From a79e9ee35e8249a1922dcaba23036105bc3304de Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Mon, 4 Dec 2017 12:43:39 +0700
Subject: [PATCH] parse and write STOP_WAITING frames for packet number 0

---
 internal/wire/stop_waiting_frame.go      |  5 +--
 internal/wire/stop_waiting_frame_test.go | 49 ++++++++++++++++--------
 2 files changed, 35 insertions(+), 19 deletions(-)

diff --git a/internal/wire/stop_waiting_frame.go b/internal/wire/stop_waiting_frame.go
index 9eb068dc..6d01cb53 100644
--- a/internal/wire/stop_waiting_frame.go
+++ b/internal/wire/stop_waiting_frame.go
@@ -6,7 +6,6 @@ import (
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
 	"github.com/lucas-clemente/quic-go/internal/utils"
-	"github.com/lucas-clemente/quic-go/qerr"
 )
 
 // A StopWaitingFrame in QUIC
@@ -73,8 +72,8 @@ func ParseStopWaitingFrame(r *bytes.Reader, packetNumber protocol.PacketNumber,
 	if err != nil {
 		return nil, err
 	}
-	if leastUnackedDelta >= uint64(packetNumber) {
-		return nil, qerr.Error(qerr.InvalidStopWaitingData, "invalid LeastUnackedDelta")
+	if leastUnackedDelta > uint64(packetNumber) {
+		return nil, errors.New("invalid LeastUnackedDelta")
 	}
 	frame.LeastUnacked = protocol.PacketNumber(uint64(packetNumber) - leastUnackedDelta)
 	return frame, nil
diff --git a/internal/wire/stop_waiting_frame_test.go b/internal/wire/stop_waiting_frame_test.go
index 58613f3f..ec22c306 100644
--- a/internal/wire/stop_waiting_frame_test.go
+++ b/internal/wire/stop_waiting_frame_test.go
@@ -27,13 +27,20 @@ var _ = Describe("StopWaitingFrame", func() {
 			Expect(b.Len()).To(BeZero())
 		})
 
-		It("rejects frames that would have 0 as LeastUnacked", func() {
+		It("parses a frame with 0 as LeastUnacked", func() {
 			b := bytes.NewReader([]byte{0x6, 0x8})
-			_, err := ParseStopWaitingFrame(b, 8, 1, protocol.VersionWhatever)
-			Expect(err).To(HaveOccurred())
+			frame, err := ParseStopWaitingFrame(b, 8, 1, protocol.VersionWhatever)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(frame.LeastUnacked).To(Equal(protocol.PacketNumber(0)))
 			Expect(b.Len()).To(BeZero())
 		})
 
+		It("rejects frames that underflow LeastUnacked", func() {
+			b := bytes.NewReader([]byte{0x6, 0x9})
+			_, err := ParseStopWaitingFrame(b, 8, 1, protocol.VersionWhatever)
+			Expect(err).To(MatchError("invalid LeastUnackedDelta"))
+		})
+
 		It("errors on EOFs", func() {
 			data := []byte{0x06, 0x03}
 			_, err := ParseStopWaitingFrame(bytes.NewReader(data), 5, 1, protocol.VersionWhatever)
@@ -46,19 +53,29 @@ var _ = Describe("StopWaitingFrame", func() {
 	})
 
 	Context("when writing", func() {
-		Context("in big endian", func() {
-			It("writes a sample frame", func() {
-				b := &bytes.Buffer{}
-				frame := &StopWaitingFrame{
-					LeastUnacked:    10,
-					PacketNumber:    13,
-					PacketNumberLen: protocol.PacketNumberLen6,
-				}
-				err := frame.Write(b, versionBigEndian)
-				Expect(err).ToNot(HaveOccurred())
-				Expect(b.Bytes()[0]).To(Equal(uint8(0x06)))
-				Expect(b.Bytes()[1:7]).To(Equal([]byte{0, 0, 0, 0, 0, 3}))
-			})
+		It("writes a sample frame", func() {
+			b := &bytes.Buffer{}
+			frame := &StopWaitingFrame{
+				LeastUnacked:    10,
+				PacketNumber:    13,
+				PacketNumberLen: protocol.PacketNumberLen6,
+			}
+			err := frame.Write(b, versionBigEndian)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(b.Bytes()[0]).To(Equal(uint8(0x06)))
+			Expect(b.Bytes()[1:7]).To(Equal([]byte{0, 0, 0, 0, 0, 3}))
+		})
+
+		It("writes a frame for LeastUnacked = 0", func() {
+			b := &bytes.Buffer{}
+			frame := &StopWaitingFrame{
+				LeastUnacked:    0,
+				PacketNumber:    8,
+				PacketNumberLen: protocol.PacketNumberLen1,
+			}
+			err := frame.Write(b, versionBigEndian)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(b.Bytes()).To(Equal([]byte{0x6, 0x8}))
 		})
 
 		It("errors when PacketNumber was not set", func() {