read response from BLE

[syntaxxxxx]

hi all

i am writing to write payload request with json with response

payload request is sent dan device received the data, but the problem is, i got response ??? like this when i read response

this is my implementation code

private suspend fun sendRequest(body: String = ""): String {
    withContext(Dispatchers.IO) {
        peripheral.write(request, body.toByteArray(Charsets.UTF_8), WriteType.WithResponse)
    }

    peripheral.observe(request).firstOrNull()

    return peripheral.read(response).toString(Charsets.UTF_8).also {
        Timber.d("BLE woy -> Response $it")
    }
}

thanks!

[twyatt]

The following discussion may be applicable/helpful? #507

[twyatt]

What do you mean the response is truncated?
If you provide some logs and sample code that would be helpful.

[syntaxxxxx]

private suspend fun sendRequest(body: String = ""): ByteArray {
    withContext(Dispatchers.IO) {
        peripheral.write(request, body.toByteArray(Charsets.UTF_8), WriteType.WithResponse)
    }

    return peripheral.read(response).also {
        Timber.d("BLE woy -> Response $it")
    }
    
    // Output for ByteArray -> [@bada

[syntaxxxxx]

private val UART_SERVICE_UUID = UUID.fromString("6E411111-B5A5-F393-E0A9-E50E24DCCA9E")
private val TX_CHARACTERISTIC_UUID = UUID.fromString("6E411112-B5A5-F393-E0A9-E50E24DCCA9E")
private val RX_CHARACTERISTIC_UUID = UUID.fromString("6E411113-B5A5-F393-E0A9-E50E24DCCA9E")

private val request = characteristicOf(
    UART_SERVICE_UUID.toString(),
    TX_CHARACTERISTIC_UUID.toString()
)

private val response = descriptorOf(
    UART_SERVICE_UUID.toString(),
    RX_CHARACTERISTIC_UUID.toString(),
    "00002902-0000-1000-8000-00805f9b34fb"
)

[twyatt]

// Output for ByteArray -> [@bada

Are you referring to the [@bada as indication that it is truncated? The toString for ByteArray doesn't represent its contents, if that's what you were assuming? You'll want to convert it using your desired encoding, or you could inspect the "raw" data using toHexString.

Additionally, your example code could potentially miss packets, you should execute your read before your write.

[syntaxxxxx]

i got the point

thanks a lot! @twyatt

[syntaxxxxx]

hi travis! @twyatt

i back again

i still got response ??? like this when i read response

this is my implementation code

 peripheral.read(response).also {
     println("execute lah 5 ${byteArrayToString(it)}")
 }

private suspend fun writeExampleValue(peripheral: Peripheral) {
    val value = 1
    val data = byteArrayOf(value.toByte())
    peripheral.write(request, data = data, WriteType.WithResponse)
}

[twyatt]

to shared module and consume in android and ios specific platform

I believe the code example I shared will work in commonMain source set.

SensorTag sample is a good example/reference for how to share Kable code w/ the supported platforms.

[syntaxxxxx]

yes it works in commonMain source set. but for requestMtu(512) Unresolved reference, how to solved that to support android and ios platform?

private val peripheral = scope.peripheral(advertisement) {
    onServicesDiscovered {
        requestMtu(512)
    }
    logging {
        level = Data
    }
}

Does code above can be shared?

[twyatt]

The MTU cannot be changed on iOS — I can't remember the exact value, but it is less than 512. Something to be aware of.

As for how to have the code work w/ multiple platforms, one possible approach could be:

// common
internal expect fun PeripheralBuilder.configure()
private val peripheral = scope.peripheral(advertisement) {
    configure()
    logging {
        level = Data
    }
}

// Android
internal actual fun PeripheralBuilder.configure() {
    onServicesDiscovered {
        requestMtu(512)
    }
}

// iOS
internal actual fun PeripheralBuilder.configure() {
    // No-op
}

[syntaxxxxx]

hai travis @twyatt

it works thanks in advance!

I have question. What possibilities can lead to Kable throwing a GattRequestRejectedException, other than:

• • Device is busy (i.e. a previous request is still in-progress)
• • An Android internal failure occurred (i.e. an underlying [RemoteException] was thrown)

• @throws GattRequestRejectedException if underlying BluetoothGatt method call returns false.

• @throws GattStatusException if response has a non-GATT_SUCCESS status.

[twyatt]

Device is busy (i.e. a previous request is still in-progress)

Kable has safe guards (per Peripheral object) to prevent executing multiple requests at once, so this shouldn't happen. If you create multiple Peripherals that represent the same physical peripheral (e.g. call scope.peripheral(advertisement) multiple times with the same advertisement) and then use them simultaneously then that would be skirting around the safe guards.

What possibilities can lead to Kable throwing a GattRequestRejectedException, other than

As you referenced, there are a number of causes of that failure, but specifically looking from the perspective of the code, it is thrown at:

kable/core/src/androidMain/kotlin/Connection.kt

Line 70 in f5bf08b

if (!bluetoothGatt.action()) throw GattRequestRejectedException()

Android's BluetoothGatt describes for many of its functions that they return a boolean of:

true, if the read operation was initiated successfully

Looking at the BluetoothGatt source code, it returns false when RemoteException is caught. I hadn't really dug deeper as to when Android internally throws RemoteException, I believe I just found various blog posts about it and noted what they identified as to when Android might return false, then then added those notes to Kable documentation.