what causes the error "Unknown object" ?

[12-3-8-s9b9o9j9t]

I'm trying to work with Bluetooth LE with bluez, and for now start advertising.

I have the following program : (I'm sorry, it's pretty big but I don't know what might help or not)

// constants
namespace ble{
    const std::string BLUEZ_SERVICE_NAME = "org.bluez";
    const std::string ADAPTER_INTERFACE = BLUEZ_SERVICE_NAME + ".Adapter1";
    const std::string ADVERTISING_MANAGER_INTERFACE = BLUEZ_SERVICE_NAME + ".LEAdvertisingManager1";
}

<--! introspection xml to generate the adaptor (not all properties are here, but it works whith a python example) -->
<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
    "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<node name="/org/bluez/test/advertisement">
    <interface name="org.bluez.LEAdvertisement1">
    <method name="Release"/>
    <property name="Type" type="s" access="read"/>
    <property name="LocalName" type="s" access="read"/>
    <property name="Discoverable" type="b" access="read"/>
    </interface>
</node>

// class implementing the adaptor
static const std::string PATH_BASE = "/org/bluez/test/advertisement";
class Advertisement : public sdbus::AdaptorInterfaces<org::bluez::LEAdvertisement1_adaptor>{
private:
    std::string ad_type;
    std::string local_name;
    bool discoverable;

public:
    Advertisement(sdbus::IConnection& bus, int index, std::string advertising_type)
        : AdaptorInterfaces(bus, std::move(PATH_BASE + std::to_string(index)))
        , ad_type(advertising_type)
        , local_name("RPI 4B")
        , discoverable(true){
        registerAdaptor();
    }

    ~Advertisement(){
        unregisterAdaptor();
    }
...
// methods

// main
typedef std::unique_ptr<sdbus::IConnection> Bus;
typedef std::unique_ptr<sdbus::IProxy> Proxy;

Bus bus;

/**
 * @brief find the path to an adapter implementing the org.bluez.LEAdvertisingManager1 interface, if any
 * 
 * @return sdbus::ObjectPath the path to such an adapter if found, else an empty path
 */
sdbus::ObjectPath find_adapter(){
    Proxy proxy = sdbus::createProxy(ble::BLUEZ_SERVICE_NAME, "/");

    typedef std::map<sdbus::ObjectPath, std::map<std::string, std::map<std::string, sdbus::Variant>>> ManagedObjects;
    ManagedObjects objects;

    proxy->callMethod("GetManagedObjects").onInterface(ble::DBUS_OM_IFACE).storeResultsTo(objects);
    for(ManagedObjects::iterator it = objects.begin(); it != objects.end(); it++){
        if(it->second.find(ble::ADVERTISING_MANAGER_INTERFACE) != it->second.end()){
            return it->first;
        }        
    }
    return sdbus::ObjectPath();
}

int main(){
    bus = sdbus::createSystemBusConnection();
    sdbus::ObjectPath adapter_path(find_adapter());
    
    if(adapter_path.empty()){
        std::cout<<ble::ADVERTISING_MANAGER_INTERFACE<<" interface not found"<<std::endl;
    }
    else{
        Proxy proxy = sdbus::createProxy(ble::BLUEZ_SERVICE_NAME, adapter_path);
        proxy->setProperty("Powered").onInterface(ble::ADAPTER_INTERFACE).toValue(sdbus::Variant(true));

        Advertisement adv(*bus, 0, "peripheral");
        sdbus::ObjectPath adv_path(adv.getObjectPath());

        std::cout<<"Registering advertisement..."<<std::endl;
        proxy->callMethod("RegisterAdvertisement").onInterface(ble::ADVERTISING_MANAGER_INTERFACE).withArguments(adv_path, std::map<std::string, sdbus::Variant>());
        std::cout<<"Advertising forever..."<<std::endl;
        bus->enterEventLoop();

        proxy->callMethod("UnregisterAdvertisement").onInterface(ble::ADVERTISING_MANAGER_INTERFACE).withArguments(adv_path);
    }
    return 0;
}

In the console I can see Registering advertisement... being print, and then I get the error [org.bluez.Error.Failed] Failed to register advertisement, whith the only reason I can think of being the

error time=1657202924.104971 sender=:1.163 -> destination=:1.113 error_name=org.freedesktop.DBus.Error.UnknownObject reply_serial=479
string "Unknown object '/org/bluez/test/advertisement0'." 

in dbus-monitor. What am I missing/doing wrong ?

Edit :
When I comment the lines where I call RegisterAdvertisement and UnregisterAdvertisement, I can see in d-feet that my program creates three services, the first one when introspected gives what I can expect from my Advertisement object, the second one is empty and charges forever and produce an error g-io-error-quark: timeout (24) (or something like that, the message is not in english), and the third one gives the error g-dbus-error-quark: GDBus.Error.org.freedesktop.DBus.Error.UnkownObject: Unknown object '\'. (41)

Also the services names are always :1.x, :1.x+2 and :1.x+3.

[12-3-8-s9b9o9j9t]

Ok, I re-read the main page to understand sdbus-c++, I saw that I could register my proxies on the same connexion as my object, I didn't have the error "Unknown object" anymore, but a timeout... something I remembered I had 2 weeks ago.

Then I though it might be because I am not in asyncronous mode and the method return is void, and I saw the dontExpectReply(), used it, and it works !!

I'm so glad I found the problem and I don't have to use a cursed c implementation of dbus like bluez did !