Add Fibonacci strategy

retry.go

@@ -51,6 +51,21 @@ func init() {
 // capture the most common use cases.
 type Strategy func(nth int) time.Duration
 
+// Fibonacci creates a Strategy that returns fib(n) units, where
+// fib is the fibonacci function, f(n) = f(n-1) + f(n-2).
+func Fibonacci(units time.Duration) Strategy {
+	return func(n int) time.Duration {
+		f := [...]time.Duration{1,0}
+		if n <= 0 {
+			return 0
+		}
+		for i := 1; i < n; i++ {
+			f[0], f[1] = f[0] + f[1], f[0]
+		}
+		return f[0] * units
+	}
+}
+
 // Exponential creates an exponential backoff Strategy that returns
 // 2ⁿ units. The values returned by Exponential will increase up to
 // the maximum value of time.Duration and will not overflow.

retry_test.go

@@ -34,16 +34,30 @@ func TestExponentialBackoff(t *testing.T) {
 	}
 }
 
+func TestFibonacciBackoff(t *testing.T) {
+	ans := []time.Duration{0, 1, 1, 2, 3, 5, 8, 13, 21, 34}
+	backoff := Fibonacci(1)
+	for i, v := range ans {
+		if x := backoff(i); x != v {
+			t.Errorf("fibonacci backoff(%d) = %s, should be %s", i, x, v)
+		} else {
+			t.Logf("fibonacci backoff(%d) = %s", i, x)
+		}
+	}
+	if backoff(-1) != 0 {
+		t.Errorf("fibonacci backoff(-1) = %s, should be 0ns", backoff(-1))
+	}
+}
+
 func TestIntervalBackoff(t *testing.T) {
-	x := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
-	const jitter = 50
-	backoff := Seconds(x...)
+	ans := []time.Duration{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
+	backoff := Intervals(ans...)
 
-	for i, v := range x {
-		t.Logf("fixed backoff(%d) = %s", i, backoff(i))
-		if backoff(i) != time.Duration(v)*time.Second {
-			t.Errorf("fixed backoff(%d) = %s, should be > %s", i, backoff(i),
-				time.Duration(v)*time.Second)
+	for i, v := range ans {
+		if x := backoff(i); x != v {
+			t.Errorf("fixed backoff(%d) = %s, should be %s", i, x, v)
+		} else {
+			t.Logf("fixed backoff(%d) = %s", i, x)
 		}
 	}
 }