btsocket 0.1.0

Python library for BlueZ Bluetooth Management API

A Python library to interact with Bluez Bluetooth Management API on Linux. At this time it should be seen as a very early stage proof of concept. If you are new to Bluetooth this might not be the best library to start with

Overview

This library aims to offer assistance to accessing the BlueZ Bluetooth Management API using Python. With the mgmt API there are no commands for reading and writing data on a connected device. This library has to have root privilege to access most things.

Three Levels

This library has tried to split things in to the how, what and when. The aim is by keeping the transport, protocol, and programming paradigm separate a plug and play approach can be taken. For example, if the Python bug in sockets gets fixed, just that part can be updated without too much disruption. It should also be possible to use different programming paradigms (models) for how commands and responses are handled and still use the socket and protocol pieces.

Socket (How)

This library came into being because of a Bug in Python as documented at: https://bugs.python.org/issue36132

Python currently does not allow any way to initialize hci_channel, so you cannot use a user channel socket and so instead btmgmt_socket in btsocket/btmgmt_socket.py accesses the user channel by using the underlying libc socket.

Protocol (What)

The file btsocket/btmgmt_protocol.py is to assist in encoding and decoding the binary format that is used to communicate

This module assists in encoding and decoding the binary data

Programming Paradigm (When)

Handling communication with the sockets can be done a number of different ways and there are trade-offs for each of them. Initially this library is supporting two types. A procedural approach with btsocket/btmgmt_sync.py and a callback (or event-driven) approach with btsocket/btmgmt_callback.py.

For actions like turning the controller on and off then these can be done with either methodology. For listening for async events like the discovery of devices, then only the callback model is practical.

Commands

For the vast majority of the commands, the process of creating the mgmt socket is required to have the CAP_NET_ADMIN capability (e.g. root/sudo would have this).

The documentation for commands is at: https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc/mgmt-api.txt

That documentation has been used to auto-generate parts of btmgmt_protocol.py

To take one command as an example; powered command:

Set Powered Command
===================

    Command Code:           0x0005
    Controller Index:       <controller id>
    Command Parameters:     Powered (1 Octet)
    Return Parameters:      Current_Settings (4 Octets)

To power-on adapter at index zero, the following command would be sent with the synchronous API

from btsocket import btmgmt_sync
response = btmgmt_sync.send('SetPowered', 0, 1)

The format of the send command is :

response = send(<command_name>, <adapter index>, <positional paramters>)

The command name is taken from the heading in the documentation with the spaces and the word “Command” removed. A typical response is given below:

Response(
    header=<
        event_code=CommandCompleteEvent,
        controller_idx=0,
        param_len=7>,
    event_frame=<
        command_opcode=SetPowered,
        status=Success>,
    cmd_response_frame=<
        current_settings=2752>)

An example of the Python to access the values in the response is:

print(response.event_frame.command_opcode,
      response.event_frame.status)

Callbacks on Events

The structure for running with callbacks on events is below.

Getting the event loop and running until complete should be familiar to regular users of asyncio.

mgmt = btmgmt_callback.Mgmt() sets up the sockets and the readers and writers to the sockets.

mgmt.add_event_callback takes two arguments, the first is the btmgmt event and the second is the callback function to use when that event is detected.

mgmt.send is how to send commands and is similar to the synchronous API except it doesn’t get a response. You will have to add an event callback to access the response. The command(s) are not sent until mgmt.start() as this is what starts the writers and readers of the sockets.

from btsocket import btmgmt_callback
from btsocket import btmgmt_protocol

def device_found(response, mgmt_obj):
    print('New device found', data.event_frame.address)
    # To exit set running to False
    mgmt_obj.stop()

def app():
    mgmt = btmgmt_callback.Mgmt()
    mgmt.add_event_callback(btmgmt.Events.DeviceFoundEvent, device_found)
    mgmt.send('StartDiscovery', 0, 6)
    mgmt.start()


if __name__ == '__main__':
    app()

There are more examples in the examples folder