src/java.base/share/classes/jdk/internal/jimage/BasicImageReader.java

/*
 * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package jdk.internal.jimage;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.IntBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Objects;
import java.util.stream.IntStream;
import jdk.internal.jimage.decompressor.Decompressor;

/**
 * @implNote This class needs to maintain JDK 8 source compatibility.
 *
 * It is used internally in the JDK to implement jimage/jrtfs access,
 * but also compiled and delivered as part of the jrtfs.jar to support access
 * to the jimage file provided by the shipped JDK by tools running on JDK 8.
 */
public class BasicImageReader implements AutoCloseable {
    @SuppressWarnings({ "removal", "suppression" })
    private static boolean isSystemProperty(String key, String value, String def) {
        // No lambdas during bootstrap
        return AccessController.doPrivileged(
            new PrivilegedAction<Boolean>() {
                @Override
                public Boolean run() {
                    return value.equals(System.getProperty(key, def));
                }
            });
    }

    private static final boolean IS_64_BIT =
            isSystemProperty("sun.arch.data.model", "64", "32");
    private static final boolean USE_JVM_MAP =
            isSystemProperty("jdk.image.use.jvm.map", "true", "true");
    private static final boolean MAP_ALL =
            isSystemProperty("jdk.image.map.all", "true", IS_64_BIT ? "true" : "false");

    private final Path imagePath;
    private final ByteOrder byteOrder;
    private final String name;
    private final ByteBuffer memoryMap;
    private final FileChannel channel;
    private final ImageHeader header;
    private final long indexSize;
    private final IntBuffer redirect;
    private final IntBuffer offsets;
    private final ByteBuffer locations;
    private final ByteBuffer strings;
    private final ImageStringsReader stringsReader;
    private final Decompressor decompressor;

    @SuppressWarnings({ "removal", "this-escape", "suppression" })
    protected BasicImageReader(Path path, ByteOrder byteOrder)
            throws IOException {
        this.imagePath = Objects.requireNonNull(path);
        this.byteOrder = Objects.requireNonNull(byteOrder);
        this.name = this.imagePath.toString();

        ByteBuffer map;

        if (USE_JVM_MAP && BasicImageReader.class.getClassLoader() == null) {
            // Check to see if the jvm has opened the file using libjimage
            // native entry when loading the image for this runtime
            map = NativeImageBuffer.getNativeMap(name);
         } else {
            map = null;
        }

        // Open the file only if no memory map yet or is 32 bit jvm
        if (map != null && MAP_ALL) {
            channel = null;
        } else {
            channel = FileChannel.open(imagePath, StandardOpenOption.READ);
            // No lambdas during bootstrap
            AccessController.doPrivileged(new PrivilegedAction<Void>() {
                @Override
                public Void run() {
                    if (BasicImageReader.class.getClassLoader() == null) {
                        try {
                            Class<?> fileChannelImpl =
                                Class.forName("sun.nio.ch.FileChannelImpl");
                            Method setUninterruptible =
                                    fileChannelImpl.getMethod("setUninterruptible");
                            setUninterruptible.invoke(channel);
                        } catch (ClassNotFoundException |
                                 NoSuchMethodException |
                                 IllegalAccessException |
                                 InvocationTargetException ex) {
                            // fall thru - will only happen on JDK-8 systems where this code
                            // is only used by tools using jrt-fs (non-critical.)
                        }
                    }

                    return null;
                }
            });
        }

        // If no memory map yet and 64 bit jvm then memory map entire file
        if (MAP_ALL && map == null) {
            map = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
        }

        // Assume we have a memory map to read image file header
        ByteBuffer headerBuffer = map;
        int headerSize = ImageHeader.getHeaderSize();

        // If no memory map then read header from image file
        if (headerBuffer == null) {
            headerBuffer = ByteBuffer.allocateDirect(headerSize);
            if (channel.read(headerBuffer, 0L) == headerSize) {
                headerBuffer.rewind();
            } else {
                throw new IOException("\"" + name + "\" is not an image file");
            }
        } else if (headerBuffer.capacity() < headerSize) {
            throw new IOException("\"" + name + "\" is not an image file");
        }

        // Interpret the image file header
        header = readHeader(intBuffer(headerBuffer, 0, headerSize));
        indexSize = header.getIndexSize();

        // If no memory map yet then must be 32 bit jvm not previously mapped
        if (map == null) {
            // Just map the image index
            map = channel.map(FileChannel.MapMode.READ_ONLY, 0, indexSize);
        }

        memoryMap = map.asReadOnlyBuffer();

        // Interpret the image index
        if (memoryMap.capacity() < indexSize) {
            throw new IOException("The image file \"" + name + "\" is corrupted");
        }
        redirect = intBuffer(memoryMap, header.getRedirectOffset(), header.getRedirectSize());
        offsets = intBuffer(memoryMap, header.getOffsetsOffset(), header.getOffsetsSize());
        locations = slice(memoryMap, header.getLocationsOffset(), header.getLocationsSize());
        strings = slice(memoryMap, header.getStringsOffset(), header.getStringsSize());

        stringsReader = new ImageStringsReader(this);
        decompressor = new Decompressor();
    }

    protected BasicImageReader(Path imagePath) throws IOException {
        this(imagePath, ByteOrder.nativeOrder());
    }

    public static BasicImageReader open(Path imagePath) throws IOException {
        return new BasicImageReader(imagePath, ByteOrder.nativeOrder());
    }

    public ImageHeader getHeader() {
        return header;
    }

    private ImageHeader readHeader(IntBuffer buffer) throws IOException {
        ImageHeader result = ImageHeader.readFrom(buffer);

        if (result.getMagic() != ImageHeader.MAGIC) {
            throw new IOException("\"" + name + "\" is not an image file");
        }

        if (result.getMajorVersion() != ImageHeader.MAJOR_VERSION ||
            result.getMinorVersion() != ImageHeader.MINOR_VERSION) {
            throw new IOException("The image file \"" + name + "\" is not " +
                "the correct version. Major: " + result.getMajorVersion() +
                ". Minor: " + result.getMinorVersion());
        }

        return result;
    }

    private static ByteBuffer slice(ByteBuffer buffer, int position, int capacity) {
        // Note that this is the only limit and position manipulation of
        // BasicImageReader private ByteBuffers.  The synchronize could be avoided
        // by cloning the buffer to make a local copy, but at the cost of creating
        // a new object.
        synchronized(buffer) {
            buffer.limit(position + capacity);
            buffer.position(position);
            return buffer.slice();
        }
    }

    private IntBuffer intBuffer(ByteBuffer buffer, int offset, int size) {
        return slice(buffer, offset, size).order(byteOrder).asIntBuffer();
    }

    public static void releaseByteBuffer(ByteBuffer buffer) {
        Objects.requireNonNull(buffer);

        if (!MAP_ALL) {
            ImageBufferCache.releaseBuffer(buffer);
        }
    }

    public String getName() {
        return name;
    }

    public ByteOrder getByteOrder() {
        return byteOrder;
    }

    public Path getImagePath() {
        return imagePath;
    }

    @Override
    public void close() throws IOException {
        if (channel != null) {
            channel.close();
        }
    }

    public ImageStringsReader getStrings() {
        return stringsReader;
    }

    public ImageLocation findLocation(String module, String name) {
        int index = getLocationIndex(module, name);
        if (index < 0) {
            return null;
        }
        long[] attributes = getAttributes(offsets.get(index));
        if (!ImageLocation.verify(module, name, attributes, stringsReader)) {
            return null;
        }
        return new ImageLocation(attributes, stringsReader);
    }

    public ImageLocation findLocation(String name) {
        int index = getLocationIndex(name);
        if (index < 0) {
            return null;
        }
        long[] attributes = getAttributes(offsets.get(index));
        if (!ImageLocation.verify(name, attributes, stringsReader)) {
            return null;
        }
        return new ImageLocation(attributes, stringsReader);
    }

    public boolean verifyLocation(String module, String name) {
        int index = getLocationIndex(module, name);
        if (index < 0) {
            return false;
        }
        int locationOffset = offsets.get(index);
        return ImageLocation.verify(module, name, locations, locationOffset, stringsReader);
    }

    // Details of the algorithm used here can be found in
    // jdk.tools.jlink.internal.PerfectHashBuilder.
    public int getLocationIndex(String name) {
        int count = header.getTableLength();
        int index = redirect.get(ImageStringsReader.hashCode(name) % count);
        if (index < 0) {
            // index is twos complement of location attributes index.
            return -index - 1;
        } else if (index > 0) {
            // index is hash seed needed to compute location attributes index.
            return ImageStringsReader.hashCode(name, index) % count;
        } else {
            // No entry.
            return -1;
        }
    }

    private int getLocationIndex(String module, String name) {
        int count = header.getTableLength();
        int index = redirect.get(ImageStringsReader.hashCode(module, name) % count);
        if (index < 0) {
            // index is twos complement of location attributes index.
            return -index - 1;
        } else if (index > 0) {
            // index is hash seed needed to compute location attributes index.
            return ImageStringsReader.hashCode(module, name, index) % count;
        } else {
            // No entry.
            return -1;
        }
    }

    public String[] getEntryNames() {
        int[] attributeOffsets = new int[offsets.capacity()];
        offsets.get(attributeOffsets);
        return IntStream.of(attributeOffsets)
                        .filter(o -> o != 0)
                        .mapToObj(o -> ImageLocation.readFrom(this, o).getFullName())
                        .sorted()
                        .toArray(String[]::new);
    }

    ImageLocation getLocation(int offset) {
        return ImageLocation.readFrom(this, offset);
    }

    public long[] getAttributes(int offset) {
        if (offset < 0 || offset >= locations.limit()) {
            throw new IndexOutOfBoundsException("offset");
        }
        return ImageLocation.decompress(locations, offset);
    }

    public String getString(int offset) {
        if (offset < 0 || offset >= strings.limit()) {
            throw new IndexOutOfBoundsException("offset");
        }
        return ImageStringsReader.stringFromByteBuffer(strings, offset);
    }

    public int match(int offset, String string, int stringOffset) {
        if (offset < 0 || offset >= strings.limit()) {
            throw new IndexOutOfBoundsException("offset");
        }
        return ImageStringsReader.stringFromByteBufferMatches(strings, offset, string, stringOffset);
    }

    private byte[] getBufferBytes(ByteBuffer buffer) {
        Objects.requireNonNull(buffer);
        byte[] bytes = new byte[buffer.limit()];
        buffer.get(bytes);

        return bytes;
    }

    private ByteBuffer readBuffer(long offset, long size) {
        if (offset < 0 || Integer.MAX_VALUE <= offset) {
            throw new IndexOutOfBoundsException("Bad offset: " + offset);
        }

        if (size < 0 || Integer.MAX_VALUE <= size) {
            throw new IndexOutOfBoundsException("Bad size: " + size);
        }

        if (MAP_ALL) {
            ByteBuffer buffer = slice(memoryMap, (int)offset, (int)size);
            buffer.order(ByteOrder.BIG_ENDIAN);

            return buffer;
        } else {
            if (channel == null) {
                throw new InternalError("Image file channel not open");
            }

            ByteBuffer buffer = ImageBufferCache.getBuffer(size);
            int read;
            try {
                read = channel.read(buffer, offset);
                buffer.rewind();
            } catch (IOException ex) {
                ImageBufferCache.releaseBuffer(buffer);
                throw new RuntimeException(ex);
            }

            if (read != size) {
                ImageBufferCache.releaseBuffer(buffer);
                throw new RuntimeException("Short read: " + read +
                                           " instead of " + size + " bytes");
            }

            return buffer;
        }
    }

    public byte[] getResource(String name) {
        Objects.requireNonNull(name);
        ImageLocation location = findLocation(name);

        return location != null ? getResource(location) : null;
    }

    public byte[] getResource(ImageLocation loc) {
        ByteBuffer buffer = getResourceBuffer(loc);

        if (buffer != null) {
            byte[] bytes = getBufferBytes(buffer);
            ImageBufferCache.releaseBuffer(buffer);

            return bytes;
        }

        return null;
    }

    public ByteBuffer getResourceBuffer(ImageLocation loc) {
        Objects.requireNonNull(loc);
        long offset = loc.getContentOffset() + indexSize;
        long compressedSize = loc.getCompressedSize();
        long uncompressedSize = loc.getUncompressedSize();

        if (compressedSize < 0 || Integer.MAX_VALUE < compressedSize) {
            throw new IndexOutOfBoundsException(
                "Bad compressed size: " + compressedSize);
        }

        if (uncompressedSize < 0 || Integer.MAX_VALUE < uncompressedSize) {
            throw new IndexOutOfBoundsException(
                "Bad uncompressed size: " + uncompressedSize);
        }

        if (compressedSize == 0) {
            return readBuffer(offset, uncompressedSize);
        } else {
            ByteBuffer buffer = readBuffer(offset, compressedSize);

            if (buffer != null) {
                byte[] bytesIn = getBufferBytes(buffer);
                ImageBufferCache.releaseBuffer(buffer);
                byte[] bytesOut;

                try {
                    bytesOut = decompressor.decompressResource(byteOrder,
                            (int strOffset) -> getString(strOffset), bytesIn);
                } catch (IOException ex) {
                    throw new RuntimeException(ex);
                }

                return ByteBuffer.wrap(bytesOut);
            }
        }

        return null;
    }

    public InputStream getResourceStream(ImageLocation loc) {
        Objects.requireNonNull(loc);
        byte[] bytes = getResource(loc);

        return new ByteArrayInputStream(bytes);
    }
}