1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
package ioutil2
import (
"errors"
"io"
)
var ErrExceedLimit = errors.New("write exceed limit")
func NewSectionWriter(w io.WriterAt, off int64, n int64) *SectionWriter {
return &SectionWriter{w, off, off, off + n}
}
type SectionWriter struct {
w io.WriterAt
base int64
off int64
limit int64
}
func (s *SectionWriter) Write(p []byte) (n int, err error) {
if s.off >= s.limit {
return 0, ErrExceedLimit
}
if max := s.limit - s.off; int64(len(p)) > max {
return 0, ErrExceedLimit
}
n, err = s.w.WriteAt(p, s.off)
s.off += int64(n)
return
}
var errWhence = errors.New("Seek: invalid whence")
var errOffset = errors.New("Seek: invalid offset")
func (s *SectionWriter) Seek(offset int64, whence int) (int64, error) {
switch whence {
default:
return 0, errWhence
case 0:
offset += s.base
case 1:
offset += s.off
case 2:
offset += s.limit
}
if offset < s.base {
return 0, errOffset
}
s.off = offset
return offset - s.base, nil
}
func (s *SectionWriter) WriteAt(p []byte, off int64) (n int, err error) {
if off < 0 || off >= s.limit-s.base {
return 0, errOffset
}
off += s.base
if max := s.limit - off; int64(len(p)) > max {
return 0, ErrExceedLimit
}
return s.w.WriteAt(p, off)
}
// Size returns the size of the section in bytes.
func (s *SectionWriter) Size() int64 { return s.limit - s.base }
|
