par2-rs

PAR2 verification and repair in pure Rust. No C bindings, no external par2 binary.

[dependencies]
par2-rs = "0.10"

Usage

use par2_rs::{DiskFileAccess, Par2FileSet, Repairability, scan_packets_from_path, verify_all};
use std::path::Path;

fn main() -> par2_rs::Result<()> {
    let packets = scan_packets_from_path(Path::new("release.par2"))?
        .into_iter()
        .map(|(packet, _offset)| packet)
        .collect();
    let set = Par2FileSet::from_packets(packets)?;

    let access = DiskFileAccess::new("/downloads/release".into(), &set);
    let result = verify_all(&set, &access);

    println!("{} recovery blocks available", result.recovery_blocks_available);
    match result.repairable {
        Repairability::NotNeeded => println!("everything verified clean"),
        Repairability::Repairable { blocks_needed, .. } => {
            println!("repairable: {blocks_needed} blocks to rebuild")
        }
        Repairability::Insufficient { blocks_needed, .. } => {
            println!("not enough recovery data: {blocks_needed} blocks short")
        }
        other => println!("{other:?}"),
    }
    Ok(())
}

Par2Repairer drives the full sequence: scan, verify, solve, repair, verify again.

Par2RepairSession retains verification evidence while a download is still arriving, so assessment is incremental and repair uses what is already known. Its source can be files under a base directory, a FileAccess implementation, or an already-parsed set; repair output is always real files.

Capabilities

All PAR2 packet types: Main, File Description, IFSC, Recovery Slice, Creator.
Packets from any number of .par2 files aggregate into one set.
Slice-level verification from IFSC CRC32 + MD5 pairs, so damage is localised rather than condemning a whole file.
16 KB quick-check for cheap file identification; full-file MD5 for sets with no IFSC data.
Placement-aware repair: renamed and moved files are matched by content.
Malformed or truncated packets are skipped by scanning forward, rather than failing the set.

Verifying data that is not on disk

verify_all reads through the FileAccess trait. DiskFileAccess is the ordinary implementation, but supplying your own allows verification against bytes that are still arriving over a network, or that are assembled from a source with no file paths at all.

Feature flags

native-crypto (default): AWS-LC-backed MD5.
metal / wgpu: GPU-accelerated repair through reedsolomon-rs, with CPU fallback when no suitable device or driver is present. On native Apple Silicon, metal also enables policy-driven creation through CreationBackend.

Performance

2.0× means rarpar finished in half the time:

CPU	Arch	Instruction set	par2 (heavy)
AMD EPYC 9R14 (Zen 4)	x86-64	GFNI + AVX-512	1.8×
Intel Xeon Platinum 8488C (Sapphire Rapids)	x86-64	GFNI + AVX-512	1.7×
Intel Core i5-1240P (Alder Lake)	x86-64	GFNI + AVX2	1.9×
AMD Ryzen 5 3600 (Zen 2)	x86-64	AVX2	1.5×
Intel Atom C3538 (Denverton)	x86-64	SSSE3 (no AVX)	1.3×
Apple M5 Max	arm64	NEON	7.1×
Arm Cortex-A72	arm64	NEON	1.2×
Arm Neoverse N1	arm64	NEON	1.4×
Arm Neoverse V2	arm64	NEON	1.5×

The Apple row is the CPU lane, measured against upstream's published macOS arm64 reference binary.

Per-case charts for every machine, the full methodology, and the versions these numbers were measured with: rarpar benchmarks.

Provenance

This is an independent Rust implementation, heavily informed by par2cmdline-turbo, Anime Tosho's speed-focused fork of par2cmdline. Both are GPL-2.0-or-later. That work is also the benchmark reference this crate is measured against.

The PAR2 format itself is specified in the Parity Volume Set Specification 2.0.

Versioned API and migration notes are in CHANGELOG.md.

License

GPL-3.0-or-later. See LICENSE.

par2-rs 0.10.2