android/defcontainer/DefaultContainerService.java

/*
 * Copyright (C) 2010 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.defcontainer;

import com.android.internal.app.IMediaContainerService;
import com.android.internal.content.NativeLibraryHelper;
import com.android.internal.content.PackageHelper;

import android.app.IntentService;
import android.content.Intent;
import android.content.pm.MacAuthenticatedInputStream;
import android.content.pm.ContainerEncryptionParams;
import android.content.pm.IPackageManager;
import android.content.pm.LimitedLengthInputStream;
import android.content.pm.PackageInfo;
import android.content.pm.PackageInfoLite;
import android.content.pm.PackageManager;
import android.content.pm.PackageParser;
import android.content.res.ObbInfo;
import android.content.res.ObbScanner;
import android.net.Uri;
import android.os.Environment;
import android.os.FileUtils;
import android.os.IBinder;
import android.os.ParcelFileDescriptor;
import android.os.Process;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.StatFs;
import android.provider.Settings;
import android.util.DisplayMetrics;
import android.util.Slog;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.DigestException;
import java.security.GeneralSecurityException;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.Mac;
import javax.crypto.NoSuchPaddingException;

import libcore.io.ErrnoException;
import libcore.io.IoUtils;
import libcore.io.Libcore;
import libcore.io.Streams;
import libcore.io.StructStatFs;

/*
 * This service copies a downloaded apk to a file passed in as
 * a ParcelFileDescriptor or to a newly created container specified
 * by parameters. The DownloadManager gives access to this process
 * based on its uid. This process also needs the ACCESS_DOWNLOAD_MANAGER
 * permission to access apks downloaded via the download manager.
 */
public class DefaultContainerService extends IntentService {
    private static final String TAG = "DefContainer";
    private static final boolean localLOGV = true;

    private static final String LIB_DIR_NAME = "lib";

    private IMediaContainerService.Stub mBinder = new IMediaContainerService.Stub() {
        /**
         * Creates a new container and copies resource there.
         * @param paackageURI the uri of resource to be copied. Can be either
         * a content uri or a file uri
         * @param cid the id of the secure container that should
         * be used for creating a secure container into which the resource
         * will be copied.
         * @param key Refers to key used for encrypting the secure container
         * @param resFileName Name of the target resource file(relative to newly
         * created secure container)
         * @return Returns the new cache path where the resource has been copied into
         *
         */
        public String copyResourceToContainer(final Uri packageURI, final String cid,
                final String key, final String resFileName, final String publicResFileName,
                boolean isExternal, boolean isForwardLocked) {
            if (packageURI == null || cid == null) {
                return null;
            }

            return copyResourceInner(packageURI, cid, key, resFileName, publicResFileName,
                    isExternal, isForwardLocked);
        }

        /**
         * Copy specified resource to output stream
         *
         * @param packageURI the uri of resource to be copied. Should be a file
         *            uri
         * @param encryptionParams parameters describing the encryption used for
         *            this file
         * @param outStream Remote file descriptor to be used for copying
         * @return returns status code according to those in
         *         {@link PackageManager}
         */
        public int copyResource(final Uri packageURI, ContainerEncryptionParams encryptionParams,
                ParcelFileDescriptor outStream) {
            if (packageURI == null || outStream == null) {
                return PackageManager.INSTALL_FAILED_INVALID_URI;
            }

            ParcelFileDescriptor.AutoCloseOutputStream autoOut
                    = new ParcelFileDescriptor.AutoCloseOutputStream(outStream);

            try {
                copyFile(packageURI, autoOut, encryptionParams);
                return PackageManager.INSTALL_SUCCEEDED;
            } catch (FileNotFoundException e) {
                Slog.e(TAG, "Could not copy URI " + packageURI.toString() + " FNF: "
                        + e.getMessage());
                return PackageManager.INSTALL_FAILED_INVALID_URI;
            } catch (IOException e) {
                Slog.e(TAG, "Could not copy URI " + packageURI.toString() + " IO: "
                        + e.getMessage());
                return PackageManager.INSTALL_FAILED_INSUFFICIENT_STORAGE;
            } catch (DigestException e) {
                Slog.e(TAG, "Could not copy URI " + packageURI.toString() + " Security: "
                                + e.getMessage());
                return PackageManager.INSTALL_FAILED_INVALID_APK;
            }
        }

        /**
         * Determine the recommended install location for package
         * specified by file uri location.
         * @param fileUri the uri of resource to be copied. Should be a
         * file uri
         * @return Returns PackageInfoLite object containing
         * the package info and recommended app location.
         */
        public PackageInfoLite getMinimalPackageInfo(final String packagePath, int flags,
                long threshold) {
            PackageInfoLite ret = new PackageInfoLite();

            if (packagePath == null) {
                Slog.i(TAG, "Invalid package file " + packagePath);
                ret.recommendedInstallLocation = PackageHelper.RECOMMEND_FAILED_INVALID_APK;
                return ret;
            }

            DisplayMetrics metrics = new DisplayMetrics();
            metrics.setToDefaults();

            PackageParser.PackageLite pkg = PackageParser.parsePackageLite(packagePath, 0);
            if (pkg == null) {
                Slog.w(TAG, "Failed to parse package");

                final File apkFile = new File(packagePath);
                if (!apkFile.exists()) {
                    ret.recommendedInstallLocation = PackageHelper.RECOMMEND_FAILED_INVALID_URI;
                } else {
                    ret.recommendedInstallLocation = PackageHelper.RECOMMEND_FAILED_INVALID_APK;
                }

                return ret;
            }

            ret.packageName = pkg.packageName;
            ret.installLocation = pkg.installLocation;
            ret.verifiers = pkg.verifiers;

            ret.recommendedInstallLocation = recommendAppInstallLocation(pkg.installLocation,
                    packagePath, flags, threshold);

            return ret;
        }

        @Override
        public boolean checkInternalFreeStorage(Uri packageUri, boolean isForwardLocked,
                long threshold) throws RemoteException {
            final File apkFile = new File(packageUri.getPath());
            try {
                return isUnderInternalThreshold(apkFile, isForwardLocked, threshold);
            } catch (IOException e) {
                return true;
            }
        }

        @Override
        public boolean checkExternalFreeStorage(Uri packageUri, boolean isForwardLocked)
                throws RemoteException {
            final File apkFile = new File(packageUri.getPath());
            try {
                return isUnderExternalThreshold(apkFile, isForwardLocked);
            } catch (IOException e) {
                return true;
            }
        }

        public ObbInfo getObbInfo(String filename) {
            try {
                return ObbScanner.getObbInfo(filename);
            } catch (IOException e) {
                Slog.d(TAG, "Couldn't get OBB info for " + filename);
                return null;
            }
        }

        @Override
        public long calculateDirectorySize(String path) throws RemoteException {
            Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);

            final File directory = new File(path);
            if (directory.exists() && directory.isDirectory()) {
                return MeasurementUtils.measureDirectory(path);
            } else {
                return 0L;
            }
        }

        @Override
        public long[] getFileSystemStats(String path) {
            Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);

            try {
                final StructStatFs stat = Libcore.os.statfs(path);
                final long totalSize = stat.f_blocks * stat.f_bsize;
                final long availSize = stat.f_bavail * stat.f_bsize;
                return new long[] { totalSize, availSize };
            } catch (ErrnoException e) {
                throw new IllegalStateException(e);
            }
        }

    };

    public DefaultContainerService() {
        super("DefaultContainerService");
        setIntentRedelivery(true);
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        if (PackageManager.ACTION_CLEAN_EXTERNAL_STORAGE.equals(intent.getAction())) {
            IPackageManager pm = IPackageManager.Stub.asInterface(
                    ServiceManager.getService("package"));
            String pkg = null;
            try {
                while ((pkg=pm.nextPackageToClean(pkg)) != null) {
                    eraseFiles(Environment.getExternalStorageAppDataDirectory(pkg));
                    eraseFiles(Environment.getExternalStorageAppMediaDirectory(pkg));
                    eraseFiles(Environment.getExternalStorageAppObbDirectory(pkg));
                }
            } catch (RemoteException e) {
            }
        }
    }

    void eraseFiles(File path) {
        if (path.isDirectory()) {
            String[] files = path.list();
            if (files != null) {
                for (String file : files) {
                    eraseFiles(new File(path, file));
                }
            }
        }
        path.delete();
    }

    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    private String copyResourceInner(Uri packageURI, String newCid, String key, String resFileName,
            String publicResFileName, boolean isExternal, boolean isForwardLocked) {

        if (isExternal) {
            // Make sure the sdcard is mounted.
            String status = Environment.getExternalStorageState();
            if (!status.equals(Environment.MEDIA_MOUNTED)) {
                Slog.w(TAG, "Make sure sdcard is mounted.");
                return null;
            }
        }

        // The .apk file
        String codePath = packageURI.getPath();
        File codeFile = new File(codePath);

        // Calculate size of container needed to hold base APK.
        final int sizeMb;
        try {
            sizeMb = calculateContainerSize(codeFile, isForwardLocked);
        } catch (IOException e) {
            Slog.w(TAG, "Problem when trying to copy " + codeFile.getPath());
            return null;
        }

        // Create new container
        final String newCachePath = PackageHelper.createSdDir(sizeMb, newCid, key, Process.myUid(),
                isExternal);
        if (newCachePath == null) {
            Slog.e(TAG, "Failed to create container " + newCid);
            return null;
        }

        if (localLOGV) {
            Slog.i(TAG, "Created container for " + newCid + " at path : " + newCachePath);
        }

        final File resFile = new File(newCachePath, resFileName);
        if (FileUtils.copyFile(new File(codePath), resFile)) {
            if (localLOGV) {
                Slog.i(TAG, "Copied " + codePath + " to " + resFile);
            }
        } else {
            Slog.e(TAG, "Failed to copy " + codePath + " to " + resFile);
            // Clean up container
            PackageHelper.destroySdDir(newCid);
            return null;
        }

        try {
            Libcore.os.chmod(resFile.getAbsolutePath(), 0640);
        } catch (ErrnoException e) {
            Slog.e(TAG, "Could not chown APK: " + e.getMessage());
            PackageHelper.destroySdDir(newCid);
            return null;
        }

        if (isForwardLocked) {
            File publicZipFile = new File(newCachePath, publicResFileName);
            try {
                PackageHelper.extractPublicFiles(resFile.getAbsolutePath(), publicZipFile);
                if (localLOGV) {
                    Slog.i(TAG, "Copied resources to " + publicZipFile);
                }
            } catch (IOException e) {
                Slog.e(TAG, "Could not chown public APK " + publicZipFile.getAbsolutePath() + ": "
                        + e.getMessage());
                PackageHelper.destroySdDir(newCid);
                return null;
            }

            try {
                Libcore.os.chmod(publicZipFile.getAbsolutePath(), 0644);
            } catch (ErrnoException e) {
                Slog.e(TAG, "Could not chown public resource file: " + e.getMessage());
                PackageHelper.destroySdDir(newCid);
                return null;
            }
        }

        final File sharedLibraryDir = new File(newCachePath, LIB_DIR_NAME);
        if (sharedLibraryDir.mkdir()) {
            int ret = NativeLibraryHelper.copyNativeBinariesIfNeededLI(codeFile, sharedLibraryDir);
            if (ret != PackageManager.INSTALL_SUCCEEDED) {
                Slog.e(TAG, "Could not copy native libraries to " + sharedLibraryDir.getPath());
                PackageHelper.destroySdDir(newCid);
                return null;
            }
        } else {
            Slog.e(TAG, "Could not create native lib directory: " + sharedLibraryDir.getPath());
            PackageHelper.destroySdDir(newCid);
            return null;
        }

        if (!PackageHelper.finalizeSdDir(newCid)) {
            Slog.e(TAG, "Failed to finalize " + newCid + " at path " + newCachePath);
            // Clean up container
            PackageHelper.destroySdDir(newCid);
            return null;
        }

        if (localLOGV) {
            Slog.i(TAG, "Finalized container " + newCid);
        }

        if (PackageHelper.isContainerMounted(newCid)) {
            if (localLOGV) {
                Slog.i(TAG, "Unmounting " + newCid + " at path " + newCachePath);
            }

            // Force a gc to avoid being killed.
            Runtime.getRuntime().gc();
            PackageHelper.unMountSdDir(newCid);
        } else {
            if (localLOGV) {
                Slog.i(TAG, "Container " + newCid + " not mounted");
            }
        }

        return newCachePath;
    }

    private static void copyToFile(InputStream inputStream, OutputStream out) throws IOException {
        byte[] buffer = new byte[16384];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) >= 0) {
            out.write(buffer, 0, bytesRead);
        }
    }

    private void copyFile(Uri pPackageURI, OutputStream outStream,
            ContainerEncryptionParams encryptionParams) throws FileNotFoundException, IOException,
            DigestException {
        String scheme = pPackageURI.getScheme();
        InputStream inStream = null;
        try {
            if (scheme == null || scheme.equals("file")) {
                final InputStream is = new FileInputStream(new File(pPackageURI.getPath()));
                inStream = new BufferedInputStream(is);
            } else if (scheme.equals("content")) {
                final ParcelFileDescriptor fd;
                try {
                    fd = getContentResolver().openFileDescriptor(pPackageURI, "r");
                } catch (FileNotFoundException e) {
                    Slog.e(TAG, "Couldn't open file descriptor from download service. "
                            + "Failed with exception " + e);
                    throw e;
                }

                if (fd == null) {
                    Slog.e(TAG, "Provider returned no file descriptor for " +
                            pPackageURI.toString());
                    throw new FileNotFoundException("provider returned no file descriptor");
                } else {
                    if (localLOGV) {
                        Slog.i(TAG, "Opened file descriptor from download service.");
                    }
                    inStream = new ParcelFileDescriptor.AutoCloseInputStream(fd);
                }
            } else {
                Slog.e(TAG, "Package URI is not 'file:' or 'content:' - " + pPackageURI);
                throw new FileNotFoundException("Package URI is not 'file:' or 'content:'");
            }

            /*
             * If this resource is encrypted, get the decrypted stream version
             * of it.
             */
            ApkContainer container = new ApkContainer(inStream, encryptionParams);

            try {
                /*
                 * We copy the source package file to a temp file and then
                 * rename it to the destination file in order to eliminate a
                 * window where the package directory scanner notices the new
                 * package file but it's not completely copied yet.
                 */
                copyToFile(container.getInputStream(), outStream);

                if (!container.isAuthenticated()) {
                    throw new DigestException();
                }
            } catch (GeneralSecurityException e) {
                throw new DigestException("A problem occured copying the file.");
            }
        } finally {
            IoUtils.closeQuietly(inStream);
        }
    }

    private static class ApkContainer {
        private static final int MAX_AUTHENTICATED_DATA_SIZE = 16384;

        private final InputStream mInStream;

        private MacAuthenticatedInputStream mAuthenticatedStream;

        private byte[] mTag;

        public ApkContainer(InputStream inStream, ContainerEncryptionParams encryptionParams)
                throws IOException {
            if (encryptionParams == null) {
                mInStream = inStream;
            } else {
                mInStream = getDecryptedStream(inStream, encryptionParams);
                mTag = encryptionParams.getMacTag();
            }
        }

        public boolean isAuthenticated() {
            if (mAuthenticatedStream == null) {
                return true;
            }

            return mAuthenticatedStream.isTagEqual(mTag);
        }

        private Mac getMacInstance(ContainerEncryptionParams encryptionParams) throws IOException {
            final Mac m;
            try {
                final String macAlgo = encryptionParams.getMacAlgorithm();

                if (macAlgo != null) {
                    m = Mac.getInstance(macAlgo);
                    m.init(encryptionParams.getMacKey(), encryptionParams.getMacSpec());
                } else {
                    m = null;
                }

                return m;
            } catch (NoSuchAlgorithmException e) {
                throw new IOException(e);
            } catch (InvalidKeyException e) {
                throw new IOException(e);
            } catch (InvalidAlgorithmParameterException e) {
                throw new IOException(e);
            }
        }

        public InputStream getInputStream() {
            return mInStream;
        }

        private InputStream getDecryptedStream(InputStream inStream,
                ContainerEncryptionParams encryptionParams) throws IOException {
            final Cipher c;
            try {
                c = Cipher.getInstance(encryptionParams.getEncryptionAlgorithm());
                c.init(Cipher.DECRYPT_MODE, encryptionParams.getEncryptionKey(),
                        encryptionParams.getEncryptionSpec());
            } catch (NoSuchAlgorithmException e) {
                throw new IOException(e);
            } catch (NoSuchPaddingException e) {
                throw new IOException(e);
            } catch (InvalidKeyException e) {
                throw new IOException(e);
            } catch (InvalidAlgorithmParameterException e) {
                throw new IOException(e);
            }

            final long encStart = encryptionParams.getEncryptedDataStart();
            final long end = encryptionParams.getDataEnd();
            if (end < encStart) {
                throw new IOException("end <= encStart");
            }

            final Mac mac = getMacInstance(encryptionParams);
            if (mac != null) {
                final long macStart = encryptionParams.getAuthenticatedDataStart();
                if (macStart >= Integer.MAX_VALUE) {
                    throw new IOException("macStart >= Integer.MAX_VALUE");
                }

                final long furtherOffset;
                if (macStart >= 0 && encStart >= 0 && macStart < encStart) {
                    /*
                     * If there is authenticated data at the beginning, read
                     * that into our MAC first.
                     */
                    final long authenticatedLengthLong = encStart - macStart;
                    if (authenticatedLengthLong > MAX_AUTHENTICATED_DATA_SIZE) {
                        throw new IOException("authenticated data is too long");
                    }
                    final int authenticatedLength = (int) authenticatedLengthLong;

                    final byte[] authenticatedData = new byte[(int) authenticatedLength];

                    Streams.readFully(inStream, authenticatedData, (int) macStart,
                            authenticatedLength);
                    mac.update(authenticatedData, 0, authenticatedLength);

                    furtherOffset = 0;
                } else {
                    /*
                     * No authenticated data at the beginning. Just skip the
                     * required number of bytes to the beginning of the stream.
                     */
                    if (encStart > 0) {
                        furtherOffset = encStart;
                    } else {
                        furtherOffset = 0;
                    }
                }

                /*
                 * If there is data at the end of the stream we want to ignore,
                 * wrap this in a LimitedLengthInputStream.
                 */
                if (furtherOffset >= 0 && end > furtherOffset) {
                    inStream = new LimitedLengthInputStream(inStream, furtherOffset, end - encStart);
                } else if (furtherOffset > 0) {
                    inStream.skip(furtherOffset);
                }

                mAuthenticatedStream = new MacAuthenticatedInputStream(inStream, mac);

                inStream = mAuthenticatedStream;
            } else {
                if (encStart >= 0) {
                    if (end > encStart) {
                        inStream = new LimitedLengthInputStream(inStream, encStart, end - encStart);
                    } else {
                        inStream.skip(encStart);
                    }
                }
            }

            return new CipherInputStream(inStream, c);
        }

    }

    private static final int PREFER_INTERNAL = 1;
    private static final int PREFER_EXTERNAL = 2;

    private int recommendAppInstallLocation(int installLocation, String archiveFilePath, int flags,
            long threshold) {
        int prefer;
        boolean checkBoth = false;

        final boolean isForwardLocked = (flags & PackageManager.INSTALL_FORWARD_LOCK) != 0;

        check_inner : {
            /*
             * Explicit install flags should override the manifest settings.
             */
            if ((flags & PackageManager.INSTALL_INTERNAL) != 0) {
                prefer = PREFER_INTERNAL;
                break check_inner;
            } else if ((flags & PackageManager.INSTALL_EXTERNAL) != 0) {
                prefer = PREFER_EXTERNAL;
                break check_inner;
            }

            /* No install flags. Check for manifest option. */
            if (installLocation == PackageInfo.INSTALL_LOCATION_INTERNAL_ONLY) {
                prefer = PREFER_INTERNAL;
                break check_inner;
            } else if (installLocation == PackageInfo.INSTALL_LOCATION_PREFER_EXTERNAL) {
                prefer = PREFER_EXTERNAL;
                checkBoth = true;
                break check_inner;
            } else if (installLocation == PackageInfo.INSTALL_LOCATION_AUTO) {
                // We default to preferring internal storage.
                prefer = PREFER_INTERNAL;
                checkBoth = true;
                break check_inner;
            }

            // Pick user preference
            int installPreference = Settings.System.getInt(getApplicationContext()
                    .getContentResolver(),
                    Settings.Secure.DEFAULT_INSTALL_LOCATION,
                    PackageHelper.APP_INSTALL_AUTO);
            if (installPreference == PackageHelper.APP_INSTALL_INTERNAL) {
                prefer = PREFER_INTERNAL;
                break check_inner;
            } else if (installPreference == PackageHelper.APP_INSTALL_EXTERNAL) {
                prefer = PREFER_EXTERNAL;
                break check_inner;
            }

            /*
             * Fall back to default policy of internal-only if nothing else is
             * specified.
             */
            prefer = PREFER_INTERNAL;
        }

        final boolean emulated = Environment.isExternalStorageEmulated();

        final File apkFile = new File(archiveFilePath);

        boolean fitsOnInternal = false;
        if (checkBoth || prefer == PREFER_INTERNAL) {
            try {
                fitsOnInternal = isUnderInternalThreshold(apkFile, isForwardLocked, threshold);
            } catch (IOException e) {
                return PackageHelper.RECOMMEND_FAILED_INVALID_URI;
            }
        }

        boolean fitsOnSd = false;
        if (!emulated && (checkBoth || prefer == PREFER_EXTERNAL)) {
            try {
                fitsOnSd = isUnderExternalThreshold(apkFile, isForwardLocked);
            } catch (IOException e) {
                return PackageHelper.RECOMMEND_FAILED_INVALID_URI;
            }
        }

        if (prefer == PREFER_INTERNAL) {
            if (fitsOnInternal) {
                return PackageHelper.RECOMMEND_INSTALL_INTERNAL;
            }
        } else if (!emulated && prefer == PREFER_EXTERNAL) {
            if (fitsOnSd) {
                return PackageHelper.RECOMMEND_INSTALL_EXTERNAL;
            }
        }

        if (checkBoth) {
            if (fitsOnInternal) {
                return PackageHelper.RECOMMEND_INSTALL_INTERNAL;
            } else if (!emulated && fitsOnSd) {
                return PackageHelper.RECOMMEND_INSTALL_EXTERNAL;
            }
        }

        /*
         * If they requested to be on the external media by default, return that
         * the media was unavailable. Otherwise, indicate there was insufficient
         * storage space available.
         */
        if (!emulated && (checkBoth || prefer == PREFER_EXTERNAL)
                && !Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            return PackageHelper.RECOMMEND_MEDIA_UNAVAILABLE;
        } else {
            return PackageHelper.RECOMMEND_FAILED_INSUFFICIENT_STORAGE;
        }
    }

    /**
     * Measure a file to see if it fits within the free space threshold.
     *
     * @param apkFile file to check
     * @param threshold byte threshold to compare against
     * @return true if file fits under threshold
     * @throws FileNotFoundException when APK does not exist
     */
    private boolean isUnderInternalThreshold(File apkFile, boolean isForwardLocked, long threshold)
            throws IOException {
        long size = apkFile.length();
        if (size == 0 && !apkFile.exists()) {
            throw new FileNotFoundException();
        }

        if (isForwardLocked) {
            size += PackageHelper.extractPublicFiles(apkFile.getAbsolutePath(), null);
        }

        final StatFs internalStats = new StatFs(Environment.getDataDirectory().getPath());
        final long availInternalSize = (long) internalStats.getAvailableBlocks()
                * (long) internalStats.getBlockSize();

        return (availInternalSize - size) > threshold;
    }


    /**
     * Measure a file to see if it fits in the external free space.
     *
     * @param apkFile file to check
     * @return true if file fits
     * @throws IOException when file does not exist
     */
    private boolean isUnderExternalThreshold(File apkFile, boolean isForwardLocked)
            throws IOException {
        if (Environment.isExternalStorageEmulated()) {
            return false;
        }

        final int sizeMb = calculateContainerSize(apkFile, isForwardLocked);

        final int availSdMb;
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
            final StatFs sdStats = new StatFs(Environment.getExternalStorageDirectory().getPath());
            final int blocksToMb = (1 << 20) / sdStats.getBlockSize();
            availSdMb = sdStats.getAvailableBlocks() * blocksToMb;
        } else {
            availSdMb = -1;
        }

        return availSdMb > sizeMb;
    }

    /**
     * Calculate the container size for an APK. Takes into account the
     *
     * @param apkFile file from which to calculate size
     * @return size in megabytes (2^20 bytes)
     * @throws IOException when there is a problem reading the file
     */
    private int calculateContainerSize(File apkFile, boolean forwardLocked) throws IOException {
        // Calculate size of container needed to hold base APK.
        long sizeBytes = apkFile.length();
        if (sizeBytes == 0 && !apkFile.exists()) {
            throw new FileNotFoundException();
        }

        // Check all the native files that need to be copied and add that to the
        // container size.
        sizeBytes += NativeLibraryHelper.sumNativeBinariesLI(apkFile);

        if (forwardLocked) {
            sizeBytes += PackageHelper.extractPublicFiles(apkFile.getPath(), null);
        }

        int sizeMb = (int) (sizeBytes >> 20);
        if ((sizeBytes - (sizeMb * 1024 * 1024)) > 0) {
            sizeMb++;
        }

        /*
         * Add buffer size because we don't have a good way to determine the
         * real FAT size. Your FAT size varies with how many directory entries
         * you need, how big the whole filesystem is, and other such headaches.
         */
        sizeMb++;

        return sizeMb;
    }
}