Qubit Binary Codec

Buffer-oriented binary codecs for Rust.

Overview

Qubit Binary Codec provides low-level codecs for caller-managed byte buffers. It does not depend on std::io; stream reader and writer adapters live in qubit-io-binary.

This crate provides:

• BinaryCodec for fixed-width scalar encoding and decoding.
• Leb128Codec for unsigned and signed LEB128 values.
• ZigZagCodec for ZigZag signed integer mapping over unsigned LEB128.
• Strict and NonStrict sealed LEB128 decode policies.
• Leb128DecodePolicy for the built-in LEB128 policy markers.
• Leb128DecodeError and Leb128DecodeErrorKind.
• Essential qubit-codec primitives used by the binary surface: Codec, ByteOrder, ByteOrderSpec, BigEndian, and LittleEndian.

Design Goals

• Buffer First: operate on caller-owned byte slices without requiring Read or Write.
• Hot-Path Efficiency: provide unchecked static codec methods for callers that already validated buffer bounds, plus Codec implementations with Unit = u8 for generic codec pipelines.
• Precise Layering: depend only on qubit-codec, leaving stream adapters to qubit-io-binary.
• Canonical Encoding: always emit canonical LEB128 bytes while allowing configurable decode strictness.
• Typed Byte Order: select endian behavior through type-level byte-order markers.
• Small Dependency Graph: keep binary wire-format code usable by low-level crates without pulling in generic I/O utilities.

Features

Fixed-Width Binary Scalars

• Integer Coverage: encodes and decodes explicit-width primitive integer types: u8, i8, u16, i16, u32, i32, u64, i64, u128, and i128. Platform-width usize and isize are intentionally not fixed-width binary scalar types.
• Floating-Point Coverage: supports f32 and f64 while preserving their IEEE 754 bit patterns.
• Byte Order Support: supports BigEndian and LittleEndian type markers.
• Unchecked Hot Path: decode_unchecked and encode_unchecked avoid repeated bounds checks after the caller validates capacity.

LEB128 Values

• Unsigned Values: supports u8, u16, u32, u64, u128, and usize.
• Signed Values: supports i8, i16, i32, i64, i128, and isize.
• Strict Decode Policy: Strict rejects non-canonical payloads.
• Non-Strict Decode Policy: NonStrict accepts compatible payloads when canonical form is not required.
• Sealed Policy Trait: Leb128DecodePolicy is intentionally sealed; use the built-in Strict or NonStrict markers.

ZigZag Values

• Signed Integer Mapping: maps signed integers to unsigned LEB128 payloads.
• Incomplete Input Reporting: reports partial LEB128 payloads through Leb128DecodeError.

Focused Public API

• prelude module: imports binary codec types and core byte-order markers.
• Core codec trait: BinaryCodec, Leb128Codec, and ZigZagCodec implement qubit_codec::Codec with Unit = u8 and a codec-specific Value.
• No std::io adapters: stream helpers live in qubit-io-binary.

Documentation

• User Guide
• API Reference
• Chinese README

Installation

Add this to your Cargo.toml:

[dependencies]
qubit-codec-binary = "0.1"

Quick Start

use qubit_codec_binary::{
    BigEndian,
    BinaryCodec,
    Leb128Codec,
    NonStrict,
};

let mut fixed = [0_u8; BinaryCodec::<u32, BigEndian>::MAX_UNITS_PER_VALUE];
unsafe {
    BinaryCodec::<u32, BigEndian>::encode_unchecked(0x0102_0304, &mut fixed, 0);
}
assert_eq!([1, 2, 3, 4], fixed);

let mut compact = [0_u8; Leb128Codec::<u64, NonStrict>::MAX_UNITS_PER_VALUE];
let written = unsafe { Leb128Codec::<u64, NonStrict>::encode_unchecked(300, &mut compact, 0) };
assert_eq!(2, written);

Unchecked API Contracts

The low-level codec methods are intentionally unsafe. Callers must validate buffer bounds before using them:

• BinaryCodec::decode_unchecked and BinaryCodec::encode_unchecked require exactly MIN_UNITS_PER_VALUE readable bytes or MAX_UNITS_PER_VALUE writable bytes from index. For fixed-width values these bounds are equal.
• Leb128Codec and ZigZagCodec expose MIN_UNITS_PER_VALUE and MAX_UNITS_PER_VALUE. Their encode_unchecked methods require MAX_UNITS_PER_VALUE writable bytes from index, even when the encoded value is shorter.
• Leb128Codec::decode_unchecked and ZigZagCodec::decode_unchecked require at least MIN_UNITS_PER_VALUE readable byte from index. Callers should normally provide up to MAX_UNITS_PER_VALUE readable bytes unless EOF makes that impossible. Incomplete, malformed, and non-canonical input is reported through Leb128DecodeError.
• Leb128DecodeError::start_index() identifies where the attempted value starts. error_index() identifies where the error became observable. For incomplete input, error_index() is the one-past-available boundary and additional() reports how many more bytes are needed before decoding can make progress.

Higher-level code should wrap these unsafe calls behind safe APIs after checking the appropriate bounds. Import owned-value adapters and buffered engines directly from qubit-codec; this crate does not re-export generic codec adapters. See the User Guide for binary codec examples.

API Reference

BinaryCodec Operations

Leb128Codec Operations

ZigZagCodec Operations

LEB128 Decode Policies

Crate Boundary

qubit-codec-binary only contains buffer-level binary codecs. Use qubit-codec for shared core traits, qubit-io for generic std::io helpers, and qubit-io-binary for stream-oriented binary readers and writers.

Performance Considerations

BinaryCodec, Leb128Codec, and ZigZagCodec are zero-sized codec types with no runtime allocation. Their unchecked methods and Codec implementations with Unit = u8 are intended for validated hot paths where a caller has already checked buffer capacity or is operating inside a buffered stream adapter.

Testing & Code Coverage

This project keeps binary wire-format behavior covered by integration tests under tests/.

Running Tests

# Run all tests
cargo test

# Run with coverage report
./coverage.sh

# Generate text format report
./coverage.sh text

# Align code with CI requirements
./align-ci.sh

# Run CI checks (format, clippy, test, coverage, audit)
RS_CI_SKIP_TOOLCHAIN_UPDATE=1 ./ci-check.sh

Dependencies

Runtime dependencies are intentionally small:

• qubit-codec provides shared codec and byte-order primitives.
• thiserror provides the public LEB128 error type implementation.

License

Copyright (c) 2026. Haixing Hu.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

See LICENSE for the full license text.

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Development Guidelines

• Keep this crate focused on buffer-level binary codecs.
• Add tests for canonical and non-canonical wire-format cases.
• Document public APIs and safety contracts.
• Ensure all checks pass before submitting a PR.

Author

Haixing Hu

Related Projects

• qubit-codec: shared core codec traits and byte-order markers.
• qubit-io-binary: stream adapters for these binary codecs.
• qubit-io: generic std::io helpers.
• More Rust libraries from Qubit are available under the qubit-ltd GitHub organization.

Repository: https://github.com/qubit-ltd/rs-codec-binary