// 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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// Windows cryptographically secure pseudorandom number
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// generator.
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package rand
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import (
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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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// Implemented by using Windows CryptoAPI 2.0.
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func init() { Reader = &rngReader{} }
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// A rngReader satisfies reads by reading from the Windows CryptGenRandom API.
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type rngReader struct {
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used int32 // atomic; whether this rngReader has been used
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prov syscall.Handle
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mu sync.Mutex
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}
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func (r *rngReader) 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(60*time.Second, warnBlocked)
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defer t.Stop()
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}
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r.mu.Lock()
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if r.prov == 0 {
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const provType = syscall.PROV_RSA_FULL
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const flags = syscall.CRYPT_VERIFYCONTEXT | syscall.CRYPT_SILENT
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err := syscall.CryptAcquireContext(&r.prov, nil, nil, provType, flags)
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if err != nil {
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r.mu.Unlock()
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return 0, os.NewSyscallError("CryptAcquireContext", err)
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}
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}
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r.mu.Unlock()
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if len(b) == 0 {
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return 0, nil
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}
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err = syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])
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if err != nil {
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return 0, os.NewSyscallError("CryptGenRandom", err)
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}
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return len(b), nil
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}
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