forked from rubrikinc/kronos
/
checksumfile.go
121 lines (109 loc) · 3.27 KB
/
checksumfile.go
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
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
package checksumfile_updated
import (
"bytes"
"crypto/md5"
"fmt"
"strings"
"hash"
"io/ioutil"
"os"
"path/filepath"
"syscall"
"github.com/cockroachdb/cockroach/pkg/util/protoutil"
"github.com/cockroachdb/cockroach/pkg/util/randutil"
"github.com/pkg/errors"
)
// ErrChecksumMismatch is returned when checksum and data don't match for a file
var ErrChecksumMismatch = errors.New("checksum and data don't match")
func tempFileSuffix() string {
rng, _ := randutil.NewPseudoRand()
return "tmp." + string(randutil.RandBytes(rng, 6))
}
// checksumedFile only supports complete rewrites. It internally serializes the
// content and checksum in a binary format before writing.
type checksumedFile struct {
filename string
hashGenerator hash.Hash
}
func newChecksumedFile(name string) checksumedFile {
return checksumedFile{filename: name, hashGenerator: md5.New()}
}
func (c *checksumedFile) read() ([]byte, error) {
content, err := ioutil.ReadFile(c.filename)
if err != nil {
return nil, err
}
fe := &FileExtent{}
if err := protoutil.Unmarshal(content, fe); err != nil {
return nil, err
}
if !valid(fe.Checksum, fe.Data, c.hashGenerator) {
return nil, ErrChecksumMismatch
}
return fe.Data, nil
}
func (c *checksumedFile) write(p []byte) error {
cksm, err := computeHash(p, c.hashGenerator)
if err != nil {
return err
}
fe, err := protoutil.Marshal(&FileExtent{Checksum: cksm, Data: p})
if err != nil {
return err
}
if err := ioutil.WriteFile(c.filename, fe, 0644); err != nil {
return err
}
return sync(c.filename)
}
// Read reads data written to filename using the Write function. It returns an
// error if the checksums don't match or file doesn't exist.
func Read(filename string) ([]byte, error) {
cksmFile := newChecksumedFile(filename)
contents, err := cksmFile.read()
if err != nil {
return nil, errors.Wrapf(err, "could not read from file %s", filename)
}
return contents, nil
}
func sync(path string) error {
f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0)
if err != nil{
if strings.Contains(err.Error(), "is a directory"){
f, err = os.Open(path)
if err != nil{
return err
}
} else {
return err
}
}
defer f.Close()
if err := f.Sync(); err != nil {
if strings.Contains(err.Error(), "The handle is invalid"){
fmt.Println("failed to sync:", err)
} else {
return err
}
}
return f.Close()
}
// Write writes p to filename along with its checksum in a binary format.
// This data can be read using the Read function. Write returns an error if
// data could not be completely written for some reason. It never corrupts the
// existing file.
func Write(filename string, p []byte) error {
tempFileName := filename + tempFileSuffix()
tempChecksumedFile := newChecksumedFile(tempFileName)
if err := tempChecksumedFile.write(p); err != nil {
return errors.Wrapf(err, "could not write to temp file %s", tempFileName)
}
if wb, err := tempChecksumedFile.read(); err != nil || !bytes.Equal(wb, p) {
return errors.Wrapf(err, "could not validate data written to temp file %s", tempFileName)
}
if err := syscall.Rename(tempFileName, filename); err != nil {
return errors.Wrapf(err, "could not rename temp file %s to %s", tempFileName, filename)
}
// Sync the directory to make the rename durable.
return sync(filepath.Dir(filename))
}