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// 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.
//go:build aix || darwin || dragonfly || freebsd || nacl || netbsd || openbsd || solaris || linux
// +build aix darwin dragonfly freebsd nacl netbsd openbsd solaris linux
package rand
import (
"context"
"fmt"
"sync"
"syscall"
"golang.org/x/sys/unix"
)
// 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, nil
}
select {
case <-ctx.Done():
return 0, ctx.Err()
default:
if err != syscall.EAGAIN && err != syscall.EINTR {
return n, err
}
}
}
}
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