zlibcompressed

zlibcompressed refers to data that has been compressed using the zlib software library, which implements the zlib data format. The zlib format is most commonly used with the Deflate compression algorithm and is designed to be compact, portable, and stream-friendly. The zlib library, part of the widely distributed libz package, provides APIs for compressing and decompressing data in memory or as streams, and is used across many programming languages and platforms.

Structure: a zlib stream begins with a small two-byte header that identifies the compression method (deflate) and a window size, with an optional flag indicating a preset dictionary. The payload is a sequence of deflate-compressed blocks, and the stream ends with a four-byte Adler-32 checksum of the uncompressed data. This checksum allows receivers to verify integrity after decompression; there is no internal password or encryption in zlib compression.

Usage: zlib compressed data appears in various contexts, including embedded payloads, network protocols, and within file formats that require a compact binary form. It is also used by PNG image files in their image data chunks and is supported by many languages via standard libraries.

Relation to other formats: gzip and zip also use the Deflate algorithm but employ different wrappers and metadata (for example, gzip uses its own header and trailer with a CRC-32). The zlib format is distinct from gzip while sharing the same underlying compression technique; understanding this distinction helps in correctly reading, generating, and validating streams labeled as zlibcompressed.

See also: Deflate, gzip, PNG, libz, compression.