Compression Lua Reference Documentation
chilkat.Compression
Current Version: 11.7.0
Markdown version of this page for AI tools (v 11.7.0) · all AI docs
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
local chilkat = require("chilkat")
local compression = chilkat.Compression.new()Creates the object (chilkat.Compression() does the same). Lua's garbage collector frees it when it is no longer referenced; compression:dispose() frees it at once, and in Lua 5.4 and later local compression <close> = chilkat.Compression.new() frees it when the block ends. Calling a method of a disposed object raises an error.
Errors
A method that fails returns nil followed by the error text, as io.open does: local body, err = compression:method(...), where err is the object's last_error_text. Wrap the call in assert() to raise an error with that text instead. Methods that answer a question return true or false, numbers are returned as they are (check last_method_success where the description says a value means failure), and property reads and writes never fail for Chilkat reasons.
Misuse raises a Lua error: a wrong argument type or a missing argument (bad argument #1 to ...), an unknown property name, a write to a read-only property, an out-of-range integer, or an object of the wrong class.
Names are Chilkat's in snake_case: QuickGetStr is quick_get_str, LastErrorText is last_error_text. Properties are fields (compression.verbose_logging = true) and methods use the colon (compression:method(...)). Strings are UTF-8; binary data is a Lua string of bytes. Indexes are 0-based, as in every Chilkat API. Unlocking: call chilkat.unlock_bundle("...") once at startup.
Properties
Algorithm
local strVal = compression.algorithm
compression.algorithm = strVal
Specifies the compression algorithm to use. Supported values are
deflate, zlib, gzip, bzip2, and lzw.
The zlib option is the deflate algorithm with a zlib header.
The gzip option (starting in v11.7.0) is the deflate algorithm in the gzip format (RFC 1952): a gzip
header, the deflate data, and a trailer with the CRC-32 and size of the uncompressed data. When decompressing in one
call, the CRC-32 and size are checked. Before v11.7.0, gzip was not recognized and was treated as
deflate.
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
local strVal = compression.charset
compression.charset = strVal
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
local strVal = compression.debug_log_file_path
compression.debug_log_file_path = strVal
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
local intVal = compression.deflate_level
compression.deflate_level = intVal
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
local strVal = compression.encoding_mode
compression.encoding_mode = strVal
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
local boolVal = compression.first_chunk
compression.first_chunk = boolVal
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
local intVal = compression.heartbeat_ms
compression.heartbeat_ms = intVal
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
local boolVal = compression.last_chunk
compression.last_chunk = boolVal
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
local strVal = compression.last_error_html
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
local strVal = compression.last_error_text
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
local strVal = compression.last_error_xml
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
local boolVal = compression.last_method_success
compression.last_method_success = boolVal
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
local strVal = compression.uncommon_options
compression.uncommon_options = strVal
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
local boolVal = compression.verbose_logging
compression.verbose_logging = boolVal
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
local strVal = compression.version
Methods
CompressBd
-- ok is true, or nil and err on failure
local ok, err = compression:compress_bd(bd)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressBd2
-- bd_out is a chilkat.BinData
-- ok is true, or nil and err on failure
local ok, err = compression:compress_bd2(bd_in, bd_out)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressEncryptFile
-- src_path is a string
-- dest_path is a string
-- ok is true, or nil and err on failure
local ok, err = compression:compress_encrypt_file(crypt_params, src_path, dest_path)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressFile
-- dest_path is a string
-- ok is true, or nil and err on failure
local ok, err = compression:compress_file(src_path, dest_path)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressSb
-- bin_data is a chilkat.BinData
-- ok is true, or nil and err on failure
local ok, err = compression:compress_sb(sb, bin_data)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressStream
-- ok is true, or nil and err on failure
local ok, err = compression:compress_stream(strm)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
CompressStringENC
-- str is a string, or nil and err on failure
local str, err = compression:compress_string_enc(str)
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 the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressBd
-- ok is true, or nil and err on failure
local ok, err = compression:decompress_bd(bd)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressBd2
-- bd_out is a chilkat.BinData
-- ok is true, or nil and err on failure
local ok, err = compression:decompress_bd2(bd_in, bd_out)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressFile
-- dest_path is a string
-- ok is true, or nil and err on failure
local ok, err = compression:decompress_file(src_path, dest_path)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressSb
-- sb is a chilkat.StringBuilder
-- ok is true, or nil and err on failure
local ok, err = compression:decompress_sb(bin_data, sb)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressStream
-- ok is true, or nil and err on failure
local ok, err = compression:decompress_stream(strm)
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 on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecompressStringENC
-- str is a string, or nil and err on failure
local str, err = compression:decompress_string_enc(encoded_compressed_data)
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 the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DecryptDecompressFile
-- src_path is a string
-- dest_path is a string
-- ok is true, or nil and err on failure
local ok, err = compression:decrypt_decompress_file(crypt_params, src_path, dest_path)
Decrypts and decompresses a file, writing the restored data to a destination file.
This is the reverse operation of CompressEncryptFile.
Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
Events
All Chilkat methods are synchronous: the call returns when the work is done. During a long-running call, chilkat.Compression reports progress to the functions given to set_event_handler, in a table keyed by event name (plain functions, not methods: closures carry whatever state they need):
compression:set_event_handler({
percent_done = function(pct) print(pct .. "%") end, -- return true to abort
progress_info = function(name, value) print(name, value) end,
})
compression.heartbeat_ms = 250 -- abort_check is called 4 times per secondInstalls the handlers, replacing any installed before; compression:set_event_handler(nil) removes them. The event names are checked when the table is installed: a misspelled one raises an error.
The abort_check handler is called at the interval set by the heartbeat_ms property (0, the default, disables it); percent_done is called when an operation's completion percentage is known; progress_info delivers named progress values. A true return from abort_check or percent_done aborts the running method, which then fails in the usual way (nil, err). An error raised in a handler aborts the method and is raised again from the method call; the object remains usable.
AbortCheck
compression:set_event_handler({ abort_check = function() ... end })
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
local deadline = os.time() + 30 -- give up after 30 seconds
compression.heartbeat_ms = 250 -- call the handler 4 times per second
compression:set_event_handler({ abort_check = function() return os.time() > deadline end })PercentDone
compression:set_event_handler({ percent_done = function(pct_done) ... end })
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:set_event_handler({
percent_done = function(pct_done) -- 0 to 100
print("Percent done: " .. pct_done)
return false -- return true to abort the method in progress
end,
})ProgressInfo
compression:set_event_handler({ progress_info = function(name, value) ... end })
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:set_event_handler({
progress_info = function(name, value) print(name .. ": " .. value) end,
})