roka-qr

Zero-dependency QR code encoder + decoder for Rust, with built-in PNG and PBM image I/O.

Implements ISO/IEC 18004 end-to-end: byte / alphanumeric / numeric mode decoding, all four error-correction levels (L/M/Q/H), all 40 versions, plus encoding and decoding from PNG or PBM images.

Highlights

• Zero external crate dependencies. std only.
• Encode + decode in one crate — fills a gap on crates.io.
• Self-contained image I/O — PNG encode + decode (including DEFLATE inflate), PBM P1 / P4. No image or flate2 needed.
• Round-trip tested against qrencode and zbarimg.
• No unsafe. 120+ tests, including RFC test vectors for the components (SHA-1, HMAC, RS, BCH).

Quick start

Encode a string and write it as PNG:

use roka_qr::{Encoder, EcLevel};

let code = Encoder::new(b"https://example.com")
    .ec_level(EcLevel::M)
    .build()?;

let png_bytes = code
    .render()
    .scale(8)
    .quiet_zone(4)
    .build()
    .to_png();

std::fs::write("qr.png", png_bytes)?;
# Ok::<(), Box<dyn std::error::Error>>(())

Scan a QR code from a PNG file:

use roka_qr::Reader;

let bytes = std::fs::read("qr.png")?;
let code = Reader::from_png(&bytes)?;
println!("payload: {}", std::str::from_utf8(code.payload())?);
# Ok::<(), Box<dyn std::error::Error>>(())

When to use this crate

• You want both encoding and decoding of QR codes in one place. The popular qrcode crate only encodes; rqrr only decodes.
• You can't (or don't want to) pull in image + flate2 + a separate QR decoder.
• You're building security-sensitive software (auth, payments) and want a fully audit-friendly QR layer.

Constraints

• No camera/perspective correction. Input images must already be aligned and binarized. For phone-camera input, run them through a deskew/threshold step first.
• Decode supports byte / alphanumeric / numeric modes; encode only emits byte mode (sufficient for arbitrary 8-bit payloads). Kanji mode is not supported.

Performance

Indicative numbers on M2 (release); see BUDGETS.md:

Regression gates live in tests/perf_gate.rs.

License

Dual-licensed under Apache 2.0 or MIT, at your option.

Part of the roka project by GOLIA Inc.