Harden JitteredBackoff: nil-safe, clamp jitter, and seed RNG

backoff.go

@@ -3,9 +3,15 @@ package durex
 import (
 	"math"
 	"math/rand"
+	"sync"
 	"time"
 )
 
+var (
+	jitterRandMu sync.Mutex
+	jitterRand   = rand.New(rand.NewSource(time.Now().UnixNano()))
+)
+
 // BackoffStrategy calculates the delay before retrying a failed command.
 type BackoffStrategy interface {
 	// NextDelay returns the delay before the next retry attempt.
@@ -72,14 +78,31 @@ type JitteredBackoff struct {
 
 // NextDelay implements BackoffStrategy.
 func (b JitteredBackoff) NextDelay(attempt int) time.Duration {
+	if b.Strategy == nil {
+		return 0
+	}
+
 	base := b.Strategy.NextDelay(attempt)
 	if b.JitterRate <= 0 {
 		return base
 	}
 
-	jitterRange := float64(base) * b.JitterRate
-	jitter := (rand.Float64()*2 - 1) * jitterRange // -jitterRange to +jitterRange
-	return time.Duration(float64(base) + jitter)
+	jitterRate := b.JitterRate
+	if jitterRate > 1 {
+		jitterRate = 1
+	}
+
+	jitterRange := float64(base) * jitterRate
+	jitterRandMu.Lock()
+	randomValue := jitterRand.Float64()
+	jitterRandMu.Unlock()
+	jitter := (randomValue*2 - 1) * jitterRange // -jitterRange to +jitterRange
+	delay := time.Duration(float64(base) + jitter)
+	if delay < 0 {
+		return 0
+	}
+
+	return delay
 }
 
 // DefaultExponentialBackoff returns a sensible default exponential backoff.

backoff_test.go

@@ -148,6 +148,30 @@ func TestJitteredBackoff(t *testing.T) {
 	}
 }
 
+func TestJitteredBackoff_NilStrategy(t *testing.T) {
+	backoff := durex.JitteredBackoff{JitterRate: 0.5}
+
+	delay := backoff.NextDelay(1)
+	if delay != 0 {
+		t.Errorf("Expected 0 with nil strategy, got %v", delay)
+	}
+}
+
+func TestJitteredBackoff_ClampsNegativeDelay(t *testing.T) {
+	base := durex.ConstantBackoff{Delay: 100 * time.Millisecond}
+	backoff := durex.JitteredBackoff{
+		Strategy:   base,
+		JitterRate: 10.0,
+	}
+
+	for i := 0; i < 100; i++ {
+		delay := backoff.NextDelay(1)
+		if delay < 0 {
+			t.Fatalf("Expected non-negative delay, got %v", delay)
+		}
+	}
+}
+
 func TestJitteredBackoff_ZeroJitter(t *testing.T) {
 	base := durex.ConstantBackoff{Delay: 100 * time.Millisecond}
 	backoff := durex.JitteredBackoff{