don't send packets containing only a StopWaitingFrame

fixes #41

packet_packer.go

@@ -101,6 +101,11 @@ func (p *packetPacker) composeNextPacket(stopWaitingFrame *frames.StopWaitingFra
 	payloadLength := 0
 	var payloadFrames []frames.Frame
 
+	// don't send out packets that only contain a StopWaitingFrame
+	if len(controlFrames) == 0 && p.streamFrameQueue.Len() == 0 {
+		return nil, nil
+	}
+
 	// TODO: handle the case where there are more controlFrames than we can put into one packet
 	if stopWaitingFrame != nil {
 		payloadFrames = append(payloadFrames, stopWaitingFrame)

packet_packer_test.go

@@ -69,6 +69,13 @@ var _ = Describe("Packet packer", func() {
 		Expect(p.frames[0]).To(Equal(swf))
 	})
 
+	It("does not pack a packet containing only a StopWaitingFrame", func() {
+		swf := &frames.StopWaitingFrame{LeastUnacked: 10}
+		p, err := packer.PackPacket(swf, []frames.Frame{}, false)
+		Expect(p).To(BeNil())
+		Expect(err).ToNot(HaveOccurred())
+	})
+
 	It("packs many control frames into 1 packets", func() {
 		f := &frames.AckFrame{LargestObserved: 1}
 		b := &bytes.Buffer{}