mark stream completed when CancelWrite is called after receiving STOP_SENDING (#4605)

* garbage collect stream when CancelWrite is called after receiving STOP_SENDING

* review comments

* Hold lock while checking isNewlyCompleted

---------

Co-authored-by: Marco Munizaga <git@marcopolo.io>

send_stream.go

@@ -379,7 +379,7 @@ func (s *sendStream) isNewlyCompleted() bool {
 	// 1. the application called CancelWrite, or
 	// 2. we received a STOP_SENDING, and
 	// 		* the application consumed the error via Write, or
-	//		* the application called CLsoe
+	//		* the application called Close
 	if s.cancelWriteErr != nil && (s.cancellationFlagged || s.finishedWriting) {
 		s.completed = true
 		return true
@@ -421,6 +421,17 @@ func (s *sendStream) cancelWriteImpl(errorCode qerr.StreamErrorCode, remote bool
 	s.mutex.Lock()
 	if !remote {
 		s.cancellationFlagged = true
+		if s.cancelWriteErr != nil {
+			completed := s.isNewlyCompleted()
+			s.mutex.Unlock()
+			// The user has called CancelWrite. If the previous cancellation was
+			// because of a STOP_SENDING, we don't need to flag the error to the
+			// user any more.
+			if completed {
+				s.sender.onStreamCompleted(s.streamID)
+			}
+			return
+		}
 	}
 	if s.cancelWriteErr != nil {
 		s.mutex.Unlock()

send_stream_test.go

@@ -909,6 +909,20 @@ var _ = Describe("Send Stream", func() {
 				})
 			})
 
+			It("discards the stream when CancelWrite is called after receiving STOP_SENDING", func() {
+				mockSender.EXPECT().queueControlFrame(&wire.ResetStreamFrame{
+					StreamID:  streamID,
+					ErrorCode: 101,
+				})
+				str.handleStopSendingFrame(&wire.StopSendingFrame{
+					StreamID:  streamID,
+					ErrorCode: 101,
+				})
+
+				mockSender.EXPECT().onStreamCompleted(gomock.Any())
+				str.CancelWrite(101)
+			})
+
 			It("unblocks Write", func() {
 				mockSender.EXPECT().onHasStreamData(streamID, str)
 				mockSender.EXPECT().queueControlFrame(gomock.Any())