http2commonCanonHeader map[string]string // lower-case -> Go-Canonical-Case
)

func http2buildCommonHeaderMapsOnce() {
	http2commonBuildOnce.Do(http2buildCommonHeaderMaps)
}

func http2buildCommonHeaderMaps() {
	common := []string{
		"accept",
		"accept-charset",
		"accept-encoding",
		"accept-language",
		"accept-ranges",
		"age",