/
file_header.go
82 lines (64 loc) · 1.17 KB
/
file_header.go
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package block
import (
"encoding/binary"
"io"
"os"
)
const headerSize int64 = 2
type FileHeader struct {
inner *os.File
usage uint16 // 2 bytes
}
func NewFileHeader(file *os.File) *FileHeader {
return &FileHeader{
inner: file,
usage: 1,
}
}
func (h *FileHeader) Size() int64 {
return headerSize
}
func (h *FileHeader) Load() error {
if _, err := h.inner.Seek(0, io.SeekStart); err != nil {
return err
}
var usage uint16
if err := binary.Read(h.inner, binary.LittleEndian, &usage); err != nil {
if err == io.EOF {
return h.save()
}
return err
}
h.usage = usage
return nil
}
func (h *FileHeader) Usage() uint16 {
return h.usage
}
func (h *FileHeader) IncreaseUsage() error {
h.usage++
return h.save()
}
func (h *FileHeader) DecreaseUsage() error {
h.usage--
if h.usage == 0 {
return io.EOF
}
return h.save()
}
func (h *FileHeader) ResetUsage(usage uint16) error {
if usage < 1 {
usage = 1
}
h.usage = usage
return h.save()
}
func (h *FileHeader) save() error {
if _, err := h.inner.Seek(0, io.SeekStart); err != nil {
return err
}
if err := binary.Write(h.inner, binary.LittleEndian, h.usage); err != nil {
return err
}
return nil
}