Add a "clear backed-up data" method to the backup mechanism

It's now possible to ask that the backup manager wipe the saved data for a given
application from the backing store.  LocalTransport implements this now but the
Google backend does not yet.  When the data is wiped, the on-device backup state
is also wiped to ensure that the next backup pushes all necessary data.

Bmgr has not yet been modified to actually call into this method, but it will
be soon.

services/java/com/android/server/BackupManagerService.java

@@ -81,6 +81,7 @@ class BackupManagerService extends IBackupManager.Stub {
     private static final int MSG_RUN_BACKUP = 1;
     private static final int MSG_RUN_FULL_BACKUP = 2;
     private static final int MSG_RUN_RESTORE = 3;
+    private static final int MSG_RUN_CLEAR = 4;
 
     // Timeout interval for deciding that a bind or clear-data has taken too long
     static final long TIMEOUT_INTERVAL = 10 * 1000;
@@ -148,6 +149,16 @@ class BackupManagerService extends IBackupManager.Stub {
         }
     }
 
+    private class ClearParams {
+        public IBackupTransport transport;
+        public PackageInfo packageInfo;
+
+        ClearParams(IBackupTransport _transport, PackageInfo _info) {
+            transport = _transport;
+            packageInfo = _info;
+        }
+    }
+
     // Where we keep our journal files and other bookkeeping
     private File mBaseStateDir;
     private File mDataDir;
@@ -386,6 +397,13 @@ class BackupManagerService extends IBackupManager.Stub {
                 (new PerformRestoreThread(params.transport, params.observer, params.token)).start();
                 break;
             }
+
+            case MSG_RUN_CLEAR:
+            {
+                ClearParams params = (ClearParams)msg.obj;
+                (new PerformClearThread(params.transport, params.packageInfo)).start();
+                break;
+            }
             }
         }
     }
@@ -1071,6 +1089,37 @@ class BackupManagerService extends IBackupManager.Stub {
         }
     }
 
+    class PerformClearThread extends Thread {
+        IBackupTransport mTransport;
+        PackageInfo mPackage;
+
+        PerformClearThread(IBackupTransport transport, PackageInfo packageInfo) {
+            mTransport = transport;
+            mPackage = packageInfo;
+        }
+
+        @Override
+        public void run() {
+            try {
+                // Clear the on-device backup state to ensure a full backup next time
+                File stateDir = new File(mBaseStateDir, mTransport.transportDirName());
+                File stateFile = new File(stateDir, mPackage.packageName);
+                stateFile.delete();
+
+                // Tell the transport to remove all the persistent storage for the app
+                mTransport.clearBackupData(mPackage);
+            } catch (RemoteException e) {
+                // can't happen; the transport is local
+            } finally {
+                try {
+                    mTransport.finishBackup();
+                } catch (RemoteException e) {
+                    // can't happen; the transport is local
+                }
+            }
+        }
+    }
+
 
     // ----- IBackupManager binder interface -----
 
@@ -1142,6 +1191,52 @@ class BackupManagerService extends IBackupManager.Stub {
         }
     }
 
+    // Clear the given package's backup data from the current transport
+    public void clearBackupData(String packageName) {
+        if (DEBUG) Log.v(TAG, "clearBackupData() of " + packageName);
+        PackageInfo info;
+        try {
+            info = mPackageManager.getPackageInfo(packageName, PackageManager.GET_SIGNATURES);
+        } catch (NameNotFoundException e) {
+            Log.d(TAG, "No such package '" + packageName + "' - not clearing backup data");
+            return;
+        }
+
+        // If the caller does not hold the BACKUP permission, it can only request a
+        // wipe of its own backed-up data.
+        HashSet<ApplicationInfo> apps;
+        if ((mContext.checkPermission("android.permission.BACKUP", Binder.getCallingPid(),
+                Binder.getCallingUid())) == PackageManager.PERMISSION_DENIED) {
+            apps = mBackupParticipants.get(Binder.getCallingUid());
+        } else {
+            // a caller with full permission can ask to back up any participating app
+            // !!! TODO: allow data-clear of ANY app?
+            if (DEBUG) Log.v(TAG, "Privileged caller, allowing clear of other apps");
+            apps = new HashSet<ApplicationInfo>();
+            int N = mBackupParticipants.size();
+            for (int i = 0; i < N; i++) {
+                HashSet<ApplicationInfo> s = mBackupParticipants.valueAt(i);
+                if (s != null) {
+                    apps.addAll(s);
+                }
+            }
+        }
+
+        // now find the given package in the set of candidate apps
+        for (ApplicationInfo app : apps) {
+            if (app.packageName.equals(packageName)) {
+                if (DEBUG) Log.v(TAG, "Found the app - running clear process");
+                // found it; fire off the clear request
+                synchronized (mQueueLock) {
+                    Message msg = mBackupHandler.obtainMessage(MSG_RUN_CLEAR,
+                            new ClearParams(getTransport(mCurrentTransport), info));
+                    mBackupHandler.sendMessage(msg);
+                }
+                break;
+            }
+        }
+    }
+
     // Run a backup pass immediately for any applications that have declared
     // that they have pending updates.
     public void backupNow() throws RemoteException {