Backoff and Randomness additions for use in client utilities

Updated String to use int, and int not to panic, and panic to test panic
Format fixes.

pkg/util/backoff.go

@@ -70,6 +70,13 @@ func (p *Backoff) Next(id string, eventTime time.Time) {
 	entry.lastUpdate = p.Clock.Now()
 }
 
+// Reset forces clearing of all backoff data for a given key.
+func (p *Backoff) Reset(id string) {
+	p.Lock()
+	defer p.Unlock()
+	delete(p.perItemBackoff, id)
+}
+
 // Returns True if the elapsed time since eventTime is smaller than the current backoff window
 func (p *Backoff) IsInBackOffSince(id string, eventTime time.Time) bool {
 	p.Lock()

pkg/util/backoff_test.go

@@ -46,6 +46,14 @@ func TestSlowBackoff(t *testing.T) {
 		}
 		b.Next(id, tc.Now())
 	}
+
+	//Now confirm that the Reset cancels backoff.
+	b.Next(id, tc.Now())
+	b.Reset(id)
+	if b.Get(id) != 0 {
+		t.Errorf("Reset didn't clear the backoff.")
+	}
+
 }
 
 func TestBackoffReset(t *testing.T) {

pkg/util/rand/rand.go

@@ -32,19 +32,12 @@ var rng = struct {
 	rand: rand.New(rand.NewSource(time.Now().UTC().UnixNano())),
 }
 
-// String generates a random alphanumeric string n characters long.  This will
-// panic if n is less than zero.
-func String(n int) string {
-	if n < 0 {
-		panic("out-of-bounds value")
-	}
-	b := make([]rune, n)
+// Intn generates an integer in range 0->max.
+// By design this should panic if input is invalid, <= 0.
+func Intn(max int) int {
 	rng.Lock()
 	defer rng.Unlock()
-	for i := range b {
-		b[i] = letters[rng.rand.Intn(numLetters)]
-	}
-	return string(b)
+	return rng.rand.Intn(max)
 }
 
 // Seed seeds the rng with the provided seed.
@@ -62,3 +55,13 @@ func Perm(n int) []int {
 	defer rng.Unlock()
 	return rng.rand.Perm(n)
 }
+
+// String generates a random alphanumeric string n characters long.  This will
+// panic if n is less than zero.
+func String(length int) string {
+	b := make([]rune, length)
+	for i := range b {
+		b[i] = letters[Intn(numLetters)]
+	}
+	return string(b)
+}

pkg/util/rand/rand_test.go

@@ -37,6 +37,27 @@ func TestString(t *testing.T) {
 	}
 }
 
+// Confirm that panic occurs on invalid input.
+func TestRangePanic(t *testing.T) {
+	defer func() {
+		if err := recover(); err == nil {
+			t.Errorf("Panic didn't occur!")
+		}
+	}()
+	// Should result in an error...
+	Intn(0)
+}
+
+func TestIntn(t *testing.T) {
+	// 0 is invalid.
+	for _, max := range []int{1, 2, 10, 123} {
+		inrange := Intn(max)
+		if inrange < 0 || inrange > max {
+			t.Errorf("%v out of range (0,%v)", inrange, max)
+		}
+	}
+}
+
 func TestPerm(t *testing.T) {
 	Seed(5)
 	rand.Seed(5)