# compcol
A collection of compression algorithms in pure Rust.
`compcol` puts every supported algorithm — RLE, deflate, zlib, gzip,
LZMA, xz, Zstandard, Brotli, LZ4, Snappy, LZW, LZO, LZX, Quantum, plus
decoders for RAR 1/2/3/5 — behind one uniform streaming trait, with
each algorithm gated by its own Cargo feature so downstream crates
only pay for what they pull in. A runtime by-name factory makes
algorithms selectable from configuration or a CLI flag, and a
`compcol` binary turns the library into a Unix-style filter.
## Design principles
- **Pure Rust.** No `bindgen`, no FFI, no C dependencies. The crate has
**zero runtime dependencies** — nothing in `[dependencies]`.
- **100% safe.** `unsafe_code = "forbid"` is set crate-wide; the library
never opts out.
- **`no_std`.** The library is `#![no_std]`. `alloc` is used by
everything except the bare-bones `rle` algorithm; algorithms that need
large windows or work buffers pull in `alloc` automatically.
- **Streaming.** The caller owns both buffers; the codec preserves its
state across calls. Works in a 1-byte-on-both-sides streaming loop.
- **Per-algorithm features.** `default = ["alloc", "rle", "deflate",
"zlib", "gzip", "factory"]`. Everything else is opt-in.
- **`all` meta-feature.** `features = ["all"]` is a single name that
enables every algorithm — useful for downstream crates and the CLI
install command instead of a 20-item feature list.
## Supported algorithms
| RLE | `rle` | `.rle` | full | full | — |
| Deflate (RFC 1951) | `deflate` | `.deflate` | full (lazy LZ77 + dynamic / fixed / stored Huffman; cross-block matching) | full | `python3 -c "import zlib"` |
| Zlib (RFC 1950) | `zlib` | `.zz` | full | full | `python3 -c "import zlib"` |
| Gzip (RFC 1952) | `gzip` | `.gz` | full | full | `gzip(1)` |
| LZ4 block format | `lz4` | `.lz4` | LZ77 hash matcher | full | — |
| Snappy | `snappy` | `.sz` | LZ77 hash matcher (raw block format) | full | — |
| LZW (`compress(1)` `.Z`) | `lzw` | `.lzw` | full | full | `compress(1)` / `uncompress(1)` |
| LZMA (legacy `.lzma`) | `lzma` | `.lzma` | full | full | `python3 -m lzma` (FORMAT_ALONE) |
| xz | `xz` | `.xz` | compressed-LZMA2 chunks + uncompressed fallback | full envelope + all reset variants | `xz(1)` both directions |
| Zstandard (RFC 8478) | `zstd` | `.zst` | LZ77 + Huffman literals + FSE_Compressed_Mode sequences + repeat offsets + RLE blocks | full Compressed_Block | `zstd(1)` both directions |
| Brotli (RFC 7932) | `brotli` | `.br` | LZ77 + length-limited Huffman + 704-symbol IC alphabet + static-dictionary refs | full (with 122 KiB static dictionary) | `brotli(1)` both directions |
| LZO (LZO1X-1) | `lzo` | `.lzo` | LZ77 hash matcher | full | `python3 -c "import lzo"` |
| LZX (Microsoft CAB / WIM) | `lzx` | `.lzx` | uncompressed blocks only | full (verbatim + aligned-offset + uncompressed; E8 filter) | — |
| Quantum (Stac, old CAB) | `quantum` | `.q` | `Unsupported` (no public encoder exists) | full (libmspack-equivalent) | libmspack regression fixtures |
| LZFSE (Apple) | `lzfse` | `.lzfse` | `Unsupported` (decoder-only) | `bvx-` raw + `bvxn` (LZVN); `bvx2` returns `Unsupported` | hand-built fixtures (no Apple toolchain bundled) |
| ADC (Apple DMG) | `adc` | `.adc` | LZSS-style greedy match-finder | full | hand-built fixtures |
| RAR 1.x | `rar1` | `.rar` | `Unsupported` (license) | building blocks only (Huffman tables not license-clean) | — |
| RAR 2.x | `rar2` | `.rar` | `Unsupported` (license) | full LZ77+Huffman + audio predictor | real rar-2.60 fixtures |
| RAR 3.x | `rar3` | `.rar` | `Unsupported` (license) | full LZ77+Huffman + E8 filter; PPMd & VM filters refused | libarchive RAR3 fixtures |
| RAR 5.x | `rar5` | `.rar` | `Unsupported` (license) | full LZ77+Huffman + x86 filter; Delta/ARM refused | RARLAB-CLI fixtures |
The RAR encoders are permanently `Unsupported` per RARLAB's unRAR
license terms (every clean-room RAR reader — libarchive, The
Unarchiver, 7-Zip — ships decoder-only for the same reason).
Every other algorithm decodes real-world output from its reference
toolchain and produces output that the same reference toolchain
accepts. Some encoders (zstd, brotli) lag the reference's compression
ratio because they skip features like FSE-compressed Huffman weight
tables (zstd) or encoder-side static-dictionary lookups for non-English
text (brotli); the wire format is always conformant.
## Library usage
```toml
# Cargo.toml
[dependencies]
compcol = { version = "0.1", features = ["gzip", "factory"] }
```
### The trait
```rust
use compcol::{Algorithm, Encoder, Decoder, Progress, Error};
pub struct Progress {
pub consumed: usize, // bytes read from input
pub written: usize, // bytes written to output
pub done: bool, // true once finish() has fully drained
}
pub trait Encoder {
fn encode(&mut self, input: &[u8], output: &mut [u8]) -> Result<Progress, Error>;
fn finish(&mut self, output: &mut [u8]) -> Result<Progress, Error>;
fn reset(&mut self);
}
pub trait Decoder {
fn decode(&mut self, input: &[u8], output: &mut [u8]) -> Result<Progress, Error>;
fn finish(&mut self, output: &mut [u8]) -> Result<Progress, Error>;
fn reset(&mut self);
/// Advance the decompressed stream by up to `n` bytes without
/// emitting them. Default impl reads-and-discards through a small
/// scratch buffer; algorithms can override for cheaper skipping.
fn skip(&mut self, input: &[u8], n: usize) -> Result<Progress, Error>;
}
pub trait Algorithm {
const NAME: &'static str;
type Encoder: Encoder;
type Decoder: Decoder;
fn encoder() -> Self::Encoder;
fn decoder() -> Self::Decoder;
}
```
### Streaming a round-trip
```rust
use compcol::gzip::{Encoder, Decoder};
use compcol::{Encoder as _, Decoder as _};
let input = b"hello world hello world hello world";
// Encode.
let mut enc = Encoder::new();
let mut buf = [0u8; 256];
let mut encoded = Vec::new();
let p = enc.encode(input, &mut buf).unwrap();
encoded.extend_from_slice(&buf[..p.written]);
loop {
let p = enc.finish(&mut buf).unwrap();
encoded.extend_from_slice(&buf[..p.written]);
if p.done { break; }
}
// Decode.
let mut dec = Decoder::new();
let mut decoded = Vec::new();
let p = dec.decode(&encoded, &mut buf).unwrap();
decoded.extend_from_slice(&buf[..p.written]);
let p = dec.finish(&mut buf).unwrap();
decoded.extend_from_slice(&buf[..p.written]);
assert!(p.done);
assert_eq!(decoded, input);
```
### Runtime selection via the factory
```rust
use compcol::{factory, Encoder as _, Decoder as _};
let mut enc = factory::encoder_by_name("gzip")
.expect("gzip not compiled in");
let mut out = [0u8; 1024];
let p = enc.encode(b"hello", &mut out).unwrap();
// ...
println!("available algorithms: {:?}", factory::names());
```
`factory::extension(name)` returns the conventional file extension for
each algorithm (e.g. `"gz"` for gzip, `"zst"` for zstd).
### Skipping decompressed bytes
Useful for tar-style archive browsing — read a header, skip past the
file body, read the next header:
```rust
use compcol::gzip::Decoder;
use compcol::Decoder as _;
let mut dec = Decoder::new();
// Skip past the first 100 decompressed bytes…
let p = dec.skip(&compressed[..], 100).unwrap();
// …then decode the next 50:
let mut out = [0u8; 50];
let p = dec.decode(&compressed[p.consumed..], &mut out).unwrap();
```
The default `skip` implementation just reads-and-discards through a
small scratch buffer, so it works for every algorithm. Individual
decoders are free to override with a smarter implementation when the
format allows it (e.g. fast-forwarding through stored deflate blocks
without LZ77 expansion).
## CLI usage
The `compcol` binary ships with the crate. Install with:
```sh
cargo install --path . --features all
```
…or pick a subset:
```sh
cargo install --path . --features "gzip,zstd,brotli,lz4,factory"
```
```text
Usage: compcol -t ALGO [OPTIONS] [INPUT]
Required:
-t, --type ALGO Algorithm (use --list to see what's compiled in)
Mode:
-d, --decompress Decompress instead of compress
Output (mutually exclusive):
-c, --stdout Write to stdout, keep input file
-o, --output PATH Write to PATH
(default, INPUT given) Write to <INPUT>.<ext> on compress, or strip
<ext> on decompress; remove INPUT on success
(default, no INPUT) Read stdin, write stdout
Misc:
-k, --keep Keep input file even in in-place mode
-f, --force Overwrite an existing output file
-L, --list List available algorithms and exit
-V, --version Print version and exit
-h, --help Print this help and exit
```
### Examples
```sh
# Pipe-style use (gzip via stdin → stdout)
# In-place compression (mirrors gzip(1) semantics: removes the original)
compcol -t gzip README.md # → README.md.gz, removes README.md
# Keep the original
compcol -t gzip -k README.md # → README.md.gz, keeps README.md
# Decompress
compcol -t gzip -d README.md.gz # → README.md, removes README.md.gz
# Force overwrite of an existing output file
compcol -t gzip -f README.md
# Round-trip into a pager
# Mix algorithms
compcol -t zstd payload.bin # → payload.bin.zst
compcol -t brotli payload.bin # → payload.bin.br
# List what's compiled in
compcol --list
```
Exit codes: `0` success, `1` runtime / I/O error, `2` usage / argument
error.
## Cargo feature topology
```toml
[features]
default = ["alloc", "rle", "deflate", "zlib", "gzip", "factory"]
# Meta-feature: pulls in every algorithm. Equivalent to `--all-features`.
all = ["alloc", "factory",
"rle", "deflate", "zlib", "gzip",
"lzma", "xz",
"zstd", "brotli", "lz4", "snappy", "lzw",
"lzo", "lzx", "quantum", "lzfse", "adc",
"rar1", "rar2", "rar3", "rar5"]
alloc = []
factory = ["alloc"] # by-name lookup, returns Box<dyn …>
rle = [] # no_std clean (alloc not required)
deflate = ["alloc"]
zlib = ["deflate"]
gzip = ["deflate"]
lzma = ["alloc"]
xz = ["lzma"]
zstd = ["alloc"]
brotli = ["alloc"]
lz4 = ["alloc"]
snappy = ["alloc"]
lzw = ["alloc"]
lzo = ["alloc"]
lzx = ["alloc"]
quantum = ["alloc"]
lzfse = ["alloc"] # decoder-only, bvx2 returns Unsupported
adc = ["alloc"]
rar1 = ["alloc"]
rar2 = ["alloc"]
rar3 = ["alloc"]
rar5 = ["alloc"]
```
A bare `--no-default-features` build produces a library with just the
trait surface — useful for the most constrained embedded targets.
Adding `rle` gives an algorithm that doesn't need `alloc`. Adding any
other algorithm feature pulls in `alloc` and the codec.
`features = ["all"]` enables every algorithm and is the most ergonomic
choice when you don't know in advance which formats you'll see.
The `compcol` binary is gated on `features = ["factory"]` so a
`--no-default-features` library build doesn't try to compile it.
## Errors
`compcol::Error` is a single crate-wide enum so trait objects work
without GATs:
```rust
pub enum Error {
Corrupt, // generic malformed input
UnexpectedEnd, // finish() called mid-stream
OutputTooSmall, // codec has a minimum atomic output size
BadHeader, // container header malformed
InvalidBlockType, // deflate BTYPE=3, etc.
InvalidHuffmanTree, // code lengths violate Kraft inequality
InvalidDistance, // LZ77 back-reference out of range
ChecksumMismatch, // Adler-32 / CRC-32 mismatch
TrailerMismatch, // gzip ISIZE doesn't match output length
Unsupported, // option / mode this build doesn't implement
}
```
## Development
```sh
cargo build # builds lib + bin (default features)
cargo build --no-default-features # bare no_std lib
cargo build --no-default-features --features rle # narrowest alloc-free build
cargo build --no-default-features --features all # every algorithm, still no_std
cargo test --all-features # full test suite
cargo clippy --all-features --all-targets -- -D warnings # lint clean
cargo fmt --all --check # format clean
```
The crate currently ships with **~566 tests across 23 test binaries**,
including round-trip tests for every algorithm with an encoder,
cross-validation against system `gzip` / `xz` / `zstd` / `brotli` /
`compress` / `lz4` / `python3 lzo` / `python3 lzma`, and hand-crafted
hex fixtures for every decoder-only format (RAR 2/3/5, Quantum, LZX).
A simple benchmark harness lives at `examples/bench.rs`. Run it with:
```sh
cargo run --release --features all --example bench
```
It measures each compiled-in algorithm's encoder/decoder throughput
and compression ratio on a small fixed corpus and compares against
the system reference when one is installed. A snapshot of the output
is kept in [`BENCH.md`](./BENCH.md).
## License
MIT. © 2026 Karpeles Lab Inc.