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89 lines
2.3 KiB
89 lines
2.3 KiB
package rand
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import (
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crand "crypto/rand"
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"encoding/binary"
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"fmt"
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mrand "math/rand"
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)
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const (
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strChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" // 62 characters
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)
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func init() {
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Reseed()
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}
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// NewRand returns a prng, that is seeded with OS randomness.
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// The OS randomness is obtained from crypto/rand, however, like with any math/rand.Rand
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// object none of the provided methods are suitable for cryptographic usage.
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//
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// Note that the returned instance of math/rand's Rand is not
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// suitable for concurrent use by multiple goroutines.
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//
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// For concurrent use, call Reseed to reseed math/rand's default source and
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// use math/rand's top-level convenience functions instead.
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func NewRand() *mrand.Rand {
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seed := crandSeed()
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// nolint:gosec // G404: Use of weak random number generator
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return mrand.New(mrand.NewSource(seed))
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}
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// Reseed conveniently re-seeds the default Source of math/rand with
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// randomness obtained from crypto/rand.
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//
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// Note that this does not make math/rand suitable for cryptographic usage.
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//
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// Use math/rand's top-level convenience functions remain suitable
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// for concurrent use by multiple goroutines.
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func Reseed() {
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seed := crandSeed()
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mrand.Seed(seed)
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}
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// Str constructs a random alphanumeric string of given length
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// from math/rand's global default Source.
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func Str(length int) string {
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if length <= 0 {
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return ""
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}
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chars := make([]byte, 0, length)
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for {
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// nolint:gosec // G404: Use of weak random number generator
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val := mrand.Int63()
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for i := 0; i < 10; i++ {
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v := int(val & 0x3f) // rightmost 6 bits
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if v >= 62 { // only 62 characters in strChars
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val >>= 6
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continue
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} else {
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chars = append(chars, strChars[v])
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if len(chars) == length {
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return string(chars)
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}
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val >>= 6
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}
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}
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}
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}
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// Bytes returns n random bytes generated from math/rand's global default Source.
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func Bytes(n int) []byte {
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bs := make([]byte, n)
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for i := 0; i < len(bs); i++ {
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// nolint:gosec // G404: Use of weak random number generator
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bs[i] = byte(mrand.Int() & 0xFF)
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}
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return bs
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}
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func crandSeed() int64 {
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var seed int64
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err := binary.Read(crand.Reader, binary.BigEndian, &seed)
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if err != nil {
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panic(fmt.Sprintf("could nor read random seed from crypto/rand: %v", err))
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}
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return seed
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}
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