AutoUpdate/MAutoUpdate/Zip DLL/ZipFile.Read.cs

// ZipFile.Read.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2009-2011 Dino Chiesa.
// All rights reserved.
//
// This code module is part of DotNetZip, a zipfile class library.
//
// ------------------------------------------------------------------
//
// This code is licensed under the Microsoft Public License.
// See the file License.txt for the license details.
// More info on: http://dotnetzip.codeplex.com
//
// ------------------------------------------------------------------
//
// last saved (in emacs):
// Time-stamp: <2011-August-05 11:38:59>
//
// ------------------------------------------------------------------
//
// This module defines the methods for Reading zip files.
//
// ------------------------------------------------------------------
//


using System;
using System.IO;
using System.Collections.Generic;

namespace Ionic.Zip
{
    /// <summary>
    ///   A class for collecting the various options that can be used when
    ///   Reading zip files for extraction or update.
    /// </summary>
    ///
    /// <remarks>
    ///   <para>
    ///     When reading a zip file, there are several options an
    ///     application can set, to modify how the file is read, or what
    ///     the library does while reading.  This class collects those
    ///     options into one container.
    ///   </para>
    ///
    ///   <para>
    ///     Pass an instance of the <c>ReadOptions</c> class into the
    ///     <c>ZipFile.Read()</c> method.
    ///   </para>
    ///
    /// <seealso cref="ZipFile.Read(String, ReadOptions)"/>.
    /// <seealso cref="ZipFile.Read(Stream, ReadOptions)"/>.
    /// </remarks>
    public class ReadOptions
    {
        /// <summary>
        /// An event handler for Read operations.  When opening large zip
        /// archives, you may want to display a progress bar or other
        /// indicator of status progress while reading.  This parameter
        /// allows you to specify a ReadProgress Event Handler directly.
        /// When you call <c>Read()</c>, the progress event is invoked as
        /// necessary.
        /// </summary>
        public EventHandler<ReadProgressEventArgs> ReadProgress { get; set; }

        /// <summary>
        /// The <c>System.IO.TextWriter</c> to use for writing verbose status messages
        /// during operations on the zip archive.  A console application may wish to
        /// pass <c>System.Console.Out</c> to get messages on the Console. A graphical
        /// or headless application may wish to capture the messages in a different
        /// <c>TextWriter</c>, such as a <c>System.IO.StringWriter</c>.
        /// </summary>
        public TextWriter StatusMessageWriter { get; set; }

        /// <summary>
        /// The <c>System.Text.Encoding</c> to use when reading in the zip archive. Be
        /// careful specifying the encoding.  If the value you use here is not the same
        /// as the Encoding used when the zip archive was created (possibly by a
        /// different archiver) you will get unexpected results and possibly exceptions.
        /// </summary>
        ///
        /// <seealso cref="ZipFile.ProvisionalAlternateEncoding"/>
        ///
        public System.Text.Encoding @Encoding { get; set; }
    }


    public partial class ZipFile
    {
        /// <summary>
        /// Reads a zip file archive and returns the instance.
        /// </summary>
        ///
        /// <remarks>
        /// <para>
        /// The stream is read using the default <c>System.Text.Encoding</c>, which is the
        /// <c>IBM437</c> codepage.
        /// </para>
        /// </remarks>
        ///
        /// <exception cref="System.Exception">
        /// Thrown if the <c>ZipFile</c> cannot be read. The implementation of this method
        /// relies on <c>System.IO.File.OpenRead</c>, which can throw a variety of exceptions,
        /// including specific exceptions if a file is not found, an unauthorized access
        /// exception, exceptions for poorly formatted filenames, and so on.
        /// </exception>
        ///
        /// <param name="fileName">
        /// The name of the zip archive to open.  This can be a fully-qualified or relative
        /// pathname.
        /// </param>
        ///
        /// <seealso cref="ZipFile.Read(String, ReadOptions)"/>.
        ///
        /// <returns>The instance read from the zip archive.</returns>
        ///
        public static ZipFile Read(string fileName)
        {
            return ZipFile.Read(fileName, null, null, null);
        }


        /// <summary>
        ///   Reads a zip file archive from the named filesystem file using the
        ///   specified options.
        /// </summary>
        ///
        /// <remarks>
        /// <para>
        ///   This version of the <c>Read()</c> method allows the caller to pass
        ///   in a <c>TextWriter</c> an <c>Encoding</c>, via an instance of the
        ///   <c>ReadOptions</c> class.  The <c>ZipFile</c> is read in using the
        ///   specified encoding for entries where UTF-8 encoding is not
        ///   explicitly specified.
        /// </para>
        /// </remarks>
        ///
        /// <example>
        ///
        /// <para>
        ///   This example shows how to read a zip file using the Big-5 Chinese
        ///   code page (950), and extract each entry in the zip file, while
        ///   sending status messages out to the Console.
        /// </para>
        ///
        /// <para>
        ///   For this code to work as intended, the zipfile must have been
        ///   created using the big5 code page (CP950). This is typical, for
        ///   example, when using WinRar on a machine with CP950 set as the
        ///   default code page.  In that case, the names of entries within the
        ///   Zip archive will be stored in that code page, and reading the zip
        ///   archive must be done using that code page.  If the application did
        ///   not use the correct code page in ZipFile.Read(), then names of
        ///   entries within the zip archive would not be correctly retrieved.
        /// </para>
        ///
        /// <code lang="C#">
        /// string zipToExtract = "MyArchive.zip";
        /// string extractDirectory = "extract";
        /// var options = new ReadOptions
        /// {
        ///   StatusMessageWriter = System.Console.Out,
        ///   Encoding = System.Text.Encoding.GetEncoding(950)
        /// };
        /// using (ZipFile zip = ZipFile.Read(zipToExtract, options))
        /// {
        ///   foreach (ZipEntry e in zip)
        ///   {
        ///      e.Extract(extractDirectory);
        ///   }
        /// }
        /// </code>
        ///
        ///
        /// <code lang="VB">
        /// Dim zipToExtract as String = "MyArchive.zip"
        /// Dim extractDirectory as String = "extract"
        /// Dim options as New ReadOptions
        /// options.Encoding = System.Text.Encoding.GetEncoding(950)
        /// options.StatusMessageWriter = System.Console.Out
        /// Using zip As ZipFile = ZipFile.Read(zipToExtract, options)
        ///     Dim e As ZipEntry
        ///     For Each e In zip
        ///      e.Extract(extractDirectory)
        ///     Next
        /// End Using
        /// </code>
        /// </example>
        ///
        ///
        /// <example>
        ///
        /// <para>
        ///   This example shows how to read a zip file using the default
        ///   code page, to remove entries that have a modified date before a given threshold,
        ///   sending status messages out to a <c>StringWriter</c>.
        /// </para>
        ///
        /// <code lang="C#">
        /// var options = new ReadOptions
        /// {
        ///   StatusMessageWriter = new System.IO.StringWriter()
        /// };
        /// using (ZipFile zip =  ZipFile.Read("PackedDocuments.zip", options))
        /// {
        ///   var Threshold = new DateTime(2007,7,4);
        ///   // We cannot remove the entry from the list, within the context of
        ///   // an enumeration of said list.
        ///   // So we add the doomed entry to a list to be removed later.
        ///   // pass 1: mark the entries for removal
        ///   var MarkedEntries = new System.Collections.Generic.List&lt;ZipEntry&gt;();
        ///   foreach (ZipEntry e in zip)
        ///   {
        ///     if (e.LastModified &lt; Threshold)
        ///       MarkedEntries.Add(e);
        ///   }
        ///   // pass 2: actually remove the entry.
        ///   foreach (ZipEntry zombie in MarkedEntries)
        ///      zip.RemoveEntry(zombie);
        ///   zip.Comment = "This archive has been updated.";
        ///   zip.Save();
        /// }
        /// // can now use contents of sw, eg store in an audit log
        /// </code>
        ///
        /// <code lang="VB">
        /// Dim options as New ReadOptions
        /// options.StatusMessageWriter = New System.IO.StringWriter
        /// Using zip As ZipFile = ZipFile.Read("PackedDocuments.zip", options)
        ///     Dim Threshold As New DateTime(2007, 7, 4)
        ///     ' We cannot remove the entry from the list, within the context of
        ///     ' an enumeration of said list.
        ///     ' So we add the doomed entry to a list to be removed later.
        ///     ' pass 1: mark the entries for removal
        ///     Dim MarkedEntries As New System.Collections.Generic.List(Of ZipEntry)
        ///     Dim e As ZipEntry
        ///     For Each e In zip
        ///         If (e.LastModified &lt; Threshold) Then
        ///             MarkedEntries.Add(e)
        ///         End If
        ///     Next
        ///     ' pass 2: actually remove the entry.
        ///     Dim zombie As ZipEntry
        ///     For Each zombie In MarkedEntries
        ///         zip.RemoveEntry(zombie)
        ///     Next
        ///     zip.Comment = "This archive has been updated."
        ///     zip.Save
        /// End Using
        /// ' can now use contents of sw, eg store in an audit log
        /// </code>
        /// </example>
        ///
        /// <exception cref="System.Exception">
        ///   Thrown if the zipfile cannot be read. The implementation of
        ///   this method relies on <c>System.IO.File.OpenRead</c>, which
        ///   can throw a variety of exceptions, including specific
        ///   exceptions if a file is not found, an unauthorized access
        ///   exception, exceptions for poorly formatted filenames, and so
        ///   on.
        /// </exception>
        ///
        /// <param name="fileName">
        /// The name of the zip archive to open.
        /// This can be a fully-qualified or relative pathname.
        /// </param>
        ///
        /// <param name="options">
        /// The set of options to use when reading the zip file.
        /// </param>
        ///
        /// <returns>The ZipFile instance read from the zip archive.</returns>
        ///
        /// <seealso cref="ZipFile.Read(Stream, ReadOptions)"/>
        ///
        public static ZipFile Read(string fileName,
                                   ReadOptions options)
        {
            if (options == null)
                throw new ArgumentNullException("options");
            return Read(fileName,
                        options.StatusMessageWriter,
                        options.Encoding,
                        options.ReadProgress);
        }

        /// <summary>
        /// Reads a zip file archive using the specified text encoding,  the specified
        /// TextWriter for status messages, and the specified ReadProgress event handler,
        /// and returns the instance.
        /// </summary>
        ///
        /// <param name="fileName">
        /// The name of the zip archive to open.
        /// This can be a fully-qualified or relative pathname.
        /// </param>
        ///
        /// <param name="readProgress">
        /// An event handler for Read operations.
        /// </param>
        ///
        /// <param name="statusMessageWriter">
        /// The <c>System.IO.TextWriter</c> to use for writing verbose status messages
        /// during operations on the zip archive.  A console application may wish to
        /// pass <c>System.Console.Out</c> to get messages on the Console. A graphical
        /// or headless application may wish to capture the messages in a different
        /// <c>TextWriter</c>, such as a <c>System.IO.StringWriter</c>.
        /// </param>
        ///
        /// <param name="encoding">
        /// The <c>System.Text.Encoding</c> to use when reading in the zip archive. Be
        /// careful specifying the encoding.  If the value you use here is not the same
        /// as the Encoding used when the zip archive was created (possibly by a
        /// different archiver) you will get unexpected results and possibly exceptions.
        /// </param>
        ///
        /// <returns>The instance read from the zip archive.</returns>
        ///
        private static ZipFile Read(string fileName,
                                   TextWriter statusMessageWriter,
                                   System.Text.Encoding encoding,
                                   EventHandler<ReadProgressEventArgs> readProgress)
        {
            ZipFile zf = new ZipFile();
            zf.AlternateEncoding = encoding ?? DefaultEncoding;
            zf.AlternateEncodingUsage = ZipOption.Always;
            zf._StatusMessageTextWriter = statusMessageWriter;
            zf._name = fileName;
            if (readProgress != null)
                zf.ReadProgress = readProgress;

            if (zf.Verbose) zf._StatusMessageTextWriter.WriteLine("reading from {0}...", fileName);

            ReadIntoInstance(zf);
            zf._fileAlreadyExists = true;

            return zf;
        }

        /// <summary>
        ///   Reads a zip archive from a stream.
        /// </summary>
        ///
        /// <remarks>
        ///
        /// <para>
        ///   When reading from a file, it's probably easier to just use
        ///   <see cref="ZipFile.Read(String,
        ///   ReadOptions)">ZipFile.Read(String, ReadOptions)</see>.  This
        ///   overload is useful when when the zip archive content is
        ///   available from an already-open stream. The stream must be
        ///   open and readable and seekable when calling this method.  The
        ///   stream is left open when the reading is completed.
        /// </para>
        ///
        /// <para>
        ///   Using this overload, the stream is read using the default
        ///   <c>System.Text.Encoding</c>, which is the <c>IBM437</c>
        ///   codepage. If you want to specify the encoding to use when
        ///   reading the zipfile content, see
        ///   <see cref="ZipFile.Read(Stream,
        ///   ReadOptions)">ZipFile.Read(Stream, ReadOptions)</see>.  This
        /// </para>
        ///
        /// <para>
        ///   Reading of zip content begins at the current position in the
        ///   stream.  This means if you have a stream that concatenates
        ///   regular data and zip data, if you position the open, readable
        ///   stream at the start of the zip data, you will be able to read
        ///   the zip archive using this constructor, or any of the ZipFile
        ///   constructors that accept a <see cref="System.IO.Stream" /> as
        ///   input. Some examples of where this might be useful: the zip
        ///   content is concatenated at the end of a regular EXE file, as
        ///   some self-extracting archives do.  (Note: SFX files produced
        ///   by DotNetZip do not work this way; they can be read as normal
        ///   ZIP files). Another example might be a stream being read from
        ///   a database, where the zip content is embedded within an
        ///   aggregate stream of data.
        /// </para>
        ///
        /// </remarks>
        ///
        /// <example>
        /// <para>
        ///   This example shows how to Read zip content from a stream, and
        ///   extract one entry into a different stream. In this example,
        ///   the filename "NameOfEntryInArchive.doc", refers only to the
        ///   name of the entry within the zip archive.  A file by that
        ///   name is not created in the filesystem.  The I/O is done
        ///   strictly with the given streams.
        /// </para>
        ///
        /// <code>
        /// using (ZipFile zip = ZipFile.Read(InputStream))
        /// {
        ///    zip.Extract("NameOfEntryInArchive.doc", OutputStream);
        /// }
        /// </code>
        ///
        /// <code lang="VB">
        /// Using zip as ZipFile = ZipFile.Read(InputStream)
        ///    zip.Extract("NameOfEntryInArchive.doc", OutputStream)
        /// End Using
        /// </code>
        /// </example>
        ///
        /// <param name="zipStream">the stream containing the zip data.</param>
        ///
        /// <returns>The ZipFile instance read from the stream</returns>
        ///
        public static ZipFile Read(Stream zipStream)
        {
            return Read(zipStream, null, null, null);
        }

        /// <summary>
        ///   Reads a zip file archive from the given stream using the
        ///   specified options.
        /// </summary>
        ///
        /// <remarks>
        ///
        /// <para>
        ///   When reading from a file, it's probably easier to just use
        ///   <see cref="ZipFile.Read(String,
        ///   ReadOptions)">ZipFile.Read(String, ReadOptions)</see>.  This
        ///   overload is useful when when the zip archive content is
        ///   available from an already-open stream. The stream must be
        ///   open and readable and seekable when calling this method.  The
        ///   stream is left open when the reading is completed.
        /// </para>
        ///
        /// <para>
        ///   Reading of zip content begins at the current position in the
        ///   stream.  This means if you have a stream that concatenates
        ///   regular data and zip data, if you position the open, readable
        ///   stream at the start of the zip data, you will be able to read
        ///   the zip archive using this constructor, or any of the ZipFile
        ///   constructors that accept a <see cref="System.IO.Stream" /> as
        ///   input. Some examples of where this might be useful: the zip
        ///   content is concatenated at the end of a regular EXE file, as
        ///   some self-extracting archives do.  (Note: SFX files produced
        ///   by DotNetZip do not work this way; they can be read as normal
        ///   ZIP files). Another example might be a stream being read from
        ///   a database, where the zip content is embedded within an
        ///   aggregate stream of data.
        /// </para>
        /// </remarks>
        ///
        /// <param name="zipStream">the stream containing the zip data.</param>
        ///
        /// <param name="options">
        ///   The set of options to use when reading the zip file.
        /// </param>
        ///
        /// <exception cref="System.Exception">
        ///   Thrown if the zip archive cannot be read.
        /// </exception>
        ///
        /// <returns>The ZipFile instance read from the stream.</returns>
        ///
        /// <seealso cref="ZipFile.Read(String, ReadOptions)"/>
        ///
        public static ZipFile Read(Stream zipStream, ReadOptions options)
        {
            if (options == null)
                throw new ArgumentNullException("options");

            return Read(zipStream,
                        options.StatusMessageWriter,
                        options.Encoding,
                        options.ReadProgress);
        }



        /// <summary>
        /// Reads a zip archive from a stream, using the specified text Encoding, the
        /// specified TextWriter for status messages,
        /// and the specified ReadProgress event handler.
        /// </summary>
        ///
        /// <remarks>
        /// <para>
        /// Reading of zip content begins at the current position in the stream.  This
        /// means if you have a stream that concatenates regular data and zip data, if
        /// you position the open, readable stream at the start of the zip data, you
        /// will be able to read the zip archive using this constructor, or any of the
        /// ZipFile constructors that accept a <see cref="System.IO.Stream" /> as
        /// input. Some examples of where this might be useful: the zip content is
        /// concatenated at the end of a regular EXE file, as some self-extracting
        /// archives do.  (Note: SFX files produced by DotNetZip do not work this
        /// way). Another example might be a stream being read from a database, where
        /// the zip content is embedded within an aggregate stream of data.
        /// </para>
        /// </remarks>
        ///
        /// <param name="zipStream">the stream containing the zip data.</param>
        ///
        /// <param name="statusMessageWriter">
        /// The <c>System.IO.TextWriter</c> to which verbose status messages are written
        /// during operations on the <c>ZipFile</c>.  For example, in a console
        /// application, System.Console.Out works, and will get a message for each entry
        /// added to the ZipFile.  If the TextWriter is <c>null</c>, no verbose messages
        /// are written.
        /// </param>
        ///
        /// <param name="encoding">
        /// The text encoding to use when reading entries that do not have the UTF-8
        /// encoding bit set.  Be careful specifying the encoding.  If the value you use
        /// here is not the same as the Encoding used when the zip archive was created
        /// (possibly by a different archiver) you will get unexpected results and
        /// possibly exceptions.  See the <see cref="ProvisionalAlternateEncoding"/>
        /// property for more information.
        /// </param>
        ///
        /// <param name="readProgress">
        /// An event handler for Read operations.
        /// </param>
        ///
        /// <returns>an instance of ZipFile</returns>
        private static ZipFile Read(Stream zipStream,
                                   TextWriter statusMessageWriter,
                                   System.Text.Encoding encoding,
                                   EventHandler<ReadProgressEventArgs> readProgress)
        {
            if (zipStream == null)
                throw new ArgumentNullException("zipStream");

            ZipFile zf = new ZipFile();
            zf._StatusMessageTextWriter = statusMessageWriter;
            zf._alternateEncoding = encoding ?? ZipFile.DefaultEncoding;
            zf._alternateEncodingUsage = ZipOption.Always;
            if (readProgress != null)
                zf.ReadProgress += readProgress;
            zf._readstream = (zipStream.Position == 0L)
                ? zipStream
                : new OffsetStream(zipStream);
            zf._ReadStreamIsOurs = false;
            if (zf.Verbose) zf._StatusMessageTextWriter.WriteLine("reading from stream...");

            ReadIntoInstance(zf);
            return zf;
        }



        private static void ReadIntoInstance(ZipFile zf)
        {
            Stream s = zf.ReadStream;
            try
            {
                zf._readName = zf._name; // workitem 13915
                if (!s.CanSeek)
                {
                    ReadIntoInstance_Orig(zf);
                    return;
                }

                zf.OnReadStarted();

                // change for workitem 8098
                //zf._originPosition = s.Position;

                // Try reading the central directory, rather than scanning the file.

                uint datum = ReadFirstFourBytes(s);

                if (datum == ZipConstants.EndOfCentralDirectorySignature)
                    return;


                // start at the end of the file...
                // seek backwards a bit, then look for the EoCD signature.
                int nTries = 0;
                bool success = false;

                // The size of the end-of-central-directory-footer plus 2 bytes is 18.
                // This implies an archive comment length of 0.  We'll add a margin of
                // safety and start "in front" of that, when looking for the
                // EndOfCentralDirectorySignature
                long posn = s.Length - 64;
                long maxSeekback = Math.Max(s.Length - 0x4000, 10);
                do
                {
                    if (posn < 0) posn = 0;  // BOF
                    s.Seek(posn, SeekOrigin.Begin);
                    long bytesRead = SharedUtilities.FindSignature(s, (int)ZipConstants.EndOfCentralDirectorySignature);
                    if (bytesRead != -1)
                        success = true;
                    else
                    {
                        if (posn==0) break; // started at the BOF and found nothing
                        nTries++;
                        // Weird: with NETCF, negative offsets from SeekOrigin.End DO
                        // NOT WORK. So rather than seek a negative offset, we seek
                        // from SeekOrigin.Begin using a smaller number.
                        posn -= (32 * (nTries + 1) * nTries);
                    }
                }
                while (!success && posn > maxSeekback);

                if (success)
                {
                    // workitem 8299
                    zf._locEndOfCDS = s.Position - 4;

                    byte[] block = new byte[16];
                    s.Read(block, 0, block.Length);

                    zf._diskNumberWithCd = BitConverter.ToUInt16(block, 2);

                    if (zf._diskNumberWithCd == 0xFFFF)
                        throw new ZipException("Spanned archives with more than 65534 segments are not supported at this time.");

                    zf._diskNumberWithCd++; // I think the number in the file differs from reality by 1

                    int i = 12;

                    uint offset32 = (uint) BitConverter.ToUInt32(block, i);
                    if (offset32 == 0xFFFFFFFF)
                    {
                        Zip64SeekToCentralDirectory(zf);
                    }
                    else
                    {
                        zf._OffsetOfCentralDirectory = offset32;
                        // change for workitem 8098
                        s.Seek(offset32, SeekOrigin.Begin);
                    }

                    ReadCentralDirectory(zf);
                }
                else
                {
                    // Could not find the central directory.
                    // Fallback to the old method.
                    // workitem 8098: ok
                    //s.Seek(zf._originPosition, SeekOrigin.Begin);
                    s.Seek(0L, SeekOrigin.Begin);
                    ReadIntoInstance_Orig(zf);
                }
            }
            catch (Exception ex1)
            {
                if (zf._ReadStreamIsOurs && zf._readstream != null)
                {
                    try
                    {
#if NETCF
                        zf._readstream.Close();
#else
                        zf._readstream.Dispose();
#endif
                        zf._readstream = null;
                    }
                    finally { }
                }

                throw new ZipException("Cannot read that as a ZipFile", ex1);
            }

            // the instance has been read in
            zf._contentsChanged = false;
        }



        private static void Zip64SeekToCentralDirectory(ZipFile zf)
        {
            Stream s = zf.ReadStream;
            byte[] block = new byte[16];

            // seek back to find the ZIP64 EoCD.
            // I think this might not work for .NET CF ?
            s.Seek(-40, SeekOrigin.Current);
            s.Read(block, 0, 16);

            Int64 offset64 = BitConverter.ToInt64(block, 8);
            zf._OffsetOfCentralDirectory = 0xFFFFFFFF;
            zf._OffsetOfCentralDirectory64 = offset64;
            // change for workitem 8098
            s.Seek(offset64, SeekOrigin.Begin);
            //zf.SeekFromOrigin(Offset64);

            uint datum = (uint)Ionic.Zip.SharedUtilities.ReadInt(s);
            if (datum != ZipConstants.Zip64EndOfCentralDirectoryRecordSignature)
                throw new BadReadException(String.Format("  Bad signature (0x{0:X8}) looking for ZIP64 EoCD Record at position 0x{1:X8}", datum, s.Position));

            s.Read(block, 0, 8);
            Int64 Size = BitConverter.ToInt64(block, 0);

            block = new byte[Size];
            s.Read(block, 0, block.Length);

            offset64 = BitConverter.ToInt64(block, 36);
            // change for workitem 8098
            s.Seek(offset64, SeekOrigin.Begin);
            //zf.SeekFromOrigin(Offset64);
        }


        private static uint ReadFirstFourBytes(Stream s)
        {
            uint datum = (uint)Ionic.Zip.SharedUtilities.ReadInt(s);
            return datum;
        }



        private static void ReadCentralDirectory(ZipFile zf)
        {
            // We must have the central directory footer record, in order to properly
            // read zip dir entries from the central directory.  This because the logic
            // knows when to open a spanned file when the volume number for the central
            // directory differs from the volume number for the zip entry.  The
            // _diskNumberWithCd was set when originally finding the offset for the
            // start of the Central Directory.

            // workitem 9214
            bool inputUsesZip64 = false;
            ZipEntry de;
            // in lieu of hashset, use a dictionary
            var previouslySeen = new Dictionary<String, object>(StringComparer.Ordinal);
            while ((de = ZipEntry.ReadDirEntry(zf, previouslySeen)) != null)
            {
                de.ResetDirEntry();
                zf.OnReadEntry(true, null);

                if (zf.Verbose)
                    zf.StatusMessageTextWriter.WriteLine("entry {0}", de.FileName);

                zf._entries.Add(de.FileName,de);
                if (!zf._entriesInsensitive.ContainsKey(de.FileName))
                    zf._entriesInsensitive.Add(de.FileName,de);

                // workitem 9214
                if (de._InputUsesZip64) inputUsesZip64 = true;
                previouslySeen.Add(de.FileName, null); // to prevent dupes
            }

            // workitem 9214; auto-set the zip64 flag
            if (inputUsesZip64) zf.UseZip64WhenSaving = Zip64Option.Always;

            // workitem 8299
            if (zf._locEndOfCDS > 0)
                zf.ReadStream.Seek(zf._locEndOfCDS, SeekOrigin.Begin);

            ReadCentralDirectoryFooter(zf);

            if (zf.Verbose && !String.IsNullOrEmpty(zf.Comment))
                zf.StatusMessageTextWriter.WriteLine("Zip file Comment: {0}", zf.Comment);

            // We keep the read stream open after reading.

            if (zf.Verbose)
                zf.StatusMessageTextWriter.WriteLine("read in {0} entries.", zf._entries.Count);

            zf.OnReadCompleted();
        }




        // build the TOC by reading each entry in the file.
        private static void ReadIntoInstance_Orig(ZipFile zf)
        {
            zf.OnReadStarted();
            zf._entries.Clear();
            zf._entriesInsensitive.Clear();

            ZipEntry e;
            if (zf.Verbose)
                if (zf.Name == null)
                    zf.StatusMessageTextWriter.WriteLine("Reading zip from stream...");
                else
                    zf.StatusMessageTextWriter.WriteLine("Reading zip {0}...", zf.Name);

            // work item 6647:  PK00 (packed to removable disk)
            bool firstEntry = true;
            ZipContainer zc = new ZipContainer(zf);
            while ((e = ZipEntry.ReadEntry(zc, firstEntry)) != null)
            {
                if (zf.Verbose)
                    zf.StatusMessageTextWriter.WriteLine("  {0}", e.FileName);

                zf._entries.Add(e.FileName,e);
                if (!zf._entriesInsensitive.ContainsKey(e.FileName))
                    zf._entriesInsensitive.Add(e.FileName,e);
                firstEntry = false;
            }

            // read the zipfile's central directory structure here.
            // workitem 9912
            // But, because it may be corrupted, ignore errors.
            try
            {
                ZipEntry de;
                // in lieu of hashset, use a dictionary
                var previouslySeen = new Dictionary<String,Object>(StringComparer.Ordinal);
                while ((de = ZipEntry.ReadDirEntry(zf, previouslySeen)) != null)
                {
                    // Housekeeping: Since ZipFile exposes ZipEntry elements in the enumerator,
                    // we need to copy the comment that we grab from the ZipDirEntry
                    // into the ZipEntry, so the application can access the comment.
                    // Also since ZipEntry is used to Write zip files, we need to copy the
                    // file attributes to the ZipEntry as appropriate.
                    ZipEntry e1 = zf._entries[de.FileName];
                    if (e1 != null)
                    {
                        e1._Comment = de.Comment;
                        if (de.IsDirectory) e1.MarkAsDirectory();
                    }
                    previouslySeen.Add(de.FileName,null); // to prevent dupes
                }

                // workitem 8299
                if (zf._locEndOfCDS > 0)
                    zf.ReadStream.Seek(zf._locEndOfCDS, SeekOrigin.Begin);

                ReadCentralDirectoryFooter(zf);

                if (zf.Verbose && !String.IsNullOrEmpty(zf.Comment))
                    zf.StatusMessageTextWriter.WriteLine("Zip file Comment: {0}", zf.Comment);
            }
            catch (ZipException) { }
            catch (IOException) { }

            zf.OnReadCompleted();
        }




        private static void ReadCentralDirectoryFooter(ZipFile zf)
        {
            Stream s = zf.ReadStream;
            int signature = Ionic.Zip.SharedUtilities.ReadSignature(s);

            byte[] block = null;
            int j = 0;
            if (signature == ZipConstants.Zip64EndOfCentralDirectoryRecordSignature)
            {
                // We have a ZIP64 EOCD
                // This data block is 4 bytes sig, 8 bytes size, 44 bytes fixed data,
                // followed by a variable-sized extension block.  We have read the sig already.
                // 8 - datasize (64 bits)
                // 2 - version made by
                // 2 - version needed to extract
                // 4 - number of this disk
                // 4 - number of the disk with the start of the CD
                // 8 - total number of entries in the CD on this disk
                // 8 - total number of entries in the CD
                // 8 - size of the CD
                // 8 - offset of the CD
                // -----------------------
                // 52 bytes

                block = new byte[8 + 44];
                s.Read(block, 0, block.Length);

                Int64 DataSize = BitConverter.ToInt64(block, 0);  // == 44 + the variable length

                if (DataSize < 44)
                    throw new ZipException("Bad size in the ZIP64 Central Directory.");

                zf._versionMadeBy = BitConverter.ToUInt16(block, j);
                j += 2;
                zf._versionNeededToExtract = BitConverter.ToUInt16(block, j);
                j += 2;
                zf._diskNumberWithCd = BitConverter.ToUInt32(block, j);
                j += 2;

                //zf._diskNumberWithCd++; // hack!!

                // read the extended block
                block = new byte[DataSize - 44];
                s.Read(block, 0, block.Length);
                // discard the result

                signature = Ionic.Zip.SharedUtilities.ReadSignature(s);
                if (signature != ZipConstants.Zip64EndOfCentralDirectoryLocatorSignature)
                    throw new ZipException("Inconsistent metadata in the ZIP64 Central Directory.");

                block = new byte[16];
                s.Read(block, 0, block.Length);
                // discard the result

                signature = Ionic.Zip.SharedUtilities.ReadSignature(s);
            }

            // Throw if this is not a signature for "end of central directory record"
            // This is a sanity check.
            if (signature != ZipConstants.EndOfCentralDirectorySignature)
            {
                s.Seek(-4, SeekOrigin.Current);
                throw new BadReadException(String.Format("Bad signature ({0:X8}) at position 0x{1:X8}",
                                                         signature, s.Position));
            }

            // read the End-of-Central-Directory-Record
            block = new byte[16];
            zf.ReadStream.Read(block, 0, block.Length);

            // off sz  data
            // -------------------------------------------------------
            //  0   4  end of central dir signature (0x06054b50)
            //  4   2  number of this disk
            //  6   2  number of the disk with start of the central directory
            //  8   2  total number of entries in the  central directory on this disk
            // 10   2  total number of entries in  the central directory
            // 12   4  size of the central directory
            // 16   4  offset of start of central directory with respect to the starting disk number
            // 20   2  ZIP file comment length
            // 22  ??  ZIP file comment

            if (zf._diskNumberWithCd == 0)
            {
                zf._diskNumberWithCd = BitConverter.ToUInt16(block, 2);
                //zf._diskNumberWithCd++; // hack!!
            }

            // read the comment here
            ReadZipFileComment(zf);
        }



        private static void ReadZipFileComment(ZipFile zf)
        {
            // read the comment here
            byte[] block = new byte[2];
            zf.ReadStream.Read(block, 0, block.Length);

            Int16 commentLength = (short)(block[0] + block[1] * 256);
            if (commentLength > 0)
            {
                block = new byte[commentLength];
                zf.ReadStream.Read(block, 0, block.Length);

                // workitem 10392 - prefer ProvisionalAlternateEncoding,
                // first.  The fix for workitem 6513 tried to use UTF8
                // only as necessary, but that is impossible to test
                // for, in this direction. There's no way to know what
                // characters the already-encoded bytes refer
                // to. Therefore, must do what the user tells us.

                string s1 = zf.AlternateEncoding.GetString(block, 0, block.Length);
                zf.Comment = s1;
            }
        }


        // private static bool BlocksAreEqual(byte[] a, byte[] b)
        // {
        //     if (a.Length != b.Length) return false;
        //     for (int i = 0; i < a.Length; i++)
        //     {
        //         if (a[i] != b[i]) return false;
        //     }
        //     return true;
        // }



        /// <summary>
        /// Checks the given file to see if it appears to be a valid zip file.
        /// </summary>
        /// <remarks>
        ///
        /// <para>
        ///   Calling this method is equivalent to calling <see cref="IsZipFile(string,
        ///   bool)"/> with the testExtract parameter set to false.
        /// </para>
        /// </remarks>
        ///
        /// <param name="fileName">The file to check.</param>
        /// <returns>true if the file appears to be a zip file.</returns>
        public static bool IsZipFile(string fileName)
        {
            return IsZipFile(fileName, false);
        }


        /// <summary>
        /// Checks a file to see if it is a valid zip file.
        /// </summary>
        ///
        /// <remarks>
        /// <para>
        ///   This method opens the specified zip file, reads in the zip archive,
        ///   verifying the ZIP metadata as it reads.
        /// </para>
        ///
        /// <para>
        ///   If everything succeeds, then the method returns true.  If anything fails -
        ///   for example if an incorrect signature or CRC is found, indicating a
        ///   corrupt file, the the method returns false.  This method also returns
        ///   false for a file that does not exist.
        /// </para>
        ///
        /// <para>
        ///   If <paramref name="testExtract"/> is true, as part of its check, this
        ///   method reads in the content for each entry, expands it, and checks CRCs.
        ///   This provides an additional check beyond verifying the zip header and
        ///   directory data.
        /// </para>
        ///
        /// <para>
        ///   If <paramref name="testExtract"/> is true, and if any of the zip entries
        ///   are protected with a password, this method will return false.  If you want
        ///   to verify a <c>ZipFile</c> that has entries which are protected with a
        ///   password, you will need to do that manually.
        /// </para>
        ///
        /// </remarks>
        ///
        /// <param name="fileName">The zip file to check.</param>
        /// <param name="testExtract">true if the caller wants to extract each entry.</param>
        /// <returns>true if the file contains a valid zip file.</returns>
        public static bool IsZipFile(string fileName, bool testExtract)
        {
            bool result = false;
            try
            {
                if (!File.Exists(fileName)) return false;

                using (var s = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
                {
                    result = IsZipFile(s, testExtract);
                }
            }
            catch (IOException) { }
            catch (ZipException) { }
            return result;
        }


        /// <summary>
        /// Checks a stream to see if it contains a valid zip archive.
        /// </summary>
        ///
        /// <remarks>
        /// <para>
        /// This method reads the zip archive contained in the specified stream, verifying
        /// the ZIP metadata as it reads.  If testExtract is true, this method also extracts
        /// each entry in the archive, dumping all the bits into <see cref="Stream.Null"/>.
        /// </para>
        ///
        /// <para>
        /// If everything succeeds, then the method returns true.  If anything fails -
        /// for example if an incorrect signature or CRC is found, indicating a corrupt
        /// file, the the method returns false.  This method also returns false for a
        /// file that does not exist.
        /// </para>
        ///
        /// <para>
        /// If <c>testExtract</c> is true, this method reads in the content for each
        /// entry, expands it, and checks CRCs.  This provides an additional check
        /// beyond verifying the zip header data.
        /// </para>
        ///
        /// <para>
        /// If <c>testExtract</c> is true, and if any of the zip entries are protected
        /// with a password, this method will return false.  If you want to verify a
        /// ZipFile that has entries which are protected with a password, you will need
        /// to do that manually.
        /// </para>
        /// </remarks>
        ///
        /// <seealso cref="IsZipFile(string, bool)"/>
        ///
        /// <param name="stream">The stream to check.</param>
        /// <param name="testExtract">true if the caller wants to extract each entry.</param>
        /// <returns>true if the stream contains a valid zip archive.</returns>
        public static bool IsZipFile(Stream stream, bool testExtract)
        {
            if (stream == null)
                throw new ArgumentNullException("stream");

            bool result = false;
            try
            {
                if (!stream.CanRead) return false;

                var bitBucket = Stream.Null;

                using (ZipFile zip1 = ZipFile.Read(stream, null, null, null))
                {
                    if (testExtract)
                    {
                        foreach (var e in zip1)
                        {
                            if (!e.IsDirectory)
                            {
                                e.Extract(bitBucket);
                            }
                        }
                    }
                }
                result = true;
            }
            catch (IOException) { }
            catch (ZipException) { }
            return result;
        }




    }

}