go-aah/aah#20 - random string generation using crypto and byte mask

Author: jeevatkm

random_key.go

@@ -0,0 +1,97 @@
+// Copyright (c) Jeevanandam M. (https://github.com/jeevatkm)
+// go-aah/essentials source code and usage is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package ess
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"io"
+	mrand "math/rand"
+	"sync"
+	"time"
+)
+
+const (
+	letterBytes   = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+	letterIdxBits = 6                    // 6 bits to represent a letter index
+	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
+	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
+)
+
+var (
+	mRandSrc mrand.Source
+	mr       *sync.Mutex
+)
+
+//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+// Random String methods
+//___________________________________
+
+// RandomString method generates the random string for given length using
+// `crypto/rand`.
+func RandomString(length int) string {
+	return hex.EncodeToString(GenerateRandomKey(length / 2))
+}
+
+// RandomStringbm method generates the random string for given length using
+// `math/rand.Source` and byte mask.
+func RandomStringbm(length int) string {
+	return string(GenerateRandomKeybm(length))
+}
+
+//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+// Random key methods
+//___________________________________
+
+// GenerateRandomKey method generates the random bytes for given length using
+// `crypto/rand`.
+func GenerateRandomKey(length int) []byte {
+	k := make([]byte, length)
+	if _, err := io.ReadFull(rand.Reader, k); err != nil {
+		// fallback to math based random key generater
+		return GenerateRandomKeybm(length)
+	}
+	return k
+}
+
+// GenerateRandomKeybm method generates the random bytes for given length using
+// `math/rand.Source` and byte mask.
+// StackOverflow Ref - http://stackoverflow.com/a/31832326
+func GenerateRandomKeybm(length int) []byte {
+	b := make([]byte, length)
+	// A randSrc() generates 63 random bits, enough for letterIdxMax characters!
+	for i, cache, remain := length-1, randSrc(), letterIdxMax; i >= 0; {
+		if remain == 0 {
+			cache, remain = randSrc(), letterIdxMax
+		}
+		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
+			b[i] = letterBytes[idx]
+			i--
+		}
+		cache >>= letterIdxBits
+		remain--
+	}
+
+	return b
+}
+
+//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+// Unexported methods
+//___________________________________
+
+func randSrc() int64 {
+	mr.Lock()
+	defer mr.Unlock()
+	return mRandSrc.Int63()
+}
+
+//‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
+// init
+//___________________________________
+
+func init() {
+	mRandSrc = mrand.NewSource(time.Now().UnixNano())
+	mr = &sync.Mutex{}
+}

random_key_test.go

@@ -0,0 +1,43 @@
+// Copyright (c) Jeevanandam M. (https://github.com/jeevatkm)
+// go-aah/essentials source code and usage is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package ess
+
+import (
+	"testing"
+
+	"aahframework.org/test.v0/assert"
+)
+
+func TestEssRandomKey(t *testing.T) {
+	key1 := GenerateRandomKey(32)
+	assert.NotNil(t, key1)
+	assert.True(t, len(key1) == 32)
+
+	key2 := GenerateRandomKeybm(64)
+	assert.NotNil(t, key2)
+	assert.True(t, len(key2) == 64)
+}
+
+func TestEssRandomString(t *testing.T) {
+	str1 := RandomString(32)
+	assert.True(t, len(str1) == 32)
+	assert.NotNil(t, str1)
+
+	str2 := RandomStringbm(32)
+	assert.True(t, len(str2) == 32)
+	assert.NotNil(t, str2)
+}
+
+func BenchmarkGenerateRandomKey(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		GenerateRandomKey(16)
+	}
+}
+
+func BenchmarkGenerateRandomKeybm(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		GenerateRandomKeybm(32)
+	}
+}