(JavaScript) 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.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

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

var compress = new CkCompression();
compress.Algorithm = "zlib";

// This will accumulate the compressed output.
var bdOut = new CkBinData();

// ------------------------------------------------------------------
// Simulate input arriving in chunks.
// ------------------------------------------------------------------

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

// ------------------------------------------------------------------
// Compress the first chunk
// ------------------------------------------------------------------

compress.FirstChunk = true;
compress.LastChunk = false;

var bdIn = new CkBinData();
bdIn.AppendString(part1,"utf-8");

success = compress.CompressBd2(bdIn,bdOut);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

// ------------------------------------------------------------------
// 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) {
    console.log(compress.LastErrorText);
    return;
}

// ------------------------------------------------------------------
// 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) {
    console.log(compress.LastErrorText);
    return;
}

// Get the final compressed result as base64 for display
var compressedBase64 = bdOut.GetEncoded("base64");

console.log("Compressed data (base64):");
console.log(compressedBase64);

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

var bdDecompressed = new CkBinData();

compress.FirstChunk = true;
compress.LastChunk = true;

success = compress.DecompressBd2(bdOut,bdDecompressed);
if (success == false) {
    console.log(compress.LastErrorText);
    return;
}

// Convert decompressed bytes back to a string
var resultText = bdDecompressed.GetString("utf-8");

console.log("Decompressed text:");
console.log(resultText);