B4X

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.

B4X

Dim success As Boolean = False

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

Dim compress As ChilkatCompression
compress.Initialize("compress")
compress.Algorithm = "zlib"

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

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

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

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

compress.FirstChunk = True
compress.LastChunk = False

Dim bdIn As ChilkatBinData
bdIn.Initialize
bdIn.AppendString(part1, "utf-8")

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


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

compress.FirstChunk = False
compress.LastChunk = False

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

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


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

compress.FirstChunk = False
compress.LastChunk = True

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

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


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

Log("Compressed data (base64):")
Log(compressedBase64)

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

Dim bdDecompressed As ChilkatBinData
bdDecompressed.Initialize

compress.FirstChunk = True
compress.LastChunk = True

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


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

Log("Decompressed text:")
Log(resultText)