Xdnd: rename XdndHandler to X11DropTarget

src/Avalonia.X11/Selections/DragDrop/DragDropDataTransfer.cs

@@ -15,7 +15,8 @@ internal sealed class DragDropDataTransfer(
     IntPtr display,
     IntPtr sourceWindow,
     IntPtr targetWindow,
-    IInputRoot inputRoot)
+    IInputRoot inputRoot,
+    byte xdndVersion)
     : PlatformDataTransfer
 {
     public IntPtr SourceWindow { get; } = sourceWindow;
@@ -32,10 +33,8 @@ internal sealed class DragDropDataTransfer(
     protected override PlatformDataTransferItem[] ProvideItems()
         => reader.CreateItems();
 
-    public override void Dispose()
+    private void SendXdndFinished()
     {
-        reader.Dispose();
-
         var evt = new XEvent
         {
             ClientMessageEvent = new XClientMessageEvent
@@ -56,4 +55,12 @@ internal sealed class DragDropDataTransfer(
         XSendEvent(display, SourceWindow, false, (IntPtr)EventMask.NoEventMask, ref evt);
         XFlush(display);
     }
+
+    public override void Dispose()
+    {
+        reader.Dispose();
+
+        if (xdndVersion >= 5)
+            SendXdndFinished();
+    }
 }

src/Avalonia.X11/Selections/DragDrop/XdndHandler.cs → src/Avalonia.X11/Selections/DragDrop/X11DropTarget.cs

@@ -11,8 +11,10 @@ namespace Avalonia.X11.Selections.DragDrop;
 /// Manages XDND (drag and drop) for a given X11 window.
 /// Specs: https://www.freedesktop.org/wiki/Specifications/XDND/
 /// </summary>
-internal sealed class XdndHandler
+internal sealed class X11DropTarget
 {
+    // Spec: every application that supports XDND version N must also support all previous versions (3 to N-1).
+    private const byte MinXdndVersion = 3;
     private const byte XdndVersion = 5;
 
     private readonly IDragDropDevice _dragDropDevice;
@@ -21,7 +23,7 @@ internal sealed class XdndHandler
     private readonly X11Atoms _atoms;
     private DragDropDataTransfer? _currentDrag;
 
-    public XdndHandler(IDragDropDevice dragDropDevice, IXdndWindow window, IntPtr _display, X11Atoms atoms)
+    public X11DropTarget(IDragDropDevice dragDropDevice, IXdndWindow window, IntPtr _display, X11Atoms atoms)
     {
         _dragDropDevice = dragDropDevice;
         _window = window;
@@ -40,7 +42,7 @@ internal sealed class XdndHandler
         // Spec: If the version number in the XdndEnter message is higher than what the target can support,
         // the target should ignore the source.
         var version = (byte)((message.ptr2 >> 24) & 0xFF);
-        if (version > XdndVersion)
+        if (version is < MinXdndVersion or > XdndVersion)
             return;
 
         // If we ever receive a new XdndEnter message while a drag is in progress, it means something went wrong.
@@ -82,7 +84,8 @@ internal sealed class XdndHandler
             _display,
             sourceWindow,
             _window.Handle,
-            inputRoot);
+            inputRoot,
+            version);
     }
 
     public void HandleXdndPosition(in XClientMessageEvent message)

src/Avalonia.X11/X11Window.cs

@@ -71,7 +71,7 @@ namespace Avalonia.X11
         private bool _usePositioningFlags = false;
         private X11WindowMode _mode;
         private IWindowIconImpl? _iconImpl;
-        private readonly XdndHandler? _xdndHandler;
+        private readonly X11DropTarget? _dropTarget;
 
         private enum XSyncState
         {
@@ -280,7 +280,7 @@ namespace Avalonia.X11
             });
 
             if (AvaloniaLocator.Current.GetService<IDragDropDevice>() is { } dragDropDevice)
-                _xdndHandler = new XdndHandler(dragDropDevice, this, _x11.Display, _x11.Atoms);
+                _dropTarget = new X11DropTarget(dragDropDevice, this, _x11.Display, _x11.Atoms);
 
             platform.X11Screens.Changed += OnScreensChanged;
         }
@@ -700,13 +700,13 @@ namespace Avalonia.X11
                     }
                 }
                 else if (messageType == _x11.Atoms.XdndEnter)
-                    _xdndHandler?.HandleXdndEnter(ev.ClientMessageEvent);
+                    _dropTarget?.HandleXdndEnter(ev.ClientMessageEvent);
                 else if (messageType == _x11.Atoms.XdndPosition)
-                    _xdndHandler?.HandleXdndPosition(ev.ClientMessageEvent);
+                    _dropTarget?.HandleXdndPosition(ev.ClientMessageEvent);
                 else if (messageType == _x11.Atoms.XdndLeave)
-                    _xdndHandler?.HandleXdndLeave(ev.ClientMessageEvent);
+                    _dropTarget?.HandleXdndLeave(ev.ClientMessageEvent);
                 else if (messageType == _x11.Atoms.XdndDrop)
-                    _xdndHandler?.HandleXdndDrop(ev.ClientMessageEvent);
+                    _dropTarget?.HandleXdndDrop(ev.ClientMessageEvent);
             }
             else if (ev.type == XEventName.KeyPress || ev.type == XEventName.KeyRelease)
             {