Minor improvements to random module

CHANGELOG.md

@@ -1,4 +1,8 @@
-## 8.18.7 (unreleased)
+## 8.18.8 (unreleased)
+### Implementation changes and bug fixes
+- [PR #1665](https://github.com/rqlite/rqlite/pull/1665): Minor improvements to `random` module.
+
+## 8.18.7 (February 1st 2024)
 ### Implementation changes and bug fixes
 - [PR #1663](https://github.com/rqlite/rqlite/pull/1663): Remove unnecessary WAL-close during Raft snapshotting.
 

random/random.go

@@ -14,16 +14,15 @@ func init() {
 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
 }
 
-// String returns a random string of 20 characters
+// String returns a random string, 20 characters long.
 func String() string {
 	mu.Lock()
 	defer mu.Unlock()
 	var output strings.Builder
-	chars := "abcdedfghijklmnopqrstABCDEFGHIJKLMNOP"
+	chars := "abcdedfghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
 	for i := 0; i < 20; i++ {
 		random := r.Intn(len(chars))
-		randomChar := chars[random]
+		output.WriteString(string(chars[random]))
-		output.WriteString(string(randomChar))
 	}
 	return output.String()
 }
@@ -35,16 +34,16 @@ func Float64() float64 {
 	return r.Float64()
 }
 
-// Intn returns a random int
+// Intn returns a random int >=0 and < n.
 func Intn(n int) int {
 	mu.Lock()
 	defer mu.Unlock()
 	return r.Intn(n)
 }
 
-// Jitter adds a little bit of randomness to a given duration. This is
+// Jitter returns a randomly-chosen duration between d and 2d.
-// useful to prevent nodes across the cluster performing certain operations
-// all at the same time.
 func Jitter(d time.Duration) time.Duration {
-	return d + time.Duration(Float64()*float64(d))
+	mu.Lock()
+	defer mu.Unlock()
+	return d + time.Duration(r.Float64()*float64(d))
 }

random/random_test.go

@@ -7,13 +7,13 @@ import (
 
 func Test_StringLength(t *testing.T) {
 	str := String()
-	if len(str) != 20 {
+	if exp, got := 20, len(str); exp != got {
-		t.Errorf("String() returned a string of length %d; want 20", len(str))
+		t.Errorf("String() returned a string of length %d; want %d", got, exp)
 	}
 }
 
 func Test_StringUniqueness(t *testing.T) {
-	const numStrings = 10
+	const numStrings = 100
 	strs := make(map[string]bool, numStrings)
 
 	for i := 0; i < numStrings; i++ {
@@ -26,7 +26,7 @@ func Test_StringUniqueness(t *testing.T) {
 }
 
 func Test_Float64Uniqueness(t *testing.T) {
-	const numFloat64s = 10
+	const numFloat64s = 100
 	floats := make(map[float64]bool, numFloat64s)
 
 	for i := 0; i < numFloat64s; i++ {
@@ -39,7 +39,7 @@ func Test_Float64Uniqueness(t *testing.T) {
 }
 
 func Test_IntnUniqueness(t *testing.T) {
-	const numIntns = 10
+	const numIntns = 100
 	intns := make(map[int]bool, numIntns)
 
 	for i := 0; i < numIntns; i++ {
@@ -53,9 +53,12 @@ func Test_IntnUniqueness(t *testing.T) {
 
 func Test_Jitter(t *testing.T) {
 	for n := 0; n < 100; n++ {
-		d := Jitter(100 * time.Millisecond)
+		dur := 100 * time.Millisecond
-		if d < 100*time.Millisecond || d >= 200*time.Millisecond {
+		lower := dur
-			t.Errorf("Jitter(100ms) returned a duration of %s; want between 0 and 200ms", d)
+		upper := 2 * dur
+		if got := Jitter(dur); got < lower || got >= upper {
+			t.Errorf("Jitter(%s) returned a duration of %s; want between %s and %s",
+				dur, got, lower, upper)
 		}
 	}
 }