add option to write StreamFrames without Data length field

work towards #77

frames/stream_frame.go

@@ -16,6 +16,7 @@ type StreamFrame struct {
 	streamIDLen    protocol.ByteCount
 	Offset         protocol.ByteCount
 	Data           []byte
+	DataLenPresent bool
 }
 
 var (
@@ -33,7 +34,7 @@ func ParseStreamFrame(r *bytes.Reader) (*StreamFrame, error) {
 	}
 
 	frame.FinBit = typeByte&0x40 > 0
-	dataLenPresent := typeByte&0x20 > 0
+	frame.DataLenPresent = typeByte&0x20 > 0
 	offsetLen := typeByte & 0x1C >> 2
 	if offsetLen != 0 {
 		offsetLen++
@@ -53,7 +54,7 @@ func ParseStreamFrame(r *bytes.Reader) (*StreamFrame, error) {
 	frame.Offset = protocol.ByteCount(offset)
 
 	var dataLen uint16
-	if dataLenPresent {
+	if frame.DataLenPresent {
 		dataLen, err = utils.ReadUint16(r)
 		if err != nil {
 			return nil, err
@@ -79,10 +80,14 @@ func ParseStreamFrame(r *bytes.Reader) (*StreamFrame, error) {
 // WriteStreamFrame writes a stream frame.
 func (f *StreamFrame) Write(b *bytes.Buffer, packetNumber protocol.PacketNumber, packetNumberLen protocol.PacketNumberLen, version protocol.VersionNumber) error {
 	typeByte := uint8(0x80) // sets the leftmost bit to 1
+
 	if f.FinBit {
 		typeByte ^= 0x40
 	}
-	typeByte ^= 0x20 // dataLenPresent
+
+	if f.DataLenPresent {
+		typeByte ^= 0x20
+	}
 
 	offsetLength := f.getOffsetLength()
 
@@ -130,8 +135,12 @@ func (f *StreamFrame) Write(b *bytes.Buffer, packetNumber protocol.PacketNumber,
 		return errInvalidOffsetLen
 	}
 
+	if f.DataLenPresent {
 		utils.WriteUint16(b, uint16(len(f.Data)))
+	}
+
 	b.Write(f.Data)
+
 	return nil
 }
 
@@ -178,7 +187,12 @@ func (f *StreamFrame) MinLength() protocol.ByteCount {
 		f.calculateStreamIDLength()
 	}
 
-	return 1 + f.streamIDLen + f.getOffsetLength() + 2 + 1
+	length := protocol.ByteCount(1) + f.streamIDLen + f.getOffsetLength()
+	if f.DataLenPresent {
+		length += 2
+	}
+
+	return length + 1
 }
 
 // MaybeSplitOffFrame removes the first n bytes and returns them as a separate frame. If n >= len(n), nil is returned and nothing is modified.

frames/stream_frame_test.go

@@ -17,6 +17,7 @@ var _ = Describe("StreamFrame", func() {
 			Expect(frame.FinBit).To(BeFalse())
 			Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
 			Expect(frame.Offset).To(BeZero())
+			Expect(frame.DataLenPresent).To(BeTrue())
 			Expect(frame.Data).To(Equal([]byte("foobar")))
 		})
 
@@ -27,6 +28,7 @@ var _ = Describe("StreamFrame", func() {
 			Expect(frame.FinBit).To(BeFalse())
 			Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
 			Expect(frame.Offset).To(BeZero())
+			Expect(frame.DataLenPresent).To(BeFalse())
 			Expect(frame.Data).To(Equal([]byte("foobar")))
 		})
 	})
@@ -37,6 +39,7 @@ var _ = Describe("StreamFrame", func() {
 			(&StreamFrame{
 				StreamID:       1,
 				Data:           []byte("foobar"),
+				DataLenPresent: true,
 			}).Write(b, 1, protocol.PacketNumberLen6, 0)
 			Expect(b.Bytes()).To(Equal([]byte{0xa0, 0x1, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'}))
 		})
@@ -63,6 +66,52 @@ var _ = Describe("StreamFrame", func() {
 			Expect(f.MinLength()).To(Equal(protocol.ByteCount(b.Len())))
 		})
 
+		Context("data length field", func() {
+			It("writes the data length", func() {
+				dataLen := 0x1337
+				b := &bytes.Buffer{}
+				f := &StreamFrame{
+					StreamID:       1,
+					Data:           bytes.Repeat([]byte{'f'}, dataLen),
+					DataLenPresent: true,
+					Offset:         0,
+				}
+				f.Write(b, 1, protocol.PacketNumberLen6, 0)
+				headerLength := f.MinLength() - 1
+				Expect(b.Bytes()[0] & 0x20).To(Equal(uint8(0x20)))
+				Expect(b.Bytes()[headerLength-2 : headerLength]).To(Equal([]byte{0x37, 0x13}))
+			})
+
+			It("omits the data length field", func() {
+				dataLen := 0x1337
+				b := &bytes.Buffer{}
+				f := &StreamFrame{
+					StreamID:       1,
+					Data:           bytes.Repeat([]byte{'f'}, dataLen),
+					DataLenPresent: false,
+					Offset:         0,
+				}
+				f.Write(b, 1, protocol.PacketNumberLen6, 0)
+				Expect(b.Bytes()[0] & 0x20).To(Equal(uint8(0)))
+				Expect(b.Bytes()[1 : b.Len()-dataLen]).ToNot(ContainSubstring(string([]byte{0x37, 0x13})))
+				minLength := f.MinLength()
+				f.DataLenPresent = true
+				Expect(minLength).To(Equal(f.MinLength() - 2))
+			})
+
+			It("calculates the correcct min-length", func() {
+				f := &StreamFrame{
+					StreamID:       0xCAFE,
+					Data:           []byte("foobar"),
+					DataLenPresent: false,
+					Offset:         0xDEADBEEF,
+				}
+				minLengthWithoutDataLen := f.MinLength()
+				f.DataLenPresent = true
+				Expect(f.MinLength()).To(Equal(minLengthWithoutDataLen + 2))
+			})
+		})
+
 		Context("offset lengths", func() {
 			It("does not write an offset if the offset is 0", func() {
 				b := &bytes.Buffer{}

session_test.go

@@ -420,7 +420,7 @@ var _ = Describe("Session", func() {
 		})
 
 		It("should call OnSent", func() {
-			session.QueueStreamFrame(&frames.StreamFrame{StreamID: 5})
+			session.QueueStreamFrame(&frames.StreamFrame{StreamID: 5, DataLenPresent: true})
 			session.sendPacket()
 			Expect(cong.nCalls).To(Equal(2)) // OnPacketSent + GetCongestionWindow
 			Expect(cong.argsOnPacketSent[1]).To(Equal(protocol.ByteCount(27)))