dexlib2/src/main/java/org/jf/dexlib2/dexbacked/raw/OdexHeaderItem.java

/*
 * Copyright 2013, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.jf.dexlib2.dexbacked.raw;

import org.jf.dexlib2.dexbacked.BaseDexBuffer;

public class OdexHeaderItem {
    public static final int ITEM_SIZE = 40;

    private static final byte[] MAGIC_VALUE = new byte[] { 0x64, 0x65, 0x79, 0x0A, 0x00, 0x00, 0x00, 0x00 };
    private static final int[] SUPPORTED_ODEX_VERSIONS = new int[] { 35, 36 };

    public static final int MAGIC_OFFSET = 0;
    public static final int MAGIC_LENGTH = 8;
    public static final int DEX_OFFSET = 8;
    public static final int DEX_LENGTH_OFFSET = 12;
    public static final int DEPENDENCIES_OFFSET = 16;
    public static final int DEPENDENCIES_LENGTH_OFFSET = 20;
    public static final int AUX_OFFSET = 24;
    public static final int AUX_LENGTH_OFFSET = 28;
    public static final int FLAGS_OFFSET = 32;

    /**
     * Verifies the magic value at the beginning of an odex file
     *
     * @param buf A byte array containing at least the first 8 bytes of an odex file
     * @param offset The offset within the buffer to the beginning of the odex header
     * @return True if the magic value is valid
     */
    public static boolean verifyMagic(byte[] buf, int offset) {
        if (buf.length - offset < 8) {
            return false;
        }

        for (int i=0; i<4; i++) {
            if (buf[offset + i] != MAGIC_VALUE[i]) {
                return false;
            }
        }
        for (int i=4; i<7; i++) {
            if (buf[offset + i] < '0' ||
                    buf[offset + i] > '9') {
                return false;
            }
        }
        if (buf[offset + 7] != MAGIC_VALUE[7]) {
            return false;
        }

        return true;
    }

    /**
     * Gets the dex version from an odex header
     *
     * @param buf A byte array containing at least the first 7 bytes of an odex file
     * @param offset The offset within the buffer to the beginning of the odex header
     * @return The odex version if the header is valid or -1 if the header is invalid
     */
    public static int getVersion(byte[] buf, int offset) {
        if (!verifyMagic(buf, offset)) {
            return -1;
        }

        return getVersionUnchecked(buf, offset);
    }

    private static int getVersionUnchecked(byte[] buf, int offset) {
        int version = (buf[offset + 4] - '0') * 100;
        version += (buf[offset + 5] - '0') * 10;
        version += buf[offset + 6] - '0';

        return version;
    }

    public static boolean isSupportedOdexVersion(int version) {
        for (int i=0; i<SUPPORTED_ODEX_VERSIONS.length; i++) {
            if (SUPPORTED_ODEX_VERSIONS[i] == version) {
                return true;
            }
        }
        return false;
    }

    public static int getDexOffset(byte[] buf) {
        BaseDexBuffer bdb = new BaseDexBuffer(buf);
        return bdb.readSmallUint(DEX_OFFSET);
    }

    public static int getDependenciesOffset(byte[] buf) {
        BaseDexBuffer bdb = new BaseDexBuffer(buf);
        return bdb.readSmallUint(DEPENDENCIES_OFFSET);
    }
}