Snap: Improve Web-browser Native Messaging host functionality

This commit allows for the snap distribution of KeepassXC to self-manage native messaging manifests
This is done by making the binary aware of the snapd environment changes that currently prevent this.
Furthermore, the snap sandbox is expanded to the bare minimum needed to access these privileged files.

Please note if running a self-compiled / untrusted KeepassXC snap build (I.E, installed with --dangerous)
that you must manually run `sudo snap connect keepassxc:browser-native-messaging` to grant permissions.

This will work on all distributions that expose `/snap/bin/` - such as Ubuntu, Debian, etc.
For systems which don't provide `/snap/`, such as Fedora, follow instructions for enabling "Classic" snaps.
e.g., `sudo ln -s /var/lib/snapd/snap /snap`

snap/snapcraft.yaml

@@ -10,7 +10,7 @@ apps:
     command: usr/bin/keepassxc
     common-id: org.keepassxc.KeePassXC.desktop
     extensions: [kde-neon]
-    plugs: [home, unity7, network, network-bind, removable-media, raw-usb, password-manager-service]
+    plugs: [home, unity7, network, network-bind, removable-media, raw-usb, password-manager-service, browser-native-messaging]
     autostart: org.keepassxc.KeePassXC.desktop
   cli:
     command: usr/bin/keepassxc-cli
@@ -21,6 +21,18 @@ apps:
     extensions: [kde-neon]
     plugs: [home]
 
+plugs:
+  browser-native-messaging:
+    interface: personal-files
+    write:
+      - $HOME/.mozilla/native-messaging-hosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.config/chromium/NativeMessagingHosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.config/google-chrome/NativeMessagingHosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.config/microsoft-edge/NativeMessagingHosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.config/vivaldi/NativeMessagingHosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.config/BraveSoftware/Brave-Browser/NativeMessagingHosts/org.keepassxc.keepassxc_browser.json
+      - $HOME/.local/share/torbrowser/tbb/x86_64/tor-browser_en-US/Browser/TorBrowser/Data/Browser/.mozilla/native-messaging-hosts
+
 slots:
   session-dbus-interface:
     interface: dbus

src/browser/BrowserSettingsWidget.cpp

@@ -31,23 +31,13 @@ BrowserSettingsWidget::BrowserSettingsWidget(QWidget* parent)
     m_ui->setupUi(this);
 
     // clang-format off
-    QString snapInstructions;
-#if defined(KEEPASSXC_DIST_SNAP)
-    snapInstructions = "<br /><br />" +
-            tr("Due to Snap sandboxing, you must run a script to enable browser integration."
-               "<br />"
-               "You can obtain this script from %1")
-               .arg("<a href=\"https://keepassxc.org/download#linux\">https://keepassxc.org</a>");
-#endif
-
     m_ui->extensionLabel->setOpenExternalLinks(true);
     m_ui->extensionLabel->setText(
-        tr("KeePassXC-Browser is needed for the browser integration to work. <br />Download it for %1 and %2 and %3. %4")
+        tr("KeePassXC-Browser is needed for the browser integration to work. <br />Download it for %1 and %2 and %3.")
             .arg("<a href=\"https://addons.mozilla.org/firefox/addon/keepassxc-browser/\">Firefox</a>",
                  "<a href=\"https://chrome.google.com/webstore/detail/keepassxc-browser/oboonakemofpalcgghocfoadofidjkkk\">"
                  "Google Chrome / Chromium / Vivaldi / Brave</a>",
-                 "<a href=\"https://microsoftedge.microsoft.com/addons/detail/pdffhmdngciaglkoonimfcmckehcpafo\">Microsoft Edge</a>",
-                 snapInstructions));
+                 "<a href=\"https://microsoftedge.microsoft.com/addons/detail/pdffhmdngciaglkoonimfcmckehcpafo\">Microsoft Edge</a>"));
     // clang-format on
 
     m_ui->tabWidget->setEnabled(m_ui->enableBrowserSupport->isChecked());
@@ -149,16 +139,11 @@ void BrowserSettingsWidget::loadSettings()
     m_ui->useCustomProxy->setVisible(false);
     m_ui->customProxyLocation->setVisible(false);
     m_ui->customProxyLocationBrowseButton->setVisible(false);
-    m_ui->browsersGroupBox->setVisible(false);
-    m_ui->browsersGroupBox->setEnabled(false);
     m_ui->updateBinaryPath->setChecked(false);
     m_ui->updateBinaryPath->setVisible(false);
     // No custom browser for snaps
     m_ui->customBrowserSupport->setVisible(false);
     m_ui->customBrowserGroupBox->setVisible(false);
-    // Show notice to user
-    m_ui->messageWidget->showMessage(tr("Please see special instructions for browser extension use below"),
-                                     MessageWidget::Warning);
 #endif
 #ifdef KEEPASSXC_DIST_FLATPAK
     // The sandbox makes custom proxy locations very unintuitive

src/browser/NativeMessageInstaller.cpp

@@ -226,6 +226,16 @@ QString NativeMessageInstaller::getNativeMessagePath(SupportedBrowsers browser)
     } else {
         basePath = QDir::homePath() + "/.config";
     }
+#elif defined(KEEPASSXC_DIST_SNAP)
+    // Same as Flatpak above, with the exception that Snap also redefines $HOME
+    // Therefore we must explicitly reference $SNAP_REAL_HOME
+    if (browser == SupportedBrowsers::TOR_BROWSER) {
+	basePath = qEnvironmentVariable("SNAP_REAL_HOME") + "/.local/share";
+    } else if (browser == SupportedBrowsers::FIREFOX) {
+        basePath = qEnvironmentVariable("SNAP_REAL_HOME");
+    } else {
+        basePath = qEnvironmentVariable("SNAP_REAL_HOME") + "/.config";
+    }
 #elif defined(Q_OS_LINUX) || (defined(Q_OS_UNIX) && !defined(Q_OS_MACOS))
     if (browser == SupportedBrowsers::TOR_BROWSER) {
         basePath = QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation);
@@ -296,6 +306,8 @@ QString NativeMessageInstaller::getInstalledProxyPath() const
     path = QProcessEnvironment::systemEnvironment().value("APPIMAGE");
 #elif defined(KEEPASSXC_DIST_FLATPAK)
     path = constructFlatpakPath();
+#elif defined(KEEPASSXC_DIST_SNAP)
+    path = "/snap/bin/keepassxc.proxy";
 #else
     path = QCoreApplication::applicationDirPath() + QStringLiteral("/keepassxc-proxy");
 #ifdef Q_OS_WIN