use crate::{    data,    data::{File, delta, file::decode::Error},}; /// A return value of a resolve function, which given an [`ObjectId`][gix_hash::ObjectId] determines where an object can be found.#[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone)]#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]pub enum ResolvedBase {    /// Indicate an object is within this pack, at the given entry, and thus can be looked up locally.    InPack(data::Entry),    /// Indicates the object of `kind` was found outside of the pack.    OutOfPack {        /// The kind of object we found when reading the header of the out-of-pack base.        kind: gix_object::Kind,        /// The amount of deltas encountered if the object was packed as well.        num_deltas: Option<u32>,    },} /// Additional information and statistics about a successfully decoded object produced by [`File::decode_header()`].////// Useful to understand the effectiveness of the pack compression or the cost of decompression.#[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone, Copy)]#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]pub struct Outcome {    /// The kind of resolved object.    pub kind: gix_object::Kind,    /// The decompressed size of the object.    pub object_size: u64,    /// The amount of deltas in the chain of objects that had to be resolved beforehand.    pub num_deltas: u32,} /// Obtain object information quickly.impl<T> File<T>where    T: crate::FileData,{    /// Resolve the object header information starting at `entry`, following the chain of entries as needed.    ///    /// The `entry` determines which object to decode, and is commonly obtained with the help of a pack index file or through pack iteration.    /// `inflate` will be used for (partially) decompressing entries, and will be reset before first use, but not after the last use.    ///    /// `resolve` is a function to lookup objects with the given [`ObjectId`][gix_hash::ObjectId], in case the full object id    /// is used to refer to a base object, instead of an in-pack offset.    ///    /// For delta entries, this only probes the initial delta header bytes to determine the result    /// object size. It can reject streams that end or overflow within that probe, but it does not    /// fully validate that the compressed stream produces exactly the decompressed size declared in    /// the pack entry header. Use [`File::decode_entry()`][crate::data::File::decode_entry()] when    /// callers need that full validation.    pub fn decode_header(        &self,        mut entry: data::Entry,        inflate: &mut gix_zlib::Inflate,        resolve: &dyn Fn(&gix_hash::oid) -> Option<ResolvedBase>,    ) -> Result<Outcome, Error> {        use crate::data::entry::Header::*;        let mut num_deltas = 0;        let mut first_delta_decompressed_size = None::<u64>;        loop {            match entry.header {                Tree | Blob | Commit | Tag => {                    return Ok(Outcome {                        kind: entry.header.as_kind().expect("always valid for non-refs"),                        object_size: first_delta_decompressed_size.unwrap_or(entry.decompressed_size),                        num_deltas,                    });                }                OfsDelta { base_distance } => {                    num_deltas += 1;                    if first_delta_decompressed_size.is_none() {                        first_delta_decompressed_size = Some(self.decode_delta_object_size(inflate, &entry)?);                    }                    entry = self.entry(entry.checked_base_pack_offset(base_distance).ok_or(                        crate::data::entry::decode::Error::Corrupt {                            message: "an ofs-delta base distance pointing before pack start",                        },                    )?)?;                }                RefDelta { base_id } => {                    num_deltas += 1;                    if first_delta_decompressed_size.is_none() {                        first_delta_decompressed_size = Some(self.decode_delta_object_size(inflate, &entry)?);                    }                    match resolve(base_id.as_ref()) {                        Some(ResolvedBase::InPack(base_entry)) => entry = base_entry,                        Some(ResolvedBase::OutOfPack {                            kind,                            num_deltas: origin_num_deltas,                        }) => {                            return Ok(Outcome {                                kind,                                object_size: first_delta_decompressed_size.unwrap_or(entry.decompressed_size),                                num_deltas: origin_num_deltas.unwrap_or_default() + num_deltas,                            });                        }                        None => return Err(Error::DeltaBaseUnresolved(base_id)),                    }                }            }        }    }     /// Decode the result object size from the initial delta header bytes in `inflate`, using `entry`    /// for offsets.    ///    /// This intentionally mirrors Git's cheap header probe: only the first 20 decompressed bytes    /// are inspected, which is enough for the two `u64` varints that make up a valid delta header.    /// If the zlib stream ends within that probe, we can reject declared-size mismatches here.    /// Otherwise this result only proves that the delta header prefix is parseable; full    /// decompression through `decode_entry()` must still validate that the stream length matches    /// the pack entry header.    #[inline]    fn decode_delta_object_size(&self, inflate: &mut gix_zlib::Inflate, entry: &data::Entry) -> Result<u64, Error> {        let mut buf = [0_u8; 20];        let max_size = entry.decompressed_size.min(buf.len() as u64) as usize;        let (status, _consumed_in, consumed_out) =            self.decompress_entry_from_data_offset_unchecked(entry.data_offset, inflate, &mut buf[..max_size])?;        if status == gix_zlib::Status::StreamEnd {            if consumed_out as u64 != entry.decompressed_size {                return Err(data::entry::decode::Error::Corrupt {                    message: "pack entry decompressed to fewer bytes than declared in the entry header",                }                .into());            }        } else if entry.decompressed_size == max_size as u64 {            return Err(data::entry::decode::Error::Corrupt {                message: "pack entry decompressed to more bytes than declared in the entry header",            }            .into());        }        let buf = &buf[..consumed_out];        let (_base_size, offset) = delta::decode_header_size(buf)?;        let (result_size, _offset) = delta::decode_header_size(&buf[offset..])?;        Ok(result_size)    }} #[cfg(test)]mod tests {    use super::*;     #[test]    fn size_of_decode_entry_outcome() {        assert_eq!(            std::mem::size_of::<Outcome>(),            16,            "this shouldn't change without use noticing as it's returned a lot"        );    }}