sc.serveG.check()
	var streamID uint32
	var send int32
	if st == nil {
		send = sc.inflow.add(n)
	} else {
		streamID = st.id
		send = st.inflow.add(n)
	}
	if send == 0 {
		return
	}
	sc.writeFrame(http2FrameWriteRequest{
		write:  http2writeWindowUpdate{streamID: streamID, n: uint32(send)},
		stream: st,
	})
}