forked from AdaLogics/go-fuzz-headers
/
bytesource.go
74 lines (65 loc) · 2 KB
/
bytesource.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
// Copyright 2023 The go-fuzz-headers Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package bytesource
import (
"bytes"
"encoding/binary"
"io"
"math/rand"
)
type ByteSource struct {
*bytes.Reader
fallback rand.Source
}
// New returns a new ByteSource from a given slice of bytes.
func New(input []byte) *ByteSource {
s := &ByteSource{
Reader: bytes.NewReader(input),
fallback: rand.NewSource(0),
}
if len(input) > 0 {
s.fallback = rand.NewSource(int64(s.consumeUint64()))
}
return s
}
func (s *ByteSource) Uint64() uint64 {
// Return from input if it was not exhausted.
if s.Len() > 0 {
return s.consumeUint64()
}
// Input was exhausted, return random number from fallback (in this case fallback should not be
// nil). Try first having a Uint64 output (Should work in current rand implementation),
// otherwise return a conversion of Int63.
if s64, ok := s.fallback.(rand.Source64); ok {
return s64.Uint64()
}
return uint64(s.fallback.Int63())
}
func (s *ByteSource) Int63() int64 {
return int64(s.Uint64() >> 1)
}
func (s *ByteSource) Seed(seed int64) {
s.fallback = rand.NewSource(seed)
s.Reader = bytes.NewReader(nil)
}
// consumeUint64 reads 8 bytes from the input and convert them to a uint64. It assumes that the the
// bytes reader is not empty.
func (s *ByteSource) consumeUint64() uint64 {
var bytes [8]byte
_, err := s.Read(bytes[:])
if err != nil && err != io.EOF {
panic("failed reading source") // Should not happen.
}
return binary.BigEndian.Uint64(bytes[:])
}