i was wondering if it is possible to send messages from the backend (for example a running task that receives information from an external system) to the UI. In my case it needs to be a specific session (no broadcast) and only on a specific screen
plan B would be polling the backend frequently but i was hoping to get something more "realtime"
I was trying to work something out like this, but i keep getting a NotSerializableException.
#Push
class StorageAccess : Screen(), MessageListener {
#Inject
private lateinit var stationWSService: StationWebSocketService
#Inject
private lateinit var notifications: Notifications
#Subscribe
private fun onInit(event: InitEvent) {
}
#Subscribe("stationPicker")
private fun onStationPickerValueChange(event: HasValue.ValueChangeEvent<StorageUnit>) {
val current = AppUI.getCurrent()
current.userSession.id ?: return
val prevValue = event.prevValue
if (prevValue != null) {
stationWSService.remove(current.userSession.id)
}
val value = event.value ?: return
stationWSService.listen(current.userSession.id, value, this)
}
override fun messageReceived(message: String) {
val current = AppUI.getCurrent()
current.access {
notifications.create().withCaption(message).show()
}
}
#Subscribe
private fun onAfterDetach(event: AfterDetachEvent) {
val current = AppUI.getCurrent()
current.userSession.id ?: return
stationWSService.remove(current.userSession.id)
}
}
-- The callback interface
interface MessageListener : Serializable {
fun messageReceived(message: String);
}
-- The listen method of my backend service
private val listeners: MutableMap<String, MutableMap<UUID, MessageListener>> = HashMap()
override fun listen(id: UUID, storageUnit: StorageUnit, callback: MessageListener) {
val unitStationIP: String = storageUnit.unitStationIP ?: return
if (!listeners.containsKey(unitStationIP))
listeners[unitStationIP] = HashMap()
listeners[unitStationIP]?.set(id, callback)
}
The Exception i get is NotSerializableException: com.haulmont.cuba.web.sys.WebNotifications which happens during adding the listener to the backend: stationWSService.listen(current.userSession.id, value, this)
as far as i understand this is the place where the UI sends the information to the backend - and with it the entire status of the class StorageAccess, including all its members.
is there an elegant solution to this?
regards
There is an add-on that solves exactly this problem: https://github.com/cuba-platform/global-events-addon
Related
I'm super frustrated with a Kotlin/Mockito problem
What I want to accomplish is very simple, I've an AuthorizationFilter on my springboot application and for test purposes I want to mock its behavior to let the test requests pass by
My AuthorizationFilter indeed calls an API which will then provide the user auth status. so I thought that the simplest way to mock this is just have the AuthApi mocked into the filter and return whatever status I want... BUT IT WORKS RANDOMLY
#Component
class AuthorizationFilter(
val authApi: authApi
) : OncePerRequestFilter() {
override fun doFilterInternal(request: HttpServletRequest, response: HttpServletResponse, filterChain: FilterChain) {
if (request.method.equals("OPTIONS")) {
filterChain.doFilter(request, response)
return
}
val token = request.getHeader("authorization")
if (token == null) {
response.sendError(401)
return
}
runCatching {
authApi.authorize(token.replace("Bearer ", ""))
}.onSuccess {
AuthorizationContext.set(it)
filterChain.doFilter(request, response)
}.onFailure {
it.printStackTrace()
response.sendError(401)
}
}
}
the authApi authorize method is irrelevant to this question, but just let it be clear it will NEVER return null... it might throw an exception but wont return null
#TestInstance(TestInstance.Lifecycle.PER_CLASS)
#ExtendWith(SpringExtension::class)
#SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
#ActiveProfiles("test")
class SocketIOServerTest {
#MockBean
lateinit var mockedApiComponent: AuthApi
#Autowired
lateinit var boardRepository: BoardRepository
#Autowired
private lateinit var servletRegistrationBean: ServletRegistrationBean<SocketIOServer>
private lateinit var socketIOServer: SocketIOServer
#LocalServerPort
private val serverPort: String? = null
lateinit var clientSocket: Socket
private val userId = 1
private val groupId = 123
private val admin = false
private val auth = Authorization("token", userId, groupId, admin)
private val objectMapper = ObjectMapper()
#BeforeAll
fun connect() {
AuthorizationContext.set(auth)
Mockito.`when`(mockedApiComponent.authorize(anyOrNull())).thenReturn(auth)
socketIOServer = servletRegistrationBean.servlet
clientSocket = IO.socket("http://localhost:${serverPort}", IO.Options.builder().setExtraHeaders(mutableMapOf(Pair("Authorization", listOf("Bearer token")))).build())
clientSocket.on(Socket.EVENT_CONNECT) {
println("client connected")
}
clientSocket.on(Socket.EVENT_DISCONNECT) {
println("client disconnected")
}
clientSocket.connect()
}
#Test
fun testPingPong() {
var finished = false
clientSocket.on("pong") {
println("event: ${it[0]}")
val pongTime = (it[0] as String).substring(18, 31).toLong()
assertTrue(System.currentTimeMillis() - pongTime < 1000)
finished = true
}
clientSocket.emit("ping")
while (!finished) Thread.yield()
}
#Test
fun testBasicNotification(){
clientSocket.on("basic_notification"){
println(Arrays.toString(it))
}
socketIOServer.send(SocketIOEvent("${groupId}","basic_notification","data"))
Thread.sleep(1000)
}
#Test
fun testBoardNotification() {
clientSocket.on("entity_create") {
val event = it[0] as String
println("event: $event")
val eventValue = objectMapper.readValue(event, Map::class.java)
val entityValue = eventValue["entity"] as Map<*, *>
assertEquals("BOARD", eventValue["entity_type"])
assertEquals("board name", entityValue["name"])
assertEquals(groupId, entityValue["groupId"])
assertEquals(userId, entityValue["created_by"])
assertEquals(userId, entityValue["last_modified_by"])
}
val board = boardRepository.save(Board(groupId, "board name"))
//boardRepository.delete(board)
}}
Just to be clear, THE TEST WORKS, the assertions are correct and although it has some random behavior at the end it works.... BUT IT PRINTS A BIG STACK TRACE DUE SOME CRAZY BEHAVIOR
As you can see I'm using a SocketIO client which sends several requests out of my code... some of them get authenticated and some of them throw nullpointerexception on this line
.onSuccess {
AuthorizationContext.set(it) //this line
filterChain.doFilter(request, response)
}.
because it is null, because somehow the mockedApiComponent.authorize() returned null... again which would be impossible on the real component and which shouldn't be happening because the mock clearly states which object to return
I've exhaustively debbuged this code, thinking that somehow junit got two beans of the AuthApi
but the whole execution shows the same object id which matches the mock... and even weirder that the token parameter used on authorize is always the same
can anyone help me?
I've exhaustively debbuged this code, thinking that somehow junit got two beans of the AuthApi but the whole execution shows the same object id which matches the mock... and even weirder that the token parameter used on authorize is always the same
This looks to me disturbing, like some problem with async code at runtime. I would try to do a couple of things:
Check for when the context is null in: AuthorizationContext.set(it) and put some more debug code to know what is happening. Or just debug from there
Use a recover{} block to deal with the NullPointerException and debug from there to see original problem in stack trace
What happens when instead runCatching{} you use mapCatching{}?
Here is a breakdown of how the current third party SDK implementation works.
class Handler(val context: Context) {
val device = Controller.getInstance(context,Listener())
fun connectBT(BTDevice:BluetoothDevice){
device.connectBT(BTDevice)
}
}
and then the Listener implementation
class Listener: BBDeviceController.BBDeviceControllerListener{
override fun onBTConnected(device: BluetoothDevice?) {
println("Device Connected")
// Send back to function that device is connect
}
}
This is a straightforward example, but the idea is, when you press a button it will call connectBT() and then contain the result like so:
val handler = Handler(this)
val res = handler.connectBT(btDevice)
I know you can use suspendCoroutine on the function handler.connectBT() however the issue is how do I get the listeners result from the SDK to return back to the main function that called it?
When using suspendCoroutine, you need to call resume/resumeWithException/etc on the continuation object. You can store/pass this object anywhere, for example to your listener:
class Handler(val context: Context) {
val listener = Listener()
val device = Controller.getInstance(context, listener)
suspend fun connectBT(BTDevice:BluetoothDevice){
suspendCoroutine<Unit> { continuation ->
listener.continuation = continuation
device.connectBT(BTDevice)
}
}
}
class Listener: BBDeviceController.BBDeviceControllerListener{
var continuation: Continuation<Unit>? = null
override fun onBTConnected(device: BluetoothDevice?) {
println("Device Connected")
if (continuation != null) {
continuation?.resume(Unit)
continuation = null
}
}
}
I'm attempting to use Kotlin's Flow class as a message queue to transfer data from a producer (a camera) to a set of workers (image analyzers) running on separate coroutines.
The producer in my case is a camera, and will run substantially faster than the workers. Back pressure should be handled by dropping data so that the image analyzers are always operating on the latest images from the camera.
When using channels, this solution works, but seems messy and does not provide an easy way for me to translate the data between the camera and the analyzers (like flow.map).
class ImageAnalyzer<Result> {
fun analyze(image: Bitmap): Result {
// perform some work on the image and return a Result. This can take a long time.
}
}
class CameraAdapter {
private val imageChannel = Channel<Bitmap>(capacity = Channel.RENDEZVOUS)
private val imageReceiveMutex = Mutex()
// additional code to make this camera work and listen to lifecycle events of the enclosing activity.
protected fun sendImageToStream(image: CameraOutput) {
// use channel.offer to ensure the latest images are processed
runBlocking { imageChannel.offer(image) }
}
#OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroy() {
runBlocking { imageChannel.close() }
}
/**
* Get the stream of images from the camera.
*/
fun getImageStream(): ReceiveChannel<Bitmap> = imageChannel
}
class ImageProcessor<Result>(workers: List<ImageAnalyzer<Result>>) {
private val analysisResults = Channel<Result>(capacity = Channel.RENDEZVOUS)
private val cancelMutex = Mutex()
var finished = false // this can be set elsewhere when enough images have been analyzed
fun subscribeTo(channel: ReceiveChannel<Bitmap>, processingCoroutineScope: CoroutineScope) {
// omit some checks to make sure this is not already subscribed
processingCoroutineScope.launch {
val workerScope = this
workers.forEachIndexed { index, worker ->
launch(Dispatchers.Default) {
startWorker(channel, workerScope, index, worker)
}
}
}
}
private suspend fun startWorker(
channel: ReceiveChannel<Bitmap>,
workerScope: CoroutineScope,
workerId: Int,
worker: ImageAnalyzer
) {
for (bitmap in channel) {
analysisResults.send(worker.analyze(bitmap))
cancelMutex.withLock {
if (finished && workerScope.isActive) {
workerScope.cancel()
}
}
}
}
}
class ExampleApplication : CoroutineScope {
private val cameraAdapter: CameraAdapter = ...
private val imageProcessor: ImageProcessor<Result> = ...
fun analyzeCameraStream() {
imageProcessor.subscribeTo(cameraAdapter.getImageStream())
}
}
What's the proper way to do this? I would like to use a ChannelFlow instead of a Channel to pass data between the camera and the ImageProcessor. This would allow me to call flow.map to add metadata to the images before they're sent to the analyzers. However, when doing so, each ImageAnalyzer gets a copy of the same image instead of processing different images in parallel. Is it possible to use a Flow as a message queue rather than a broadcaster?
I got this working with flows! It was important to keep the flows backed by a channel throughout this sequence so that each worker would pick up unique images to operate on. I've confirmed this functionality through unit tests.
Here's my updated code for posterity:
class ImageAnalyzer<Result> {
fun analyze(image: Bitmap): Result {
// perform some work on the image and return a Result. This can take a long time.
}
}
class CameraAdapter {
private val imageStream = Channel<Bitmap>(capacity = Channel.RENDEZVOUS)
private val imageReceiveMutex = Mutex()
// additional code to make this camera work and listen to lifecycle events of the enclosing activity.
protected fun sendImageToStream(image: CameraOutput) {
// use channel.offer to enforce the drop back pressure strategy
runBlocking { imageChannel.offer(image) }
}
#OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun onDestroy() {
runBlocking { imageChannel.close() }
}
/**
* Get the stream of images from the camera.
*/
fun getImageStream(): Flow<Bitmap> = imageChannel.receiveAsFlow()
}
class ImageProcessor<Result>(workers: List<ImageAnalyzer<Result>>) {
private val analysisResults = Channel<Result>(capacity = Channel.RENDEZVOUS)
private val cancelMutex = Mutex()
var finished = false // this can be set elsewhere when enough images have been analyzed
fun subscribeTo(flow: Flow<Bitmap>, processingCoroutineScope: CoroutineScope): Job {
// omit some checks to make sure this is not already subscribed
return processingCoroutineScope.launch {
val workerScope = this
workers.forEachIndexed { index, worker ->
launch(Dispatchers.Default) {
startWorker(flow, workerScope, index, worker)
}
}
}
}
private suspend fun startWorker(
flow: Flow<Bitmap>,
workerScope: CoroutineScope,
workerId: Int,
worker: ImageAnalyzer
) {
while (workerScope.isActive) {
flow.collect { bitmap ->
analysisResults.send(worker.analyze(bitmap))
cancelMutex.withLock {
if (finished && workerScope.isActive) {
workerScope.cancel()
}
}
}
}
}
fun getAnalysisResults(): Flow<Result> = analysisResults.receiveAsFlow()
}
class ExampleApplication : CoroutineScope {
private val cameraAdapter: CameraAdapter = ...
private val imageProcessor: ImageProcessor<Result> = ...
fun analyzeCameraStream() {
imageProcessor.subscribeTo(cameraAdapter.getImageStream())
}
}
It appears that, so long as the flow is backed by a channel, the subscribers will each get a unique image.
I remember that in kotlin language there is a option to get value by get() property, but can't find how to write it.
What I mean is: I have a LiveData into my ViewModel and I need that access to post in LiveData has only ViewModel and outside just option to get for subscribe.
How I implemented it for now is
class MyViewModel(ctx: Context) : AndroidViewModel(ctx as Application)
{
private val _showLoadingPB = SingleLiveEvent<Boolean>()
fun showLoadingPB(): SingleLiveEvent<Boolean>
{
return _showLoadingPB
}
...
}
But I remember that there is an option to write it like this
class MyViewModel(ctx: Context) : AndroidViewModel(ctx as Application)
{
private val _showLoadingPB = SingleLiveEvent<Boolean>()
val showLoadingPB: SingleLiveEvent<Boolean>
get() => _showLoadingPB
}
How to make it works?
I remembered how it should be
class MyViewModel(ctx: Context) : AndroidViewModel(ctx as Application)
{
private val _showLoadingPB = SingleLiveEvent<Boolean>()
val showLoadingPB: LiveData<Boolean>
get() = _showLoadingPB
}
This way user can't assign new value to your SingleLiveEvent as well as post new event in LiveData, he can just observe it.
In the new project that I'm currently working on I have no RxJava dependency at all, because until now I didn't need that - coroutines solve threading problem pretty gracefully.
At this point I stumbled upon on a requirement to have a BehaviorSubject-alike behavior, where one can subscribe to a stream of data and receive the latest value upon subscription. As I've learned, Channels provide very similar behavior in Kotlin, so I decided to give them a try.
From this article I've learned, that ConflatedBroadcastChannel is the type of channel that mimics BehaviorSubject, so I declared following:
class ChannelSender {
val channel = ConflatedBroadcastChannel<String>()
fun sendToChannel(someString: String) {
GlobalScope.launch(Dispatchers.Main) { channel.send(someString) }
}
}
For listening to the channel I do this:
class ChannelListener(val channelSender: ChannelSender) {
fun listenToChannel() {
channelSender.channel.consumeEach { someString ->
if (someString == "A") foo.perform()
else bar.perform()
}
}
}
This works as expected, but at this point I'm having difficulties understanding how to unit test ChannelListener.
I've tried to find something related here, but none of example-channel-**.kt classes were helpful.
Any help, suggestion or correction related to my incorrect assumptions is appreciated. Thanks.
With the help of Alexey I could manage to end up having following code, which answers the question:
class ChannelListenerTest {
private val val channelSender: ChannelSender = mock()
private val sut = ChannelListener(channelSender)
private val broadcastChannel = ConflatedBroadcastChannel<String>()
private val timeLimit = 1_000L
private val endMarker = "end"
#Test
fun `some description here`() = runBlocking {
whenever(channelSender.channel).thenReturn(broadcastChannel)
val sender = launch(Dispatchers.Default) {
broadcastChannel.offer("A")
yield()
}
val receiver = launch(Dispatchers.Default) {
while (isActive) {
val i = waitForEvent()
if (i == endMarker) break
yield()
}
}
try {
withTimeout(timeLimit) {
sut.listenToChannel()
sender.join()
broadcastChannel.offer(endMarker) // last event to signal receivers termination
receiver.join()
}
verify(foo).perform()
} catch (e: CancellationException) {
println("Test timed out $e")
}
}
private suspend fun waitForEvent(): String =
with(broadcastChannel.openSubscription()) {
val value = receive()
cancel()
value
}
}