bluez: Verify that Advertisement Monitor has been registered

Author: bojanpotocnik

CHANGELOG.rst

@@ -14,6 +14,7 @@ Added
 -----
 * Added optional hack to use Bluetooth address instead of UUID on macOS.
 * Added ``BleakScanner.find_device_by_name()`` class method.
+* Added check to verify that BlueZ Advertisement Monitor was actually registered. Solves #1136.
 
 Changed
 -------

bleak/backends/bluezdbus/advertisement_monitor.py

@@ -7,7 +7,7 @@
 """
 
 import logging
-from typing import Iterable, NamedTuple, Tuple, Union, no_type_check
+from typing import Iterable, NamedTuple, Tuple, Union, no_type_check, Optional
 
 from dbus_fast.service import ServiceInterface, dbus_property, method, PropertyAccess
 
@@ -60,14 +60,22 @@ def __init__(
         super().__init__(defs.ADVERTISEMENT_MONITOR_INTERFACE)
         # dbus_fast marshaling requires list instead of tuple
         self._or_patterns = [list(p) for p in or_patterns]
+        self._activated: Optional[bool] = None
+
+    @property
+    def active(self) -> Optional[bool]:
+        """``True`` if this monitor has been activated, ``False`` if released, or ``None`` if neither has occurred."""
+        return self._activated
 
     @method()
     def Release(self):
         logger.debug("Release")
+        self._activated = False
 
     @method()
     def Activate(self):
         logger.debug("Activate")
+        self._activated = True
 
     # REVISIT: mypy is broke, so we have to add redundant @no_type_check
     # https://github.com/python/mypy/issues/6583

bleak/backends/bluezdbus/manager.py

@@ -448,7 +448,7 @@ async def passive_scan(
 
                 # this should be a unique path to allow multiple python interpreters
                 # running bleak and multiple scanners within a single interpreter
-                monitor_path = f"/org/bleak/{os.getpid()}/{id(monitor)}"
+                monitor_path = f"/org/bleak/{os.getpid()}/{AdvertisementMonitor.__name__}{id(monitor)}"
 
                 reply = await self._bus.call(
                     Message(
@@ -471,10 +471,47 @@ async def passive_scan(
 
                 assert_reply(reply)
 
-                # It is important to export after registering, otherwise BlueZ
-                # won't use the monitor
+                # It is important to export AFTER registering, otherwise BlueZ won't use the monitor
                 self._bus.export(monitor_path, monitor)
 
+                # During export, MGMT command "Add Advertisement Patterns Monitor (0x0052)" is executed.
+                # If Linux kernel is too old to support this command, MGMT event "Command Status (0x0002)"
+                # is returned with "Status: Unknown Command (0x01)" - bleak cannot detect this error and
+                # trying to scan would result in no devices ever reported, as Adv. Monitor was not registered.
+                # Running bluetoothd with -d flag gives the following output for 'journalctl --unit=bluetooth -f':
+                #   bluetoothd[...]: Path /org/bleak/.../AdvertisementMonitor... reserved for Adv Monitor app :...
+                #   ...
+                #   bluetoothd[...]: src/shared/mgmt.c:send_request() [0x0000] command 0x0052
+                #   bluetoothd[...]: src/shared/mgmt.c:can_read_data() [0x0000] command 0x52 status: 0x01
+                #   bluetoothd[...]: Failed to Add Adv Patterns Monitor with status 0x01
+                #   bluetoothd[...]: src/adv_monitor.c:monitor_release() Calling Release() on Adv Monitor
+                #                    of owner :... at path /org/bleak/.../AdvertisementMonitor...
+                #   bluetoothd[...]: Merged_pattern not found when removing monitor
+                #   ...
+                # Note that `monitor.Release()` cannot be invoked if control is not passed to the event loop.
+                # Rather than using asyncio.sleep(), read property to ensure that all queued D-Bus calls are executed.
+                reply = await self._bus.call(
+                    Message(
+                        destination=defs.BLUEZ_SERVICE,
+                        path=adapter_path,
+                        interface=defs.PROPERTIES_INTERFACE,
+                        member="Get",
+                        signature="ss",
+                        body=[
+                            defs.ADVERTISEMENT_MONITOR_MANAGER_INTERFACE,
+                            "SupportedFeatures",
+                        ],
+                    )
+                )
+                assert_reply(reply)
+
+                # Monitor might not be Activate-d yet, but for sure it shall not be Release-d
+                if monitor.active is False:
+                    raise BleakError(
+                        "Advertising Monitor (required for passive scanning) is not supported by this kernel"
+                        " (Linux kernel >= 5.10 is required)"
+                    )
+
                 async def stop():
                     # need to remove callbacks first, otherwise we get TxPower
                     # and RSSI properties removed during stop which causes