Android(安卓)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 callpublic 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 mFingerprints = new ArrayList();//...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 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 Android Keystore     *         facility.     * @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() {    @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。

@Overridepublic 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

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