clipboard: Implement local fallback clipboard transfers

This requires implementing a "pipe" so we can have 2 streams running:
  contentprovider => serializer => outputstream
  inputstream => deserializer => reader
And the pipe shoves the data from the outputstream into the inputstream.

5 files changed, 646 insertions, 4 deletions

diff --git a/gdk/gdkclipboard.c b/gdk/gdkclipboard.c
index 7ba9632991..b19b0904aa 100644
--- a/gdk/gdkclipboard.c
+++ b/gdk/gdkclipboard.c
@@ -26,6 +26,7 @@
 #include "gdkcontentproviderprivate.h"
 #include "gdkdisplay.h"
 #include "gdkintl.h"
+#include "gdkpipeiostreamprivate.h"
 
 typedef struct _GdkClipboardPrivate GdkClipboardPrivate;
 
@@ -124,6 +125,20 @@ gdk_clipboard_finalize (GObject *object)
 }
 
 static void
+gdk_clipboard_read_local_write_done (GObject      *clipboard,
+                                     GAsyncResult *result,
+                                     gpointer      stream)
+{
+  /* we don't care about the error, we just want to clean up */
+  gdk_clipboard_write_finish (GDK_CLIPBOARD (clipboard), result, NULL);
+
+  /* XXX: Do we need to close_async() here? */
+  g_output_stream_close (stream, NULL, NULL);
+
+  g_object_unref (stream);
+}
+
+static void
 gdk_clipboard_read_local_async (GdkClipboard        *clipboard,
                                 GdkContentFormats   *formats,
                                 int                  io_priority,
@@ -132,24 +147,51 @@ gdk_clipboard_read_local_async (GdkClipboard        *clipboard,
                                 gpointer             user_data)
 {
   GdkClipboardPrivate *priv = gdk_clipboard_get_instance_private (clipboard);
+  GdkContentFormats *content_formats;
+  const char *mime_type;
   GTask *task;
 
   task = g_task_new (clipboard, cancellable, callback, user_data);
   g_task_set_priority (task, io_priority);
   g_task_set_source_tag (task, gdk_clipboard_read_local_async);
-  g_task_set_task_data (task, gdk_content_formats_ref (formats), (GDestroyNotify) gdk_content_formats_unref);
 
   if (priv->content == NULL)
     {
       g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_NOT_FOUND,
                                      _("Cannot read from empty clipboard."));
+      g_object_unref (task);
+      return;
     }
-  else
+
+  content_formats = gdk_content_provider_ref_formats (priv->content);
+
+  if (!gdk_content_formats_match (content_formats, formats, NULL, &mime_type)
+      || mime_type == NULL)
     {
       g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
-                               _("Reading local content via streams not supported yet."));
+                                     _("No compatible formats to transfer clipboard contents."));
+    }
+  else
+    {
+      GOutputStream *output_stream;
+      GIOStream *stream;
+      
+      stream = gdk_pipe_io_stream_new ();
+      output_stream = g_io_stream_get_output_stream (stream);
+      gdk_clipboard_write_async (clipboard,
+                                 mime_type,
+                                 output_stream,
+                                 io_priority,
+                                 cancellable,
+                                 gdk_clipboard_read_local_write_done,
+                                 g_object_ref (output_stream));
+      g_task_set_task_data (task, (gpointer) mime_type, NULL);
+      g_task_return_pointer (task, g_object_ref (g_io_stream_get_input_stream (stream)), g_object_unref);
+
+      g_object_unref (stream);
     }
 
+  gdk_content_formats_unref (content_formats);
   g_object_unref (task);
 }
 
@@ -163,7 +205,7 @@ gdk_clipboard_read_local_finish (GdkClipboard  *clipboard,
   g_return_val_if_fail (g_task_get_source_tag (G_TASK (result)) == gdk_clipboard_read_local_async, NULL);
 
   if (out_mime_type)
-    *out_mime_type = NULL;
+    *out_mime_type = g_task_get_task_data (G_TASK (result));
 
   return g_task_propagate_pointer (G_TASK (result), error);
 }
@@ -770,6 +812,86 @@ gdk_clipboard_new (GdkDisplay *display)
 }
 
 static void
+gdk_clipboard_write_done (GObject      *content,
+                          GAsyncResult *result,
+                          gpointer      task)
+{
+  GError *error = NULL;
+
+  if (gdk_content_provider_write_mime_type_finish (GDK_CONTENT_PROVIDER (content), result, &error))
+    g_task_return_boolean (task, TRUE);
+  else
+    g_task_return_error (task, error);
+
+  g_object_unref (task);
+}
+
+void
+gdk_clipboard_write_async (GdkClipboard        *clipboard,
+                           const char          *mime_type,
+                           GOutputStream       *stream,
+                           int                  io_priority,
+                           GCancellable        *cancellable,
+                           GAsyncReadyCallback  callback,
+                           gpointer             user_data)
+{
+  GdkClipboardPrivate *priv = gdk_clipboard_get_instance_private (clipboard);
+  GdkContentFormats *formats;
+  GTask *task;
+
+  g_return_if_fail (GDK_IS_CLIPBOARD (clipboard));
+  g_return_if_fail (priv->local);
+  g_return_if_fail (mime_type != NULL);
+  g_return_if_fail (mime_type == g_intern_string (mime_type));
+  g_return_if_fail (G_IS_OUTPUT_STREAM (stream));
+  g_return_if_fail (cancellable == NULL || G_IS_CANCELLABLE (cancellable));
+  g_return_if_fail (callback != NULL);
+
+  task = g_task_new (clipboard, cancellable, callback, user_data);
+  g_task_set_priority (task, io_priority);
+  g_task_set_source_tag (task, gdk_clipboard_write_async);
+
+  if (priv->content == NULL)
+    {
+      g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_NOT_FOUND,
+                               _("Cannot read from empty clipboard."));
+      g_object_unref (task);
+      return;
+    }
+
+  formats = gdk_content_provider_ref_formats (priv->content);
+  if (gdk_content_formats_contain_mime_type (formats, mime_type))
+    {
+      gdk_content_provider_write_mime_type_async (priv->content,
+                                                  mime_type,
+                                                  stream,
+                                                  io_priority,
+                                                  cancellable,
+                                                  gdk_clipboard_write_done,
+                                                  task);
+      gdk_content_formats_unref (formats);
+      return;
+    }
+
+  g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
+                           _("FIXME: Implement serializing."));
+  gdk_content_formats_unref (formats);
+  g_object_unref (task);
+  return;
+}
+
+gboolean
+gdk_clipboard_write_finish (GdkClipboard  *clipboard,
+                            GAsyncResult  *result,
+                            GError       **error)
+{
+  g_return_val_if_fail (g_task_is_valid (result, clipboard), FALSE);
+  g_return_val_if_fail (g_task_get_source_tag (G_TASK (result)) == gdk_clipboard_write_async, FALSE);
+
+  return g_task_propagate_boolean (G_TASK (result), error); 
+}
+
+static void
 gdk_clipboard_content_changed_cb (GdkContentProvider *provider,
                                   GdkClipboard       *clipboard);
 
diff --git a/gdk/gdkclipboardprivate.h b/gdk/gdkclipboardprivate.h
index b171068a5f..73b198eacf 100644
--- a/gdk/gdkclipboardprivate.h
+++ b/gdk/gdkclipboardprivate.h
@@ -57,6 +57,16 @@ GdkClipboard *          gdk_clipboard_new                       (GdkDisplay
 
 void                    gdk_clipboard_claim_remote              (GdkClipboard           *clipboard,
                                                                  GdkContentFormats      *formats);
+void                    gdk_clipboard_write_async               (GdkClipboard           *clipboard,
+                                                                 const char             *mime_type,
+                                                                 GOutputStream          *stream,
+                                                                 int                     io_priority,
+                                                                 GCancellable           *cancellable,
+                                                                 GAsyncReadyCallback     callback,
+                                                                 gpointer                user_data);
+gboolean                gdk_clipboard_write_finish              (GdkClipboard           *clipboard,
+                                                                 GAsyncResult           *result,
+                                                                 GError                **error);
 
 G_END_DECLS
 
diff --git a/gdk/gdkpipeiostream.c b/gdk/gdkpipeiostream.c
new file mode 100644
index 0000000000..c7e0b6c32e
--- /dev/null
+++ b/gdk/gdkpipeiostream.c
@@ -0,0 +1,476 @@
+/* GDK - The GIMP Drawing Kit
+ *
+ * Copyright (C) 2017 Benjamin Otte <otte@gnome.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "config.h"
+
+#include "gdkpipeiostreamprivate.h"
+
+#include <string.h>
+
+/* PIPE */
+
+typedef enum {
+  GDK_IO_PIPE_EMPTY,
+  GDK_IO_PIPE_INPUT_BUFFER,
+  GDK_IO_PIPE_OUTPUT_BUFFER
+} GdkIOPipeState;
+
+typedef struct _GdkIOPipe GdkIOPipe;
+
+struct _GdkIOPipe
+{
+  gint ref_count;
+
+  GMutex mutex;
+  GCond cond;
+  guchar *buffer;
+  gsize size;
+  GdkIOPipeState state : 2;
+  guint input_closed : 1;
+  guint output_closed : 1;
+};
+
+static GdkIOPipe *
+gdk_io_pipe_new (void)
+{
+  GdkIOPipe *pipe;
+
+  pipe = g_slice_new0 (GdkIOPipe);
+  pipe->ref_count = 1;
+
+  g_mutex_init (&pipe->mutex);
+  g_cond_init (&pipe->cond);
+
+  return pipe;
+}
+
+static GdkIOPipe *
+gdk_io_pipe_ref (GdkIOPipe *pipe)
+{
+  g_atomic_int_inc (&pipe->ref_count);
+
+  return pipe;
+}
+
+static void
+gdk_io_pipe_unref (GdkIOPipe *pipe)
+{
+  if (!g_atomic_int_dec_and_test (&pipe->ref_count))
+    return;
+
+  g_cond_clear (&pipe->cond);
+  g_mutex_clear (&pipe->mutex);
+}
+
+static void
+gdk_io_pipe_lock (GdkIOPipe *pipe)
+{
+  g_mutex_lock (&pipe->mutex);
+}
+
+static void
+gdk_io_pipe_unlock (GdkIOPipe *pipe)
+{
+  g_mutex_unlock (&pipe->mutex);
+}
+
+/* INPUT STREAM */
+
+#define GDK_TYPE_PIPE_INPUT_STREAM            (gdk_pipe_input_stream_get_type ())
+#define GDK_PIPE_INPUT_STREAM(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GDK_TYPE_PIPE_INPUT_STREAM, GdkPipeInputStream))
+#define GDK_IS_PIPE_INPUT_STREAM(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GDK_TYPE_PIPE_INPUT_STREAM))
+#define GDK_PIPE_INPUT_STREAM_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GDK_TYPE_PIPE_INPUT_STREAM, GdkPipeInputStreamClass))
+#define GDK_IS_PIPE_INPUT_STREAM_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GDK_TYPE_PIPE_INPUT_STREAM))
+#define GDK_PIPE_INPUT_STREAM_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GDK_TYPE_PIPE_INPUT_STREAM, GdkPipeInputStreamClass))
+
+typedef struct _GdkPipeInputStream GdkPipeInputStream;
+typedef struct _GdkPipeInputStreamClass GdkPipeInputStreamClass;
+
+struct _GdkPipeInputStream
+{
+  GInputStream parent;
+
+  GdkIOPipe *pipe;
+};
+
+struct _GdkPipeInputStreamClass
+{
+  GInputStreamClass parent_class;
+};
+
+GType gdk_pipe_input_stream_get_type (void) G_GNUC_CONST;
+
+G_DEFINE_TYPE (GdkPipeInputStream, gdk_pipe_input_stream, G_TYPE_INPUT_STREAM)
+
+static void
+gdk_pipe_input_stream_finalize (GObject *object)
+{
+  GdkPipeInputStream *pipe = GDK_PIPE_INPUT_STREAM (object);
+
+  g_clear_pointer (&pipe->pipe, gdk_io_pipe_unref);
+
+  G_OBJECT_CLASS (gdk_pipe_input_stream_parent_class)->finalize (object);
+}
+
+static gssize
+gdk_pipe_input_stream_read (GInputStream  *stream,
+                            void          *buffer,
+                            gsize          count,
+                            GCancellable  *cancellable,
+                            GError       **error)
+{
+  GdkPipeInputStream *pipe_stream = GDK_PIPE_INPUT_STREAM (stream);
+  GdkIOPipe *pipe = pipe_stream->pipe;
+  gsize amount;
+
+  gdk_io_pipe_lock (pipe);
+
+  switch (pipe->state)
+  {
+    case GDK_IO_PIPE_EMPTY:
+      if (pipe->output_closed)
+        {
+          amount = 0;
+          break;
+        }
+      pipe->buffer = buffer;
+      pipe->size = count;
+      pipe->state = GDK_IO_PIPE_INPUT_BUFFER;
+      do
+        g_cond_wait (&pipe->cond, &pipe->mutex);
+      while (pipe->size == count && 
+             pipe->state == GDK_IO_PIPE_INPUT_BUFFER &&
+             !pipe->output_closed);
+      if (pipe->state == GDK_IO_PIPE_INPUT_BUFFER)
+        {
+          amount = count - pipe->size;
+          pipe->state = GDK_IO_PIPE_EMPTY;
+          pipe->size = 0;
+        }
+      else
+        {
+          amount = count;
+        }
+      break;
+
+    case GDK_IO_PIPE_OUTPUT_BUFFER:
+      amount = MIN (count, pipe->size);
+      
+      memcpy (buffer, pipe->buffer, amount);
+      count -= amount;
+      pipe->size -= amount;
+
+      if (pipe->size == 0)
+        pipe->state = GDK_IO_PIPE_EMPTY;
+      else
+        pipe->buffer += amount;
+      break;
+
+    case GDK_IO_PIPE_INPUT_BUFFER:
+    default:
+      g_assert_not_reached ();
+      amount = 0;
+      break;
+  }
+    
+  g_cond_broadcast (&pipe->cond);
+  gdk_io_pipe_unlock (pipe);
+
+  return amount;
+}
+
+static gboolean
+gdk_pipe_input_stream_close (GInputStream  *stream,
+                             GCancellable  *cancellable,
+                             GError       **error)
+{
+  GdkPipeInputStream *pipe_stream = GDK_PIPE_INPUT_STREAM (stream);
+  GdkIOPipe *pipe = pipe_stream->pipe;
+
+  gdk_io_pipe_lock (pipe);
+
+  pipe->input_closed = TRUE;
+  g_cond_broadcast (&pipe->cond);
+    
+  gdk_io_pipe_unlock (pipe);
+
+  return TRUE;
+}
+
+static void
+gdk_pipe_input_stream_class_init (GdkPipeInputStreamClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GInputStreamClass *input_stream_class = G_INPUT_STREAM_CLASS (class);
+
+  object_class->finalize = gdk_pipe_input_stream_finalize;
+
+  input_stream_class->read_fn = gdk_pipe_input_stream_read;
+  input_stream_class->close_fn = gdk_pipe_input_stream_close;
+}
+
+static void
+gdk_pipe_input_stream_init (GdkPipeInputStream *pipe)
+{
+}
+
+/* OUTPUT STREAM */
+
+#define GDK_TYPE_PIPE_OUTPUT_STREAM            (gdk_pipe_output_stream_get_type ())
+#define GDK_PIPE_OUTPUT_STREAM(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GDK_TYPE_PIPE_OUTPUT_STREAM, GdkPipeOutputStream))
+#define GDK_IS_PIPE_OUTPUT_STREAM(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GDK_TYPE_PIPE_OUTPUT_STREAM))
+#define GDK_PIPE_OUTPUT_STREAM_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GDK_TYPE_PIPE_OUTPUT_STREAM, GdkPipeOutputStreamClass))
+#define GDK_IS_PIPE_OUTPUT_STREAM_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GDK_TYPE_PIPE_OUTPUT_STREAM))
+#define GDK_PIPE_OUTPUT_STREAM_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GDK_TYPE_PIPE_OUTPUT_STREAM, GdkPipeOutputStreamClass))
+
+typedef struct _GdkPipeOutputStream GdkPipeOutputStream;
+typedef struct _GdkPipeOutputStreamClass GdkPipeOutputStreamClass;
+
+struct _GdkPipeOutputStream
+{
+  GOutputStream parent;
+
+  GdkIOPipe *pipe;
+};
+
+struct _GdkPipeOutputStreamClass
+{
+  GOutputStreamClass parent_class;
+};
+
+GType gdk_pipe_output_stream_get_type (void) G_GNUC_CONST;
+
+G_DEFINE_TYPE (GdkPipeOutputStream, gdk_pipe_output_stream, G_TYPE_OUTPUT_STREAM)
+
+static void
+gdk_pipe_output_stream_finalize (GObject *object)
+{
+  GdkPipeOutputStream *pipe = GDK_PIPE_OUTPUT_STREAM (object);
+
+  g_clear_pointer (&pipe->pipe, gdk_io_pipe_unref);
+
+  G_OBJECT_CLASS (gdk_pipe_output_stream_parent_class)->finalize (object);
+}
+
+static gssize
+gdk_pipe_output_stream_write (GOutputStream  *stream,
+                              const void     *buffer,
+                              gsize           count,
+                              GCancellable   *cancellable,
+                              GError        **error)
+{
+  GdkPipeOutputStream *pipe_stream = GDK_PIPE_OUTPUT_STREAM (stream);
+  GdkIOPipe *pipe = pipe_stream->pipe;
+  gsize amount;
+
+  gdk_io_pipe_lock (pipe);
+
+  switch (pipe->state)
+  {
+    case GDK_IO_PIPE_EMPTY:
+      pipe->buffer = (void *) buffer;
+      pipe->size = count;
+      pipe->state = GDK_IO_PIPE_OUTPUT_BUFFER;
+      while (pipe->size == count && 
+             pipe->state == GDK_IO_PIPE_OUTPUT_BUFFER &&
+             !pipe->input_closed)
+        g_cond_wait (&pipe->cond, &pipe->mutex);
+      if (pipe->state == GDK_IO_PIPE_OUTPUT_BUFFER)
+        {
+          amount = count - pipe->size;
+          pipe->state = GDK_IO_PIPE_EMPTY;
+          pipe->size = 0;
+          if (pipe->input_closed && amount == 0)
+            amount = count;
+        }
+      else
+        {
+          amount = count;
+        }
+      break;
+
+    case GDK_IO_PIPE_INPUT_BUFFER:
+      amount = MIN (count, pipe->size);
+      
+      memcpy (pipe->buffer, buffer, amount);
+      count -= amount;
+      pipe->size -= amount;
+
+      if (pipe->size == 0)
+        pipe->state = GDK_IO_PIPE_EMPTY;
+      else
+        pipe->buffer += amount;
+      break;
+
+    case GDK_IO_PIPE_OUTPUT_BUFFER:
+    default:
+      g_assert_not_reached ();
+      amount = 0;
+      break;
+  }
+    
+  g_cond_broadcast (&pipe->cond);
+  gdk_io_pipe_unlock (pipe);
+
+  return amount;
+}
+
+static gboolean
+gdk_pipe_output_stream_close (GOutputStream  *stream,
+                              GCancellable  *cancellable,
+                              GError       **error)
+{
+  GdkPipeOutputStream *pipe_stream = GDK_PIPE_OUTPUT_STREAM (stream);
+  GdkIOPipe *pipe = pipe_stream->pipe;
+
+  gdk_io_pipe_lock (pipe);
+
+  pipe->output_closed = TRUE;
+    
+  g_cond_broadcast (&pipe->cond);
+  gdk_io_pipe_unlock (pipe);
+
+  return TRUE;
+}
+
+static void
+gdk_pipe_output_stream_class_init (GdkPipeOutputStreamClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GOutputStreamClass *output_stream_class = G_OUTPUT_STREAM_CLASS (class);
+
+  object_class->finalize = gdk_pipe_output_stream_finalize;
+
+  output_stream_class->write_fn = gdk_pipe_output_stream_write;
+  output_stream_class->close_fn = gdk_pipe_output_stream_close;
+}
+
+static void
+gdk_pipe_output_stream_init (GdkPipeOutputStream *pipe)
+{
+}
+
+/* IOSTREAM */
+
+#define GDK_TYPE_PIPE_IO_STREAM            (gdk_pipe_io_stream_get_type ())
+#define GDK_PIPE_IO_STREAM(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), GDK_TYPE_PIPE_IO_STREAM, GdkPipeIOStream))
+#define GDK_IS_PIPE_IO_STREAM(obj)         (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GDK_TYPE_PIPE_IO_STREAM))
+#define GDK_PIPE_IO_STREAM_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GDK_TYPE_PIPE_IO_STREAM, GdkPipeIOStreamClass))
+#define GDK_IS_PIPE_IO_STREAM_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GDK_TYPE_PIPE_IO_STREAM))
+#define GDK_PIPE_IO_STREAM_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GDK_TYPE_PIPE_IO_STREAM, GdkPipeIOStreamClass))
+
+typedef struct _GdkPipeIOStream GdkPipeIOStream;
+typedef struct _GdkPipeIOStreamClass GdkPipeIOStreamClass;
+
+struct _GdkPipeIOStream
+{
+  GIOStream parent;
+
+  GInputStream *input_stream;
+  GOutputStream *output_stream;
+  GdkIOPipe *pipe;
+};
+
+struct _GdkPipeIOStreamClass
+{
+  GIOStreamClass parent_class;
+};
+
+GType gdk_pipe_io_stream_get_type (void) G_GNUC_CONST;
+
+G_DEFINE_TYPE (GdkPipeIOStream, gdk_pipe_io_stream, G_TYPE_IO_STREAM)
+
+static void
+gdk_pipe_io_stream_finalize (GObject *object)
+{
+  GdkPipeIOStream *pipe = GDK_PIPE_IO_STREAM (object);
+
+  g_clear_object (&pipe->input_stream);
+  g_clear_object (&pipe->output_stream);
+  g_clear_pointer (&pipe->pipe, gdk_io_pipe_unref);
+
+  G_OBJECT_CLASS (gdk_pipe_io_stream_parent_class)->finalize (object);
+}
+
+static GInputStream *
+gdk_pipe_io_stream_get_input_stream (GIOStream *stream)
+{
+  GdkPipeIOStream *pipe = GDK_PIPE_IO_STREAM (stream);
+
+  return pipe->input_stream;
+}
+
+static GOutputStream *
+gdk_pipe_io_stream_get_output_stream (GIOStream *stream)
+{
+  GdkPipeIOStream *pipe = GDK_PIPE_IO_STREAM (stream);
+
+  return pipe->output_stream;
+}
+
+static gboolean
+gdk_pipe_io_stream_close (GIOStream     *stream,
+                          GCancellable  *cancellable,
+                          GError       **error)
+{
+  /* overwrite so we don't close the 2 streams */
+  return TRUE;
+}
+
+static void
+gdk_pipe_io_stream_class_init (GdkPipeIOStreamClass *class)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+  GIOStreamClass *io_class = G_IO_STREAM_CLASS (class);
+
+  object_class->finalize = gdk_pipe_io_stream_finalize;
+
+  io_class->get_input_stream = gdk_pipe_io_stream_get_input_stream;
+  io_class->get_output_stream = gdk_pipe_io_stream_get_output_stream;
+  io_class->close_fn = gdk_pipe_io_stream_close;
+}
+
+static void
+gdk_pipe_io_stream_init (GdkPipeIOStream *pipe)
+{
+  pipe->pipe = gdk_io_pipe_new ();
+
+  pipe->input_stream = g_object_new (GDK_TYPE_PIPE_INPUT_STREAM, NULL);
+  GDK_PIPE_INPUT_STREAM (pipe->input_stream)->pipe = gdk_io_pipe_ref (pipe->pipe);
+
+  pipe->output_stream = g_object_new (GDK_TYPE_PIPE_OUTPUT_STREAM, NULL);
+  GDK_PIPE_OUTPUT_STREAM (pipe->output_stream)->pipe = gdk_io_pipe_ref (pipe->pipe);
+}
+
+/**
+ * gdk_pipe_io_stream_new:
+ *
+ * Creates a #GIOStream whose input- and output-stream behave like a pipe.
+ * Data written into the output stream becomes available for reading on
+ * the input stream.
+ *
+ * Note that this is data transfer in the opposite direction to
+ * g_output_stream_splice().
+ *
+ * Returns: a new #GIOStream
+ **/
+GIOStream *
+gdk_pipe_io_stream_new (void)
+{
+  return g_object_new (GDK_TYPE_PIPE_IO_STREAM, NULL);
+}
diff --git a/gdk/gdkpipeiostreamprivate.h b/gdk/gdkpipeiostreamprivate.h
new file mode 100644
index 0000000000..50af59defe
--- /dev/null
+++ b/gdk/gdkpipeiostreamprivate.h
@@ -0,0 +1,33 @@
+/* GDK - The GIMP Drawing Kit
+ *
+ * Copyright (C) 2017 Benjamin Otte <otte@gnome.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __GDK_PIPE_IO_STREAM_H__
+#define __GDK_PIPE_IO_STREAM_H__
+
+#include <gdk/gdkversionmacros.h>
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+
+GIOStream *             gdk_pipe_io_stream_new                          (void);
+
+
+G_END_DECLS
+
+#endif /* __GDK_PIPE_IO_STREAM_H__ */
diff --git a/gdk/meson.build b/gdk/meson.build
index 968dd5d14f..b13e9c79da 100644
--- a/gdk/meson.build
+++ b/gdk/meson.build
@@ -28,6 +28,7 @@ gdk_public_sources = files([
   'gdkmonitor.c',
   'gdkpango.c',
   'gdkpixbuf-drawable.c',
+  'gdkpipeiostream.c',
   'gdkproperty.c',
   'gdkrectangle.c',
   'gdkrgba.c',