Droidcon - Building First Class Sdks: A Fabric Case Study

The Android app ecosystem is an international phenomenon. Developers need better tools now, more than ever, and the number of third-party SDKs is also growing to meet the developer's needs. Unfortunately, many of these SDKs are poorly developed and extremely difficult to use. In fact, at Twitter on the Fabric team, we've detected a significant percentage of issues caused by third-party SDKs.

Fabric, formerly Crashlytics, is well-known for its focus on SDK quality, and has been deployed on billions of devices. In this session, attendees will learn the skills to develop and distribute SDKs for Android. We’ll cover an overview of Fabric, deep dive into technical decisions we made, and present the learnings on developing an SDK for stability, testability, performance, overall footprint size, and, most importantly, exceptional ease of implementation. Over the course of the session, we'll develop a simple but well-architected SDK and uncover and explain many of the challenges we encountered when building SDKs at Twitter. Topics include device feature detection, supporting multiple application types (from Widgets to Services to Foreground GUI applications), API design, deploying artifacts, and coding patterns to support developer customization. We'll conclude with advanced topics, from less-known but very useful tricks to minimizing impact on application start-up time to reducing memory footprint and persistent CPU use.

Transcript

1. dev.twitter.com @tsmith Building First Class SDKs A Fabric Case Study Ty Smith Sr. Android Engineer
6. Fabric Sample App Cannonball Open source for Android & iOS: github.com/twitterdev #LetMeExplainYou
7. Build an SDK
8. Considerations
9. Considerations What need are you serving?
10. Considerations What need are you serving? Library Project, JARs, ApkLibs, and AARs.
11. Considerations What need are you serving? Library Project, JARs, ApkLibs, and AARs. Open or Closed Source - Associated licensing
12. Considerations What need are you serving? Library Project, JARs, ApkLibs, and AARs. Open or Closed Source - Associated licensing Hosting the artifacts
13. Powerful Lightweight
14. Powerful
15. Ease of Integration
16. Ease of Integration Fabric.with(this, new Crashlytics());
17. Detecting Dependencies <manifest … package="com.example.SDK" > <application ... > … <meta-data android:value="11235813213455" android:name=“com.fabric.ApiKey” /> </application> </manifest>
18. Detecting Dependencies public static Fabric with(Context context) { Context appContext = context.getApplicationContext(); ApplicationInfo ai = context.getPackageManager() .getApplicationInfo(ac.getPackageName(), PackageManager.GET_META_DATA); String apiKey = ai.metaData.getString(API_KEY); return new Fabric(appContext, apiKey); }
19. Detecting Dependencies public TwitterApiClient { final Session session; public TwitterApiClient(Session session) { this.session = session; } public TwitterApiClient() { this.session = Twitter.getSessionManager().getActiveSession(); } }
20. Extensible API
21. Extensible Crashlytics.start(this, 5); Crashlytics.setListener(createCrashlyticsListener()); Crashlytics.setPinningInfo(createPinningInfoProvider()) Crashlytics.getInstance().setDebugMode(true);
22. Extensible Crashlytics.setListener(createCrashlyticsListener()); Crashlytics.setPinningInfo(createPinningInfoProvider()); Crashlytics.getInstance().setDebugMode(true); Crashlytics.start(this, 5);
23. Extensible Crashlytics.start(this, delay, listener, pinningInfo, debugMode);
24. Extensible Crashlytics.start(this, 0, null, null, null, true);
25. Fluent Pattern Crashlytics crashlytics = new Crashlytics.Builder() .delay(1) .listener(createCrashlyticsListener()) .pinningInfo(createPinningInfoProvider()) .build(); Fabric.with(this, crashlytics);
26. Fluent Pattern `Fabric.with(new Fabric.Builder(this) .kits(new Crashlytics()) .debuggable(true) .logger(new DefaultLogger(Log.VERBOSE)) .looper(getCustomLooper()) .executor(getCustomExecutorService()) .build());
27. Callbacks Fabric fabric = new Fabric.Builder(this) .kits(new Crashlytics()) .initializationCallback( new Callback<Fabric>() { void success(Fabric fabric) { } void failure(Exception exception) { } }) .build();
28. Extensible Interfaces interface Logger { void d(String tag, String text, Throwable throwable); void v(String tag, String text, Throwable throwable); void i(String tag, String text, Throwable throwable); void w(String tag, String text, Throwable throwable); void e(String tag, String text, Throwable throwable); }
29. Sane Defaults public class DefaultLogger { public DefaultLogger(int logLevel) { this.logLevel = logLevel; } void d(String tag, String text, Throwable throwable) { if (isLoggable(tag, Log.DEBUG)) Log.d(tag, text, throwable); } ... }
30. Extensible Classes class MyApiClient extends TwitterApiClient { interface MyService { @GET(“/1.1/statuses/show.json”) Tweet getTweet(@Query(“id”) int id); } MyService getMyService() { return getService(MyService.class); } }
31. Extensible View Styles <style name="tw__TweetLightStyle"> <item name="tw__container_bg_color"> @color/tw__tweet_light_container_bg_color </item> <item name="tw__primary_text_color"> @color/tw__tweet_light_primary_text_color </item> <item name="tw__action_color"> @color/tw__tweet_action_color </item> </style>
32. Great API Traits Intuitive
33. Great API Traits Intuitive Consistent
34. Great API Traits Intuitive Consistent Easy to use, hard to misuse
35. Handling Failure
36. Throw expected exceptions /** * Sets the {@link io.fabric.sdk.android.Logger} * @throws java.lang.IllegalArgumentException */ public Builder logger(Logger logger) { if (logger == null) { throw new IllegalArgumentException( "Logger must not be null."); } this.logger = logger; return this; }
37. Catch unexpected exceptions try { //Do all the things! } catch (Exception e){ //Log something meaningful }
38. Gracefully Degrade if (TextUtils.isEmpty(apiKey) if (debuggable){ throw new IllegalArgumentException(“apiKey is null!"); } else { return null; } }
39. Runtime Detection
40. Minimizing Permissions <uses-permission android:name="android.permission.INTERNET"/>
41. Minimizing Permissions crashlytics.setUserEmail(“appuser@domain.com”);
42. Permissions Detection protected boolean canCheckNetworkState(Context context) { String permission = Manifest.permission.ACCESS_NETWORK_STATE; int result = context.checkCallingOrSelfPermission(permission); return (result == PackageManager.PERMISSION_GRANTED); }
43. Optional Features <manifest … package="com.example.SDK" > <application ... > … </application> <uses-feature android:name="android.hardware.camera" android:required=”false” /> </manifest>
44. Features Detection protected boolean hasCamera(Context context) { PackageManager pm = context.getPackageManager(); String camera = PackageManager.FEATURE_CAMERA; return pm.hasSystemFeature(camera); }
45. Android Version Detection if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO) { return formatID(Build.HARDWARE);} } return null;
46. Intent Detection try { startActivityForResult(new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH), 0); } catch (ActivityNotFoundException e){ }
47. Intent Detection Cont. PackageManager pm = context.getApplicationContext().getPackageManager(); List<ResolveInfo> activities = pm.queryIntentActivities( new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH),0); if (activities.size() > 0) { //an app exists that can recognize speech }
48. Classpath Detection private boolean hasOkHttpOnClasspath() { try { Class.forName("com.squareup.okhttp.OkHttpClient"); return true; } catch (ClassNotFoundException e) { } return false; } provided 'com.squareup.okhttp:okhttp:2.0.0'
49. Classpath Detection Cont public class DefaultClient implements Client { private final Client client; public DefaultClient() { if (hasOkHttpOnClasspath()) { client = new OkClient(); } else { client = new UrlConnectionClient(); } } … }
50. Testable SDKs
51. Make it Testable/Mockable Avoid static methods
52. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly
53. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly Utilize interfaces around your public API
54. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly Utilize interfaces around your public API Avoid mocking more than one level deep
55. Hard to Test package com.example; public final class Tweeter { private Network network; public static Tweeter getInstance() {...} private Tweeter() { this.network = new Network(); } public List<Tweet> getTweets() { return network.getTweets(); } }
56. Easy to Test package com.example; public final class Tweeter { private Network network; public static Tweeter getInstance() {...} private public Tweeter(Network network) { this.network = new Network() network; } public List<Tweet> getTweets() { return getNetwork().getTweets(); } … }
57. Powerful SDKs •Ease of Integration •Extensibility •Handling Failure •Runtime detection •Testable
58. Lightweight
59. Binary Size
60. 3rd Party Library Mindfulness PROTOBUF KB OURS KB
61. Reporting Binary Size task reportSdkFootprint << { def sdkProject = project(':clients:SdkProject') def nonSdkProject = project(':clients:NonSdkProject') def crashlyticsFootprint = getSizeDifference( new File("${sdkProject.buildDir}.../Sdk.apk"), new File("${nonSdkProject.buildDir}.../NonSdk.apk") ) println crashlyticsFootprint }
62. Dalvik Method Count
63. Dalvik Method Count >./gradlew assemble … Unable to execute dex: method ID not in [0, 0xffff]: 65536 Conversion to Dalvik format failed: Unable to execute dex: method ID not in [0, 0xffff]: 65536
64. Dalvik Method Count > git clone git@github.com:mihaip/dex-method-counts.git > cd dex-method-counts > ant jar > ./dex-method-counts path/to/App.apk Read in 65490 method IDs. <root>: 65490 : 3 accessibilityservice: 6 bluetooth: 2 content: 248 pm: 22 res: 45 com: 53881 example: 283 sdk: 283
65. Minimize Network Usage
66. Network Usage 10X SMALLER 100X FASTER XML PROTOBUF
67. Batching Requests High Power Low Power Idle 24% 30% 63% 14% 70%
68. Modularity How to avoid a “Monolith Abomination”
69. Modularity Fabric.with(this, new Twitter()); Fabric.with(this, new TweetUi(), new TweetComposer());
70. Fabric.aar Cache Settings Concurrency Events Network Persistence
71. Fabric.aar Cache Settings Concurrency Events Network Persistence Core SDK Common Services
72. Fabric.aar Cache Settings Concurrency Events Network Persistence Core A C B Features SDK Common Services
73. Fabric.aar Cache Settings Concurrency Events Network Persistence Core A C B Interface Interface Features SDK Common Services
74. Fabric.aar Cache Settings Concurrency Events Network Persistence TwitterCore.aar TweetUi.aar Digits.aar TweetComposer. aar Twitter.aar Interface Features SDK Common Services
75. Reduce Startup Time
76. Startup Time Thread.start(); Executors.newSingleThreadExecutor();
77. Startup Time class MyThreadFactory implements ThreadFactory { @Override public Thread newThread(Runnable runnable) { Thread thread = new Thread(runnable); thread.setPriority( Process.THREAD_PRIORITY_BACKGROUND); return thread; } }
78. Improving Startup Time in Fabric Shared Resources
79. Improving Startup Time in Fabric Shared Resources Sync and Async Initialization
80. Improving Startup Time in Fabric Shared Resources Sync and Async Initialization On Demand Functionality
81. Lightweight SDKs • Binary size • Dalvik Method Count • Network usage • Modularity • Startup time
82. Support
83. Support “An API is like a baby”
84. Support “An API is like a baby” Documentation - Javadocs and Instructions
85. Support “An API is like a baby” Documentation - Javadocs and Instructions A Minimalist Approach to Sample Code
86. Support “An API is like a baby” Documentation - Javadocs and Instructions A Minimalist Approach to Sample Code Deprecation and Maintenance plan
87. Lightweight Powerful
88. Questions? dev.twitter.com @tsmith