How do I create a D-Bus service that dynamically creates multiple objects?

Question

I'm new to D-Bus (and to Python, double whammy!) and I am trying to figure out the best way to do something that was discussed in the tutorial.

However, a text editor application could as easily own multiple bus names (for example, org.kde.KWrite in addition to generic TextEditor), have multiple objects (maybe /org/kde/documents/4352 where the number changes according to the document), and each object could implement multiple interfaces, such as org.freedesktop.DBus.Introspectable, org.freedesktop.BasicTextField, org.kde.RichTextDocument.

For example, say I want to create a wrapper around flickrapi such that the service can expose a handful of Flickr API methods (say, urls_lookupGroup()). This is relatively straightforward if I want to assume that the service will always be specifying the same API key and that the auth information will be the same for everyone using the service.

Especially in the latter case, I cannot really assume this will be true.

Based on the documentation quoted above, I am assuming there should be something like this:

# Get the connection proxy object.
flickrConnectionService = bus.get_object("com.example.FlickrService",
                                         "/Connection")

# Ask the connection object to connect, the return value would be
# maybe something like "/connection/5512" ...
flickrObjectPath = flickrConnectionService.connect("MY_APP_API_KEY",
                                                   "MY_APP_API_SECRET",
                                                   flickrUsername)

# Get the service proxy object.
flickrService = bus.get_object("com.example.FlickrService",
                               flickrObjectPath);

# As the flickr service object to get group information.
groupInfo = flickrService.getFlickrGroupInfo('s3a-belltown')

So, my questions:

1) Is this how this should be handled?

2) If so, how will the service know when the client is done? Is there a way to detect if the current client has broken connection so that the service can cleanup its dynamically created objects? Also, how would I create the individual objects in the first place?

3) If this is not how this should be handled, what are some other suggestions for accomplishing something similar?

I've read through a number of D-Bus tutorials and various documentation and about the closest I've come to seeing what I am looking for is what I quoted above. However, none of the examples look to actually do anything like this so I am not sure how to proceed.

Answer 1

1) Mostly yes, I would only change one thing in the connect method as I explain in 2).

2) D-Bus connections are not persistent, everything is done with request/response messages, no connection state is stored unless you implement this in third objects as you do with your flickerObject. The d-bus objects in python bindings are mostly proxies that abstract the remote objects as if you were "connected" to them, but what it really does is to build messages based on the information you give to D-Bus object instantiation (object path, interface and so). So the service cannot know when the client is done if client doesn't announce it with other explicit call.

To handle unexpected client finalization you can create a D-Bus object in the client and send the object path to the service when connecting, change your connect method to accept also an ObjectPath parameter. The service can listen to NameOwnerChanged signal to know if a client has died.

To create the individual object you only have to instantiate an object in the same service as you do with your "/Connection", but you have to be sure that you are using an unexisting name. You could have a "/Connection/Manager", and various "/Connection/1", "/Connection/2"...

3) If you need to store the connection state, you have to do something like that.