/
kv.go
135 lines (115 loc) · 2.79 KB
/
kv.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
122
123
124
125
126
127
128
129
130
131
132
133
134
135
package main
import (
"encoding/binary"
"errors"
"io"
"os"
)
const (
KeySizeSize = 2
ValueSizeSize = 8
)
type KV struct {
file *os.File
index map[string]KeyDir
}
type KeyDir struct {
valueSize int64
valueOffset int64
}
func NewKV() (*KV, error) {
file, err := os.OpenFile("data", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
if err != nil {
return nil, err
}
index := make(map[string]KeyDir)
kv := KV{file: file, index: index}
err = buildIndex(&kv)
if err != nil {
return nil, err
}
return &kv, nil
}
func buildIndex(kv *KV) error {
_, err := kv.file.Seek(0, io.SeekStart)
if err != nil {
return err
}
offset := int64(0)
for {
keyValueSizeBytes := make([]byte, KeySizeSize+ValueSizeSize)
_, err = kv.file.Read(keyValueSizeBytes)
if err != nil {
if err.Error() == "EOF" {
return nil
}
return err
}
keySize := int64(binary.BigEndian.Uint16(keyValueSizeBytes[0:KeySizeSize]))
valueSize := int64(binary.BigEndian.Uint64(keyValueSizeBytes[KeySizeSize:]))
offset += KeySizeSize + ValueSizeSize
keyValueBytes := make([]byte, keySize+valueSize)
_, err = kv.file.Read(keyValueBytes)
if err != nil {
return err
}
key := string(keyValueBytes[:keySize])
kv.index[key] = KeyDir{valueSize: valueSize, valueOffset: offset + keySize}
offset += keySize + valueSize
}
}
func (kv *KV) Close() error {
return kv.file.Close()
}
func (kv *KV) Get(key string) (string, error) {
keyDir, exists := kv.index[key]
if !exists {
return "", errors.New("key Not found")
}
return readAt(kv.file, keyDir.valueOffset, keyDir.valueSize)
}
func readAt(file *os.File, offset int64, size int64) (string, error) {
_, err := file.Seek(offset, io.SeekStart)
if err != nil {
return "", err
}
contentBytes := make([]byte, size)
_, err = file.Read(contentBytes)
if err != nil {
return "", err
}
return string(contentBytes), nil
}
func (kv *KV) Set(key string, value string) error {
keyBytes := []byte(key)
valueBytes := []byte(value)
keySizeBytes := int16ToBuffer(uint16(len(keyBytes)))
valueSizeBytes := int64ToBuffer(uint64(len(valueBytes)))
fileInfo, err := kv.file.Stat()
if err != nil {
return err
}
offset := fileInfo.Size()
order := [][]byte{
keySizeBytes, valueSizeBytes, keyBytes, valueBytes,
}
var bytesToWrite []byte
for _, r := range order {
bytesToWrite = append(bytesToWrite, r...)
}
if _, err := kv.file.Write(bytesToWrite); err != nil {
return err
}
kv.index[key] = KeyDir{valueSize: int64(len(valueBytes)), valueOffset: offset + int64(KeySizeSize+ValueSizeSize) + int64(len(keyBytes))}
return nil
}
func int64ToBuffer(number uint64) []byte {
buf := make([]byte, 8)
binary.BigEndian.PutUint64(buf, number)
return buf
}
func int16ToBuffer(number uint16) []byte {
buf := make([]byte, 2)
binary.BigEndian.PutUint16(buf, number)
return buf
}