lib/rand: Various fixes (#6474)

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greatroar 2020-03-30 23:26:28 +02:00 committed by GitHub
parent d7a257b391
commit c930b2e9e2
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3 changed files with 13 additions and 48 deletions

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@ -9,10 +9,7 @@
package rand package rand
import ( import (
"crypto/md5"
cryptoRand "crypto/rand" cryptoRand "crypto/rand"
"encoding/binary"
"io"
mathRand "math/rand" mathRand "math/rand"
"reflect" "reflect"
) )
@ -20,16 +17,16 @@ import (
// Reader is the standard crypto/rand.Reader, re-exported for convenience // Reader is the standard crypto/rand.Reader, re-exported for convenience
var Reader = cryptoRand.Reader var Reader = cryptoRand.Reader
// randomCharset contains the characters that can make up a randomString(). // randomCharset contains the characters that can make up a rand.String().
const randomCharset = "2345679abcdefghijkmnopqrstuvwxyzACDEFGHJKLMNPQRSTUVWXYZ" const randomCharset = "2345679abcdefghijkmnopqrstuvwxyzACDEFGHJKLMNPQRSTUVWXYZ"
var ( var (
// defaultSecureSource is a concurrency safe math/rand.Source with a // defaultSecureSource is a concurrency safe math/rand.Source with a
// cryptographically sound base. // cryptographically sound base.
defaltSecureSource = newSecureSource() defaultSecureSource = newSecureSource()
// defaultSecureRand is a math/rand.Rand based on the secure source. // defaultSecureRand is a math/rand.Rand based on the secure source.
defaultSecureRand = mathRand.New(defaltSecureSource) defaultSecureRand = mathRand.New(defaultSecureSource)
) )
// String returns a strongly random string of characters (taken from // String returns a strongly random string of characters (taken from
@ -43,19 +40,14 @@ func String(l int) string {
return string(bs) return string(bs)
} }
// Int63 returns a strongly random int63 // Int63 returns a strongly random int63.
func Int63() int64 { func Int63() int64 {
return defaltSecureSource.Int63() return defaultSecureSource.Int63()
} }
// Int64 returns a strongly random int64 // Int64 returns a strongly random int64.
func Int64() int64 { func Int64() int64 {
var bs [8]byte return int64(defaultSecureSource.Uint64())
_, err := io.ReadFull(cryptoRand.Reader, bs[:])
if err != nil {
panic("randomness failure: " + err.Error())
}
return int64(binary.BigEndian.Uint64(bs[:]))
} }
// Intn returns, as an int, a non-negative strongly random number in [0,n). // Intn returns, as an int, a non-negative strongly random number in [0,n).
@ -64,18 +56,7 @@ func Intn(n int) int {
return defaultSecureRand.Intn(n) return defaultSecureRand.Intn(n)
} }
// SeedFromBytes calculates a weak 64 bit hash from the given byte slice, // Shuffle the order of elements in slice.
// suitable for use a predictable random seed.
func SeedFromBytes(bs []byte) int64 {
h := md5.New()
h.Write(bs)
s := h.Sum(nil)
// The MD5 hash of the byte slice is 16 bytes long. We interpret it as two
// uint64s and XOR them together.
return int64(binary.BigEndian.Uint64(s[0:]) ^ binary.BigEndian.Uint64(s[8:]))
}
// Shuffle the order of elements
func Shuffle(slice interface{}) { func Shuffle(slice interface{}) {
rv := reflect.ValueOf(slice) rv := reflect.ValueOf(slice)
swap := reflect.Swapper(slice) swap := reflect.Swapper(slice)

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@ -8,23 +8,6 @@ package rand
import "testing" import "testing"
func TestSeedFromBytes(t *testing.T) {
// should always return the same seed for the same bytes
tcs := []struct {
bs []byte
v int64
}{
{[]byte("hello world"), -3639725434188061933},
{[]byte("hello worlx"), -2539100776074091088},
}
for _, tc := range tcs {
if v := SeedFromBytes(tc.bs); v != tc.v {
t.Errorf("Unexpected seed value %d != %d", v, tc.v)
}
}
}
func TestRandomString(t *testing.T) { func TestRandomString(t *testing.T) {
for _, l := range []int{0, 1, 2, 3, 4, 8, 42} { for _, l := range []int{0, 1, 2, 3, 4, 8, 42} {
s := String(l) s := String(l)

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@ -37,6 +37,10 @@ func (s *secureSource) Seed(int64) {
} }
func (s *secureSource) Int63() int64 { func (s *secureSource) Int63() int64 {
return int64(s.Uint64() & (1<<63 - 1))
}
func (s *secureSource) Uint64() uint64 {
var buf [8]byte var buf [8]byte
// Read eight bytes of entropy from the buffered, secure random number // Read eight bytes of entropy from the buffered, secure random number
@ -50,8 +54,5 @@ func (s *secureSource) Int63() int64 {
} }
// Grab those bytes as an uint64 // Grab those bytes as an uint64
v := binary.BigEndian.Uint64(buf[:]) return binary.BigEndian.Uint64(buf[:])
// Mask of the high bit and return the resulting int63
return int64(v & (1<<63 - 1))
} }