Dart

Compressing StringBuilder Data Using CompressSb (Single Call and Chunked)

See more Compression Examples

This example demonstrates how to compress text stored in a StringBuilder using the CompressSb method in two ways:

1. Single-call compression, where the entire input is compressed in one operation.
2. Chunked compression, where the input is split into multiple parts and processed sequentially using the FirstChunk and LastChunk properties.

The example shows how compressed output is appended to a BinData object, and how the result can be verified by decompressing back to the original text. This is useful for both simple use cases and scenarios where data is processed incrementally (such as streaming or large inputs).

---

Key Points

• CompressSb converts text to bytes using the Charset property (UTF-8 recommended).
• Compressed data is appended to a BinData object.
• When both FirstChunk and LastChunk are true, compression is done in a single call.
• For chunked processing:
  • First chunk → FirstChunk = true, LastChunk = false
  • Middle chunks → both false
  • Final chunk → LastChunk = true
• Chunked compression is useful when processing data incrementally.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example assumes the Chilkat API has already been unlocked.
  // See Global Unlock Sample for sample code.

  final compress = CkCompression();
  compress.algorithm = 'zlib';

  // ================================================================
  // 1) Single-call compression (entire data in one call)
  // ================================================================

  final sb = CkStringBuilder();
  sb.append('The quick brown fox jumps over the lazy dog. ');
  sb.append('This is a simple example using CompressSb.');

  final bdCompressed = CkBinData();

  // When both FirstChunk and LastChunk are true (the defaults),
  // the entire compression happens in a single call.
  compress.firstChunk = true;
  compress.lastChunk = true;

  try {
    compress.compressSb(sb, bdCompressed);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final compressedBase64 = bdCompressed.getEncoded('base64');

  print('Single-call compressed (base64):');
  print(compressedBase64);

  // ================================================================
  // 2) Chunked compression using FirstChunk / LastChunk
  // ================================================================

  final bdChunkedOut = CkBinData();

  // First chunk
  compress.firstChunk = true;
  compress.lastChunk = false;

  final sbPart = CkStringBuilder();
  sbPart.append('The quick brown fox ');

  try {
    compress.compressSb(sbPart, bdChunkedOut);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Middle chunk
  compress.firstChunk = false;
  compress.lastChunk = false;

  sbPart.clear();
  sbPart.append('jumps over the lazy dog. ');

  try {
    compress.compressSb(sbPart, bdChunkedOut);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Final chunk
  compress.firstChunk = false;
  compress.lastChunk = true;

  sbPart.clear();
  sbPart.append('This is a chunked CompressSb example.');

  try {
    compress.compressSb(sbPart, bdChunkedOut);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final chunkedBase64 = bdChunkedOut.getEncoded('base64');

  print('Chunked compressed (base64):');
  print(chunkedBase64);

  // ================================================================
  // 3) Decompress to verify correctness
  // ================================================================

  final sbDecompressed = CkStringBuilder();

  // Decompress in a single call (entire data already assembled)
  compress.firstChunk = true;
  compress.lastChunk = true;

  try {
    compress.decompressSb(bdChunkedOut, sbDecompressed);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Decompressed text:');
  print(sbDecompressed.getAsString());
}