Android P 指纹 Framework

从Android的官方API可以查到，向上层提供接口的是FingerprintManager，它的代码在路径frameworks/base/core/java/android/hardware/fingerprint下。

/**
 * A class that coordinates access to the fingerprint hardware.
 * @deprecated See {@link BiometricPrompt} which shows a system-provided dialog upon starting
 * authentication. In a world where devices may have different types of biometric authentication,
 * it's much more realistic to have a system-provided authentication dialog since the method may
 * vary by vendor/device.
 */
@Deprecated
@SystemService(Context.FINGERPRINT_SERVICE)
@RequiresFeature(PackageManager.FEATURE_FINGERPRINT)
public class FingerprintManager implements BiometricFingerprintConstants

frameworks/base/core/java/android/hardware/fingerprint目录下内容其实很少，一共只有几个文件。

这里除了FingerprintManager之外，就只有Fingerprint一个类了，其他都是aidl文件。

粗略的看了下Fingerprint类，它里面的内容超级少，主要是包含了几个成员变量，用来记录指纹的信息。

/**
 * Container for fingerprint metadata.
 * @hide
 */
public final class Fingerprint extends BiometricAuthenticator.BiometricIdentifier {
    private CharSequence mName;
    private int mGroupId;
    private int mFingerId;
    private long mDeviceId; // physical device this is associated with

    public Fingerprint(CharSequence name, int groupId, int fingerId, long deviceId) {
        mName = name;
        mGroupId = groupId;
        mFingerId = fingerId;
        mDeviceId = deviceId;
    }
    //...
}

如果仔细看代码的话，可以发现一个很神奇的东西，那个就Fingerprint类的所有成员都是private的，并且没有提供任何public的set方法！

这个就厉害了，因为有做过指纹部分的朋友一定记得指纹提供一个rename的接口。没有public的set方法，那它又是怎么实现rename接口的呢？

带着问题看源码！

rename方法在Manager中的实现如下：

/**
 * Renames the given fingerprint template
 * @param fpId the fingerprint id
 * @param userId the user who this fingerprint belongs to
 * @param newName the new name
 *
 * @hide
 */
@RequiresPermission(MANAGE_FINGERPRINT)
public void rename(int fpId, int userId, String newName) {
        // Renames the given fpId
        if (mService != null) {
            try {
                mService.rename(fpId, userId, newName);
            } catch (RemoteException e) {
                throw e.rethrowFromSystemServer();
            }
        } else {
            Slog.w(TAG, "rename(): Service not connected!");
        }
}

这里先直接找到Manager的服务类：FingerprintService

指纹服务的相关代码在frameworks\base\services\core\java\com\android\server\fingerprint下。

/**
 * A service to manage multiple clients that want to access the fingerprint HAL API.
 * The service is responsible for maintaining a list of clients and dispatching all
 * fingerprint-related events.
 *
 * @hide
 */
public class FingerprintService extends SystemService implements IHwBinder.DeathRecipient

看一下它里面的rename是在内部类FingerprintServiceWrapper中实现的，具体如下：

@Override // Binder call
public void rename(final int fingerId, final int groupId, final String name) {
    checkPermission(MANAGE_FINGERPRINT);
    if (!isCurrentUserOrProfile(groupId)) {
        return;
    }
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            mFingerprintUtils.renameFingerprintForUser(mContext, fingerId,
                    groupId, name);
        }
    }
}

找到同文件夹下FingerprintUtils类，这个是工具类，里面维护了一组FingerprintsUserState，具体得继续看FingerprintsUserState；

FingerprintsUserState中维护了一组Fingerprint，下面具体看下rename操作：

@GuardedBy("this")
private final ArrayList<Fingerprint> mFingerprints = new ArrayList<Fingerprint>();
//...

public void renameFingerprint(int fingerId, CharSequence name) {
    synchronized (this) {
        for (int i = 0; i < mFingerprints.size(); i++) {
            if (mFingerprints.get(i).getFingerId() == fingerId) {
                Fingerprint old = mFingerprints.get(i);
                mFingerprints.set(i, new Fingerprint(name, old.getGroupId(), 
                        old.getFingerId(), old.getDeviceId()));
                scheduleWriteStateLocked();
                break;
            }
        }
    }
}

这里可以看到，在rename的实现时，代码直接霸气的new一个Fingerprint对象，然后覆盖List中对应id的对象。

OK，以上只是一个小小的流程。

下面看下FingerprintManager的主要API：

public void enroll(byte [] token, CancellationSignal cancel, int flags,
            int userId, EnrollmentCallback callback);
public void remove(Fingerprint fp, int userId, RemovalCallback callback);
public void rename(int fpId, int userId, String newName);
public List<Fingerprint> getEnrolledFingerprints()；


//不是hide的方法
public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel,int flags, @NonNull AuthenticationCallback callback, @Nullable Handler handler);
public boolean hasEnrolledFingerprints();
public boolean isHardwareDetected()

真正对三方开放的API只有最下面的三个，分别用来授权、判断是否录入过指纹、判断设备是否支持指纹器件。

这里面要特别提一下authenicate方法；

   /**
     * Request authentication of a crypto object. This call warms up the fingerprint hardware
     * and starts scanning for a fingerprint. It terminates when
     * {@link AuthenticationCallback#onAuthenticationError(int, CharSequence)} or
     * {@link AuthenticationCallback#onAuthenticationSucceeded(AuthenticationResult)} is called, at
     * which point the object is no longer valid. The operation can be canceled by using the
     * provided cancel object.
     *
     * @param crypto object associated with the call or null if none required.
     * @param cancel an object that can be used to cancel authentication
     * @param flags optional flags; should be 0
     * @param callback an object to receive authentication events
     * @param handler an optional handler to handle callback events
     *
     * @throws IllegalArgumentException if the crypto operation is not supported or is not backed
     *         by <a href="{@docRoot}training/articles/keystore.html">Android Keystore
     *         facility</a>.
     * @throws IllegalStateException if the crypto primitive is not initialized.
     * @deprecated See {@link BiometricPrompt#authenticate(CancellationSignal, Executor,
     * BiometricPrompt.AuthenticationCallback)} and {@link BiometricPrompt#authenticate(
     * BiometricPrompt.CryptoObject, CancellationSignal, Executor,
     * BiometricPrompt.AuthenticationCallback)}
     */
    @Deprecated
    @RequiresPermission(anyOf = {USE_BIOMETRIC, USE_FINGERPRINT})
    public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel,
            int flags, @NonNull AuthenticationCallback callback, @Nullable Handler handler) {
        authenticate(crypto, cancel, flags, callback, handler, mContext.getUserId());
    }

其中flags暂时没用起来，直接设置为0。

这里稍微讲下crypto objiect。它是的一个内部类。暂时支持三种类型对象。如下：

   /**
     * A wrapper class for the crypto objects supported by FingerprintManager. Currently the
     * framework supports {@link Signature}, {@link Cipher} and {@link Mac} objects.
     * @deprecated See {@link android.hardware.biometrics.BiometricPrompt.CryptoObject}
     */

这个参数用于加密，保护指纹在使用过程中不被恶意软件截获和篡改。
Google的示例中用的是Cipher的加密对象。
需要结束监听的话，使用CancellationSignal对象的cancel方法即可。

上面提到过Manager里面的API具体实现都是Service中。

Manager中保存有Service的对象private IFingerprintService mService;

这对象看命名方式就可以大概猜到是个AIDL了；

/**
 * Communication channel from client to the fingerprint service.
 * @hide
 */
interface IFingerprintService

它是在Manager的构造函数作为参数传入的，找到创建Manager的地方：

frameworks/base/core/java/android/app/SystemServiceRegistry.java

registerService(Context.FINGERPRINT_SERVICE, FingerprintManager.class,
        new CachedServiceFetcher<FingerprintManager>() {
    @Override
    public FingerprintManager createService(ContextImpl ctx) throws ServiceNotFoundException {
        final IBinder binder;
        if (ctx.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.O) {
            binder = ServiceManager.getServiceOrThrow(Context.FINGERPRINT_SERVICE);
        } else {
            binder = ServiceManager.getService(Context.FINGERPRINT_SERVICE);
        }
        IFingerprintService service = IFingerprintService.Stub.asInterface(binder);
        return new FingerprintManager(ctx.getOuterContext(), service);
}});

从这里看，关键字是Context.FINGERPRINT_SERVICE这个服务！

这时候，灵机一动看一眼FingerprintService（通过搜索可以搜到FingerprintService），它的onStart方法中有发布这个服务，发布的是它的内部类FingerprintServiceWrapper，这里就解释了为什么之前Manager里面的rename方法最后会在FingerprintServiceWrapper被搜索到。

@Override
public void onStart() {
    publishBinderService(Context.FINGERPRINT_SERVICE, new FingerprintServiceWrapper());
    SystemServerInitThreadPool.get().submit(this::getFingerprintDaemon, TAG + ".onStart");
    listenForUserSwitches();
}

而FingerprintService本身是在frameworks/base/services/java/com/android/server/SystemServer.java中启动的；

if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) {
    traceBeginAndSlog("StartFingerprintSensor");
    mSystemServiceManager.startService(FingerprintService.class);
    traceEnd();
}

下面来看一下一个消息反馈的AIDL：IFingerprintServiceReceiver；

/**
 * Communication channel from the FingerprintService back to FingerprintManager.
 * @hide
 */
oneway interface IFingerprintServiceReceiver {
    void onEnrollResult(long deviceId, int fingerId, int groupId, int remaining);
    void onAcquired(long deviceId, int acquiredInfo, int vendorCode);
    void onAuthenticationSucceeded(long deviceId, in Fingerprint fp, int userId);
    void onAuthenticationFailed(long deviceId);
    void onError(long deviceId, int error, int vendorCode);
    void onRemoved(long deviceId, int fingerId, int groupId, int remaining);
    void onEnumerated(long deviceId, int fingerId, int groupId, int remaining);
}

它的实例在Manager中；

private IFingerprintServiceReceiver mServiceReceiver = new IFingerprintServiceReceiver.Stub

作为参数被传递给Service，实现消息反馈机制。

如果仔细看下FingerprintService所在的文件夹，除了之前提到过的FingerprintService、FingerprintUtils和FingerprintsUserState以外就只剩下大量和ClientMonitor 相关的类了；

/**
 * Abstract base class for keeping track and dispatching events from fingerprint HAL to the
 * the current client.  Subclasses are responsible for coordinating the interaction with
 * fingerprint HAL for the specific action (e.g. authenticate, enroll, enumerate, etc.).
 */
public abstract class ClientMonitor implements IBinder.DeathRecipient

它的子类包括AuthenticationClient、EnrollClient、EnumerateClient、InternalEnumerateClient、InternalRemovalClient和RemovalClient。

它们是真正负责和更下层的HAL层交互的类。

HAL层有关的内容这里暂不讨论。

这样的话，大概的一组流程被整理出来，FingerprintManager内部持有FingerprintService内部类FingerprintServiceWrapper的AIDL，FingerprintManager的API都是调用FingerprintServiceWrapper提供的接口实现的，同时通过参数实现IFingerprintServiceReceiver消息回传。

这里还有一点可以提一下，那就是指纹授权时的震动；

frameworks/base/services/core/java/com/android/server/fingerprint/AuthenticationClient.java中会在授权成功或失败后调用vibrateSuccess()和vibrateError()方法实现不同的震动效果
frameworks/base/services/core/java/com/android/server/fingerprint/ClientMonitor.java有vibrateSuccess()和vibrateError()两个方法的具体实现
在ClientMonitor中可以看到frameworks\base\core\java\android\os\VibrationEffect.java是真正实现震动的类
可以通过用VibrationEffect的createOneShot或createWaveform方法创建想要的震动效果

Android P 指纹 Framework

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