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128 lines
3.5 KiB
128 lines
3.5 KiB
/*
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Copyright 2015 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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// Package rand provides utilities related to randomization.
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package rand
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import (
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"math/rand"
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"sync"
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"time"
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)
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var rng = struct {
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sync.Mutex
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rand *rand.Rand
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}{
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rand: rand.New(rand.NewSource(time.Now().UnixNano())),
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}
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// Int returns a non-negative pseudo-random int.
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func Int() int {
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rng.Lock()
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defer rng.Unlock()
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return rng.rand.Int()
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}
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// Intn generates an integer in range [0,max).
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// By design this should panic if input is invalid, <= 0.
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func Intn(max int) int {
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rng.Lock()
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defer rng.Unlock()
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return rng.rand.Intn(max)
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}
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// IntnRange generates an integer in range [min,max).
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// By design this should panic if input is invalid, <= 0.
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func IntnRange(min, max int) int {
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rng.Lock()
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defer rng.Unlock()
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return rng.rand.Intn(max-min) + min
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}
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// IntnRange generates an int64 integer in range [min,max).
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// By design this should panic if input is invalid, <= 0.
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func Int63nRange(min, max int64) int64 {
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rng.Lock()
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defer rng.Unlock()
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return rng.rand.Int63n(max-min) + min
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}
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// Seed seeds the rng with the provided seed.
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func Seed(seed int64) {
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rng.Lock()
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defer rng.Unlock()
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rng.rand = rand.New(rand.NewSource(seed))
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}
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// Perm returns, as a slice of n ints, a pseudo-random permutation of the integers [0,n)
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// from the default Source.
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func Perm(n int) []int {
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rng.Lock()
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defer rng.Unlock()
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return rng.rand.Perm(n)
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}
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const (
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// We omit vowels from the set of available characters to reduce the chances
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// of "bad words" being formed.
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alphanums = "bcdfghjklmnpqrstvwxz2456789"
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// No. of bits required to index into alphanums string.
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alphanumsIdxBits = 5
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// Mask used to extract last alphanumsIdxBits of an int.
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alphanumsIdxMask = 1<<alphanumsIdxBits - 1
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// No. of random letters we can extract from a single int63.
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maxAlphanumsPerInt = 63 / alphanumsIdxBits
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)
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// String generates a random alphanumeric string, without vowels, which is n
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// characters long. This will panic if n is less than zero.
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// How the random string is created:
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// - we generate random int63's
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// - from each int63, we are extracting multiple random letters by bit-shifting and masking
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// - if some index is out of range of alphanums we neglect it (unlikely to happen multiple times in a row)
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func String(n int) string {
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b := make([]byte, n)
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rng.Lock()
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defer rng.Unlock()
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randomInt63 := rng.rand.Int63()
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remaining := maxAlphanumsPerInt
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for i := 0; i < n; {
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if remaining == 0 {
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randomInt63, remaining = rng.rand.Int63(), maxAlphanumsPerInt
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}
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if idx := int(randomInt63 & alphanumsIdxMask); idx < len(alphanums) {
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b[i] = alphanums[idx]
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i++
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}
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randomInt63 >>= alphanumsIdxBits
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remaining--
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}
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return string(b)
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}
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// SafeEncodeString encodes s using the same characters as rand.String. This reduces the chances of bad words and
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// ensures that strings generated from hash functions appear consistent throughout the API.
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func SafeEncodeString(s string) string {
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r := make([]byte, len(s))
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for i, b := range []rune(s) {
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r[i] = alphanums[(int(b) % len(alphanums))]
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}
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return string(r)
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}
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