use a monotonous timer for the connection (#3570)

There's no point in having the timer fire multiple times for the same
timestamp. By using a monotonuos timer we avoid busy-looping in cases where the
timer fires, but we can't actually send a packet.

connection_timer_test.go

@@ -0,0 +1,62 @@
+package quic
+
+import (
+	"time"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+func (t *connectionTimer) Deadline() time.Time { return t.timer.Deadline() }
+
+var _ = Describe("Timer", func() {
+	It("sets an idle timeout", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), time.Time{}, time.Time{}, time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Hour)))
+	})
+
+	It("sets an ACK timer", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), time.Time{}, time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Minute)))
+	})
+
+	It("sets a loss timer", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), now.Add(time.Second), time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Second)))
+	})
+
+	It("sets a pacing timer", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), now.Add(time.Second), now.Add(time.Millisecond))
+		Expect(t.Deadline()).To(Equal(now.Add(time.Millisecond)))
+	})
+
+	It("doesn't reset to an earlier time", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), time.Time{}, time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Minute)))
+		t.SetRead()
+
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), time.Time{}, time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Hour)))
+	})
+
+	It("allows the pacing timer to be set to send immediately", func() {
+		now := time.Now()
+		t := newTimer()
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), time.Time{}, time.Time{})
+		Expect(t.Deadline()).To(Equal(now.Add(time.Minute)))
+		t.SetRead()
+
+		t.SetTimer(now.Add(time.Hour), now.Add(time.Minute), time.Time{}, deadlineSendImmediately)
+		Expect(t.Deadline()).To(Equal(deadlineSendImmediately))
+	})
+})