implement basic flow control

fixes #37

session.go

@@ -24,6 +24,7 @@ type receivedPacket struct {
 
 var (
 	errRstStreamOnInvalidStream    = errors.New("RST_STREAM received for unknown stream")
+	errWindowUpdateOnInvalidStream = errors.New("WINDOW_UPDATE received for unknown stream")
 )
 
 // StreamCallback gets a stream frame and returns a reply frame
@@ -172,6 +173,7 @@ func (s *Session) handlePacket(remoteAddr interface{}, publicHeader *PublicHeade
 			fmt.Printf("\t<- %#v\n", frame)
 		case *frames.WindowUpdateFrame:
 			fmt.Printf("\t<- %#v\n", frame)
+			err = s.handleWindowUpdateFrame(frame)
 		case *frames.BlockedFrame:
 			fmt.Printf("BLOCKED frame received for connection %x stream %d\n", s.connectionID, frame.StreamID)
 		default:
@@ -215,6 +217,25 @@ func (s *Session) handleStreamFrame(frame *frames.StreamFrame) error {
 	return nil
 }
 
+func (s *Session) handleWindowUpdateFrame(frame *frames.WindowUpdateFrame) error {
+	if frame.StreamID == 0 {
+		// TODO: handle connection level WindowUpdateFrames
+		// return errors.New("Connection level flow control not yet implemented")
+		return nil
+	}
+	s.streamsMutex.RLock()
+	stream, ok := s.streams[frame.StreamID]
+	s.streamsMutex.RUnlock()
+
+	if !ok {
+		return errWindowUpdateOnInvalidStream
+	}
+
+	stream.UpdateFlowControlWindow(frame.ByteOffset)
+
+	return nil
+}
+
 // TODO: Handle frame.byteOffset
 func (s *Session) handleRstStreamFrame(frame *frames.RstStreamFrame) error {
 	s.streamsMutex.RLock()

session_test.go

@@ -172,7 +172,27 @@ var _ = Describe("Session", func() {
 				StreamID:  5,
 				ErrorCode: 42,
 			})
-			Expect(err).To(MatchError("RST_STREAM received for unknown stream"))
+			Expect(err).To(MatchError(errRstStreamOnInvalidStream))
+		})
+	})
+
+	Context("handling WINDOW_UPDATE frames", func() {
+		It("updates the Flow Control Windows of a stream", func() {
+			_, err := session.NewStream(5)
+			Expect(err).ToNot(HaveOccurred())
+			err = session.handleWindowUpdateFrame(&frames.WindowUpdateFrame{
+				StreamID:   5,
+				ByteOffset: 0x8000,
+			})
+			Expect(err).ToNot(HaveOccurred())
+		})
+
+		It("errors when the stream is not known", func() {
+			err := session.handleWindowUpdateFrame(&frames.WindowUpdateFrame{
+				StreamID:   5,
+				ByteOffset: 1337,
+			})
+			Expect(err).To(MatchError(errWindowUpdateOnInvalidStream))
 		})
 	})
 

stream.go

@@ -2,6 +2,8 @@ package quic
 
 import (
 	"io"
+	"sync"
+	"sync/atomic"
 
 	"github.com/lucas-clemente/quic-go/frames"
 	"github.com/lucas-clemente/quic-go/protocol"
@@ -26,6 +28,9 @@ type stream struct {
 	frameQueue     []*frames.StreamFrame // TODO: replace with heap
 	remoteErr      error
 	currentErr     error
+
+	flowControlWindow uint64
+	windowUpdateCond  *sync.Cond
 }
 
 // newStream creates a new Stream
@@ -34,6 +39,8 @@ func newStream(session streamHandler, StreamID protocol.StreamID) *stream {
 		session:           session,
 		streamID:          StreamID,
 		streamFrames:      make(chan *frames.StreamFrame, 8), // ToDo: add config option for this number
+		flowControlWindow: 0x4000,                            // 16 byte, TODO: read this from the negotiated connection parameters (TagCFCW)
+		windowUpdateCond:  sync.NewCond(&sync.Mutex{}),
 	}
 }
 
@@ -138,11 +145,30 @@ func (s *stream) ReadByte() (byte, error) {
 	return p[0], err
 }
 
+func (s *stream) UpdateFlowControlWindow(n uint64) {
+	if n > s.flowControlWindow {
+		atomic.StoreUint64((*uint64)(&s.flowControlWindow), n)
+		s.windowUpdateCond.Broadcast()
+	}
+}
+
 func (s *stream) Write(p []byte) (int, error) {
 	if s.remoteErr != nil {
 		return 0, s.remoteErr
 	}
-	data := make([]byte, len(p))
+
+	dataWritten := 0
+
+	for dataWritten < len(p) {
+		s.windowUpdateCond.L.Lock()
+		remainingBytesInWindow := int64(s.flowControlWindow) - int64(s.writeOffset)
+		for ; remainingBytesInWindow == 0; remainingBytesInWindow = int64(s.flowControlWindow) - int64(s.writeOffset) {
+			s.windowUpdateCond.Wait()
+		}
+		s.windowUpdateCond.L.Unlock()
+
+		dataLen := utils.Min(len(p), int(remainingBytesInWindow))
+		data := make([]byte, dataLen)
 		copy(data, p)
 		err := s.session.QueueStreamFrame(&frames.StreamFrame{
 			StreamID: s.streamID,
@@ -152,7 +178,11 @@ func (s *stream) Write(p []byte) (int, error) {
 		if err != nil {
 			return 0, err
 		}
-	s.writeOffset += uint64(len(p))
+
+		dataWritten += dataLen
+		s.writeOffset += uint64(dataLen)
+	}
+
 	return len(p), nil
 }
 
@@ -171,7 +201,7 @@ func (s *stream) AddStreamFrame(frame *frames.StreamFrame) error {
 	return nil
 }
 
-// RegisterError is called by session to indicate that an error occured and the
+// RegisterError is called by session to indicate that an error occurred and the
 // stream should be closed.
 func (s *stream) RegisterError(err error) {
 	s.remoteErr = err

stream_test.go

@@ -246,6 +246,80 @@ var _ = Describe("Stream", func() {
 			Expect(n).To(BeZero())
 			Expect(err).To(Equal(testErr))
 		})
+
+		Context("flow control", func() {
+			It("writes everything if the flow control window is big enough", func() {
+				str.flowControlWindow = 4
+				n, err := str.Write([]byte{0xDE, 0xCA, 0xFB, 0xAD})
+				Expect(n).To(Equal(4))
+				Expect(err).ToNot(HaveOccurred())
+			})
+
+			It("waits for a flow control window update", func() {
+				var b bool
+				str.flowControlWindow = 1
+				_, err := str.Write([]byte{0x42})
+				Expect(err).ToNot(HaveOccurred())
+
+				go func() {
+					time.Sleep(2 * time.Millisecond)
+					b = true
+					str.UpdateFlowControlWindow(3)
+				}()
+				n, err := str.Write([]byte{0x13, 0x37})
+				Expect(b).To(BeTrue())
+				Expect(n).To(Equal(2))
+				Expect(err).ToNot(HaveOccurred())
+			})
+
+			It("splits writing of frames when given more data than the flow control windows size", func() {
+				str.flowControlWindow = 2
+				var b bool
+
+				go func() {
+					time.Sleep(time.Millisecond)
+					b = true
+					str.UpdateFlowControlWindow(4)
+				}()
+
+				n, err := str.Write([]byte{0xDE, 0xCA, 0xFB, 0xAD})
+				Expect(len(handler.frames)).To(Equal(2))
+				Expect(b).To(BeTrue())
+				Expect(n).To(Equal(4))
+				Expect(err).ToNot(HaveOccurred())
+			})
+
+			It("writes after a flow control window update", func() {
+				var b bool
+				str.flowControlWindow = 1
+				_, err := str.Write([]byte{0x42})
+				Expect(err).ToNot(HaveOccurred())
+
+				go func() {
+					time.Sleep(time.Millisecond)
+					b = true
+					str.UpdateFlowControlWindow(3)
+				}()
+				n, err := str.Write([]byte{0xDE, 0xAD})
+				Expect(b).To(BeTrue())
+				Expect(n).To(Equal(2))
+				Expect(err).ToNot(HaveOccurred())
+			})
+		})
+	})
+
+	Context("flow control window updating", func() {
+		It("updates the flow control window", func() {
+			str.flowControlWindow = 3
+			str.UpdateFlowControlWindow(4)
+			Expect(str.flowControlWindow).To(Equal(uint64(4)))
+		})
+
+		It("never shrinks the flow control window", func() {
+			str.flowControlWindow = 100
+			str.UpdateFlowControlWindow(50)
+			Expect(str.flowControlWindow).To(Equal(uint64(100)))
+		})
 	})
 
 	Context("getting next str frame", func() {