discourse/lib/crawler_detection.rb

module CrawlerDetection

  def self.to_matcher(string, type: nil)
    escaped = string.split('|').map { |agent| Regexp.escape(agent) }.join('|')

    if type == :real && Rails.env == "test"
      # we need this bypass so we properly render views
      escaped << "|Rails Testing"
    end

    Regexp.new(escaped, Regexp::IGNORECASE)
  end

  def self.crawler?(user_agent)
    return true if user_agent.nil?

    # this is done to avoid regenerating regexes
    @non_crawler_matchers ||= {}
    @matchers ||= {}

    possibly_real = (@non_crawler_matchers[SiteSetting.non_crawler_user_agents] ||= to_matcher(SiteSetting.non_crawler_user_agents, type: :real))

    if user_agent.match?(possibly_real)
      known_bots = (@matchers[SiteSetting.crawler_user_agents] ||= to_matcher(SiteSetting.crawler_user_agents))
      user_agent.match?(known_bots)
    else
      true
    end

  end
end