Merge pull request #544 from NordicSemiconductor/improvement/mtu

Max usable MTU set to 515 (512 bytes of data)
NordicSemiconductor · Feb 16, 2024 · f924120 · f924120
2 parents 695fbf4 + 20ed79f
commit f924120
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Showing 2 changed files with 11 additions and 6 deletions.
diff --git a/ble/src/main/java/no/nordicsemi/android/ble/BleManager.java b/ble/src/main/java/no/nordicsemi/android/ble/BleManager.java
@@ -1986,6 +1986,9 @@ protected void disableBatteryLevelNotifications() {
 	 * <p>
 	 * The returned request must be either enqueued using {@link Request#enqueue()} for
 	 * asynchronous use, or awaited using await() in synchronous execution.
+	 * <p>
+	 * Starting from version 2.7.3 the maximum packet size is 512 bytes, even if the MTU is set to
+	 * 517. See: <a href="https://github.com/NordicSemiconductor/Android-BLE-Library/issues/541">#541</a>.
 	 *
 	 * @return The request.
 	 */

diff --git a/ble/src/main/java/no/nordicsemi/android/ble/BleManagerHandler.java b/ble/src/main/java/no/nordicsemi/android/ble/BleManagerHandler.java
@@ -173,6 +173,7 @@ abstract class BleManagerHandler extends RequestHandler {
 	 * The current MTU (Maximum Transfer Unit). The maximum number of bytes that can be sent in
 	 * a single packet is MTU-3.
 	 */
+	@IntRange(from = 23, to = 515)
 	private int mtu = 23;
 	/**
 	 * Current connection parameters. Those values are only available starting from Android Oreo.
@@ -1732,13 +1733,14 @@ final boolean isReliableWriteInProgress() {
 	/**
 	 * Returns the current MTU (Maximum Transfer Unit).
 	 */
+	@IntRange(from = 23, to = 515)
 	final int getMtu() {
 		return mtu;
 	}
 
 	final void overrideMtu(@IntRange(from = 23, to = 517) final int mtu) {
 		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
-			this.mtu = mtu;
+			this.mtu = Math.min(515, mtu);
 		}
 	}
 
@@ -2043,7 +2045,7 @@ protected void onCharacteristicIndicated(@NonNull final BluetoothGatt gatt,
 	 */
 	@Deprecated
 	protected void onMtuChanged(@NonNull final BluetoothGatt gatt,
-								@IntRange(from = 23, to = 517) final int mtu) {
+								@IntRange(from = 23, to = 515) final int mtu) {
 		// do nothing
 	}
 
@@ -2696,10 +2698,10 @@ public void onMtuChanged(@NonNull final BluetoothGatt gatt,
 								 final int status) {
 			if (status == BluetoothGatt.GATT_SUCCESS) {
 				log(Log.INFO, () -> "MTU changed to: " + mtu);
-				BleManagerHandler.this.mtu = mtu;
-				BleManagerHandler.this.onMtuChanged(gatt, mtu);
+				BleManagerHandler.this.mtu = Math.min(515, mtu);
+				BleManagerHandler.this.onMtuChanged(gatt, BleManagerHandler.this.mtu);
 				if (request instanceof MtuRequest) {
-					((MtuRequest) request).notifyMtuChanged(gatt.getDevice(), mtu);
+					((MtuRequest) request).notifyMtuChanged(gatt.getDevice(), BleManagerHandler.this.mtu);
 					request.notifySuccess(gatt.getDevice());
 				}
 			} else {
@@ -3184,7 +3186,7 @@ final void onMtuChanged(@NonNull final BluetoothGattServer server,
 							@NonNull final BluetoothDevice device,
 							final int mtu) {
 		log(Log.INFO, () -> "[Server] MTU changed to: " + mtu);
-		BleManagerHandler.this.mtu = mtu;
+		BleManagerHandler.this.mtu = Math.min(515, mtu);
 		nextRequest(checkCondition());
 	}