Passing MTU to service (#134)

dfu/src/main/java/no/nordicsemi/android/dfu/BaseDfuImpl.java

@@ -95,6 +95,7 @@
 	protected DfuProgressInfo mProgressInfo;
 	protected int mImageSizeInBytes;
 	protected int mInitPacketSizeInBytes;
+	private int mCurrentMtu;
 
 	protected class BaseBluetoothGattCallback extends DfuGattCallback {
 		// The Implementation object is created depending on device services, so after the device is connected and services were scanned.
@@ -171,6 +172,10 @@ public void onMtuChanged(final BluetoothGatt gatt, final int mtu, final int stat
 				logi("MTU changed to: " + mtu);
 			} else {
 				logw("Changing MTU failed: " + status + " (mtu: " + mtu + ")");
+				if (status == 4 /* Invalid PDU */ && mCurrentMtu > 23 && mCurrentMtu - 3 > mBuffer.length) {
+					mBuffer = new byte[mCurrentMtu - 3]; // Maximum payload size is MTU - 3 bytes
+					logi("MTU restored to: " + mCurrentMtu);
+				}
 			}
 			mRequestCompleted = true;
 			notifyLock();
@@ -270,6 +275,7 @@ public boolean initialize(final Intent intent, final BluetoothGatt gatt, final i
 
 		final int currentPart = intent.getIntExtra(DfuBaseService.EXTRA_PART_CURRENT, 1);
 		int totalParts = intent.getIntExtra(DfuBaseService.EXTRA_PARTS_TOTAL, 1);
+		mCurrentMtu = intent.getIntExtra(DfuBaseService.EXTRA_CURRENT_MTU, 23);
 
 		// Sending App together with SD or BL is not supported. It must be spilt into two parts.
 		if (fileType > DfuBaseService.TYPE_APPLICATION) {

dfu/src/main/java/no/nordicsemi/android/dfu/DfuBaseService.java

@@ -169,6 +169,11 @@ public abstract class DfuBaseService extends IntentService implements DfuProgres
 	 * (even if it has been set to a higher value before).
 	 */
 	public static final String EXTRA_MTU = "no.nordicsemi.android.dfu.extra.EXTRA_MTU";
+	/**
+	 * This extra value will be used when MTU request returned with an error. That means, that
+	 * MTU has been requested before and may not be changed again. This value will be used instead.
+	 */
+	public static final String EXTRA_CURRENT_MTU = "no.nordicsemi.android.dfu.extra.EXTRA_CURRENT_MTU";
 	/**
 	 * Set this flag to true to enable experimental buttonless feature in Secure DFU. When the
 	 * experimental Buttonless DFU Service is found on a device, the service will use it to

dfu/src/main/java/no/nordicsemi/android/dfu/DfuServiceInitiator.java

@@ -25,6 +25,8 @@
 import android.app.Notification;
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
+import android.bluetooth.BluetoothDevice;
+import android.bluetooth.BluetoothGatt;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
@@ -78,6 +80,7 @@ public class DfuServiceInitiator {
 	private int numberOfPackets = 12;
 
 	private int mtu = 517;
+	private int currentMtu = 23;
 
 	private Parcelable[] legacyDfuUuids;
 	private Parcelable[] secureDfuUuids;
@@ -256,6 +259,28 @@ public DfuServiceInitiator setMtu(final int mtu) {
 		return this;
 	}
 
+	/**
+	 * Sets the current MTU value. This method should be used only if the device is already
+	 * connected and MTU has been requested before DFU service is started.
+	 * The SoftDevice allows to change MTU only once, while the following requests fail with
+	 * Invalid PDU error. In case this error is received, the MTU will be set to the value
+	 * specified using this method. There is no verification of this value. If it's set to
+	 * too high value, some of the packets will not be sent and DFU will not succeed.
+	 * <p>
+	 * By default value 23 is used for compatibility reasons.
+	 * <p>
+	 * Higher MTU values were supported since SDK 15.0.
+	 *
+	 * @param mtu the MTU value received in
+	 *            {@link android.bluetooth.BluetoothGattCallback#onMtuChanged(BluetoothGatt, int, int)} or
+	 *            {@link android.bluetooth.BluetoothGattServerCallback#onMtuChanged(BluetoothDevice, int)}.
+	 * @return the builder
+	 */
+	public DfuServiceInitiator setCurrentMtu(final int mtu) {
+		this.currentMtu = mtu;
+		return this;
+	}
+
 	/**
 	 * Disables MTU request.
 	 * @return the builder
@@ -623,6 +648,7 @@ public DfuServiceController start(@NonNull final Context context, @NonNull final
 		intent.putExtra(DfuBaseService.EXTRA_FORCE_DFU, forceDfu);
 		if (mtu > 0)
 			intent.putExtra(DfuBaseService.EXTRA_MTU, mtu);
+		intent.putExtra(DfuBaseService.EXTRA_CURRENT_MTU, currentMtu);
 		intent.putExtra(DfuBaseService.EXTRA_UNSAFE_EXPERIMENTAL_BUTTONLESS_DFU, enableUnsafeExperimentalButtonlessDfu);
 		if (packetReceiptNotificationsEnabled != null) {
 			intent.putExtra(DfuBaseService.EXTRA_PACKET_RECEIPT_NOTIFICATIONS_ENABLED, packetReceiptNotificationsEnabled);