I am trying to send an image from a server to a mobile device using sockets. The server uses python and the client uses kotlin. The image is sent as a byte array and should be saved on the device. I have this code for the server side:

# Open the image
imageSend = Image.open("result.jpg").tobytes()
# Get the size of the byte array
tam_respuesta = len(imageSend)
# Send the size of the image
cliente_socket.sendall(struct.pack('!I', tam_respuesta))
# Send the image
cliente_socket.sendall(imageSend)

And this is the receiving part of the client:

private fun recibirMensaje(socketChannel: SocketChannel): String? {
        return try {
            // Receive the message size
            val tamMensajeBuffer = ByteBuffer.allocate(4)
            while (tamMensajeBuffer.hasRemaining()) {
                if (socketChannel.read(tamMensajeBuffer) <= 0) {
                    return null
                }
            }
            tamMensajeBuffer.flip()
            val tamMensaje = tamMensajeBuffer.int
            Log.d("Conexion", "Se van a recibir $tamMensaje bytes")

            // Receive the image data
            val dataBuffer = ByteBuffer.allocate(tamMensaje)
            while (dataBuffer.hasRemaining()) {
                if (socketChannel.read(dataBuffer) <= 0) {
                    return null
                }
            }
            dataBuffer.flip()
            // Check for null array
            if(dataBuffer.array() == null){
                Log.d("Conexion", "Array is null")
            }
            // Create a bitmap from the byte array
            val bitmap: Bitmap = BitmapFactory.decodeByteArray(dataBuffer.array(), 0, dataBuffer.array().size)
            // Path for external storage
            val storageDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)

            // Create the file
            val imageFile = File(storageDir, "test.jpg")

            var outputStream: FileOutputStream? = null
            try {
                outputStream = FileOutputStream(imageFile)

                // Save bitmap as JPG
                bitmap.compress(Bitmap.CompressFormat.JPEG, 100, outputStream)
                outputStream.flush()
            } catch (e: IOException) {
                e.printStackTrace()
            } finally {
                outputStream?.close()
            }
            // Image saved
            "Ok"
        } catch (e: Exception) {
            Log.d("conexion",e.printStackTrace().toString())
            null
        }
    }

It fails when transforming the byte array to bitmap. The connection itself is stablished and the data is sent. I printed the size of the received array and is the same as the sent one. Also when sending an image it does work, and I can receive strings on the mobile device.

The error I get is:

--- Failed to create image decoder with message 'unimplemented'

java.lang.NullPointerException: decodeByteArray(...) must not be null
    at com.example.testsockets.Sockets.recibirMensaje(Sockets.kt:95)
    at com.example.testsockets.Sockets.access$recibirMensaje(Sockets.kt:21)
    at com.example.testsockets.Sockets$enviarMensaje$1.invokeSuspend(Sockets.kt:57)
    at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
    at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)
    at kotlinx.coroutines.internal.LimitedDispatcher.run(LimitedDispatcher.kt:42)
    at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:95)
    at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)
    at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)
kotlin.Unit

Is as if it does not recognize that array as an image. I tried removing dataBuffer.flip() but it is the same.