Tcl

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.

Tcl

load ./chilkat.dll

set success 0

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

set compress [new_CkCompression]

CkCompression_put_Algorithm $compress "zlib"

# This will accumulate the compressed output.
set bdOut [new_CkBinData]

# ------------------------------------------------------------------
# Simulate input arriving in chunks.
# ------------------------------------------------------------------

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

# ------------------------------------------------------------------
# Compress the first chunk
# ------------------------------------------------------------------

CkCompression_put_FirstChunk $compress 1
CkCompression_put_LastChunk $compress 0

set bdIn [new_CkBinData]

CkBinData_AppendString $bdIn $part1 "utf-8"

set success [CkCompression_CompressBd2 $compress $bdIn $bdOut]
if {$success == 0} then {
    puts [CkCompression_lastErrorText $compress]
    delete_CkCompression $compress
    delete_CkBinData $bdOut
    delete_CkBinData $bdIn
    exit
}

# ------------------------------------------------------------------
# Compress a middle chunk
# ------------------------------------------------------------------

CkCompression_put_FirstChunk $compress 0
CkCompression_put_LastChunk $compress 0

CkBinData_Clear $bdIn
CkBinData_AppendString $bdIn $part2 "utf-8"

set success [CkCompression_CompressBd2 $compress $bdIn $bdOut]
if {$success == 0} then {
    puts [CkCompression_lastErrorText $compress]
    delete_CkCompression $compress
    delete_CkBinData $bdOut
    delete_CkBinData $bdIn
    exit
}

# ------------------------------------------------------------------
# Compress the final chunk
# ------------------------------------------------------------------

CkCompression_put_FirstChunk $compress 0
CkCompression_put_LastChunk $compress 1

CkBinData_Clear $bdIn
CkBinData_AppendString $bdIn $part3 "utf-8"

set success [CkCompression_CompressBd2 $compress $bdIn $bdOut]
if {$success == 0} then {
    puts [CkCompression_lastErrorText $compress]
    delete_CkCompression $compress
    delete_CkBinData $bdOut
    delete_CkBinData $bdIn
    exit
}

# Get the final compressed result as base64 for display
set compressedBase64 [CkBinData_getEncoded $bdOut "base64"]

puts "Compressed data (base64):"
puts "$compressedBase64"

# ------------------------------------------------------------------
# Decompress to verify correctness
# ------------------------------------------------------------------

set bdDecompressed [new_CkBinData]

CkCompression_put_FirstChunk $compress 1
CkCompression_put_LastChunk $compress 1

set success [CkCompression_DecompressBd2 $compress $bdOut $bdDecompressed]
if {$success == 0} then {
    puts [CkCompression_lastErrorText $compress]
    delete_CkCompression $compress
    delete_CkBinData $bdOut
    delete_CkBinData $bdIn
    delete_CkBinData $bdDecompressed
    exit
}

# Convert decompressed bytes back to a string
set resultText [CkBinData_getString $bdDecompressed "utf-8"]

puts "Decompressed text:"
puts "$resultText"

delete_CkCompression $compress
delete_CkBinData $bdOut
delete_CkBinData $bdIn
delete_CkBinData $bdDecompressed