Droidcon Montreal - 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
   

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6. Fabric Sample App
   Cannonball
   Open source for iOS & Android:
   github.com/twitterdev
   

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7. Build
   an
   SDK
   

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8. Considerations
   

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9. Considerations
   What need are you serving?
   

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10. Considerations
    What need are you serving?
    Library Project, JARs, ApkLibs, and AARs.
    

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11. Considerations
    What need are you serving?
    Library Project, JARs, ApkLibs, and AARs.
    Open or Closed Source - Associated licensing
    

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12. Considerations
    What need are you serving?
    Library Project, JARs, ApkLibs, and AARs.
    Open or Closed Source - Associated licensing
    Hosting the artifacts
    

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13. Powerful
    Lightweight
    

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14. Powerful
    

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15. Ease of
    Integration
    

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16. Ease of Integration
    Fabric.with(this, new Crashlytics());
    

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17. Detecting Dependencies
    package="com.example.SDK" >
    
    …
    android:name=“com.fabric.ApiKey” />
    
    
    

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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);
    }
    

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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);
    }
    

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20. Detecting Dependencies
    public TwitterApiClient {
    final Session session;
    public TwitterApiClient(Session session) {
    this.session = session;
    }
    public TwitterApiClient() {
    this.session =
    Twitter.getSessionManager().getActiveSession();
    }
    }
    

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21. Extensible
    API
    

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22. Extensible
    Crashlytics.start(this, 5);
    Crashlytics.setListener(createCrashlyticsListener());
    Crashlytics.setPinningInfo(createPinningInfoProvider())
    Crashlytics.getInstance().setDebugMode(true);
    

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23. Extensible
    Crashlytics.setListener(createCrashlyticsListener());
    Crashlytics.setPinningInfo(createPinningInfoProvider());
    Crashlytics.getInstance().setDebugMode(true);
    Crashlytics.start(this, 5);
    

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24. Extensible
    Crashlytics.start(this, delay, listener,
    pinningInfo, debugMode);
    

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25. Extensible
    Crashlytics.start(this, 0, null, null, null, true);
    

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26. Fluent Pattern
    Crashlytics crashlytics = new Crashlytics.Builder()
    .delay(1)
    .listener(createCrashlyticsListener())
    .pinningInfo(createPinningInfoProvider())
    .build();
    Fabric.with(this, crashlytics);
    

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27. Fluent Pattern
    Fabric.with(new Fabric.Builder(this)
    .kits(new Crashlytics())
    .debuggable(true)
    .logger(new DefaultLogger(Log.VERBOSE))
    .looper(getCustomLooper())
    .executor(getCustomExecutorService())
    .build());
    

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28. Callbacks
    Fabric fabric = new Fabric.Builder(this)
    .kits(new Crashlytics())
    .initializationCallback(
    new Callback() {
    void success(Fabric fabric) { }
    void failure(Exception exception) { }
    })
    .build();
    

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29. 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);
    }
    

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30. 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);
    }
    ...
    }
    

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31. 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);
    }
    }
    

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32. Extensible View Styles
    <br/><item name="tw__container_bg_color"><br/>@color/tw__tweet_light_container_bg_color<br/></item><br/><item name="tw__primary_text_color"><br/>@color/tw__tweet_light_primary_text_color<br/></item><br/><item name="tw__action_color"><br/>@color/tw__tweet_action_color<br/></item><br/>
    

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33. Great API Traits
    Intuitive
    

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34. Great API Traits
    Intuitive
    Consistent
    

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35. Great API Traits
    Intuitive
    Consistent
    Easy to use, hard to misuse
    

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36. Handling
    Failure
    

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37. 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;
    }
    

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38. Catch unexpected exceptions
    try {
    //Do all the things!
    } catch (Exception e){
    //Log something meaningful
    }
    

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39. Gracefully Degrade
    if (TextUtils.isEmpty(apiKey)
    if (debuggable){
    throw new IllegalArgumentException(“apiKey is null!");
    } else {
    return null;
    }
    }
    

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40. Runtime
    Detection
    

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41. Minimizing Permissions
    
    

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42. Minimizing Permissions
    crashlytics.setUserEmail(“appuser@domain.com”);
    

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43. Permissions Detection
    protected boolean canCheckNetworkState(Context context)
    {
    String permission =
    Manifest.permission.ACCESS_NETWORK_STATE;
    int result =
    context.checkCallingOrSelfPermission(permission);
    return (result == PackageManager.PERMISSION_GRANTED);
    }
    

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44. Optional Features
    package="com.example.SDK" >
    
    …
    
    android:name="android.hardware.camera"
    android:required=”false” />
    
    

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45. Features Detection
    protected boolean hasCamera(Context context) {
    PackageManager pm = context.getPackageManager();
    String camera = PackageManager.FEATURE_CAMERA;
    return pm.hasSystemFeature(camera);
    }
    

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46. Android Version Detection
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO)
    {
    return formatID(Build.HARDWARE);}
    }
    return null;
    

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47. Intent Detection
    try {
    startActivityForResult(new
    Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH),
    0);
    } catch (ActivityNotFoundException e){ }
    

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48. Intent Detection Cont.
    PackageManager pm =
    context.getApplicationContext().getPackageManager();
    List activities = pm.queryIntentActivities(
    new Intent(RecognizerIntent.ACTION_RECOGNIZE_SPEECH),0);
    if (activities.size() > 0) {
    //an app exists that can recognize speech
    }
    

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49. 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'
    

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50. Library Detection Cont
    public class DefaultClient implements Client {
    private final Client client;
    public DefaultClient() {
    if (hasOkHttpOnClasspath()) {
    client = new OkClient();
    } else {
    client = new UrlConnectionClient();
    }
    }
    …
    }
    

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51. Testable
    SDKs
    

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52. Make it Testable/Mockable
    Avoid static methods
    

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53. Make it Testable/Mockable
    Avoid static methods
    Avoid final classes and accessing fields directly
    

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54. Make it Testable/Mockable
    Avoid static methods
    Avoid final classes and accessing fields directly
    Utilize interfaces around your public API
    

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55. 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
    

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56. 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 getTweets() {
    return network.getTweets();
    }
    }
    

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57. 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 getTweets() {
    return getNetwork().getTweets();
    }
    …
    }
    

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58. Powerful SDKs
    ●Ease of Integration
    ●Extensibility
    ●Handling Failure
    ●Runtime detection
    ●Testable
    

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59. Lightweight
    

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60. Binary Size
    

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61. 3rd Party Library Mindfulness
    PROTOBUF
    KB
    OURS
    KB
    

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62. 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
    }
    

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63. Dalvik
    Method
    Count
    

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64. 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
    

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65. 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.
    : 65490
    : 3
    accessibilityservice: 6
    bluetooth: 2
    content: 248
    pm: 22
    res: 45
    com: 53881
    example: 283
    sdk: 283
    

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66. Minimize
    Network
    Usage
    

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67. Network Usage
    10X SMALLER
    100X FASTER
    XML PROTOBUF
    

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68. Batching Requests
    High Power Low Power Idle
    24%
    30%
    63%
    14%
    70%
    

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69. Modularity
    How to avoid a “Monolith Abomination”
    

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70. Modularity
    Fabric.with(this, new Twitter());
    Fabric.with(this,
    new TweetUi(),
    new TweetComposer());
    

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71. Fabric.aar
    Cache Settings Concurrency Events Network
    Persistence
    

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72. Fabric.aar
    Cache Settings Concurrency Events Network
    Persistence
    KitCore
    Kit Common Services
    

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73. Fabric.aar
    Cache Settings Concurrency Events Network
    Persistence
    KitCore
    Kit A Kit C
    Kit B
    Features
    Kit Common Services
    

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74. Fabric.aar
    Cache Settings Concurrency Events Network
    Persistence
    KitCore
    Kit A Kit C
    Kit B
    KitInterface
    Interface
    Features
    Kit Common Services
    

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75. Fabric.aar
    Cache Settings Concurrency Events Network
    Persistence
    TwitterCore.aar
    TweetUi.aar Digits.aar
    TweetComposer.
    aar
    Twitter.aar
    Interface
    Features
    Kit Common Services
    

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76. 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
    

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77. Reduce
    Startup
    Time
    

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78. Startup Time
    Thread.start();
    Executors.newSingleThreadExecutor();
    

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79. 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;
    }
    }
    

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80. Improving Startup Time in Fabric
    Shared Resources
    

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81. Improving Startup Time in Fabric
    Shared Resources
    Sync and Async Initialization
    

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82. Improving Startup Time in Fabric
    Shared Resources
    Sync and Async Initialization
    Priorities
    

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83. Improving Startup Time in Fabric
    Shared Resources
    Sync and Async Initialization
    Priorities
    Dependencies
    

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84. Lightweight SDKs
    ● Binary size
    ● Dalvik Method Count
    ● Network usage
    ● Modularity
    ● Startup time
    

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85. Support
    

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86. Support
    “An API is like a baby”
    

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87. Support
    “An API is like a baby”
    Documentation - Javadocs and Instructions
    

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88. Support
    “An API is like a baby”
    Documentation - Javadocs and Instructions
    A Minimalist Approach to Sample Code
    

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89. Support
    “An API is like a baby”
    Documentation - Javadocs and Instructions
    A Minimalist Approach to Sample Code
    Deprecation and Maintenance plan
    

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90. Lightweight
    Powerful
    

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91. Questions?
    dev.twitter.com
    @tsmith
    

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