util/zip/ZipFile.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 * Copyright (c) 1995, 2015, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util.zip;

import java.io.Closeable;
import java.io.InputStream;
import java.io.IOException;
import java.io.EOFException;
import java.io.File;
import java.io.FileNotFoundException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.WeakHashMap;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import dalvik.system.CloseGuard;

import static java.util.zip.ZipConstants64.*;

/**
 * This class is used to read entries from a zip file.
 *
 * <p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor
 * or method in this class will cause a {@link NullPointerException} to be
 * thrown.
 *
 * @author      David Connelly
 */
public
class ZipFile implements ZipConstants, Closeable {
    private long jzfile;           // address of jzfile data
    private final String name;     // zip file name
    private final int total;       // total number of entries
    private final boolean locsig;  // if zip file starts with LOCSIG (usually true)
    private volatile boolean closeRequested = false;

    // Android-added: CloseGuard support
    // Not declared @ReachabilitySensitive, since all relevant methods, including finalize()
    // synchronize on this, preventing premature finalization.
    private final CloseGuard guard = CloseGuard.get();

    // Android-changed, needed for alternative OPEN_DELETE implementation
    // that doesn't use unlink before closing the file.
    private final File fileToRemoveOnClose;

    private static final int STORED = ZipEntry.STORED;
    private static final int DEFLATED = ZipEntry.DEFLATED;

    /**
     * Mode flag to open a zip file for reading.
     */
    public static final int OPEN_READ = 0x1;

    /**
     * Mode flag to open a zip file and mark it for deletion.  The file will be
     * deleted some time between the moment that it is opened and the moment
     * that it is closed, but its contents will remain accessible via the
     * <tt>ZipFile</tt> object until either the close method is invoked or the
     * virtual machine exits.
     */
    public static final int OPEN_DELETE = 0x4;

    private static final boolean usemmap;

    static {
        // Android-changed: always use mmap.
        usemmap = true;
    }

    /**
     * Opens a zip file for reading.
     *
     * <p>First, if there is a security manager, its <code>checkRead</code>
     * method is called with the <code>name</code> argument as its argument
     * to ensure the read is allowed.
     *
     * <p>The UTF-8 {@link java.nio.charset.Charset charset} is used to
     * decode the entry names and comments.
     *
     * @param name the name of the zip file
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     * @throws SecurityException if a security manager exists and its
     *         <code>checkRead</code> method doesn't allow read access to the file.
     *
     * @see SecurityManager#checkRead(java.lang.String)
     */
    public ZipFile(String name) throws IOException {
        this(new File(name), OPEN_READ);
    }

    /**
     * Opens a new <code>ZipFile</code> to read from the specified
     * <code>File</code> object in the specified mode.  The mode argument
     * must be either <tt>OPEN_READ</tt> or <tt>OPEN_READ | OPEN_DELETE</tt>.
     *
     * <p>First, if there is a security manager, its <code>checkRead</code>
     * method is called with the <code>name</code> argument as its argument to
     * ensure the read is allowed.
     *
     * <p>The UTF-8 {@link java.nio.charset.Charset charset} is used to
     * decode the entry names and comments
     *
     * @param file the ZIP file to be opened for reading
     * @param mode the mode in which the file is to be opened
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     * @throws SecurityException if a security manager exists and
     *         its <code>checkRead</code> method
     *         doesn't allow read access to the file,
     *         or its <code>checkDelete</code> method doesn't allow deleting
     *         the file when the <tt>OPEN_DELETE</tt> flag is set.
     * @throws IllegalArgumentException if the <tt>mode</tt> argument is invalid
     * @see SecurityManager#checkRead(java.lang.String)
     * @since 1.3
     */
    public ZipFile(File file, int mode) throws IOException {
        this(file, mode, StandardCharsets.UTF_8);
    }

    /**
     * Opens a ZIP file for reading given the specified File object.
     *
     * <p>The UTF-8 {@link java.nio.charset.Charset charset} is used to
     * decode the entry names and comments.
     *
     * @param file the ZIP file to be opened for reading
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     */
    public ZipFile(File file) throws ZipException, IOException {
        this(file, OPEN_READ);
    }

    private ZipCoder zc;

    /**
     * Opens a new <code>ZipFile</code> to read from the specified
     * <code>File</code> object in the specified mode.  The mode argument
     * must be either <tt>OPEN_READ</tt> or <tt>OPEN_READ | OPEN_DELETE</tt>.
     *
     * <p>First, if there is a security manager, its <code>checkRead</code>
     * method is called with the <code>name</code> argument as its argument to
     * ensure the read is allowed.
     *
     * @param file the ZIP file to be opened for reading
     * @param mode the mode in which the file is to be opened
     * @param charset
     *        the {@linkplain java.nio.charset.Charset charset} to
     *        be used to decode the ZIP entry name and comment that are not
     *        encoded by using UTF-8 encoding (indicated by entry's general
     *        purpose flag).
     *
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     *
     * @throws SecurityException
     *         if a security manager exists and its <code>checkRead</code>
     *         method doesn't allow read access to the file,or its
     *         <code>checkDelete</code> method doesn't allow deleting the
     *         file when the <tt>OPEN_DELETE</tt> flag is set
     *
     * @throws IllegalArgumentException if the <tt>mode</tt> argument is invalid
     *
     * @see SecurityManager#checkRead(java.lang.String)
     *
     * @since 1.7
     */
    public ZipFile(File file, int mode, Charset charset) throws IOException
    {
        if (((mode & OPEN_READ) == 0) ||
            ((mode & ~(OPEN_READ | OPEN_DELETE)) != 0)) {
            throw new IllegalArgumentException("Illegal mode: 0x"+
                                               Integer.toHexString(mode));
        }

        // Android-changed: Error out early if the file is too short or non-existent.
        long length = file.length();
        if (length < ZipConstants.ENDHDR) {
            if (length == 0 && !file.exists()) {
                throw new FileNotFoundException("File doesn't exist: " + file);
            } else {
                throw new ZipException("File too short to be a zip file: " + file.length());
            }
        }

        // Android-changed, handle OPEN_DELETE case in #close().
        fileToRemoveOnClose = ((mode & OPEN_DELETE) != 0) ? file : null;

        String name = file.getPath();
        // Android-changed: SecurityManager is always null
        // SecurityManager sm = System.getSecurityManager();
        // if (sm != null) {
        //     sm.checkRead(name);
        //     if ((mode & OPEN_DELETE) != 0) {
        //         sm.checkDelete(name);
        //     }
        // }
        if (charset == null)
            throw new NullPointerException("charset is null");
        this.zc = ZipCoder.get(charset);
        // Android-changed: Skip perf counters
        // long t0 = System.nanoTime();
        jzfile = open(name, mode, file.lastModified(), usemmap);
        // Android-changed: Skip perf counters
        // sun.misc.PerfCounter.getZipFileOpenTime().addElapsedTimeFrom(t0);
        // sun.misc.PerfCounter.getZipFileCount().increment();
        this.name = name;
        this.total = getTotal(jzfile);
        this.locsig = startsWithLOC(jzfile);
        Enumeration<? extends ZipEntry> entries = entries();

        guard.open("close");

        // Android-changed: Error out early if the zipfile has no entries.
        if (size() == 0 || !entries.hasMoreElements()) {
            close();
            throw new ZipException("No entries");
        }

    }

    /**
     * Opens a zip file for reading.
     *
     * <p>First, if there is a security manager, its <code>checkRead</code>
     * method is called with the <code>name</code> argument as its argument
     * to ensure the read is allowed.
     *
     * @param name the name of the zip file
     * @param charset
     *        the {@linkplain java.nio.charset.Charset charset} to
     *        be used to decode the ZIP entry name and comment that are not
     *        encoded by using UTF-8 encoding (indicated by entry's general
     *        purpose flag).
     *
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     * @throws SecurityException
     *         if a security manager exists and its <code>checkRead</code>
     *         method doesn't allow read access to the file
     *
     * @see SecurityManager#checkRead(java.lang.String)
     *
     * @since 1.7
     */
    public ZipFile(String name, Charset charset) throws IOException
    {
        this(new File(name), OPEN_READ, charset);
    }

    /**
     * Opens a ZIP file for reading given the specified File object.
     * @param file the ZIP file to be opened for reading
     * @param charset
     *        The {@linkplain java.nio.charset.Charset charset} to be
     *        used to decode the ZIP entry name and comment (ignored if
     *        the <a href="package-summary.html#lang_encoding"> language
     *        encoding bit</a> of the ZIP entry's general purpose bit
     *        flag is set).
     *
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     *
     * @since 1.7
     */
    public ZipFile(File file, Charset charset) throws IOException
    {
        this(file, OPEN_READ, charset);
    }

    /**
     * Returns the zip file comment, or null if none.
     *
     * @return the comment string for the zip file, or null if none
     *
     * @throws IllegalStateException if the zip file has been closed
     *
     * Since 1.7
     */
    public String getComment() {
        synchronized (this) {
            ensureOpen();
            byte[] bcomm = getCommentBytes(jzfile);
            if (bcomm == null)
                return null;
            return zc.toString(bcomm, bcomm.length);
        }
    }

    /**
     * Returns the zip file entry for the specified name, or null
     * if not found.
     *
     * @param name the name of the entry
     * @return the zip file entry, or null if not found
     * @throws IllegalStateException if the zip file has been closed
     */
    public ZipEntry getEntry(String name) {
        if (name == null) {
            throw new NullPointerException("name");
        }
        long jzentry = 0;
        synchronized (this) {
            ensureOpen();
            jzentry = getEntry(jzfile, zc.getBytes(name), true);
            if (jzentry != 0) {
                ZipEntry ze = getZipEntry(name, jzentry);
                freeEntry(jzfile, jzentry);
                return ze;
            }
        }
        return null;
    }

    private static native long getEntry(long jzfile, byte[] name,
                                        boolean addSlash);

    // freeEntry releases the C jzentry struct.
    private static native void freeEntry(long jzfile, long jzentry);

    // the outstanding inputstreams that need to be closed,
    // mapped to the inflater objects they use.
    private final Map<InputStream, Inflater> streams = new WeakHashMap<>();

    /**
     * Returns an input stream for reading the contents of the specified
     * zip file entry.
     *
     * <p> Closing this ZIP file will, in turn, close all input
     * streams that have been returned by invocations of this method.
     *
     * @param entry the zip file entry
     * @return the input stream for reading the contents of the specified
     * zip file entry.
     * @throws ZipException if a ZIP format error has occurred
     * @throws IOException if an I/O error has occurred
     * @throws IllegalStateException if the zip file has been closed
     */
    public InputStream getInputStream(ZipEntry entry) throws IOException {
        if (entry == null) {
            throw new NullPointerException("entry");
        }
        long jzentry = 0;
        ZipFileInputStream in = null;
        synchronized (this) {
            ensureOpen();
            if (!zc.isUTF8() && (entry.flag & EFS) != 0) {
                // Android-changed: addSlash set to true, android is fine with "/" at the end
                jzentry = getEntry(jzfile, zc.getBytesUTF8(entry.name), true);
            } else {
                // Android-changed: addSlash set to true, android is fine with "/" at the end
                jzentry = getEntry(jzfile, zc.getBytes(entry.name), true);
            }
            if (jzentry == 0) {
                return null;
            }
            in = new ZipFileInputStream(jzentry);

            switch (getEntryMethod(jzentry)) {
            case STORED:
                synchronized (streams) {
                    streams.put(in, null);
                }
                return in;
            case DEFLATED:
                // MORE: Compute good size for inflater stream:
                long size = getEntrySize(jzentry) + 2; // Inflater likes a bit of slack
                // Android-changed: Use 64k buffer size, performs better than 8k.
                // if (size > 65536) size = 8192;
                if (size > 65536) size = 65536;
                if (size <= 0) size = 4096;
                Inflater inf = getInflater();
                InputStream is =
                    new ZipFileInflaterInputStream(in, inf, (int)size);
                synchronized (streams) {
                    streams.put(is, inf);
                }
                return is;
            default:
                throw new ZipException("invalid compression method");
            }
        }
    }

    private class ZipFileInflaterInputStream extends InflaterInputStream {
        private volatile boolean closeRequested = false;
        private boolean eof = false;
        private final ZipFileInputStream zfin;

        ZipFileInflaterInputStream(ZipFileInputStream zfin, Inflater inf,
                int size) {
            super(zfin, inf, size);
            this.zfin = zfin;
        }

        public void close() throws IOException {
            if (closeRequested)
                return;
            closeRequested = true;

            super.close();
            Inflater inf;
            synchronized (streams) {
                inf = streams.remove(this);
            }
            if (inf != null) {
                releaseInflater(inf);
            }
        }

        // Override fill() method to provide an extra "dummy" byte
        // at the end of the input stream. This is required when
        // using the "nowrap" Inflater option.
        protected void fill() throws IOException {
            if (eof) {
                throw new EOFException("Unexpected end of ZLIB input stream");
            }
            len = in.read(buf, 0, buf.length);
            if (len == -1) {
                buf[0] = 0;
                len = 1;
                eof = true;
            }
            inf.setInput(buf, 0, len);
        }

        public int available() throws IOException {
            if (closeRequested)
                return 0;
            long avail = zfin.size() - inf.getBytesWritten();
            return (avail > (long) Integer.MAX_VALUE ?
                    Integer.MAX_VALUE : (int) avail);
        }

        protected void finalize() throws Throwable {
            close();
        }
    }

    /*
     * Gets an inflater from the list of available inflaters or allocates
     * a new one.
     */
    private Inflater getInflater() {
        Inflater inf;
        synchronized (inflaterCache) {
            while (null != (inf = inflaterCache.poll())) {
                if (false == inf.ended()) {
                    return inf;
                }
            }
        }
        return new Inflater(true);
    }

    /*
     * Releases the specified inflater to the list of available inflaters.
     */
    private void releaseInflater(Inflater inf) {
        if (false == inf.ended()) {
            inf.reset();
            synchronized (inflaterCache) {
                inflaterCache.add(inf);
            }
        }
    }

    // List of available Inflater objects for decompression
    private Deque<Inflater> inflaterCache = new ArrayDeque<>();

    /**
     * Returns the path name of the ZIP file.
     * @return the path name of the ZIP file
     */
    public String getName() {
        return name;
    }

    private class ZipEntryIterator implements Enumeration<ZipEntry>, Iterator<ZipEntry> {
        private int i = 0;

        public ZipEntryIterator() {
            ensureOpen();
        }

        public boolean hasMoreElements() {
            return hasNext();
        }

        public boolean hasNext() {
            synchronized (ZipFile.this) {
                ensureOpen();
                return i < total;
            }
        }

        public ZipEntry nextElement() {
            return next();
        }

        public ZipEntry next() {
            synchronized (ZipFile.this) {
                ensureOpen();
                if (i >= total) {
                    throw new NoSuchElementException();
                }
                long jzentry = getNextEntry(jzfile, i++);
                if (jzentry == 0) {
                    String message;
                    if (closeRequested) {
                        message = "ZipFile concurrently closed";
                    } else {
                        message = getZipMessage(ZipFile.this.jzfile);
                    }
                    throw new ZipError("jzentry == 0" +
                                       ",\n jzfile = " + ZipFile.this.jzfile +
                                       ",\n total = " + ZipFile.this.total +
                                       ",\n name = " + ZipFile.this.name +
                                       ",\n i = " + i +
                                       ",\n message = " + message
                        );
                }
                ZipEntry ze = getZipEntry(null, jzentry);
                freeEntry(jzfile, jzentry);
                return ze;
            }
        }
    }

    /**
     * Returns an enumeration of the ZIP file entries.
     * @return an enumeration of the ZIP file entries
     * @throws IllegalStateException if the zip file has been closed
     */
    public Enumeration<? extends ZipEntry> entries() {
        return new ZipEntryIterator();
    }

    /**
     * Return an ordered {@code Stream} over the ZIP file entries.
     * Entries appear in the {@code Stream} in the order they appear in
     * the central directory of the ZIP file.
     *
     * @return an ordered {@code Stream} of entries in this ZIP file
     * @throws IllegalStateException if the zip file has been closed
     * @since 1.8
     */
    public Stream<? extends ZipEntry> stream() {
        return StreamSupport.stream(Spliterators.spliterator(
                new ZipEntryIterator(), size(),
                Spliterator.ORDERED | Spliterator.DISTINCT |
                        Spliterator.IMMUTABLE | Spliterator.NONNULL), false);
    }

    private ZipEntry getZipEntry(String name, long jzentry) {
        ZipEntry e = new ZipEntry();
        e.flag = getEntryFlag(jzentry);  // get the flag first
        if (name != null) {
            e.name = name;
        } else {
            byte[] bname = getEntryBytes(jzentry, JZENTRY_NAME);
            if (!zc.isUTF8() && (e.flag & EFS) != 0) {
                e.name = zc.toStringUTF8(bname, bname.length);
            } else {
                e.name = zc.toString(bname, bname.length);
            }
        }
        e.xdostime = getEntryTime(jzentry);
        e.crc = getEntryCrc(jzentry);
        e.size = getEntrySize(jzentry);
        e.csize = getEntryCSize(jzentry);
        e.method = getEntryMethod(jzentry);
        e.setExtra0(getEntryBytes(jzentry, JZENTRY_EXTRA), false);
        byte[] bcomm = getEntryBytes(jzentry, JZENTRY_COMMENT);
        if (bcomm == null) {
            e.comment = null;
        } else {
            if (!zc.isUTF8() && (e.flag & EFS) != 0) {
                e.comment = zc.toStringUTF8(bcomm, bcomm.length);
            } else {
                e.comment = zc.toString(bcomm, bcomm.length);
            }
        }
        return e;
    }

    private static native long getNextEntry(long jzfile, int i);

    /**
     * Returns the number of entries in the ZIP file.
     * @return the number of entries in the ZIP file
     * @throws IllegalStateException if the zip file has been closed
     */
    public int size() {
        ensureOpen();
        return total;
    }

    /**
     * Closes the ZIP file.
     * <p> Closing this ZIP file will close all of the input streams
     * previously returned by invocations of the {@link #getInputStream
     * getInputStream} method.
     *
     * @throws IOException if an I/O error has occurred
     */
    public void close() throws IOException {
        if (closeRequested)
            return;
        guard.close();
        closeRequested = true;

        synchronized (this) {
            // Close streams, release their inflaters
            synchronized (streams) {
                if (false == streams.isEmpty()) {
                    Map<InputStream, Inflater> copy = new HashMap<>(streams);
                    streams.clear();
                    for (Map.Entry<InputStream, Inflater> e : copy.entrySet()) {
                        e.getKey().close();
                        Inflater inf = e.getValue();
                        if (inf != null) {
                            inf.end();
                        }
                    }
                }
            }

            // Release cached inflaters
            Inflater inf;
            synchronized (inflaterCache) {
                while (null != (inf = inflaterCache.poll())) {
                    inf.end();
                }
            }

            if (jzfile != 0) {
                // Close the zip file
                long zf = this.jzfile;
                jzfile = 0;

                close(zf);
            }
            // Android-changed, explicit delete for OPEN_DELETE ZipFile.
            if (fileToRemoveOnClose != null) {
                fileToRemoveOnClose.delete();
            }
        }
    }

    /**
     * Ensures that the system resources held by this ZipFile object are
     * released when there are no more references to it.
     *
     * <p>
     * Since the time when GC would invoke this method is undetermined,
     * it is strongly recommended that applications invoke the <code>close</code>
     * method as soon they have finished accessing this <code>ZipFile</code>.
     * This will prevent holding up system resources for an undetermined
     * length of time.
     *
     * @throws IOException if an I/O error has occurred
     * @see    java.util.zip.ZipFile#close()
     */
    protected void finalize() throws IOException {
        // Android-note: finalize() won't be invoked while important instance methods are running.
        // Both those methods and this method synchronize on "this", ensuring reachability
        // until the monitor is released.
        if (guard != null) {
            guard.warnIfOpen();
        }

        close();  // Synchronizes on "this".
    }

    private static native void close(long jzfile);

    private void ensureOpen() {
        if (closeRequested) {
            throw new IllegalStateException("zip file closed");
        }

        if (jzfile == 0) {
            throw new IllegalStateException("The object is not initialized.");
        }
    }

    private void ensureOpenOrZipException() throws IOException {
        if (closeRequested) {
            throw new ZipException("ZipFile closed");
        }
    }

    /*
     * Inner class implementing the input stream used to read a
     * (possibly compressed) zip file entry.
     */
   private class ZipFileInputStream extends InputStream {
        private volatile boolean zfisCloseRequested = false;
        protected long jzentry; // address of jzentry data
        private   long pos;     // current position within entry data
        protected long rem;     // number of remaining bytes within entry
        protected long size;    // uncompressed size of this entry

        ZipFileInputStream(long jzentry) {
            pos = 0;
            rem = getEntryCSize(jzentry);
            size = getEntrySize(jzentry);
            this.jzentry = jzentry;
        }

        public int read(byte b[], int off, int len) throws IOException {
            // Android-changed: Always throw an exception on read if the zipfile
            // has already been closed.
            ensureOpenOrZipException();

            synchronized (ZipFile.this) {
                long rem = this.rem;
                long pos = this.pos;
                if (rem == 0) {
                    return -1;
                }
                if (len <= 0) {
                    return 0;
                }
                if (len > rem) {
                    len = (int) rem;
                }

                // Android-changed: Moved
                //ensureOpenOrZipException();
                len = ZipFile.read(ZipFile.this.jzfile, jzentry, pos, b,
                                   off, len);
                if (len > 0) {
                    this.pos = (pos + len);
                    this.rem = (rem - len);
                }
            }
            if (rem == 0) {
                close();
            }
            return len;
        }

        public int read() throws IOException {
            byte[] b = new byte[1];
            if (read(b, 0, 1) == 1) {
                return b[0] & 0xff;
            } else {
                return -1;
            }
        }

        public long skip(long n) {
            if (n > rem)
                n = rem;
            pos += n;
            rem -= n;
            if (rem == 0) {
                close();
            }
            return n;
        }

        public int available() {
            return rem > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) rem;
        }

        public long size() {
            return size;
        }

        public void close() {
            if (zfisCloseRequested)
                return;
            zfisCloseRequested = true;

            rem = 0;
            synchronized (ZipFile.this) {
                if (jzentry != 0 && ZipFile.this.jzfile != 0) {
                    freeEntry(ZipFile.this.jzfile, jzentry);
                    jzentry = 0;
                }
            }
            synchronized (streams) {
                streams.remove(this);
            }
        }

        protected void finalize() {
            close();
        }
    }

    /**
     * Returns {@code true} if, and only if, the zip file begins with {@code
     * LOCSIG}.
     * @hide
     */
    public boolean startsWithLocHeader() {
        return locsig;
    }

    /** @hide */
    // @VisibleForTesting
    public int getFileDescriptor() {
        return getFileDescriptor(jzfile);
    }

    private static native int getFileDescriptor(long jzfile);

    private static native long open(String name, int mode, long lastModified,
                                    boolean usemmap) throws IOException;
    private static native int getTotal(long jzfile);
    private static native boolean startsWithLOC(long jzfile);
    private static native int read(long jzfile, long jzentry,
                                   long pos, byte[] b, int off, int len);

    // access to the native zentry object
    private static native long getEntryTime(long jzentry);
    private static native long getEntryCrc(long jzentry);
    private static native long getEntryCSize(long jzentry);
    private static native long getEntrySize(long jzentry);
    private static native int getEntryMethod(long jzentry);
    private static native int getEntryFlag(long jzentry);
    private static native byte[] getCommentBytes(long jzfile);

    private static final int JZENTRY_NAME = 0;
    private static final int JZENTRY_EXTRA = 1;
    private static final int JZENTRY_COMMENT = 2;
    private static native byte[] getEntryBytes(long jzentry, int type);

    private static native String getZipMessage(long jzfile);
}