error when receiving stream data with a larger offset than the final offset

This could happen when a peer send a STREAM frame with the Fin bit set,
and then sends STREAM frames with a higher offset.

internal/flowcontrol/stream_flow_controller.go

@@ -12,10 +12,12 @@ import (
 type streamFlowController struct {
 	baseFlowController
 
-	connection connectionFlowControllerI
-
 	streamID protocol.StreamID
+
+	connection              connectionFlowControllerI
 	contributesToConnection bool // does the stream contribute to connection level flow control
+
+	receivedFinalOffset bool
 }
 
 var _ StreamFlowController = &streamFlowController{}
@@ -50,7 +52,12 @@ func (c *streamFlowController) UpdateHighestReceived(byteOffset protocol.ByteCou
 	c.mutex.Lock()
 	defer c.mutex.Unlock()
 
-	// TODO(#382): check for StreamDataAfterTermination errors, when receiving an offset after we already received a final offset
+	if c.receivedFinalOffset && byteOffset > c.highestReceived {
+		return qerr.StreamDataAfterTermination
+	}
+	if final {
+		c.receivedFinalOffset = true
+	}
 	if byteOffset == c.highestReceived {
 		return nil
 	}

internal/flowcontrol/stream_flow_controller_test.go

@@ -110,6 +110,20 @@ var _ = Describe("Stream Flow controller", func() {
 				err := controller.UpdateHighestReceived(99, true)
 				Expect(err).To(MatchError(qerr.StreamDataAfterTermination))
 			})
+
+			It("accepts delayed data after receiving a final offset", func() {
+				err := controller.UpdateHighestReceived(300, true)
+				Expect(err).ToNot(HaveOccurred())
+				err = controller.UpdateHighestReceived(250, false)
+				Expect(err).ToNot(HaveOccurred())
+			})
+
+			It("errors when receiving a higher offset after receiving a final offset", func() {
+				err := controller.UpdateHighestReceived(200, true)
+				Expect(err).ToNot(HaveOccurred())
+				err = controller.UpdateHighestReceived(250, false)
+				Expect(err).To(MatchError(qerr.StreamDataAfterTermination))
+			})
 		})
 
 		Context("registering data read", func() {