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Android7.0指紋服務(wù)FingerprintService實例介紹

 更新時間：2018年01月05日 09:25:14   作者：qh_94d8  
這篇文章主要介紹了Android7.0指紋服務(wù)FingerprintService介紹,需要的朋友可以參考下

指紋服務(wù)是Android系統(tǒng)中一個較為簡單的服務(wù)（相比于AMS，WMS等），也比較獨立，功能上包括幾點

  • 指紋的錄入與刪除
  • 指紋認證
  • 指紋的安全策略（錯誤次數(shù)判定）

和其他的system service 一樣，應(yīng)用程序通過FingerprintManager實現(xiàn)與FingerprintService的通信，除了上面所說的功能之外，F(xiàn)ingerprintManager提供了一些別的的接口，重要的接口都會要求系統(tǒng)級別的權(quán)限，并且也不是公開的api（指紋的錄入，刪除，重命名，重置錯誤計數(shù)等）   

 /**
  * Obtain the list of enrolled fingerprints templates.
  * @return list of current fingerprint items
  *
  * @hide
  */
 @RequiresPermission(USE_FINGERPRINT)
 public List<Fingerprint> getEnrolledFingerprints(int userId) {
  if (mService != null) try {
   return mService.getEnrolledFingerprints(userId, mContext.getOpPackageName());
  } catch (RemoteException e) {
   throw e.rethrowFromSystemServer();
  }
  return null;
 }
 /**
  * @hide
  */
 @RequiresPermission(allOf = {
   USE_FINGERPRINT,
   INTERACT_ACROSS_USERS})
 public boolean hasEnrolledFingerprints(int userId) {
  if (mService != null) try {
   return mService.hasEnrolledFingerprints(userId, mContext.getOpPackageName());
  } catch (RemoteException e) {
   throw e.rethrowFromSystemServer();
  }
  return false;
 }
 /**
  * Determine if fingerprint hardware is present and functional.
  *
  * @return true if hardware is present and functional, false otherwise.
  */
 @RequiresPermission(USE_FINGERPRINT)
 public boolean isHardwareDetected() {
  if (mService != null) {
   try {
    long deviceId = 0; /* TODO: plumb hardware id to FPMS */
    return mService.isHardwareDetected(deviceId, mContext.getOpPackageName());
   } catch (RemoteException e) {
    throw e.rethrowFromSystemServer();
   }
  } else {
   Log.w(TAG, "isFingerprintHardwareDetected(): Service not connected!");
  }
  return false;
 }

FingerprintService的啟動過程

FingerprintService在system server中創(chuàng)建并初始化，當檢測到手機支持指紋功能的時候就會啟動這個service

...
if (mPackageManager.hasSystemFeature(PackageManager.FEATURE_FINGERPRINT)) {
  mSystemServiceManager.startService(FingerprintService.class);
 }
...

FingerprintService在初始化后會建立和HAL層的通信，即連接到fingerprintd，拿到用于通信的IFingerprintDaemon對象（binder）

public void onStart() {
  publishBinderService(Context.FINGERPRINT_SERVICE, new FingerprintServiceWrapper());
  IFingerprintDaemon daemon = getFingerprintDaemon();
  listenForUserSwitches();
 }
public IFingerprintDaemon getFingerprintDaemon() {
  if (mDaemon == null) {
   mDaemon = IFingerprintDaemon.Stub.asInterface(ServiceManager.getService(FINGERPRINTD));
   if (mDaemon != null) {
    try {
     mDaemon.asBinder().linkToDeath(this, 0);
     mDaemon.init(mDaemonCallback);
     mHalDeviceId = mDaemon.openHal();
     if (mHalDeviceId != 0) {
      updateActiveGroup(ActivityManager.getCurrentUser(), null);
     } else {
      Slog.w(TAG, "Failed to open Fingerprint HAL!");
      MetricsLogger.count(mContext, "fingerprintd_openhal_error", 1);
      mDaemon = null;
     }
    } catch (RemoteException e) {
     Slog.e(TAG, "Failed to open fingeprintd HAL", e);
     mDaemon = null; // try again later!
    }
   } else {
    Slog.w(TAG, "fingerprint service not available");
   }
  }
  return mDaemon;
 }

本質(zhì)上來說，除去安全相關(guān)的策略外，指紋的功能是依賴硬件實現(xiàn)的，F(xiàn)ingerprintService也只是充當了framework java層與native層的消息傳遞者罷了，所以指紋的識別，錄入和監(jiān)聽都是向fingerprintd發(fā)送命令和獲取相應(yīng)的結(jié)果

指紋監(jiān)聽認證過程

以指紋認證為例，介紹這一過程，錄入和刪除的過程和認證類似，不重復(fù)描述

FingerprintManager

public void authenticate(@Nullable CryptoObject crypto, @Nullable CancellationSignal cancel,
   int flags, @NonNull AuthenticationCallback callback, Handler handler, int userId) {
  if (callback == null) {
   throw new IllegalArgumentException("Must supply an authentication callback");
  }
  if (cancel != null) {
   if (cancel.isCanceled()) {
    Log.w(TAG, "authentication already canceled");
    return;
   } else {
    cancel.setOnCancelListener(new OnAuthenticationCancelListener(crypto));
   }
  }
  if (mService != null) try {
   useHandler(handler);
   mAuthenticationCallback = callback;
   mCryptoObject = crypto;
   long sessionId = crypto != null ? crypto.getOpId() : 0;
   mService.authenticate(mToken, sessionId, userId, mServiceReceiver, flags,
     mContext.getOpPackageName());
  } catch (RemoteException e) {
   Log.w(TAG, "Remote exception while authenticating: ", e);
   if (callback != null) {
    // Though this may not be a hardware issue, it will cause apps to give up or try
    // again later.
    callback.onAuthenticationError(FINGERPRINT_ERROR_HW_UNAVAILABLE,
      getErrorString(FINGERPRINT_ERROR_HW_UNAVAILABLE));
   }
  }
 }

可以看到，最終仍然是向FingerprintService發(fā)送消息，但是開啟指紋認證的函數(shù)傳入了兩個比較重要的參數(shù)，一個是CancellationSignal對象，用于取消指紋認證，另一個是指紋認證的回調(diào)對象AuthenticationCallback

public static abstract class AuthenticationCallback {
  public void onAuthenticationError(int errorCode, CharSequence errString) { }
  public void onAuthenticationHelp(int helpCode, CharSequence helpString) { }
  public void onAuthenticationSucceeded(AuthenticationResult result) { }
  public void onAuthenticationFailed() { }
  public void onAuthenticationAcquired(int acquireInfo) {}
 };

看函數(shù)名稱也能知道其功能，他們分別代表了指紋認證時的回調(diào)結(jié)果（成功，失敗，檢測到指紋，認證異常等），參數(shù)包含了具體的信息，這些信息在FingerprintManager中都有對應(yīng)的常量定義，有興趣可以查看代碼

FingerprintService

public void authenticate(final IBinder token, final long opId, final int groupId,
    final IFingerprintServiceReceiver receiver, final int flags,
    final String opPackageName) {
   final int callingUid = Binder.getCallingUid();
   final int callingUserId = UserHandle.getCallingUserId();
   final int pid = Binder.getCallingPid();
   final boolean restricted = isRestricted();
   mHandler.post(new Runnable() {
    @Override
    public void run() {
     if (!canUseFingerprint(opPackageName, true /* foregroundOnly */,
       callingUid, pid)) {
      if (DEBUG) Slog.v(TAG, "authenticate(): reject " + opPackageName);
      return;
     }
     MetricsLogger.histogram(mContext, "fingerprint_token", opId != 0L ? 1 : 0);
     // Get performance stats object for this user.
     HashMap<Integer, PerformanceStats> pmap
       = (opId == 0) ? mPerformanceMap : mCryptoPerformanceMap;
     PerformanceStats stats = pmap.get(mCurrentUserId);
     if (stats == null) {
      stats = new PerformanceStats();
      pmap.put(mCurrentUserId, stats);
     }
     mPerformanceStats = stats;
     startAuthentication(token, opId, callingUserId, groupId, receiver,
       flags, restricted, opPackageName);
    }
   });
  }

前面會有對包名，userid以及應(yīng)用進程是否在在前臺的檢查，繼續(xù)看

private void startAuthentication(IBinder token, long opId, int callingUserId, int groupId,
    IFingerprintServiceReceiver receiver, int flags, boolean restricted,
    String opPackageName) {
  updateActiveGroup(groupId, opPackageName);
  if (DEBUG) Slog.v(TAG, "startAuthentication(" + opPackageName + ")");
  AuthenticationClient client = new AuthenticationClient(getContext(), mHalDeviceId, token,
    receiver, mCurrentUserId, groupId, opId, restricted, opPackageName) {
   @Override
   public boolean handleFailedAttempt() {
    mFailedAttempts++;
    if (mFailedAttempts == MAX_FAILED_ATTEMPTS) {
     mPerformanceStats.lockout++;
    }
    if (inLockoutMode()) {
     // Failing multiple times will continue to push out the lockout time.
     scheduleLockoutReset();
     return true;
    }
    return false;
   }
   @Override
   public void resetFailedAttempts() {
    FingerprintService.this.resetFailedAttempts();
   }
   @Override
   public void notifyUserActivity() {
    FingerprintService.this.userActivity();
   }
   @Override
   public IFingerprintDaemon getFingerprintDaemon() {
    return FingerprintService.this.getFingerprintDaemon();
   }
  };
  if (inLockoutMode()) {
   Slog.v(TAG, "In lockout mode; disallowing authentication");
   // Don't bother starting the client. Just send the error message.
   if (!client.onError(FingerprintManager.FINGERPRINT_ERROR_LOCKOUT)) {
    Slog.w(TAG, "Cannot send timeout message to client");
   }
   return;
  }
  startClient(client, true /* initiatedByClient */);
 }

AuthenticationClient繼承自ClientMonitor，用于處理指紋認證相關(guān)的功能事務(wù)，ClientMonitor的其他子類如RemovalMonior，EnrollMonitor也是如此，ClientMonitor會直接與fingerprintd通信，其核心是調(diào)用其start()或stop()方法，
對于AuthenticationClient而言

private void startClient(ClientMonitor newClient, boolean initiatedByClient) {
  ClientMonitor currentClient = mCurrentClient;
  if (currentClient != null) {
   if (DEBUG) Slog.v(TAG, "request stop current client " + currentClient.getOwnerString());
   currentClient.stop(initiatedByClient);
   mPendingClient = newClient;
   mHandler.removeCallbacks(mResetClientState);
   mHandler.postDelayed(mResetClientState, CANCEL_TIMEOUT_LIMIT);
  } else if (newClient != null) {
   mCurrentClient = newClient;
   if (DEBUG) Slog.v(TAG, "starting client "
     + newClient.getClass().getSuperclass().getSimpleName()
     + "(" + newClient.getOwnerString() + ")"
     + ", initiatedByClient = " + initiatedByClient + ")");
   newClient.start();
  }
 }
public int start() {
  IFingerprintDaemon daemon = getFingerprintDaemon();
  if (daemon == null) {
   Slog.w(TAG, "start authentication: no fingeprintd!");
   return ERROR_ESRCH;
  }
  try {
   final int result = daemon.authenticate(mOpId, getGroupId());
   if (result != 0) {
    Slog.w(TAG, "startAuthentication failed, result=" + result);
    MetricsLogger.histogram(getContext(), "fingeprintd_auth_start_error", result);
    onError(FingerprintManager.FINGERPRINT_ERROR_HW_UNAVAILABLE);
    return result;
   }
   if (DEBUG) Slog.w(TAG, "client " + getOwnerString() + " is authenticating...");
  } catch (RemoteException e) {
   Slog.e(TAG, "startAuthentication failed", e);
   return ERROR_ESRCH;
  }
  return 0; // success
 }

向底層發(fā)送認證命令后就只需要等待認證結(jié)果就可以了，前面我們說到在初始化的時候會建立與fingerprintd的通信，其核心是下面這行代碼

mDaemon.init(mDaemonCallback);

mDaemonCallback是一個binder對象，接受來自底層的結(jié)果，然后通過FingerprintService和FingerManager一層層把結(jié)果發(fā)送到應(yīng)用程序中去。

8.0的一些變化

8.0上的fingerprintd變化很大，甚至都不叫fingerprintd了，當然這是native層的東西，這里不討論，對于FingerprintService而言，一個顯著的變化是安全策略的調(diào)整

  • 8.0之前，指紋只能錯誤5次，達到5次時會禁止指紋認證，同時開啟30秒倒計時，等待結(jié)束后重置錯誤計數(shù)，繼續(xù)認證
  • 8.0之后，依然是每錯誤5次就會倒計時30秒，然而30秒結(jié)束后錯誤計數(shù)并不會被清空，8.0上加入了最大20次的限制，累計錯誤20次之后就無法使用指紋認證功能了，只能用密碼的方式才能重置錯誤計數(shù)
private static final int MAX_FAILED_ATTEMPTS_LOCKOUT_TIMED = 5;
private static final int MAX_FAILED_ATTEMPTS_LOCKOUT_PERMANENT = 20;
private int getLockoutMode() {
  if (mFailedAttempts >= MAX_FAILED_ATTEMPTS_LOCKOUT_PERMANENT) {
   return AuthenticationClient.LOCKOUT_PERMANENT;
  } else if (mFailedAttempts > 0 && mTimedLockoutCleared == false &&
    (mFailedAttempts % MAX_FAILED_ATTEMPTS_LOCKOUT_TIMED == 0)) {
   return AuthenticationClient.LOCKOUT_TIMED;
  }
  return AuthenticationClient.LOCKOUT_NONE;
 }

總結(jié)

以上所述是小編給大家介紹的Android7.0指紋服務(wù)FingerprintService實例介紹，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復(fù)大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！

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