Editing Zlib (section)

== Capabilities ==

=== Encapsulation ===
Raw [[DEFLATE]] compressed data (RFC 1951)<ref>{{cite IETF |rfc=1951}}</ref> are typically written with a zlib or gzip wrapper encapsulating the data, by adding a header and footer. This provides stream identification and error detection that are not provided by the raw DEFLATE data.

The zlib wrapper (RFC 1950)<ref name=RFC1950>{{cite IETF |rfc=1950}}</ref> is smaller than the gzip wrapper (RFC 1952),<ref>{{cite IETF |rfc=1952}}</ref> as the latter stores a file name and other file system information.

=== Algorithm ===
{{As of|2018|9}}, zlib only supports one algorithm, called [[DEFLATE]], which uses a combination of a variation of [[LZ77 and LZ78#LZ77|LZ77]] (Lempel–Ziv 1977) and [[Huffman coding]].<ref>{{cite IETF |rfc=1951}}</ref> This algorithm provides good compression on a wide variety of data with minimal use of system resources. This is also the algorithm used in the [[ZIP (file format)|Zip archive format]]. The header makes allowance for other algorithms, but none are currently implemented.

=== 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.