gix-index 0.56.0

A work-in-progress crate of the gitoxide project dedicated implementing the git index file
Documentation 
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use gix_error::ExnResult;
pub(crate) const SIZE: usize = 4 /*signature*/ + 4 /*version*/ + 4 /* num entries */;

use crate::{Version, util::from_be_u32};

pub(crate) const SIGNATURE: &[u8] = b"DIRC";

pub(crate) fn decode(data: &[u8], object_hash: gix_hash::Kind) -> ExnResult<(Version, u32, &[u8])> {
    use gix_error::ErrorExt;

    if data.len() < (3 * 4) + object_hash.len_in_bytes() {
        return Err(
            gix_error::corruption("File is too small even for header with zero entries and smallest hash")
                .raise_erased(),
        );
    }

    let (signature, data) = data.split_at(4);
    if signature != SIGNATURE {
        return Err(
            gix_error::corruption("Signature mismatch - this doesn't claim to be a header file").raise_erased(),
        );
    }

    let (version, data) = data.split_at(4);
    let version = match from_be_u32(version) {
        2 => Version::V2,
        3 => Version::V3,
        4 => Version::V4,
        unknown => {
            return Err(gix_error::validation(format!("Index version {unknown} is not supported")).raise_erased());
        }
    };
    let (entries, data) = data.split_at(4);
    let entries = from_be_u32(entries);

    Ok((version, entries, data))
}