Using bluetooth with python and dbus

Question

As the title suggests.

I am having hard time in finding a decent python dbus module for this one. There was a lot of smoke, mirrors & traps on the way.

First, let' see what I did.

The first booby-trap was dbus-python. Couldn't make it to work at all. Even the examples are broken.

It seems to be outdated, and replaced by pydbus

(The copyright owners / authors for both of them seem to be the same)

Let's see pydbus then. Also there, the examples don't work that great:

from pydbus import SystemBus
bus = SystemBus()
dev = bus.get('.NetworkManager', 'Devices/0')

gives

KeyError: 'object does not export any interfaces; you might need to pass object path as the 2nd argument for get()'

However, if we try something completely contrary to that error message..

dev = bus.get('.NetworkManager')

we get a nice object with lots of methods:

dir(dev)
['ActivateConnection',
 'ActivatingConnection',
 'ActiveConnections',
 'AddAndActivateConnection',
 'AllDevices',
 'Capabilities',
 'CheckConnectivity',
 'CheckPermissions',
 'CheckpointCreate',
 'CheckpointDestroy',
 'CheckpointRollback',
 'Connectivity',
 ....
 ]

So far so good. Let's see if we can get our hands on bluetooth with that one:

dev = bus.get('org.bluez')
dir(dev)
['Introspect',
 'RegisterAgent',
 'RegisterProfile',
 'RequestDefaultAgent',
 'UnregisterAgent',
 'UnregisterProfile'
 ]

So, again a nice object with some methods. However most of the things are missing. Let's take a look for example at this:

https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/device-api.txt

Can't get that mentioned "Connect" method with pydbus..?

Please don't suggest me to use subprocess.Popen with bluetoothctl - how lame is that. Besides, I want to learn dbus.

Questions:

• How to get access to all bluetooth methods?
• What would be the correct dbus python binding to use (that actually works)?
• Any working example would be highly appreciated.
• I want to achieve bt pairing using python

Some references:

• Another SO question: Bluez Programming
• Dbus specs: https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc
• Source code for the celebrated bluetoothctl program that comes with modern debian linux distros: https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/client/main.c
• Nice dbus article: https://medium.com/cesar-update/exposing-a-d-bus-interface-in-linux-part-2-90374a9e381b

EDIT:

There is, of course, the python bluez library. But that's GPL licensed. And there is no way to pair devices with bluez, right?

Answer 1

EDIT: I created a demo for all of this (python + dbus + bluetooth) here: https://github.com/elsampsa/btdemo

Have fun.

no need to go further from here - just use that repo

Some more libraries & tutorials I found on the way:

An article at Medium: https://medium.com/@trstringer/talking-to-systemd-through-dbus-with-python-53b903ee88b1

Bluetool library: https://github.com/emlid/bluetool

dbus specs: https://dbus.freedesktop.org/doc/dbus-specification.html#standard-interfaces

My comments about dbus-python were premature. Bluetool uses it, and by following bluetool's code I was able to go forward a bit:

import dbus

def my_pprint(obj, intend = 0):
    if isinstance(obj, dict):
        for key, value in obj.items():
            print(intend*" "+str(key)+" : ")
            my_pprint(value, intend = intend + 4)
        print()
    elif isinstance(obj, list):
        for value in obj:
            my_pprint(value, intend = intend + 4)
        print()
    elif isinstance(obj, dbus.Byte ):
         print(intend*" "+ hex(obj) )
    else:
        print(intend*" "+str(obj))
    

bus = dbus.SystemBus()
proxy_object = bus.get_object("org.bluez","/")
manager = dbus.Interface(proxy_object, "org.freedesktop.DBus.ObjectManager")
objects = manager.GetManagedObjects()
my_pprint(objects) # see DUMP 1 in the end of this answer

i.e., the bluez dbus interface implements an object manager, giving a nice nested structure of objects (see the dump below)

What is (not) implemented at the bluez dbus interface, can be confirmed with this:

gdbus introspect --system --dest [Service] --object-path [Object path]

where Server & Object path come from the API docs here

For example:

gdbus introspect --system --dest org.bluez --object-path /org/bluez
gdbus introspect --system --dest org.bluez --object-path /
gdbus introspect --system --dest org.bluez --object-path /org/bluez/hci0

I'll update this answer once I achieve pairing..

DUMP1 from the code snippet

/org/bluez : 
    org.freedesktop.DBus.Introspectable : 

    org.bluez.AgentManager1 : 

    org.bluez.ProfileManager1 : 

/org/bluez/hci0 : 
    org.freedesktop.DBus.Introspectable : 

    org.bluez.Adapter1 : 
        Address : 
            9C:B6:D0:8C:5D:D6
        AddressType : 
            public
        Name : 
            sampsa-xps13
        ...
        ...
        
    org.freedesktop.DBus.Properties : 

    org.bluez.GattManager1 : 

    org.bluez.LEAdvertisingManager1 : 
        ActiveInstances : 
            
        SupportedInstances : 
            
        SupportedIncludes : 
                tx-power
                appearance
                local-name


    org.bluez.Media1 : 

    org.bluez.NetworkServer1 : 
    
/org/bluez/hci0/dev_58_C9_35_2F_A1_EF : 
    org.freedesktop.DBus.Introspectable : 

    org.bluez.Device1 : 
        Address : 
            58:C9:35:2F:A1:EF
        AddressType : 
            public
        Name : 
            Nokia 5
        Alias : 
            Nokia 5
        Class : 
            5898764
        Icon : 
            phone
        Paired : 
            1
        Trusted : 
            0
        Blocked : 
            0
        ...
        ...

    org.freedesktop.DBus.Properties : 

    org.bluez.Network1 : 
        Connected : 
            0

    org.bluez.MediaControl1 : 
        Connected : 
            0

[any other devices follow]