implement stream frame splitting in StreamFrame

frames/stream_frame.go

@@ -93,3 +93,23 @@ func (f *StreamFrame) Write(b *bytes.Buffer) error {
 func (f *StreamFrame) MaxLength() int {
 	return 1 + 4 + 8 + 2 + 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.
+func (f *StreamFrame) MaybeSplitOffFrame(n int) *StreamFrame {
+	if n >= f.MaxLength()-1+len(f.Data) {
+		return nil
+	}
+	n -= f.MaxLength() - 1
+
+	defer func() {
+		f.Data = f.Data[n:]
+		f.Offset += uint64(n)
+	}()
+
+	return &StreamFrame{
+		FinBit:   false,
+		StreamID: f.StreamID,
+		Offset:   f.Offset,
+		Data:     f.Data[:n],
+	}
+}

frames/stream_frame_test.go

@@ -9,59 +9,88 @@ import (
 )
 
 var _ = Describe("StreamFrame", func() {
-	Context("stream frames", func() {
-		Context("when parsing", func() {
-			It("accepts sample frame", func() {
-				b := bytes.NewReader([]byte{0xa0, 0x1, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'})
-				frame, err := ParseStreamFrame(b)
-				Expect(err).ToNot(HaveOccurred())
-				Expect(frame.FinBit).To(BeFalse())
-				Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
-				Expect(frame.Offset).To(BeZero())
-				Expect(frame.Data).To(Equal([]byte("foobar")))
-			})
-
-			It("accepts frame without datalength", func() {
-				b := bytes.NewReader([]byte{0x80, 0x1, 'f', 'o', 'o', 'b', 'a', 'r'})
-				frame, err := ParseStreamFrame(b)
-				Expect(err).ToNot(HaveOccurred())
-				Expect(frame.FinBit).To(BeFalse())
-				Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
-				Expect(frame.Offset).To(BeZero())
-				Expect(frame.Data).To(Equal([]byte("foobar")))
-			})
+	Context("when parsing", func() {
+		It("accepts sample frame", func() {
+			b := bytes.NewReader([]byte{0xa0, 0x1, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'})
+			frame, err := ParseStreamFrame(b)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(frame.FinBit).To(BeFalse())
+			Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
+			Expect(frame.Offset).To(BeZero())
+			Expect(frame.Data).To(Equal([]byte("foobar")))
 		})
 
-		Context("when writing", func() {
-			It("writes sample frame", func() {
-				b := &bytes.Buffer{}
-				(&StreamFrame{
-					StreamID: 1,
-					Data:     []byte("foobar"),
-				}).Write(b)
-				Expect(b.Bytes()).To(Equal([]byte{0xa3, 0x1, 0, 0, 0, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'}))
-			})
+		It("accepts frame without datalength", func() {
+			b := bytes.NewReader([]byte{0x80, 0x1, 'f', 'o', 'o', 'b', 'a', 'r'})
+			frame, err := ParseStreamFrame(b)
+			Expect(err).ToNot(HaveOccurred())
+			Expect(frame.FinBit).To(BeFalse())
+			Expect(frame.StreamID).To(Equal(protocol.StreamID(1)))
+			Expect(frame.Offset).To(BeZero())
+			Expect(frame.Data).To(Equal([]byte("foobar")))
+		})
+	})
 
-			It("writes offsets", func() {
-				b := &bytes.Buffer{}
-				(&StreamFrame{
-					StreamID: 1,
-					Offset:   16,
-					Data:     []byte("foobar"),
-				}).Write(b)
-				Expect(b.Bytes()).To(Equal([]byte{0xbf, 0x1, 0, 0, 0, 0x10, 0, 0, 0, 0, 0, 0, 0, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'}))
-			})
+	Context("when writing", func() {
+		It("writes sample frame", func() {
+			b := &bytes.Buffer{}
+			(&StreamFrame{
+				StreamID: 1,
+				Data:     []byte("foobar"),
+			}).Write(b)
+			Expect(b.Bytes()).To(Equal([]byte{0xa3, 0x1, 0, 0, 0, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'}))
+		})
 
-			It("has proper max length", func() {
-				b := &bytes.Buffer{}
-				f := &StreamFrame{
-					StreamID: 1,
-					Data:     []byte("f"),
-					Offset:   1,
-				}
-				f.Write(b)
-				Expect(f.MaxLength()).To(Equal(b.Len()))
-			})
+		It("writes offsets", func() {
+			b := &bytes.Buffer{}
+			(&StreamFrame{
+				StreamID: 1,
+				Offset:   16,
+				Data:     []byte("foobar"),
+			}).Write(b)
+			Expect(b.Bytes()).To(Equal([]byte{0xbf, 0x1, 0, 0, 0, 0x10, 0, 0, 0, 0, 0, 0, 0, 0x06, 0x00, 'f', 'o', 'o', 'b', 'a', 'r'}))
+		})
+
+		It("has proper max length", func() {
+			b := &bytes.Buffer{}
+			f := &StreamFrame{
+				StreamID: 1,
+				Data:     []byte("f"),
+				Offset:   1,
+			}
+			f.Write(b)
+			Expect(f.MaxLength()).To(Equal(b.Len()))
+		})
+	})
+
+	Context("splitting off earlier stream frames", func() {
+		It("splits off nothing", func() {
+			f := &StreamFrame{
+				StreamID: 1,
+				Data:     []byte("bar"),
+				Offset:   3,
+			}
+			Expect(f.MaybeSplitOffFrame(1000)).To(BeNil())
+			Expect(f.Offset).To(Equal(uint64(3)))
+		})
+
+		It("splits off initial frame", func() {
+			f := &StreamFrame{
+				StreamID: 1,
+				Data:     []byte("foobar"),
+				Offset:   3,
+				FinBit:   true,
+			}
+			previous := f.MaybeSplitOffFrame(f.MaxLength() - 1 + 3)
+			Expect(previous).ToNot(BeNil())
+			Expect(previous.StreamID).To(Equal(protocol.StreamID(1)))
+			Expect(previous.Data).To(Equal([]byte("foo")))
+			Expect(previous.Offset).To(Equal(uint64(3)))
+			Expect(previous.FinBit).To(BeFalse())
+			Expect(f.StreamID).To(Equal(protocol.StreamID(1)))
+			Expect(f.Data).To(Equal([]byte("bar")))
+			Expect(f.Offset).To(Equal(uint64(6)))
+			Expect(f.FinBit).To(BeTrue())
 		})
 	})
 })