def host
        # Remove port number.
        h = host_with_port
        if colon_index = h.index(":")
          h[0, colon_index]
        else
          h
        end
      end

      def host
        split_authority(self.authority)[0]
      end

      def authority
        forwarded_authority || host_authority || server_authority
      end

      def forwarded_authority
        if value = get_header(HTTP_X_FORWARDED_HOST)
          wrap_ipv6(split_header(value).first)
        end
      end

      def host_authority
        get_header(HTTP_HOST)
      end

      def server_authority
        host = self.server_name
        port = self.server_port

        if host
          if port
            "#{host}:#{port}"
          else
            host
          end
        end
      end

      def split_authority(authority)
        if match = AUTHORITY.match(authority)
          if address = match[:ip6]
            return match[:host], address, match[:port]&.to_i
          else
            return match[:host], match[:host], match[:port]&.to_i
          end
        end

        # Give up!
        return authority, authority, nil
      end

      AUTHORITY = /
        # The host:
        (?<host>
          # An IPv6 address:
          (\[(?<ip6>.*)\])
          |
          # An IPv4 address:
          (?<ip4>[\d\.]+)
          |
          # A hostname:
          (?<name>[a-zA-Z0-9\.\-]+)
        )
        # The optional port:
        (:(?<port>\d+))?
      /x

      AUTHORITY = /^
        # The host:
        (?<host>
          # An IPv6 address:
          (\[(?<ip6>.*)\])
          |
          # An IPv4 address:
          (?<ip4>[\d\.]+)
          |
          # A hostname:
          (?<name>[a-zA-Z0-9\.\-]+)
        )
        # The optional port:
        (:(?<port>\d+))?
      $/x