ucobs/CLAUDE.md

μCOBS (ucobs)

Identity

• Crate name: ucobs (on crates.io)
• Display name: μCOBS
• Mission: Become THE COBS crate for Rust — embedded and non-embedded alike

First Principles

1. Correct — 100% COBS spec-compliant (Cheshire & Baker 1999). No shortcuts, no deviations.
2. Interoperable — proven byte-for-byte compatibility with corncobs, cobs crates and Python cobs packages.
3. Insanely tested — canonical vectors, property-based tests (proptest), fuzz targets (cargo-fuzz), cross-crate interop, miri, mutation testing, randomized payloads. If you think testing is done, you're 10% done.
4. Fast — benchmark against every competing implementation. Must be at least as fast, ideally fastest. Benchmarks run via just bench.
5. Tiny — no_std, zero-alloc, zero runtime dependencies. ~140 lines of implementation. Runs on 8-bit MCUs and servers alike.
6. Trustworthy — small enough to audit by hand. No unsafe. No panics in release. Fuzz-hardened.

Architecture

Single-file library: src/lib.rs

Public API (3 functions)

pub const fn encode(src: &[u8], dest: &mut [u8]) -> Option<usize>
pub fn decode(src: &[u8], dest: &mut [u8]) -> Option<usize>
pub const fn max_encoded_len(src_len: usize) -> usize

Convention: Output does NOT include trailing 0x00 sentinel. Caller appends it for framing.

Development

# Run all quality gates (tests, clippy, fmt, doc, fuzz, miri, mutants)
just test

# Unit + property + interop tests only
just test-unit

# Benchmarks (iai-callgrind, requires valgrind)
just bench

# Fuzz (requires nightly + cargo-fuzz)
just test-fuzz

Dev Dependencies (test-only)

• cobs — cross-validation against the cobs 0.5 crate
• corncobs — cross-validation against another COBS implementation
• iai-callgrind — deterministic instruction-count benchmarks
• mutants — mutation testing annotations
• proptest — property-based testing
• rand — randomized test payloads

Roadmap

• quickcheck in addition to proptest
• Even more fuzz targets and edge-case generators