macOS backend

The macOS backend of Bleak is written with pyobjc directives for interfacing with Foundation and CoreBluetooth APIs.

Specific features for the macOS backend

The most noticeable difference between the other backends of bleak and this backend, is that CoreBluetooth doesn’t scan for other devices via Bluetooth address. Instead, UUIDs are utilized that are often unique between the device that is scanning and the device that is being scanned.

In the example files, this is handled in this fashion:

mac_addr = (
    "24:71:89:cc:09:05"
    if platform.system() != "Darwin"
    else "243E23AE-4A99-406C-B317-18F1BD7B4CBE"
)

As stated above, this will however only work the macOS machine that performed the scan and thus cached the device as 243E23AE-4A99-406C-B317-18F1BD7B4CBE.

Pairing

There is no pairing functionality implemented in macOS right now, since it does not seem to be any explicit pairing methods in CoreBluetooth.

Instead, macOS will prompt the user the first time a characteristic that requires authorization/authentication is accessed. This means that a GATT read or write operation could block for a long time waiting for the user to responsed. So timeouts should be set accordingly.

Calling the bleak.BleakClient.pair() method will raise a NotImplementedError on macOS. But setting pair=True in bleak.BleakClient will be silently ignored.

Notifications

CoreBluetooth does not differentiate between data from a notification and data from a read. This can cause confusion in cases where a device may send a notification message on a characteristic as a signal that the characteristic needs to be read again.

Bleak can accept a notification_discriminator callback in the cb dict parameter that is passed to the bleak.BleakClient.start_notify() method that can differentiate between these types of data.

event = asyncio.Event()

async def notification_handler(char, data):
    event.set()

def notification_check_handler(data):
    # We can identify notifications on this characteristic because they
    # only contain 1 byte of data. Read responses will have more than
    # 1 byte.
    return len(data) == 1

await client.start_notify(
    char,
    notification_handler,
    cb={"notification_discriminator": notification_check_handler},
)

while True:
    await event.wait()
    # We received a notification - prepare to receive another
    event.clear()
    # Then read the characteristic to get the full value
    data = await client.read_gatt_char(char)
    # Do stuff with data

API

Scanner

class bleak.backends.corebluetooth.scanner.BleakScannerCoreBluetooth(detection_callback: Callable[[BLEDevice, AdvertisementData], Coroutine[Any, Any, None] | None] | None, service_uuids: list[str] | None, scanning_mode: Literal['active', 'passive'], *, cb: CBScannerArgs, **kwargs: Any)[source]

The native macOS Bleak BLE Scanner.

Documentation: https://developer.apple.com/documentation/corebluetooth/cbcentralmanager

CoreBluetooth doesn’t explicitly use Bluetooth addresses to identify peripheral devices because private devices may obscure their Bluetooth addresses. To cope with this, CoreBluetooth utilizes UUIDs for each peripheral. Bleak uses this for the BLEDevice address on macOS.

Parameters:
  • detection_callback – Optional function that will be called each time a device is discovered or advertising data has changed.

  • service_uuids – Optional list of service UUIDs to filter on. Only advertisements containing this advertising data will be received. Required on macOS >= 12.0, < 12.3 (unless you create an app with py2app).

  • scanning_mode – Set to "passive" to avoid the "active" scanning mode. Not supported on macOS! Will raise BleakError if set to "passive"

  • **timeout (float) – The scanning timeout to be used, in case of missing stopScan_ method.

async start() None[source]

Start scanning for devices

async stop() None[source]

Stop scanning for devices

Client

BLE Client for CoreBluetooth on macOS

class bleak.backends.corebluetooth.client.BleakClientCoreBluetooth(address_or_ble_device: BLEDevice | str, services: set[str] | None = None, **kwargs: Any)[source]

CoreBluetooth class interface for BleakClient

Parameters:
  • address_or_ble_device (BLEDevice or str) – The Bluetooth address of the BLE peripheral to connect to or the BLEDevice object representing it.

  • services – Optional set of service UUIDs that will be used.

Keyword Arguments:

timeout (float) – Timeout for required BleakScanner.find_device_by_address call. Defaults to 10.0.

async connect(pair: bool, **kwargs: Any) None[source]

Connect to a specified Peripheral

Keyword Arguments:

timeout (float) – Timeout for required BleakScanner.find_device_by_address call. Defaults to 10.0.

async disconnect() None[source]

Disconnect from the peripheral device

async get_rssi() int[source]

To get RSSI value in dBm of the connected Peripheral

property is_connected: bool

Checks for current active connection

property mtu_size: int

Get ATT MTU size for active connection

async pair(*args: Any, **kwargs: Any) None[source]

Attempt to pair with a peripheral.

Raises:

NotImplementedError – This is not available on macOS since there is not explicit API to do a pairing. Instead, the docs state that it “auto-pairs”, when trying to read a characteristic that requires encryption.

Reference:

async read_gatt_char(characteristic: BleakGATTCharacteristic, **kwargs: Any) bytearray[source]

Perform read operation on the specified GATT characteristic.

Parameters:

characteristic (BleakGATTCharacteristic) – The characteristic to read from.

Returns:

(bytearray) The read data.

async read_gatt_descriptor(descriptor: BleakGATTDescriptor, **kwargs: Any) bytearray[source]

Perform read operation on the specified GATT descriptor.

Parameters:
  • handle (int) – The handle of the descriptor to read from.

  • use_cached (bool) – False forces Windows to read the value from the device again and not use its own cached value. Defaults to False.

Returns:

(bytearray) The read data.

async start_notify(characteristic: BleakGATTCharacteristic, callback: Callable[[bytearray], None], *, cb: CBStartNotifyArgs, **kwargs: Any) None[source]

Activate notifications/indications on a characteristic.

async stop_notify(characteristic: BleakGATTCharacteristic) None[source]

Deactivate notification/indication on a specified characteristic.

Parameters:

(BleakGATTCharacteristic (characteristic) – The characteristic to deactivate notification/indication on.

async unpair() None[source]

Remove pairing information for a peripheral.

Raises:

NotImplementedError – This is not available on macOS since there is not explicit API to do a pairing.

async write_gatt_char(characteristic: BleakGATTCharacteristic, data: Buffer, response: bool) None[source]

Perform a write operation on the specified GATT characteristic.

Parameters:
  • characteristic – The characteristic to write to.

  • data – The data to send.

  • response – If write-with-response operation should be done.

async write_gatt_descriptor(descriptor: BleakGATTDescriptor, data: Buffer) None[source]

Perform a write operation on the specified GATT descriptor.

Parameters:
  • descriptor – The descriptor to read from.

  • data – The data to send (any bytes-like object).