How to build a messenger V3.0

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Rakhimov Andrii [email protected]

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➔ ➔ ➔ ➔ ➔ ➔ Agenda

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Story Story

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Story

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Features ➔

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Features ➔ ➔

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Features ➔ ➔ ➔

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Features ➔ ➔ ➔ ➔

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Features ➔ ➔ ➔ ➔ ➔

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Features ➔ ➔ ➔ ➔ ➔ ➔

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Features ➔ ➔ ➔ ➔ ➔ ➔ ➔

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➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending ➔ Delivery status ➔ Typing ➔ Online status ➔ Pagination ➔ Ofﬂine send ➔ Delete chat Features

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➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending ➔ Delivery status ➔ Typing ➔ Online status ➔ Pagination ➔ Ofﬂine send ➔ Delete chat ➔ Blacklist user Features

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➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending ➔ Delivery status ➔ Typing ➔ Online status ➔ Pagination ➔ Ofﬂine send ➔ Delete chat ➔ Blacklist user ➔ Different types of chats ➔ Search Features

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Business needs

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WEB client Business needs

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WEB client Business needs

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WEB client Business needs

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Telegram Codebase 546 743 LOC

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Resources

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Resources

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Resources

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Variety of market solutions

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Transport

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HTTP

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HTTP

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HTTP + Firebase Cloud Messaging

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HTTP + Firebase Cloud Messaging

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HTTP + Firebase Cloud Messaging

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Bidirectional transport

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Bidirectional transport

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Messaging protocols

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WEB client

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WEB client

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WEB client Reconnects

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Socket.IO

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Bidirectional transport

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Acknowledgment

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Acknowledgment

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Duplicate messages

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Duplicate messages

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Time sync and message order

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Time sync and message order

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Time sync and message order

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Android

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Battery concerns

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Battery concerns val lifecycleObserver = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_START) fun onEnterForeground() { socketClient.connect() } @OnLifecycleEvent(Lifecycle.Event.ON_STOP) fun onEnterBackground() { socketClient.disconnect() } } ProcessLifecycleOwner.get().lifecycle.addObserver(lifecycleObserver)

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Auth

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Auth val authListener = object : AuthListener { override fun logIn() { socketClient.connect() } override fun logOut() { socketClient.disconnect() } } userOperations.register(authListener)

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Auth

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FCM val fcmListener = object : MessageListener { override fun onMessageReceived() { socketClient.connect() } } fcmOperations.register(fcmListener)

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Auth Reconnects

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Auth val authListener = object : AuthListener { override fun logIn() { socketClient.connect() } override fun logOut() { socketClient.disconnect() //more things to do... } } userOperations.register(authListener)

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Auth Reconnects State Machines

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State machines sealed class LifecycleState { object AppStarted: LifecycleState() object AppEnteredForeground: LifecycleState() object AppEnteredBackground: LifecycleState() object LoggedIn: LifecycleState() object LoggedOut: LifecycleState() object Reconnected: LifecycleState() object Disconnected : LifecycleState() data class MessageReceived(val message: Any): LifecycleState() }

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State machines private val authListener = object : AuthListener { override fun logIn() { lifecycleListener.onStateChanged(LifecycleState.LoggedIn) } override fun logOut() { lifecycleListener.onStateChanged(LifecycleState.LoggedOut) } } authOperations.register(authListener)

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State machines fun onStateChanged(state: LyfecycleState) { when(state){ Reconnected ->... AppStarted -> { socketClient.connect() unreadCounterOperations.syncUnreadCounter()... } AppEnteredForeground ->... AppEnteredBackground -> { socketClient.disconnect()... } LoggedIn ->... }

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State machines

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foreground services

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Firebase Cloud Messaging

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+ Workmanager =

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Clean Architecture Dependency rule

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Architecture

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MVP

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MVP

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MVP

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MVP

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MVP & State Machine

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RxRedux

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StateMachine Actions //Input Actions sealed class Action { object LoadNextPageAction : Action() data class ErrorLoadingPageAction(val error: Throwable, val page: Int) : Action() data class PageLoadedAction(val itemsLoaded:List, val page: Int) : Action() data class StartLoadingNextPage(val page: Int) : Action() }

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StateMachine States sealed class State { object LoadingFirstPageState : State() data class ErrorLoadingFirstPageState(val errorMessage: String) :State() data class ShowContentState(val items: List, val page: Int) : State() }

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StateMachine Setup class PaginationStateMachine @Inject constructor( private val githubOperations: GithubOperatinos) { val input: PublishSubject = PublishSubject.create() val state: Observable = input .reduxStore( initialState = State.LoadingFirstPageState, sideEffects = listOf( ::loadFirstPageSideEffect, ::loadNextPageSideEffect, ::showAndHideLoadingErrorSideEffect ), reducer = ::reducer )

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StateMachine Side Effect private fun loadFirstPageSideEffect(actions: Observable, state: StateAccessor): Observable{ return actions.ofType(Action.LoadFirstPageAction::class.java) .filter { state() !is ContainsItems } // If first page was loaded, do nothing .switchMap { val state = state() val nextPage = (if (state is ContainsItems) state.page else 0) + 1 githubOperations.loadRepositories(nextPage) .map { result -> PageLoadedAction(itemsLoaded = result.items, page = nextPage) } .onErrorReturn { error -> ErrorLoadingPageAction(error, nextPage) } .startWith(StartLoadingNextPage(nextPage)) } }

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StateMachine Reducer //Takes Actions and the current state to calculate the new state. private fun reducer(state: State, action: Action): State { return when (action) { is StartLoadingNextPage -> State.LoadingFirstPageState is PageLoadedAction -> State.ShowContentState(items = action.items, page = action.page) is ErrorLoadingPageAction -> State.ErrorLoadingFirstPageState(action.error.localizedMessage) } }

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Displaying state open fun render(state: PaginationStateMachine.State) = when (state) { PaginationStateMachine.State.LoadingFirstPageState -> { recyclerView.gone() loading.visible() error.gone() } is PaginationStateMachine.State.ShowContentState -> { showRecyclerView(items = state.items, showLoadingNext = false) } is PaginationStateMachine.State.ErrorLoadingFirstPageState -> { recyclerView.gone() loading.gone() error.visible() snackBar?.dismiss() } Compose Dreams

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Performance matters

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DistinctUntilChanged val state: Observable = input .reduxStore( initialState = State.LoadingFirstPageState, sideEffects = listOf( ::loadFirstPageSideEffect, ::loadNextPageSideEffect, ::showAndHideLoadingErrorSideEffect ), reducer = ::reducer ) .distinctUntilChanged()

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Flat view hierarchy

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Flat view hierarchy Drawable Canvas Drawable android.text.Layout android.text.Layout

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Flat view hierarchy

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Startup Time public class App extends MultiDexApplication { … @Override public void onCreate() { super.onCreate(); initWhenIdle(); } private void initWhenIdle() { Looper.myQueue().addIdleHandler(() -> { appComponent.socketMessageHandler().start(); return false; }); } }