Gzpeek: Tool to Parse Gzip Metadata

3 days ago

Gzip streams contain metadata including the operating system that performed the compression.
The gzip header includes a byte identifying the compressor's OS (e.g., 0 for Windows, 3 for Unix).
Different tools and libraries set the OS flag differently, making it unreliable but potentially useful as a hint.
The modification time in the metadata is a Unix timestamp, but many implementations set it to 0.
The FTEXT flag indicates if data is ASCII text, but it's rarely used and often set to 0.
An extra flag (XFL) indicates compression effort (e.g., 2 for max compression, 4 for fastest).
Optional fields include the original filename and a comment, though many tools don't set them.
gzpeek is a command-line tool written in Zig to inspect gzip metadata, extracting OS, filename, modification time, etc.

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