package volume
import (
"time"
"encoding/binary"
"errors"
"os"
"io"
)
//文件基本信息结构体
type FileInfo struct {
Fid uint64
Offset uint64
Size uint64
Ctime time.Time
Mtime time.Time
Atime time.Time
FileName string
}
//文件信息编码到切片中
func (iv *FileInfo)MarshalBinary() []byte {
data := make([]byte, 48 + len(iv.FileName))
binary.BigEndian.PutUint64(data[0:8], iv.Fid)
binary.BigEndian.PutUint64(data[8:16], iv.Offset)
binary.BigEndian.PutUint64(data[16:24], iv.Size)
binary.BigEndian.PutUint64(data[24:32], uint64(iv.Ctime.Unix()))
binary.BigEndian.PutUint64(data[32:40], uint64(iv.Mtime.Unix()))
binary.BigEndian.PutUint64(data[40:48], uint64(iv.Atime.Unix()))
copy(data[48:], []byte(iv.FileName))
return data
}
//文件信息解码到结构体中
func (iv *FileInfo)UnMarshalBinary(data []byte) (err error) {
defer func() {
if r := recover(); r != nil {
err = r.(error)
}
}()
iv.Fid = binary.BigEndian.Uint64(data[0:8])
iv.Offset = binary.BigEndian.Uint64(data[8:16])
iv.Size = binary.BigEndian.Uint64(data[16:24])
iv.Ctime = time.Unix(int64(binary.BigEndian.Uint64(data[24:32])), 0)
iv.Mtime = time.Unix(int64(binary.BigEndian.Uint64(data[32:40])), 0)
iv.Atime = time.Unix(int64(binary.BigEndian.Uint64(data[40:48])), 0)
iv.FileName = string(data[48:])
return err
}
//文件结构体
type File struct {
DataFile *os.File
Info *FileInfo
offset uint64 //偏移量
}
//读取文件
func (f *File)Read(b []byte) (n int, err error) {
//计算文件开始读取位置和结束位置
start := f.Info.Offset + f.offset
end := f.Info.Offset + f.Info.Size
length := end - start
if len(b) > int(length) {
b = b[:length]
}
n, err = f.DataFile.ReadAt(b, int64(start)) //读取文件 从start位置开始 读取b个数据
f.offset += uint64(n)
if f.offset >= f.Info.Size {
err = io.EOF
}
return
}
//写文件
func (f *File)Write(b []byte) (n int, err error) {
start := f.Info.Offset + f.offset
end := f.Info.Offset + f.Info.Size
length := end - start
if len(b) > int(length) {
//b = b[:length]
return 0, errors.New("you should create a new File to write")
}else {
n, err = f.DataFile.WriteAt(b, int64(start))
f.offset += uint64(n)
return
}
}
//读取文件偏移量
//0意味着相对于文件的原始位置，1意味着相对于当前偏移量，2意味着相对于文件结尾
func (f *File)Seek(offset int64, whence int) (int64, error) {
switch whence {
case 0:
f.offset = uint64(offset)
case 1:
f.offset = uint64(int64(f.offset) + offset)
case 2:
f.offset = uint64(int64(f.Info.Size) + offset)
}
return int64(f.offset), nil
//if f.offset > f.Info.Size {
// f.offset = 0
// return int64(f.offset), errors.New("offset > file.size")
//}else {
// return int64(f.offset), nil
//}
}
