我无法列出 Raspberry Pi 附近的 BLE 设备（python、btmgmt）

Question

我想使用从 cron 脚本调用的 python 脚本来扫描 Raspberry 环境中的 ble 设备。但是当我在 cron 中执行此操作时（我的意思是我添加到 sudo crontab -e），我最终总是得到一个空列表。

当我以 pi 用户身份登录时 - btmgmt 可以（仅）在 su 权限下正常工作：

pi@Pluto:~ $ btmgmt find
Unable to start discovery. status 0x14 (Permission Denied)

pi@Pluto:~ $ sudo btmgmt find
Discovery started
hci0 type 7 discovering on
hci0 dev_found: 77:F8:D7:8A:1E:E5 type LE Random rssi -83 flags 0x0000 
...

所以在我的python脚本中我写道：

flog.write("P01:\r\n")
out = subprocess.Popen(['sudo', '/usr/bin/btmgmt', 'find'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
stdout, stderr = out.communicate()
flog.write("stderr: " + str(stderr) + "\r\n")
cDvc = stdout.split('\n')
flog.write("Amount of lines = " + str(len(cDvc)) + "\r\n")
for line in cDvc:
    line = line + '\r\n'
    if debugflag:
        print(line)
        flog.write(line)
..

从 shell 提示符运行此脚本工作正常.. 在日志文件 (flog) 中我得到：...

P01:
stderr: None
Amount of lines = 40
Discovery started
hci0 type 7 discovering on
hci0 dev_found: 70:D0:FD:74:34:AC type LE Random rssi -59 flags 0x0000 
AD flags 0x1a 
..

运行与 crontab -e 行相同的脚本：没有设备出现，我找不到原因：

...
P01:
stderr: None
Amount of lines = 1
P02:
...

有人可以帮我从这里出去吗？

Answer 1

如果您使用 BlueZ DBus API 来获取信息，则无需使用 sudo。它还避免了您必须使用 btmgmt，因为我不确定它是否打算以这种方式编写脚本

DBus API 的文档位于：

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

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

pydbus 库对于访问 BlueZ DBus API 非常有帮助：https ://pypi.org/project/pydbus/

一些帮助您入门的有用信息：

1. bluez 的 Dbus 服务称为“org.bluez”
2. 默认蓝牙适配器通常将“/org/bluez/hci0”作为其 DBus 对象路径。
3. BlueZ/DBus 有一个对象管理器，用于存储有关设备的信息

我做了以下脚本来测试这个想法：

from datetime import datetime
import os
import pydbus
from gi.repository import GLib

discovery_time = 60
log_file = '/home/pi/device.log'

# Create an empty log file
def write_to_log(address, rssi):
    if os.path.exists(log_file):
        open_mode = 'a'
    else:
        open_mode = 'w'

    with open(log_file, open_mode) as dev_log:
        now = datetime.now()
        current_time = now.strftime('%H:%M:%S')
        dev_log.write(f'Device seen[{current_time}]: {address} @ {rssi} dBm\n')

bus = pydbus.SystemBus()
mainloop = GLib.MainLoop()

class DeviceMonitor:
    def __init__(self, path_obj):
        self.device = bus.get('org.bluez', path_obj)
        self.device.onPropertiesChanged = self.prop_changed
        print(f'Device added to monitor {self.device.Address}')

    def prop_changed(self, iface, props_changed, props_removed):
        rssi = props_changed.get('RSSI', None)
        if rssi is not None:
            print(f'\tDevice Seen: {self.device.Address} @ {rssi} dBm')
            write_to_log(self.device.Address, rssi)


def end_discovery():
    """Handler for end of discovery"""
    mainloop.quit()
    adapter.StopDiscovery()

def new_iface(path, iface_props):
    """If a new dbus interfaces is a device, add it to be  monitored"""
    device_addr = iface_props.get('org.bluez.Device1', {}).get('Address')
    if device_addr:
        DeviceMonitor(path)

# BlueZ object manager
mngr = bus.get('org.bluez', '/')
mngr.onInterfacesAdded = new_iface

# Connect to the DBus api for the Bluetooth adapter
adapter = bus.get('org.bluez', '/org/bluez/hci0')
adapter.DuplicateData = False

# Iterate around already known devices and add to monitor
mng_objs = mngr.GetManagedObjects()
for path in mng_objs:
    device = mng_objs[path].get('org.bluez.Device1', {}).get('Address', [])
    if device:
        DeviceMonitor(path)

# Run discovery for discovery_time
adapter.StartDiscovery()
GLib.timeout_add_seconds(discovery_time, end_discovery)
print('Finding nearby devices...')
try:
    mainloop.run()
except KeyboardInterrupt:
    end_discovery()