Gtk: Write GTK logs to debuglog instead of stdout

NAPS2.Lib.Gtk/EntryPoints/GtkEntryPoint.cs

@@ -12,6 +12,7 @@ public static class GtkEntryPoint
     public static int Run(string[] args)
     {
         GLib.ExceptionManager.UnhandledException += UnhandledGtkException;
+        GLibLogInterceptor.WriteToDebugLog();
         EtoPlatform.Current = new GtkEtoPlatform();
 
         var subArgs = args.Skip(1).ToArray();

NAPS2.Lib.Gtk/Util/GLibLogInterceptor.cs

@@ -0,0 +1,84 @@
+using System.Globalization;
+using System.Runtime.InteropServices;
+using GLib;
+using Log = NAPS2.Logging.Log;
+
+namespace NAPS2.Util;
+
+public static class GLibLogInterceptor
+{
+    /// <summary>
+    /// Intercepts GLib/Gtk logging and writes it to the NAPS2 debuglog instead of stdout.
+    /// </summary>
+    public static void WriteToDebugLog()
+    {
+        g_log_set_writer_func(Write, IntPtr.Zero, IntPtr.Zero);
+    }
+
+    private static void Write(LogLevelFlags flags, IntPtr fields, nint nFields, IntPtr userData)
+    {
+        string glibDomain = "?";
+        string message = "?";
+        string priority = "?";
+
+        var size = Marshal.SizeOf<GLogField>();
+        for (int i = 0; i < nFields; i++)
+        {
+            var field = Marshal.PtrToStructure<GLogField>(fields + i * size);
+            if (field.key == "PRIORITY")
+            {
+                var valueStr = Marshal.PtrToStringUTF8(field.value)!;
+                if (int.TryParse(valueStr, CultureInfo.InvariantCulture, out var parsedPriority))
+                {
+                    if (parsedPriority is < 0 or > 4)
+                    {
+                        // Only log warning or worse
+                        return;
+                    }
+                    priority = parsedPriority switch
+                    {
+                        0 => "EMERG",
+                        1 => "ALERT",
+                        2 => "CRITICAL",
+                        3 => "ERROR",
+                        4 => "WARNING",
+                        _ => throw new InvalidOperationException()
+                    };
+                }
+            }
+            if (field.key == "GLIB_DOMAIN")
+            {
+                var valueStr = Marshal.PtrToStringUTF8(field.value)!;
+                glibDomain = valueStr;
+            }
+            if (field.key == "MESSAGE")
+            {
+                var valueStr = Marshal.PtrToStringUTF8(field.value)!;
+                message = valueStr;
+            }
+        }
+
+        Log.Debug($"{glibDomain}-{priority}: {message}");
+    }
+
+    [DllImport("libglib-2.0.so.0")]
+    private static extern uint g_log_set_writer_func(
+        GLogWriterFunc log_func,
+        IntPtr user_data,
+        IntPtr user_data_free);
+
+
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate void GLogWriterFunc(
+        LogLevelFlags flags,
+        IntPtr fields,
+        nint nFields,
+        IntPtr user_data);
+
+    struct GLogField
+    {
+        public string key;
+        public IntPtr value;
+        public nint length;
+    }
+}

NAPS2.Lib/Logging/Log.cs

@@ -23,6 +23,11 @@ public static IEventLogger EventLogger
         set => _eventLogger = value ?? throw new ArgumentNullException(nameof(value));
     }
 
+    public static void Debug(string message)
+    {
+        _logger.LogDebug(message);
+    }
+
     public static void Info(string message)
     {
         _logger.LogInformation(message);