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// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Windows cryptographically secure pseudorandom number
// generator.

package rand

import (
        "os"
        "sync"
        "syscall"
)

// Implemented by using Windows CryptoAPI 2.0.

func init() { Reader = &rngReader{} }

// A rngReader satisfies reads by reading from the Windows CryptGenRandom API.
type rngReader struct {
        prov syscall.Handle
        mu   sync.Mutex
}

func (r *rngReader) Read(b []byte) (n int, err error) {
        r.mu.Lock()
        if r.prov == 0 {
                const provType = syscall.PROV_RSA_FULL
                const flags = syscall.CRYPT_VERIFYCONTEXT | syscall.CRYPT_SILENT
                err := syscall.CryptAcquireContext(&r.prov, nil, nil, provType, flags)
                if err != nil {
                        r.mu.Unlock()
                        return 0, os.NewSyscallError("CryptAcquireContext", err)
                }
        }
        r.mu.Unlock()
        err = syscall.CryptGenRandom(r.prov, uint32(len(b)), &b[0])
        if err != nil {
                return 0, os.NewSyscallError("CryptGenRandom", err)
        }
        return len(b), nil
}