don't send the same StopWaitingFrame twice

fixes #229

ackhandler/stop_waiting_manager_test.go

@@ -0,0 +1,35 @@
+package ackhandler
+
+import (
+	"github.com/lucas-clemente/quic-go/frames"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("StopWaitingManager", func() {
+	var manager *stopWaitingManager
+	BeforeEach(func() {
+		manager = &stopWaitingManager{}
+	})
+
+	It("returns nil in the beginning", func() {
+		Expect(manager.GetStopWaitingFrame()).To(BeNil())
+	})
+
+	It("returns a StopWaitingFrame, when a new ACK arrives", func() {
+		manager.ReceivedAck(&frames.AckFrame{LargestAcked: 10})
+		Expect(manager.GetStopWaitingFrame()).To(Equal(&frames.StopWaitingFrame{LeastUnacked: 11}))
+	})
+
+	It("does not decrease the LeastUnacked", func() {
+		manager.ReceivedAck(&frames.AckFrame{LargestAcked: 10})
+		manager.ReceivedAck(&frames.AckFrame{LargestAcked: 9})
+		Expect(manager.GetStopWaitingFrame()).To(Equal(&frames.StopWaitingFrame{LeastUnacked: 11}))
+	})
+
+	It("does not send the same StopWaitingFrame twice", func() {
+		manager.ReceivedAck(&frames.AckFrame{LargestAcked: 10})
+		Expect(manager.GetStopWaitingFrame()).ToNot(BeNil())
+		Expect(manager.GetStopWaitingFrame()).To(BeNil())
+	})
+})