VB.NET

Streaming Compression

See more Compression Examples

Compress and decompress using a stream. VB.NET

Dim success As Boolean = False

' This example assumes the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim fac As New Chilkat.FileAccess
Dim compress As New Chilkat.Compression
compress.Algorithm = "deflate"

Dim streamC As New Chilkat.Stream

' This example sets the source and sink of the stream to files.
' A stream can have use other streams as a source or sink,
' or the application can itself be the source/sink by directly
' reading or writing a stream.  (See below for an example of this..)
streamC.SourceFile = "qa_data/hamlet.xml"
streamC.SinkFile = "qa_output/hamlet_compressed.dat"

' Compress from source to sink.
success = compress.CompressStream(streamC)
If (success <> True) Then
    Debug.WriteLine(compress.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("File-to-file deflate compression successful.")
' Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
' the size of the file as a string, then convert to an integer value.
Debug.WriteLine("Original size = " & fac.FileSize(streamC.SourceFile))
Debug.WriteLine("Compressed size = " & fac.FileSize(streamC.SinkFile))

' Now do file-to-file decompression
Dim streamD As New Chilkat.Stream
streamD.SourceFile = "qa_output/hamlet_compressed.dat"
streamD.SinkFile = "qa_output/hamlet_restored.xml"

' Decompress from source to sink.
success = compress.DecompressStream(streamD)
If (success <> True) Then
    Debug.WriteLine(compress.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("File-to-file deflate decompression successful.")

' Let's double-check to see that the files are equal in size and content:

Dim bFilesEqual As Boolean = fac.FileContentsEqual(streamC.SourceFile,streamD.SinkFile)
If (bFilesEqual <> True) Then
    Debug.WriteLine("The output file is not equal to the input file!")
Else
    Debug.WriteLine("The file was successfully compressed and decompressed.")
End If


' ---------------------------------------------------------------------
' Now let's decompress again, but this time w/ the application reading
' the decompressed data directly from a stream.
Dim streamA As New Chilkat.Stream

streamA.SourceFile = "qa_output/hamlet_compressed.dat"

' Start decompressing in a background thread.
Dim task As Chilkat.Task = compress.DecompressStreamAsync(streamA)
success = task.Run()

' Read decompressed data from streamA:
Dim decompressedText As String
While (streamA.EndOfStream <> True)
    If (streamA.DataAvailable = True) Then
        decompressedText = streamA.ReadString()
        Debug.WriteLine(decompressedText)
    End If

End While

' Let's make sure the background task finished and that the decompress was successful.
' It should already be the case that the task is finished.
While (task.Finished <> True)
    task.SleepMs(20)
End While

' The decompressor may have finished, but it is possible that data
' remains to be flushed.  
If (streamA.DataAvailable = True) Then
    decompressedText = streamA.ReadString()
    Debug.WriteLine(decompressedText)
End If


' Did streamA succeed in reading the entire file?
If (task.TaskSuccess <> True) Then
    Debug.WriteLine("async decompress failed:")
    Debug.WriteLine(task.ResultErrorText)
    success = False
End If


Debug.WriteLine("The async decompress was successful.")