qubit-codec 0.17.4

Core codec traits and buffer conversion primitives for Rust
Documentation 
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// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================

use core::convert::Infallible;
use core::num::NonZeroUsize;

use qubit_codec::Codec;
use qubit_codec::DecodeFailure;

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
struct DomainDecodeError;

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
struct PlainCodec;

#[derive(Debug, Eq, PartialEq)]
struct NonDefaultValue(Vec<u8>);

impl Codec for PlainCodec {
    type Value = NonDefaultValue;
    type Unit = u8;
    type DecodeError = DomainDecodeError;
    type EncodeError = Infallible;

    const MIN_UNITS_PER_VALUE: usize = 1;

    const MAX_ENCODE_UNITS_PER_VALUE: usize = 1;

    const MAX_DECODE_UNITS_PER_VALUE: usize = 2;

    unsafe fn decode(
        &mut self,
        input: &[u8],
        input_index: usize,
    ) -> Result<(NonDefaultValue, NonZeroUsize), DecodeFailure<Self::DecodeError>> {
        if input[input_index] == 0xff {
            return Err(DecodeFailure::invalid(DomainDecodeError, NonZeroUsize::MIN));
        }
        Ok((NonDefaultValue(vec![input[input_index]]), NonZeroUsize::MIN))
    }

    unsafe fn encode(
        &mut self,
        value: &NonDefaultValue,
        output: &mut [u8],
        output_index: usize,
    ) -> Result<usize, Self::EncodeError> {
        output[output_index] = value.0[0];
        Ok(1)
    }
}

#[test]
fn test_decode_failure_reports_incomplete_control_flow() {
    let required_total = crate::nonzero(3);
    let failure = DecodeFailure::<DomainDecodeError>::incomplete(required_total);

    assert_eq!(DecodeFailure::incomplete(required_total), failure,);
    assert_eq!(Some(required_total), failure.required_total());
    assert_eq!(None, failure.invalid_source());
    assert_eq!(None, failure.consumed_units());
}

#[test]
fn test_decode_failure_preserves_incomplete_domain_error() {
    let required_total = crate::nonzero(3);
    let failure = DecodeFailure::incomplete_with_source(DomainDecodeError, required_total);

    assert_eq!(
        DecodeFailure::incomplete_with_source(DomainDecodeError, required_total),
        failure,
    );
    assert_eq!(Some(&DomainDecodeError), failure.incomplete_source());
    assert_eq!(Some(required_total), failure.required_total());
}

#[test]
fn test_decode_failure_reports_invalid_domain_error() {
    let consumed = crate::nonzero(2);
    let failure = DecodeFailure::invalid(DomainDecodeError, consumed);

    assert_eq!(DecodeFailure::invalid(DomainDecodeError, consumed), failure);
    assert_eq!(None, failure.required_total());
    assert_eq!(Some(&DomainDecodeError), failure.invalid_source());
    assert_eq!(Some(consumed), failure.consumed_units());
}

#[test]
fn test_decode_failure_reports_invalid_unknown_consumption() {
    let failure = DecodeFailure::invalid_unknown(DomainDecodeError);

    assert_eq!(DecodeFailure::invalid_unknown(DomainDecodeError), failure);
    assert_eq!(None, failure.required_total());
    assert_eq!(Some(&DomainDecodeError), failure.invalid_source());
    assert_eq!(None, failure.consumed_units());
}

#[test]
fn test_codec_trait_is_safe_and_accepts_non_copy_non_default_values() {
    let mut codec = PlainCodec;

    // SAFETY: The input contains one unit, satisfying PlainCodec's decode bound.
    let (decoded_value, _) = unsafe { codec.decode(&[0x41], 0) }.expect("plain codec should decode a value");
    assert_eq!(NonDefaultValue(vec![0x41]), decoded_value);

    let value = NonDefaultValue(vec![0x42]);
    let expected_len = codec.encode_len(&value);
    assert_eq!(1, expected_len);
    let mut output = [0_u8; 1];
    // SAFETY: The one-slot output satisfies PlainCodec's declared encoding bound.
    let written = unsafe { codec.encode(&value, &mut output, 0) }.expect("plain codec encode is infallible");
    assert_eq!(expected_len, written);
    assert_eq!([0x42], output);
}