Set powered state of the Adapter and Look for PropertiesChanged signal

bluez_adapter_set_properties.c

/*
 * bluez_adapter_set_properties.c - Set the Powered property of Adapter
 * 	- The example uses GDBUS to set the Adapter Powered state to "on" and "off"
 * 	  in sequence.
 *	- It also registers signal handling for the PropertiesChanged event and prints
 *	  the current powere state of the Adapter
 * gcc `pkg-config --cflags glib-2.0 gio-2.0` -Wall -Wextra -o ./bin/bluez_adapter_set_properties ./bluez_adapter_set_properties.c `pkg-config --libs glib-2.0 gio-2.0`
 */
#include <glib.h>
#include <gio/gio.h>

GDBusConnection *con;
static void bluez_signal_adapter_changed(GDBusConnection *conn,
					const gchar *sender,
					const gchar *path,
					const gchar *interface,
					const gchar *signal,
					GVariant *params,
					void *userdata)
{
	(void)conn;
	(void)sender;
	(void)path;
	(void)interface;

	static int exit = 0;
	GVariantIter *properties = NULL;
	GVariantIter *unknown = NULL;
	const char *iface;
	const char *key;
	GVariant *value = NULL;
	const gchar *signature = g_variant_get_type_string(params);

	if(strcmp(signature, "(sa{sv}as)") != 0) {
		g_print("Invalid signature for %s: %s != %s", signal, signature, "(sa{sv}as)");
		goto done;
	}

	g_variant_get(params, "(&sa{sv}as)", &iface, &properties, &unknown);
	while(g_variant_iter_next(properties, "{&sv}", &key, &value)) {
		if(!g_strcmp0(key, "Powered")) {
			if(!g_variant_is_of_type(value, G_VARIANT_TYPE_BOOLEAN)) {
				g_print("Invalid argument type for %s: %s != %s", key,
						g_variant_get_type_string(value), "b");
				goto done;
			}
			g_print("Adapter is Powered \"%s\"\n", g_variant_get_boolean(value) ? "on" : "off");
			exit++;
		}
	}
done:
	if(properties != NULL)
		g_variant_iter_free(properties);
	if(value != NULL)
		g_variant_unref(value);

	if(exit == 2)
		g_main_loop_quit((GMainLoop *)userdata);
}

static int bluez_adapter_set_property(const char *prop, GVariant *value)
{
	GVariant *result;
	GError *error = NULL;

	result = g_dbus_connection_call_sync(con,
					     "org.bluez",
					     "/org/bluez/hci0",
					     "org.freedesktop.DBus.Properties",
					     "Set",
					     g_variant_new("(ssv)", "org.bluez.Adapter1", prop, value),
					     NULL,
					     G_DBUS_CALL_FLAGS_NONE,
					     -1,
					     NULL,
					     &error);
	if(error != NULL)
		return 1;

	g_variant_unref(result);
	return 0;
}

int main(void)
{
	GMainLoop *loop;
	int rc;
	guint sub;

	con = g_bus_get_sync(G_BUS_TYPE_SYSTEM, NULL, NULL);
	if(con == NULL) {
		g_print("Not able to get connection to system bus\n");
		return 1;
	}

	loop = g_main_loop_new(NULL, FALSE);

	sub = g_dbus_connection_signal_subscribe(con,
						"org.bluez",
						"org.freedesktop.DBus.Properties",
						"PropertiesChanged",
						NULL,
						"org.bluez.Adapter1",
						G_DBUS_SIGNAL_FLAGS_NONE,
						bluez_signal_adapter_changed,
						loop,
						NULL);

	rc = bluez_adapter_set_property("Powered", g_variant_new("b", TRUE));
	if(rc) {
		g_print("Not able to enable the adapter\n");
		g_main_loop_quit(loop);
	}

	rc = bluez_adapter_set_property("Powered", g_variant_new("b", FALSE));
	if(rc) {
		g_print("Not able to disable the adapter\n");
		g_main_loop_quit(loop);
	}
	g_main_loop_run(loop);

	g_dbus_connection_signal_unsubscribe(con, sub);
	g_object_unref(con);
	return 0;
}