improve DLC parameters

apps/bench.py

@@ -899,14 +899,26 @@ class L2capServer(StreamedPacketIO):
 # RfcommClient
 # -----------------------------------------------------------------------------
 class RfcommClient(StreamedPacketIO):
-    def __init__(self, device, channel, uuid, l2cap_mtu, max_frame_size, window_size):
+    def __init__(
+        self,
+        device,
+        channel,
+        uuid,
+        l2cap_mtu,
+        max_frame_size,
+        initial_credits,
+        max_credits,
+        credits_threshold,
+    ):
         super().__init__()
         self.device = device
         self.channel = channel
         self.uuid = uuid
         self.l2cap_mtu = l2cap_mtu
         self.max_frame_size = max_frame_size
-        self.window_size = window_size
+        self.initial_credits = initial_credits
+        self.max_credits = max_credits
+        self.credits_threshold = credits_threshold
         self.rfcomm_session = None
         self.ready = asyncio.Event()
 
@@ -940,12 +952,17 @@ class RfcommClient(StreamedPacketIO):
         logging.info(color(f'### Opening session for channel {channel}...', 'yellow'))
         try:
             dlc_options = {}
-            if self.max_frame_size:
+            if self.max_frame_size is not None:
                 dlc_options['max_frame_size'] = self.max_frame_size
-            if self.window_size:
-                dlc_options['window_size'] = self.window_size
+            if self.initial_credits is not None:
+                dlc_options['initial_credits'] = self.initial_credits
             rfcomm_session = await rfcomm_mux.open_dlc(channel, **dlc_options)
             logging.info(color(f'### Session open: {rfcomm_session}', 'yellow'))
+            if self.max_credits is not None:
+                rfcomm_session.rx_max_credits = self.max_credits
+            if self.credits_threshold is not None:
+                rfcomm_session.rx_credits_threshold = self.credits_threshold
+
         except bumble.core.ConnectionError as error:
             logging.info(color(f'!!! Session open failed: {error}', 'red'))
             await rfcomm_mux.disconnect()
@@ -969,8 +986,19 @@ class RfcommClient(StreamedPacketIO):
 # RfcommServer
 # -----------------------------------------------------------------------------
 class RfcommServer(StreamedPacketIO):
-    def __init__(self, device, channel, l2cap_mtu):
+    def __init__(
+        self,
+        device,
+        channel,
+        l2cap_mtu,
+        max_frame_size,
+        initial_credits,
+        max_credits,
+        credits_threshold,
+    ):
         super().__init__()
+        self.max_credits = max_credits
+        self.credits_threshold = credits_threshold
         self.dlc = None
         self.ready = asyncio.Event()
 
@@ -981,7 +1009,12 @@ class RfcommServer(StreamedPacketIO):
         rfcomm_server = bumble.rfcomm.Server(device, **server_options)
 
         # Listen for incoming DLC connections
-        channel_number = rfcomm_server.listen(self.on_dlc, channel)
+        dlc_options = {}
+        if max_frame_size is not None:
+            dlc_options['max_frame_size'] = max_frame_size
+        if initial_credits is not None:
+            dlc_options['initial_credits'] = initial_credits
+        channel_number = rfcomm_server.listen(self.on_dlc, channel, **dlc_options)
 
         # Setup the SDP to advertise this channel
         device.sdp_service_records = make_sdp_records(channel_number)
@@ -1004,6 +1037,10 @@ class RfcommServer(StreamedPacketIO):
         dlc.sink = self.on_packet
         self.io_sink = dlc.write
         self.dlc = dlc
+        if self.max_credits is not None:
+            dlc.rx_max_credits = self.max_credits
+        if self.credits_threshold is not None:
+            dlc.rx_credits_threshold = self.credits_threshold
 
     async def drain(self):
         assert self.dlc
@@ -1321,7 +1358,9 @@ def create_mode_factory(ctx, default_mode):
                 uuid=ctx.obj['rfcomm_uuid'],
                 l2cap_mtu=ctx.obj['rfcomm_l2cap_mtu'],
                 max_frame_size=ctx.obj['rfcomm_max_frame_size'],
-                window_size=ctx.obj['rfcomm_window_size'],
+                initial_credits=ctx.obj['rfcomm_initial_credits'],
+                max_credits=ctx.obj['rfcomm_max_credits'],
+                credits_threshold=ctx.obj['rfcomm_credits_threshold'],
             )
 
         if mode == 'rfcomm-server':
@@ -1329,6 +1368,10 @@ def create_mode_factory(ctx, default_mode):
                 device,
                 channel=ctx.obj['rfcomm_channel'],
                 l2cap_mtu=ctx.obj['rfcomm_l2cap_mtu'],
+                max_frame_size=ctx.obj['rfcomm_max_frame_size'],
+                initial_credits=ctx.obj['rfcomm_initial_credits'],
+                max_credits=ctx.obj['rfcomm_max_credits'],
+                credits_threshold=ctx.obj['rfcomm_credits_threshold'],
             )
 
         raise ValueError('invalid mode')
@@ -1427,9 +1470,19 @@ def create_role_factory(ctx, default_role):
     help='RFComm maximum frame size',
 )
 @click.option(
-    '--rfcomm-window-size',
+    '--rfcomm-initial-credits',
     type=int,
-    help='RFComm window size',
+    help='RFComm initial credits',
+)
+@click.option(
+    '--rfcomm-max-credits',
+    type=int,
+    help='RFComm max credits',
+)
+@click.option(
+    '--rfcomm-credits-threshold',
+    type=int,
+    help='RFComm credits threshold',
 )
 @click.option(
     '--l2cap-psm',
@@ -1530,7 +1583,9 @@ def bench(
     rfcomm_uuid,
     rfcomm_l2cap_mtu,
     rfcomm_max_frame_size,
-    rfcomm_window_size,
+    rfcomm_initial_credits,
+    rfcomm_max_credits,
+    rfcomm_credits_threshold,
     l2cap_psm,
     l2cap_mtu,
     l2cap_mps,
@@ -1545,7 +1600,9 @@ def bench(
     ctx.obj['rfcomm_uuid'] = rfcomm_uuid
     ctx.obj['rfcomm_l2cap_mtu'] = rfcomm_l2cap_mtu
     ctx.obj['rfcomm_max_frame_size'] = rfcomm_max_frame_size
-    ctx.obj['rfcomm_window_size'] = rfcomm_window_size
+    ctx.obj['rfcomm_initial_credits'] = rfcomm_initial_credits
+    ctx.obj['rfcomm_max_credits'] = rfcomm_max_credits
+    ctx.obj['rfcomm_credits_threshold'] = rfcomm_credits_threshold
     ctx.obj['l2cap_psm'] = l2cap_psm
     ctx.obj['l2cap_mtu'] = l2cap_mtu
     ctx.obj['l2cap_mps'] = l2cap_mps

apps/rfcomm_bridge.py

@@ -24,7 +24,7 @@ from typing import Optional
 import click
 
 from bumble.colors import color
-from bumble.device import Device, Connection
+from bumble.device import Device, DeviceConfiguration, Connection
 from bumble import core
 from bumble import hci
 from bumble import rfcomm
@@ -37,7 +37,8 @@ from bumble import utils
 # -----------------------------------------------------------------------------
 DEFAULT_RFCOMM_UUID = "E6D55659-C8B4-4B85-96BB-B1143AF6D3AE"
 DEFAULT_MTU = 4096
-DEFAULT_TCP_PORT = 9544
+DEFAULT_CLIENT_TCP_PORT = 9544
+DEFAULT_SERVER_TCP_PORT = 9545
 
 TRACE_MAX_SIZE = 48
 
@@ -149,7 +150,7 @@ class ServerBridge:
 
     def on_disconnection(self, reason: int):
         print(
-            color("@@@ Bluetooth disconnection:", "blue"),
+            color("@@@ Bluetooth disconnection:", "red"),
             hci.HCI_Constant.error_name(reason),
         )
 
@@ -271,6 +272,7 @@ class ClientBridge:
             self.address, transport=core.BT_BR_EDR_TRANSPORT
         )
         print(color(f"@@@ Bluetooth connection: {self.connection}", "blue"))
+        self.connection.on("disconnection", self.on_disconnection)
 
         if self.encrypt:
             print(color("@@@ Encrypting Bluetooth connection", "blue"))
@@ -278,19 +280,16 @@ class ClientBridge:
             print(color("@@@ Bluetooth connection encrypted", "blue"))
 
         self.rfcomm_client = rfcomm.Client(self.connection)
-        self.rfcomm_mux = await self.rfcomm_client.start()
-
-        def on_disconnection(reason):
-            print(
-                color("@@@ Bluetooth disconnection:", "red"),
-                hci.HCI_Constant.error_name(reason),
-            )
-            self.connection = None
-
-        self.connection.on("disconnection", on_disconnection)
+        try:
+            self.rfcomm_mux = await self.rfcomm_client.start()
+        except BaseException as e:
+            print(color("!!! Failed to setup RFCOMM connection", "red"), e)
+            raise
 
     async def start(self, device: Device) -> None:
         self.device = device
+        await device.set_connectable(False)
+        await device.set_discoverable(False)
 
         # Called when a TCP connection is established
         async def on_tcp_connection(reader, writer):
@@ -303,9 +302,15 @@ class ClientBridge:
                 return
             self.tcp_connected = True
 
-            await self.pipe(reader, writer)
-            writer.close()
-            await writer.wait_closed()
+            try:
+                await self.pipe(reader, writer)
+            except BaseException as error:
+                print(color("!!! Exception while piping data:", "red"), error)
+                return
+            finally:
+                writer.close()
+                await writer.wait_closed()
+                self.tcp_connected = False
 
         await asyncio.start_server(
             on_tcp_connection,
@@ -339,12 +344,12 @@ class ClientBridge:
         # Connect a new RFCOMM channel
         await self.connect()
         assert self.rfcomm_mux
-        print(color(f'*** Opening RFCOMM channel {channel}', 'green'))
+        print(color(f"*** Opening RFCOMM channel {channel}", "green"))
         try:
             rfcomm_channel = await self.rfcomm_mux.open_dlc(channel)
-            print(color(f'*** RFCOMM channel open: {rfcomm_channel}', "green"))
+            print(color(f"*** RFCOMM channel open: {rfcomm_channel}", "green"))
         except Exception as error:
-            print(color(f'!!! RFCOMM open failed: {error}', 'red'))
+            print(color(f"!!! RFCOMM open failed: {error}", "red"))
             return
 
         # Pipe data from RFCOMM to TCP
@@ -383,6 +388,13 @@ class ClientBridge:
 
         print(color("~~~ Bye bye", "magenta"))
 
+    def on_disconnection(self, reason: int) -> None:
+        print(
+            color("@@@ Bluetooth disconnection:", "red"),
+            hci.HCI_Constant.error_name(reason),
+        )
+        self.connection = None
+
 
 # -----------------------------------------------------------------------------
 async def run(device_config, hci_transport, bridge):
@@ -393,7 +405,14 @@ async def run(device_config, hci_transport, bridge):
     ):
         print("<<< connected")
 
-        device = Device.from_config_file_with_hci(device_config, hci_source, hci_sink)
+        if device_config:
+            device = Device.from_config_file_with_hci(
+                device_config, hci_source, hci_sink
+            )
+        else:
+            device = Device.from_config_with_hci(
+                DeviceConfiguration(), hci_source, hci_sink
+            )
         device.classic_enabled = True
 
         # Let's go
@@ -412,11 +431,28 @@ async def run(device_config, hci_transport, bridge):
 # -----------------------------------------------------------------------------
 @click.group()
 @click.pass_context
-@click.option("--device-config", help="Device configuration file", required=True)
-@click.option("--hci-transport", help="HCI transport", required=True)
+@click.option(
+    "--device-config",
+    metavar="CONFIG_FILE",
+    help="Device configuration file",
+)
+@click.option(
+    "--hci-transport", metavar="TRANSPORT_NAME", help="HCI transport", required=True
+)
 @click.option("--trace", is_flag=True, help="Trace bridged data to stdout")
-@click.option("--channel", help="RFCOMM channel number", type=int, default=0)
-@click.option("--uuid", help="UUID for the RFCOMM channel", default=DEFAULT_RFCOMM_UUID)
+@click.option(
+    "--channel",
+    metavar="CHANNEL_NUMER",
+    help="RFCOMM channel number",
+    type=int,
+    default=0,
+)
+@click.option(
+    "--uuid",
+    metavar="UUID",
+    help="UUID for the RFCOMM channel",
+    default=DEFAULT_RFCOMM_UUID,
+)
 def cli(
     context,
     device_config,
@@ -437,7 +473,7 @@ def cli(
 @cli.command()
 @click.pass_context
 @click.option("--tcp-host", help="TCP host", default="localhost")
-@click.option("--tcp-port", help="TCP port", default=DEFAULT_TCP_PORT)
+@click.option("--tcp-port", help="TCP port", default=DEFAULT_SERVER_TCP_PORT)
 def server(context, tcp_host, tcp_port):
     bridge = ServerBridge(
         context.obj["channel"],
@@ -454,7 +490,7 @@ def server(context, tcp_host, tcp_port):
 @click.pass_context
 @click.argument("bluetooth-address")
 @click.option("--tcp-host", help="TCP host", default="_")
-@click.option("--tcp-port", help="TCP port", default=DEFAULT_TCP_PORT)
+@click.option("--tcp-port", help="TCP port", default=DEFAULT_CLIENT_TCP_PORT)
 @click.option("--encrypt", is_flag=True, help="Encrypt the connection")
 def client(context, bluetooth_address, tcp_host, tcp_port, encrypt):
     bridge = ClientBridge(

bumble/l2cap.py

@@ -833,7 +833,9 @@ class ClassicChannel(EventEmitter):
 
         # Wait for the connection to succeed or fail
         try:
-            return await self.connection_result
+            return await self.connection.abort_on(
+                'disconnection', self.connection_result
+            )
         finally:
             self.connection_result = None
 
@@ -2226,7 +2228,7 @@ class ChannelManager:
         # Connect
         try:
             await channel.connect()
-        except Exception as e:
+        except BaseException as e:
             del connection_channels[source_cid]
             raise e
 

bumble/rfcomm.py

@@ -106,9 +106,11 @@ CRC_TABLE = bytes([
     0XBA, 0X2B, 0X59, 0XC8, 0XBD, 0X2C, 0X5E, 0XCF
 ])
 
-RFCOMM_DEFAULT_L2CAP_MTU      = 2048
-RFCOMM_DEFAULT_WINDOW_SIZE    = 7
-RFCOMM_DEFAULT_MAX_FRAME_SIZE = 2000
+RFCOMM_DEFAULT_L2CAP_MTU        = 2048
+RFCOMM_DEFAULT_INITIAL_CREDITS  = 7
+RFCOMM_DEFAULT_MAX_CREDITS      = 32
+RFCOMM_DEFAULT_CREDIT_THRESHOLD = RFCOMM_DEFAULT_MAX_CREDITS // 2
+RFCOMM_DEFAULT_MAX_FRAME_SIZE   = 2000
 
 RFCOMM_DYNAMIC_CHANNEL_NUMBER_START = 1
 RFCOMM_DYNAMIC_CHANNEL_NUMBER_END   = 30
@@ -365,12 +367,12 @@ class RFCOMM_MCC_PN:
     ack_timer: int
     max_frame_size: int
     max_retransmissions: int
-    window_size: int
+    initial_credits: int
 
     def __post_init__(self) -> None:
-        if self.window_size < 1 or self.window_size > 7:
+        if self.initial_credits < 1 or self.initial_credits > 7:
             logger.warning(
-                f'Error Recovery Window size {self.window_size} is out of range [1, 7].'
+                f'Initial credits {self.initial_credits} is out of range [1, 7].'
             )
 
     @staticmethod
@@ -382,7 +384,7 @@ class RFCOMM_MCC_PN:
             ack_timer=data[3],
             max_frame_size=data[4] | data[5] << 8,
             max_retransmissions=data[6],
-            window_size=data[7] & 0x07,
+            initial_credits=data[7] & 0x07,
         )
 
     def __bytes__(self) -> bytes:
@@ -396,7 +398,7 @@ class RFCOMM_MCC_PN:
                 (self.max_frame_size >> 8) & 0xFF,
                 self.max_retransmissions & 0xFF,
                 # Only 3 bits are meaningful.
-                self.window_size & 0x07,
+                self.initial_credits & 0x07,
             ]
         )
 
@@ -450,17 +452,21 @@ class DLC(EventEmitter):
         self,
         multiplexer: Multiplexer,
         dlci: int,
-        max_frame_size: int,
-        window_size: int,
+        tx_max_frame_size: int,
+        tx_initial_credits: int,
+        rx_max_frame_size: int,
+        rx_initial_credits: int,
     ) -> None:
         super().__init__()
         self.multiplexer = multiplexer
         self.dlci = dlci
-        self.max_frame_size = max_frame_size
-        self.window_size = window_size
-        self.rx_credits = window_size
-        self.rx_threshold = window_size // 2
-        self.tx_credits = window_size
+        self.rx_max_frame_size = rx_max_frame_size
+        self.rx_initial_credits = rx_initial_credits
+        self.rx_max_credits = RFCOMM_DEFAULT_MAX_CREDITS
+        self.rx_credits = rx_initial_credits
+        self.rx_credits_threshold = RFCOMM_DEFAULT_CREDIT_THRESHOLD
+        self.tx_max_frame_size = tx_max_frame_size
+        self.tx_credits = tx_initial_credits
         self.tx_buffer = b''
         self.state = DLC.State.INIT
         self.role = multiplexer.role
@@ -478,7 +484,7 @@ class DLC(EventEmitter):
         # Compute the MTU
         max_overhead = 4 + 1  # header with 2-byte length + fcs
         self.mtu = min(
-            max_frame_size, self.multiplexer.l2cap_channel.peer_mtu - max_overhead
+            tx_max_frame_size, self.multiplexer.l2cap_channel.peer_mtu - max_overhead
         )
 
     @property
@@ -645,9 +651,9 @@ class DLC(EventEmitter):
             cl=0xE0,
             priority=7,
             ack_timer=0,
-            max_frame_size=self.max_frame_size,
+            max_frame_size=self.rx_max_frame_size,
             max_retransmissions=0,
-            window_size=self.window_size,
+            initial_credits=self.rx_initial_credits,
         )
         mcc = RFCOMM_Frame.make_mcc(mcc_type=MccType.PN, c_r=0, data=bytes(pn))
         logger.debug(f'>>> PN Response: {pn}')
@@ -655,8 +661,8 @@ class DLC(EventEmitter):
         self.change_state(DLC.State.CONNECTING)
 
     def rx_credits_needed(self) -> int:
-        if self.rx_credits <= self.rx_threshold:
-            return self.window_size - self.rx_credits
+        if self.rx_credits <= self.rx_credits_threshold:
+            return self.rx_max_credits - self.rx_credits
 
         return 0
 
@@ -749,7 +755,7 @@ class Multiplexer(EventEmitter):
     connection_result: Optional[asyncio.Future]
     disconnection_result: Optional[asyncio.Future]
     open_result: Optional[asyncio.Future]
-    acceptor: Optional[Callable[[int], bool]]
+    acceptor: Optional[Callable[[int], Optional[Tuple[int, int]]]]
     dlcs: Dict[int, DLC]
 
     def __init__(self, l2cap_channel: l2cap.ClassicChannel, role: Role) -> None:
@@ -761,6 +767,8 @@ class Multiplexer(EventEmitter):
         self.connection_result = None
         self.disconnection_result = None
         self.open_result = None
+        self.open_pn: Optional[RFCOMM_MCC_PN] = None
+        self.open_rx_max_credits = 0
         self.acceptor = None
 
         # Become a sink for the L2CAP channel
@@ -869,9 +877,16 @@ class Multiplexer(EventEmitter):
             else:
                 if self.acceptor:
                     channel_number = pn.dlci >> 1
-                    if self.acceptor(channel_number):
+                    if dlc_params := self.acceptor(channel_number):
                         # Create a new DLC
-                        dlc = DLC(self, pn.dlci, pn.max_frame_size, pn.window_size)
+                        dlc = DLC(
+                            self,
+                            dlci=pn.dlci,
+                            tx_max_frame_size=pn.max_frame_size,
+                            tx_initial_credits=pn.initial_credits,
+                            rx_max_frame_size=dlc_params[0],
+                            rx_initial_credits=dlc_params[1],
+                        )
                         self.dlcs[pn.dlci] = dlc
 
                         # Re-emit the handshake completion event
@@ -889,8 +904,17 @@ class Multiplexer(EventEmitter):
             # Response
             logger.debug(f'>>> PN Response: {pn}')
             if self.state == Multiplexer.State.OPENING:
-                dlc = DLC(self, pn.dlci, pn.max_frame_size, pn.window_size)
+                assert self.open_pn
+                dlc = DLC(
+                    self,
+                    dlci=pn.dlci,
+                    tx_max_frame_size=pn.max_frame_size,
+                    tx_initial_credits=pn.initial_credits,
+                    rx_max_frame_size=self.open_pn.max_frame_size,
+                    rx_initial_credits=self.open_pn.initial_credits,
+                )
                 self.dlcs[pn.dlci] = dlc
+                self.open_pn = None
                 dlc.connect()
             else:
                 logger.warning('ignoring PN response')
@@ -928,7 +952,7 @@ class Multiplexer(EventEmitter):
         self,
         channel: int,
         max_frame_size: int = RFCOMM_DEFAULT_MAX_FRAME_SIZE,
-        window_size: int = RFCOMM_DEFAULT_WINDOW_SIZE,
+        initial_credits: int = RFCOMM_DEFAULT_INITIAL_CREDITS,
     ) -> DLC:
         if self.state != Multiplexer.State.CONNECTED:
             if self.state == Multiplexer.State.OPENING:
@@ -936,17 +960,19 @@ class Multiplexer(EventEmitter):
 
             raise InvalidStateError('not connected')
 
-        pn = RFCOMM_MCC_PN(
+        self.open_pn = RFCOMM_MCC_PN(
             dlci=channel << 1,
             cl=0xF0,
             priority=7,
             ack_timer=0,
             max_frame_size=max_frame_size,
             max_retransmissions=0,
-            window_size=window_size,
+            initial_credits=initial_credits,
         )
-        mcc = RFCOMM_Frame.make_mcc(mcc_type=MccType.PN, c_r=1, data=bytes(pn))
-        logger.debug(f'>>> Sending MCC: {pn}')
+        mcc = RFCOMM_Frame.make_mcc(
+            mcc_type=MccType.PN, c_r=1, data=bytes(self.open_pn)
+        )
+        logger.debug(f'>>> Sending MCC: {self.open_pn}')
         self.open_result = asyncio.get_running_loop().create_future()
         self.change_state(Multiplexer.State.OPENING)
         self.send_frame(
@@ -1039,15 +1065,13 @@ class Client:
 
 # -----------------------------------------------------------------------------
 class Server(EventEmitter):
-    acceptors: Dict[int, Callable[[DLC], None]]
-
     def __init__(
         self, device: Device, l2cap_mtu: int = RFCOMM_DEFAULT_L2CAP_MTU
     ) -> None:
         super().__init__()
         self.device = device
-        self.multiplexer = None
-        self.acceptors = {}
+        self.acceptors: Dict[int, Callable[[DLC], None]] = {}
+        self.dlc_configs: Dict[int, Tuple[int, int]] = {}
 
         # Register ourselves with the L2CAP channel manager
         self.l2cap_server = device.create_l2cap_server(
@@ -1055,7 +1079,13 @@ class Server(EventEmitter):
             handler=self.on_connection,
         )
 
-    def listen(self, acceptor: Callable[[DLC], None], channel: int = 0) -> int:
+    def listen(
+        self,
+        acceptor: Callable[[DLC], None],
+        channel: int = 0,
+        max_frame_size: int = RFCOMM_DEFAULT_MAX_FRAME_SIZE,
+        initial_credits: int = RFCOMM_DEFAULT_INITIAL_CREDITS,
+    ) -> int:
         if channel:
             if channel in self.acceptors:
                 # Busy
@@ -1075,6 +1105,8 @@ class Server(EventEmitter):
                 return 0
 
         self.acceptors[channel] = acceptor
+        self.dlc_configs[channel] = (max_frame_size, initial_credits)
+
         return channel
 
     def on_connection(self, l2cap_channel: l2cap.ClassicChannel) -> None:
@@ -1092,15 +1124,14 @@ class Server(EventEmitter):
         # Notify
         self.emit('start', multiplexer)
 
-    def accept_dlc(self, channel_number: int) -> bool:
-        return channel_number in self.acceptors
+    def accept_dlc(self, channel_number: int) -> Optional[Tuple[int, int]]:
+        return self.dlc_configs.get(channel_number)
 
     def on_dlc(self, dlc: DLC) -> None:
         logger.debug(f'@@@ new DLC connected: {dlc}')
 
         # Let the acceptor know
-        acceptor = self.acceptors.get(dlc.dlci >> 1)
-        if acceptor:
+        if acceptor := self.acceptors.get(dlc.dlci >> 1):
             acceptor(dlc)
 
     def __enter__(self) -> Self: