Correctly compute Metrics.Rate with sub-second duration results

Fixes tsenart#208

lib/metrics.go

@@ -113,8 +113,11 @@ func (m *Metrics) Add(r *Result) {
 // derived summary metrics which don't need to be run on every Add call.
 func (m *Metrics) Close() {
 	m.init()
+	m.Rate = float64(m.Requests)
 	m.Duration = m.Latest.Sub(m.Earliest)
-	m.Rate = float64(m.Requests) / m.Duration.Seconds()
+	if secs := m.Duration.Seconds(); secs > 0 {
+		m.Rate /= secs
+	}
 	m.Wait = m.End.Sub(m.Latest)
 	m.BytesIn.Mean = float64(m.BytesIn.Total) / float64(m.Requests)
 	m.BytesOut.Mean = float64(m.BytesOut.Total) / float64(m.Requests)

lib/metrics_test.go

@@ -64,3 +64,15 @@ func TestMetrics_Add(t *testing.T) {
 		t.Errorf("\ngot:  %+v\nwant: %+v", got, want)
 	}
 }
+
+// https://github.com/tsenart/vegeta/issues/208
+func TestMetrics_NoInfiniteRate(t *testing.T) {
+	t.Parallel()
+
+	m := Metrics{Requests: 1, Duration: time.Microsecond}
+	m.Close()
+
+	if got, want := m.Rate, 1.0; got != want {
+		t.Errorf("got rate %f, want %f", got, want)
+	}
+}