Crous

A compact, canonical binary serializer and human-readable alternative to JSON, written in Rust.

Overview

Crous is a production-grade binary serialization format that provides:

• Compact binary encoding — 2×–5× smaller than equivalent JSON
• Human-readable text notation — unique syntax with deterministic binary mapping
• Zero-copy decoding — borrow directly from input buffers
• Schema evolution — stable field IDs, unknown-field skipping
• Streaming support — block-framed format with per-block checksums
• Pluggable compression — zstd/snappy per-block, with plugin trait
• Cross-language FFI — clean C bindings with documented ownership

Quick Start

use crous_core::{Encoder, Decoder, Value};

// Encode
let value = Value::Object(vec![
    ("name".into(), Value::Str("Alice".into())),
    ("age".into(), Value::UInt(30)),
    ("active".into(), Value::Bool(true)),
]);

let mut encoder = Encoder::new();
encoder.encode_value(&value).unwrap();
let bytes = encoder.finish().unwrap();

// Decode (zero-copy)
let mut decoder = Decoder::new(&bytes);
let decoded = decoder.decode_next().unwrap();
assert_eq!(decoded.to_owned_value(), value);

Human-Readable Syntax

{
    name: "Alice";
    age: 30;
    tags: ["admin", "user"];
    config: {
        theme: "dark";
        notifications: true;
    };
    avatar: b64#iVBORw0KGgo=;
}

Workspace Crates

Python Implementation

A pure-Python implementation is included in python/crous/, providing full encode/decode compatibility with the Rust implementation:

import crous

# Encode
data = crous.encode({"name": "Alice", "age": 30, "active": True})

# Decode
obj = crous.decode(data)
print(obj)  # {'name': 'Alice', 'age': 30, 'active': True}

# Human-readable text format
text = crous.pretty_print(crous.Value.from_python(obj))
print(text)

Cross-language interop verified: Rust-encoded files decode correctly in Python and vice versa.

# Run Python tests
cd python && python -m pytest tests/ -v

CLI Usage

# Install
cargo install --path crous-cli

# Convert JSON to Crous
crous from-json data.json -o data.crous

# Pretty-print a Crous file
crous pretty data.crous

# Inspect block layout
crous inspect data.crous

# Convert back to JSON
crous to-json data.crous

# Quick benchmark
crous bench data.json -n 10000

Derive Macro

use crous_derive::{Crous, CrousSchema};

#[derive(Debug, PartialEq, Crous, CrousSchema)]
struct Person {
    #[crous(id = 1)] name: String,
    #[crous(id = 2)] age: u8,
    #[crous(id = 3)] tags: Vec<String>,
}

let alice = Person {
    name: "Alice".into(),
    age: 30,
    tags: vec!["admin".into()],
};

// Encode
let value = alice.to_crous_value();
let mut encoder = Encoder::new();
encoder.encode_value(&value).unwrap();
let bytes = encoder.finish().unwrap();

Binary Format Summary

File:    [Header 8B] [Block]* [Trailer Block]
Header:  "CROUSv1" (7B) | flags (1B)
Block:   type(1B) | length(varint) | compression(1B) | checksum(8B) | payload

Wire types: Null, Bool, VarUInt (LEB128), VarInt (ZigZag+LEB128), Fixed64, LenDelimited, StartObject, EndObject, StartArray, EndArray, Reference.

Build & Test

cargo build --workspace
cargo test --workspace --all-features
cargo clippy --workspace --all-features
cargo bench -p crous-core

Fuzzing

cargo +nightly fuzz run fuzz_decode     # arbitrary byte decoder
cargo +nightly fuzz run fuzz_roundtrip  # structured Value roundtrip
cargo +nightly fuzz run fuzz_text       # text parser
cargo +nightly fuzz run fuzz_varint     # varint codec

Performance

Crous vs JSON (serde_json) on Apple Silicon (M-series):

Crous decode throughput: 1.2 GiB/s for small objects.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.