(Xojo Plugin) Chunked Compression Using CompressBd2 with FirstChunk and LastChunk

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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.

Chilkat Xojo Plugin Download

Xojo Plugin for Windows, Linux, Mac OS X, and ARM, ARM64

Dim success As Boolean
success = False

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

Dim compress As New Chilkat.Compression
compress.Algorithm = "zlib"

// This will accumulate the compressed output.
Dim bdOut As New Chilkat.BinData

// ------------------------------------------------------------------
// 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 = True
compress.LastChunk = False

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

success = compress.CompressBd2(bdIn,bdOut)
If (success = False) Then
    System.DebugLog(compress.LastErrorText)
    Return
End If

// ------------------------------------------------------------------
// Compress a middle chunk
// ------------------------------------------------------------------

compress.FirstChunk = False
compress.LastChunk = False

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

success = compress.CompressBd2(bdIn,bdOut)
If (success = False) Then
    System.DebugLog(compress.LastErrorText)
    Return
End If

// ------------------------------------------------------------------
// Compress the final chunk
// ------------------------------------------------------------------

compress.FirstChunk = False
compress.LastChunk = True

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

success = compress.CompressBd2(bdIn,bdOut)
If (success = False) Then
    System.DebugLog(compress.LastErrorText)
    Return
End If

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

System.DebugLog("Compressed data (base64):")
System.DebugLog(compressedBase64)

// ------------------------------------------------------------------
// Decompress to verify correctness
// ------------------------------------------------------------------

Dim bdDecompressed As New Chilkat.BinData

compress.FirstChunk = True
compress.LastChunk = True

success = compress.DecompressBd2(bdOut,bdDecompressed)
If (success = False) Then
    System.DebugLog(compress.LastErrorText)
    Return
End If

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

System.DebugLog("Decompressed text:")
System.DebugLog(resultText)