AnDevCon 2014 - 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 Crashlytics team, we've detected a significant percentage of issues caused by third-party SDKs.

Crashlytics is well known for its focus on SDK quality, and has been deployed on hundreds of millions of devices. In this session, attendees will learn the skills to develop and distribute SDKs for Android. We'll explore how to design and build an SDK for stability, testability, performance, overall footprint size, and, most importantly, exceptional ease of implementation. Over the course of the class, 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 iOS & Android: github.com/twitterdev
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 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); }
20. Detecting Dependencies public TwitterApiClient { final Session session; public TwitterApiClient(Session session) { this.session = session; } public TwitterApiClient() { this.session = Twitter.getSessionManager().getActiveSession(); } }
21. Extensible API
22. Extensible Crashlytics.start(this);
23. Extensible Crashlytics.start(this, 5); Crashlytics.setListener(createCrashlyticsListener()); Crashlytics.setPinningInfo(createPinningInfoProvider()) Crashlytics.getInstance().setDebugMode(true);
24. Extensible Crashlytics.setListener(createCrashlyticsListener()); Crashlytics.setPinningInfo(createPinningInfoProvider()); Crashlytics.getInstance().setDebugMode(true); Crashlytics.start(this, 5);
25. Extensible Crashlytics.start(this, delay, listener, pinningInfo, debugMode);
26. Extensible Crashlytics.start(this, 0, null, null, null, true);
27. Fluent Pattern Crashlytics crashlytics = new Crashlytics.Builder() .delay(1) .listener(createCrashlyticsListener()) .pinningInfo(createPinningInfoProvider()) .build(); Fabric.with(this, crashlytics);
28. Fluent Pattern Fabric.with(new Fabric.Builder(this) .kits(new Crashlytics()) .debuggable(true) .logger(new DefaultLogger(Log.VERBOSE)) .looper(getCustomLooper()) .executor(getCustomExecutorService()) .build());
29. Callbacks Fabric fabric = new Fabric.Builder(this) .kits(new Crashlytics()) .initializationCallback( new Callback<Fabric>() { void success(Fabric fabric) { } void failure(Exception exception) { } }) .build();
30. 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); }
31. 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); } ... }
32. 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); } }
33. 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>
34. Great API Traits Intuitive
35. Great API Traits Intuitive Consistent
36. Great API Traits Intuitive Consistent Easy to use, hard to misuse
37. Handling Failure
38. Catch unexpected exceptions try { //Do all the things! } catch (Exception e){ //Log something meaningful }
39. 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; }
40. Gracefully Degrade if (TextUtils.isEmpty(apiKey) if (debuggable){ throw new IllegalArgumentException(“apiKey is null!"); } else { return null; } }
41. Runtime Detection
42. Minimizing Permissions <uses-permission android:name="android.permission.INTERNET"/>
43. Minimizing Permissions crashlytics.setUserEmail(“appuser@domain.com”);
44. Permissions Detection protected boolean canCheckNetworkState(Context context) { String permission = Manifest.permission.ACCESS_NETWORK_STATE; int result = context.checkCallingOrSelfPermission(permission); return (result == PackageManager.PERMISSION_GRANTED); }
45. Optional Features <manifest … package="com.example.SDK" > <application ... > … </application> <uses-feature android:name="android.hardware.camera" android:required=”false” /> </manifest>
46. Features Detection protected boolean hasCamera(Context context) { PackageManager pm = context.getPackageManager(); String camera = PackageManager.FEATURE_CAMERA; return pm.hasSystemFeature(camera); }
47. Android Version Detection if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO) { return formatID(Build.HARDWARE);} } return null;
48. Intent Detection try { startActivityForResult(new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH), 0); } catch (ActivityNotFoundException e){ }
49. 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 }
50. 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'
51. Library Detection Cont public class DefaultClient implements Client { private final Client client; public DefaultClient() { if (hasOkHttpOnClasspath()) { client = new OkClient(); } else { client = new UrlConnectionClient(); } } … }
52. Multiple Application Types
53. Multiple Application Types package com.example; import android.app.Service; public class MyService extends Service { }
54. UI from Application Context WeakReference<Activity> activity = new WeakReference<>(); @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH) void registerLifecycleCallbacks(Application app) { app.registerActivityLifecycleCallbacks( new ActivityLifecycleCallbacks() { @Override public void onActivityResumed(Activity activity) { activity.set(activity); } }); }
55. UI from Application Context WeakReference<Activity> activity = new WeakReference<>(); … public void showErrorDialog(String error) { final Activity activity = currentActivity.get(); if (activity != null && !activity.isFinishing()) { new AlertDialog.Builder(activity) .setMessage(error).create().show(); } } }
56. Testable SDKs
57. Make it Testable/Mockable Avoid static methods
58. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly
59. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly Utilize interfaces around entry points
60. Make it Testable/Mockable Avoid static methods Avoid final classes and accessing fields directly Utilize interfaces around entry points Provide test package in separate artifact
61. 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(); } }
62. 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(); } … }
63. Using in Tests package com.example.Tweeter; public class MyTest extends AndroidTestCase { Tweeter tweeter; @Override public void setup() { tweeter = mock(Tweeter.class); } ... }
64. Powerful SDKs •Ease of Integration •Extensibility •Handling Failure •Runtime detection •Support all app types •Testable
65. Lightweight
66. Binary Size
67. Binary Size
68. 3rd Party Library Mindfulness
69. 3rd Party Library Mindfulness
70. 3rd Party Library Mindfulness PROTOBUF KB OURS KB
71. 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 }
72. 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 }
73. Dalvik Method Count
74. 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
75. 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
76. Modularity How to avoid a “Monolith Abomination”
77. Modularity Fabric.with(this, new Twitter()); Fabric.with(this, new TweetUi(), new TweetComposer());
78. Fabric.aar Cache Settings Concurrency Events Network Persistence
79. Fabric.aar Cache Settings Concurrency Events Network Persistence KitCore Kit Common Services
80. Fabric.aar Cache Settings Concurrency Events Network Persistence KitCore Kit A Kit C Kit B Features Kit Common Services
81. Fabric.aar Cache Settings Concurrency Events Network Persistence KitCore Kit A Kit C Kit B KitInterface Interface Features Kit Common Services
82. Fabric.aar Cache Settings Concurrency Events Network Persistence TwitterCore.aar TweetUi.aar Digits.aar TweetComposer. aar Twitter.aar Interface Features Kit Common Services
83. How big are Fabric AARs? Fabric: 190kb Crashlytics: 90kb Beta: 13kb Answers: 20kb Twitter API & SSO: 296kb Tweet UI: 120kb Tweet Composer: 5kb Digits: 236kb
84. Minimize Network Usage
85. Network Usage 10X SMALLER 100X FASTER XML PROTOBUF
86. Batching Requests High Power Low Power Idle 24% 30% 63% 14% 70%
87. Reduce Startup Time
88. Startup Time Thread.start(); Executors.newSingleThreadExecutor();
89. 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; } }
90. Improving Startup Time in Fabric Shared Resources
91. Improving Startup Time in Fabric Shared Resources Sync and Async Initialization
92. Improving Startup Time in Fabric Shared Resources Sync and Async Initialization Priorities
93. Improving Startup Time in Fabric Shared Resources Sync and Async Initialization Priorities Dependencies
94. NDK implements Reporter Crashlytics @DependsOn(Reporter.class) dependency { compile ‘...:crashlytics:+@aar’ } Sync Initialization (Handler installed) Async Initialization (Upload Crash) Sync Initialization (Handler installed) Async Initialization (Read Crash) set pending crash interface Reporter extends Dependency Control returned to developer
95. Lightweight SDKs • Binary size • 3rd party library mindfulness • Dalvik Method Count • Modularity • Network usage • Startup time
96. Support
97. Support “An API is like a baby”
98. Support “An API is like a baby” Documentation - Javadocs and Instructions
99. Support “An API is like a baby” Documentation - Javadocs and Instructions A Minimalist Approach to Sample Code
100. Support “An API is like a baby” Documentation - Javadocs and Instructions A Minimalist Approach to Sample Code Deprecation and Maintenance plan
101. Lightweight Powerful
102. Questions? dev.twitter.com @tsmith