nsz-rs

A Rust port of nsz: lossless zstd compression of Nintendo Switch NSP dumps into NSZ, and back.

Built as a library for oxyromon, with a small nszrs CLI that mirrors the subset of nsz flags oxyromon uses.

Status

NCZ files produced by nsz-rs use the same on-disk format as nsz and can be decompressed by either tool. As in nsz, only Program and PublicData NCAs whose sections tile the file are compressed; everything else is copied verbatim. Both directions stream one member at a time, so memory use doesn't grow with the dump size, and a failed run removes its partial output.

nszrs shows a progress bar per file when stderr is a terminal. nszrs -D verifies every NCA against the CNMT and fails on a mismatch. Compressing a rights-managed NCA without its ticket (or a title.keys entry) is an error rather than a silent uncompressed copy.

CLI

cargo build --release
nszrs -D -F -o out/ game.nsz          # decompress
nszrs -C -L -o out/ game.nsp          # solid compress, long-distance matching
nszrs -C -B -s 20 -o out/ game.nsp    # block compress, 1 MiB blocks

Library

The CLI and its progress bar sit behind the default cli feature; embed the library without them:

nsz-rs = { version = "0.2", default-features = false }

use nsz_rs::keys::Keys;
use nsz_rs::pipeline::{Compression, compress_nsp, decompress_nsz};

// Keys are passed as a loader, called only if the container needs them.
let keys = || Keys::load("prod.keys", true);
let solid = Compression { level: 18, ldm: true, block_size_exponent: None };
// The last argument receives input bytes consumed; the calls add up to the
// input file size, ready to feed a progress bar.
compress_nsp("game.nsp".as_ref(), "game.nsz".as_ref(), keys, &solid, false, &mut |_| {})?;
// keys, fix_padding, verify, strict, progress
let report = decompress_nsz(
    "game.nsz".as_ref(), "game.nsp".as_ref(), keys, false, true, true, &mut |n| bar.inc(n),
)?;

You need your own prod.keys dumped from your own console, but only to compress NCAs or to verify against a CNMT: containers without NCAs (homebrew, for instance) and unverified decompression never load it.

Credits

nsz-rs is a port of nsz by Nico Bosshard, which itself builds on NUT by Blake Warner. The NCZ format, the key derivation and the container handling all come from their work; this crate only re-implements it in Rust.

License

MIT, see LICENSE. The original nsz copyright notice is retained as the license requires.