mirror of https://github.com/golang/go.git
79 lines
1.6 KiB
Go
79 lines
1.6 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build unix
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// Unix cryptographically secure pseudorandom number
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// generator.
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package rand
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import (
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"bufio"
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"errors"
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"io"
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"os"
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"sync"
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"sync/atomic"
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"syscall"
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"time"
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)
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const urandomDevice = "/dev/urandom"
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func init() {
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Reader = &reader{}
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}
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// A reader satisfies reads by reading from urandomDevice
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type reader struct {
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f io.Reader
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mu sync.Mutex
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used int32 // atomic; whether this reader has been used
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}
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// altGetRandom if non-nil specifies an OS-specific function to get
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// urandom-style randomness.
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var altGetRandom func([]byte) (ok bool)
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func warnBlocked() {
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println("crypto/rand: blocked for 60 seconds waiting to read random data from the kernel")
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}
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func (r *reader) Read(b []byte) (n int, err error) {
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if atomic.CompareAndSwapInt32(&r.used, 0, 1) {
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// First use of randomness. Start timer to warn about
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// being blocked on entropy not being available.
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t := time.AfterFunc(time.Minute, warnBlocked)
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defer t.Stop()
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}
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if altGetRandom != nil && altGetRandom(b) {
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return len(b), nil
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}
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r.mu.Lock()
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defer r.mu.Unlock()
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if r.f == nil {
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f, err := os.Open(urandomDevice)
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if err != nil {
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return 0, err
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}
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r.f = bufio.NewReader(hideAgainReader{f})
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}
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return r.f.Read(b)
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}
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// hideAgainReader masks EAGAIN reads from /dev/urandom.
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// See golang.org/issue/9205
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type hideAgainReader struct {
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r io.Reader
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}
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func (hr hideAgainReader) Read(p []byte) (n int, err error) {
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n, err = hr.r.Read(p)
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if errors.Is(err, syscall.EAGAIN) {
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err = nil
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}
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return
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}
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