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
|
// Copyright 2019 the u-root Authors. All rights reserved
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build darwin dragonfly freebsd nacl netbsd openbsd plan9 solaris linux
// Package rand implements cancelable reads from a cryptographically safe
// random number source.
package rand
import (
"context"
"fmt"
"sync"
"syscall"
"golang.org/x/sys/unix"
)
// Reader is a cryptographically safe random number source.
var Reader = DefaultReaderWithContext(context.Background())
// Read blockingly reads from a random number source.
func Read(b []byte) (int, error) {
return Reader.Read(b)
}
// ReadContext is a context-aware reader for random numbers.
func ReadContext(ctx context.Context, b []byte) (int, error) {
return Reader.ReadContext(ctx, b)
}
// ContextReader is a cancelable io.Reader.
type ContextReader interface {
// Read behaves like a blocking io.Reader.Read.
//
// Read wraps ReadContext with a background context.
Read(b []byte) (n int, err error)
// ReadContext is an io.Reader that blocks until data is available or
// until ctx is done.
ReadContext(ctx context.Context, b []byte) (n int, err error)
}
// contextReader is a cancelable io.Reader.
type contextReader interface {
ReadContext(context.Context, []byte) (int, error)
}
// ctxReader takes a contextReader and turns it into a ContextReader.
type ctxReader struct {
contextReader
ctx context.Context
}
func (cr ctxReader) Read(b []byte) (int, error) {
return cr.contextReader.ReadContext(cr.ctx, b)
}
// DefaultReaderWithContext returns a context-aware io.Reader.
//
// Because this stores the context, only use this in situations where an
// io.Reader is unavoidable.
func DefaultReaderWithContext(ctx context.Context) ContextReader {
return ctxReader{
ctx: ctx,
contextReader: defaultContextReader,
}
}
// urandomReader is a contextReader.
type urandomReader struct {
once sync.Once
// fd is expected to be non-blocking.
fd int
}
func (r *urandomReader) init() error {
var realErr error
r.once.Do(func() {
fd, err := unix.Open("/dev/urandom", unix.O_RDONLY, 0)
if err != nil {
realErr = fmt.Errorf("open(/dev/urandom): %v", err)
return
}
r.fd = fd
})
return realErr
}
// ReadContext implements a cancelable read from /dev/urandom.
func (r *urandomReader) ReadContext(ctx context.Context, b []byte) (int, error) {
if err := r.init(); err != nil {
return 0, err
}
for {
n, err := unix.Read(r.fd, b)
if err == nil {
return n, err
}
select {
case <-ctx.Done():
return 0, ctx.Err()
default:
if err != nil && err != syscall.EAGAIN && err != syscall.EINTR {
return n, err
}
}
}
}
|
