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A Massively Spiffy Yet Delicately Unobtrusive Compression Library
(Also Free, Not to Mention Unencumbered by Patents)
(Not Related to the Linux zlibc Compressing File-I/O Library)
Welcome to the zlib home page, web pages originally created by Greg Roelofs and maintained by Mark Adler. If this page seems suspiciously similar to the PNG Home Page, rest assured that the similarity is completely coincidental. No, really.
zlib was written by Jean-loup Gailly (compression) and Mark Adler (decompression).
zlib 1.3.1
January 22, 2024
Version 1.3.1 has these key updates from 1.3:
- Reject overflows of zip header fields in minizip.
- Fix bug in inflateSync() for data held in bit buffer.
- Add LIT_MEM define to use more memory for a small deflate speedup.
- Fix decision on the emission of Zip64 end records in minizip.
- Add bounds checking to ERR_MSG() macro, used by zError().
- Neutralize zip file traversal attacks in miniunz.
- Fix a bug in ZLIB_DEBUG compiles in check_match().
Version 1.3 has these key updates from 1.2.13:
- Building using K&R (pre-ANSI) function definitions is no longer supported.
- Fixed a bug in deflateBound() for level 0 and memLevel 9.
- Fixed a bug when gzungetc() is used immediately after gzopen().
- Fixed a bug when using gzflush() with a very small buffer.
- Fixed a crash when gzsetparams() is attempted for a transparent write.
- Fixed test/example.c to work with FORCE_STORED.
- Fixed minizip to allow it to open an empty zip file.
- Fixed reading disk number start on zip64 files in minizip.
- Fixed a logic error in minizip argument processing.
You can also look at the complete Change Log.
- Canonical URL: https://zlib.net/ (US)
![[DDJ's zlib image]](images/zlib_ddj.png)
zlib is designed to be a 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 data format is itself portable across
platforms. Unlike the LZW compression method used in Unix compress(1)
and in the GIF image format, the compression method currently used in zlib
essentially never expands the data. (LZW can double or triple the file size in
extreme cases.) zlib's memory footprint is also independent of the input data
and can be reduced, if necessary, at some cost in compression. A more precise,
technical discussion of both points is available on
another page.
zlib was written by Jean-loup Gailly (compression) and Mark Adler (decompression). Jean-loup is also the primary author of gzip(1), the author of the comp.compression FAQ list and the former maintainer of Info-ZIP's Zip; Mark is also the author of gzip's and UnZip's main decompression routines and was the original author of Zip. Not surprisingly, the compression algorithm used in zlib is essentially the same as that in gzip and Zip, namely, the `deflate' method that originated in PKWARE's PKZIP 2.x.
Mark can be reached via e-mail at
.
Please read the FAQ and
the manual before asking for help.
Nearly all of the questions we get already have an
answer in the zlib documentation. Questions on the usage of zlib are
best answered on Stack Overflow.
zlib development contributions and issues are best addressed on
zlib's GitHub repository.
The deflate and zlib specifications both achieved official Internet RFC status in May 1996, and zlib itself was adopted in version 1.1 of the Java Development Kit (JDK), both as a raw class and as a component of the JAR archive format.
The lovely zlib-vise image above was provided courtesy of Bruce Gardner, art director of Dr. Dobb's Journal. It appears in Mark Nelson's article in the January 1997 issue (see below).
The current release is publicly available here:
-
zlib source code, version 1.3.1, tar.gz format (1477K,
SHA-256 hash 9a93b2b7dfdac77ceba5a558a580e74667dd6fede4585b91eefb60f03b72df23):
-
zlib source code, version 1.3.1, tar.xz format (1275K,
SHA-256 hash 38ef96b8dfe510d42707d9c781877914792541133e1870841463bfa73f883e32):
-
zlib source code, version 1.3.1, zipfile format (1616K,
SHA-256 hash 72af66d44fcc14c22013b46b814d5d2514673dda3d115e64b690c1ad636e7b17):
Permalink for the most recent release:
Note that zlib is an integral part of libpng and has been tested extensively as part of many PNG-supporting applications.
zlib Information
-
zlib Frequently Asked Questions
-
Zlib-announce mailing list
- New versions of zlib are announced on this list.
-
Zlib-devel mailing list
-
zlib Manual
-
zlib Usage Example
-
zlib Technical Details
-
zlib-related specifications:
-
Deflate stream disassembler.
infgen.c produces a readable description of a gzip, zlib, or
raw deflate stream.
-
zlib's Deflate Algorithm
-
zlib's deflate flush modes
-
zlib License
-
All released versions of zlib
-
zlib on github
CRC (Cyclic Redundancy Check) Bonus Information
-
Ross Williams' classic "A Painless Guide to CRC Error Detection Algorithms"
-
Code to generate any CRC, with a list of CRC
descriptions. crcany.c can take a description of a CRC and
compute that CRC efficiently. It includes bit-wise, table-driven
byte-wise, and table-driven word-wise CRC algorithms.
-
Code to modify a message so that it generates the
desired CRC. spoof.c takes an abbreviated description of
the CRC, the exclusive-or of the current CRC of the message and the
desired CRC, the length of the message, and a list of bit locations in
a message, and tells you which of those bits should be inverted in the
message to get the desired CRC. Note that it does not need the message
itself, due to the linearity property of CRCs.
ZIP File Processing Bonus Software
-
Code to read a zip file as a stream and extract
its contents. sunzip.c will read a zip file from stdin
and extract the files therein that use compression methods 0, 8, 9, or
12 (stored, deflate, deflate64, or bzip2). It accepts Zip64 input.
-
Code to merge multiple zip files into a single
zip file. zipknit.c accepts Zip64 input files, and will
create Zip64 output if the combined size of the merged zip file
warrants it. All compression formats are permitted, since no
decompression or recompression is performed. Encrypted entries are
permitted, and pass through unscathed.
Related External Links
-
zlib for Linux, both shared and
static plus headers (RPM format, many
architectures)
-
zlib for Solaris (alternate)
-
zlib for macOS (Mac OS X): zlib is already included as part of macOS
-
zlib for Palm Pilot
-
zlib for Newton OS
-
zlib for Windows CE
-
zlib for Windows
9x/NT/2000/XP/2003 (DLL version, plus related utilities)
-
zlib for Windows 9x/NT (DLL and static version)
-
DotNetZip zip file manipulation for .NET, and more (including replacements for the
buggy Microsoft GZipStream and DeflateStream classes)
-
zlib for .NET in C#
-
zlib DLL wrapper for .NET in C#
-
Zip for .NET
-
Mark Nelson's
ZlibTool article (January 1997)
-
zlib C++ wrapper for the
gz*functions. -
C++ zlib and gzip filters in an iostream framework.
-
zlib
32-bit OCX
(C++ source and binaries for use with Visual Basic 4.x or
Delphi 2.0)
- (unsupported VB5 binary also available)
-
zlib Delphi 5 interface
- (includes compiled object files and corresponding C++ Builder 5 project files)
-
zlib Perl interface (source code; look for Compress-Zlib*.tar.gz)
-
zlib Python
interface (online manual; part of the standard library as of
Python 1.5)
-
zlib Tcl
interface mkZiplib
-
zlib Haskell
interface
-
zlib Java interface (see also JAR format)
-
zlib reimplementation in pure
Java
- (not tested by us, but looks like a good alternative to java.util.zip)
-
Mark Nelson's
JavaZip article (with source code) (December 1997)
-
Random access for gzip archives, for Java
Gilles Vollant's zlib-based
mini-zip and
mini-unzip
- (see also Info-ZIP's UnZip, which optionally can be compiled with zlib)
Scott Ludwig's zlib-based
CExe executable compressor for Win32
zlib technical issues, including spec errors
Zip Files: History, Explanation and Implementation
zlib information in Japanese
zlib information in Russian
Real World Scanning and Halftones
(second edition includes a section on zlib)
Markus Oberhumer's
LZO `real-time' data compression library
- (not tested by us, but looks like a good alternative if you need more speed and less compression)
lz4, a very fast compression algorithm
- (not tested by us, but looks like an even better alternative if you need more speed and less compression)
Zstandard, a better compression algorithm
- (not tested by us, but appears to be a better alternative to zlib in both dimensions of compression and speed, as well as decompression speed)
libbzip2
- (not tested by us, but looks like a good alternative if you need more compression and less speed)
PPP Deflate Protocol
(RFC 1979)
Info-ZIP Home Page
Portable Network Graphics (PNG)
Home Page
gzip Home Page
pigz (parallel gzip) Home Page
DataCompression.info
comp.compression Frequently Asked Questions list
Send comments or questions about zlib to the authors at
after checking the FAQ and the
manual.
Please report broken links to
(PGP key).
This page last updated May 4nd, 2025.
|
Web page copyright © 1996-2025
Greg Roelofs,
Jean-loup Gailly and
Mark Adler. zlib software copyright © 1995-2025 Jean-loup Gailly and Mark Adler. |
zlib.org domain name donated by Andrew Green. |