file.go

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

    //}

}