Visual Basic 6.0

Chunked Compression Using CompressBd2 with FirstChunk and LastChunk

See more Compression Examples

This example demonstrates how to compress data in multiple segments using the CompressBd2 method together with the FirstChunk and LastChunk properties. Instead of compressing all data in a single call, the input is divided into smaller chunks and processed sequentially, which is useful when handling streaming data or large inputs.

The example shows how to correctly mark the first, middle, and final chunks so that the compression stream is properly initialized and finalized. The compressed output is accumulated in a separate BinData object without modifying the input chunks. Finally, the example decompresses the combined result to verify that the original data is restored correctly.

This approach is ideal for scenarios where data is received incrementally, such as reading from a network stream, processing large files in parts, or handling real-time data feeds.

Visual Basic 6.0

Dim success As Long
success = 0

' This example assumes the Chilkat API has already been unlocked.
' See Global Unlock Sample for sample code.

Dim compress As New ChilkatCompression
compress.Algorithm = "zlib"

' This will accumulate the compressed output.
Dim bdOut As New ChilkatBinData

' ------------------------------------------------------------------
' Simulate input arriving in chunks.
' ------------------------------------------------------------------

Dim part1 As String
part1 = "The quick brown fox "
Dim part2 As String
part2 = "jumps over the lazy dog. "
Dim part3 As String
part3 = "This text is split into chunks."

' ------------------------------------------------------------------
' Compress the first chunk
' ------------------------------------------------------------------

compress.FirstChunk = 1
compress.LastChunk = 0

Dim bdIn As New ChilkatBinData
success = bdIn.AppendString(part1,"utf-8")

success = compress.CompressBd2(bdIn,bdOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' ------------------------------------------------------------------
' Compress a middle chunk
' ------------------------------------------------------------------

compress.FirstChunk = 0
compress.LastChunk = 0

success = bdIn.Clear()
success = bdIn.AppendString(part2,"utf-8")

success = compress.CompressBd2(bdIn,bdOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' ------------------------------------------------------------------
' Compress the final chunk
' ------------------------------------------------------------------

compress.FirstChunk = 0
compress.LastChunk = 1

success = bdIn.Clear()
success = bdIn.AppendString(part3,"utf-8")

success = compress.CompressBd2(bdIn,bdOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Get the final compressed result as base64 for display
Dim compressedBase64 As String
compressedBase64 = bdOut.GetEncoded("base64")

Debug.Print "Compressed data (base64):"
Debug.Print compressedBase64

' ------------------------------------------------------------------
' Decompress to verify correctness
' ------------------------------------------------------------------

Dim bdDecompressed As New ChilkatBinData

compress.FirstChunk = 1
compress.LastChunk = 1

success = compress.DecompressBd2(bdOut,bdDecompressed)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Convert decompressed bytes back to a string
Dim resultText As String
resultText = bdDecompressed.GetString("utf-8")

Debug.Print "Decompressed text:"
Debug.Print resultText