What’s all that hype about BLE? Software Engineer relayr Hugo Doménech Juárez @hudomju 1

relayr bring things to life 2

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Why are startups shifting to hardware products? - Sensors are cheap! 8

Prototyping tools -3d Printer -CNC Machine -Laser Cutter -3d Scanner 9

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What do all these products have in common? -The way they communicate! 13

Bluetooth Low Energy 14

Bluetooth Classic 15

Relationship between Bluetooth and Android 16

Eclair 2.0 (API 5) BlueZ Android 1.x 4.3 (API 18) Bluedroid JellyBean Bluetooth Smart 5.0 (API 20) Lollipop Full BLE Older Broadcom stack - Samsung & HTC < 4.0 Motorola Bluetooth Stack 17

Bluetooth Low Energy 18

Central Peripheral Observer Broadcaster Android 4.3+ Android 5.0+ 19

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BLE Scanning example 21

BLE Scanning 22

BLE Scanning boolean hasBleFeature() { return getPackageManager().hasSystemFeature(FEATURE_BLUETOOTH_LE)); } 23

BLE Scanning mBluetoothAdapter.startLeScan(mLeScanCallback); mBluetoothAdapter.stopLeScan(mLeScanCallback); BluetoothManager manager = (BluetoothManager) getSystemService(BLUETOOTH_SERVICE); mBluetoothAdapter = bluetoothManager.getAdapter(); 24

BLE Scanning private BluetoothAdapter.LeScanCallback mLeScanCallback = new BluetoothAdapter.LeScanCallback() { @Override public void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) { // You are not in the UI thread // or in the thread you subscribed for what matters! } }; 25

BLE Scanning /** * Decodes the services uuid from the advertisement packet since * {@link android.bluetooth.BluetoothDevice#getUuids()} returns null most of * the times. */ public static List decodeServicesUuid(byte[] data); /** * Decodes the device name from the Complete Local Name or Shortened * Local Name field in the * Advertisement packet. {@link * android.bluetooth.BluetoothDevice#getName()} does it already, * although some phones skip it. i.e. Sony Xperia Z1 (C6903) with Android 4.3 * where getName() always returns null. */ public static String decodeDeviceName(byte[] data); 26

BLE Scanning: Lollipop improvements mBluetoothAdapter.startScan(filters, scanSettings, scanCallback) name deviceAddress uuid serviceDataUuid serviceData manufacturerId manufacturerData Low Power Balanced Low Latency 27

interface ScanCallback { public void onScanResult(int callbackType, ScanResult result); public void onBatchScanResults(List results); public void onScanFailed(int errorCode) } BLE Scanning: Lollipop improvements 28

Advertisement GATT server Hardware feature - chipset needs to support it - nexus 9 vs nexus 5 & 7 BluetoothAdapter.isMultipleAdvertisementSupported() Peripheral mode: Lollipop features 29

Let’s connect to other BLE devices! 30

The GATT Protocol Peripheral Central Read - Write - Subscribe Respond - Push GATT Peripheral GATT protocol Service Service Characteristic Characteristic Value Indications Notifications Descriptor Descriptor Descriptor 31 Server Client Generic Attribute Profile

The GATT Protocol class BluetoothAdapterLeScanCallback { void onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) { device.connectGatt(context, false, mBluetoothGattReceiver); } } class BluetoothGattReceiver { @Override public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {} } 32

The BluetoothGatt discoverServices writeCharacteristic readCharacteristic writeDescriptor setCharacteristicNotification readDescriptor readRemoteRssi beginReliableWrite executeReliableWrite abortReliableWrite readMtu 33

The BluetoothGattCallback onServicesDiscovered onCharacteristicWrite onCharacteristicRead onDescriptorWrite onCharacteristicChanged onDescriptorRead onRemoteRssiRead onReliableWriteCompleted onMtuChanged 34

Why would you write characteristics? A practical example 35

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Data subscriptions: Indication / Notification gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(ENABLE_NOTIFICATION_VALUE); gatt.writeDescriptor(descriptor); gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(ENABLE_INDICATION_VALUE); gatt.writeDescriptor(descriptor); gatt.setCharacteristicNotification(characteristic, enable); descriptor.setValue(DISABLE_NOTIFICATION_VALUE); gatt.writeDescriptor(descriptor); @Override public void onCharacteristicChanged( BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) { } 39

Reliable Write ?= Long Write gatt.beginReliableWrite(); characteristic.setValue(data); gatt.reliableWriteCharacteristic(mBluetoothGatt, characteristic, subscriber); gatt.executeReliableWrite(); 40 18 byte: 16 bytes content + 1 offset + 1 length package Regular Write supports 18 bytes

Disconnecting GATT vs Closing GATT gatt.disconnect(); @Override public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) { if (newState == STATE_DISCONNECTED && noLongerInterestedInTheDevice) { gatt.close(); } } gatt.close(); 41

Stack metrics: why you should close your GATT - Constants defined in BlueDroid - Max concurrent active notifications - BTA_GATTC_NOTIF_REG_MAX - (4) Android 4.3 - (7) Android 4.4 - (15) Android 5.0+ - Max concurrent GATT connections - BTA_GATTC_CON_MAX - (4) Android 4.3 - (7) Android 4.4+ 42

… and one last thing Security 43

Security Pairing Bonding Encryption Re-establishment - Just Works - Passkey Entry - Out Of Band 44

Security: Instability static class UndocumentedBleStuff { static boolean isUndocumentedErrorStatus(int status) { return status == 133 || status == 137; } static void fixUndocumentedBleStatusProblem(BluetoothGatt gatt, BluetoothGattReceiver receiver) { DeviceCompatibilityUtils.refresh(gatt); gatt.getDevice().connectGatt(RelayrApp.get(), false, receiver); } } GATT_INSUFFICIENT_AUTHENTICATION GATT_INSUFFICIENT_ENCRYPTION 45

Security: Instability boolean refresh(BluetoothGatt gatt) { try { Method localMethod = gatt.getClass().getMethod("refresh", new Class[0]); if (localMethod != null) { return (Boolean) localMethod.invoke(gatt); } } catch (Exception localException) { Log.e(TAG, "An exception occurred while performing: refresh”, localException.getCause()); } return false; } 46

Security: Instability class DeviceCompatibilityUtils { boolean createBond(BluetoothDevice device) { if (isSdk19()) return doCreateBond(device); return callMethod(device, "createBond"); } @TargetApi(Build.VERSION_CODES.KITKAT) boolean doCreateBond(BluetoothDevice device) { return device.createBond(); } boolean removeBond(BluetoothDevice device) { return callMethod(device, "removeBond"); } } 47

So we can develop now for Android Wearables right? 48

Bluetooth SIG (Special Interest Group) 49

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Questions? Hugo Doménech @hudomju 51

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