core/java/android/content/pm/ManifestDigest.java

/*
 * Copyright (C) 2012 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 android.content.pm;

import android.os.Parcel;
import android.os.Parcelable;
import android.util.Slog;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import libcore.io.IoUtils;

/**
 * Represents the manifest digest for a package. This is suitable for comparison
 * of two packages to know whether the manifests are identical.
 *
 * @hide
 */
public class ManifestDigest implements Parcelable {
    private static final String TAG = "ManifestDigest";

    /** The digest of the manifest in our preferred order. */
    private final byte[] mDigest;

    /** What we print out first when toString() is called. */
    private static final String TO_STRING_PREFIX = "ManifestDigest {mDigest=";

    /** Digest algorithm to use. */
    private static final String DIGEST_ALGORITHM = "SHA-256";

    ManifestDigest(byte[] digest) {
        mDigest = digest;
    }

    private ManifestDigest(Parcel source) {
        mDigest = source.createByteArray();
    }

    static ManifestDigest fromInputStream(InputStream fileIs) {
        if (fileIs == null) {
            return null;
        }

        final MessageDigest md;
        try {
            md = MessageDigest.getInstance(DIGEST_ALGORITHM);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(DIGEST_ALGORITHM + " must be available", e);
        }

        final DigestInputStream dis = new DigestInputStream(new BufferedInputStream(fileIs), md);
        try {
            byte[] readBuffer = new byte[8192];
            while (dis.read(readBuffer, 0, readBuffer.length) != -1) {
                // not using
            }
        } catch (IOException e) {
            Slog.w(TAG, "Could not read manifest");
            return null;
        } finally {
            IoUtils.closeQuietly(dis);
        }

        final byte[] digest = md.digest();
        return new ManifestDigest(digest);
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public boolean equals(Object o) {
        if (!(o instanceof ManifestDigest)) {
            return false;
        }

        final ManifestDigest other = (ManifestDigest) o;

        return this == other || Arrays.equals(mDigest, other.mDigest);
    }

    @Override
    public int hashCode() {
        return Arrays.hashCode(mDigest);
    }

    @Override
    public String toString() {
        final StringBuilder sb = new StringBuilder(TO_STRING_PREFIX.length()
                + (mDigest.length * 3) + 1);

        sb.append(TO_STRING_PREFIX);

        final int N = mDigest.length;
        for (int i = 0; i < N; i++) {
            final byte b = mDigest[i];
            IntegralToString.appendByteAsHex(sb, b, false);
            sb.append(',');
        }
        sb.append('}');

        return sb.toString();
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeByteArray(mDigest);
    }

    public static final Parcelable.Creator<ManifestDigest> CREATOR
            = new Parcelable.Creator<ManifestDigest>() {
        public ManifestDigest createFromParcel(Parcel source) {
            return new ManifestDigest(source);
        }

        public ManifestDigest[] newArray(int size) {
            return new ManifestDigest[size];
        }
    };

}