use byteorder::WriteBytesExt;use git_object as object; #[derive(thiserror::Error, Debug)]pub enum Error {    #[error("{message}: {:?}", std::str::from_utf8(.number))]    ParseIntegerError {        source: btoi::ParseIntegerError,        message: &'static str,        number: Vec<u8>,    },    #[error("{0}")]    InvalidHeader(&'static str),    #[error(transparent)]    ObjectHeader(#[from] object::Error),} pub fn decode(input: &[u8]) -> Result<(object::Kind, u64, usize), Error> {    let header_end = input        .iter()        .position(|&b| b == 0)        .ok_or_else(|| Error::InvalidHeader("Did not find 0 byte in header"))?;    let header = &input[..header_end];    let mut split = header.split(|&b| b == b' ');    match (split.next(), split.next()) {        (Some(kind), Some(size)) => Ok((            object::Kind::from_bytes(kind)?,            btoi::btoi(size).map_err(|source| Error::ParseIntegerError {                message: "Object size in header could not be parsed",                number: size.to_owned(),                source,            })?,            header_end + 1, // account for 0 byte        )),        _ => Err(Error::InvalidHeader("Expected '<type> <size>'")),    }} fn kind_to_bytes_with_space(object: object::Kind) -> &'static [u8] {    use object::Kind::*;    match object {        Tree => b"tree ",        Blob => b"blob ",        Commit => b"commit ",        Tag => b"tag ",    }} pub fn encode(object: object::Kind, size: u64, mut out: impl std::io::Write) -> Result<usize, std::io::Error> {    let mut written = out.write(kind_to_bytes_with_space(object))?;    written += itoa::write(&mut out, size)?;    out.write_u8(0)?;    Ok(written + 1)} #[cfg(test)]mod tests {    mod encode_decode_round_trip {        use crate::loose::object::header;        use git_object::bstr::ByteSlice;         #[test]        fn all() -> Result<(), Box<dyn std::error::Error>> {            let mut buf = [0; 20];            for (kind, size, expected) in &[                (git_object::Kind::Tree, 1234, &b"tree 1234\0"[..]),                (git_object::Kind::Blob, 0, b"blob 0\0"),                (git_object::Kind::Commit, 24241, b"commit 24241\0"),                (git_object::Kind::Tag, 9999999999, b"tag 9999999999\0"),            ] {                let written = header::encode(*kind, *size, &mut buf[..])?;                assert_eq!(buf[..written].as_bstr(), expected.as_bstr());                let (actual_kind, actual_size, actual_read) = header::decode(&buf[..written])?;                assert_eq!(actual_kind, *kind);                assert_eq!(actual_size, *size);                assert_eq!(actual_read, written);            }            Ok(())        }    }}