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package pack
import (
"bytes"
"encoding/binary"
"errors"
"hash"
"io"
)
var (
// packHeader is the expected header that begins all valid packfiles.
packHeader = []byte{'P', 'A', 'C', 'K'}
// errBadPackHeader is a sentinel error value returned when the given
// pack header does not match the expected one.
errBadPackHeader = errors.New("gitobj/pack: bad pack header")
)
// DecodePackfile opens the packfile given by the io.ReaderAt "r" for reading.
// It does not apply any delta-base chains, nor does it do reading otherwise
// beyond the header.
//
// If the header is malformed, or otherwise cannot be read, an error will be
// returned without a corresponding packfile.
func DecodePackfile(r io.ReaderAt, hash hash.Hash) (*Packfile, error) {
header := make([]byte, 12)
if _, err := r.ReadAt(header[:], 0); err != nil {
return nil, err
}
if !bytes.HasPrefix(header, packHeader) {
return nil, errBadPackHeader
}
version := binary.BigEndian.Uint32(header[4:])
objects := binary.BigEndian.Uint32(header[8:])
return &Packfile{
Version: version,
Objects: objects,
r: r,
hash: hash,
}, nil
}
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