Adopting RxJava on Airbnb Android

Presentation at Droidcon DE on June 17th, 2016

Transcript

1. Adopting RxJava on Airbnb Android FELIPE LIMA / JUNE 17, 2016 / DROIDCON DE
2. Why RxJava?
3. We make shitty software
4. Mobile Engineering is hard
6. ReactiveX AN API FOR ASYNCHRONOUS PROGRAMMING WITH OBSERVABLE STREAMS
7. Streams
8. Reactive programming
10. Programming Paradigms 101
11. Object Oriented programming
12. • Class based • Objects as first class citizens • State management • Side causes: Hidden inputs • Side effects: Hidden outputs • Hard to unit test: Mocking libraries Object Oriented Programming The status quo
13. Side-Effects are the Complexity Iceberg.
14. Functional programming
15. • Higher order functions • Pure functions • Referential transparency • Easy to reason about • Easy to unit test Functional Programming http://blog.jenkster.com/2015/12/what-is-functional-programming.html
16. Now back to reactive…
17. • Observable & Observer Concepts
18. • Observable & Observer • Subscriber Concepts
19. • Observable & Observer • Subscriber • Subscription Concepts
20. • Observable & Observer • Subscriber • Subscription • Producer Concepts
21. • Observable & Observer • Subscriber • Subscription • Producer • Hot & Cold Observables Concepts
22. • Observable & Observer • Subscriber • Subscription • Producer • Hot & Cold Observables • Backpressure Concepts
23. • Observable & Observer • Subscriber • Subscription • Producer • Hot & Cold Observables • Backpressure • Scheduler Concepts
24. • Observable & Observer • Subscriber • Subscription • Producer • Hot & Cold Observables • Backpressure • Scheduler • Subject Concepts
25. • Observable & Observer • Subscriber • Subscription • Producer • Hot & Cold Observables • Backpressure • Scheduler • Subject • And more! Concepts
26. /**
 * Returns a new Observable by applying a function that you supply to each item emitted * by the source Observable that returns an Observable, and then emitting the items * emitted by the most recently emitted of these Observables.
 *
 * The resulting Observable completes if both the upstream Observable and the last * inner Observable, if any, complete.
 * If the upstream Observable signals an onError, the inner Observable is unsubscribed * and the error delivered in-sequence.
 * 
 * @param fund
 * a function that, when applied to an item emitted by the source Observable, * returns an Observable
 * @return an Observable that emits the items emitted by the Observable returned from * applying {@code func} to the most recently emitted item emitted by the source * Observable
 */ public final <R> Observable<R> switchMap( Func1<? super T, ? extends Observable<? extends R>> func) {
 return switchOnNext(map(func));
 }
27. WAT?!
28. Adoption challenges
29. • Team Size: Getting everyone onboard and up to speed • Learning Curve: Steep, time consuming • Terminology: Lots of new concepts • Debugging: Unreadable stack traces Adoption Challenges
30. java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread. at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:62) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: rx.exceptions.OnErrorFailedException: Error occurred when trying to propagate error to Observer.onError at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:192) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:254) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:186) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: rx.exceptions.CompositeException: 2 exceptions occurred. at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:192) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:254) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:186) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: rx.exceptions.CompositeException$CompositeExceptionCausalChain: Chain of Causes for CompositeException In Order Received => at android.util.Log.getStackTraceString(Log.java:499) at com.android.internal.os.RuntimeInit.Clog_e(RuntimeInit.java:59) at com.android.internal.os.RuntimeInit.access$200(RuntimeInit.java:43) at com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:91) at com.bugsnag.android.ExceptionHandler.uncaughtException(ExceptionHandler.java:56) at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693) at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:66) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: com.airbnb.airrequest.NetworkException at com.airbnb.airrequest.ObservableFactory.lambda$responseMapper$1(ObservableFactory.java:59) at com.airbnb.airrequest.ObservableFactory.access$lambda$1(ObservableFactory.java:-1) at com.airbnb.airrequest.ObservableFactory$$Lambda$4.call(Unknown:-1) at rx.internal.operators.OperatorMap$1.onNext(OperatorMap.java:54) at rx.internal.operators.OperatorUnsubscribeOn$1.onNext(OperatorUnsubscribeOn.java:52) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:207) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:422) at java.util.concurrent.FutureTask.run(FutureTask.java:237) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:152) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:265) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) at java.lang.Thread.run(Thread.java:818) Caused by: java.lang.ClassCastException: com.airbnb.android.responses.AirBatchResponse cannot be cast to com.airbnb.android.responses.ErrorResponse at com.airbnb.android.utils.NetworkUtil.error(NetworkUtil.java:357) at com.airbnb.android.utils.NetworkUtil.isExpiredOauthError(NetworkUtil.java:363) at com.airbnb.android.requests.base.ErrorLoggingAction.checkForExpiredToken(ErrorLoggingAction.java:96) at com.airbnb.android.requests.base.ErrorLoggingAction.call(ErrorLoggingAction.java:83) at com.airbnb.android.requests.base.ErrorLoggingAction.call(ErrorLoggingAction.java:33) at rx.Observable$10.onError(Observable.java:4561) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:65) at com.airbnb.rxgroups.GroupSubscriptionTransformer$1.onError(GroupSubscriptionTransformer.java:45) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:71) at rx.subjects.SubjectSubscriptionManager$SubjectObserver.onError(SubjectSubscriptionManager.java:227) at rx.internal.operators.NotificationLite.accept(NotificationLite.java:147) at rx.subjects.ReplaySubject$UnboundedReplayState.accept(ReplaySubject.java:465) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserverFromIndex(ReplaySubject.java:514) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserver(ReplaySubject.java:502) at rx.subjects.ReplaySubject.caughtUp(ReplaySubject.java:427) at rx.subjects.ReplaySubject.onError(ReplaySubject.java:387) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:254) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:186) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) Caused by: java.lang.ClassCastException: rx.exceptions.CompositeException cannot be cast to com.airbnb.airrequest.NetworkException at com.airbnb.android.requests.AirBatchRequestObserver.onError(AirBatchRequestObserver.java:60) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:68) at com.airbnb.rxgroups.GroupSubscriptionTransformer$1.onError(GroupSubscriptionTransformer.java:45) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:71) at rx.subjects.SubjectSubscriptionManager$SubjectObserver.onError(SubjectSubscriptionManager.java:227) at rx.internal.operators.NotificationLite.accept(NotificationLite.java:147) at rx.subjects.ReplaySubject$UnboundedReplayState.accept(ReplaySubject.java:465) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserverFromIndex(ReplaySubject.java:514) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserver(ReplaySubject.java:502) at rx.subjects.ReplaySubject.caughtUp(ReplaySubject.java:427) at rx.subjects.ReplaySubject.onError(ReplaySubject.java:387) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:254) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:186) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
31. Caused by: java.lang.ClassCastException: rx.exceptions.CompositeException cannot be cast to com.airbnb.airrequest.NetworkException at com.airbnb.android.requests.AirBatchRequestObserver.onError(AirBatchRequestObserver.java:60) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:68) at com.airbnb.rxgroups.GroupSubscriptionTransformer$1.onError(GroupSubscriptionTransformer.java:45) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:71) at rx.subjects.SubjectSubscriptionManager$SubjectObserver.onError(SubjectSubscriptionManager.java:227) at rx.internal.operators.NotificationLite.accept(NotificationLite.java:147) at rx.subjects.ReplaySubject$UnboundedReplayState.accept(ReplaySubject.java:465) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserverFromIndex(ReplaySubject.java:514) at rx.subjects.ReplaySubject$UnboundedReplayState.replayObserver(ReplaySubject.java:502) at rx.subjects.ReplaySubject.caughtUp(ReplaySubject.java:427) at rx.subjects.ReplaySubject.onError(ReplaySubject.java:387) at rx.Observable$30.onError(Observable.java:8280) at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157) at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.checkTerminated(OperatorObserveOn.java:254) at rx.internal.operators.OperatorObserveOn$ObserveOnSubscriber.call(OperatorObserveOn.java:186) at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:145) at android.app.ActivityThread.main(ActivityThread.java:6141) at java.lang.reflect.Method.invoke(Method.java:-2) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
32. Common Pitfalls
33. subscribe()
34. return observableFactory.<T>toObservable(this) .compose(this.<T>transform(observableRequest)) .observeOn(Schedulers.io()) .map(new ResponseMetadataOperator<>(this)) .flatMap(this::mapResponse) .observeOn(AndroidSchedulers.mainThread())
 .<AirResponse<T>>compose(group.transform(tag))
 .doOnError(new ErrorLoggingAction(request))
 .doOnError(NetworkUtil::checkForExpiredToken) .subscribeOn(Schedulers.io())
 .subscribe(request.observer());
35. observeOn()
36. return observableFactory.<T>toObservable(this) .compose(this.<T>transform(observableRequest)) .observeOn(Schedulers.io()) .map(new ResponseMetadataOperator<>(this)) .flatMap(this::mapResponse) .observeOn(AndroidSchedulers.mainThread())
 .<AirResponse<T>>compose(group.transform(tag))
 .doOnError(new ErrorLoggingAction(request))
 .doOnError(NetworkUtil::checkForExpiredToken)
 .subscribe(request.observer());
37. subscribeOn()
38. return observableFactory.<T>toObservable(this) .compose(this.<T>transform(observableRequest)) .observeOn(Schedulers.io()) .map(new ResponseMetadataOperator<>(this)) .flatMap(this::mapResponse) .observeOn(AndroidSchedulers.mainThread())
 .<AirResponse<T>>compose(group.transform(tag))
 .doOnError(new ErrorLoggingAction(request))
 .doOnError(NetworkUtil::checkForExpiredToken) .subscribeOn(Schedulers.io())
 .subscribe(request.observer());
39. flatMap()
41. Error Handling
42. try { return observableFactory.<T>toObservable(this) .compose(this.<T>transform(observableRequest)) .observeOn(Schedulers.io()) .map(new ResponseMetadataOperator<>(this)) .flatMap(this::mapResponse) .observeOn(AndroidSchedulers.mainThread())
 .subscribe(request.observer()); } catch(Exception e) { Log.e(TAG, "whoops :("); }
43. return observableRequest .rawRequest() .<Observable<Response<T>>>newCall() .observeOn(Schedulers.io()) .unsubscribeOn(Schedulers.io()) .flatMap(responseMapper(airRequest)) .onErrorResumeNext(errorMapper(airRequest));
44. return observableFactory.<T>toObservable(this) .compose(this.<T>transform(observableRequest)) .observeOn(Schedulers.io()) .map(new ResponseMetadataOperator<>(this)) .flatMap(this::mapResponse) .observeOn(AndroidSchedulers.mainThread())
 .<AirResponse<T>>compose(group.transform(tag))
 .doOnError(new ErrorLoggingAction(request))
 .doOnError(NetworkUtil::checkForExpiredToken) .subscribeOn(Schedulers.io())
 .subscribe(request.observer());
45. Unit Testing
46. @Test public void testErrorResponseNonJSON() { server.enqueue(new MockResponse() .setBody("something bad happened") .setResponseCode(500)); TestRequest request = new TestRequest.Builder<String>().build(); TestSubscriber<AirResponse<String>> subscriber = new TestSubscriber<>(); observableFactory.<String>toObservable(request).subscribe(subscriber); subscriber.awaitTerminalEvent(3L, TimeUnit.SECONDS); NetworkException exception = (NetworkException) subscriber.getOnErrorEvents().get(0); assertThat(exception.errorResponse(), equalTo(null)); assertThat(exception.bodyString(), equalTo("something bad happened")); }
47. @Test public void testUnicodeHeader() { server.enqueue(new MockResponse().setBody("\"Hello World\"")); TestRequest request = new TestRequest.Builder<String>() .header("Bogus", "Ӿ嶆櫮מ") .build(); observableFactory.toObservable(request) .toBlocking() .first(); RecordedRequest recordedRequest = server.takeRequest(); assertThat(recordedRequest.getHeader("Bogus"), equalTo("????")); }
48. Memory Leaks
49. private final CompositeSubscription pendingSubscriptions = new CompositeSubscription(); @Override public void onCreate() { pendingSubscriptions.add( observable.subscribe(observer)); } @Override public void onDestroy() { pendingSubscriptions.clear(); }
50. compose()
52. Additional Resources
53. Reactive.community: Ben Christensen, Reactive Extensions at Netflix HTTPS://WWW.YOUTUBE.COM/WATCH?V=ET_SMMXKE5S
54. Cycle.js and functional reactive user interfaces Andre Stalz HTTPS://WWW.YOUTUBE.COM/WATCH?V=UNZNFTSKSYG
55. LDN Functionals Kris Jenkins: What is Functional Programming? HTTPS://WWW.YOUTUBE.COM/WATCH?V=TQRTTSIPYE4
56. Questions?
57. Thanks!