Random string generation

randstr_test.go

package randstr_test

import (
	"crypto/rand"
	weak "math/rand"
	"testing"
	"time"
)

const (
	randChars    = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	randCharsLen = len(randChars)
)

// RandStringWeak uses a time-based pseudo random generated string.
// This func is fine for tests and limited use values.
func RandStringWeak(n int, t time.Time) string {
	src := weak.NewSource(t.UTC().UnixNano())

	b := make([]byte, n)
	for i := range b {
		b[i] = randChars[src.Int63()%int64(randCharsLen)]
	}

	return string(b)
}

// RandString returns a random string using a crptographically secure RNG source.
// It will panic if n < 0. If n==0 it will return an empty string.
// This func may block if there isn't enough entrophy in the RNG source.
func RandString(n int) string {
	bs := make([]byte, n)
	if _, err := rand.Read(bs); err != nil {
		return ""
	}

	for i, b := range bs {
		bs[i] = randChars[int(b)%randCharsLen]
	}

	return string(bs)
}

func TestRandStr(t *testing.T) {
	var tests = []struct {
		name string
		len  int
	}{
		{name: "len=0", len: 0},
		{name: "len=1", len: 1},
		{name: "len=2", len: 2},
		{name: "len=3", len: 3},
		{name: "len=4", len: 4},
		{name: "len=8", len: 8},
		{name: "len=16", len: 16},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			out := RandString(tc.len)
			t.Logf("%s\n", out)
			if len(out) != tc.len {
				t.Errorf("RandString() = %v, got %v want %v", out, len(out), tc.len)
			}
		})
	}
}

func TestRandStrWeak(t *testing.T) {
	var tests = []struct {
		name string
		len  int
	}{
		{name: "len=0", len: 0},
		{name: "len=1", len: 1},
		{name: "len=2", len: 2},
		{name: "len=3", len: 3},
		{name: "len=4", len: 4},
		{name: "len=8", len: 8},
		{name: "len=16", len: 16},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			out := RandStringWeak(tc.len, time.Now())
			t.Logf("%s\n", out)
			if len(out) != tc.len {
				t.Errorf("RandStringWeak() = %v, got %v want %v", out, len(out), tc.len)
			}
		})
	}
}

func BenchmarkRandString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		RandString(10)
	}
}

func BenchmarkRandStringWeak(b *testing.B) {
	for i := 0; i < b.N; i++ {
		RandStringWeak(10, time.Now())
	}
}