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package packfile
import (
"fmt"
objecttype "codeberg.org/lindenii/furgit/object/type"
)
// EntryHeader is one parsed pack entry header prefix.
type EntryHeader struct {
// Type is the entry type tag from the first header byte.
Type objecttype.Type
// Size is the declared resulting object size.
Size int64
// HeaderSize is the number of bytes consumed by the type/size header.
HeaderSize int
}
// ParseEntryHeader parses one pack entry type/size header from data.
func ParseEntryHeader(data []byte) (EntryHeader, error) {
var zero EntryHeader
if len(data) == 0 {
return zero, fmt.Errorf("packfile: truncated entry header")
}
first := data[0]
header := EntryHeader{
Type: objecttype.Type((first >> 4) & 0x07),
Size: int64(first & 0x0f),
HeaderSize: 1,
}
shift := uint(4)
b := first
for b&0x80 != 0 {
if header.HeaderSize >= len(data) {
return zero, fmt.Errorf("packfile: truncated entry header")
}
b = data[header.HeaderSize]
header.HeaderSize++
header.Size |= int64(b&0x7f) << shift
shift += 7
}
if header.Size < 0 {
return zero, fmt.Errorf("packfile: negative entry size")
}
return header, nil
}
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