release connection-level flow control credit when a stream is reset

internal/flowcontrol/interface.go

@@ -18,8 +18,12 @@ type StreamFlowController interface {
 	flowController
 	// for receiving
 	// UpdateHighestReceived should be called when a new highest offset is received
-	// final has to be to true if this is the final offset of the stream, as contained in a STREAM frame with FIN bit, and the RESET_STREAM frame
+	// final has to be to true if this is the final offset of the stream,
+	// as contained in a STREAM frame with FIN bit, and the RESET_STREAM frame
 	UpdateHighestReceived(offset protocol.ByteCount, final bool) error
+	// Abandon should be called when reading from the stream is aborted early,
+	// and there won't be any further calls to AddBytesRead.
+	Abandon()
 }
 
 // The ConnectionFlowController is the flow controller for the connection.

internal/flowcontrol/stream_flow_controller.go

@@ -93,6 +93,12 @@ func (c *streamFlowController) AddBytesRead(n protocol.ByteCount) {
 	c.connection.AddBytesRead(n)
 }
 
+func (c *streamFlowController) Abandon() {
+	if unread := c.highestReceived - c.bytesRead; unread > 0 {
+		c.connection.AddBytesRead(unread)
+	}
+}
+
 func (c *streamFlowController) AddBytesSent(n protocol.ByteCount) {
 	c.baseFlowController.AddBytesSent(n)
 	c.connection.AddBytesSent(n)

internal/flowcontrol/stream_flow_controller_test.go

@@ -149,6 +149,13 @@ var _ = Describe("Stream Flow controller", func() {
 				err = controller.UpdateHighestReceived(201, true)
 				Expect(err).To(MatchError("StreamDataAfterTermination: Received inconsistent final offset for stream 10 (old: 200, new: 201 bytes)"))
 			})
+
+			It("tells the connection flow controller when a stream is abandoned", func() {
+				controller.AddBytesRead(5)
+				Expect(controller.UpdateHighestReceived(100, true)).To(Succeed())
+				controller.Abandon()
+				Expect(controller.connection.(*connectionFlowController).bytesRead).To(Equal(protocol.ByteCount(100)))
+			})
 		})
 
 		It("saves when data is read", func() {
@@ -198,6 +205,13 @@ var _ = Describe("Stream Flow controller", func() {
 				Expect(controller.connection.(*connectionFlowController).receiveWindowSize).To(Equal(protocol.ByteCount(float64(controller.receiveWindowSize) * protocol.ConnectionFlowControlMultiplier)))
 			})
 
+			It("sends a connection-level window update when a large stream is abandoned", func() {
+				Expect(controller.UpdateHighestReceived(90, true)).To(Succeed())
+				Expect(controller.connection.GetWindowUpdate()).To(BeZero())
+				controller.Abandon()
+				Expect(controller.connection.GetWindowUpdate()).ToNot(BeZero())
+			})
+
 			It("doesn't increase the window after a final offset was already received", func() {
 				Expect(controller.UpdateHighestReceived(90, true)).To(Succeed())
 				controller.AddBytesRead(30)