How to list all object paths under a dbus service?

Question

This is a follow-up question to A list of available DBus services.

The following python code will list all available DBus services.

import dbus
for service in dbus.SystemBus().list_names():
    print(service)

How do we list out the object paths under the services in python? It is ok if the answer does not involve python although it is preferred.

I am using Ubuntu 14.04

Solution 1

QT setups provide the most convenient way to do it, via qdbus:

qdbus --system org.freedesktop.UPower

prints

/
/org
/org/freedesktop
/org/freedesktop/UPower
/org/freedesktop/UPower/Wakeups
/org/freedesktop/UPower/devices
/org/freedesktop/UPower/devices/line_power_ADP0
/org/freedesktop/UPower/devices/DisplayDevice
/org/freedesktop/UPower/devices/battery_BAT0

---

As to the python way... per the official docs (under standard interfaces):

There are some standard interfaces that may be useful across various D-Bus applications.

org.freedesktop.DBus.Introspectable

This interface has one method:

org.freedesktop.DBus.Introspectable.Introspect (out STRING xml_data)

Objects instances may implement Introspect which returns an XML description of the object, including its interfaces (with signals and methods), objects below it in the object path tree, and its properties.

So here's a very simplistic example that should get you started. It uses xml.etree.ElementTree and dbus:

#!/usr/bin/env python

import dbus
from xml.etree import ElementTree

def rec_intro(bus, service, object_path):
    print(object_path)
    obj = bus.get_object(service, object_path)
    iface = dbus.Interface(obj, 'org.freedesktop.DBus.Introspectable')
    xml_string = iface.Introspect()
    for child in ElementTree.fromstring(xml_string):
        if child.tag == 'node':
            if object_path == '/':
                object_path = ''
            new_path = '/'.join((object_path, child.attrib['name']))
            rec_intro(bus, service, new_path)

bus = dbus.SystemBus()
rec_intro(bus, 'org.freedesktop.UPower', '/org/freedesktop/UPower')

It recursively introspects org.freedesktop.UPower starting from e.g. /org/freedesktop/UPower and prints all object paths (node names):

/org/freedesktop/UPower
/org/freedesktop/UPower/Wakeups
/org/freedesktop/UPower/devices
/org/freedesktop/UPower/devices/DisplayDevice
/org/freedesktop/UPower/devices/battery_BAT0
/org/freedesktop/UPower/devices/line_power_ADP0

which is pretty much what you'd get if you used d-feet (not that you'd need it):

Solution 2

I am not sure you can do this programmatically in Python. You might but it will be a huge headache to figure out how. I tried to do it before and ended up hating Dbus. Anyhow I recommend to use d-feet if you want to investigate things. Below is a screenshot that I stole from my blog.

Once you know the program name, object path, etc. you can then use Python to access those things.

Example

progname = 'org.freedesktop.NetworkManager'
objpath  = '/org/freedesktop/NetworkManager'
intfname = 'org.freedesktop.NetworkManager'
methname = 'GetDevices'

bus = dbus.SystemBus()

obj = bus.get_object(progname, objpath)
interface = dbus.Interface(obj, intfname)     # Get the interface to obj
method = interface.get_dbus_method(methname)  # The method on that interface

method()                                      # And finally calling the method

As you see, it's a pain in the ass to get a simple thing done. But this is the easiest workflow you can get with Dbus!

So use a GUI tool to find out the object paths, interfaces, etc. Then use the code snippet above as a template to access those things. Also I suggest you do this via IPython's interpreter to see what methods, properties, etc. each object has (by hitting tab).

Solution 3

If the service has an object implementing org.freedesktop.DBus.ObjectManager, its method GetManagedObjects returns “all objects, interfaces and properties in a single method call.” For example, UDisks2 has such an object.

Solution 4

What I know from my experience to get the object paths of a bus name (service) it is possible to introspect with object path '/' i.e. (using the above example)

introspectfunc('org.freedesktop.UPower', '/') 

this should return:

<node name="/"> 
<node name="org"/>
<node name="org"/>
<node name="org"/>
<node name="org"/>
<node name="org"/>
<node name="org"/></node>

then introspect with path '/org'

introspectfunc('org.freedesktop.UPower', '/org')

this should return:

<node name="/org"> 
<node name="freedesktop"/>
<node name="freedesktop"/>
<node name="freedesktop"/>
<node name="freedesktop"/>
<node name="freedesktop"/>
<node name="freedesktop"/></node>

and so on:

introspectfunc('org.freedesktop.UPower', '/org/freedesktop')
introspectfunc('org.freedesktop.UPower', '/org/freedesktop/UPower')
etc.

It is like going through the folder structure of the hard drive where the object path '/' is the root and every node is subfolder. This seems the best way to retrieve the object paths of a particular bus name (service) and to construct a collection containing the object paths

Solution 5

Here's another way using Python and GDBus. The python-dbus module is I believe being deprecated (very slowly), and its not the best API. There are a few other promising projects for Python which can be found by googling.

For the Gtk/GLib/GObject world, the simplest is to use GDBus which is built in to Gio library (which comes with GLib). This is the recommended way for new Gtk-based code (rather than dbus module). If you are writing a Gtk app or trying to script a Gtk-based desktop environment (Gnome, Xfce, Cinnamon, Mate, Pantheon etc.), these libraries are probably already available. You can use in Python through Gobject Introspection (python gi module). Python gi API Docs here.

Here is an example introspect function which returns a single DBusNodeInfo.

from gi.repository import Gio, GLib


def introspect(bus, name, object_path):
    res = bus.call_sync(
        name,  # bus_name
        object_path,  # object_path
        'org.freedesktop.DBus.Introspectable',  # interface_name
        'Introspect',  # method_name
        None,  # parameters
        GLib.VariantType("(s)"),  # reply_type
        Gio.DBusCallFlags.NONE,  # flags
        -1,  # timeout_msecs
        None  # cancellable
    )

    if not res:
        return None

    return Gio.DBusNodeInfo.new_for_xml(res[0])

(API docs link: Gio.DBusConnection.call_sync.)

Note that you will need to get the bus doing something like

bus = Gio.bus_get_sync(Gio.BusType.SYSTEM)

or

bus = Gio.bus_get_sync(Gio.BusType.SESSION)

(See Gio.bus_get_sync docs)

DBusNodeInfo has nodes, interfaces and path properties. The path property contains just the last segment of the actual path (e.g. "bar", not "/foo/bar"). nodes is a list of DBusNodeInfo, but note that these are not recursively introspected, you must iterate over them, build the absolute path by joining to the parent path with a slash, and call introspect again.

As you can see, the library includes XML parser and parse tree API, unlike python-dbus, so there is no need to use Python's xml.etree etc.

Recursive introspection

Building on the above introspect function you could do something like (Python 3 code):

def introspect_tree(bus, name, object_path):
    node = introspect(bus, name, object_path)

    if node:
        yield object_path, node

        if object_path == '/':
            object_path = ''

        for child in node.nodes:
            yield from introspect_tree(bus, name, f"{object_path}/{child.path}")

This is a generator of (object_path, node) pairs, where object_path is the absolute path and node is the DBusNodeInfo object.

If you just the want paths:

bus = Gio.bus_get_sync(Gio.BusType.SYSTEM)
for path, node in introspect_tree(bus, 'org.freedesktop.UPower', '/org/freedesktop/UPower'):
    print(path)

Prints:

/org/freedesktop/UPower
/org/freedesktop/UPower/Wakeups
/org/freedesktop/UPower/devices
/org/freedesktop/UPower/devices/DisplayDevice
/org/freedesktop/UPower/devices/battery_BAT0
/org/freedesktop/UPower/devices/line_power_ADP0

Introspecting interfaces

The interfaces property of DBusNodeInfo objects contains a list of Gio.DBusInterfaceInfo objects of the interfaces the object has. From there, you have name, methods, properties and signals properties.

Asynchronous API

Note that the above code is all synchronous, which is fine for command line apps and simple tools. However, there is also an asynchronous API which you will definitely want to use for GUI apps. All the functions that end with _sync have async versions e.g. call_sync has call and call_finish. There's also support for timeouts and cancellation (see timeout_msec and cancellable parameters of call/call_sync for example). Pretty easy to use once you figure it out, can be hard to find the docs though. Reading existing source code is a good way, especially the d-feet app source code which demonstrates asynchronous use of the APIs mentioned here.

gdbus CLI tool

Another fantastic part of GDBus is the gdbus command line tool which comes with the library (should be available in your Gtk-based desktop environments). Like qdbus (mentioned above), it has tab completion and excellent introspection functionality built in and is very useful for quick exploration and discovering names and paths.

Try:

gdbus introspect -r --system --dest org.freedesktop.UPower --object-path /org/freedesktop/UPower

View more solutions

Comments

[Admin]

It is ok if the answer does not involve python although it is preferred.

[Khurshid Alam]

How do I create a list of object paths from rec_intro(bus, 'org.freedesktop.UPower', '/org/freedesktop/UPower') ?

[Khurshid Alam]

No, I mean creating a python list of object paths, so that I can check (in my script) if particular object-path exists in the list. It prints the objectpath alright., But I want something like k = rec_intro(bus, 'org.freedesktop.UPower', '/org/freedesktop/UPower'). I suppose it is possible by modifying the function little bit.

[Khurshid Alam]

Example code with qbus: bus = dbus.SessionBus()..... obj_path = '/org/gnome/Gnote/RemoteControl'.......... cmd = 'qdbus org.gnome.Gnote'......... while obj_path not in ((subprocess.check_output(cmd, shell=True)).decode("utf-8")).split("\n"): ........pass

[don_crissti]

@KhurshidAlam - initialize a list before the function e.g. mylist=[] then replace print with mylist.append and then as the last command in that function block return mylist - that's pretty much what there is... you can then iterate over the list or whatever e.g. add at the bottom of the script for x in mylist: print("OBJ_PATH", x) to have them printed with a OBJ_PATH prefix...

[WinEunuuchs2Unix]

d-feet is missing org.gnome.SettingsDaemon.Power which I was looking to inspect. I'm feeling kind of defeated :(

[SurpriseDog]

Perhaps you meant: intf.get_dbus_method...