///pub mod object {    ///    pub mod header {        //! loose object header encoding and decoding        use byteorder::WriteBytesExt;        use git_object as object;         /// Returned by [`decode()`]        #[derive(thiserror::Error, Debug)]        #[allow(missing_docs)]        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),        }         /// Decode a loose object header, being `<kind> <size>\0`, returns ([`Kind`][object::Kind], `size`, `consumed bytes`).        ///        /// `size` is the uncompressed size of the payload in bytes.        pub fn decode(input: &[u8]) -> Result<(object::Kind, u64, usize), Error> {            let header_end = input                .iter()                .position(|&b| b == 0)                .ok_or(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 ",            }        }         /// Encode the objects `Kind` and `size` into a format suitable for use with [`decode()`].        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(())                }            }        }    }}