SimpleApkV2

SimpleApkV2.java

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Arrays;

public class SimpleApkV2 {

    private SimpleApkV2() {

    }

    private static abstract class ApkV2Parser {

        private final Path sourceDir;

        ApkV2Parser(String sourceDir) {
            this.sourceDir = Paths.get(sourceDir);
            parse();
        }

        private void parse() {
            final byte[] apkSignV2 = {'A', 'P', 'K', ' ', 'S', 'i', 'g', ' ',
                    'B', 'l', 'o', 'c', 'k', ' ', '4', '2'};
            try (var channel = FileChannel.open(sourceDir, StandardOpenOption.READ)) {
                int apkSize = (int) channel.size();
                var apk = channel.map(FileChannel.MapMode.READ_ONLY, 0, apkSize);
                apk.order(ByteOrder.LITTLE_ENDIAN);

                int offset;
                for (int i = 0; ; i++) {
                    if (apk.getShort(apkSize - 0x2 - i) == i) {
                        if (apk.getInt(apkSize - 0x16 - i) == 0x6054b50) {
                            offset = apk.getInt(apkSize - 0x6 - i);
                            break;
                        }
                    }
                    if (i == 0xffff) {
                        System.out.println("invalid APK format");
                        return;
                    }
                }

                var buffer = new byte[0x10];
                apk.position(offset - 0x10);
                apk.get(buffer);
                if (!Arrays.equals(apkSignV2, buffer)) {
                    System.out.println("APK Sig Block 42");
                    return;
                }

                int blockSize = (int) apk.getLong(offset - 0x18);
                apk.position(offset - blockSize - 0x8);
                if (blockSize != apk.getLong()) {
                    System.out.println("invalid APK sig block");
                    return;
                }

                while (apk.remaining() > apkSize - offset + 0x18) {
                    int size = (int) apk.getLong();
                    int id = apk.getInt();
                    int newPosition = apk.position() + size - 0x4;
                    handle(id, size, apk);
                    apk.position(newPosition);
                }

                if (apk.remaining() != apkSize - offset + 0x18) {
                    System.out.println("have more data");
                }
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }

        protected abstract void handle(int id, int size, ByteBuffer block);

    }

    public static void main(String[] args) {
        new DummyParser(args[0]);
    }

    private static class DummyParser extends ApkV2Parser {
        DummyParser(String sourceDir) {
            super(sourceDir);
        }

        @Override
        protected void handle(int id, int size, ByteBuffer block) {
            switch (id) {
                default ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(unknown), size: " + size);
                case 0x7109871a ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(signature scheme v2), size: " + size);
                case 0xf05368c0 ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(signature scheme v3), size: " + size);
                case 0x1b93ad61 ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(signature scheme v3.1), size: " + size);
                case 0x2b09189e ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(source stamp V1), size: " + size);
                case 0x6dff800d ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(source stamp V2), size: " + size);
                case 0x2146444e ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(play store security metadata), " + size);
                case 0x504b4453 ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(dependencies metadata), size: " + size);
                case 0x42726577 ->
                        System.out.println("id: 0x" + Integer.toHexString(id) + "(padding), size: " + size);
                case 0x71777777 -> {
                    byte[] bytes = new byte[size - 0x4];
                    block.get(bytes, 0, bytes.length);
                    String channel = new String(bytes);
                    System.out.println("id: 0x" + Integer.toHexString(id) + "(meituan channel), " + channel);
                }
            }
        }
    }
}