use gix_error::{OptionExt, Result, ResultExt, bail, corruption};
use std::io;
use gix_utils::decode::leb64_from_read;
use super::{BLOB, COMMIT, OFS_DELTA, REF_DELTA, TAG, TREE};
use crate::data;
fn corrupt(message: &'static str) -> gix_error::Message {
gix_error::message!("Pack entry is truncated: {message}").corrupted()
}
impl data::Entry {
pub fn from_bytes(d: &[u8], pack_offset: data::Offset, object_hash: gix_hash::Kind) -> Result<data::Entry> {
let (type_id, size, mut consumed) = parse_header_info(d)?;
let hash_len = object_hash.len_in_bytes();
use crate::data::entry::Header::*;
let object = match type_id {
OFS_DELTA => {
let (distance, leb_bytes) = parse_leb64(&d[consumed..])?;
let delta = OfsDelta {
base_distance: distance,
};
consumed += leb_bytes;
delta
}
REF_DELTA => {
let hash = d
.get(consumed..)
.and_then(|d| d.get(..hash_len))
.ok_or_raise(|| corrupt("ref-delta base object id"))?;
let delta = RefDelta {
base_id: gix_hash::ObjectId::try_from(hash)
.or_raise(|| corrupt("unsupported object hash length"))?,
};
consumed += hash_len;
delta
}
BLOB => Blob,
TREE => Tree,
COMMIT => Commit,
TAG => Tag,
other => {
bail!("Object type {other} is unsupported".corrupted());
}
};
Ok(data::Entry {
header: object,
decompressed_size: size,
data_offset: pack_offset + consumed as u64,
encoded_header_size: encoded_header_size(consumed)?,
})
}
pub fn from_read(r: &mut dyn io::Read, pack_offset: data::Offset, hash_len: usize) -> io::Result<data::Entry> {
let (type_id, size, mut consumed) = streaming_parse_header_info(r)?;
use crate::data::entry::Header::*;
let object = match type_id {
OFS_DELTA => {
let (distance, leb_bytes) = leb64_from_read(&mut *r)?;
let delta = OfsDelta {
base_distance: distance,
};
consumed += leb_bytes;
delta
}
REF_DELTA => {
let mut buf = gix_hash::Kind::buf();
let hash = &mut buf[..hash_len];
r.read_exact(hash)?;
#[allow(clippy::redundant_slicing)]
let delta = RefDelta {
base_id: gix_hash::ObjectId::from_bytes_or_panic(&hash[..]),
};
consumed += hash_len;
delta
}
BLOB => Blob,
TREE => Tree,
COMMIT => Commit,
TAG => Tag,
other => return Err(io::Error::other(format!("Object type {other} is unsupported"))),
};
Ok(data::Entry {
header: object,
decompressed_size: size,
data_offset: pack_offset + consumed as u64,
encoded_header_size: encoded_header_size(consumed)
.map_err(|err| io::Error::new(io::ErrorKind::InvalidData, err))?,
})
}
}
fn encoded_header_size(consumed: usize) -> Result<u16> {
u16::try_from(consumed).or_raise(|| corrupt("entry header size does not fit into u16"))
}
#[inline]
fn streaming_parse_header_info(read: &mut dyn io::Read) -> std::result::Result<(u8, u64, usize), io::Error> {
let mut byte = [0u8; 1];
read.read_exact(&mut byte)?;
let mut c = byte[0];
let mut i = 1;
let type_id = (c >> 4) & 0b0000_0111;
let mut size = u64::from(c) & 0b0000_1111;
let mut shift = 4u32;
while c & 0b1000_0000 != 0 {
read.read_exact(&mut byte)?;
c = byte[0];
i += 1;
let component = u64::from(c & 0b0111_1111)
.checked_shl(shift)
.ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "pack entry header overflowed"))?;
size = size
.checked_add(component)
.ok_or_else(|| io::Error::new(io::ErrorKind::InvalidData, "pack entry header overflowed"))?;
shift += 7;
}
Ok((type_id, size, i))
}
#[inline]
fn parse_header_info(data: &[u8]) -> Result<(u8, u64, usize)> {
let mut c = *data
.first()
.ok_or_raise(|| corrupt("need a pack entry header, got empty input"))?;
let mut i = 1;
let type_id = (c >> 4) & 0b0000_0111;
let mut size = u64::from(c) & 0b0000_1111;
let mut shift = 4u32;
while c & 0b1000_0000 != 0 {
c = *data
.get(i)
.ok_or_raise(|| corrupt("pack entry header continuation byte"))?;
i += 1;
let component = u64::from(c & 0b0111_1111)
.checked_shl(shift)
.ok_or_raise(|| corruption("Pack entry header value overflowed while decoding"))?;
size = size
.checked_add(component)
.ok_or_raise(|| corruption("Pack entry header value overflowed while decoding"))?;
shift += 7;
}
Ok((type_id, size, i))
}
fn parse_leb64(data: &[u8]) -> Result<(u64, usize)> {
let mut i = 0;
let mut c = *data.first().ok_or_raise(|| corrupt("an ofs-delta base distance"))?;
i += 1;
let mut value = u64::from(c) & 0x7f;
while c & 0x80 != 0 {
c = *data
.get(i)
.ok_or_raise(|| corrupt("an ofs-delta base distance continuation byte"))?;
i += 1;
value = value
.checked_add(1)
.and_then(|value| value.checked_shl(7))
.and_then(|value| value.checked_add(u64::from(c) & 0x7f))
.ok_or_raise(|| corruption("Pack entry header value overflowed while decoding"))?;
}
Ok((value, i))
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn accepts_non_canonical_pack_entry_header_encoding() -> gix_testtools::TestResult {
let pack_offset = 42;
let entry = data::Entry::from_bytes(&[0xb3, 0x00], pack_offset, gix_hash::Kind::Sha1)?;
assert_eq!(entry.header, data::entry::Header::Blob);
assert_eq!(
entry.decompressed_size, 3,
"`0xb3` is `1011_0011`: the low nibble `0011` is size 3, and the continued `0x00` adds no size bits"
);
assert_eq!(
entry.encoded_header_size, 2,
"the decoded entry records the actual encoded header length, not the canonical length, and has an extra byte 0x00"
);
assert_eq!(
entry.header.size(entry.decompressed_size),
1,
"canonical re-encoding of a blob with size 3 needs only the single byte `0x33`"
);
assert_eq!(
entry.header_size(),
2,
"`header_size()` reports the two bytes actually consumed from `b3 00`, unlike `Header::size()` which canonicalizes to one byte"
);
assert_eq!(entry.pack_offset(), pack_offset);
assert_eq!(entry.data_offset, pack_offset + 2);
Ok(())
}
#[test]
fn non_canonical_pack_entry_header_keeps_ofs_delta_base_offsets_correct() -> gix_testtools::TestResult {
let pack_offset = 100;
let base_distance = 5;
let entry = data::Entry::from_bytes(&[0xe4, 0x00, base_distance], pack_offset, gix_hash::Kind::Sha1)?;
assert_eq!(
entry.header,
data::entry::Header::OfsDelta {
base_distance: base_distance.into()
},
"the base_distance is correct, which wouldn't be the case without using the consumed size"
);
assert_eq!(
entry.header_size(),
3,
"`e4 00` consumes two size-header bytes before the one-byte ofs-delta base distance. entry.size() would be 2"
);
assert_eq!(
entry.pack_offset(),
pack_offset,
"`pack_offset()` subtracts the actual three-byte header from `data_offset`, preserving the entry start"
);
assert_eq!(
entry.checked_base_pack_offset(base_distance.into()),
Some(pack_offset - u64::from(base_distance)),
"ofs-delta base distances are relative to the entry start, so preserving `pack_offset()` keeps the base lookup correct"
);
Ok(())
}
#[test]
fn oversized_encoded_header_size_is_rejected() {
let err = encoded_header_size(usize::from(u16::MAX) + 1).expect_err("the encoded size exceeds u16");
assert!(err.is_corrupted());
assert!(
err.downcast_any_ref::<std::num::TryFromIntError>().is_some(),
"the integer conversion failure remains available"
);
insta::assert_debug_snapshot!(gix_testtools::redact_debug_snapshot(&err, &[]), "entry header lengths that cannot be stored in the Entry metadata must be rejected", @"
Pack entry is truncated: entry header size does not fit into u16
Caused by:
0: out of range integral type conversion attempted
");
}
}