Restore the Tagged User-Agent on Linux with WebKitGTK's Own Prefix (#16466)

Linux webviews lost the BBL-Slicer, dark|light and BBL-Language tags
with the stock WebKitGTK User-Agent, so the bundled pages stayed light
and dropped every message to the host. The tags come back on Linux, now
appended to the string WebKitGTK reports for itself instead of the Mac
one. Windows and macOS are untouched.

src/slic3r/GUI/Widgets/WebView.cpp

@@ -56,7 +56,12 @@ namespace fs = boost::filesystem;
 #define WEBKIT_API
 struct WebKitWebView;
 struct WebKitJavascriptResult;
+struct WebKitSettings;
 extern "C" {
+WEBKIT_API WebKitSettings *
+webkit_settings_new                                  (void);
+WEBKIT_API const gchar *
+webkit_settings_get_user_agent                       (WebKitSettings            *settings);
 WEBKIT_API void
 webkit_web_view_run_javascript                       (WebKitWebView             *web_view,
                                                       const gchar               *script,
@@ -284,6 +289,23 @@ static WebViewRef *webview_ref(wxWebView *webView)
     return webView ? static_cast<WebViewRef *>(webView->GetRefData()) : nullptr;
 }
 
+#ifdef __linux__
+// WebKitGTK's own User-Agent with the tags the bundled pages (globalapi.js) and Bambu's cloud read
+// appended. wx's GTK backend cannot report the stock string, so it comes from a throwaway settings object.
+static wxString linux_user_agent()
+{
+    static const wxString stock = [] {
+        WebKitSettings *settings = webkit_settings_new();
+        wxString        ua       = wxString::FromUTF8(webkit_settings_get_user_agent(settings));
+        g_object_unref(settings);
+        return ua;
+    }();
+    return wxString::Format("%s BBL-Slicer/v%s (%s) BBL-Language/%s", stock, Slic3r::GUI::wxGetApp().get_bbl_client_version(),
+                            Slic3r::GUI::wxGetApp().dark_mode() ? "dark" : "light",
+                            Slic3r::GUI::wxGetApp().current_language_code().BeforeFirst('_'));
+}
+#endif
+
 wxWebView* WebView::CreateWebView(wxWindow * parent, wxString const & url)
 {
 #if wxUSE_WEBVIEW_EDGE
@@ -336,7 +358,9 @@ wxWebView* WebView::CreateWebView(wxWindow * parent, wxString const & url)
             s_schemes_registered = true;
         }
         webView->Create(parent, wxID_ANY, url2, wxDefaultPosition, wxDefaultSize, wxBORDER_NONE);
-#ifndef __linux__
+#ifdef __linux__
+        webView->SetUserAgent(linux_user_agent());
+#else
         webView->SetUserAgent(wxString::Format("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) BBL-Slicer/v%s (%s) BBL-Language/%s",
                                                Slic3r::GUI::wxGetApp().get_bbl_client_version(), Slic3r::GUI::wxGetApp().dark_mode() ? "dark" : "light", language_code.mb_str()));
 #endif
@@ -472,7 +496,9 @@ void WebView::RecreateAll()
     wxString language_code = Slic3r::GUI::wxGetApp().current_language_code().BeforeFirst('_');
     language_code          = language_code.ToStdString();
     for (auto webView : g_webviews) {
-#ifndef __linux__
+#ifdef __linux__
+        webView->SetUserAgent(linux_user_agent());
+#else
         webView->SetUserAgent(wxString::Format("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) BBL-Slicer/v%s (%s) BBL-Language/%s",
                                                Slic3r::GUI::wxGetApp().get_bbl_client_version(), dark ? "dark" : "light", language_code.mb_str()));
 #endif