http2: schedule RSTStream writes onto its stream's queue

Fixes golang/go#17243

Change-Id: I76f972f908757b103e2ab8d9b1701312308d66e5
Reviewed-on: https://go-review.googlesource.com/33238
Reviewed-by: Tom Bergan <tombergan@google.com>

http2/writesched.go

@@ -62,6 +62,13 @@ type FrameWriteRequest struct {
 // 0 is used for non-stream frames such as PING and SETTINGS.
 func (wr FrameWriteRequest) StreamID() uint32 {
 	if wr.stream == nil {
+		if se, ok := wr.write.(StreamError); ok {
+			// (*serverConn).resetStream doesn't set
+			// stream because it doesn't necessarily have
+			// one. So special case this type of write
+			// message.
+			return se.StreamID
+		}
 		return 0
 	}
 	return wr.stream.id
@@ -142,17 +149,13 @@ func (wr FrameWriteRequest) Consume(n int32) (FrameWriteRequest, FrameWriteReque
 
 // String is for debugging only.
 func (wr FrameWriteRequest) String() string {
-	var streamID uint32
-	if wr.stream != nil {
-		streamID = wr.stream.id
-	}
 	var des string
 	if s, ok := wr.write.(fmt.Stringer); ok {
 		des = s.String()
 	} else {
 		des = fmt.Sprintf("%T", wr.write)
 	}
-	return fmt.Sprintf("[FrameWriteRequest stream=%d, ch=%v, writer=%v]", streamID, wr.done != nil, des)
+	return fmt.Sprintf("[FrameWriteRequest stream=%d, ch=%v, writer=%v]", wr.StreamID(), wr.done != nil, des)
 }
 
 // writeQueue is used by implementations of WriteScheduler.

http2/writesched_test.go

@@ -115,3 +115,11 @@ func TestFrameWriteRequestData(t *testing.T) {
 		t.Errorf("Consume(remainder):\n%v", err)
 	}
 }
+
+func TestFrameWriteRequest_StreamID(t *testing.T) {
+	const streamID = 123
+	wr := FrameWriteRequest{write: streamError(streamID, ErrCodeNo)}
+	if got := wr.StreamID(); got != streamID {
+		t.Errorf("FrameWriteRequest(StreamError) = %v; want %v", got, streamID)
+	}
+}