How to build a messenger(revised)

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How to build a messenger for Android? Rakhimov Andrii Lead Android Engineer at Lalafo [email protected]

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➔ Story ➔ Transport ➔ Properties of transport and protocol ➔ Architecture ➔ MVP & MVI ➔ Learnings Agenda

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Story Story

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Story

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Features ➔ Real time send/delivery 1:1, 1:n

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Features ➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending

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Features ➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending ➔ Delivery status

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Features ➔ Real time send/delivery 1:1, 1:n ➔ Image/File sending ➔ Delivery status ➔ Typing

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

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

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

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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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Telegram Codebase 546 743 LOC

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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 + Simple and widely used

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HTTP + Simple and widely used - Reopening connection is expensive

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HTTP + Simple and widely used - Reopening connection is expensive - Unnecessary requests to server

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HTTP + Simple and widely used - Reopening connection is expensive - Unnecessary requests to server - Slow, not real-time

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HTTP + Firebase Cloud Messaging

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HTTP + Firebase Cloud Messaging + Close to real-time

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HTTP + Firebase Cloud Messaging + Close to real-time + Emulation of bidirectional communication

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HTTP + Firebase Cloud Messaging + Close to real-time + Emulation of bidirectional communication - Third party service

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HTTP + Firebase Cloud Messaging + Close to real-time + Emulation of bidirectional communication - Third party service - HTTP downsides

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Bidirectional transport

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Bidirectional transport

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Messaging protocols

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Socket.IO (Websocket under the hood) + Fast

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Socket.IO (Websocket under the hood) + Fast + Bidirectional

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Socket.IO (Websocket under the hood) + Fast + Bidirectional + Support web

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Socket.IO (Websocket under the hood) + Fast + Bidirectional + Support web + Do not waste connection and resources

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Socket.IO (Websocket under the hood) + Fast + Bidirectional + Reconnects + Support web + Do not waste connection and resources - 200+ issues for Android lib, not maintained for 2 years

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Best Practices To work With 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 ➔ Validate if time is differed widely, and send appropriate time from backend ➔ Store diff on client ➔ Send and show messages accordingly

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Battery concerns

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Battery concerns ProcessLifecycleOwner.get() .getLifecycle() .addObserver(new LifecycleObserver() { @OnLifecycleEvent(Lifecycle.Event.ON_START) public void onEnterForeground() { messengerClient.connect(); } @OnLifecycleEvent(Lifecycle.Event.ON_STOP) public void onEnterBackground() { messengerClient.disconnect(); } });

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Battery concerns ➔ Don’t keep socket connection open, after user leaves the app

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Battery concerns ➔ Don’t keep socket connection open, after user leaves the app ➔ Don’t use foreground Service to keep connection open

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Battery concerns ➔ Don’t keep socket connection open, after user leaves the app ➔ Don’t use foreground Service to keep connection open ➔ Use Firebase Cloud Messaging to notify the app about new messages

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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; }); } }

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time ◆ Speed

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time ◆ Speed ◆ Security

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time ◆ Speed ◆ Security ◆ Features

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time ◆ Speed ◆ Security ◆ Features ◆ Web support

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How to choose and design a transport? ➔ Determine your business needs and choose appropriate transport ◆ Time ◆ Speed ◆ Security ◆ Features ◆ Web support ➔ Remember about Android(battery, startup time)

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Architecture

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Architecture ➔ Extensible and composable

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Architecture ➔ Extensible and composable ➔ Maintainable

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Architecture ➔ Extensible and composable ➔ Maintainable ➔ Reusable

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Architecture ➔ Extensible and composable ➔ Maintainable ➔ Reusable ➔ Testable

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Clean Architecture Dependency rule

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Architecture

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MVP & MVI

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MVP & MVI

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MVP & MVI

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MVP & MVI

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MVP issues ➔ Many events can trigger same UI changes as result broken UI

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MVP issues ➔ Many events can trigger same UI changes as result broken UI ➔ Scales badly on huge and complex screens, presenters polluted with logic

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MVP issues ➔ Many events can trigger same UI changes as result broken UI ➔ Scales badly on huge and complex screens, presenters polluted with logic ➔ Testability

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MVP & MVI

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MVVM & MVI

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MVP & MVI

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/** * 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() } StateMachine Actions

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

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StateMachine Side Effect /** * Load the first Page */ private fun loadFirstPageSideEffect(actions: Observable, state: StateAccessor): Observable { return actions.ofType(Action.LoadFirstPageAction::class.java) .filter { state() !is ContainsItems } // If first page has already been 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 /** * The state 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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Learnings ➔ Fair estimates

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Fair estimates

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Learnings ➔ Fair estimates ➔ Use appropriate technology for the task

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No content

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Learnings ➔ Fair estimates ➔ Use appropriate technology for the task ➔ Design for ﬂexibility

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Learnings ➔ Fair estimates ➔ Use appropriate technology for the task ➔ Design for ﬂexibility ➔ Start small and validate hypothesis early

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Cost of change

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Learnings ➔ Fair estimates ➔ Use appropriate technology for the task ➔ Design for ﬂexibility ➔ Start small and validate hypothesis early

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Thank you! Rakhimov Andrii Lead Android Engineer at Lalafo [email protected] https://github.com/ar-g