module Zlib
This module provides access to the zlib library. Zlib is designed to be a portable, free, general-purpose, legally unencumbered – that is, not covered by any patents – lossless data-compression library for use on virtually any computer hardware and operating system.
The zlib compression library provides in-memory compression and decompression functions, including integrity checks of the uncompressed data.
The zlib compressed data format is described in RFC 1950, which is a wrapper around a deflate stream which is described in RFC 1951.
The library also supports reading and writing files in gzip (.gz) format with an interface similar to that of IO. The gzip format is described in RFC 1952 which is also a wrapper around a deflate stream.
The zlib format was designed to be compact and fast for use in memory and on communications channels. The gzip format was designed for single-file compression on file systems, has a larger header than zlib to maintain directory information, and uses a different, slower check method than zlib.
See your system’s zlib.h for further information about zlib
Sample usage¶ ↑
Using the wrapper to compress strings with default parameters is quite simple:
require "zlib" data_to_compress = File.read("don_quixote.txt") puts "Input size: #{data_to_compress.size}" #=> Input size: 2347740 data_compressed = Zlib::Deflate.deflate(data_to_compress) puts "Compressed size: #{data_compressed.size}" #=> Compressed size: 887238 uncompressed_data = Zlib::Inflate.inflate(data_compressed) puts "Uncompressed data is: #{uncompressed_data}" #=> Uncompressed data is: The Project Gutenberg EBook of Don Quixote...
Class tree¶ ↑
(if you have GZIP_SUPPORT)
Constants
- ASCII
-
Represents text data as guessed by deflate.
NOTE: The underlying constant Z_ASCII was deprecated in favor of Z_TEXT in zlib 1.2.2. New applications should not use this constant.
- BEST_COMPRESSION
-
Slowest compression level, but with the best space savings.
- BEST_SPEED
-
Fastest compression level, but with the lowest space savings.
- BINARY
-
Represents binary data as guessed by deflate.
- DEFAULT_COMPRESSION
-
Default compression level which is a good trade-off between space and time
- DEFAULT_STRATEGY
-
Default deflate strategy which is used for normal data.
- DEF_MEM_LEVEL
-
The default memory level for allocating zlib deflate compression state.
- FILTERED
-
Deflatestrategy for data produced by a filter (or predictor). The effect ofFILTEREDis to force more Huffman codes and less string matching; it is somewhat intermediate betweenDEFAULT_STRATEGYandHUFFMAN_ONLY. Filtered data consists mostly of small values with a somewhat random distribution. - FINISH
-
Processes all pending input and flushes pending output.
- FIXED
-
Deflatestrategy which prevents the use of dynamic Huffman codes, allowing for a simpler decoder for specialized applications. - FULL_FLUSH
-
Flushes all output as with
SYNC_FLUSH, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. LikeSYNC_FLUSH, usingFULL_FLUSHtoo often can seriously degrade compression. - HUFFMAN_ONLY
-
Deflatestrategy which uses Huffman codes only (no string matching). - MAX_MEM_LEVEL
-
The maximum memory level for allocating zlib deflate compression state.
- MAX_WBITS
-
The maximum size of the zlib history buffer. Note that zlib allows larger values to enable different inflate modes. See
Zlib::Inflate.newfor details. - NO_COMPRESSION
-
No compression, passes through data untouched. Use this for appending pre-compressed data to a deflate stream.
- NO_FLUSH
-
NO_FLUSHis the default flush method and allows deflate to decide how much data to accumulate before producing output in order to maximize compression. - OS_AMIGA
-
OS code for Amiga hosts
- OS_ATARI
-
OS code for Atari hosts
- OS_CODE
-
The OS code of current host
- OS_CPM
-
OS code for CP/M hosts
- OS_MACOS
-
OS code for Mac OS hosts
- OS_MSDOS
-
OS code for MSDOS hosts
- OS_OS2
-
OS code for OS2 hosts
- OS_QDOS
-
OS code for QDOS hosts
- OS_RISCOS
-
OS code for RISC OS hosts
- OS_TOPS20
-
OS code for TOPS-20 hosts
- OS_UNIX
-
OS code for UNIX hosts
- OS_UNKNOWN
-
OS code for unknown hosts
- OS_VMCMS
-
OS code for VM OS hosts
- OS_VMS
-
OS code for VMS hosts
- OS_WIN32
-
OS code for
Win32hosts - OS_ZSYSTEM
-
OS code for Z-System hosts
- RLE
-
Deflatecompression strategy designed to be almost as fast asHUFFMAN_ONLY, but give better compression for PNG image data. - SYNC_FLUSH
-
The
SYNC_FLUSHmethod flushes all pending output to the output buffer and the output is aligned on a byte boundary. Flushing may degrade compression so it should be used only when necessary, such as at a request or response boundary for a network stream. - TEXT
-
Represents text data as guessed by deflate.
- UNKNOWN
-
Represents an unknown data type as guessed by deflate.
- VERSION
-
The Ruby/zlib version string.
- ZLIB_VERSION
-
The string which represents the version of zlib.h
Public Class Methods
Source
static VALUE
rb_zlib_adler32(int argc, VALUE *argv, VALUE klass)
{
return do_checksum(argc, argv, adler32);
}
Calculates Adler-32 checksum for string, and returns updated value of adler. If string is omitted, it returns the Adler-32 initial value. If adler is omitted, it assumes that the initial value is given to adler. If string is an IO instance, reads from the IO until the IO returns nil and returns Adler-32 of all read data.
Example usage:
require "zlib" data = "foo" puts "Adler32 checksum: #{Zlib.adler32(data).to_s(16)}" #=> Adler32 checksum: 2820145
Source
static VALUE
rb_zlib_adler32_combine(VALUE klass, VALUE adler1, VALUE adler2, VALUE len2)
{
return ULONG2NUM(
adler32_combine(NUM2ULONG(adler1), NUM2ULONG(adler2), NUM2LONG(len2)));
}
Combine two Adler-32 check values in to one. adler1 is the first Adler-32 value, adler2 is the second Adler-32 value. len2 is the length of the string used to generate adler2.
Source
static VALUE
rb_zlib_crc32(int argc, VALUE *argv, VALUE klass)
{
return do_checksum(argc, argv, crc32);
}
Calculates CRC checksum for string, and returns updated value of crc. If string is omitted, it returns the CRC initial value. If crc is omitted, it assumes that the initial value is given to crc. If string is an IO instance, reads from the IO until the IO returns nil and returns CRC checksum of all read data.
FIXME: expression.
Source
static VALUE
rb_zlib_crc32_combine(VALUE klass, VALUE crc1, VALUE crc2, VALUE len2)
{
return ULONG2NUM(
crc32_combine(NUM2ULONG(crc1), NUM2ULONG(crc2), NUM2LONG(len2)));
}
Combine two CRC-32 check values in to one. crc1 is the first CRC-32 value, crc2 is the second CRC-32 value. len2 is the length of the string used to generate crc2.
Source
static VALUE
rb_zlib_crc_table(VALUE obj)
{
#if !defined(HAVE_TYPE_Z_CRC_T)
/* z_crc_t is defined since zlib-1.2.7. */
typedef unsigned long z_crc_t;
#endif
const z_crc_t *crctbl;
VALUE dst;
int i;
crctbl = get_crc_table();
dst = rb_ary_new2(256);
for (i = 0; i < 256; i++) {
rb_ary_push(dst, rb_uint2inum(crctbl[i]));
}
return dst;
}
Returns the table for calculating CRC checksum as an array.
Source
static VALUE
rb_deflate_s_deflate(int argc, VALUE *argv, VALUE klass)
{
struct zstream z;
VALUE src, level, dst, args[2];
int err, lev;
rb_scan_args(argc, argv, "11", &src, &level);
lev = ARG_LEVEL(level);
StringValue(src);
zstream_init_deflate(&z);
err = deflateInit(&z.stream, lev);
if (err != Z_OK) {
raise_zlib_error(err, z.stream.msg);
}
ZSTREAM_READY(&z);
args[0] = (VALUE)&z;
args[1] = src;
dst = rb_ensure(deflate_run, (VALUE)args, zstream_ensure_end, (VALUE)&z);
return dst;
}
Compresses the given string. Valid values of level are Zlib::NO_COMPRESSION, Zlib::BEST_SPEED, Zlib::BEST_COMPRESSION, Zlib::DEFAULT_COMPRESSION, or an integer from 0 to 9.
This method is almost equivalent to the following code:
def deflate(string, level) z = Zlib::Deflate.new(level) dst = z.deflate(string, Zlib::FINISH) z.close dst end
See also Zlib.inflate
Source
static VALUE
zlib_gunzip(VALUE klass, VALUE src)
{
struct gzfile gz0;
struct gzfile *gz = &gz0;
int err;
StringValue(src);
gzfile_init(gz, &inflate_funcs, zlib_gunzip_end);
err = inflateInit2(&gz->z.stream, -MAX_WBITS);
if (err != Z_OK) {
raise_zlib_error(err, gz->z.stream.msg);
}
gz->io = Qundef;
gz->z.input = src;
ZSTREAM_READY(&gz->z);
return rb_ensure(zlib_gunzip_run, (VALUE)gz, zlib_gzip_ensure, (VALUE)gz);
}
Decode the given gzipped string.
This method is almost equivalent to the following code:
def gunzip(string) sio = StringIO.new(string) gz = Zlib::GzipReader.new(sio, encoding: Encoding::ASCII_8BIT) gz.read ensure gz&.close end
See also Zlib.gzip
Source
static VALUE
zlib_s_gzip(int argc, VALUE *argv, VALUE klass)
{
struct gzfile gz0;
struct gzfile *gz = &gz0;
int err;
VALUE src, opts, level=Qnil, strategy=Qnil, args[2];
if (OPTHASH_GIVEN_P(opts)) {
ID keyword_ids[2];
VALUE kwargs[2];
keyword_ids[0] = id_level;
keyword_ids[1] = id_strategy;
rb_get_kwargs(opts, keyword_ids, 0, 2, kwargs);
if (kwargs[0] != Qundef) {
level = kwargs[0];
}
if (kwargs[1] != Qundef) {
strategy = kwargs[1];
}
}
rb_scan_args(argc, argv, "10", &src);
StringValue(src);
gzfile_init(gz, &deflate_funcs, zlib_gzip_end);
gz->level = ARG_LEVEL(level);
err = deflateInit2(&gz->z.stream, gz->level, Z_DEFLATED,
-MAX_WBITS, DEF_MEM_LEVEL, ARG_STRATEGY(strategy));
if (err != Z_OK) {
zlib_gzip_end(gz);
raise_zlib_error(err, gz->z.stream.msg);
}
ZSTREAM_READY(&gz->z);
args[0] = (VALUE)gz;
args[1] = src;
return rb_ensure(zlib_gzip_run, (VALUE)args, zlib_gzip_ensure, (VALUE)gz);
}
Gzip the given string. Valid values of level are Zlib::NO_COMPRESSION, Zlib::BEST_SPEED, Zlib::BEST_COMPRESSION, Zlib::DEFAULT_COMPRESSION (default), or an integer from 0 to 9.
This method is almost equivalent to the following code:
def gzip(string, level: nil, strategy: nil) sio = StringIO.new sio.binmode gz = Zlib::GzipWriter.new(sio, level, strategy) gz.write(string) gz.close sio.string end
See also Zlib.gunzip
Source
static VALUE
rb_inflate_s_inflate(VALUE obj, VALUE src)
{
struct zstream z;
VALUE dst, args[2];
int err;
StringValue(src);
zstream_init_inflate(&z);
err = inflateInit(&z.stream);
if (err != Z_OK) {
raise_zlib_error(err, z.stream.msg);
}
ZSTREAM_READY(&z);
args[0] = (VALUE)&z;
args[1] = src;
dst = rb_ensure(inflate_run, (VALUE)args, zstream_ensure_end, (VALUE)&z);
return dst;
}
Decompresses string. Raises a Zlib::NeedDict exception if a preset dictionary is needed for decompression.
This method is almost equivalent to the following code:
def inflate(string) zstream = Zlib::Inflate.new buf = zstream.inflate(string) zstream.finish zstream.close buf end
See also Zlib.deflate
Source
static VALUE
rb_zlib_version(VALUE klass)
{
return rb_str_new2(zlibVersion());
}
Returns the string which represents the version of zlib library.