Recipe 16.10. Complete Listing of the Compress.vb Module


Sample code folder: Chapter 16\Compression

This recipe contains the full code for the Compress module described in Recipes 16.6 and 16.7:

 Imports System Imports System.Text Imports System.IO Imports System.IO.Compression Module Compress    Public Function StringCompress( _          ByVal originalText As String) As Byte( )       ' ----- Generate a compressed version of a string.       '       First, convert the string to a byte array.       Dim workBytes( ) As Byte = _          Encoding.UTF8.GetBytes(originalText)       ' ----- Bytes will flow through a memory stream.       Dim memoryStream As New MemoryStream( )       ' ----- Use the newly created memory stream for the       '       compressed data.       Dim zipStream As New GZipStream(memoryStream, _          CompressionMode.Compress, True)       zipStream.Write(workBytes, 0, workBytes.Length)       zipStream.Flush( )       ' ----- Close the compression stream.       zipStream.Close( )       ' ----- Return the compressed bytes.       Return memoryStream.ToArray    End Function    Public Function BytesDecompress( _          ByVal compressed( ) As Byte) As String       ' ----- Uncompress a previously compressed string.       '       Extract the length for the decompressed string.       Dim lastFour(3) As Byte       Array.Copy(compressed, compressed.Length - 4, _          lastFour, 0, 4)       Dim bufferLength As Integer = _          BitConverter.ToInt32(lastFour, 0)       ' ----- Create an uncompressed bytes buffer.       Dim buffer(bufferLength - 1) As Byte       ' ----- Bytes will flow through a memory stream.       Dim memoryStream As New MemoryStream(compressed)       ' ----- Create the decompression stream.       Dim decompressedStream As New GZipStream( _          memoryStream, CompressionMode.Decompress, True)       ' ----- Read and decompress the data into the buffer.       decompressedStream.Read(buffer, 0, bufferLength)       ' ----- Convert the bytes to a string.       Return Encoding.UTF8.GetString(buffer)    End Function    Public Sub FileCompress(ByVal sourceFile As String, _          ByVal destinationFile As String)       ' ----- Decompress a previously compressed string.       '       First, create the input file stream.       Dim sourceStream As New FileStream( _          sourceFile, FileMode.Open, FileAccess.Read)       ' ----- Create the output file stream.       Dim destinationStream As New FileStream( _       destinationFile, FileMode.Create, FileAccess.Write)       ' ----- Bytes will be processed by a compression       '       stream.       Dim compressedStream As New GZipStream( _          destinationStream, CompressionMode.Compress, True)       ' ----- Process bytes from one file into the other.       Const BlockSize As Integer = 4096       Dim buffer(BlockSize) As Byte       Dim bytesRead As Integer       Do          bytesRead = sourceStream.Read(buffer, 0, BlockSize)          If (bytesRead = 0) Then Exit Do          compressedStream.Write(buffer, 0, bytesRead)       Loop       ' ----- Close all the streams.       sourceStream.Close( )       compressedStream.Close( )       destinationStream.Close( )    End Sub    Public Sub FileDecompress(ByVal sourceFile As String, _          ByVal destinationFile As String)       ' ----- Compress the entire contents of a file, and       '       store it in a new file. First, get the files       '       as streams.       Dim sourceStream As New FileStream( _          sourceFile, FileMode.Open, FileAccess.Read)       Dim destinationStream As New FileStream( _          destinationFile, FileMode.Create, FileAccess.Write)       ' ----- Bytes will be processed through a       '       decompression stream.       Dim decompressedStream As New GZipStream( _          sourceStream, CompressionMode.Decompress, True)       ' ----- Process bytes from one file into the other.       Const BlockSize As Integer = 4096       Dim buffer(BlockSize) As Byte       Dim bytesRead As Integer       Do          bytesRead = decompressedStream.Read(buffer, _             0, BlockSize)          If (bytesRead = 0) Then Exit Do          destinationStream.Write(buffer, 0, bytesRead)       Loop       ' ----- Close all the streams.       sourceStream.Close( )       decompressedStream.Close( )       destinationStream.Close( )    End Sub End Module 




Visual Basic 2005 Cookbook(c) Solutions for VB 2005 Programmers
Visual Basic 2005 Cookbook: Solutions for VB 2005 Programmers (Cookbooks (OReilly))
ISBN: 0596101775
EAN: 2147483647
Year: 2006
Pages: 400

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