Feedback on BlueZ DBus API

[Barry Byford <31baz66@gmail.com>]

Hello,


Over the last couple of years I=E2=80=99ve been doing some work with access=
ing
BlueZ from the Python programming language. More recently I=E2=80=99ve been
trying to create a library to lower the barrier to getting started
with Bluetooth on Linux. On that library we have recently done a
retrospective of where we are.

(TL;DR https://github.com/ukBaz/python-bluezero/issues/126)

The discussion spilled over to twitter where there was a suggestion
that some of our concerns should be shared back to the BlueZ project.
https://twitter.com/sandeepmistry/status/891836962952314880


I am not sure how relevant our feedback is to the broader user base of
the BlueZ project. However, it is true that we can=E2=80=99t complain that =
our
needs aren=E2=80=99t being addressed by BlueZ if we don=E2=80=99t give feed=
back.


I also accept that part of the issue here is with me as I don=E2=80=99t com=
e
from a background where I know about the low level details of
Bluetooth and the C language. I am coming at this from the direction
of learning enough to rapidly prototype Python applications that
contain some Bluetooth functionality.


Context:

In my volunteering role as a STEM ambassador I have been a mentor on a
few school projects for engineering challenges where Bluetooth
functionality would have been helpful.

These school projects typically use hardware like Raspberry Pi=E2=80=99s, B=
BC
micro:bits and tablets/phones where Bluetooth hardware is readily
available.

My goal is to be able to create workshops that can be run at schools,
STEM fairs and community maker events that help people get started
exploring what is possible with Bluetooth and Python.


Building From Source:

My first bit of feedback is that things with BlueZ are a lot better
now than they were a few short years ago. However this is the first
challenge as it takes a long time for updates to appear in operating
systems.

The default Raspberry Pi OS is still shipping with BlueZ 5.23 which
isn=E2=80=99t much use for BLE. Even when Raspbian moves to being a Debian
Stretch based release, it will be BlueZ 5.43. This means that much of
the DBus API will be behind the experimental flag and will be missing
some of the great recent updates such as AcquireWrite, AcquireNotify
and set name in scan response.

While building from source is something I=E2=80=99ve become comfortable wit=
h,
getting organisers of workshop machines and users to do this is often
too large a barrier to entry.


Python DBus Library:

As I=E2=80=99ve written about before on this list, there is not an obvious
choice when it comes to a Python DBus library. I think the BlueZ
=E2=80=98test=E2=80=99 Python examples use the dbus-python library. There s=
eems to be
concerns about this Python library. Pydbus seems to be a recommended
library although there seems to be several holes in it for use with
BlueZ. The owner of the library appears to have moved on to another
project so updates (or merging of pull requests) seems to be sporadic.


Beacons:

Again another topic that has been discussed on this mailing list
before. There seems to have been a number of people that want to have
a Linux SBC continuously passively scan for beacons. This is something
that is not supported by the BlueZ DBus API. I believe the concern is
with flooding the bus. Could something similar to AcquireNotify be
done to solve this?


Testing:

It would be good to be able to test the Python apps without real
hardware. It would be good if BlueZ could provide some way of
mock/fake/stub so that unit testing could be easily done.

The library python-dbusmock showed some promise however the bluez5.py
template needs some work.


Our New Direction - Python Only Solution:

Because of the issues raised above, investigation has started on using
only Python standard libraries to find a solution for our library.
This will allow our library to move faster than OS updates allow as it
will be easy to install directly from PyPI with fewer dependencies.

The current investigation is looking to by-pass bluetoothd by using
HCI. What we have so far can be seen at:
https://github.com/TheBubbleworks/python-hcipy


Regards,

Barry