add rfcomm options and fix l2cap mtu negotiation

bumble/avdtp.py

@@ -1470,10 +1470,10 @@ class Protocol(EventEmitter):
             f'[{transaction_label}] {message}'
         )
         max_fragment_size = (
-            self.l2cap_channel.mtu - 3
+            self.l2cap_channel.peer_mtu - 3
         )  # Enough space for a 3-byte start packet header
         payload = message.payload
-        if len(payload) + 2 <= self.l2cap_channel.mtu:
+        if len(payload) + 2 <= self.l2cap_channel.peer_mtu:
             # Fits in a single packet
             packet_type = self.PacketType.SINGLE_PACKET
         else:

bumble/hid.py

@@ -416,7 +416,7 @@ class Device(HID):
             data = bytearray()
             data.append(report_id)
             data.extend(ret.data)
-            if len(data) < self.l2cap_ctrl_channel.mtu:  # type: ignore[union-attr]
+            if len(data) < self.l2cap_ctrl_channel.peer_mtu:  # type: ignore[union-attr]
                 self.send_control_data(report_type=report_type, data=data)
             else:
                 self.send_handshake_message(Message.Handshake.ERR_INVALID_PARAMETER)

bumble/l2cap.py

@@ -173,7 +173,7 @@ L2CAP_MTU_CONFIGURATION_PARAMETER_TYPE = 0x01
 @dataclasses.dataclass
 class ClassicChannelSpec:
     psm: Optional[int] = None
-    mtu: int = L2CAP_MIN_BR_EDR_MTU
+    mtu: int = L2CAP_DEFAULT_MTU
 
 
 @dataclasses.dataclass
@@ -749,6 +749,8 @@ class ClassicChannel(EventEmitter):
     sink: Optional[Callable[[bytes], Any]]
     state: State
     connection: Connection
+    mtu: int
+    peer_mtu: int
 
     def __init__(
         self,
@@ -765,6 +767,7 @@ class ClassicChannel(EventEmitter):
         self.signaling_cid = signaling_cid
         self.state = self.State.CLOSED
         self.mtu = mtu
+        self.peer_mtu = L2CAP_MIN_BR_EDR_MTU
         self.psm = psm
         self.source_cid = source_cid
         self.destination_cid = 0
@@ -861,7 +864,7 @@ class ClassicChannel(EventEmitter):
             [
                 (
                     L2CAP_MAXIMUM_TRANSMISSION_UNIT_CONFIGURATION_OPTION_TYPE,
-                    struct.pack('<H', L2CAP_DEFAULT_MTU),
+                    struct.pack('<H', self.mtu),
                 )
             ]
         )
@@ -926,8 +929,8 @@ class ClassicChannel(EventEmitter):
         options = L2CAP_Control_Frame.decode_configuration_options(request.options)
         for option in options:
             if option[0] == L2CAP_MTU_CONFIGURATION_PARAMETER_TYPE:
-                self.mtu = struct.unpack('<H', option[1])[0]
-                logger.debug(f'MTU = {self.mtu}')
+                self.peer_mtu = struct.unpack('<H', option[1])[0]
+                logger.debug(f'peer MTU = {self.peer_mtu}')
 
         self.send_control_frame(
             L2CAP_Configure_Response(
@@ -1026,7 +1029,7 @@ class ClassicChannel(EventEmitter):
         return (
             f'Channel({self.source_cid}->{self.destination_cid}, '
             f'PSM={self.psm}, '
-            f'MTU={self.mtu}, '
+            f'MTU={self.mtu}/{self.peer_mtu}, '
             f'state={self.state.name})'
         )
 

bumble/rfcomm.py

@@ -104,6 +104,7 @@ 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
 
@@ -473,7 +474,7 @@ 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.mtu - max_overhead
+            max_frame_size, self.multiplexer.l2cap_channel.peer_mtu - max_overhead
         )
 
     def change_state(self, new_state: State) -> None:
@@ -908,8 +909,11 @@ class Client:
     multiplexer: Optional[Multiplexer]
     l2cap_channel: Optional[l2cap.ClassicChannel]
 
-    def __init__(self, connection: Connection) -> None:
+    def __init__(
+        self, connection: Connection, l2cap_mtu: int = RFCOMM_DEFAULT_L2CAP_MTU
+    ) -> None:
         self.connection = connection
+        self.l2cap_mtu = l2cap_mtu
         self.l2cap_channel = None
         self.multiplexer = None
 
@@ -917,7 +921,7 @@ class Client:
         # Create a new L2CAP connection
         try:
             self.l2cap_channel = await self.connection.create_l2cap_channel(
-                spec=l2cap.ClassicChannelSpec(RFCOMM_PSM)
+                spec=l2cap.ClassicChannelSpec(psm=RFCOMM_PSM, mtu=self.l2cap_mtu)
             )
         except ProtocolError as error:
             logger.warning(f'L2CAP connection failed: {error}')
@@ -955,7 +959,9 @@ class Client:
 class Server(EventEmitter):
     acceptors: Dict[int, Callable[[DLC], None]]
 
-    def __init__(self, device: Device) -> None:
+    def __init__(
+        self, device: Device, l2cap_mtu: int = RFCOMM_DEFAULT_L2CAP_MTU
+    ) -> None:
         super().__init__()
         self.device = device
         self.multiplexer = None
@@ -963,7 +969,8 @@ class Server(EventEmitter):
 
         # Register ourselves with the L2CAP channel manager
         self.l2cap_server = device.create_l2cap_server(
-            spec=l2cap.ClassicChannelSpec(psm=RFCOMM_PSM), handler=self.on_connection
+            spec=l2cap.ClassicChannelSpec(psm=RFCOMM_PSM, mtu=l2cap_mtu),
+            handler=self.on_connection,
         )
 
     def listen(self, acceptor: Callable[[DLC], None], channel: int = 0) -> int: