Device connect/disconnect notification via Bluez DBus API - dbus

Question

How can I receive a signal or notification when a connection is created or destroyed through bluez dbus API?
Polling Connected() of all devices under /org/bluez/hci0 works but it is not an efficient way, IMHO.

Answer 1

You need to listen on PropertiesChanged signal on the org.bluez.Device1 interface. I don't have direct example for the device interface, but the template is below,
static void bluez_signal_device_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;
(void)userdata;
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, "Connected")) {
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("Device is \"%s\"\n", g_variant_get_boolean(value) ? "Connected" : "Disconnected");
}
}
done:
if(properties != NULL)
g_variant_iter_free(properties);
if(value != NULL)
g_variant_unref(value);
}
GDBusConnection *con = g_bus_get_sync(G_BUS_TYPE_SYSTEM, NULL, NULL);
prop_changed = g_dbus_connection_signal_subscribe(con,
"org.bluez",
"org.freedesktop.DBus.Properties",
"PropertiesChanged",
NULL,
"org.bluez.Device1",
G_DBUS_SIGNAL_FLAGS_NONE,
bluez_signal_device_changed,
NULL,
NULL);
With the above sample code, signal handling function bluez_signal_device_changed is called whenever a property is change in the Device` interface.
You can find more examples in https://gist.github.com/parthitce and explanation in https://www.linumiz.com/