Android example source code file (PackageManagerBackupAgent.java)

This example Android source code file (PackageManagerBackupAgent.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

android, app, application, bytearrayinputstream, content, datainputstream, dataoutputstream, debug, global_metadata_key, hashmap, io, ioexception, list, metadata, packageinfo, parcelfiledescriptor, signature, string, unable, util

The PackageManagerBackupAgent.java Android example source code

/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.server;

import android.app.backup.BackupAgent;
import android.app.backup.BackupDataInput;
import android.app.backup.BackupDataOutput;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.pm.Signature;
import android.os.Build;
import android.os.ParcelFileDescriptor;
import android.util.Slog;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

/**
 * We back up the signatures of each package so that during a system restore,
 * we can verify that the app whose data we think we have matches the app
 * actually resident on the device.
 *
 * Since the Package Manager isn't a proper "application" we just provide a
 * direct IBackupAgent implementation and hand-construct it at need.
 */
public class PackageManagerBackupAgent extends BackupAgent {
    private static final String TAG = "PMBA";
    private static final boolean DEBUG = false;

    // key under which we store global metadata (individual app metadata
    // is stored using the package name as a key)
    private static final String GLOBAL_METADATA_KEY = "@meta@";

    private List<PackageInfo> mAllPackages;
    private PackageManager mPackageManager;
    // version & signature info of each app in a restore set
    private HashMap<String, Metadata> mRestoredSignatures;
    // The version info of each backed-up app as read from the state file
    private HashMap<String, Metadata> mStateVersions = new HashMap();

    private final HashSet<String> mExisting = new HashSet();
    private int mStoredSdkVersion;
    private String mStoredIncrementalVersion;
    private boolean mHasMetadata;

    public class Metadata {
        public int versionCode;
        public Signature[] signatures;

        Metadata(int version, Signature[] sigs) {
            versionCode = version;
            signatures = sigs;
        }
    }

    // We're constructed with the set of applications that are participating
    // in backup.  This set changes as apps are installed & removed.
    PackageManagerBackupAgent(PackageManager packageMgr, List<PackageInfo> packages) {
        mPackageManager = packageMgr;
        mAllPackages = packages;
        mRestoredSignatures = null;
        mHasMetadata = false;
    }

    public boolean hasMetadata() {
        return mHasMetadata;
    }

    public Metadata getRestoredMetadata(String packageName) {
        if (mRestoredSignatures == null) {
            Slog.w(TAG, "getRestoredMetadata() before metadata read!");
            return null;
        }

        return mRestoredSignatures.get(packageName);
    }

    public Set<String> getRestoredPackages() {
        if (mRestoredSignatures == null) {
            Slog.w(TAG, "getRestoredPackages() before metadata read!");
            return null;
        }

        // This is technically the set of packages on the originating handset
        // that had backup agents at all, not limited to the set of packages
        // that had actually contributed a restore dataset, but it's a
        // close enough approximation for our purposes and does not require any
        // additional involvement by the transport to obtain.
        return mRestoredSignatures.keySet();
    }
    
    // The backed up data is the signature block for each app, keyed by
    // the package name.
    public void onBackup(ParcelFileDescriptor oldState, BackupDataOutput data,
            ParcelFileDescriptor newState) {
        if (DEBUG) Slog.v(TAG, "onBackup()");

        ByteArrayOutputStream outputBuffer = new ByteArrayOutputStream();  // we'll reuse these
        DataOutputStream outputBufferStream = new DataOutputStream(outputBuffer);
        parseStateFile(oldState);

        // If the stored version string differs, we need to re-backup all
        // of the metadata.  We force this by removing everything from the
        // "already backed up" map built by parseStateFile().
        if (mStoredIncrementalVersion == null
                || !mStoredIncrementalVersion.equals(Build.VERSION.INCREMENTAL)) {
            Slog.i(TAG, "Previous metadata " + mStoredIncrementalVersion + " mismatch vs "
                    + Build.VERSION.INCREMENTAL + " - rewriting");
            mExisting.clear();
        }

        try {
            /*
             * Global metadata:
             *
             * int SDKversion -- the SDK version of the OS itself on the device
             *                   that produced this backup set.  Used to reject
             *                   backups from later OSes onto earlier ones.
             * String incremental -- the incremental release name of the OS stored in
             *                       the backup set.
             */
            if (!mExisting.contains(GLOBAL_METADATA_KEY)) {
                if (DEBUG) Slog.v(TAG, "Storing global metadata key");
                outputBufferStream.writeInt(Build.VERSION.SDK_INT);
                outputBufferStream.writeUTF(Build.VERSION.INCREMENTAL);
                writeEntity(data, GLOBAL_METADATA_KEY, outputBuffer.toByteArray());
            } else {
                if (DEBUG) Slog.v(TAG, "Global metadata key already stored");
                // don't consider it to have been skipped/deleted
                mExisting.remove(GLOBAL_METADATA_KEY);
            }

            // For each app we have on device, see if we've backed it up yet.  If not,
            // write its signature block to the output, keyed on the package name.
            for (PackageInfo pkg : mAllPackages) {
                String packName = pkg.packageName;
                if (packName.equals(GLOBAL_METADATA_KEY)) {
                    // We've already handled the metadata key; skip it here
                    continue;
                } else {
                    PackageInfo info = null;
                    try {
                        info = mPackageManager.getPackageInfo(packName,
                                PackageManager.GET_SIGNATURES);
                    } catch (NameNotFoundException e) {
                        // Weird; we just found it, and now are told it doesn't exist.
                        // Treat it as having been removed from the device.
                        mExisting.add(packName);
                        continue;
                    }

                    if (mExisting.contains(packName)) {
                        // We have backed up this app before.  Check whether the version
                        // of the backup matches the version of the current app; if they
                        // don't match, the app has been updated and we need to store its
                        // metadata again.  In either case, take it out of mExisting so that
                        // we don't consider it deleted later.
                        mExisting.remove(packName);
                        if (info.versionCode == mStateVersions.get(packName).versionCode) {
                            continue;
                        }
                    }
                    
                    if (info.signatures == null || info.signatures.length == 0)
                    {
                        Slog.w(TAG, "Not backing up package " + packName
                                + " since it appears to have no signatures.");
                        continue;
                    }

                    // We need to store this app's metadata
                    /*
                     * Metadata for each package:
                     *
                     * int version       -- [4] the package's versionCode
                     * byte[] signatures -- [len] flattened Signature[] of the package
                     */

                    // marshal the version code in a canonical form
                    outputBuffer.reset();
                    outputBufferStream.writeInt(info.versionCode);
                    writeSignatureArray(outputBufferStream, info.signatures);

                    if (DEBUG) {
                        Slog.v(TAG, "+ writing metadata for " + packName
                                + " version=" + info.versionCode
                                + " entityLen=" + outputBuffer.size());
                    }
                    
                    // Now we can write the backup entity for this package
                    writeEntity(data, packName, outputBuffer.toByteArray());
                }
            }

            // At this point, the only entries in 'existing' are apps that were
            // mentioned in the saved state file, but appear to no longer be present
            // on the device.  Write a deletion entity for them.
            for (String app : mExisting) {
                if (DEBUG) Slog.v(TAG, "- removing metadata for deleted pkg " + app);
                try {
                    data.writeEntityHeader(app, -1);
                } catch (IOException e) {
                    Slog.e(TAG, "Unable to write package deletions!");
                    return;
                }
            }
        } catch (IOException e) {
            // Real error writing data
            Slog.e(TAG, "Unable to write package backup data file!");
            return;
        }

        // Finally, write the new state blob -- just the list of all apps we handled
        writeStateFile(mAllPackages, newState);
    }
    
    private static void writeEntity(BackupDataOutput data, String key, byte[] bytes)
            throws IOException {
        data.writeEntityHeader(key, bytes.length);
        data.writeEntityData(bytes, bytes.length);
    }

    // "Restore" here is a misnomer.  What we're really doing is reading back the
    // set of app signatures associated with each backed-up app in this restore
    // image.  We'll use those later to determine what we can legitimately restore.
    public void onRestore(BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)
            throws IOException {
        List<ApplicationInfo> restoredApps = new ArrayList();
        HashMap<String, Metadata> sigMap = new HashMap();
        if (DEBUG) Slog.v(TAG, "onRestore()");
        int storedSystemVersion = -1;

        while (data.readNextHeader()) {
            String key = data.getKey();
            int dataSize = data.getDataSize();

            if (DEBUG) Slog.v(TAG, "   got key=" + key + " dataSize=" + dataSize);

            // generic setup to parse any entity data
            byte[] inputBytes = new byte[dataSize];
            data.readEntityData(inputBytes, 0, dataSize);
            ByteArrayInputStream inputBuffer = new ByteArrayInputStream(inputBytes);
            DataInputStream inputBufferStream = new DataInputStream(inputBuffer);

            if (key.equals(GLOBAL_METADATA_KEY)) {
                int storedSdkVersion = inputBufferStream.readInt();
                if (DEBUG) Slog.v(TAG, "   storedSystemVersion = " + storedSystemVersion);
                if (storedSystemVersion > Build.VERSION.SDK_INT) {
                    // returning before setting the sig map means we rejected the restore set
                    Slog.w(TAG, "Restore set was from a later version of Android; not restoring");
                    return;
                }
                mStoredSdkVersion = storedSdkVersion;
                mStoredIncrementalVersion = inputBufferStream.readUTF();
                mHasMetadata = true;
                if (DEBUG) {
                    Slog.i(TAG, "Restore set version " + storedSystemVersion
                            + " is compatible with OS version " + Build.VERSION.SDK_INT
                            + " (" + mStoredIncrementalVersion + " vs "
                            + Build.VERSION.INCREMENTAL + ")");
                }
            } else {
                // it's a file metadata record
                int versionCode = inputBufferStream.readInt();
                Signature[] sigs = readSignatureArray(inputBufferStream);
                if (DEBUG) {
                    Slog.i(TAG, "   read metadata for " + key
                            + " dataSize=" + dataSize
                            + " versionCode=" + versionCode + " sigs=" + sigs);
                }
                
                if (sigs == null || sigs.length == 0) {
                    Slog.w(TAG, "Not restoring package " + key
                            + " since it appears to have no signatures.");
                    continue;
                }

                ApplicationInfo app = new ApplicationInfo();
                app.packageName = key;
                restoredApps.add(app);
                sigMap.put(key, new Metadata(versionCode, sigs));
            }
        }

        // On successful completion, cache the signature map for the Backup Manager to use
        mRestoredSignatures = sigMap;
    }

    private static void writeSignatureArray(DataOutputStream out, Signature[] sigs)
            throws IOException {
        // write the number of signatures in the array
        out.writeInt(sigs.length);

        // write the signatures themselves, length + flattened buffer
        for (Signature sig : sigs) {
            byte[] flat = sig.toByteArray();
            out.writeInt(flat.length);
            out.write(flat);
        }
    }

    private static Signature[] readSignatureArray(DataInputStream in) {
        try {
            int num;
            try {
                num = in.readInt();
            } catch (EOFException e) {
                // clean termination
                Slog.w(TAG, "Read empty signature block");
                return null;
            }
            
            if (DEBUG) Slog.v(TAG, " ... unflatten read " + num);
            
            // Sensical?
            if (num > 20) {
                Slog.e(TAG, "Suspiciously large sig count in restore data; aborting");
                throw new IllegalStateException("Bad restore state");
            }
            
            Signature[] sigs = new Signature[num];
            for (int i = 0; i < num; i++) {
                int len = in.readInt();
                byte[] flatSig = new byte[len];
                in.read(flatSig);
                sigs[i] = new Signature(flatSig);
            }
            return sigs;
        } catch (IOException e) {
            Slog.e(TAG, "Unable to read signatures");
            return null;
        }
    }

    // Util: parse out an existing state file into a usable structure
    private void parseStateFile(ParcelFileDescriptor stateFile) {
        mExisting.clear();
        mStateVersions.clear();
        mStoredSdkVersion = 0;
        mStoredIncrementalVersion = null;

        // The state file is just the list of app names we have stored signatures for
        // with the exception of the metadata block, to which is also appended the
        // version numbers corresponding with the last time we wrote this PM block.
        // If they mismatch the current system, we'll re-store the metadata key.
        FileInputStream instream = new FileInputStream(stateFile.getFileDescriptor());
        DataInputStream in = new DataInputStream(instream);

        int bufSize = 256;
        byte[] buf = new byte[bufSize];
        try {
            String pkg = in.readUTF();
            if (pkg.equals(GLOBAL_METADATA_KEY)) {
                mStoredSdkVersion = in.readInt();
                mStoredIncrementalVersion = in.readUTF();
                mExisting.add(GLOBAL_METADATA_KEY);
            } else {
                Slog.e(TAG, "No global metadata in state file!");
                return;
            }

            // The global metadata was first; now read all the apps
            while (true) {
                pkg = in.readUTF();
                int versionCode = in.readInt();
                mExisting.add(pkg);
                mStateVersions.put(pkg, new Metadata(versionCode, null));
            }
        } catch (EOFException eof) {
            // safe; we're done
        } catch (IOException e) {
            // whoops, bad state file.  abort.
            Slog.e(TAG, "Unable to read Package Manager state file: " + e);
        }
    }

    // Util: write out our new backup state file
    private void writeStateFile(List<PackageInfo> pkgs, ParcelFileDescriptor stateFile) {
        FileOutputStream outstream = new FileOutputStream(stateFile.getFileDescriptor());
        DataOutputStream out = new DataOutputStream(outstream);

        try {
            // by the time we get here we know we've stored the global metadata record
            out.writeUTF(GLOBAL_METADATA_KEY);
            out.writeInt(Build.VERSION.SDK_INT);
            out.writeUTF(Build.VERSION.INCREMENTAL);

            // now write all the app names too
            for (PackageInfo pkg : pkgs) {
                out.writeUTF(pkg.packageName);
                out.writeInt(pkg.versionCode);
            }
        } catch (IOException e) {
            Slog.e(TAG, "Unable to write package manager state file!");
            return;
        }
    }
}