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// Copyright 2018 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.
// Package randutil contains internal randomness utilities for various
// crypto packages.
package randutil
import (
"io"
"sync"
)
var (
closedChanOnce sync.Once
closedChan chan struct{}
)
// MaybeReadByte reads a single byte from r with ~50% probability. This is used
// to ensure that callers do not depend on non-guaranteed behaviour, e.g.
// assuming that rsa.GenerateKey is deterministic w.r.t. a given random stream.
//
// This does not affect tests that pass a stream of fixed bytes as the random
// source (e.g. a zeroReader).
func MaybeReadByte(r io.Reader) {
closedChanOnce.Do(func() {
closedChan = make(chan struct{})
close(closedChan)
})
select {
case <-closedChan:
return
case <-closedChan:
var buf [1]byte
r.Read(buf[:])
}
}
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