monochromatic-git-policy-cli 0.5.31

//! What:
//!  The nine 32-bit stat fields an index entry and the untracked-cache extension store, and the Git varint.
//! Why:
//!  Both file layouts write the same fields (the entry puts the mode between inode and owner), and both use Git's
//!  offset varint for lengths; one definition keeps the readers and writers of the in-process index update in step.
//!
//! In TS you'd write (pseudocode):
//! ```ts
//! type StatData = { ctimeSec: number; ctimeNsec: number; mtimeSec: number; mtimeNsec: number; dev: number; ino: number; uid: number; gid: number; size: number };
//! ```

/// The stat fields of one file as an index stores them (each truncated to 32 bits); all zero is the "never statted" value.
#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
pub struct StatData {
    /// Change time, seconds.
    pub ctime_sec: u32,
    /// Change time, nanoseconds.
    pub ctime_nsec: u32,
    /// Modification time, seconds.
    pub mtime_sec: u32,
    /// Modification time, nanoseconds.
    pub mtime_nsec: u32,
    /// Device.
    pub dev: u32,
    /// Inode.
    pub ino: u32,
    /// Owner.
    pub uid: u32,
    /// Group.
    pub gid: u32,
    /// Size.
    pub size: u32,
}

/// A big-endian `u32` at `at`.
pub fn be32(bytes: &[u8], at: usize) -> Option<u32> {
    let quad: &[u8] = bytes.get(at..at.checked_add(4)?)?;
    return Some(u32::from_be_bytes([quad[0], quad[1], quad[2], quad[3]]));
}

impl StatData {
    /// The fields in the order the untracked cache stores them (36 bytes), as `stat_data_to_disk`.
    pub fn to_cache_bytes(&self, out: &mut Vec<u8>) {
        for value in [self.ctime_sec, self.ctime_nsec, self.mtime_sec, self.mtime_nsec, self.dev, self.ino, self.uid, self.gid, self.size] {
            out.extend_from_slice(&value.to_be_bytes());
        }
    }

    /// The fields from 36 bytes in the untracked cache's order (`stat_data_from_disk`).
    pub fn from_cache_bytes(bytes: &[u8]) -> Option<StatData> {
        return Some(StatData {
            ctime_sec: be32(bytes, 0)?,
            ctime_nsec: be32(bytes, 4)?,
            mtime_sec: be32(bytes, 8)?,
            mtime_nsec: be32(bytes, 12)?,
            dev: be32(bytes, 16)?,
            ino: be32(bytes, 20)?,
            uid: be32(bytes, 24)?,
            gid: be32(bytes, 28)?,
            size: be32(bytes, 32)?,
        });
    }
}

/// The bytes of one stat record in the untracked cache.
pub const CACHE_STAT_LENGTH: usize = 36;

/// Append `value` as Git's offset varint (`encode_varint` in `varint.c`).
pub fn encode_varint(value: u64, out: &mut Vec<u8>) {
    let mut reversed: Vec<u8> = vec![(value & 127) as u8];
    let mut rest: u64 = value >> 7;
    while rest > 0 {
        rest -= 1;
        reversed.push(128 | (rest & 127) as u8);
        rest >>= 7;
    }
    reversed.reverse();
    out.extend_from_slice(reversed.as_slice());
}

/// The varint at the start of `bytes` and the bytes after it (`decode_varint`), or `None` when it is cut off or overflows.
pub fn decode_varint(bytes: &[u8]) -> Option<(u64, &[u8])> {
    let mut used: usize = 1;
    let mut byte: u8 = *bytes.first()?;
    let mut value: u64 = u64::from(byte & 127);
    while byte & 128 != 0 {
        byte = *bytes.get(used)?;
        used += 1;
        value = value.checked_add(1)?;
        if value > (u64::MAX >> 7) {
            return None;
        }
        value = (value << 7) | u64::from(byte & 127);
    }
    return Some((value, &bytes[used..]));
}

#[cfg(test)]
#[path = "index_stat_tests.rs"]
mod tests;