Bluetooth Low energy Chat Application Series #2
Post 2 : Setting up Gatt Server
Overview of Chat application -
1. How Bluetooth Low energy device works : https://medium.com/@tgunix/bluetooth-low-energy-chat-application-series-1-f09c16d35b4a
2. Setting up Gatt Server : https://medium.com/@tgunix/bluetooth-low-energy-chat-application-series-2-75e1208179ae
3. Setting up Gatt Client: https://medium.com/@tgunix/bluetooth-low-energy-chat-application-series-3-e1940622ad90
4. Sending Data over Bluetooth Low energy network
5. Some common errors and how to resolve them(Do check this if you are getting some weird error)
Things to do
1. Add permissions
2. Setup UUIDs for your service, Characteristics and meta-data
3. Setup Gatt Server
Add permissions
<uses-permission android:name=”android.permission.BLUETOOTH”/>
<uses-permission android:name=”android.permission.BLUETOOTH_ADMIN”/><uses-feature android:name=”android.hardware.bluetooth_le” android:required=”true”/>Setup UUIDs
Use this url to generate UUID : https://www.uuidgenerator.net/
val SERVICE_ID = “364710c0–6359–4bdf-9946–9f54d07eb8d3”
val USER_META_DATA_ID = “770bf5dc-53f8–4d55–8506–15a51baee22d”
val SERVICE_UUID = UUID.fromString(SERVICE_ID)
val USER_META_DATA_UUID = UUID.fromString(USER_META_DATA_ID)Setup Gatt Server
1. Get BluetoothManager : Goto step 2 after some delay eg : 2 seconds
2. Setup BluetoothLeAdvertiser
3. Create GattServerCallback : In this callback you will receive message
4. Open GattServer
5. Add your service to the GATT server
6. Create AdvertiseCallback : To know whether scan is started or not
7. Start advertising your GATT server
Note : All above points are necessary
1. Get BluetoothManager
val bluetoothManager = getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager
# Goto to step 2 after some delay eg — 2 seconds
# Eg — Use a handler
Handler.postDelayed({callStep2()}, 2000L)2. Setup BluetoothLeAdvertiser
val mBluetoothLeAdvertiser = mBluetoothAdapter.bluetoothLeAdvertiser;3. Create GattServerCallback
inner class GattServerCallback : BluetoothGattServerCallback() {
override fun onDescriptorReadRequest(device: BluetoothDevice?, requestId: Int, offset: Int, descriptor: BluetoothGattDescriptor?) {}override fun onConnectionStateChange(device: BluetoothDevice?, status: Int, newState: Int) {
super.onConnectionStateChange(device, status, newState);
}//RECEIVER END
override fun onCharacteristicWriteRequest(device: BluetoothDevice?, requestId: Int, characteristic: BluetoothGattCharacteristic?, preparedWrite: Boolean, responseNeeded: Boolean, offset: Int, value: ByteArray?) {
}override fun onCharacteristicReadRequest(device: BluetoothDevice?, requestId: Int, offset: Int, characteristic: BluetoothGattCharacteristic?) {
super.onCharacteristicReadRequest(device, requestId, offset, characteristic)
}override fun onDescriptorWriteRequest(device: BluetoothDevice?, requestId: Int, descriptor: BluetoothGattDescriptor?, preparedWrite: Boolean, responseNeeded: Boolean, offset: Int, value: ByteArray?) {
super.onDescriptorWriteRequest(device, requestId, descriptor, preparedWrite, responseNeeded, offset, value)
}
}val gattServerCallback = GattServerCallback()
4. Open GATT Server
var mGattServer: BluetoothGattServer? = mBluetoothManager.openGattServer(context, gattServerCallback)5. Add service to the GATT Server
val service = BluetoothGattService(SERVICE_UUID, BluetoothGattService.SERVICE_TYPE_PRIMARY)service.addCharacteristic(Util.provideCharacteristic(USER_META_DATA_UUID, USER_META_DATA_DESCRIPTOR_UUID))service.addCharacteristic(Util.provideCharacteristic(ONE_TO_ONE_MSG_UUID, ONE_TO_ONE_MSG_DESCRIPTOR_UUID))mGattServer?.addService(service)
6. Create AdvertiseCallback
val mAdvertiseCallback = object : AdvertiseCallback() {
override fun onStartSuccess(settingsInEffect: AdvertiseSettings) {
sendLog(“Peripheral advertising started.”)
}override fun onStartFailure(errorCode: Int) {sendLog(“Peripheral advertising failed: $errorCode”)
}
}
7. Start advertising your GATT server
if (mBluetoothLeAdvertiser == null) {
return
}val settings = AdvertiseSettings.Builder()
.setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_BALANCED)
.setConnectable(true)
.setTimeout(0)
.setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_LOW)
.build()val parcelUuid = ParcelUuid(SERVICE_UUID)
val data = AdvertiseData.Builder()
.setIncludeDeviceName(false)// because data is greater than 31 bytes
.addServiceUuid(parcelUuid)
.build()mBluetoothLeAdvertiser?.startAdvertising(settings, data, mAdvertiseCallback);
Great work!! Gatt server is complete now
Reference
- https://developer.android.com/guide/topics/connectivity/bluetooth-le
- https://www.bignerdranch.com/blog/bluetooth-low-energy-part-1/
