Module: Zlib
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Exceptions:
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Defined in: | ext/zlib/zlib.c |
Overview
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
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Zlib::StreamEnd
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Zlib::NeedDict
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Zlib::DataError
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Zlib::StreamError
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Zlib::MemError
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Zlib::BufError
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Zlib::VersionError
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(if you have GZIP_SUPPORT)
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Zlib::GzipFile::LengthError
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Zlib::GzipFile::CRCError
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Zlib::GzipFile::NoFooter
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Constant Summary
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ASCII =
The underlying constant Z_ASCII was deprecated in favor of Z_TEXT in zlib 1.2.2. New applications should not use this constant.
See
Zlib::Deflate#data_type
.Represents text data as guessed by deflate. NOTE
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BEST_COMPRESSION =
Slowest compression level, but with the best space savings.
INT2FIX(Z_BEST_COMPRESSION)
-
BEST_SPEED =
Fastest compression level, but with the lowest space savings.
INT2FIX(Z_BEST_SPEED)
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BINARY =
:Deflate#data_type.
Represents binary data as guessed by deflate. See Zlib
-
DEFAULT_COMPRESSION =
Default compression level which is a good trade-off between space and time
INT2FIX(Z_DEFAULT_COMPRESSION)
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DEFAULT_STRATEGY =
Default deflate strategy which is used for normal data.
INT2FIX(Z_DEFAULT_STRATEGY)
-
DEF_MEM_LEVEL =
The default memory level for allocating zlib deflate compression state.
INT2FIX(DEF_MEM_LEVEL)
-
FILTERED =
::Zlib::Deflate strategy for data produced by a filter (or predictor). The effect of
FILTERED
is to force more Huffman codes and less string matching; it is somewhat intermediate between DEFAULT_STRATEGY and HUFFMAN_ONLY. Filtered data consists mostly of small values with a somewhat random distribution.INT2FIX(Z_FILTERED)
-
FINISH =
Processes all pending input and flushes pending output.
INT2FIX(Z_FINISH)
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FIXED =
::Zlib::Deflate strategy which prevents the use of dynamic Huffman codes, allowing for a simpler decoder for specialized applications.
INT2FIX(Z_FIXED)
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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. Like SYNC_FLUSH, using
FULL_FLUSH
too often can seriously degrade compression.INT2FIX(Z_FULL_FLUSH)
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HUFFMAN_ONLY =
::Zlib::Deflate strategy which uses Huffman codes only (no string matching).
INT2FIX(Z_HUFFMAN_ONLY)
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MAX_MEM_LEVEL =
The maximum memory level for allocating zlib deflate compression state.
INT2FIX(MAX_MEM_LEVEL)
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MAX_WBITS =
:Inflate
.new for details.The maximum size of the zlib history buffer. Note that zlib allows larger values to enable different inflate modes. See Zlib
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NO_COMPRESSION =
No compression, passes through data untouched. Use this for appending pre-compressed data to a deflate stream.
INT2FIX(Z_NO_COMPRESSION)
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NO_FLUSH =
NO_FLUSH
is the default flush method and allows deflate to decide how much data to accumulate before producing output in order to maximize compression.INT2FIX(Z_NO_FLUSH)
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OS_AMIGA =
OS code for Amiga hosts
INT2FIX(OS_AMIGA)
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OS_ATARI =
OS code for Atari hosts
INT2FIX(OS_ATARI)
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OS_CODE =
The OS code of current host
INT2FIX(OS_CODE)
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OS_CPM =
OS code for CP/M hosts
INT2FIX(OS_CPM)
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OS_MACOS =
OS code for Mac OS hosts
INT2FIX(OS_MACOS)
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OS_MSDOS =
OS code for MSDOS hosts
INT2FIX(OS_MSDOS)
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OS_OS2 =
OS code for OS2 hosts
INT2FIX(OS_OS2)
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OS_QDOS =
OS code for QDOS hosts
INT2FIX(OS_QDOS)
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OS_RISCOS =
OS code for RISC OS hosts
INT2FIX(OS_RISCOS)
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OS_TOPS20 =
OS code for TOPS-20 hosts
INT2FIX(OS_TOPS20)
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OS_UNIX =
OS code for UNIX hosts
INT2FIX(OS_UNIX)
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OS_UNKNOWN =
OS code for unknown hosts
INT2FIX(OS_UNKNOWN)
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OS_VMCMS =
OS code for VM OS hosts
INT2FIX(OS_VMCMS)
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OS_VMS =
OS code for VMS hosts
INT2FIX(OS_VMS)
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OS_WIN32 =
OS code for Win32 hosts
INT2FIX(OS_WIN32)
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OS_ZSYSTEM =
OS code for Z-System hosts
INT2FIX(OS_ZSYSTEM)
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RLE =
::Zlib::Deflate compression strategy designed to be almost as fast as HUFFMAN_ONLY, but give better compression for PNG image data.
INT2FIX(Z_RLE)
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SYNC_FLUSH =
The SYNC_FLUSH method 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.
INT2FIX(Z_SYNC_FLUSH)
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TEXT =
:Deflate#data_type.
Represents text data as guessed by deflate. See Zlib
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UNKNOWN =
:Deflate#data_type.
Represents an unknown data type as guessed by deflate. See Zlib
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VERSION =
The Ruby/zlib version string.
rb_str_new2(RUBY_ZLIB_VERSION)
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ZLIB_VERSION =
The string which represents the version of zlib.h
rb_str_new2(ZLIB_VERSION)
Class Method Summary
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.deflate(string[, level])
Alias for Deflate.deflate.
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.inflate(string)
Alias for Inflate.inflate.
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.adler32(string, adler)
mod_func
Calculates Adler-32 checksum for
string
, and returns updated value ofadler
. -
.adler32_combine(adler1, adler2, len2)
mod_func
Combine two Adler-32 check values in to one.
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.crc32(string, crc)
mod_func
Calculates CRC checksum for
string
, and returns updated value ofcrc
. -
.crc32_combine(crc1, crc2, len2)
mod_func
Combine two CRC-32 check values in to one.
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.crc_table
mod_func
Returns the table for calculating CRC checksum as an array.
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.zlib_version
mod_func
Returns the string which represents the version of zlib library.
Class Method Details
.adler32(string, adler) (mod_func)
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
.
Example usage:
require "zlib"
data = "foo"
puts "Adler32 checksum: #{Zlib.adler32(data).to_s(16)}"
#=> Adler32 checksum: 2820145
.adler32_combine(adler1, adler2, len2) (mod_func)
Combine two Adler-32 check values in to one. alder1
is the first Adler-32 value, adler2
is the second Adler-32 value. len2
is the length of the string used to generate adler2
.
.crc32(string, crc) (mod_func)
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
.
FIXME: expression.
.crc32_combine(crc1, crc2, len2) (mod_func)
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
.
.crc_table (mod_func)
Returns the table for calculating CRC checksum as an array.
.deflate(string[, level])
Alias for Deflate.deflate.
.inflate(string)
Alias for Inflate.inflate.
.zlib_version (mod_func)
Returns the string which represents the version of zlib library.