route_from0

# File lib/uri/generic.rb, line 842
    def route_from0(oth)
      case oth
      when Generic
      when String
        oth = URI.parse(oth)
      else
        raise ArgumentError,
          "bad argument(expected URI object or URI string)"
      end

      if self.relative?
        raise BadURIError, 
          "relative URI: #{self}"
      end
      if oth.relative?
        raise BadURIError, 
          "relative URI: #{oth}"
      end

      if self.scheme != oth.scheme
        return self, self.dup
      end
      rel = URI::Generic.new(nil, # it is relative URI
                             self.userinfo, self.host, self.port, 
                             self.registry, self.path, self.opaque,
                             self.query, self.fragment)

      if rel.userinfo != oth.userinfo ||
          rel.host.to_s.downcase != oth.host.to_s.downcase ||
          rel.port != oth.port
        if self.userinfo.nil? && self.host.nil?
          return self, self.dup
        end
        rel.set_port(nil) if rel.port == oth.default_port
        return rel, rel
      end
      rel.set_userinfo(nil)
      rel.set_host(nil)
      rel.set_port(nil)

      if rel.path && rel.path == oth.path
        rel.set_path('')
        rel.set_query(nil) if rel.query == oth.query
        return rel, rel
      elsif rel.opaque && rel.opaque == oth.opaque
        rel.set_opaque('')
        rel.set_query(nil) if rel.query == oth.query
        return rel, rel
      end

      # you can modify `rel', but can not `oth'.
      return oth, rel
    end