Compression Dart Reference Documentation
CkCompression
Current Version: 11.6.1
Chilkat.Compression
Supports
Work with byte arrays, strings,
Process data incrementally with
Return compressed bytes as text using encodings such as
Compress or decompress large files and streams with stable memory usage.
Combine compression and encryption in file workflows with integrated methods.
For an extended overview, see
Compression Class Overview.
See also
Binary Encodings
for supported encoded output formats.
Compress and decompress bytes, text, files, and streams with a flexible API.
Chilkat.Compression provides a general-purpose API for compressing
and decompressing data in memory, files, and streams. It supports multiple
algorithms, text charset conversion, encoded output, chunked processing, and
streaming operations for large data.
Multiple algorithms
deflate, zlib,
bzip2, and lzw.
Flexible data types
BinData,
StringBuilder, files, and streams.
Chunked processing
FirstChunk and
LastChunk for chunk-aware methods.
Encoded output
base64, hex, and others.
Streaming support
Compression + encryption
Charset = "utf-8" unless
another encoding is required. For encoded compressed data, set
EncodingMode to the desired output format.
Object Creation
// pubspec.yaml:
// dependencies:
// chilkat: ^11.6.1
import 'package:chilkat/chilkat.dart';
// Once per process, before any other Chilkat call:
Chilkat.unlockBundle('Anything for 30-day trial'); // shorthand for CkGlobal().unlockBundle(..)
final compression = CkCompression();
// ... the native object is released when `compression` is garbage collected, or now with compression.dispose().Creates the underlying native Chilkat object. Use a CkCompression only from the isolate that created it: Chilkat objects cannot be sent between isolates. Every call is synchronous; in a Flutter app, run long operations (network, large files) inside Isolate.run, creating the Chilkat objects inside the isolate.
Releases the native object immediately instead of waiting for garbage collection (useful for a large CkBinData or an open socket). Calling it more than once is harmless; any other use of the object afterwards throws a StateError. isDisposed tells whether it has been called.
Errors
A method that can fail throws a ChilkatException: a method whose only outcome is success or failure returns void and throws on failure; a method producing a String or an object returns it and throws where Chilkat would have returned null. The exception carries the object's LastErrorText at the time of the failure (lastErrorText), the class and method names (className, methodName) and a one-line message. Properties never throw, and methods that answer a question (has..., is..., ...) return a plain bool.
try {
compression.someMethod(...);
} on ChilkatException catch (e) {
print(e); // CkCompression.someMethod failed: <reason>
print(e.lastErrorText); // the full Chilkat log of the failed call
}Properties
Algorithm
String get algorithm
set algorithm(String value)
Specifies the compression algorithm to use. Supported values are
deflate, zlib, bzip2, and lzw.
The zlib option is the deflate algorithm with a zlib header.
Note: ppmd is deprecated and should not be used.
It was only available on 32-bit systems and specifically used the J variant.
New applications should use one of the supported algorithms listed above.
Charset
String get charset
set charset(String value)
Specifies the character encoding used when converting text to bytes before compression, and bytes back to text after decompression.
The current default is the computer’s ANSI charset, such as Windows-1252 on many
Western Windows systems. However, most modern applications should explicitly set
this property to utf-8.
Recommendation: Set Charset = "utf-8" unless you
specifically need compatibility with another encoding.
DebugLogFilePath
String get debugLogFilePath
set debugLogFilePath(String value)
If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.
Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.
Possible causes of hangs include:
- A timeout property set to 0, indicating an infinite timeout.
- A hang occurring within an event callback in the application code.
- An internal bug in the Chilkat code causing the hang.
DeflateLevel
int get deflateLevel
set deflateLevel(int value)
Sets the compression level used by the deflate and zlib
algorithms.
0means no compression.9means maximum compression.- The default value is
6.
Higher values may produce smaller output but can require more processing time.
topEncodingMode
String get encodingMode
set encodingMode(String value)
Specifies the text encoding used by methods whose names end in ENC,
such as CompressBytesENC and DecompressStringENC.
Compression methods ending in ENC return compressed binary data as
an encoded string. Decompression methods ending in ENC expect the
input string to use this same encoding.
Valid values include:
base64hexurlquoted-printable
FirstChunk
bool get firstChunk
set firstChunk(bool value)
Indicates that the next chunk-aware compression or decompression call is the first chunk in a sequence.
The default value is true
When both FirstChunk and LastChunk are
true
HeartbeatMs
int get heartbeatMs
set heartbeatMs(int value)
Specifies the interval, in milliseconds, between AbortCheck event
callbacks.
This allows an application to periodically check whether a long-running operation should be aborted.
The default value is 0, which disables AbortCheck
callbacks.
LastChunk
bool get lastChunk
set lastChunk(bool value)
Indicates that the next chunk-aware compression or decompression call is the final chunk in a sequence.
The default value is true
When both FirstChunk and LastChunk are
true
LastErrorHtml
String get lastErrorHtml
Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastErrorText
String get lastErrorText
Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
LastErrorXml
String get lastErrorXml
Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastMethodSuccess
bool get lastMethodSuccess
set lastMethodSuccess(bool value)
Indicates the success or failure of the most recent method call: true means success, false means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.
UncommonOptions
String get uncommonOptions
set uncommonOptions(String value)
Provides a way to enable specialized or uncommon behavior. This property normally remains empty.
It may be set to a comma-separated list of keywords.
Supported option:
-
Crypt2CompressHdr— Duplicates the compression/decompression header behavior used by the deprecated and removed Crypt2 compression functions.
VerboseLogging
bool get verboseLogging
set verboseLogging(bool value)
If set to true, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is false. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
String get version
Methods
CompressBd
Compresses the data contained in a BinData object.
The BinData object is modified to contain the compressed result.
This method is not FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
CompressBd2
Compresses the data in one BinData object and appends the
compressed output to another BinData object.
The input BinData is not modified.
This method is FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
CompressEncryptFile
Compresses and encrypts a file, writing the result to a destination file.
The compression and encryption are performed internally in streaming mode, so files of any size can be processed without loading the entire file into memory.
Returns normally on success; throws a ChilkatException on failure.
CompressFile
Compresses a source file and writes the compressed data to a destination file.
The file is processed internally in streaming mode, allowing files of any size to be compressed with stable memory usage.
Returns normally on success; throws a ChilkatException on failure.
CompressSb
Compresses the text contained in a StringBuilder and appends the
compressed bytes to a BinData object.
Text is converted to bytes according to the Charset property.
This method is FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
CompressStream
Compresses data from a stream source and writes the compressed data to the stream sink.
The operation is performed in streaming mode, making it suitable for very large or even continuous streams while maintaining stable memory usage.
Returns normally on success; throws a ChilkatException on failure.
CompressStringENC
Compresses a string and returns the compressed result as an encoded string.
The string is first converted to bytes using Charset, then
compressed, and finally encoded according to EncodingMode.
This method is not FirstChunk / LastChunk aware.
Throws a ChilkatException on failure (where the description says null is returned, the Dart method throws instead).
DecompressBd
Decompresses the compressed data contained in a BinData object.
The BinData object is modified to contain the decompressed result.
This method is not FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
DecompressBd2
Decompresses the data in one BinData object and appends the
decompressed output to another BinData object.
The input BinData is not modified.
This method is FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
DecompressFile
Decompresses a source file and writes the decompressed data to a destination file.
The file is processed internally in streaming mode, allowing files of any size to be decompressed without loading the entire file into memory.
Returns normally on success; throws a ChilkatException on failure.
DecompressSb
Decompresses compressed data from a BinData object and appends the
resulting text to a StringBuilder.
The decompressed bytes are converted to text using the Charset
property.
This method is FirstChunk / LastChunk aware.
Returns normally on success; throws a ChilkatException on failure.
DecompressStream
Decompresses data from a stream source and writes the decompressed data to the stream sink.
The operation is performed in streaming mode, making it suitable for very large or continuous streams while maintaining stable memory usage.
Returns normally on success; throws a ChilkatException on failure.
DecompressStringENC
Decompresses compressed data supplied as an encoded string and returns the resulting text.
The input string is decoded according to EncodingMode, then
decompressed. The resulting bytes are converted to text using
Charset.
This method is not FirstChunk / LastChunk aware.
Throws a ChilkatException on failure (where the description says null is returned, the Dart method throws instead).
DecryptDecompressFile
Decrypts and decompresses a file, writing the restored data to a destination file.
This is the reverse operation of CompressEncryptFile.
Returns normally on success; throws a ChilkatException on failure.
Events
All Chilkat methods are synchronous: the call returns when the work is done. During a call, CkCompression raises three events so your application can show progress and offer a way out. Each event is a nullable callback property on the object; assign a function to receive it, or null to stop receiving it:
final compression = CkCompression();
compression.onPercentDone = (pct) {
print('$pct%');
return false; // return true to abort the method in progress
};
compression.onProgressInfo = (name, value) => print('$name: $value');
compression.heartbeatMs = 250; // raise onAbortCheck 4 times per second during Chilkat calls
compression.onAbortCheck = () => _userPressedCancel;AbortCheck fires at regular intervals controlled by the HeartbeatMs property (0, the default, disables it); PercentDone fires when an operation's completion percentage is known; ProgressInfo delivers named progress values. Returning true from onAbortCheck or onPercentDone aborts the running method, which then throws a ChilkatException.
Events fire on the thread that called the method, before that method returns. An exception thrown inside a callback aborts the running method and is rethrown from it once the native library has returned. In a Flutter app the callbacks run inside the worker isolate that owns the object; forward progress to the UI through a SendPort, and let onAbortCheck read a flag the UI sets the same way.
AbortCheck
bool Function()? onAbortCheck
Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the HeartbeatMs property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.
Example:
compression.heartbeatMs = 250; // call onAbortCheck 4 times per second
var cancelRequested = false;
compression.onAbortCheck = () => cancelRequested;
// ... set cancelRequested = true (e.g. from a message received on a ReceivePort) to abort the method in progressPercentDone
bool Function(int pctDone)? onPercentDone
This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The pctDone argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have pctDone equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).
The PercentDone callback also acts as an AbortCheck event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.
To abort the operation, set the abort output argument to true. This will cause the method to terminate and return a failure status or corresponding failure value.
Example:
compression.onPercentDone = (pct) {
// pct ranges from 1 to 100.
print('Percent done: $pct');
return false; // return true to abort the method in progress
};ProgressInfo
void Function(String name, String value)? onProgressInfo
This event callback provides tag name/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.
Note: Some Chilkat methods don't fire any ProgressInfo events.
Example:
compression.onProgressInfo = (name, value) => print('$name: $value');