[problema]zipstorer traducida a vb.net

[_katze_]

hola a todos traduci de c-sharp una clase de compresion zip a vb.net por lo que asi la necesito se las paso pero tengo un problema al usarla en un procedimiento que se llama addstream para que busquen y quisiera saber porque me da ese error siendo que c-shar funciona a la perfeccion gracias..luego de arreglarla pueden usarla todos

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Imports System.Collections.Generic
Imports System.Text
Imports System.IO.Compression
Imports System.IO
Namespace Compression
    ''' <summary>
    ''' Unique class for compression/decompression file. Represents a Zip file.
    ''' </summary>
    Public Class ZipStorer
        Implements IDisposable
        ''' <summary>
        ''' Compression method enumeration
        ''' </summary>
        Public Enum Compression As UShort
            ''' <summary>Uncompressed storage</summary>
            Store = 0
            ''' <summary>Deflate compression method</summary>
            Deflate = 8
        End Enum

        ''' <summary>
        ''' Represents an entry in Zip file directory
        ''' </summary>
        Public Structure ZipFileEntry
            ''' <summary>Compression method</summary>
            Public Method As Compression
            ''' <summary>Full path and filename as stored in Zip</summary>
            Public FilenameInZip As String
            ''' <summary>Original file size</summary>
            Public FileSize As UInteger
            ''' <summary>Compressed file size</summary>
            Public CompressedSize As UInteger
            ''' <summary>Offset of header information inside Zip storage</summary>
            Public HeaderOffset As UInteger
            ''' <summary>Offset of file inside Zip storage</summary>
            Public FileOffset As UInteger
            ''' <summary>Size of header information</summary>
            Public HeaderSize As UInteger
            ''' <summary>32-bit checksum of entire file</summary>
            Public Crc32 As UInteger
            ''' <summary>Last modification time of file</summary>
            Public ModifyTime As DateTime
            ''' <summary>User comment for file</summary>
            Public Comment As String
            ''' <summary>True if UTF8 encoding for filename and comments, false if default (CP 437)</summary>
            Public EncodeUTF8 As Boolean

            ''' <summary>Overriden method</summary>
            ''' <returns>Filename in Zip</returns>
            Public Overrides Function ToString() As String
                Return Me.FilenameInZip
            End Function
        End Structure

#Region "Public fields"
        ''' <summary>True if UTF8 encoding for filename and comments, false if default (CP 437)</summary>
        Public EncodeUTF8 As Boolean = False
        ''' <summary>Force deflate algotithm even if it inflates the stored file. Off by default.</summary>
        Public ForceDeflating As Boolean = False
#End Region

#Region "Private fields"
        ' List of files to store
        Private Files As New List(Of ZipFileEntry)()
        ' Filename of storage file
        Private FileName As String
        ' Stream object of storage file
        Private ZipFileStream As Stream

        ' General comment
        Private Comment As String = ""
        ' Central dir image
        Private CentralDirImage As Byte() = Nothing
        ' Existing files in zip
        Private ExistingFiles As UShort = 0
        ' File access for Open method
        Private Access As FileAccess
        ' Static CRC32 Table
        Private Shared CrcTable As UInt32() = Nothing
        ' Default filename encoder
        Private Shared DefaultEncoding As Encoding = Encoding.GetEncoding(437)
#End Region

#Region "Public methods"
        ' Static constructor. Just invoked once in order to create the CRC32 lookup table.
        Shared Sub New()
            ' Generate CRC32 table
            CrcTable = New UInt32(255) {}
            For i As Integer = 0 To CrcTable.Length - 1
                Dim c As UInt32 = CType(i, UInt32)
                For j As Integer = 0 To 7
                    If Not (c And 1) = 0 Then
                        c = 3988292384UI Xor (c >> 1)
                    Else
                        c >>= 1
                    End If
                Next

                CrcTable(i) = c
            Next

        End Sub
        ''' <summary>
        ''' Method to create a new storage file
        ''' </summary>
        ''' <param name="_filename">Full path of Zip file to create</param>
        ''' <param name="_comment">General comment for Zip file</param>
        ''' <returns>A valid ZipStorer object</returns>
        Public Function Create(ByVal _filename As String, ByVal _comment As String) As ZipStorer
            Dim file As New FileStream(_filename, FileMode.Create, FileAccess.ReadWrite)

            Dim stream As Stream = file

            Dim zip As ZipStorer = Create(stream, _comment)
            zip.Comment = _comment
            zip.FileName = _filename

            Return zip
        End Function
        ''' <summary>
        ''' Method to create a new zip storage in a stream
        ''' </summary>
        ''' <param name="_stream"></param>
        ''' <param name="_comment"></param>
        ''' <returns>A valid ZipStorer object</returns>
        Public Function Create(ByVal _stream As Stream, ByVal _comment As String) As ZipStorer
            Dim zip As New ZipStorer()
            zip.Comment = _comment
            zip.ZipFileStream = _stream
            zip.Access = FileAccess.Write

            Return zip
        End Function
        ''' <summary>
        ''' Method to open an existing storage file
        ''' </summary>
        ''' <param name="_filename">Full path of Zip file to open</param>
        ''' <param name="_access">File access mode as used in FileStream constructor</param>
        ''' <returns>A valid ZipStorer object</returns>
        Public Shared Function Open(ByVal _filename As String, ByVal _access As FileAccess) As ZipStorer
            Dim stream As Stream = DirectCast(New FileStream(_filename, FileMode.Open, If(_access = FileAccess.Read, FileAccess.Read, FileAccess.ReadWrite)), Stream)

            Dim zip As ZipStorer = Open(stream, _access)
            zip.FileName = _filename

            Return zip
        End Function
        ''' <summary>
        ''' Method to open an existing storage from stream
        ''' </summary>
        ''' <param name="_stream">Already opened stream with zip contents</param>
        ''' <param name="_access">File access mode for stream operations</param>
        ''' <returns>A valid ZipStorer object</returns>
        Public Shared Function Open(ByVal _stream As Stream, ByVal _access As FileAccess) As ZipStorer
            If Not _stream.CanSeek AndAlso _access <> FileAccess.Read Then
                Throw New InvalidOperationException("Stream cannot seek")
            End If

            Dim zip As New ZipStorer()
            'zip.FileName = _filename;
            zip.ZipFileStream = _stream
            zip.Access = _access
           
            If zip.ReadFileInfo() Then
                Return zip
            End If

            Throw New InvalidDataException()
        End Function
        ''' <summary>
        ''' Add full contents of a file into the Zip storage
        ''' </summary>
        ''' <param name="_method">Compression method</param>
        ''' <param name="_pathname">Full path of file to add to Zip storage</param>
        ''' <param name="_filenameInZip">Filename and path as desired in Zip directory</param>
        ''' <param name="_comment">Comment for stored file</param>       
        Public Sub AddFile(ByVal _method As Compression, ByVal _pathname As String, ByVal _filenameInZip As String, ByVal _comment As String)
            If Access = FileAccess.Read Then
                Throw New InvalidOperationException("Writing is not alowed")
            End If

            Dim stream As New FileStream(_pathname, FileMode.Open, FileAccess.Read)
            AddStream(_method, _filenameInZip, stream, File.GetLastWriteTime(_pathname), _comment)
            stream.Close()
        End Sub
        ''' <summary>
        ''' Add full contents of a stream into the Zip storage
        ''' </summary>
        ''' <param name="_method">Compression method</param>
        ''' <param name="_filenameInZip">Filename and path as desired in Zip directory</param>
        ''' <param name="_source">Stream object containing the data to store in Zip</param>
        ''' <param name="_modTime">Modification time of the data to store</param>
        ''' <param name="_comment">Comment for stored file</param>
        Public Sub AddStream(ByVal _method As Compression, ByVal _filenameInZip As String, ByVal _source As Stream, ByVal _modTime As DateTime, ByVal _comment As String)
            If Access = FileAccess.Read Then
                Throw New InvalidOperationException("Writing is not alowed")
            End If

            Dim offset As Long
            If Me.Files.Count = 0 Then
                offset = 0
            Else
                Dim last As ZipFileEntry = Me.Files(Me.Files.Count - 1)
                offset = last.HeaderOffset + last.HeaderSize
            End If

            ' Prepare the fileinfo
            Dim zfe As New ZipFileEntry()
            zfe.Method = _method
            zfe.EncodeUTF8 = Me.EncodeUTF8
            zfe.FilenameInZip = NormalizedFilename(_filenameInZip)
            zfe.Comment = (If(_comment Is Nothing, "", _comment))

            ' Even though we write the header now, it will have to be rewritten, since we don't know compressed size or crc.
            zfe.Crc32 = 0
            ' to be updated later

            zfe.HeaderOffset = CUInt(ZipFileStream.Position)
            ' offset within file of the start of this local record
            zfe.ModifyTime = _modTime

            ' Write local header
            WriteLocalHeader(zfe)
            zfe.FileOffset = CUInt(ZipFileStream.Position)

            ' Write file to zip (store)
            Store(zfe, _source)
            _source.Close()

            Me.UpdateCrcAndSizes(zfe)

            Files.Add(zfe)
        End Sub
        ''' <summary>
        ''' Updates central directory (if pertinent) and close the Zip storage
        ''' </summary>
        ''' <remarks>This is a required step, unless automatic dispose is used</remarks>
        Public Sub Close()
            If Me.Access <> FileAccess.Read Then
                Dim centralOffset As UInteger = CUInt(Me.ZipFileStream.Position)
                Dim centralSize As UInteger = 0

                If Me.CentralDirImage IsNot Nothing Then
                    Me.ZipFileStream.Write(CentralDirImage, 0, CentralDirImage.Length)
                End If

                For i As Integer = 0 To Files.Count - 1
                    Dim pos As Long = Me.ZipFileStream.Position
                    Me.WriteCentralDirRecord(Files(i))
                    centralSize += CUInt(Me.ZipFileStream.Position - pos)
                Next

                If Me.CentralDirImage IsNot Nothing Then
                    Me.WriteEndRecord(centralSize + CUInt(CentralDirImage.Length), centralOffset)
                Else
                    Me.WriteEndRecord(centralSize, centralOffset)
                End If
            End If

            If Me.ZipFileStream IsNot Nothing Then
                Me.ZipFileStream.Flush()
                Me.ZipFileStream.Dispose()
                Me.ZipFileStream = Nothing
            End If
        End Sub
        ''' <summary>
        ''' Read all the file records in the central directory
        ''' </summary>
        ''' <returns>List of all entries in directory</returns>
        Public Function ReadCentralDir() As List(Of ZipFileEntry)
            If Me.CentralDirImage Is Nothing Then
                Throw New InvalidOperationException("Central directory currently does not exist")
            End If

            Dim result As New List(Of ZipFileEntry)()

            Dim pointer As Integer = 0
            While pointer < Me.CentralDirImage.Length
                Dim signature As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer)
                If signature <> &H2014B50 Then
                    Exit While
                End If

                Dim encodeUTF8 As Boolean = (BitConverter.ToUInt16(CentralDirImage, pointer + 8) And &H800) <> 0
                Dim method As UShort = BitConverter.ToUInt16(CentralDirImage, pointer + 10)
                Dim modifyTime As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer + 12)
                Dim crc32 As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer + 16)
                Dim comprSize As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer + 20)
                Dim fileSize As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer + 24)
                Dim filenameSize As UShort = BitConverter.ToUInt16(CentralDirImage, pointer + 28)
                Dim extraSize As UShort = BitConverter.ToUInt16(CentralDirImage, pointer + 30)
                Dim commentSize As UShort = BitConverter.ToUInt16(CentralDirImage, pointer + 32)
                Dim headerOffset As UInteger = BitConverter.ToUInt32(CentralDirImage, pointer + 42)
                Dim headerSize As UInteger = CUInt(46 + filenameSize + extraSize + commentSize)

                Dim encoder As Encoding = If(encodeUTF8, Encoding.UTF8, DefaultEncoding)

                Dim zfe As New ZipFileEntry()
                zfe.Method = CType(method, Compression)
                zfe.FilenameInZip = encoder.GetString(CentralDirImage, pointer + 46, filenameSize)
                zfe.FileOffset = GetFileOffset(headerOffset)
                zfe.FileSize = fileSize
                zfe.CompressedSize = comprSize
                zfe.HeaderOffset = headerOffset
                zfe.HeaderSize = headerSize
                zfe.Crc32 = crc32
                zfe.ModifyTime = DosTimeToDateTime(modifyTime)
                If commentSize > 0 Then
                    zfe.Comment = encoder.GetString(CentralDirImage, pointer + 46 + filenameSize + extraSize, commentSize)
                End If

                result.Add(zfe)
                pointer += (46 + filenameSize + extraSize + commentSize)
            End While

            Return result
        End Function
        ''' <summary>
        ''' Copy the contents of a stored file into a physical file
        ''' </summary>
        ''' <param name="_zfe">Entry information of file to extract</param>
        ''' <param name="_filename">Name of file to store uncompressed data</param>
        ''' <returns>True if success, false if not.</returns>
        ''' <remarks>Unique compression methods are Store and Deflate</remarks>
        Public Function ExtractFile(ByVal _zfe As ZipFileEntry, ByVal _filename As String) As Boolean
            ' Make sure the parent directory exist
            Dim paths As String = Path.GetDirectoryName(_filename)

            If Not Directory.Exists(paths) Then
                Directory.CreateDirectory(paths)
            End If
            ' Check it is directory. If so, do nothing
            If Directory.Exists(_filename) Then
                Return True
            End If

            Dim output As Stream = New FileStream(_filename, FileMode.Create, FileAccess.Write)
            Dim result As Boolean = ExtractFile(_zfe, output)
            If result Then
                output.Close()
            End If

            File.SetCreationTime(_filename, _zfe.ModifyTime)
            File.SetLastWriteTime(_filename, _zfe.ModifyTime)

            Return result
        End Function
        ''' <summary>
        ''' Copy the contents of a stored file into an opened stream
        ''' </summary>
        ''' <param name="_zfe">Entry information of file to extract</param>
        ''' <param name="_stream">Stream to store the uncompressed data</param>
        ''' <returns>True if success, false if not.</returns>
        ''' <remarks>Unique compression methods are Store and Deflate</remarks>
        Public Function ExtractFile(ByVal _zfe As ZipFileEntry, ByVal _stream As Stream) As Boolean
            If Not _stream.CanWrite Then
                Throw New InvalidOperationException("Stream cannot be written")
            End If

            ' check signature
            Dim signature As Byte() = New Byte(3) {}
            Me.ZipFileStream.Seek(_zfe.HeaderOffset, SeekOrigin.Begin)
            Me.ZipFileStream.Read(signature, 0, 4)
            If BitConverter.ToUInt32(signature, 0) <> &H4034B50 Then
                Return False
            End If

            ' Select input stream for inflating or just reading
            Dim inStream As Stream
            If _zfe.Method = Compression.Store Then
                inStream = Me.ZipFileStream
            ElseIf _zfe.Method = Compression.Deflate Then
                inStream = New DeflateStream(Me.ZipFileStream, CompressionMode.Decompress, True)
            Else
                Return False
            End If

            ' Buffered copy
            Dim buffer As Byte() = New Byte(16383) {}
            Me.ZipFileStream.Seek(_zfe.FileOffset, SeekOrigin.Begin)
            Dim bytesPending As UInteger = _zfe.FileSize
            While bytesPending > 0
                Dim bytesRead As Integer = inStream.Read(buffer, 0, CInt(Math.Min(bytesPending, buffer.Length)))
                _stream.Write(buffer, 0, bytesRead)
                bytesPending -= CUInt(bytesRead)
            End While
            _stream.Flush()

            If _zfe.Method = Compression.Deflate Then
                inStream.Dispose()
            End If
            Return True
        End Function
        ''' <summary>
        ''' Removes one of many files in storage. It creates a new Zip file.
        ''' </summary>
        ''' <param name="_zip">Reference to the current Zip object</param>
        ''' <param name="_zfes">List of Entries to remove from storage</param>
        ''' <returns>True if success, false if not</returns>
        ''' <remarks>This method only works for storage of type FileStream</remarks>
        Public Function RemoveEntries(ByRef _zip As ZipStorer, ByVal _zfes As List(Of ZipFileEntry)) As Boolean
            If Not (TypeOf _zip.ZipFileStream Is FileStream) Then
                Throw New InvalidOperationException("RemoveEntries is allowed just over streams of type FileStream")
            End If


            'Get full list of entries
            Dim fullList As List(Of ZipFileEntry) = _zip.ReadCentralDir()

            'In order to delete we need to create a copy of the zip file excluding the selected items
            Dim tempZipName As String = Path.GetTempFileName()
            Dim tempEntryName As String = Path.GetTempFileName()

            Try
                Dim tempZip As ZipStorer = Create(tempZipName, String.Empty)

                For Each zfe As ZipFileEntry In fullList
                    If Not _zfes.Contains(zfe) Then
                        If _zip.ExtractFile(zfe, tempEntryName) Then
                            tempZip.AddFile(zfe.Method, tempEntryName, zfe.FilenameInZip, zfe.Comment)
                        End If
                    End If
                Next
                _zip.Close()
                tempZip.Close()

                File.Delete(_zip.FileName)
                File.Move(tempZipName, _zip.FileName)

                _zip = ZipStorer.Open(_zip.FileName, _zip.Access)
            Catch
                Return False
            Finally
                If File.Exists(tempZipName) Then
                    File.Delete(tempZipName)
                End If
                If File.Exists(tempEntryName) Then
                    File.Delete(tempEntryName)
                End If
            End Try
            Return True
        End Function
#End Region

#Region "Private methods"
        ' Calculate the file offset by reading the corresponding local header
        Private Function GetFileOffset(ByVal _headerOffset As UInteger) As UInteger
            Dim buffer As Byte() = New Byte(1) {}

            Me.ZipFileStream.Seek(_headerOffset + 26, SeekOrigin.Begin)
            Me.ZipFileStream.Read(buffer, 0, 2)
            Dim filenameSize As UShort = BitConverter.ToUInt16(buffer, 0)
            Me.ZipFileStream.Read(buffer, 0, 2)
            Dim extraSize As UShort = BitConverter.ToUInt16(buffer, 0)

            Return CUInt(30 + filenameSize + extraSize + _headerOffset)
        End Function
        ' Local file header:
        '            local file header signature     4 bytes  (0x04034b50)
        '            version needed to extract       2 bytes
        '            general purpose bit flag        2 bytes
        '            compression method              2 bytes
        '            last mod file time              2 bytes
        '            last mod file date              2 bytes
        '            crc-32                          4 bytes
        '            compressed size                 4 bytes
        '            uncompressed size               4 bytes
        '            filename length                 2 bytes
        '            extra field length              2 bytes
        '
        '            filename (variable size)
        '            extra field (variable size)
        '       

        Private Sub WriteLocalHeader(ByRef _zfe As ZipFileEntry)
            Dim pos As Long = Me.ZipFileStream.Position
            Dim encoder As Encoding = If(_zfe.EncodeUTF8, Encoding.UTF8, DefaultEncoding)
            Dim encodedFilename As Byte() = encoder.GetBytes(_zfe.FilenameInZip)

            Me.ZipFileStream.Write(New Byte() {80, 75, 3, 4, 20, 0}, 0, 6)
            ' No extra header
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(If(_zfe.EncodeUTF8, &H800, 0))), 0, 2)
            ' filename and comment encoding
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(_zfe.Method)), 0, 2)
            ' zipping method
            Me.ZipFileStream.Write(BitConverter.GetBytes(DateTimeToDosTime(_zfe.ModifyTime)), 0, 4)
            ' zipping date and time
            Me.ZipFileStream.Write(New Byte() {0, 0, 0, 0, 0, 0, _
             0, 0, 0, 0, 0, 0}, 0, 12)
            ' unused CRC, un/compressed size, updated later
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(encodedFilename.Length)), 0, 2)
            ' filename length
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(0)), 0, 2)
            ' extra length
            Me.ZipFileStream.Write(encodedFilename, 0, encodedFilename.Length)
            _zfe.HeaderSize = CUInt(Me.ZipFileStream.Position - pos)
        End Sub
        ' Central directory's File header:
        '            central file header signature   4 bytes  (0x02014b50)
        '            version made by                 2 bytes
        '            version needed to extract       2 bytes
        '            general purpose bit flag        2 bytes
        '            compression method              2 bytes
        '            last mod file time              2 bytes
        '            last mod file date              2 bytes
        '            crc-32                          4 bytes
        '            compressed size                 4 bytes
        '            uncompressed size               4 bytes
        '            filename length                 2 bytes
        '            extra field length              2 bytes
        '            file comment length             2 bytes
        '            disk number start               2 bytes
        '            internal file attributes        2 bytes
        '            external file attributes        4 bytes
        '            relative offset of local header 4 bytes
        '
        '            filename (variable size)
        '            extra field (variable size)
        '            file comment (variable size)
        '       

        Private Sub WriteCentralDirRecord(ByVal _zfe As ZipFileEntry)
            Dim encoder As Encoding = If(_zfe.EncodeUTF8, Encoding.UTF8, DefaultEncoding)
            Dim encodedFilename As Byte() = encoder.GetBytes(_zfe.FilenameInZip)
            Dim encodedComment As Byte() = encoder.GetBytes(_zfe.Comment)

            Me.ZipFileStream.Write(New Byte() {80, 75, 1, 2, 23, &HB, _
             20, 0}, 0, 8)
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(If(_zfe.EncodeUTF8, &H800, 0))), 0, 2)
            ' filename and comment encoding
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(_zfe.Method)), 0, 2)
            ' zipping method
            Me.ZipFileStream.Write(BitConverter.GetBytes(DateTimeToDosTime(_zfe.ModifyTime)), 0, 4)
            ' zipping date and time
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.Crc32), 0, 4)
            ' file CRC
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.CompressedSize), 0, 4)
            ' compressed file size
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.FileSize), 0, 4)
            ' uncompressed file size
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(encodedFilename.Length)), 0, 2)
            ' Filename in zip
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(0)), 0, 2)
            ' extra length
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(encodedComment.Length)), 0, 2)

            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(0)), 0, 2)
            ' disk=0
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(0)), 0, 2)
            ' file type: binary
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(0)), 0, 2)
            ' Internal file attributes
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(&H8100)), 0, 2)
            ' External file attributes (normal/readable)
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.HeaderOffset), 0, 4)
            ' Offset of header
            Me.ZipFileStream.Write(encodedFilename, 0, encodedFilename.Length)
            Me.ZipFileStream.Write(encodedComment, 0, encodedComment.Length)
        End Sub
        ' End of central dir record:
        '            end of central dir signature    4 bytes  (0x06054b50)
        '            number of this disk             2 bytes
        '            number of the disk with the
        '            start of the central directory  2 bytes
        '            total number of entries in
        '            the central dir on this disk    2 bytes
        '            total number of entries in
        '            the central dir                 2 bytes
        '            size of the central directory   4 bytes
        '            offset of start of central
        '            directory with respect to
        '            the starting disk number        4 bytes
        '            zipfile comment length          2 bytes
        '            zipfile comment (variable size)
        '       

        Private Sub WriteEndRecord(ByVal _size As UInteger, ByVal _offset As UInteger)
            Dim encoder As Encoding = If(Me.EncodeUTF8, Encoding.UTF8, DefaultEncoding)
            Dim encodedComment As Byte() = encoder.GetBytes(Me.Comment)

            Me.ZipFileStream.Write(New Byte() {80, 75, 5, 6, 0, 0, _
             0, 0}, 0, 8)
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(Files.Count) + ExistingFiles), 0, 2)
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(Files.Count) + ExistingFiles), 0, 2)
            Me.ZipFileStream.Write(BitConverter.GetBytes(_size), 0, 4)
            Me.ZipFileStream.Write(BitConverter.GetBytes(_offset), 0, 4)
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(encodedComment.Length)), 0, 2)
            Me.ZipFileStream.Write(encodedComment, 0, encodedComment.Length)
        End Sub
        ' Copies all source file into storage file
        Private Sub Store(ByRef _zfe As ZipFileEntry, ByVal _source As Stream)
            Dim buffer As Byte() = New Byte(16383) {}
            Dim bytesRead As Integer
            Dim totalRead As UInteger = 0
            Dim outStream As Stream

            Dim posStart As Long = Me.ZipFileStream.Position
            Dim sourceStart As Long = _source.Position

            If _zfe.Method = Compression.Store Then
                outStream = Me.ZipFileStream
            Else
                outStream = New DeflateStream(Me.ZipFileStream, CompressionMode.Compress, True)
            End If

            _zfe.Crc32 = 0 Xor &HFFFFFFFFUI

            Do
                bytesRead = _source.Read(buffer, 0, buffer.Length)
                totalRead += CUInt(bytesRead)
                If bytesRead > 0 Then
                    outStream.Write(buffer, 0, bytesRead)

                    For i As UInteger = 0 To bytesRead - 1
                        _zfe.Crc32 = ZipStorer.CrcTable((_zfe.Crc32 Xor buffer(i)) And &HFF) Xor (_zfe.Crc32 >> 8)
                    Next
                End If
            Loop While bytesRead = buffer.Length
            outStream.Flush()

            If _zfe.Method = Compression.Deflate Then
                outStream.Dispose()
            End If

            _zfe.Crc32 = _zfe.Crc32 Xor &HFFFFFFFFUI
            _zfe.FileSize = totalRead
            _zfe.CompressedSize = CUInt(Me.ZipFileStream.Position - posStart)

            ' Verify for real compression
            If _zfe.Method = Compression.Deflate AndAlso Not Me.ForceDeflating AndAlso _source.CanSeek AndAlso _zfe.CompressedSize > _zfe.FileSize Then
                ' Start operation again with Store algorithm
                _zfe.Method = Compression.Store
                Me.ZipFileStream.Position = posStart
                Me.ZipFileStream.SetLength(posStart)
                _source.Position = sourceStart
                Me.Store(_zfe, _source)
            End If
        End Sub
        ' DOS Date and time:
        '            MS-DOS date. The date is a packed value with the following format. Bits Description
        '                0-4 Day of the month (1–31)
        '                5-8 Month (1 = January, 2 = February, and so on)
        '                9-15 Year offset from 1980 (add 1980 to get actual year)
        '            MS-DOS time. The time is a packed value with the following format. Bits Description
        '                0-4 Second divided by 2
        '                5-10 Minute (0–59)
        '                11-15 Hour (0–23 on a 24-hour clock)
        '       

        Private Function DateTimeToDosTime(ByVal _dt As DateTime) As UInteger
            Return CUInt((_dt.Second \ 2) Or (_dt.Minute << 5) Or (_dt.Hour << 11) Or (_dt.Day << 16) Or (_dt.Month << 21) Or ((_dt.Year - 1980) << 25))
        End Function
        Private Function DosTimeToDateTime(ByVal _dt As UInteger) As DateTime
            Return New DateTime(CInt(_dt >> 25) + 1980, CInt(_dt >> 21) And 15, CInt(_dt >> 16) And 31, CInt(_dt >> 11) And 31, CInt(_dt >> 5) And 63, CInt(_dt And 31) * 2)
        End Function

        ' CRC32 algorithm
        '          The 'magic number' for the CRC is 0xdebb20e3. 
        '          The proper CRC pre and post conditioning
        '          is used, meaning that the CRC register is
        '          pre-conditioned with all ones (a starting value
        '          of 0xffffffff) and the value is post-conditioned by
        '          taking the one's complement of the CRC residual.
        '          If bit 3 of the general purpose flag is set, this
        '          field is set to zero in the local header and the correct
        '          value is put in the data descriptor and in the central
        '          directory.
        '       

        Private Sub UpdateCrcAndSizes(ByRef _zfe As ZipFileEntry)
            Dim lastPos As Long = Me.ZipFileStream.Position
            ' remember position
            Me.ZipFileStream.Position = _zfe.HeaderOffset + 8
            Me.ZipFileStream.Write(BitConverter.GetBytes(CUShort(_zfe.Method)), 0, 2)
            ' zipping method
            Me.ZipFileStream.Position = _zfe.HeaderOffset + 14
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.Crc32), 0, 4)
            ' Update CRC
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.CompressedSize), 0, 4)
            ' Compressed size
            Me.ZipFileStream.Write(BitConverter.GetBytes(_zfe.FileSize), 0, 4)
            ' Uncompressed size
            Me.ZipFileStream.Position = lastPos
            ' restore position
        End Sub
        ' Replaces backslashes with slashes to store in zip header
        Private Function NormalizedFilename(ByVal _filename As String) As String
            Dim filename As String = _filename.Replace("\"c, "/"c)

            Dim pos As Integer = filename.IndexOf(":"c)
            If pos >= 0 Then
                filename = filename.Remove(0, pos + 1)
            End If

            Return filename.Trim("/"c)
        End Function
        ' Reads the end-of-central-directory record
        Private Function ReadFileInfo() As Boolean
            If Me.ZipFileStream.Length < 22 Then
                Return False
            End If

            Try
                Me.ZipFileStream.Seek(-17, SeekOrigin.[End])
                Dim br As New BinaryReader(Me.ZipFileStream)
                Do
                    Me.ZipFileStream.Seek(-5, SeekOrigin.Current)
                    Dim sig As UInt32 = br.ReadUInt32()
                    If sig = &H6054B50 Then
                        Me.ZipFileStream.Seek(6, SeekOrigin.Current)

                        Dim entries As UInt16 = br.ReadUInt16()
                        Dim centralSize As Int32 = br.ReadInt32()
                        Dim centralDirOffset As UInt32 = br.ReadUInt32()
                        Dim commentSize As UInt16 = br.ReadUInt16()

                        ' check if comment field is the very last data in file
                        If Me.ZipFileStream.Position + commentSize <> Me.ZipFileStream.Length Then
                            Return False
                        End If

                        ' Copy entire central directory to a memory buffer
                        Me.ExistingFiles = entries
                        Me.CentralDirImage = New Byte(centralSize - 1) {}
                        Me.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin)
                        Me.ZipFileStream.Read(Me.CentralDirImage, 0, centralSize)

                        ' Leave the pointer at the begining of central dir, to append new files
                        Me.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin)
                        Return True
                    End If
                Loop While Me.ZipFileStream.Position > 0
            Catch
            End Try

            Return False
        End Function
#End Region

#Region "IDisposable Members"
        ''' <summary>
        ''' Closes the Zip file stream
        ''' </summary>
        Public Sub Dispose() Implements IDisposable.Dispose
            Me.Close()
        End Sub
#End Region
    End Class
End Namespace