File: examples_test.go

package info (click to toggle)
golang-github-klauspost-reedsolomon 1.9.9-1
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, sid
  • size: 1,248 kB
  • sloc: asm: 17,464; makefile: 8
file content (209 lines) | stat: -rw-r--r-- 4,526 bytes parent folder | download | duplicates (7)
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
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
package reedsolomon_test

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"math/rand"

	"github.com/klauspost/reedsolomon"
)

func fillRandom(p []byte) {
	for i := 0; i < len(p); i += 7 {
		val := rand.Int63()
		for j := 0; i+j < len(p) && j < 7; j++ {
			p[i+j] = byte(val)
			val >>= 8
		}
	}
}

// Simple example of how to use all functions of the Encoder.
// Note that all error checks have been removed to keep it short.
func ExampleEncoder() {
	// Create some sample data
	var data = make([]byte, 250000)
	fillRandom(data)

	// Create an encoder with 17 data and 3 parity slices.
	enc, _ := reedsolomon.New(17, 3)

	// Split the data into shards
	shards, _ := enc.Split(data)

	// Encode the parity set
	_ = enc.Encode(shards)

	// Verify the parity set
	ok, _ := enc.Verify(shards)
	if ok {
		fmt.Println("ok")
	}

	// Delete two shards
	shards[10], shards[11] = nil, nil

	// Reconstruct the shards
	_ = enc.Reconstruct(shards)

	// Verify the data set
	ok, _ = enc.Verify(shards)
	if ok {
		fmt.Println("ok")
	}
	// Output: ok
	// ok
}

// This demonstrates that shards can be arbitrary sliced and
// merged and still remain valid.
func ExampleEncoder_slicing() {
	// Create some sample data
	var data = make([]byte, 250000)
	fillRandom(data)

	// Create 5 data slices of 50000 elements each
	enc, _ := reedsolomon.New(5, 3)
	shards, _ := enc.Split(data)
	err := enc.Encode(shards)
	if err != nil {
		panic(err)
	}

	// Check that it verifies
	ok, err := enc.Verify(shards)
	if ok && err == nil {
		fmt.Println("encode ok")
	}

	// Split the data set of 50000 elements into two of 25000
	splitA := make([][]byte, 8)
	splitB := make([][]byte, 8)

	// Merge into a 100000 element set
	merged := make([][]byte, 8)

	// Split/merge the shards
	for i := range shards {
		splitA[i] = shards[i][:25000]
		splitB[i] = shards[i][25000:]

		// Concencate it to itself
		merged[i] = append(make([]byte, 0, len(shards[i])*2), shards[i]...)
		merged[i] = append(merged[i], shards[i]...)
	}

	// Each part should still verify as ok.
	ok, err = enc.Verify(shards)
	if ok && err == nil {
		fmt.Println("splitA ok")
	}

	ok, err = enc.Verify(splitB)
	if ok && err == nil {
		fmt.Println("splitB ok")
	}

	ok, err = enc.Verify(merged)
	if ok && err == nil {
		fmt.Println("merge ok")
	}
	// Output: encode ok
	// splitA ok
	// splitB ok
	// merge ok
}

// This demonstrates that shards can xor'ed and
// still remain a valid set.
//
// The xor value must be the same for element 'n' in each shard,
// except if you xor with a similar sized encoded shard set.
func ExampleEncoder_xor() {
	// Create some sample data
	var data = make([]byte, 25000)
	fillRandom(data)

	// Create 5 data slices of 5000 elements each
	enc, _ := reedsolomon.New(5, 3)
	shards, _ := enc.Split(data)
	err := enc.Encode(shards)
	if err != nil {
		panic(err)
	}

	// Check that it verifies
	ok, err := enc.Verify(shards)
	if !ok || err != nil {
		fmt.Println("falied initial verify", err)
	}

	// Create an xor'ed set
	xored := make([][]byte, 8)

	// We xor by the index, so you can see that the xor can change,
	// It should however be constant vertically through your slices.
	for i := range shards {
		xored[i] = make([]byte, len(shards[i]))
		for j := range xored[i] {
			xored[i][j] = shards[i][j] ^ byte(j&0xff)
		}
	}

	// Each part should still verify as ok.
	ok, err = enc.Verify(xored)
	if ok && err == nil {
		fmt.Println("verified ok after xor")
	}
	// Output: verified ok after xor
}

// This will show a simple stream encoder where we encode from
// a []io.Reader which contain a reader for each shard.
//
// Input and output can be exchanged with files, network streams
// or what may suit your needs.
func ExampleStreamEncoder() {
	dataShards := 5
	parityShards := 2

	// Create a StreamEncoder with the number of data and
	// parity shards.
	rs, err := reedsolomon.NewStream(dataShards, parityShards)
	if err != nil {
		log.Fatal(err)
	}

	shardSize := 50000

	// Create input data shards.
	input := make([][]byte, dataShards)
	for s := range input {
		input[s] = make([]byte, shardSize)
		fillRandom(input[s])
	}

	// Convert our buffers to io.Readers
	readers := make([]io.Reader, dataShards)
	for i := range readers {
		readers[i] = io.Reader(bytes.NewBuffer(input[i]))
	}

	// Create our output io.Writers
	out := make([]io.Writer, parityShards)
	for i := range out {
		out[i] = ioutil.Discard
	}

	// Encode from input to output.
	err = rs.Encode(readers, out)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println("ok")
	// OUTPUT: ok
}