Compressing stream data

In This Topic

This topic demonstrates how to compress data that is read from a FileStream to a MemoryStream using the XceedCompressedStream class.

Although we are using a FileStream as our source and a MemoryStream as our destination, we could have also used any other type of stream. For example, we could have compressed data read from a MemoryStream to another MemoryStream or to a FileStream.

Basic steps

To compress data that is read from a stream, the following steps must be taken:

Create the source stream from which the data will be read. For the purposes of this example, our source stream will be a FileStream. But it can be any Stream object from any source as long as data can be read from it. No 'seek' or 'write' capabilities are needed.
Create the destination stream to which the compressed data will be written. For the purposes of this example, our destination stream will be a MemoryStream. It can be any Stream object for any destination as long as data can be written to it. No 'seek' or 'read' capabilities are needed.
Create a compressed stream object around the destination stream. For the purposes of this example we used the XceedCompressedStream class. However, we could have also used the GZipCompressedStream or the ZLibCompressedStream classes interchangibly. All the classes work the same. Only the parameters to the constructors change.
Read the uncompressed data from the source stream.
Write the data to the compressed stream object. Writing to the object compresses the data and, in turn, writes the compressed data to the destination stream.

Example

The following example demonstrates how to read data from a FileStream and compress it to a MemoryStream using the XceedCompressedStream class.

C#
VB.NET

using System.IO;

using Xceed.Compression;
using Xceed.Compression.Formats;

namespace FileSystemDocumentationExamples.CompressionComponent
{
  public class CompressXceedCompressedStreamExample
  {
    public void MyMainMethod()
    {
      /* Because Xceed.Compression.Formats is an optional assembly not automatically
         unlocked by Xceed Zip for .NET, we must explicitly set our license key to it
         before use or else an exception will be thrown. */
      Xceed.Compression.Formats.Licenser.LicenseKey = "<your Xceed Zip for .NET license key>";
    }

    public void Example()
    {
      /* Setup a destination data stream. This can be any Stream object for any destination as
         long as data can be written to it. No 'seek' or 'read' capabilities are needed. */
      MemoryStream destinationStream = new MemoryStream();

      /* Setup a source data stream. This can be any Stream object from any source as
         long as data can be read from it. No 'seek' or 'write' capabilities are needed. */
      using( FileStream sourceStream = new FileStream( @"D:\data.txt", FileMode.Open, FileAccess.Read, FileShare.Read ) )
      {
        /* Optional: the compression method and level can be specified. */
        CompressionMethod compressionMethod = CompressionMethod.Deflated;
        CompressionLevel compressionLevel = CompressionLevel.Normal;
        string password = String.Empty;

        // Optional: the data will be encrypted if a non-empty password is specified
        //password = "password";

        // Create a XceedCompressedStream that wraps around our destination stream
        using( XceedCompressedStream xceedCompressedStream = new XceedCompressedStream( destinationStream, compressionMethod, compressionLevel, false, password ) )
        {
          /* The XceedCompressedStream automatically closes the destination
             memory stream. So there is no need to declare the memory stream within a using
             statement or to call Close() once we are done with the stream.
            
             If you do not want the inner stream to be closed by the XceedCompressedStream,
             set its Transient property to true. */

          // Optional: Prevent XceedCompressedStream from closing 'destinationStream' automatically
          //xceedCompressedStream.Transient = true;

          int bytesRead;

          // Setup a 32K buffer
          byte[] buffer = new byte[ 32 * 1024 ];

          // Read from the source stream until there is no more data
          while( ( bytesRead = sourceStream.Read( buffer, 0, buffer.Length ) ) > 0 )
          {
            // Compress the data by writing into the compressed stream
            // Compressed data will be written into its InnerStream, in our case, 'destinationStream'
            xceedCompressedStream.Write( buffer, 0, bytesRead );
          }
        }
      }

      /* Optional: The MemoryStream's compressed data can be copied to a byte array, you can use
         MemoryStream.ToArray(). The method works even when the memory stream has been closed. */
      //byte[] compressedData = destinationStream.ToArray();
    }
  }
}

Imports System.IO

Imports Xceed.Compression
Imports Xceed.Compression.Formats

Namespace FileSystemDocumentationExamples.CompressionComponent
  Public Class CompressXceedCompressedStreamExample
    Public Sub MyMainMethod()
'       Because Xceed.Compression.Formats is an optional assembly not automatically
'         unlocked by Xceed Zip for .NET, we must explicitly set our license key to it
'         before use or else an exception will be thrown. 
      Xceed.Compression.Formats.Licenser.LicenseKey = "<your Xceed Zip for .NET license key>"
    End Sub

    Public Sub Example()
'       Setup a destination data stream. This can be any Stream object for any destination as
'         long as data can be written to it. No 'seek' or 'read' capabilities are needed. 
      Dim destinationStream As New MemoryStream()

'       Setup a source data stream. This can be any Stream object from any source as
'         long as data can be read from it. No 'seek' or 'write' capabilities are needed. 
      Using sourceStream As New FileStream("D:\data.txt", FileMode.Open, FileAccess.Read, FileShare.Read)
        ' Optional: the compression method and level can be specified. 
        Dim compressionMethod As CompressionMethod = CompressionMethod.Deflated
        Dim compressionLevel As CompressionLevel = CompressionLevel.Normal
        Dim password As String = String.Empty

        ' Optional: the data will be encrypted if a non-empty password is specified
        'password = "password";

        ' Create a XceedCompressedStream that wraps around our destination stream
        Using xceedCompressedStream As New XceedCompressedStream(destinationStream, compressionMethod, compressionLevel, False, password)
'           The XceedCompressedStream automatically closes the destination
'             memory stream. So there is no need to declare the memory stream within a using
'             statement or to call Close() once we are done with the stream.
'            
'             If you do not want the inner stream to be closed by the XceedCompressedStream,
'             set its Transient property to true. 

          ' Optional: Prevent XceedCompressedStream from closing 'destinationStream' automatically
          'xceedCompressedStream.Transient = true;

          Dim bytesRead As Integer

          ' Setup a 32K buffer
          Dim buffer(32 * 1024 - 1) As Byte

          ' Read from the source stream until there is no more data
          bytesRead = sourceStream.Read(buffer, 0, buffer.Length)
          Do While bytesRead > 0
            ' Compress the data by writing into the compressed stream
            ' Compressed data will be written into its InnerStream, in our case, 'destinationStream'
            xceedCompressedStream.Write(buffer, 0, bytesRead)
            bytesRead = sourceStream.Read(buffer, 0, buffer.Length)
          Loop
        End Using
      End Using

'       Optional: The MemoryStream's compressed data can be copied to a byte array, you can use
'         MemoryStream.ToArray(). The method works even when the memory stream has been closed. 
      'byte[] compressedData = destinationStream.ToArray();
    End Sub
  End Class
End Namespace

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