stream.go
func (id *streamID) header(tag uint64) uint64 {
	header := id.id<<3 | tag
	if !id.initiator {
		header--
	}
	return header
}
func (id *streamID) header(tag uint64) uint64 {
	header := id.id<<3 | tag
	if !id.initiator {
		header--
	}
	return header
}
// header computes the header for the given tag