GDBusConnection.call(): add 'reply_type' argument

This allows the caller to specify the reply type that they are expecting
for this call.  If the reply comes back with the wrong type, GDBus will
generate an appropriate error internally.

  - add a GVariantType * argument to g_dbus_connection_call() and
    _call_sync().

  - move the internal API for computing message types from introspection
    data to be based on GVariantType instead of strings.  Update users
    of this code.

  - have GDBusProxy pass this calculated GVariantType into
    g_dbus_connection_call().  Remove the checks done in GDBusProxy.

  - Update other users of the code (test cases, gdbus-tool, GSettings
    tool, etc).  In some cases, remove redundant checks; in some other
    cases, we are fixing bugs because no checking was done where it
    should have been.

Closes bug #619391.

15 files changed, 246 insertions, 208 deletions

diff --git a/gio/gdbus-tool.c b/gio/gdbus-tool.c
index 4826b35d6..11ffb6cd2 100644
--- a/gio/gdbus-tool.c
+++ b/gio/gdbus-tool.c
@@ -150,6 +150,7 @@ print_methods (GDBusConnection *c,
                                         "org.freedesktop.DBus.Introspectable",
                                         "Introspect",
                                         NULL,
+                                        G_VARIANT_TYPE ("(s)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 secs */
                                         NULL,
@@ -160,13 +161,6 @@ print_methods (GDBusConnection *c,
       g_error_free (error);
       goto out;
     }
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(s)")))
-    {
-      g_printerr (_("Error: Result is type `%s', expected `(s)'\n"),
-                  g_variant_get_type_string (result));
-      g_variant_unref (result);
-      goto out;
-    }
   g_variant_get (result, "(&s)", &xml_data);
 
   error = NULL;
@@ -212,6 +206,7 @@ print_paths (GDBusConnection *c,
                                         "org.freedesktop.DBus.Introspectable",
                                         "Introspect",
                                         NULL,
+                                        G_VARIANT_TYPE ("(s)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 secs */
                                         NULL,
@@ -222,13 +217,6 @@ print_paths (GDBusConnection *c,
       g_error_free (error);
       goto out;
     }
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(s)")))
-    {
-      g_printerr (_("Error: Result is type `%s', expected `(s)'\n"),
-                  g_variant_get_type_string (result));
-      g_variant_unref (result);
-      goto out;
-    }
   g_variant_get (result, "(&s)", &xml_data);
 
   //g_printerr ("xml=`%s'", xml_data);
@@ -290,6 +278,7 @@ print_names (GDBusConnection *c,
                                         "org.freedesktop.DBus",
                                         "ListNames",
                                         NULL,
+                                        G_VARIANT_TYPE ("(as)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 secs */
                                         NULL,
@@ -300,12 +289,6 @@ print_names (GDBusConnection *c,
       g_error_free (error);
       goto out;
     }
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(as)")))
-    {
-      g_printerr (_("Error: Result is type `%s', expected `(as)'\n"), g_variant_get_type_string (result));
-      g_variant_unref (result);
-      goto out;
-    }
   g_variant_get (result, "(as)", &iter);
   while (g_variant_iter_loop (iter, "s", &str))
     g_hash_table_insert (name_set, g_strdup (str), NULL);
@@ -319,6 +302,7 @@ print_names (GDBusConnection *c,
                                         "org.freedesktop.DBus",
                                         "ListActivatableNames",
                                         NULL,
+                                        G_VARIANT_TYPE ("(as)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 secs */
                                         NULL,
@@ -329,12 +313,6 @@ print_names (GDBusConnection *c,
       g_error_free (error);
       goto out;
     }
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(as)")))
-    {
-      g_printerr (_("Error: Result is type `%s', expected `(as)'\n"), g_variant_get_type_string (result));
-      g_variant_unref (result);
-      goto out;
-    }
   g_variant_get (result, "(as)", &iter);
   while (g_variant_iter_loop (iter, "s", &str))
     g_hash_table_insert (name_set, g_strdup (str), NULL);
@@ -461,6 +439,7 @@ call_helper_get_method_in_signature (GDBusConnection  *c,
                                         "org.freedesktop.DBus.Introspectable",
                                         "Introspect",
                                         NULL,
+                                        G_VARIANT_TYPE ("(s)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 secs */
                                         NULL,
@@ -468,14 +447,6 @@ call_helper_get_method_in_signature (GDBusConnection  *c,
   if (result == NULL)
     goto out;
 
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(s)")))
-    {
-      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                   _("Error: Result is type `%s', expected `(s)'\n"),
-                   g_variant_get_type_string (result));
-      goto out;
-    }
-
   g_variant_get (result, "(&s)", &xml_data);
   node_info = g_dbus_node_info_new_for_xml (xml_data, error);
   if (node_info == NULL)
@@ -833,6 +804,7 @@ handle_call (gint        *argc,
                                         interface_name,
                                         method_name,
                                         parameters,
+                                        NULL,
                                         G_DBUS_CALL_FLAGS_NONE,
                                         -1,
                                         NULL,
@@ -1056,6 +1028,7 @@ dump_interface (GDBusConnection          *c,
                                             "org.freedesktop.DBus.Properties",
                                             "GetAll",
                                             g_variant_new ("(s)", o->name),
+                                            NULL,
                                             G_DBUS_CALL_FLAGS_NONE,
                                             3000,
                                             NULL,
@@ -1094,6 +1067,7 @@ dump_interface (GDBusConnection          *c,
                                                     "org.freedesktop.DBus.Properties",
                                                     "Get",
                                                     g_variant_new ("(ss)", o->name, o->properties[n]->name),
+                                                    G_VARIANT_TYPE ("(v)"),
                                                     G_DBUS_CALL_FLAGS_NONE,
                                                     3000,
                                                     NULL,
@@ -1338,6 +1312,7 @@ handle_introspect (gint        *argc,
                                         "org.freedesktop.DBus.Introspectable",
                                         "Introspect",
                                         NULL,
+                                        G_VARIANT_TYPE ("(s)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         3000, /* 3 sec */
                                         NULL,
@@ -1348,12 +1323,6 @@ handle_introspect (gint        *argc,
       g_error_free (error);
       goto out;
     }
-  if (!g_variant_is_of_type (result, G_VARIANT_TYPE ("(s)")))
-    {
-      g_printerr (_("Error: Result is type `%s', expected `(s)'\n"),
-                  g_variant_get_type_string (result));
-      goto out;
-    }
   g_variant_get (result, "(&s)", &xml_data);
 
   error = NULL;
diff --git a/gio/gdbusconnection.c b/gio/gdbusconnection.c
index 346afcfb0..b79e0010d 100644
--- a/gio/gdbusconnection.c
+++ b/gio/gdbusconnection.c
@@ -1845,6 +1845,7 @@ initable_init (GInitable     *initable,
                                                   "org.freedesktop.DBus", /* interface */
                                                   "Hello",
                                                   NULL, /* parameters */
+                                                  G_VARIANT_TYPE ("(s)"),
                                                   G_DBUS_CALL_FLAGS_NONE,
                                                   -1,
                                                   NULL, /* TODO: cancellable */
@@ -3730,7 +3731,7 @@ validate_and_maybe_schedule_method_call (GDBusConnection            *connection,
   GVariant *parameters;
   GSource *idle_source;
   gboolean handled;
-  gchar *in_signature;
+  GVariantType *in_type;
 
   handled = FALSE;
 
@@ -3752,37 +3753,41 @@ validate_and_maybe_schedule_method_call (GDBusConnection            *connection,
       goto out;
     }
 
+  parameters = g_dbus_message_get_body (message);
+  if (parameters == NULL)
+    {
+      parameters = g_variant_new ("()");
+      g_variant_ref_sink (parameters);
+    }
+  else
+    {
+      g_variant_ref (parameters);
+    }
+
   /* Check that the incoming args are of the right type - if they are not, return
    * the org.freedesktop.DBus.Error.InvalidArgs error to the caller
-   *
-   * TODO: might also be worth caching the combined signature.
    */
-  in_signature = _g_dbus_compute_complete_signature (method_info->in_args, FALSE);
-  if (g_strcmp0 (g_dbus_message_get_signature (message), in_signature) != 0)
+  in_type = _g_dbus_compute_complete_signature (method_info->in_args);
+  if (!g_variant_is_of_type (parameters, in_type))
     {
+      gchar *type_string;
+
+      type_string = g_variant_type_dup_string (in_type);
+
       reply = g_dbus_message_new_method_error (message,
                                                "org.freedesktop.DBus.Error.InvalidArgs",
-                                               _("Signature of message, `%s', does not match expected signature `%s'"),
-                                               g_dbus_message_get_signature (message),
-                                               in_signature);
+                                               _("Type of message, `%s', does not match expected type `%s'"),
+                                               g_variant_get_type_string (parameters),
+                                               type_string);
       g_dbus_connection_send_message_unlocked (connection, reply, NULL, NULL);
+      g_variant_type_free (in_type);
+      g_variant_unref (parameters);
       g_object_unref (reply);
-      g_free (in_signature);
+      g_free (type_string);
       handled = TRUE;
       goto out;
     }
-  g_free (in_signature);
-
-  parameters = g_dbus_message_get_body (message);
-  if (parameters == NULL)
-    {
-      parameters = g_variant_new ("()");
-      g_variant_ref_sink (parameters);
-    }
-  else
-    {
-      g_variant_ref (parameters);
-    }
+  g_variant_type_free (in_type);
 
   /* schedule the call in idle */
   invocation = g_dbus_method_invocation_new (g_dbus_message_get_sender (message),
@@ -4131,6 +4136,105 @@ add_call_flags (GDBusMessage           *message,
     g_dbus_message_set_flags (message, G_DBUS_MESSAGE_FLAGS_NO_AUTO_START);
 }
 
+static GVariant *
+decode_method_reply (GDBusMessage        *reply,
+                     const gchar         *method_name,
+                     const GVariantType  *reply_type,
+                     GError             **error)
+{
+  GVariant *result;
+
+  result = NULL;
+  switch (g_dbus_message_get_message_type (reply))
+    {
+    case G_DBUS_MESSAGE_TYPE_METHOD_RETURN:
+      result = g_dbus_message_get_body (reply);
+      if (result == NULL)
+        {
+          result = g_variant_new ("()");
+          g_variant_ref_sink (result);
+        }
+      else
+        {
+          g_variant_ref (result);
+        }
+
+      if (!g_variant_is_of_type (result, reply_type))
+        {
+          gchar *type_string = g_variant_type_dup_string (reply_type);
+
+          g_set_error (error,
+                       G_IO_ERROR,
+                       G_IO_ERROR_INVALID_ARGUMENT,
+                       _("Method `%s' returned type `%s', but expected `%s'"),
+                       method_name, g_variant_get_type_string (result), type_string);
+
+          g_variant_unref (result);
+          g_free (type_string);
+          result = NULL;
+        }
+      break;
+
+    case G_DBUS_MESSAGE_TYPE_ERROR:
+      g_dbus_message_to_gerror (reply, error);
+      break;
+
+    default:
+      g_assert_not_reached ();
+      break;
+    }
+
+  return result;
+}
+
+
+typedef struct
+{
+  GSimpleAsyncResult *simple;
+  GVariantType *reply_type;
+  gchar *method_name; /* for error message */
+} CallState;
+
+static void
+g_dbus_connection_call_done (GObject      *source,
+                             GAsyncResult *result,
+                             gpointer      user_data)
+{
+  GDBusConnection *connection = G_DBUS_CONNECTION (source);
+  CallState *state = user_data;
+  GError *error = NULL;
+  GDBusMessage *reply;
+  GVariant *value;
+
+  reply = g_dbus_connection_send_message_with_reply_finish (connection,
+                                                            result, &error);
+
+  if (reply != NULL)
+    {
+      value = decode_method_reply (reply, state->method_name,
+                                   state->reply_type, &error);
+      g_object_unref (reply);
+    }
+  else
+    value = NULL;
+
+  if (value == NULL)
+    {
+      g_simple_async_result_set_from_error (state->simple, error);
+      g_error_free (error);
+    }
+  else
+    g_simple_async_result_set_op_res_gpointer (state->simple, value,
+                                               (GDestroyNotify) g_variant_unref);
+
+  g_simple_async_result_complete (state->simple);
+  g_variant_type_free (state->reply_type);
+  g_object_unref (state->simple);
+  g_free (state->method_name);
+
+  g_slice_free (CallState, state);
+}
+
 /**
  * g_dbus_connection_call:
  * @connection: A #GDBusConnection.
@@ -4139,6 +4243,7 @@ add_call_flags (GDBusMessage           *message,
  * @interface_name: D-Bus interface to invoke method on.
  * @method_name: The name of the method to invoke.
  * @parameters: A #GVariant tuple with parameters for the method or %NULL if not passing parameters.
+ * @reply_type: The expected type of the reply, or %NULL.
  * @flags: Flags from the #GDBusCallFlags enumeration.
  * @timeout_msec: The timeout in milliseconds or -1 to use the default timeout.
  * @cancellable: A #GCancellable or %NULL.
@@ -4156,6 +4261,10 @@ add_call_flags (GDBusMessage           *message,
  * not compatible with the D-Bus protocol, the operation fails with
  * %G_IO_ERROR_INVALID_ARGUMENT.
  *
+ * If @reply_type is non-%NULL then the reply will be checked for having this type and an
+ * error will be raised if it does not match.  Said another way, if you give a @reply_type
+ * then any non-%NULL return value will be of this type.
+ *
  * If the @parameters #GVariant is floating, it is consumed. This allows
  * convenient 'inline' use of g_variant_new(), e.g.:
  * |[
@@ -4167,6 +4276,7 @@ add_call_flags (GDBusMessage           *message,
  *                          g_variant_new ("(ss)",
  *                                         "Thing One",
  *                                         "Thing Two"),
+ *                          NULL,
  *                          G_DBUS_CALL_FLAGS_NONE,
  *                          -1,
  *                          NULL,
@@ -4190,6 +4300,7 @@ g_dbus_connection_call (GDBusConnection        *connection,
                         const gchar            *interface_name,
                         const gchar            *method_name,
                         GVariant               *parameters,
+                        const GVariantType     *reply_type,
                         GDBusCallFlags          flags,
                         gint                    timeout_msec,
                         GCancellable           *cancellable,
@@ -4197,6 +4308,7 @@ g_dbus_connection_call (GDBusConnection        *connection,
                         gpointer                user_data)
 {
   GDBusMessage *message;
+  CallState *state;
 
   g_return_if_fail (G_IS_DBUS_CONNECTION (connection));
   g_return_if_fail (bus_name == NULL || g_dbus_is_name (bus_name));
@@ -4206,6 +4318,17 @@ g_dbus_connection_call (GDBusConnection        *connection,
   g_return_if_fail (timeout_msec >= 0 || timeout_msec == -1);
   g_return_if_fail ((parameters == NULL) || g_variant_is_of_type (parameters, G_VARIANT_TYPE_TUPLE));
 
+  state = g_slice_new (CallState);
+  state->simple = g_simple_async_result_new (G_OBJECT (connection),
+                                             callback, user_data,
+                                             g_dbus_connection_call);
+  state->method_name = g_strjoin (".", interface_name, method_name, NULL);
+
+  if (reply_type == NULL)
+    reply_type = G_VARIANT_TYPE_ANY;
+
+  state->reply_type = g_variant_type_copy (reply_type);
+
   message = g_dbus_message_new_method_call (bus_name,
                                             object_path,
                                             interface_name,
@@ -4219,47 +4342,13 @@ g_dbus_connection_call (GDBusConnection        *connection,
                                              timeout_msec,
                                              NULL, /* volatile guint32 *out_serial */
                                              cancellable,
-                                             callback,
-                                             user_data);
+                                             g_dbus_connection_call_done,
+                                             state);
 
   if (message != NULL)
     g_object_unref (message);
 }
 
-static GVariant *
-decode_method_reply (GDBusMessage  *reply,
-                     GError       **error)
-{
-  GVariant *result;
-
-  result = NULL;
-  switch (g_dbus_message_get_message_type (reply))
-    {
-    case G_DBUS_MESSAGE_TYPE_METHOD_RETURN:
-      result = g_dbus_message_get_body (reply);
-      if (result == NULL)
-        {
-          result = g_variant_new ("()");
-          g_variant_ref_sink (result);
-        }
-      else
-        {
-          g_variant_ref (result);
-        }
-      break;
-
-    case G_DBUS_MESSAGE_TYPE_ERROR:
-      g_dbus_message_to_gerror (reply, error);
-      break;
-
-    default:
-      g_assert_not_reached ();
-      break;
-    }
-
-  return result;
-}
-
 /**
  * g_dbus_connection_call_finish:
  * @connection: A #GDBusConnection.
@@ -4278,25 +4367,19 @@ g_dbus_connection_call_finish (GDBusConnection  *connection,
                                GAsyncResult     *res,
                                GError          **error)
 {
-  GDBusMessage *reply;
-  GVariant *result;
+  GSimpleAsyncResult *simple;
 
   g_return_val_if_fail (G_IS_DBUS_CONNECTION (connection), NULL);
-  g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
+  g_return_val_if_fail (g_simple_async_result_is_valid (res, G_OBJECT (connection),
+                                                        g_dbus_connection_call), NULL);
   g_return_val_if_fail (error == NULL || *error == NULL, NULL);
 
-  result = NULL;
-
-  reply = g_dbus_connection_send_message_with_reply_finish (connection, res, error);
-  if (reply == NULL)
-    goto out;
+  simple = G_SIMPLE_ASYNC_RESULT (res);
 
-  result = decode_method_reply (reply, error);
-
-  g_object_unref (reply);
+  if (g_simple_async_result_propagate_error (simple, error))
+    return FALSE;
 
- out:
-  return result;
+  return g_variant_ref (g_simple_async_result_get_op_res_gpointer (simple));
 }
 
 /* ---------------------------------------------------------------------------------------------------- */
@@ -4309,6 +4392,7 @@ g_dbus_connection_call_finish (GDBusConnection  *connection,
  * @interface_name: D-Bus interface to invoke method on.
  * @method_name: The name of the method to invoke.
  * @parameters: A #GVariant tuple with parameters for the method or %NULL if not passing parameters.
+ * @reply_type: The expected type of the reply, or %NULL.
  * @flags: Flags from the #GDBusCallFlags enumeration.
  * @timeout_msec: The timeout in milliseconds or -1 to use the default timeout.
  * @cancellable: A #GCancellable or %NULL.
@@ -4323,6 +4407,11 @@ g_dbus_connection_call_finish (GDBusConnection  *connection,
  * operation will fail with %G_IO_ERROR_CANCELLED. If @parameters
  * contains a value not compatible with the D-Bus protocol, the operation
  * fails with %G_IO_ERROR_INVALID_ARGUMENT.
+
+ * If @reply_type is non-%NULL then the reply will be checked for having
+ * this type and an error will be raised if it does not match.  Said
+ * another way, if you give a @reply_type then any non-%NULL return
+ * value will be of this type.
  *
  * If the @parameters #GVariant is floating, it is consumed.
  * This allows convenient 'inline' use of g_variant_new(), e.g.:
@@ -4335,6 +4424,7 @@ g_dbus_connection_call_finish (GDBusConnection  *connection,
  *                               g_variant_new ("(ss)",
  *                                              "Thing One",
  *                                              "Thing Two"),
+ *                               NULL,
  *                               G_DBUS_CALL_FLAGS_NONE,
  *                               -1,
  *                               NULL,
@@ -4357,6 +4447,7 @@ g_dbus_connection_call_sync (GDBusConnection         *connection,
                              const gchar             *interface_name,
                              const gchar             *method_name,
                              GVariant                *parameters,
+                             const GVariantType      *reply_type,
                              GDBusCallFlags           flags,
                              gint                     timeout_msec,
                              GCancellable            *cancellable,
@@ -4378,6 +4469,9 @@ g_dbus_connection_call_sync (GDBusConnection         *connection,
   g_return_val_if_fail (timeout_msec >= 0 || timeout_msec == -1, NULL);
   g_return_val_if_fail ((parameters == NULL) || g_variant_is_of_type (parameters, G_VARIANT_TYPE_TUPLE), NULL);
 
+  if (reply_type == NULL)
+    reply_type = G_VARIANT_TYPE_ANY;
+
   message = g_dbus_message_new_method_call (bus_name,
                                             object_path,
                                             interface_name,
@@ -4396,7 +4490,7 @@ g_dbus_connection_call_sync (GDBusConnection         *connection,
   if (reply == NULL)
     goto out;
 
-  result = decode_method_reply (reply, error);
+  result = decode_method_reply (reply, method_name, reply_type, error);
 
  out:
   if (message != NULL)
diff --git a/gio/gdbusconnection.h b/gio/gdbusconnection.h
index 42ba47676..1055a58b1 100644
--- a/gio/gdbusconnection.h
+++ b/gio/gdbusconnection.h
@@ -179,6 +179,7 @@ void      g_dbus_connection_call                              (GDBusConnection
                                                                const gchar        *interface_name,
                                                                const gchar        *method_name,
                                                                GVariant           *parameters,
+                                                               const GVariantType *reply_type,
                                                                GDBusCallFlags      flags,
                                                                gint                timeout_msec,
                                                                GCancellable       *cancellable,
@@ -193,6 +194,7 @@ GVariant *g_dbus_connection_call_sync                         (GDBusConnection
                                                                const gchar        *interface_name,
                                                                const gchar        *method_name,
                                                                GVariant           *parameters,
+                                                               const GVariantType *reply_type,
                                                                GDBusCallFlags      flags,
                                                                gint                timeout_msec,
                                                                GCancellable       *cancellable,
diff --git a/gio/gdbusmethodinvocation.c b/gio/gdbusmethodinvocation.c
index 404652e3d..444616648 100644
--- a/gio/gdbusmethodinvocation.c
+++ b/gio/gdbusmethodinvocation.c
@@ -340,29 +340,27 @@ g_dbus_method_invocation_return_value (GDBusMethodInvocation *invocation,
   g_return_if_fail (G_IS_DBUS_METHOD_INVOCATION (invocation));
   g_return_if_fail ((parameters == NULL) || g_variant_is_of_type (parameters, G_VARIANT_TYPE_TUPLE));
 
-  if (parameters != NULL)
-    g_variant_ref_sink (parameters);
+  if (parameters == NULL)
+    parameters = g_variant_new_tuple (NULL, 0);
 
   /* if we have introspection data, check that the signature of @parameters is correct */
   if (invocation->priv->method_info != NULL)
     {
-      gchar *signature;
-      const gchar *type_string;
+      GVariantType *type;
 
-      type_string = "()";
-      if (parameters != NULL)
-        type_string = g_variant_get_type_string (parameters);
-      signature = _g_dbus_compute_complete_signature (invocation->priv->method_info->out_args, TRUE);
+      type = _g_dbus_compute_complete_signature (invocation->priv->method_info->out_args);
 
-      if (g_strcmp0 (type_string, signature) != 0)
+      if (!g_variant_is_of_type (parameters, type))
         {
-          g_warning (_("Type of return value is incorrect, got `%s', expected  `%s'"),
-                     type_string,
-                     signature);
-          g_free (signature);
+          gchar *type_string = g_variant_type_dup_string (type);
+
+          g_warning (_("Type of return value is incorrect, got `%s', expected `%s'"),
+                     g_variant_get_type_string (parameters), type_string);
+          g_variant_type_free (type);
+          g_free (type_string);
           goto out;
         }
-      g_free (signature);
+      g_variant_type_free (type);
     }
 
   reply = g_dbus_message_new_method_reply (invocation->priv->message);
@@ -377,8 +375,6 @@ g_dbus_method_invocation_return_value (GDBusMethodInvocation *invocation,
 
  out:
   g_object_unref (invocation);
-  if (parameters != NULL)
-    g_variant_unref (parameters);
 }
 
 /* ---------------------------------------------------------------------------------------------------- */
diff --git a/gio/gdbusnameowning.c b/gio/gdbusnameowning.c
index e14913217..a20a34402 100644
--- a/gio/gdbusnameowning.c
+++ b/gio/gdbusnameowning.c
@@ -403,6 +403,7 @@ has_connection (Client *client)
                           g_variant_new ("(su)",
                                          client->name,
                                          client->flags),
+                          G_VARIANT_TYPE ("(u)"),
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -681,6 +682,7 @@ g_bus_unown_name (guint owner_id)
                                                 "org.freedesktop.DBus",  /* interface name */
                                                 "ReleaseName",           /* method name */
                                                 g_variant_new ("(s)", client->name),
+                                                G_VARIANT_TYPE ("(u)"),
                                                 G_DBUS_CALL_FLAGS_NONE,
                                                 -1,
                                                 NULL,
diff --git a/gio/gdbusnamewatching.c b/gio/gdbusnamewatching.c
index 9fe944d81..8c0e7a5e1 100644
--- a/gio/gdbusnamewatching.c
+++ b/gio/gdbusnamewatching.c
@@ -368,6 +368,7 @@ invoke_get_name_owner (Client *client)
                           "org.freedesktop.DBus",  /* interface name */
                           "GetNameOwner",          /* method name */
                           g_variant_new ("(s)", client->name),
+                          G_VARIANT_TYPE ("(s)"),
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -459,6 +460,7 @@ has_connection (Client *client)
                               "org.freedesktop.DBus",  /* interface name */
                               "StartServiceByName",    /* method name */
                               g_variant_new ("(su)", client->name, 0),
+                              G_VARIANT_TYPE ("(u)"),
                               G_DBUS_CALL_FLAGS_NONE,
                               -1,
                               NULL,
diff --git a/gio/gdbusprivate.c b/gio/gdbusprivate.c
index 186ba7f58..51e8e798c 100644
--- a/gio/gdbusprivate.c
+++ b/gio/gdbusprivate.c
@@ -1035,25 +1035,29 @@ _g_dbus_initialize (void)
 
 /* ---------------------------------------------------------------------------------------------------- */
 
-gchar *
-_g_dbus_compute_complete_signature (GDBusArgInfo **args,
-                                    gboolean       include_parentheses)
+GVariantType *
+_g_dbus_compute_complete_signature (GDBusArgInfo **args)
 {
-  GString *s;
+  const GVariantType *arg_types[256];
   guint n;
 
-  if (include_parentheses)
-    s = g_string_new ("(");
-  else
-    s = g_string_new ("");
-  if (args != NULL)
+  if (args)
     for (n = 0; args[n] != NULL; n++)
-      g_string_append (s, args[n]->signature);
+      {
+        /* DBus places a hard limit of 255 on signature length.
+         * therefore number of args must be less than 256.
+         */
+        g_assert (n < 256);
 
-  if (include_parentheses)
-    g_string_append_c (s, ')');
+        arg_types[n] = G_VARIANT_TYPE (args[n]->signature);
+
+        if G_UNLIKELY (arg_types[n] == NULL)
+          return NULL;
+      }
+  else
+    n = 0;
 
-  return g_string_free (s, FALSE);
+  return g_variant_type_new_tuple (arg_types, n);
 }
 
 /* ---------------------------------------------------------------------------------------------------- */
diff --git a/gio/gdbusprivate.h b/gio/gdbusprivate.h
index 09ec56d62..ba2c8f488 100644
--- a/gio/gdbusprivate.h
+++ b/gio/gdbusprivate.h
@@ -73,8 +73,7 @@ gboolean _g_dbus_address_parse_entry (const gchar  *address_entry,
                                       GHashTable  **out_key_value_pairs,
                                       GError      **error);
 
-gchar * _g_dbus_compute_complete_signature (GDBusArgInfo **args,
-                                            gboolean       include_parentheses);
+GVariantType * _g_dbus_compute_complete_signature (GDBusArgInfo **args);
 
 /* ---------------------------------------------------------------------------------------------------- */
 
diff --git a/gio/gdbusproxy.c b/gio/gdbusproxy.c
index 51cb5f2ba..8be309f0b 100644
--- a/gio/gdbusproxy.c
+++ b/gio/gdbusproxy.c
@@ -845,6 +845,7 @@ initable_init (GInitable     *initable,
                                             "org.freedesktop.DBus.Properties",
                                             "GetAll",
                                             g_variant_new ("(s)", proxy->priv->interface_name),
+                                            G_VARIANT_TYPE ("(a{sv})"),
                                             G_DBUS_CALL_FLAGS_NONE,
                                             -1,           /* timeout */
                                             cancellable,
@@ -927,6 +928,7 @@ async_initable_init_async (GAsyncInitable      *initable,
                               "org.freedesktop.DBus.Properties",
                               "GetAll",
                               g_variant_new ("(s)", proxy->priv->interface_name),
+                              G_VARIANT_TYPE ("(a{sv})"),
                               G_DBUS_CALL_FLAGS_NONE,
                               -1,           /* timeout */
                               cancellable,
@@ -1408,45 +1410,6 @@ lookup_method_info_or_warn (GDBusProxy  *proxy,
   return info;
 }
 
-static gboolean
-validate_method_return (const char             *method_name,
-                        GVariant               *value,
-                        const GDBusMethodInfo  *expected_method_info,
-                        GError                **error)
-{
-  const gchar *type_string;
-  gchar *signature;
-  gboolean ret;
-
-  ret = TRUE;
-  signature = NULL;
-
-  if (value == NULL || expected_method_info == NULL)
-    goto out;
-
-  /* Shouldn't happen... */
-  if (g_variant_classify (value) != G_VARIANT_CLASS_TUPLE)
-    goto out;
-
-  type_string = g_variant_get_type_string (value);
-  signature = _g_dbus_compute_complete_signature (expected_method_info->out_args, TRUE);
-  if (g_strcmp0 (type_string, signature) != 0)
-    {
-      g_set_error (error,
-                   G_IO_ERROR,
-                   G_IO_ERROR_INVALID_ARGUMENT,
-                   _("Method `%s' returned signature `%s', but expected `%s'"),
-                   method_name,
-                   type_string,
-                   signature);
-      ret = FALSE;
-    }
-
- out:
-  g_free (signature);
-  return ret;
-}
-
 /**
  * g_dbus_proxy_call:
  * @proxy: A #GDBusProxy.
@@ -1514,6 +1477,7 @@ g_dbus_proxy_call (GDBusProxy          *proxy,
   const GDBusMethodInfo *expected_method_info;
   const gchar *target_method_name;
   const gchar *target_interface_name;
+  GVariantType *reply_type;
 
   g_return_if_fail (G_IS_DBUS_PROXY (proxy));
   g_return_if_fail (g_dbus_is_member_name (method_name) || g_dbus_is_interface_name (method_name));
@@ -1534,18 +1498,27 @@ g_dbus_proxy_call (GDBusProxy          *proxy,
   /* Just warn here */
   expected_method_info = lookup_method_info_or_warn (proxy, target_method_name);
 
+  if (expected_method_info)
+    reply_type = _g_dbus_compute_complete_signature (expected_method_info->out_args);
+  else
+    reply_type = NULL;
+
   g_dbus_connection_call (proxy->priv->connection,
                           proxy->priv->unique_bus_name,
                           proxy->priv->object_path,
                           target_interface_name,
                           target_method_name,
                           parameters,
+                          reply_type,
                           flags,
                           timeout_msec == -1 ? proxy->priv->timeout_msec : timeout_msec,
                           cancellable,
                           (GAsyncReadyCallback) reply_cb,
                           simple);
 
+  if (reply_type != NULL)
+    g_variant_type_free (reply_type);
+
   g_free (split_interface_name);
 }
 
@@ -1570,7 +1543,6 @@ g_dbus_proxy_call_finish (GDBusProxy    *proxy,
   GSimpleAsyncResult *simple = G_SIMPLE_ASYNC_RESULT (res);
   GVariant *value;
   const char *method_name;
-  const GDBusMethodInfo *expected_method_info;
 
   g_return_val_if_fail (G_IS_DBUS_PROXY (proxy), NULL);
   g_return_val_if_fail (G_IS_ASYNC_RESULT (res), NULL);
@@ -1586,17 +1558,6 @@ g_dbus_proxy_call_finish (GDBusProxy    *proxy,
   value = g_simple_async_result_get_op_res_gpointer (simple);
   method_name = g_object_get_data (G_OBJECT (simple), "-gdbus-proxy-method-name");
 
-  /* We may not have a method name for internally-generated proxy calls like GetAll */
-  if (value && method_name && proxy->priv->expected_interface)
-    {
-      expected_method_info = g_dbus_interface_info_lookup_method (proxy->priv->expected_interface, method_name);
-      if (!validate_method_return (method_name, value, expected_method_info, error))
-        {
-          g_variant_unref (value);
-          value = NULL;
-        }
-    }
-
  out:
   return value;
 }
@@ -1663,6 +1624,7 @@ g_dbus_proxy_call_sync (GDBusProxy      *proxy,
   const GDBusMethodInfo *expected_method_info;
   const gchar *target_method_name;
   const gchar *target_interface_name;
+  GVariantType *reply_type;
 
   g_return_val_if_fail (G_IS_DBUS_PROXY (proxy), NULL);
   g_return_val_if_fail (g_dbus_is_member_name (method_name) || g_dbus_is_interface_name (method_name), NULL);
@@ -1689,21 +1651,25 @@ g_dbus_proxy_call_sync (GDBusProxy      *proxy,
       expected_method_info = NULL;
     }
 
+  if (expected_method_info)
+    reply_type = _g_dbus_compute_complete_signature (expected_method_info->out_args);
+  else
+    reply_type = NULL;
+
   ret = g_dbus_connection_call_sync (proxy->priv->connection,
                                      proxy->priv->unique_bus_name,
                                      proxy->priv->object_path,
                                      target_interface_name,
                                      target_method_name,
                                      parameters,
+                                     reply_type,
                                      flags,
                                      timeout_msec == -1 ? proxy->priv->timeout_msec : timeout_msec,
                                      cancellable,
                                      error);
-  if (!validate_method_return (target_method_name, ret, expected_method_info, error))
-    {
-      g_variant_unref (ret);
-      ret = NULL;
-    }
+
+  if (reply_type != NULL)
+    g_variant_type_free (reply_type);
 
   g_free (split_interface_name);
 
diff --git a/gio/gsettings-tool.c b/gio/gsettings-tool.c
index fdaacdc60..c9eedfdde 100644
--- a/gio/gsettings-tool.c
+++ b/gio/gsettings-tool.c
@@ -230,7 +230,7 @@ handle_set (gint   *argc,
     session = g_bus_get_sync (G_BUS_TYPE_SESSION, NULL, NULL);
     g_dbus_connection_call_sync (session, "org.gtk.DoesNotExist", "/",
                                  "org.gtk.DoesNotExist", "Workaround",
-                                 g_variant_new ("()"), 0, -1, NULL, NULL);
+                                 g_variant_new ("()"), NULL, 0, -1, NULL, NULL);
   }
 
  out:
diff --git a/gio/tests/gdbus-connection.c b/gio/tests/gdbus-connection.c
index 266512f3e..2a481260a 100644
--- a/gio/tests/gdbus-connection.c
+++ b/gio/tests/gdbus-connection.c
@@ -234,7 +234,7 @@ test_connection_send (void)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           ca,
@@ -251,7 +251,7 @@ test_connection_send (void)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -267,7 +267,7 @@ test_connection_send (void)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "NonExistantMethod",     /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -284,7 +284,7 @@ test_connection_send (void)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           ca,
@@ -307,7 +307,7 @@ test_connection_send (void)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -462,6 +462,7 @@ test_connection_signals (void)
                                         "org.freedesktop.DBus",  /* interface name */
                                         "GetId",                 /* method name */
                                         NULL,                    /* parameters */
+                                        NULL,                    /* return type */
                                         G_DBUS_CALL_FLAGS_NONE,
                                         -1,
                                         NULL,
diff --git a/gio/tests/gdbus-example-peer.c b/gio/tests/gdbus-example-peer.c
index 316680ea6..7df19424d 100644
--- a/gio/tests/gdbus-example-peer.c
+++ b/gio/tests/gdbus-example-peer.c
@@ -280,6 +280,7 @@ main (int argc, char *argv[])
                                            "org.gtk.GDBus.TestPeerInterface",
                                            "HelloWorld",
                                            g_variant_new ("(s)", greeting),
+                                           G_VARIANT_TYPE ("(s)"),
                                            G_DBUS_CALL_FLAGS_NONE,
                                            -1,
                                            NULL,
diff --git a/gio/tests/gdbus-export.c b/gio/tests/gdbus-export.c
index b067cee80..297fb231c 100644
--- a/gio/tests/gdbus-export.c
+++ b/gio/tests/gdbus-export.c
@@ -807,7 +807,7 @@ test_dispatch_thread_func (gpointer user_data)
                                   NULL,
                                   &error);
   g_assert_error (error, G_DBUS_ERROR, G_DBUS_ERROR_INVALID_ARGS);
-  g_assert_cmpstr (error->message, ==, "GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Signature of message, `s', does not match expected signature `'");
+  g_assert_cmpstr (error->message, ==, "GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Type of message, `(s)', does not match expected type `()'");
   g_error_free (error);
   g_assert (value == NULL);
 
diff --git a/gio/tests/gdbus-names.c b/gio/tests/gdbus-names.c
index b48d695ad..d5e234240 100644
--- a/gio/tests/gdbus-names.c
+++ b/gio/tests/gdbus-names.c
@@ -176,6 +176,7 @@ test_bus_own_name (void)
                                         "org.freedesktop.DBus",  /* interface name */
                                         "NameHasOwner",          /* method name */
                                         g_variant_new ("(s)", name),
+                                        G_VARIANT_TYPE ("(b)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         -1,
                                         NULL,
@@ -201,6 +202,7 @@ test_bus_own_name (void)
                                         "org.freedesktop.DBus",  /* interface name */
                                         "NameHasOwner",          /* method name */
                                         g_variant_new ("(s)", name),
+                                        G_VARIANT_TYPE ("(b)"),
                                         G_DBUS_CALL_FLAGS_NONE,
                                         -1,
                                         NULL,
diff --git a/gio/tests/gdbus-threading.c b/gio/tests/gdbus-threading.c
index 6bfda516f..6a4e82cf8 100644
--- a/gio/tests/gdbus-threading.c
+++ b/gio/tests/gdbus-threading.c
@@ -136,7 +136,7 @@ test_delivery_in_thread_func (gpointer _data)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           NULL,
@@ -156,7 +156,7 @@ test_delivery_in_thread_func (gpointer _data)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           ca,
@@ -174,7 +174,7 @@ test_delivery_in_thread_func (gpointer _data)
                           "/org/freedesktop/DBus", /* object path */
                           "org.freedesktop.DBus",  /* interface name */
                           "GetId",                 /* method name */
-                          NULL,
+                          NULL, NULL,
                           G_DBUS_CALL_FLAGS_NONE,
                           -1,
                           ca,