Submodule compress.zlib

Overview

The compress.zlib submodule provides the ability to compress and decompress data using the zlib algorithm. You can use the zlib compressor as follows:

Create a compressor instance using the compress.zlib.new() function:

local zlib_compressor = require('compress.zlib').new()
-- or --
local zlib_compressor = require('compress').zlib.new()

Optionally, you can pass compression options (zlib_opts) specific for zlib:

local zlib_compressor = require('compress.zlib').new({
    level = 5,
    mem_level = 5,
    strategy = 'filtered'
})

To compress the specified data, use the compress() method:

compressed_data = zlib_compressor:compress('Hello world!')

To decompress data, call decompress():

decompressed_data = zlib_compressor:decompress(compressed_data)

API Reference

Functions
compress.zlib.new()	Create a `zlib` compressor instance.
Objects
zlib_compressor	A `zlib` compressor instance.
zlib_opts	Configuration options of the `zlib` compressor.

compress.zlib.new()

compress.zlib.new([zlib_opts])¶

Create a zlib compressor instance.

Parameters:	options (`table`) – `zlib` compression options (see zlib_opts)
Return:	a new `zlib` compressor instance (see zlib_compressor)
Rtype:	userdata

Example

local zlib_compressor = require('compress.zlib').new({
    level = 5,
    mem_level = 5,
    strategy = 'filtered'
})

zlib_compressor

object zlib_compressor¶

A compressor instance that exposes the API for compressing and decompressing data using the zlib algorithm. To create the zlib compressor, call compress.zlib.new().

zlib_compressor:compress(data)¶

Compress the specified data.

Parameters:	data (`string`) – data to be compressed
Return:	compressed data
Rtype:	string

Example

compressed_data = zlib_compressor:compress('Hello world!')

zlib_compressor:decompress(data)¶

Decompress the specified data.

Parameters:	data (`string`) – data to be decompressed
Return:	decompressed data
Rtype:	string

Example

decompressed_data = zlib_compressor:decompress(compressed_data)

zlib_opts

object zlib_opts¶

Configuration options of the zlib_compressor. These options can be passed to the compress.zlib.new() function.

Example

local zlib_compressor = require('compress.zlib').new({
    level = 5,
    mem_level = 5,
    strategy = 'filtered'
})

zlib_opts.level¶: Specifies the zlib compression level that enables you to adjust the compression ratio and speed. The lower level improves the compression speed at the cost of compression ratio.

Default: 6

Minimum: 0 (no compression)

Maximum: 9

zlib_opts.mem_level¶: Specifies how much memory is allocated for the zlib compressor. The larger value improves the compression speed and ratio.

Default: 8

Minimum: 1

Maximum: 9

zlib_opts.strategy¶

Specifies the compression strategy. The possible values:

default - for normal data.
huffman_only - forces Huffman encoding only (no string match). The fastest compression algorithm but not very effective in compression for most of the data.
filtered - for data produced by a filter or predictor. Filtered data consists mostly of small values with a somewhat random distribution. This compression algorithm is tuned to compress them better.
rle - limits match distances to one (run-length encoding). rle is designed to be almost as fast as huffman_only but gives better compression for PNG image data.
fixed - prevents the use of dynamic Huffman codes and provides a simpler decoder for special applications.

Version:

Submodule compress.zlib

Overview

API Reference

compress.zlib.new()

zlib_compressor

zlib_opts