Add maximumWriteValueLength to Peripheral (#809)

Author: ErikHellman

kable-core/api/android/kable-core.api

@@ -319,6 +319,7 @@ public abstract interface class com/juul/kable/Peripheral : kotlinx/coroutines/C
 	public abstract fun getName ()Ljava/lang/String;
 	public abstract fun getServices ()Lkotlinx/coroutines/flow/StateFlow;
 	public abstract fun getState ()Lkotlinx/coroutines/flow/StateFlow;
+	public abstract fun maximumWriteValueLengthForType (Lcom/juul/kable/WriteType;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public abstract fun observe (Lcom/juul/kable/Characteristic;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
 	public abstract fun read (Lcom/juul/kable/Characteristic;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public abstract fun read (Lcom/juul/kable/Descriptor;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;

kable-core/api/jvm/kable-core.api

@@ -235,6 +235,7 @@ public abstract interface class com/juul/kable/Peripheral : kotlinx/coroutines/C
 	public abstract fun getName ()Ljava/lang/String;
 	public abstract fun getServices ()Lkotlinx/coroutines/flow/StateFlow;
 	public abstract fun getState ()Lkotlinx/coroutines/flow/StateFlow;
+	public abstract fun maximumWriteValueLengthForType (Lcom/juul/kable/WriteType;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public abstract fun observe (Lcom/juul/kable/Characteristic;Lkotlin/jvm/functions/Function1;)Lkotlinx/coroutines/flow/Flow;
 	public abstract fun read (Lcom/juul/kable/Characteristic;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;
 	public abstract fun read (Lcom/juul/kable/Descriptor;Lkotlin/coroutines/Continuation;)Ljava/lang/Object;

kable-core/src/androidMain/kotlin/BluetoothDeviceAndroidPeripheral.kt

@@ -47,6 +47,9 @@ import kotlin.time.Duration
 // https://github.com/JuulLabs/kable/issues/295
 private const val DISCOVER_SERVICES_RETRIES = 5
 
+private const val DEFAULT_ATT_MTU = 23
+private const val ATT_MTU_HEADER_SIZE = 3
+
 internal class BluetoothDeviceAndroidPeripheral(
     private val bluetoothDevice: BluetoothDevice,
     private val autoConnectPredicate: () -> Boolean,
@@ -163,6 +166,9 @@ internal class BluetoothDeviceAndroidPeripheral(
             .requestConnectionPriority(priority.intValue)
     }
 
+    override suspend fun maximumWriteValueLengthForType(writeType: WriteType): Int =
+        (mtu.value ?: DEFAULT_ATT_MTU) - ATT_MTU_HEADER_SIZE
+
     @ExperimentalApi // Experimental until Web Bluetooth advertisements APIs are stable.
     override suspend fun rssi(): Int =
         connectionOrThrow().execute<OnReadRemoteRssi> {

kable-core/src/appleMain/kotlin/CBPeripheralCoreBluetoothPeripheral.kt

@@ -27,6 +27,8 @@ import kotlinx.coroutines.flow.onSubscription
 import kotlinx.coroutines.flow.updateAndGet
 import kotlinx.coroutines.sync.withLock
 import kotlinx.io.IOException
+import platform.CoreBluetooth.CBCharacteristicWriteWithResponse
+import platform.CoreBluetooth.CBCharacteristicWriteWithoutResponse
 import platform.CoreBluetooth.CBDescriptor
 import platform.CoreBluetooth.CBManagerState
 import platform.CoreBluetooth.CBManagerStatePoweredOn
@@ -144,6 +146,14 @@ internal class CBPeripheralCoreBluetoothPeripheral(
         )
     }
 
+    override suspend fun maximumWriteValueLengthForType(writeType: WriteType): Int {
+        val type = when (writeType) {
+            WithResponse -> CBCharacteristicWriteWithResponse
+            WithoutResponse -> CBCharacteristicWriteWithoutResponse
+        }
+        return cbPeripheral.maximumWriteValueLengthForType(type).toInt()
+    }
+
     @ExperimentalApi // Experimental until Web Bluetooth advertisements APIs are stable.
     @Throws(CancellationException::class, IOException::class)
     override suspend fun rssi(): Int = connectionOrThrow().execute<DidReadRssi> {

kable-core/src/commonMain/kotlin/Peripheral.kt

@@ -153,6 +153,15 @@ public interface Peripheral : CoroutineScope {
      */
     public val services: StateFlow<List<DiscoveredService>?>
 
+    /**
+     * Return the current ATT MTU size, minus the size of the ATT headers (3 bytes).
+     *
+     * On Android, this will be the default (23 - 3) unless you called [requestMtu] when connecting.
+     * For iOS, this is automatically negotiated, and can also vary depending on the writeType.
+     * On JavaScript, this will return the default (23 - 3) every time as there is no ATT MTU property available.
+     */
+    public suspend fun maximumWriteValueLengthForType(writeType: WriteType): Int
+
     /**
      * On JavaScript, requires Chrome 79+ with the
      * `chrome://flags/#enable-experimental-web-platform-features` flag enabled.

kable-core/src/jsMain/kotlin/BluetoothDeviceWebBluetoothPeripheral.kt

@@ -32,6 +32,8 @@ import kotlin.coroutines.resumeWithException
 import kotlin.time.Duration
 
 private const val ADVERTISEMENT_RECEIVED = "advertisementreceived"
+private const val DEFAULT_ATT_MTU = 23
+private const val ATT_MTU_HEADER_SIZE = 3
 
 internal class BluetoothDeviceWebBluetoothPeripheral(
     private val bluetoothDevice: BluetoothDevice,
@@ -114,6 +116,9 @@ internal class BluetoothDeviceWebBluetoothPeripheral(
         )
     }
 
+    override suspend fun maximumWriteValueLengthForType(writeType: WriteType): Int =
+        DEFAULT_ATT_MTU - ATT_MTU_HEADER_SIZE
+
     /**
      * Per [Web Bluetooth / Scanning Sample][https://googlechrome.github.io/samples/web-bluetooth/scan.html]:
      *