ARROW-863: [GLib] Use GBytes to implement zero-copy

Author: Kouhei Sutou <[email protected]>

Closes apache#572 from kou/glib-buffer-use-gbytes and squashes the following commits:

dc37de3 [Kouhei Sutou] [GLib] Use GBytes to implement zero-copy

c_glib/arrow-glib/buffer.cpp

@@ -167,18 +167,19 @@ garrow_buffer_get_capacity(GArrowBuffer *buffer)
 /**
  * garrow_buffer_get_data:
  * @buffer: A #GArrowBuffer.
- * @size: (out): The number of bytes of the data.
  *
- * Returns: (array length=size): The data of the buffer.
+ * Returns: (transfer full): The data of the buffer. The data is owned by
+ *   the buffer. You should not free or modify the data.
  *
  * Since: 0.3.0
  */
-const guint8 *
-garrow_buffer_get_data(GArrowBuffer *buffer, gint64 *size)
+GBytes *
+garrow_buffer_get_data(GArrowBuffer *buffer)
 {
   auto arrow_buffer = garrow_buffer_get_raw(buffer);
-  *size = arrow_buffer->size();
-  return arrow_buffer->data();
+  auto data = g_bytes_new_static(arrow_buffer->data(),
+                                 arrow_buffer->size());
+  return data;
 }
 
 /**

c_glib/arrow-glib/buffer.h

@@ -61,8 +61,7 @@ GArrowBuffer  *garrow_buffer_new          (const guint8 *data,
                                            gint64 size);
 gboolean       garrow_buffer_is_mutable   (GArrowBuffer *buffer);
 gint64         garrow_buffer_get_capacity (GArrowBuffer *buffer);
-const guint8  *garrow_buffer_get_data     (GArrowBuffer *buffer,
-                                           gint64 *size);
+GBytes        *garrow_buffer_get_data     (GArrowBuffer *buffer);
 gint64         garrow_buffer_get_size     (GArrowBuffer *buffer);
 GArrowBuffer  *garrow_buffer_get_parent   (GArrowBuffer *buffer);
 

c_glib/test/test-buffer.rb

@@ -32,7 +32,7 @@ def test_capacity
   end
 
   def test_data
-    assert_equal(@data, @buffer.data.pack("C*"))
+    assert_equal(@data, @buffer.data.to_s)
   end
 
   def test_size
@@ -45,11 +45,11 @@ def test_parent
 
   def test_copy
     copied_buffer = @buffer.copy(1, 3)
-    assert_equal(@data[1, 3], copied_buffer.data.pack("C*"))
+    assert_equal(@data[1, 3], copied_buffer.data.to_s)
   end
 
   def test_slice
     sliced_buffer = @buffer.slice(1, 3)
-    assert_equal(@data[1, 3], sliced_buffer.data.pack("C*"))
+    assert_equal(@data[1, 3], sliced_buffer.data.to_s)
   end
 end

c_glib/test/test-tensor.rb

@@ -49,7 +49,7 @@ def test_value_type
   end
 
   def test_buffer
-    assert_equal(@raw_data, @tensor.buffer.data)
+    assert_equal(@raw_data, @tensor.buffer.data.to_s.unpack("c*"))
   end
 
   def test_shape