swaitsandClaude Opus 4.6
531f5311d8
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
131 lines
4.8 KiB
Markdown
131 lines
4.8 KiB
Markdown
# μCOBS
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[](https://crates.io/crates/ucobs)
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[](https://docs.rs/ucobs)
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[](LICENSE)
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**The** COBS implementation for Rust.
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[Consistent Overhead Byte Stuffing](https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing)
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(COBS) encodes arbitrary bytes so that `0x00` never appears in the output,
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allowing `0x00` to serve as an unambiguous frame delimiter. Overhead is exactly
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1 byte per 254 input bytes (worst case).
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## Features
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- **`no_std`, zero-alloc** — runs anywhere, from 8-bit MCUs to servers
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- **~140 lines of implementation** — small, auditable, easy to verify
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- **100% spec-compliant** — Cheshire & Baker, IEEE/ACM Transactions on Networking, 1999
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- **Proven interoperability** — cross-validated against `corncobs`, `cobs`, and Python `cobs`
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- **Insanely tested** — canonical vectors, property-based tests, fuzz targets,
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cross-crate interop, randomized payloads, and more coming
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## Performance
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Benchmarked against the two other `no_std` COBS crates using
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[Criterion](https://github.com/bheisler/criterion.rs) across three payload
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patterns: **all zeros** (worst case — every byte triggers a code emit),
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**no zeros**, and **mixed** (0x00–0xFF cycling). Throughput in MB/s, higher
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is better.
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### Encode
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| Payload | Pattern | μCOBS | `cobs` 0.3 | `corncobs` 0.1 |
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|---------|---------|------:|-----------:|---------------:|
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| 64 B | zeros | 595 | 748 | 180 |
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| 64 B | mixed | 1,853 | 1,011 | 1,734 |
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| 64 B | nonzero | 1,884 | 1,012 | 2,110 |
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| 256 B | zeros | 654 | 817 | 184 |
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| 256 B | mixed | 1,888 | 1,002 | 1,887 |
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| 256 B | nonzero | 1,964 | 1,004 | 1,968 |
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| 4096 B | zeros | 675 | 845 | 188 |
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| 4096 B | mixed | 1,734 | 1,016 | 1,746 |
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| 4096 B | nonzero | 1,775 | 1,020 | 2,245 |
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### Decode
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| Payload | Pattern | μCOBS | `cobs` 0.3 | `corncobs` 0.1 |
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|---------|---------|------:|-----------:|---------------:|
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| 64 B | zeros | 595 | 440 | 732 |
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| 64 B | mixed | 7,041 | 504 | 7,991 |
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| 64 B | nonzero | 9,900 | 502 | 9,807 |
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| 256 B | zeros | 656 | 472 | 742 |
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| 256 B | mixed |17,024 | 645 | 16,207 |
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| 256 B | nonzero |18,456 | 647 | 19,549 |
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| 4096 B | zeros | 675 | 483 | 768 |
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| 4096 B | mixed |17,522 | 656 | 22,959 |
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| 4096 B | nonzero |37,987 | 623 | 40,005 |
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### Code size
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Measured from `.text` section of release-optimized symbols (`encode` + `decode`
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combined):
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| Crate | Code size |
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|----------------|----------:|
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| μCOBS | 541 B |
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| `cobs` 0.3 | 537 B |
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| `corncobs` 0.1 | 637 B |
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All three crates are tiny. The difference is negligible for any target.
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### Crate properties
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| Property | μCOBS | `cobs` 0.3 | `corncobs` 0.1 |
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|----------------|:------:|:-----------------:|:--------------:|
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| `no_std` | always | opt-in[^1] | always |
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| Zero-alloc | yes | opt-in[^2] | yes |
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| `unsafe`-free | yes | yes | yes |
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| Implementation | ~120 LOC | ~790 LOC | ~645 LOC |
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[^1]: Requires disabling the default `std` feature.
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[^2]: `alloc` is enabled by default via the `std` feature.
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> Measured on Intel N100, Rust 1.93.1, Linux 6.12. Run `just bench` to
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> reproduce. Full Criterion reports are generated in `target/criterion/report/`.
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## Usage
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```rust
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// Encode
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let mut buf = [0u8; 16];
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let n = ucobs::encode(&[0x11, 0x00, 0x33], &mut buf).unwrap();
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assert_eq!(&buf[..n], &[0x02, 0x11, 0x02, 0x33]);
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// Decode
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let mut out = [0u8; 16];
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let n = ucobs::decode(&[0x02, 0x11, 0x02, 0x33], &mut out).unwrap();
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assert_eq!(&out[..n], &[0x11, 0x00, 0x33]);
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// Buffer sizing
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let max = ucobs::max_encoded_len(256); // 258
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```
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## API
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| Function | Signature | Description |
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|---|---|---|
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| `encode` | `(src: &[u8], dest: &mut [u8]) -> Option<usize>` | COBS-encode `src` into `dest`. Returns byte count or `None` if buffer too small. |
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| `decode` | `(src: &[u8], dest: &mut [u8]) -> Option<usize>` | Decode COBS data. Returns byte count or `None` if input is malformed. |
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| `max_encoded_len` | `const fn(src_len: usize) -> usize` | Maximum encoded size for a given input length. |
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**Note:** The encoder does *not* append a trailing `0x00` sentinel. Append it
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yourself when framing for transport.
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## Testing
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```sh
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# Unit + property + interop tests
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just test-unit
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# All quality gates (tests, clippy, fmt, doc, fuzz, miri)
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just test
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# Fuzz testing only (requires nightly + cargo-fuzz)
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just test-fuzz
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```
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## License
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[MIT](LICENSE) — Stephen Waits
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