zlib
This article needs additional citations for verification. (March 2021) |
Initial release | 1 May 1995 |
---|---|
Stable release | 1.3.1[1]
/ 22 January 2024 |
Repository | |
Written in | C |
Operating system | Cross-platform |
Type | Data compression |
License | zlib License |
Website | zlib |
zlib (
The first public version of Zlib, 0.9, was released on 1 May 1995 and was originally intended for use with the libpng image library. It is free software, distributed under the zlib License.
Capabilities
Encapsulation
Raw
The zlib wrapper (RFC 1950)[4] is smaller than the gzip wrapper (RFC 1952),[6] as the latter stores a file name and other file system information.
Algorithm
As of September 2018[update], zlib only supports one algorithm, called
Resource use
zlib provides facilities for control of processor and memory use. A compression level value may be supplied that trades speed for compression. There are also facilities for conserving memory, useful in restricted memory environments, such as some embedded systems.
Strategy
The compression can be optimized for specific types of data. If one is using the library to always compress specific types of data, then using a specific strategy may improve compression and performance. For example, if the data contain long lengths of repeated bytes, the run-length encoding (RLE) strategy may give good results at a higher speed. For general data, the default strategy is preferred.
Error handling
Errors in compressed data may be detected and skipped. Further, if "full-flush" points are written to the compressed stream, then corrupt data can be skipped, and the decompression will resynchronize at the next flush point—although no error recovery of the corrupt data is provided. Full-flush points are useful for large data streams on unreliable channels, where some data loss is unimportant, such as in some multimedia applications. However, creating many flush points can affect the speed as well as the amount (ratio) of compression.
Data length
There is no limit to the length of data that can be compressed or decompressed. Repeated calls to the library allow an unlimited number of blocks of data to be handled. Some ancillary code (counters) may suffer from overflow for long data streams, but this does not affect the actual compression or decompression.
When compressing a long (or infinite) data stream, it is advisable to write regular full-flush points.
Applications
Today, zlib is something of a de facto standard, to the point that zlib and DEFLATE are often used interchangeably in standards documents, with thousands of applications relying on it for compression, either directly or indirectly.[8] These include:
- The Linux kernel, where zlib is used to implement compressed network protocols, compressed file systems, and to decompress the kernel image at boot time.
- GNU Binutils and GNU Debugger (GDB)
- PNG image format, which specifies DEFLATE as the stream compression for its bitmapdata.
- libwww, an API for web applications like web browsers.
- The Apache HTTP Server, which uses zlib to implement HTTP/1.1.
- Similarly, the cURL library uses zlib to decompress HTTP responses.[9]
- The OpenSSH client and server, which rely on zlib to perform the optional compression offered by the Secure Shell protocol.
- The OpenSSL and GnuTLS security libraries, which can optionally use zlib to compress TLS connections.
- The stream formats, such as Matroska.
- The rsync remote file synchronizer, which uses zlib to implement optional protocol compression.
- The dpkg and RPM package managers, which use zlib to unpack files from compressed software packages.
- The Apache Subversion and CVS version control systems, which use zlib to compress traffic to and from remote repositories.
- The Apache ORC column-oriented data storage format use ZLib as its default compression method.[10]
- The Git version control system uses zlib to store the contents of its data objects (blobs, trees, commits and tags).
- The PostgreSQL RDBMS uses zlib with custom dump format (pg_dump -Fc) for database backups.
- The class System.IO.Compression.DeflateStream of the Microsoft .NET Framework 2.0 and higher.[11]
- The "deflate" utility in TORNADO as part of VxWorks Operating System made by Wind River Systems uses zlib to compress boot ROM images.
- qpdf , raw zlib compression program, part of
- The MySQL RDBMS uses ZLib LZ77 for compression in InnoDB Tables [12]
zlib is also used in many embedded devices, such as the Apple iPhone and Sony PlayStation 3, because the code is portable, liberally licensed, and has a relatively small memory footprint.
Forks
A commonly used library built on an old codebase, zlib is also frequently forked by third-parties that claim improvements to this library:
- Intel has a high-performance fork of zlib.[13]
- CloudFlare maintains a high-performance fork with "massive" improvements.[14]
- zlib-ng is a zlib replacement fork for "next generation" systems. It removes workaround code for compilers that do not support SIMD and intrinsic functions), and uses code sanitizers, fuzzing, and code coverage to help find bugs.[15]
See also
- DEFLATE
- gzip
- LZ77 and LZ78 § LZ77
- Zip (file format)
- zlib License
- Zopfli
- List of archive formats
References
- ^ Adler, Mark (22 January 2024). "[Zlib-announce] zlib 1.3.1 released". Retrieved 23 January 2024.
- ISBN 9781593270315– via Google Books.
- ISBN 9781886411494– via Google Books.
- ^ doi:10.17487/RFC1950.
- doi:10.17487/RFC1951.
- doi:10.17487/RFC1952.
- ^ rfc1951
- ^ Gailly, Jean-loup; Adler, Mark (2002-04-18), zlib Applications
- ^ "c++ - Why does cURL use zlib?". Stack Overflow.
- ^ https://blog.cloudera.com/orcfile-in-hdp-2-better-compression-better-performance/ cite
orc.compress=Zlib
as default. - ^ System.IO.Compression.DeflateStream. MSDN Library.
- ^ "MySQL :: MySQL 8.0 Reference Manual :: 15.9.1.5 How Compression Works for InnoDB Tables". dev.mysql.com.
- ^ "github Intel ZLIB". github. 25 January 2024. Retrieved 25 January 2024.
- ^ "Fighting Cancer: The Unexpected Benefit Of Open Sourcing Our Code". The Cloudflare Blog. 8 July 2015.
- ^ Rosbach, HK (24 February 2023). "zlib-ng/zlib-ng: zlib replacement with optimizations for "next generation" systems". GitHub. zlib-ng.