func isInternalHeader(headerKey string) bool {
	return strings.HasPrefix(headerKey, ":") || strings.EqualFold(headerKey, "host")
}

// isAuthorityHeader returns true if a header refers to the authority header
func isAuthorityHeader(headerKey string) bool {
	return strings.EqualFold(headerKey, ":authority") || strings.EqualFold(headerKey, "host")
}

func dropInternal(keys []string) []string {

	// uint16Len is the length (in bytes) of a uint16.
	uint16Len = 2

	// uint32Len is the length (in bytes) of a uint32.
	uint32Len = 4

	// headerLen is the length (in bytes) of a DNS header.
	//
	// A header is comprised of 6 uint16s and no padding.
	headerLen = 6 * uint16Len
)

type nestedError struct {
	// s is the current level's error message.
	s string

	// err is the nested error.
	err error