file: add g_file_load_bytes()

This adds g_file_load_bytes() to make it more convenient to
load the contents of a GFile as GBytes.

It includes a special casing for gresources to increase the
chances that the GBytes directly references the embedded data
instead of copying to the heap.

https://bugzilla.gnome.org/show_bug.cgi?id=790272

docs/reference/gio/gio-sections.txt

@@ -184,6 +184,9 @@ g_file_mount_enclosing_volume_finish
 g_file_monitor_directory
 g_file_monitor_file
 g_file_monitor
+g_file_load_bytes
+g_file_load_bytes_async
+g_file_load_bytes_finish
 g_file_load_contents
 g_file_load_contents_async
 g_file_load_contents_finish

gio/gfile.c

@@ -8092,3 +8092,191 @@ g_file_supports_thread_contexts (GFile *file)
  iface = G_FILE_GET_IFACE (file);
  return iface->supports_thread_contexts;
 }
+
+/**
+ * g_file_load_bytes:
+ * @file: a #GFile
+ * @cancellable: (nullable): a #GCancellable or %NULL
+ * @etag_out: (out) (nullable) (optional): a location to place the current
+ *     entity tag for the file, or %NULL if the entity tag is not needed
+ * @error: a location for a #GError or %NULL
+ *
+ * Loads the contents of @file and returns it as #GBytes.
+ *
+ * If @file is a resource:// based URI, the resulting bytes will reference the
+ * embedded resource instead of a copy. Otherwise, this is equivalent to calling
+ * g_file_load_contents() and g_bytes_new_take().
+ *
+ * For resources, @etag_out will be set to %NULL.
+ *
+ * The data contained in the resulting #GBytes is always zero-terminated, but
+ * this is not included in the #GBytes length. The resulting #GBytes should be
+ * freed with g_bytes_unref() when no longer in use.
+ *
+ * Returns: (transfer full): a #GBytes or %NULL and @error is set
+ *
+ * Since: 2.56
+ */
+GBytes *
+g_file_load_bytes (GFile         *file,
+                   GCancellable  *cancellable,
+                   gchar        **etag_out,
+                   GError       **error)
+{
+  gchar *contents;
+  gsize len;
+
+  g_return_val_if_fail (G_IS_FILE (file), NULL);
+  g_return_val_if_fail (cancellable == NULL || G_IS_CANCELLABLE (cancellable), NULL);
+  g_return_val_if_fail (error == NULL || *error == NULL, NULL);
+
+  if (etag_out != NULL)
+    *etag_out = NULL;
+
+  if (g_file_has_uri_scheme (file, "resource"))
+    {
+      GBytes *bytes;
+      gchar *uri, *unescaped;
+
+      uri = g_file_get_uri (file);
+      unescaped = g_uri_unescape_string (uri + strlen ("resource://"), NULL);
+      g_free (uri);
+
+      bytes = g_resources_lookup_data (unescaped, G_RESOURCE_LOOKUP_FLAGS_NONE, error);
+      g_free (unescaped);
+
+      return bytes;
+    }
+
+  /* contents is guaranteed to be \0 terminated */
+  if (g_file_load_contents (file, cancellable, &contents, &len, etag_out, error))
+    return g_bytes_new_take (g_steal_pointer (&contents), len);
+
+  return NULL;
+}
+
+static void
+g_file_load_bytes_cb (GObject      *object,
+                      GAsyncResult *result,
+                      gpointer      user_data)
+{
+  GFile *file = G_FILE (object);
+  GTask *task = user_data;
+  GError *error = NULL;
+  gchar *etag = NULL;
+  gchar *contents = NULL;
+  gsize len = 0;
+
+  g_file_load_contents_finish (file, result, &contents, &len, &etag, &error);
+  g_task_set_task_data (task, g_steal_pointer (&etag), g_free);
+
+  if (error != NULL)
+    g_task_return_error (task, g_steal_pointer (&error));
+  else
+    g_task_return_pointer (task,
+                           g_bytes_new_take (g_steal_pointer (&contents), len),
+                           (GDestroyNotify)g_bytes_unref);
+
+  g_object_unref (task);
+}
+
+/**
+ * g_file_load_bytes_async:
+ * @file: a #GFile
+ * @cancellable: (nullable): a #GCancellable or %NULL
+ * @callback: (scope async): a #GAsyncReadyCallback to call when the
+ *     request is satisfied
+ * @user_data: (closure): the data to pass to callback function
+ *
+ * Asynchronously loads the contents of @file as #GBytes.
+ *
+ * If @file is a resource:// based URI, the resulting bytes will reference the
+ * embedded resource instead of a copy. Otherwise, this is equivalent to calling
+ * g_file_load_contents_async() and g_bytes_new_take().
+ *
+ * @callback should call g_file_load_bytes_finish() to get the result of this
+ * asynchronous operation.
+ *
+ * See g_file_load_bytes() for more information.
+ *
+ * Since: 2.56
+ */
+void
+g_file_load_bytes_async (GFile               *file,
+                         GCancellable        *cancellable,
+                         GAsyncReadyCallback  callback,
+                         gpointer             user_data)
+{
+  GError *error = NULL;
+  GBytes *bytes;
+  GTask *task;
+
+  g_return_if_fail (G_IS_FILE (file));
+  g_return_if_fail (cancellable == NULL || G_IS_CANCELLABLE (cancellable));
+
+  task = g_task_new (file, cancellable, callback, user_data);
+  g_task_set_source_tag (task, g_file_load_bytes_async);
+
+  if (!g_file_has_uri_scheme (file, "resource"))
+    {
+      g_file_load_contents_async (file,
+                                  cancellable,
+                                  g_file_load_bytes_cb,
+                                  g_steal_pointer (&task));
+      return;
+    }
+
+  bytes = g_file_load_bytes (file, cancellable, NULL, &error);
+
+  if (bytes == NULL)
+    g_task_return_error (task, g_steal_pointer (&error));
+  else
+    g_task_return_pointer (task,
+                           g_steal_pointer (&bytes),
+                           (GDestroyNotify)g_bytes_unref);
+
+  g_object_unref (task);
+}
+
+/**
+ * g_file_load_bytes_finish:
+ * @file: a #GFile
+ * @result: a #GAsyncResult provided to the callback
+ * @etag_out: (out) (nullable) (optional): a location to place the current
+ *     entity tag for the file, or %NULL if the entity tag is not needed
+ * @error: a location for a #GError, or %NULL
+ *
+ * Completes an asynchronous request to g_file_load_bytes_async().
+ *
+ * For resources, @etag_out will be set to %NULL.
+ *
+ * The data contained in the resulting #GBytes is always zero-terminated, but
+ * this is not included in the #GBytes length. The resulting #GBytes should be
+ * freed with g_bytes_unref() when no longer in use.
+ *
+ * See g_file_load_bytes() for more information.
+ *
+ * Returns: (transfer full): a #GBytes or %NULL and @error is set
+ *
+ * Since: 2.56
+ */
+GBytes *
+g_file_load_bytes_finish (GFile         *file,
+                          GAsyncResult  *result,
+                          gchar        **etag_out,
+                          GError       **error)
+{
+  GBytes *bytes;
+
+  g_return_val_if_fail (G_IS_FILE (file), NULL);
+  g_return_val_if_fail (G_IS_TASK (result), NULL);
+  g_return_val_if_fail (g_task_is_valid (G_TASK (result), file), NULL);
+  g_return_val_if_fail (error == NULL || *error == NULL, NULL);
+
+  bytes = g_task_propagate_pointer (G_TASK (result), error);
+
+  if (etag_out != NULL)
+    *etag_out = g_strdup (g_task_get_task_data (G_TASK (result)));
+
+  return bytes;
+}

gio/gfile.h

@@ -1251,6 +1251,22 @@ gboolean g_file_replace_contents_finish      (GFile                  *file,
 GLIB_AVAILABLE_IN_ALL
 gboolean g_file_supports_thread_contexts     (GFile                  *file);
 
+GLIB_AVAILABLE_IN_2_56
+GBytes  *g_file_load_bytes                   (GFile                  *file,
+                                              GCancellable           *cancellable,
+                                              gchar                 **etag_out,
+                                              GError                **error);
+GLIB_AVAILABLE_IN_2_56
+void     g_file_load_bytes_async             (GFile                  *file,
+                                              GCancellable           *cancellable,
+                                              GAsyncReadyCallback     callback,
+                                              gpointer                user_data);
+GLIB_AVAILABLE_IN_2_56
+GBytes  *g_file_load_bytes_finish            (GFile                  *file,
+                                              GAsyncResult           *result,
+                                              gchar                 **etag_out,
+                                              GError                **error);
+
 G_END_DECLS
 
 #endif /* __G_FILE_H__ */