Adding mtu_size client property (#525)

CHANGELOG.rst

@@ -14,6 +14,7 @@ and this project adheres to `Semantic Versioning <https://semver.org/spec/v2.0.0
 Added
 ~~~~~
 
+* add mtu_size property for clients
 * WinRT backend added
 * Added ``BleakScanner.discovered_devices`` property.
 

bleak/backends/bluezdbus/client.py

@@ -570,6 +570,14 @@ def is_connected(self) -> bool:
             False if self._bus is None else self._properties.get("Connected", False)
         )
 
+    @property
+    def mtu_size(self) -> int:
+        """Get ATT MTU size for active connection"""
+        warnings.warn(
+            "MTU size not supported with BlueZ; this function returns the default value of 23. Note that the actual MTU size might be larger"
+        )
+        return 23
+
     # GATT services methods
 
     async def get_services(self, **kwargs) -> BleakGATTServiceCollection:

bleak/backends/corebluetooth/PeripheralDelegate.py

@@ -20,7 +20,10 @@
     NSData,
     NSError,
 )
-from CoreBluetooth import CBCharacteristicWriteWithResponse
+from CoreBluetooth import (
+    CBCharacteristicWriteWithResponse,
+    CBCharacteristicWriteWithoutResponse,
+)
 
 from bleak.exc import BleakError
 
@@ -129,6 +132,16 @@ async def readCharacteristic_(
         else:
             return b""
 
+    def getMtuSize(self) -> int:
+        """Use type CBCharacteristicWriteWithoutResponse to get maximum write value length based on the
+        the negotiated ATT MTU size. Add the ATT header length (+3) to get the actual ATT MTU size"""
+        return (
+            self.peripheral.maximumWriteValueLengthForType_(
+                CBCharacteristicWriteWithoutResponse
+            )
+            + 3
+        )
+
     async def readDescriptor_(
         self, descriptor: CBDescriptor, use_cached=True
     ) -> NSData:

bleak/backends/corebluetooth/client.py

@@ -125,6 +125,12 @@ def is_connected(self) -> bool:
             False if manager is None else manager.isConnected
         )
 
+    @property
+    def mtu_size(self) -> int:
+        """Get ATT MTU size for active connection"""
+        manager = self._central_manager_delegate
+        return manager.connected_peripheral_delegate.getMtuSize()
+
     async def pair(self, *args, **kwargs) -> bool:
         """Attempt to pair with a peripheral.
 

bleak/backends/dotnet/client.py

@@ -305,6 +305,11 @@ def is_connected(self) -> bool:
             else self._requester.ConnectionStatus == BluetoothConnectionStatus.Connected
         )
 
+    @property
+    def mtu_size(self) -> int:
+        """Get ATT MTU size for active connection"""
+        return self._session.MaxPduSize
+
     async def pair(self, protection_level=None, **kwargs) -> bool:
         """Attempts to pair with the device.
 

bleak/backends/winrt/client.py

@@ -280,6 +280,11 @@ def is_connected(self) -> bool:
             == BluetoothConnectionStatus.CONNECTED
         )
 
+    @property
+    def mtu_size(self) -> int:
+        """Get ATT MTU size for active connection"""
+        return self._session.max_pdu_size
+
     async def pair(self, protection_level: int = None, **kwargs) -> bool:
         """Attempts to pair with the device.