dnd: Pass content to gdk_drag_begin()

Instead of just passing the GdkContentFormats, we are now passing the
GdkContentProvider to gdk_drag_begin().
This means that GDK itself can now query the data from the provider
directly instead of having to send selection events.

Use this to provide the private API gdk_drag_context_write() that allows
backends to pass an output stream that this data will be written to.
Implement this as the mechanism for providing drag data on Wayland.

And to make this all work, implement a content provider named
GtkDragContent that is implemented by reverting to the old DND
drag-data-get machinery inside GTK, so for widgets everything works just
like before.

1 files changed, 155 insertions, 1 deletions

diff --git a/gtk/gtkdnd.c b/gtk/gtkdnd.c
index 085a7a9774..dd2a0034e0 100644
--- a/gtk/gtkdnd.c
+++ b/gtk/gtkdnd.c
@@ -960,6 +960,150 @@ gtk_drag_dest_drop (GtkWidget      *widget,
  * Source side *
  ***************/
 
+#define GTK_TYPE_DRAG_CONTENT            (gtk_drag_content_get_type ())
+#define GTK_DRAG_CONTENT(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GTK_TYPE_DRAG_CONTENT, GtkDragContent))
+#define GTK_IS_DRAG_CONTENT(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GTK_TYPE_DRAG_CONTENT))
+#define GTK_DRAG_CONTENT_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GTK_TYPE_DRAG_CONTENT, GtkDragContentClass))
+#define GTK_IS_DRAG_CONTENT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GTK_TYPE_DRAG_CONTENT))
+#define GTK_DRAG_CONTENT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GTK_TYPE_DRAG_CONTENT, GtkDragContentClass))
+
+typedef struct _GtkDragContent GtkDragContent;
+typedef struct _GtkDragContentClass GtkDragContentClass;
+
+struct _GtkDragContent
+{
+  GdkContentProvider parent;
+
+  GtkWidget *widget;
+  GdkDragContext *context;
+  GdkContentFormats *formats;
+  guint32 time;
+};
+
+struct _GtkDragContentClass
+{
+  GdkContentProviderClass parent_class;
+};
+
+GType gtk_drag_content_get_type (void) G_GNUC_CONST;
+
+G_DEFINE_TYPE (GtkDragContent, gtk_drag_content, GDK_TYPE_CONTENT_PROVIDER)
+
+static GdkContentFormats *
+gtk_drag_content_ref_formats (GdkContentProvider *provider)
+{
+  GtkDragContent *content = GTK_DRAG_CONTENT (provider);
+
+  return gdk_content_formats_ref (content->formats);
+}
+
+static void
+gtk_drag_content_write_mime_type_done (GObject      *stream,
+                                       GAsyncResult *result,
+                                       gpointer      task)
+{
+  GError *error = NULL;
+
+  if (!g_output_stream_write_all_finish (G_OUTPUT_STREAM (stream),
+                                         result,
+                                         NULL,
+                                         &error))
+    {
+      g_task_return_error (task, error);
+    }
+  else
+    {
+      g_task_return_boolean (task, TRUE);
+    }
+
+  g_object_unref (task);
+}
+
+static void
+gtk_drag_content_write_mime_type_async (GdkContentProvider  *provider,
+                                        const char          *mime_type,
+                                        GOutputStream       *stream,
+                                        int                  io_priority,
+                                        GCancellable        *cancellable,
+                                        GAsyncReadyCallback  callback,
+                                        gpointer             user_data)
+{
+  GtkDragContent *content = GTK_DRAG_CONTENT (provider);
+  GtkSelectionData sdata = { 0, };
+  GTask *task;
+
+  task = g_task_new (content, cancellable, callback, user_data);
+  g_task_set_priority (task, io_priority);
+  g_task_set_source_tag (task, gtk_drag_content_write_mime_type_async);
+
+  sdata.selection = gdk_drag_get_selection (content->context);
+  sdata.target = gdk_atom_intern (mime_type, FALSE);
+  sdata.length = -1;
+  sdata.display = gtk_widget_get_display (content->widget);
+  
+  g_signal_emit_by_name (content->widget, "drag-data-get",
+                         content->context,
+                         &sdata,
+                         content->time);
+
+  if (sdata.length == -1)
+    {
+      g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_FAILED,
+                               _("Cannot provide contents as “%s”"), mime_type);
+      g_object_unref (task);
+      return;
+    }
+  g_task_set_task_data (task, sdata.data, g_free);
+
+  g_output_stream_write_all_async (stream,
+                                   sdata.data,
+                                   sdata.length,
+                                   io_priority,
+                                   cancellable,
+                                   gtk_drag_content_write_mime_type_done,
+                                   task);
+}
+
+static gboolean
+gtk_drag_content_write_mime_type_finish (GdkContentProvider  *provider,
+                                         GAsyncResult        *result,
+                                         GError             **error)
+{
+  g_return_val_if_fail (g_task_is_valid (result, provider), FALSE);
+  g_return_val_if_fail (g_task_get_source_tag (G_TASK (result)) == gtk_drag_content_write_mime_type_async, FALSE);
+
+  return g_task_propagate_boolean (G_TASK (result), error);
+}
+
+static void
+gtk_drag_content_finalize (GObject *object)
+{
+  GtkDragContent *content = GTK_DRAG_CONTENT (object);
+
+  g_clear_object (&content->widget);
+  g_clear_pointer (&content->formats, (GDestroyNotify) gdk_content_formats_unref);
+
+  G_OBJECT_CLASS (gtk_drag_content_parent_class)->finalize (object);
+}
+
+static void
+gtk_drag_content_class_init (GtkDragContentClass *class)
+{
+  GdkContentProviderClass *provider_class = GDK_CONTENT_PROVIDER_CLASS (class);
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  object_class->finalize = gtk_drag_content_finalize;
+
+  provider_class->ref_formats = gtk_drag_content_ref_formats;
+  provider_class->write_mime_type_async = gtk_drag_content_write_mime_type_async;
+  provider_class->write_mime_type_finish = gtk_drag_content_write_mime_type_finish;
+}
+
+static void
+gtk_drag_content_init (GtkDragContent *content)
+{
+}
+
 /* Like gtk_drag_begin(), but also takes a GtkIconHelper
  * so that we can set the icon from the source site information
  */
@@ -979,6 +1123,7 @@ gtk_drag_begin_internal (GtkWidget          *widget,
   GdkWindow *ipc_window;
   int dx, dy;
   GdkAtom selection;
+  GtkDragContent *content;
   guint32 time;
 
   ipc_widget = gtk_drag_get_ipc_widget (widget);
@@ -1001,13 +1146,22 @@ gtk_drag_begin_internal (GtkWidget          *widget,
   dx -= x;
   dy -= y;
 
-  context = gdk_drag_begin (ipc_window, device, target_list, actions, dx, dy);
+  content = g_object_new (GTK_TYPE_DRAG_CONTENT, NULL);
+  content->widget = g_object_ref (widget);
+  content->formats = gdk_content_formats_ref (target_list);
+  content->time = time;
+
+  context = gdk_drag_begin (ipc_window, device, GDK_CONTENT_PROVIDER (content), actions, dx, dy);
   if (context == NULL)
     {
       gtk_drag_release_ipc_widget (ipc_widget);
+      g_object_unref (content);
       return NULL;
     }
 
+  content->context = context;
+  g_object_unref (content);
+
   info = gtk_drag_get_source_info (context, TRUE);
 
   info->ipc_widget = ipc_widget;