Gzip Lazarus Pascal Reference Documentation
Gzip
Current Version: 11.6.0
Chilkat.Gzip
Compress files to
Work with byte arrays and
Compress and uncompress strings with explicit charset handling for text
data that must round-trip correctly.
Handle GZIP data represented as Base64, hex, or other supported encoded
forms when binary data must be carried as text.
Set or inspect metadata such as original filename, modified time,
comments, and extra data stored in the GZIP header.
Extract
For an extended overview, see
Gzip Class Overview.
Compress, decompress, inspect, and convert GZIP data in files or memory.
Chilkat.Gzip provides GZIP compression and decompression for
file-based and in-memory workflows. It can compress and uncompress files,
strings, byte arrays, BinData, and encoded data such as Base64
or hex. It also supports .tar.gz extraction, gzip metadata such
as original filename, timestamp, and comments, and inspection of GZIP header
information without fully expanding the compressed data.
File compression
.gz, uncompress .gz files,
and write decompressed output directly to disk.
Memory-based data
Chilkat.BinData for applications
that need compression or decompression without temporary files.
String workflows
Encoded GZIP data
GZIP metadata
Tar-gzip and XFDL
.tar.gz archives and decode XFDL content that uses
gzip-related encodings.
Gzip when the data is a single GZIP stream, a
.gz file, or a .tar.gz archive. For ZIP archives,
use Chilkat.Zip; for raw deflate or zlib-style compression, use
Chilkat.Compression.
Create / Free
uses
Chilkat.Gzip;
var
obj: TGzip;
begin
obj := TGzip.Create;
try
if not obj.IsValid then
raise Exception.Create('Failed to create a TGzip instance.');
// ... use obj ...
finally
obj.Free;
end;
end;
Allocates the underlying CkGzip object and returns a new TGzip instance. Simply adding Chilkat.Gzip 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 TGzip created by calling Create should eventually be released by calling .Free (inherited from TObject). The destructor automatically disposes the underlying CkGzip handle. A native (unmanaged) memory leak occurs if the object is never freed.
Properties
AbortCurrent
Set this property to True
If no method is currently running, the property is automatically reset to FalseFalse
Comment
An optional comment to embed in the Gzip file when a Compress* method is called.
CompressionLevel
Controls the compression level used when creating Gzip data. The value can range from
0 to 9.
0= no compression9= maximum compression
The default value is 6, which is a typical balance between compression size and speed.
Higher levels may take significantly more CPU time while producing only slightly smaller output,
depending on the data.
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.
ExtraData
Optional binary data to include in the Gzip header when a Compress* method is called.
Filename
The filename to embed in the Gzip file when a Compress* method is called.
Some Gzip extraction tools use this embedded filename as the default output filename.
HeartbeatMs
Specifies the interval, in milliseconds, between AbortCheck event callbacks.
These callbacks allow an application to cancel certain long-running operations before they finish.
The default value is 0, which means no AbortCheck callbacks are triggered.
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.
LastModStr
Specifies the last-modified date/time to embed in the Gzip file when a
Compress* method is called.
The value must be provided as an RFC 822 formatted date/time string.
Example:
Sun, 12 Apr 2026 12:45:26 GMT
If this property is not set, the current system date/time is used automatically.
UseCurrentDate
Controls the last-modified date/time assigned to files created by Uncompress* methods.
When set to True
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(binDat: TChilkatBase): Boolean;
Compresses the contents of a BinData object in place, replacing the original data
with Gzip-compressed data.
Returns True for success, False for failure.
CompressFile
const destPath: string): Boolean;
Compresses a file and writes the result as a Gzip file, typically with a .gz extension.
Returns True for success, False for failure.
CompressFile2
const embeddedFilename: string;
const destPath: string): Boolean;
Compresses a file and writes the result as a Gzip file, while allowing a different filename to be embedded inside the Gzip data.
The inFilename parameter is the actual file on disk. The
srcPath
Returns True for success, False for failure.
CompressFileBd
function CompressFileBd(const filePath: string;
bd: TChilkatBase): Boolean;
Compresses a file and stores the resulting Gzip data in a BinData object.
The compressed output is held in memory. The maximum compressed size is 4 GB.
Returns True for success, False for failure.
CompressSb
// bd is a TBinData object.
function CompressSb(sb: TChilkatBase;
const charset: string;
bd: TChilkatBase): Boolean;
Compresses the text contained in a StringBuilder and writes the Gzip-compressed
result to a BinData object.
Before compression, the string is converted to bytes using the specified character set, such as
utf-8, iso-8859-1, or shift_JIS.
Returns True for success, False for failure.
CompressStringENC
const charset: string;
const encoding: string): string;
Compresses a string and returns the Gzip-compressed data as an encoded string.
The input string is first converted to bytes using the specified character set. The compressed
binary data is then encoded using the requested encoding, such as base64,
hex, url, base32, or quoted-printable.
Returns True for success, False for failure.
CompressStringToFile
const destCharset: string;
const destPath: string): Boolean;
Compresses a string and writes the resulting Gzip data to a file.
The string is first converted to bytes using the character set specified by
destCharset.
Returns True for success, False for failure.
GetGzipInfo
function GetGzipInfo(const filePath: string;
json: TChilkatBase): Boolean;
Retrieves metadata stored in a Gzip file and returns the information in a
JsonObject.
The metadata is returned using the following JSON structure:
{
"extraData": "AAECAw==",
"filename": "example.txt",
"comment": "This is the comment"
}
- filename – the original filename embedded in the Gzip file (if present)
- comment – an optional descriptive comment (if present)
- extraData – optional additional binary data, returned as a Base64-encoded string
Any of these fields may be omitted if they were not included when the Gzip file was created.
Returns True for success, False for failure.
GetGzipInfoBd
// json is a TJsonObject object.
function GetGzipInfoBd(bd: TChilkatBase;
json: TChilkatBase): Boolean;
Retrieves metadata stored in Gzip data contained within a BinData object
and returns the information in a JsonObject.
The metadata is returned using the same JSON structure:
{
"extraData": "AAECAw==",
"filename": "example.txt",
"comment": "This is the comment"
}
- filename – the original filename embedded in the Gzip data (if present)
- comment – an optional descriptive comment (if present)
- extraData – optional additional binary data, returned as a Base64-encoded string
Any of these fields may be omitted if they were not included when the Gzip data was created.
Returns True for success, False for failure.
IsGzip
function IsGzip(bd: TChilkatBase): Boolean;
Checks whether the data contained in a BinData object is in Gzip format.
Returns TrueFalse
LoadTaskCaller
function LoadTaskCaller(task: TChilkatBase): Boolean;
SetDt
function SetDt(dt: TChilkatBase): Boolean;
Sets the last-modified date/time to embed in the Gzip file when a Compress*
method is called.
If no date/time is explicitly set, the current system date/time is used.
Returns True for success, False for failure.
SetExtraData
const encoding: string): Boolean;
Sets optional extra binary data to include in the Gzip header when a Compress*
method is called.
The data is passed as an encoded string. Supported encodings include base64,
hex, ascii, and many others.
Returns True for success, False for failure.
UncompressBd
function UncompressBd(binDat: TChilkatBase): Boolean;
Decompresses Gzip data contained in a BinData object in place, replacing the
compressed data with the uncompressed data.
Returns True for success, False for failure.
UncompressBdToFile
function UncompressBdToFile(bd: TChilkatBase;
const filePath: string): Boolean;
Decompresses Gzip data stored in a BinData object and writes the result to a file.
Returns True for success, False for failure.
UncompressFile
const destPath: string): Boolean;
Decompresses a Gzip file and writes the result to the specified output path.
The output filename is provided by the caller. The filename embedded in the Gzip data is not used.
Returns True for success, False for failure.
UncompressFileToString
const charset: string): string;
Decompresses a Gzip file that contains text and returns the uncompressed text as a string.
The charset parameter specifies the character encoding of the uncompressed text,
such as utf-8, iso-8859-1, windows-1252,
shift_JIS, big5, etc.
Returns True for success, False for failure.
UncompressStringENC
const charset: string;
const encoding: string): string;
Decompresses Gzip data provided as an encoded string and returns the uncompressed result as text.
The input string is first decoded using the specified encoding, such as base64,
hex, url, base32, quoted-printable, etc. The decoded
Gzip data is then decompressed and converted to text using the specified character set.
Returns True for success, False for failure.
UnTarGz
const destDir: string;
bNoAbsolute: Boolean): Boolean;
Extracts a .tar.gz archive to a directory.
The Gzip decompression and TAR extraction are performed in streaming mode. No temporary files are created, and memory usage remains small and constant.
If bNoAbsolute is True
Returns True for success, False for failure.
XfdlToXml
Converts encoded and compressed XFDL data to a decompressed XML string.
XFDL data is often stored in an ASCII-safe compressed form, such as
asci-gzip or asc-gzip. Despite the name, this does not always mean
the data is a standard .gz file. In some XFDL files, the compressed payload uses
the raw deflate format rather than the full Gzip file format.
Chilkat automatically detects the actual encoding and compression format used by the XFDL data. It decodes the ASCII/Base64 representation, determines whether the compressed data is Gzip or deflate, decompresses it correctly, and returns the resulting XML string.
This allows applications to call XfdlToXml without needing to manually distinguish
between XFDL variants such as Base64+Gzip and Base64+Deflate.
Returns the decoded and decompressed XML string.
XFDL (Extensible Forms Description Language) is an XML-based format used to define secure, interactive electronic forms—often including digital signatures and integrity protections—commonly used in government and enterprise applications.
Returns True for success, False for failure.
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.GzipAbortCheck(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:
gzip := TGzip.Create;
gzip.HeartbeatMs := 250; // fire OnAbortCheck 4 times per second
gzip.OnAbortCheck := MyObject.GzipAbortCheck;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.GzipPercentDone(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:
gzip := TGzip.Create;
gzip.OnPercentDone := MyObject.GzipPercentDone;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.GzipProgressInfo(Sender: TChilkatBase; const Name, Value: string);
begin
WriteLn(Name, ': ', Value);
end;To add an event handler:
gzip := TGzip.Create;
gzip.OnProgressInfo := MyObject.GzipProgressInfo;