Qubit Codec

Core codec traits and buffer conversion primitives for Rust.

Overview

Qubit Codec is the domain-neutral foundation for Qubit codec crates. It contains small traits and value types that are shared by binary, text, misc, and I/O adapter crates without pulling in std::io stream helpers or concrete format implementations.

This crate provides:

Codec<Value, Unit> for low-level single-value buffer codecs.
Encoder and Decoder traits for owned whole-value convenience APIs.
Transcoder, TranscodeProgress, and TranscodeStatus for caller-managed logical-stream conversion.
ByteOrder, ByteOrderSpec, BigEndian, and LittleEndian for byte-order metadata shared by binary and text codecs.

Concrete codecs live in sibling crates such as qubit-codec-binary, qubit-codec-text, and qubit-codec-misc.

Design Goals

Layered Boundaries: keep domain-neutral traits separate from binary, text, misc, and stream-specific implementations.
Small Public Surface: expose only the primitives that multiple codec crates need to share.
No I/O Coupling: avoid std::io dependencies so buffer codecs can remain usable in non-stream contexts.
Policy Neutrality: leave charset, malformed-input, and wire-format rules to domain crates.
Zero-Cost Markers: represent byte order as copyable type/value markers without runtime allocation.
Stable Progress Reporting: use TranscodeProgress and TranscodeStatus to make caller-managed buffer conversion explicit.

Features

Core Conversion Traits

Codec<Value, Unit>: encodes and decodes one value or codec quantum against a caller-managed unit buffer.
Encoder<Input>: converts a borrowed value into an owned output type.
Decoder<Input>: converts a borrowed encoded value into an owned decoded output type.

Buffer Transcoder Primitives

Transcoder<Input, Output>: converts input units into output units inside caller-provided buffers, then finalizes pending stream state at EOF.
TranscodeProgress: reports relative input units read and output units written.
TranscodeStatus: distinguishes complete conversion from NeedInput and NeedOutput stops.

Byte Order Markers

ByteOrder: runtime byte-order enum for public APIs.
ByteOrderSpec: type-level byte-order trait used by hot codecs.
BigEndian / LittleEndian: zero-sized marker types.

Focused Public API

prelude module: imports the commonly used core traits and markers.
No concrete formats: binary, text, and miscellaneous codecs are published in sibling crates.

Installation

Add this to your Cargo.toml:

[dependencies]
qubit-codec = "0.4"

Quick Start

use qubit_codec::{
    TranscodeProgress,
    TranscodeStatus,
    Encoder,
};

struct StringEncoder;

impl Encoder<str> for StringEncoder {
    type Output = String;
    type Error = core::convert::Infallible;

    fn encode(&self, input: &str) -> Result<Self::Output, Self::Error> {
        Ok(input.to_owned())
    }
}

let encoded = Encoder::<str>::encode(&StringEncoder, "codec")?;
assert_eq!("codec", encoded);

let progress = TranscodeProgress::complete(3, 4);
assert_eq!(TranscodeStatus::Complete, progress.status());

# Ok::<(), core::convert::Infallible>(())

API Reference

Core Codec Traits

Trait	Purpose	Typical Implementor
`Codec<Value, Unit>`	Encode/decode one value or quantum against caller buffers	Binary scalar, charset char, escaped byte, Base64 quantum
`Encoder<Input>`	Encode a borrowed input into an owned output	Convenience text, binary, or misc helper
`Decoder<Input>`	Decode a borrowed input into an owned output	Convenience text, binary, or misc helper

`Transcoder` Operations

Method	Description
`max_output_len(input_len)`	Return a finite output upper bound when known
`max_finish_output_len()`	Return a finite finalization output upper bound when known
`reset()`	Reset retained stream state while keeping configuration
`transcode(input, input_index, output, output_index)`	Convert input units into output units
`finish(output, output_index)`	Finalize EOF state, flush trailers, or reject incomplete input

`TranscodeStatus` Values

Status	Meaning
`Complete`	The current conversion step completed
`NeedInput`	More input units are required unless the caller is ready to call `finish()` at EOF
`NeedOutput`	More output capacity is required

Byte Order Types

Type	Use Case
`ByteOrder`	Runtime byte-order selection in public APIs
`ByteOrderSpec`	Type-level byte-order abstraction
`BigEndian`	Big-endian type marker
`LittleEndian`	Little-endian type marker

Crate Boundary

qubit-codec does not contain concrete binary formats, character sets, percent/Base64/hex codecs, or std::io reader/writer adapters. Keep those in domain crates so downstream users can depend on only the layers they need.

Performance Considerations

All core abstractions are trait or marker types. BigEndian and LittleEndian are zero-sized, and ByteOrder is a small copyable enum. The crate performs no heap allocation by itself; allocation behavior is controlled by concrete codec implementations in downstream crates.

Testing & Code Coverage

This project keeps the core trait contracts 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

qubit-codec has no runtime dependencies.

License

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 free of concrete format implementations.
Document public traits and marker types with examples.
Keep tests comprehensive and deterministic.
Ensure all checks pass before submitting a PR.

Author

Haixing Hu

Related Projects

qubit-codec-binary: binary buffer codecs.
qubit-codec-text: charset and Unicode buffer codecs.
qubit-codec-misc: reusable miscellaneous byte and text 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

qubit-codec 0.4.0