Add a stub method to query the time zones

README.md

@@ -33,6 +33,16 @@ for KDE.
 Then running `dbus-monitor --system` as root can be used to see the
 communication between the control center and this service.
 
+Messages to the D-Bus service can also be sent with `dbus-send`. For example
+to get the list of time zones:
+
+```sh
+dbus-send --system --print-reply --type=method_call \
+  --dest=org.freedesktop.timedate1 \
+  /org/freedesktop/timedate1 \
+  org.freedesktop.timedate1.ListTimezones
+```
+
 ## Dependencies
 
 - glib

data/org.freedesktop.timedate1.xml

@@ -23,5 +23,8 @@
    <arg name="use_ntp" type="b" direction="in"/>
    <arg name="user_interaction" type="b" direction="in"/>
   </method>
+  <method name="ListTimezones">
+   <arg name="timezones" type="as" direction="out"/>
+  </method>
  </interface>
 </node>

src/slack-timedate.cpp

@@ -33,18 +33,25 @@ static void slack_method_call (GDBusConnection *connection, const gchar *sender,
 	gint64 usec_utc;
 
 	// Set time zone
-	if (g_strcmp0 (method_name, "SetTimezone") == 0) {
+    if (g_strcmp0(method_name, "SetTimezone") == 0)
+    {
 		g_variant_get (parameters, "(&sb)", &timezone, &user_interaction);
 
-		if (slack_set_timezone (timezone)) g_dbus_method_invocation_return_value (invocation,
+		if (slack_set_timezone(timezone))
-				NULL);
+        {
-		else g_dbus_method_invocation_return_error (invocation,
+            g_dbus_method_invocation_return_value (invocation, NULL);
+        }
+		else
+        {
+            g_dbus_method_invocation_return_error (invocation,
 				G_IO_ERROR,
 				G_IO_ERROR_FAILED,
 				"Write operation failed");
-
+        }
 		g_free (timezone);
-    } else if (g_strcmp0 (method_name, "SetTime") == 0) {
+    }
+    else if (g_strcmp0(method_name, "SetTime") == 0)
+    {
 		g_variant_get (parameters, "(xbb)", &usec_utc, &relative, &user_interaction);
 
 		// Set time
@@ -58,18 +65,31 @@ static void slack_method_call (GDBusConnection *connection, const gchar *sender,
             g_dbus_method_invocation_return_error(invocation, G_IO_ERROR, G_IO_ERROR_FAILED,
                     "Failed to set system clock");
         }
-    } else if (g_strcmp0 (method_name, "SetNTP") == 0) {
+    }
+    else if (g_strcmp0(method_name, "SetNTP") == 0)
+    {
 		g_variant_get (parameters, "(bb)", &use_ntp, &user_interaction);
 
 		// Enable NTP
-		if (slack_set_ntp (use_ntp)) g_dbus_method_invocation_return_value (invocation,
+        if (slack_set_ntp (use_ntp))
-				NULL);
+        {
-		else g_dbus_method_invocation_return_error (invocation,
+            g_dbus_method_invocation_return_value (invocation, NULL);
+        }
+        else
+        {
+            g_dbus_method_invocation_return_error (invocation,
 				G_IO_ERROR,
 				G_IO_ERROR_FAILED,
 				"Error enabling NTP");
         }
-	return;
+	}
+    else if (g_strcmp0(method_name, "ListTimezones") == 0)
+    {
+        auto return_value = Glib::Variant<std::vector<Glib::ustring>>::create({});
+        auto return_tuple = Glib::Variant<std::vector<Glib::ustring>>::create_tuple({ return_value });
+
+        g_dbus_method_invocation_return_value(invocation, return_tuple.gobj());
+    }
 }
 
 static GVariant *slack_get_property (GDBusConnection *connection, const gchar *sender, const gchar *object_path, const gchar *interface_name, const gchar *prop_name, GError **slack_err, gpointer user_data) {

src/slack-timedate.h

@@ -48,6 +48,9 @@
 	"   <arg name=\"use_ntp\" type=\"b\" direction=\"in\"/>\n"      \
 	"   <arg name=\"user_interaction\" type=\"b\" direction=\"in\"/>\n" \
 	"  </method>\n"                                                 \
+	"  <method name=\"ListTimezones\">\n"                           \
+	"   <arg name=\"timezones\" type=\"as\" direction=\"out\"/>\n"  \
+	"  </method>"                                                   \
 	" </interface>\n"												\
 	"</node>\n"