How can I get my custom service object registered on the system bus?

[dbaba]

I'm looking for the way to register my custom service on D-Bus with dbus-next API. But I'm not getting it working.

What I did is:

• Create a couple of classes inheriting dbus-next Interface
• Invoke dbus.systemBus().export('/service/path', aboveObject) for each dbus-next Interface object to be exported

Then when I got a ProxyObject of the service path, I couldn't find anything in interfaces property of the ProxyObject. What am I missing?

# dbus.systemBus().getProxyObject(':1.2', '/service/path').then(x => console.log(x))
=>
ProxyObject {
  bus: MessageBus {
    _events: [Object: null prototype] {},
    _eventsCount: 0,
    _maxListeners: undefined,
    _builder: Builder { options: [Object] },
    _connection: EventEmitter {
      (snip)
    },
    _serial: 8,
    _methodReturnHandlers: {},
    _signals: EventEmitter {
      (snip)
    },
    _nameOwners: {
      'org.freedesktop.DBus': 'org.freedesktop.DBus',
      'org.bluez': ':1.428',
      'org.freedesktop.DBus.ObjectManager': 'org.freedesktop.DBus',
      ':1.2': ':1.2'
    },
    _methodHandlers: [ [Function] ],
    _serviceObjects: {  ======================> Exported paths are described here
      '/service/path': [ServiceObject],
      '/service/path/subpath': [ServiceObject],
      (snip) 
    }, 
  name: ':1.420',
    [Symbol(kCapture)]: false
  },
  name: ':1.2',
  path: '/service/path',
  interfaces: {},  ==========================> but no exported interfaces appear
  (snip) 
}

With node-dbus, it has dbus.registerService() to register a Service Object (not Interface). I'd say the Service Object registration function is required to register a set of D-Bus interfaces but I don't have any idea of the equivalent function in dbus-next.

[acrisci]

I wonder if you are connecting to the right connection. The bus you've shown that has the exported objects has name :1.420 and the bus you've connected to has name :1.2.

[EricBorland]

I'm not sure if it's related but I'm trying to implement a Bluetooth GATT server using Bluez over DBus and after exporting the interface I still receive DBus Error: No object received when trying to RegisterApplication. Using the DBus python library it works by exporting the object to the bus like this dbus.service.Object.__init__(self, dbus.SystemBus(), path) but is there any equivalent function in dbus-next?

[EricBorland]

Maybe it's related to this #17?

[ErwanHesry]

@EricBorland Any news about this problem? I'm also trying to get a BLE Gatt server over DBus, but got the same error when trying to RegisterApplication. My interface looks good, but got the error too. Here it is:

class GattServer extends dbus.interface.Interface {
    _serialNumber: string

    constructor() {
        super('org.bluez.coregatt.manager0')
        this._serialNumber = 'MY_SERIAL_NUMBER'
    }

    get SerialNumber () {
        return this._serialNumber
    }

    set SerialNumber (value) {
        this._serialNumber = value
    }

    GetManagedObjects () {
        console.log('GetManagedObjects')
        return {}
    }

    Echo (what) {
        return what;
    }
}

GattServer.configureMembers({
    properties: {
        SerialNumber: {
            signature: 's'
        }
    },
    methods: {
        GetManagedObjects: {
            inSignature: '',
            outSignature: 'a{oa{sa{sv}}}'
        },
        Echo: {
            inSignature: 'v',
            outSignature: 'v'
        },
    }
})

[EricBorland]

Hey, it's been a while but I ended up getting it working. I don't remember what exactly I was doing wrong or what I did to fix it, but the final code looked like something similar to this:

import dbus, { Message, Variant } from 'dbus-next';

const {
  ACCESS_READ,
  INTERFACES,
  Interface,
  method,
  property,
} = dbus.interface;

export default class GattApplication extends Interface {
  @property({ signature: 's', access: ACCESS_READ })
  path = '/';

  services = [];

  constructor(bus, services) {
    super(INTERFACES.GATT_APPLICATION);
    // Properties definition
    this._bus = bus;

    // Exporting interface to bus
    this._bus.exportInterface(this.path, this);

    // Initializing services
    this.addServices(services);

    // Exporting GetManagedObjects to ObjectManager
    this._bus.addMethod('GetManagedObjects', INTERFACES.OBJECT_MANAGER, this.path, 'a{oa{sa{sv}}}', this.GetManagedObjects.bind(this));
  }

  addService(service) {
    this.services.push(service);
    this._bus.exportInterface(service.getPath(), service);
  }

  addServices(services) {
    services.forEach(service => this.addService(service));
  }

  GetManagedObjects() {
    const response = {};
    this.services.forEach(service => {
      response[service.getPath()] = service.getProperties();
      service.getCharacteristics().forEach(characteristic => {
        response[characteristic.getPath()] = characteristic.getProperties();
        characteristic.getDescriptors().forEach(descriptor => {
          response[descriptor.getPath()] = descriptor.getProperties();
        });
      });
    });

    return response;
  }
}

And used like this:

const { agentManager, gattManager, advertisingManager } = await this.bus.initManagers(['agent', 'gatt', 'advertising']);
const app = new Gatt.Application(this.bus, services);
await gattManager.RegisterApplication(app.path, {});
console.log('Application successfully registered in GATT');

Where this.bus was an abstraction on top of dbus-next adding some extra methods like the initManagers that only loops over the array and initializes each manager using the initManager method from dbus-next...
Let me know if that helps.

Cheers

[ErwanHesry]

Thanks a lot @EricBorland, it helped me a lot.
I do have your abstraction on top of dbus-next, but I managed to get something that works. Well, for the first part: creating the application and send it through dbus.
The only thing I had to change is the addMethod you have in your abstraction. Here is my GattApplication class:

class GattApplication extends Interface {
  _bus:dbus.MessageBus
  path = Constants.Gatt.GATT_APPLICATION_PATH;
  name = Constants.Gatt.GATT_APPLICATION_NAME;

  services = [];

  constructor(bus, services) {
    super(Constants.Gatt.GATT_SERVICE_IFACE);
    // Properties definition
    this._bus = bus;

    // Exporting interface to bus
    this._bus.export(this.path, this);

    // Initializing services
    this.addServices(services);

    // Exporting GetManagedObjects to ObjectManager
    this.addMethod('GetManagedObjects', Constants.Gatt.DBUS_OM_IFACE, 'a{oa{sa{sv}}}', this.GetManagedObjects.bind(this));
  }

  addMethod = (name, iface, signature, cb) => {
    this._bus.addMethodHandler((msg) => {
        console.log(`CALL ${msg.member} on ${msg.path}`)
        if (msg.interface === iface && msg.path === this.path && msg.member === name) {
            this._bus.send(new dbus.Message({
                type: dbus.MessageType.METHOD_RETURN,
                replySerial: msg.serial,
                destination: msg.sender,
                signature,
                body: [cb()]
            }))
            return true
        }
        return false
    })
  }

  addService(service) {
    this.services.push(service);
    this._bus.export(service.getPath(), service);
  }

  addServices(services) {
    services.forEach(service => this.addService(service));
  }

  GetManagedObjects() {
    const response = {};
    this.services.forEach(service => {
      response[service.getPath()] = service.getProperties();
      service.getCharacteristics().forEach(characteristic => {
        response[characteristic.getPath()] = characteristic.getProperties();
        characteristic.getDescriptors().forEach(descriptor => {
          response[descriptor.getPath()] = descriptor.getProperties();
        });
      });
    });

    return response;
  }

With that GattApplication, I can registerApplication with my gattManager. However, as I don't have any service yet, Bluez returns an error No object received (which is normal I think). But now, the GetManagedObjects works (previously, I was seeing an error message that the method does not exists on my application).

Now I have to create services. Any advice on that part? I have found some example in the Python example. I'll try to convert that Python code into JS.

[ErwanHesry]

Ok, so that was definitely the lack of service. I created a dummy service emulating a battery service (uuid 180f) containing a characteristic emulating battery level (uuid 2a19). All based on the format of the application above.
Result: it works!!!

I then added an advertisement service which is sent through DBus to the Bluez LEAdvertisingManager. And voilà, my device is now discoverable.

Again, thanks a lot for your help 👍