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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2014-2020 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
// Package randutil initialises properly random value generation and
// exposes a streamlined set of functions for it, including for crypto
// random tokens.
package randutil
import (
"crypto/sha256"
"encoding/binary"
"math/rand"
"net"
"os"
"sync"
"time"
)
func init() {
// golang does not init Seed() itself
rand.Seed(time.Now().UnixNano() + int64(os.Getpid()))
}
var moreMixedSeedOnce sync.Once
func moreMixedSeed() {
moreMixedSeedOnce.Do(func() {
h := sha256.New224()
// do this instead of asking for time and pid again
var b [8]byte
rand.Read(b[:])
h.Write(b[:])
// mix in the hostname
if hostname, err := os.Hostname(); err == nil {
h.Write([]byte(hostname))
}
// mix in net interfaces hw addresses (MACs etc)
if ifaces, err := net.Interfaces(); err == nil {
for _, iface := range ifaces {
h.Write(iface.HardwareAddr)
}
}
hs := h.Sum(nil)
s := binary.LittleEndian.Uint64(hs[0:])
rand.Seed(int64(s))
})
}
const letters = "BCDFGHJKLMNPQRSTVWXYbcdfghjklmnpqrstvwxy0123456789"
// RandomString returns a random string of length length.
//
// The vowels are omitted to avoid that words are created by pure
// chance. Numbers are included.
//
// Not cryptographically secure.
func RandomString(length int) string {
out := ""
for i := 0; i < length; i++ {
out += string(letters[rand.Intn(len(letters))])
}
return out
}
// Re-exported from math/rand for streamlining.
var (
Intn = rand.Intn
Int63n = rand.Int63n
Perm = rand.Perm
Uint64 = rand.Uint64
New = rand.New
NewSource = rand.NewSource
)
// Re-exported from math/rand for streamlining.
type (
Source = rand.Source
Rand = rand.Rand
)
// RandomDuration returns a random duration up to the given length.
func RandomDuration(d time.Duration) time.Duration {
// try to switch to more mixed seed to avoid subsets of a
// fleet of machines with similar initial conditions to behave
// the same
moreMixedSeed()
return time.Duration(Int63n(int64(d)))
}
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