Compression Lazarus Pascal Reference Documentation
Compression
Current Version: 11.6.0
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.
Create / Free
uses
Chilkat.Compression;
var
obj: TCompression;
begin
obj := TCompression.Create;
try
if not obj.IsValid then
raise Exception.Create('Failed to create a TCompression instance.');
// ... use obj ...
finally
obj.Free;
end;
end;
Allocates the underlying CkCompression object and returns a new TCompression instance. Simply adding Chilkat.Compression to the unit's uses clause is enough to locate and bind to the Chilkat shared library (DLL / .so / .dylib) at runtime — no separate load step is required. Check obj.IsValid after calling Create; it is False if the underlying library could not be found/loaded or the object could not be allocated (for example, when unlicensed).
Every TCompression created by calling Create should eventually be released by calling .Free (inherited from TObject). The destructor automatically disposes the underlying CkCompression handle. A native (unmanaged) memory leak occurs if the object is never freed.
Properties
Algorithm
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Methods
CompressBd
function CompressBd(bd: TChilkatBase): Boolean;
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 True for success, False for failure.
CompressBd2
// bdOut is a TBinData object.
function CompressBd2(bdIn: TChilkatBase;
bdOut: TChilkatBase): Boolean;
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 True for success, False for failure.
CompressEncryptFile
function CompressEncryptFile(cryptParams: TChilkatBase;
const srcPath: string;
const destPath: string): Boolean;
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 True for success, False for failure.
CompressFile
const destPath: string): Boolean;
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 True for success, False for failure.
CompressSb
// binData is a TBinData object.
function CompressSb(sb: TChilkatBase;
binData: TChilkatBase): Boolean;
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 True for success, False for failure.
CompressStream
function CompressStream(strm: TChilkatBase): Boolean;
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 True for success, False for failure.
topCompressStringENC
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.
Returns True for success, False for failure.
topDecompressBd
function DecompressBd(bd: TChilkatBase): Boolean;
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 True for success, False for failure.
DecompressBd2
// bdOut is a TBinData object.
function DecompressBd2(bdIn: TChilkatBase;
bdOut: TChilkatBase): Boolean;
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 True for success, False for failure.
DecompressFile
const destPath: string): Boolean;
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 True for success, False for failure.
DecompressSb
// sb is a TStringBuilder object.
function DecompressSb(binData: TChilkatBase;
sb: TChilkatBase): Boolean;
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 True for success, False for failure.
DecompressStream
function DecompressStream(strm: TChilkatBase): Boolean;
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 True for success, False for failure.
topDecompressStringENC
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.
Returns True for success, False for failure.
topDecryptDecompressFile
function DecryptDecompressFile(cryptParams: TChilkatBase;
const srcPath: string;
const destPath: string): Boolean;
Decrypts and decompresses a file, writing the restored data to a destination file.
This is the reverse operation of CompressEncryptFile.
Returns True for success, False for failure.
LoadTaskCaller
function LoadTaskCaller(task: TChilkatBase): Boolean;
Events
Chilkat for Pascal supports three synchronous event callbacks: OnAbortCheck, OnPercentDone, and OnProgressInfo. Each is a property of the class; assign a method of one of your own objects (an of object handler) to receive the callbacks, or assign nil to unhook. The handler types are declared in the Chilkat.Base unit:
TChilkatAbortCheckEvent = function(Sender: TChilkatBase): Boolean of object;
TChilkatPercentDoneEvent = function(Sender: TChilkatBase; PctDone: Integer): Boolean of object;
TChilkatProgressInfoEvent = procedure(Sender: TChilkatBase; const Name, Value: string) of object;All Chilkat methods are synchronous, so callbacks are invoked on the thread that called the method -- if the method was called from the main thread, it is safe to access UI elements from the handler. The HeartbeatMs property controls the frequency of OnAbortCheck callbacks (the default of 0 means no AbortCheck events fire). Returning True from an OnAbortCheck or OnPercentDone handler aborts the running method.
AbortCheck
property OnAbortCheck: TChilkatAbortCheckEvent;
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.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
function TMyObject.CompressionAbortCheck(Sender: TChilkatBase): Boolean;
begin
// Called every HeartbeatMs milliseconds while a method is running.
// Return True to abort the method; return False to continue.
Result := False;
end;To add an event handler:
compression := TCompression.Create;
compression.HeartbeatMs := 250; // fire OnAbortCheck 4 times per second
compression.OnAbortCheck := MyObject.CompressionAbortCheck;PercentDone
property OnPercentDone: TChilkatPercentDoneEvent;
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.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
function TMyObject.CompressionPercentDone(Sender: TChilkatBase; PctDone: Integer): Boolean;
begin
// PctDone ranges from 1 to 100.
WriteLn('Percent done: ', PctDone);
// Return True to abort the method; return False to continue.
Result := False;
end;To add an event handler:
compression := TCompression.Create;
compression.OnPercentDone := MyObject.CompressionPercentDone;ProgressInfo
property OnProgressInfo: TChilkatProgressInfoEvent;
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.
Event callback implementation:
// A handler is a method of one of your own classes, e.g. a form:
procedure TMyObject.CompressionProgressInfo(Sender: TChilkatBase; const Name, Value: string);
begin
WriteLn(Name, ': ', Value);
end;To add an event handler:
compression := TCompression.Create;
compression.OnProgressInfo := MyObject.CompressionProgressInfo;