Skip to content

Bluetooth Low Energy (BLE)

A Bluetooth Low Energy (BLE) SMPTransport.

SMP_SERVICE_UUID: Final = UUID('8D53DC1D-1DB7-4CD3-868B-8A527460AA84') module-attribute

SMP_CHARACTERISTIC_UUID: Final = UUID('DA2E7828-FBCE-4E01-AE9E-261174997C48') module-attribute

MAC_ADDRESS_PATTERN: Final = re.compile('([0-9A-F]{2}[:]){5}[0-9A-F]{2}$', flags=re.IGNORECASE) module-attribute

UUID_PATTERN: Final = re.compile('^[a-f0-9]{8}-?[a-f0-9]{4}-?4[a-f0-9]{3}-?[89ab][a-f0-9]{3}-?[a-f0-9]{12}\\Z', flags=re.IGNORECASE) module-attribute

logger = logging.getLogger(__name__) module-attribute

GattSession

Bases: Protocol

Source code in smpclient/transport/ble.py 
34
35
class GattSession(Protocol):
    max_pdu_size: int

max_pdu_size: int instance-attribute

SMPBLETransportException

Bases: SMPClientException

Base class for SMP BLE transport exceptions.

Source code in smpclient/transport/ble.py 
53
54
class SMPBLETransportException(SMPClientException):
    """Base class for SMP BLE transport exceptions."""

SMPBLETransportDeviceNotFound

Bases: SMPBLETransportException

Raised when a BLE device is not found.

Source code in smpclient/transport/ble.py 
57
58
class SMPBLETransportDeviceNotFound(SMPBLETransportException):
    """Raised when a BLE device is not found."""

SMPBLETransportNotSMPServer

Bases: SMPBLETransportException

Raised when the SMP characteristic UUID is not found.

Source code in smpclient/transport/ble.py 
61
62
class SMPBLETransportNotSMPServer(SMPBLETransportException):
    """Raised when the SMP characteristic UUID is not found."""

SMPBLETransport

Bases: SMPTransport

A Bluetooth Low Energy (BLE) SMPTransport.

Source code in smpclient/transport/ble.py 
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
class SMPBLETransport(SMPTransport):
    """A Bluetooth Low Energy (BLE) SMPTransport."""

    def __init__(self) -> None:
        self._buffer = bytearray()
        self._notify_condition = asyncio.Condition()
        self._disconnected_event = asyncio.Event()
        self._disconnected_event.set()

        self._max_write_without_response_size = 20
        """Initially set to BLE minimum; may be mutated by the `connect()` method."""

        logger.debug(f"Initialized {self.__class__.__name__}")

    @override
    async def connect(self, address: str, timeout_s: float) -> None:
        logger.debug(f"Scanning for {address=}")
        device: BLEDevice | None = (
            await BleakScanner.find_device_by_address(address, timeout=timeout_s)
            if MAC_ADDRESS_PATTERN.match(address) or UUID_PATTERN.match(address)
            else await BleakScanner.find_device_by_name(address)
        )

        if type(device) is BLEDevice:
            self._client = BleakClient(
                device,
                services=(str(SMP_SERVICE_UUID),),
                disconnected_callback=self._set_disconnected_event,
            )
        else:
            raise SMPBLETransportDeviceNotFound(f"Device '{address}' not found")

        logger.debug(f"Found device: {device=}, connecting...")
        await self._client.connect()
        self._disconnected_event.clear()
        logger.debug(f"Connected to {device=}")

        smp_characteristic = self._client.services.get_characteristic(SMP_CHARACTERISTIC_UUID)
        if smp_characteristic is None:
            raise SMPBLETransportNotSMPServer("Missing the SMP characteristic UUID.")

        logger.debug(f"Found SMP characteristic: {smp_characteristic=}")
        logger.info(f"{smp_characteristic.max_write_without_response_size=}")
        self._max_write_without_response_size = smp_characteristic.max_write_without_response_size
        if (
            self._winrt_backend(self._client._backend)
            and self._max_write_without_response_size == 20
        ):
            # https://github.com/hbldh/bleak/pull/1552#issuecomment-2105573291
            logger.warning(
                "The SMP characteristic MTU is 20 bytes, possibly a Windows bug, checking again"
            )
            await asyncio.sleep(2)
            smp_characteristic._max_write_without_response_size = (
                self._client._backend._session.max_pdu_size - 3  # type: ignore
            )
            self._max_write_without_response_size = (
                smp_characteristic.max_write_without_response_size
            )
            logger.warning(f"{smp_characteristic.max_write_without_response_size=}")
        elif self._bluez_backend(self._client._backend):
            logger.debug("Getting MTU from BlueZ backend")
            await self._client._backend._acquire_mtu()
            logger.debug(f"Got MTU: {self._client.mtu_size}")
            self._max_write_without_response_size = self._client.mtu_size - 3

        logger.info(f"{self._max_write_without_response_size=}")
        self._smp_characteristic = smp_characteristic

        logger.debug(f"Starting notify on {SMP_CHARACTERISTIC_UUID=}")
        await self._client.start_notify(SMP_CHARACTERISTIC_UUID, self._notify_callback)
        logger.debug(f"Started notify on {SMP_CHARACTERISTIC_UUID=}")

    @override
    async def disconnect(self) -> None:
        logger.debug(f"Disonnecting from {self._client.address}")
        await self._client.disconnect()
        logger.debug(f"Disconnected from {self._client.address}")

    @override
    async def send(self, data: bytes) -> None:
        logger.debug(f"Sending {len(data)} bytes, {self.mtu=}")
        for offset in range(0, len(data), self.mtu):
            await self._client.write_gatt_char(
                self._smp_characteristic, data[offset : offset + self.mtu], response=False
            )
        logger.debug(f"Sent {len(data)} bytes")

    @override
    async def receive(self) -> bytes:
        # Note: self._buffer is mutated asynchronously by this method and self._notify_callback().
        #       self._notify_condition is used to synchronize access to self._buffer.

        async with self._notify_condition:  # wait for the header
            logger.debug(f"Waiting for notify on {SMP_CHARACTERISTIC_UUID=}")
            await self._notify_or_disconnect()

            if len(self._buffer) < smphdr.Header.SIZE:  # pragma: no cover
                raise SMPBLETransportException(
                    f"Buffer contents not big enough for SMP header: {self._buffer=}"
                )

            header: Final = smphdr.Header.loads(self._buffer[: smphdr.Header.SIZE])
            logger.debug(f"Received {header=}")

        message_length: Final = header.length + header.SIZE
        logger.debug(f"Waiting for the rest of the {message_length} byte response")

        while True:  # wait for the rest of the message
            async with self._notify_condition:
                if len(self._buffer) == message_length:
                    logger.debug(f"Finished receiving {message_length} byte response")
                    out = bytes(self._buffer)
                    self._buffer.clear()
                    return out
                elif len(self._buffer) > message_length:  # pragma: no cover
                    raise SMPBLETransportException("Length of buffer passed expected message size.")
                await self._notify_or_disconnect()

    async def _notify_callback(self, sender: BleakGATTCharacteristic, data: bytes) -> None:
        if sender.uuid != str(SMP_CHARACTERISTIC_UUID):  # pragma: no cover
            raise SMPBLETransportException(f"Unexpected notify from {sender}; {data=}")
        async with self._notify_condition:
            logger.debug(f"Received {len(data)} bytes from {SMP_CHARACTERISTIC_UUID=}")
            self._buffer.extend(data)
            self._notify_condition.notify()

    async def send_and_receive(self, data: bytes) -> bytes:
        await self.send(data)
        return await self.receive()

    @override
    @property
    def mtu(self) -> int:
        return self._max_write_without_response_size

    @staticmethod
    async def scan(timeout: int = 5) -> List[BLEDevice]:
        """Scan for BLE devices."""
        logger.debug(f"Scanning for BLE devices for {timeout} seconds")
        devices: Final = await BleakScanner(service_uuids=[str(SMP_SERVICE_UUID)]).discover(
            timeout=timeout, return_adv=True
        )
        smp_servers: Final = [
            d for d, a in devices.values() if SMP_SERVICE_UUID in {UUID(u) for u in a.service_uuids}
        ]
        logger.debug(f"Found {len(smp_servers)} SMP devices: {smp_servers=}")
        return smp_servers

    @staticmethod
    def _bluez_backend(client_backend: BaseBleakClient) -> TypeGuard[BleakClientBlueZDBus]:
        return client_backend.__class__.__name__ == "BleakClientBlueZDBus"

    @staticmethod
    def _winrt_backend(client_backend: BaseBleakClient) -> TypeGuard[BleakClientWinRT]:
        return client_backend.__class__.__name__ == "BleakClientWinRT"

    def _set_disconnected_event(self, client: BleakClient) -> None:
        if client is not self._client:
            raise SMPBLETransportException(
                f"Unexpected client disconnected: {client=}, {self._client=}"
            )
        logger.warning(f"Disconnected from {client.address}")
        self._disconnected_event.set()

    async def _notify_or_disconnect(self) -> None:
        disconnected_task: Final = asyncio.create_task(self._disconnected_event.wait())
        notify_task: Final = asyncio.create_task(self._notify_condition.wait())
        done, pending = await asyncio.wait(
            (disconnected_task, notify_task), return_when=asyncio.FIRST_COMPLETED
        )
        for task in pending:
            task.cancel()
        try:
            await asyncio.gather(*pending)
        except asyncio.CancelledError:
            pass
        if disconnected_task in done:
            raise SMPTransportDisconnected(
                f"{self.__class__.__name__} disconnected from {self._client.address}"
            )

mtu: int property

The Maximum Transmission Unit (MTU) in 8-bit bytes.

__init__() -> None

Source code in smpclient/transport/ble.py 
71
72
73
74
75
76
77
78
79
80
def __init__(self) -> None:
    self._buffer = bytearray()
    self._notify_condition = asyncio.Condition()
    self._disconnected_event = asyncio.Event()
    self._disconnected_event.set()

    self._max_write_without_response_size = 20
    """Initially set to BLE minimum; may be mutated by the `connect()` method."""

    logger.debug(f"Initialized {self.__class__.__name__}")

connect(address: str, timeout_s: float) -> None async

Connect the SMPTransport.

Parameters:

Name Type Description Default
address str

The SMP server address.

 required
timeout_s float

The connection timeout in seconds.

 required
Source code in smpclient/transport/ble.py 
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
@override
async def connect(self, address: str, timeout_s: float) -> None:
    logger.debug(f"Scanning for {address=}")
    device: BLEDevice | None = (
        await BleakScanner.find_device_by_address(address, timeout=timeout_s)
        if MAC_ADDRESS_PATTERN.match(address) or UUID_PATTERN.match(address)
        else await BleakScanner.find_device_by_name(address)
    )

    if type(device) is BLEDevice:
        self._client = BleakClient(
            device,
            services=(str(SMP_SERVICE_UUID),),
            disconnected_callback=self._set_disconnected_event,
        )
    else:
        raise SMPBLETransportDeviceNotFound(f"Device '{address}' not found")

    logger.debug(f"Found device: {device=}, connecting...")
    await self._client.connect()
    self._disconnected_event.clear()
    logger.debug(f"Connected to {device=}")

    smp_characteristic = self._client.services.get_characteristic(SMP_CHARACTERISTIC_UUID)
    if smp_characteristic is None:
        raise SMPBLETransportNotSMPServer("Missing the SMP characteristic UUID.")

    logger.debug(f"Found SMP characteristic: {smp_characteristic=}")
    logger.info(f"{smp_characteristic.max_write_without_response_size=}")
    self._max_write_without_response_size = smp_characteristic.max_write_without_response_size
    if (
        self._winrt_backend(self._client._backend)
        and self._max_write_without_response_size == 20
    ):
        # https://github.com/hbldh/bleak/pull/1552#issuecomment-2105573291
        logger.warning(
            "The SMP characteristic MTU is 20 bytes, possibly a Windows bug, checking again"
        )
        await asyncio.sleep(2)
        smp_characteristic._max_write_without_response_size = (
            self._client._backend._session.max_pdu_size - 3  # type: ignore
        )
        self._max_write_without_response_size = (
            smp_characteristic.max_write_without_response_size
        )
        logger.warning(f"{smp_characteristic.max_write_without_response_size=}")
    elif self._bluez_backend(self._client._backend):
        logger.debug("Getting MTU from BlueZ backend")
        await self._client._backend._acquire_mtu()
        logger.debug(f"Got MTU: {self._client.mtu_size}")
        self._max_write_without_response_size = self._client.mtu_size - 3

    logger.info(f"{self._max_write_without_response_size=}")
    self._smp_characteristic = smp_characteristic

    logger.debug(f"Starting notify on {SMP_CHARACTERISTIC_UUID=}")
    await self._client.start_notify(SMP_CHARACTERISTIC_UUID, self._notify_callback)
    logger.debug(f"Started notify on {SMP_CHARACTERISTIC_UUID=}")

disconnect() -> None async

Disconnect the SMPTransport.

Source code in smpclient/transport/ble.py 
141
142
143
144
145
@override
async def disconnect(self) -> None:
    logger.debug(f"Disonnecting from {self._client.address}")
    await self._client.disconnect()
    logger.debug(f"Disconnected from {self._client.address}")

send(data: bytes) -> None async

Send the encoded SMPRequest data.

Parameters:

Name Type Description Default
data bytes

The encoded SMPRequest.

 required
Source code in smpclient/transport/ble.py 
147
148
149
150
151
152
153
154
@override
async def send(self, data: bytes) -> None:
    logger.debug(f"Sending {len(data)} bytes, {self.mtu=}")
    for offset in range(0, len(data), self.mtu):
        await self._client.write_gatt_char(
            self._smp_characteristic, data[offset : offset + self.mtu], response=False
        )
    logger.debug(f"Sent {len(data)} bytes")

receive() -> bytes async

Receive the decoded SMPResponse data.

Returns:

Type Description
bytes

The SMPResponse bytes.
Source code in smpclient/transport/ble.py 
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
@override
async def receive(self) -> bytes:
    # Note: self._buffer is mutated asynchronously by this method and self._notify_callback().
    #       self._notify_condition is used to synchronize access to self._buffer.

    async with self._notify_condition:  # wait for the header
        logger.debug(f"Waiting for notify on {SMP_CHARACTERISTIC_UUID=}")
        await self._notify_or_disconnect()

        if len(self._buffer) < smphdr.Header.SIZE:  # pragma: no cover
            raise SMPBLETransportException(
                f"Buffer contents not big enough for SMP header: {self._buffer=}"
            )

        header: Final = smphdr.Header.loads(self._buffer[: smphdr.Header.SIZE])
        logger.debug(f"Received {header=}")

    message_length: Final = header.length + header.SIZE
    logger.debug(f"Waiting for the rest of the {message_length} byte response")

    while True:  # wait for the rest of the message
        async with self._notify_condition:
            if len(self._buffer) == message_length:
                logger.debug(f"Finished receiving {message_length} byte response")
                out = bytes(self._buffer)
                self._buffer.clear()
                return out
            elif len(self._buffer) > message_length:  # pragma: no cover
                raise SMPBLETransportException("Length of buffer passed expected message size.")
            await self._notify_or_disconnect()

send_and_receive(data: bytes) -> bytes async

Send the encoded SMPRequest data and receive the decoded SMPResponse.

Parameters:

Name Type Description Default
data bytes

The encoded SMPRequest.

 required

Returns:

Type Description
bytes

The SMPResponse bytes.
Source code in smpclient/transport/ble.py 
195
196
197
async def send_and_receive(self, data: bytes) -> bytes:
    await self.send(data)
    return await self.receive()

scan(timeout: int = 5) -> List[BLEDevice] async staticmethod

Scan for BLE devices.

Source code in smpclient/transport/ble.py 
204
205
206
207
208
209
210
211
212
213
214
215
@staticmethod
async def scan(timeout: int = 5) -> List[BLEDevice]:
    """Scan for BLE devices."""
    logger.debug(f"Scanning for BLE devices for {timeout} seconds")
    devices: Final = await BleakScanner(service_uuids=[str(SMP_SERVICE_UUID)]).discover(
        timeout=timeout, return_adv=True
    )
    smp_servers: Final = [
        d for d, a in devices.values() if SMP_SERVICE_UUID in {UUID(u) for u in a.service_uuids}
    ]
    logger.debug(f"Found {len(smp_servers)} SMP devices: {smp_servers=}")
    return smp_servers