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Cap GATT write chunks at 512 bytes to fix crash on Android 13+ #227

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Cap GATT write chunks at 512 bytes to fix crash on Android 13+ #227

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24 changes: 23 additions & 1 deletion app/src/main/java/org/asteroidos/sync/asteroid/AsteroidBleManager.java
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Original file line number Diff line number Diff line change
Expand Up @@ -40,8 +40,30 @@

import no.nordicsemi.android.ble.BleManager;
import no.nordicsemi.android.ble.data.Data;
import no.nordicsemi.android.ble.data.DataSplitter;

public class AsteroidBleManager extends BleManager {
// Android's BluetoothGatt.writeCharacteristic() rejects any value longer
// than the maximum GATT attribute length (512 bytes) since Android 13,
// throwing IllegalArgumentException. The default MTU-based splitter chunks
// at MTU - 3 bytes, which is 514 when the system negotiates the maximum MTU
// of 517 (as on the Pixel 8), exceeding the limit and crashing the app on
// the first long notification. Cap each chunk at 512 bytes regardless of
// the negotiated MTU. The watch reassembles the message from the chunks, so
// a smaller chunk size has no effect other than splitting into more writes.
private static final int MAX_ATTRIBUTE_LENGTH = 512;

private static final DataSplitter CAPPED_SPLITTER = (message, index, maxLength) -> {
final int size = Math.min(maxLength, MAX_ATTRIBUTE_LENGTH);
final int offset = index * size;
if (offset >= message.length)
return null;
final int length = Math.min(size, message.length - offset);
final byte[] chunk = new byte[length];
System.arraycopy(message, offset, chunk, 0, length);
return chunk;
};

public static final String TAG = AsteroidBleManager.class.toString();
@Nullable
public BluetoothGattCharacteristic batteryCharacteristic;
Expand All @@ -59,7 +81,7 @@ public AsteroidBleManager(@NonNull final Context context, SynchronizationService

public final void send(UUID characteristic, byte[] data) {
writeCharacteristic(sendingCharacteristics.get(characteristic), data,
Objects.requireNonNull(sendingCharacteristics.get(characteristic)).getWriteType()).split().enqueue();
Objects.requireNonNull(sendingCharacteristics.get(characteristic)).getWriteType()).split(CAPPED_SPLITTER).enqueue();
}

@NonNull
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