <QFile>
 #include <QContextMenuEvent>
 #include <QMenu>
 #include <QRegularExpression>
@@ -52,6 +56,9 @@
 
 #define APPNAME "BitBoxApp"
 
+// Custom scheme so we can intercept and serve local files.
+static const char* scheme = "bitboxapp";
+
 static QWebEngineView* view;
 static QWebEnginePage* mainPage;
 static QWebEnginePage* externalPage;
@@ -111,12 +118,37 @@ class WebEnginePage : public QWebEnginePage {
     }
 };
 
+// Custom scheme handler so we can force mime type detection by filename extension only.
+// 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:
+    void requestStarted(QWebEngineUrlRequestJob *request) override {
+        QUrl url = request->requestUrl();
+        QString path = url.path();
+
+        QMimeDatabase mimeDb;
+        // Force matching by extension only, not using any mimetype database.
+        QMimeType mimeType = mimeDb.mimeTypeForFile(path, QMimeDatabase::MatchExtension);
+        // Read resource from QRC (local static assets).
+        auto file = new QFile(":" + path);
+        if (file->open(QIODevice::ReadOnly)) {
+            request->reply(mimeType.name().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 +158,8 @@ 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 +182,7 @@ 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;
         }
@@ -369,6 +401,8 @@ int main(int argc, char *argv[])
 
     RequestInterceptor interceptor;
     view->page()->profile()->setUrlRequestInterceptor(&interceptor);
+    SchemeHandler schemeHandler;
+    view->page()->profile()->installUrlSchemeHandler(scheme, &schemeHandler);
     QObject::connect(
         view->page(),
         &QWebEnginePage::featurePermissionRequested,
@@ -385,7 +419,7 @@ int main(int argc, char *argv[])
     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
     {