class WEBrick::HTTPServlet::FileHandler

def service(req, res)
  # if this class is mounted on "/" and /~username is requested.
  # we're going to override path information before invoking service.
  if defined?(Etc) && @options[:UserDir] && req.script_name.empty?
    if %r|^(/~([^/]+))| =~ req.path_info
      script_name, user = $1, $2
      path_info = $'
      begin
        passwd = Etc::getpwnam(user)
        @root = File::join(passwd.dir, @options[:UserDir])
        req.script_name = script_name
        req.path_info = path_info
      rescue
        @logger.debug "#{self.class}#do_GET: getpwnam(#{user}) failed"
      end
    end
  end
  prevent_directory_traversal(req, res)
  super(req, res)
end