libmagic(3) is the backend of the file(1) command, which classifies files, e.g.:
sh
$ file assets/rust-logo-128x128-blk.png
assets/rust-logo-128x128-blk.png: PNG image data, 128 x 128, 8-bit/color RGBA, non-interlaced
This project provides libmagic Rust bindings (NOT the file command from the example). Documentation is rust-magic on Rust CI and $ man 3 libmagic.