discourse/app/controllers/robots_txt_controller.rb

# frozen_string_literal: true

class RobotsTxtController < ApplicationController
  layout false
  skip_before_action :preload_json, :check_xhr, :redirect_to_login_if_required

  OVERRIDDEN_HEADER = "# This robots.txt file has been customized at /admin/customize/robots\n"

  # NOTE: order is important!
  DISALLOWED_PATHS ||= %w{
    /auth/
    /assets/browser-update*.js
    /email/
    /session
    /session/
    /admin
    /admin/
    /user-api-key
    /user-api-key/
    /*?api_key*
    /*?*api_key*
  }

  def index
    if (overridden = SiteSetting.overridden_robots_txt.dup).present?
      overridden.prepend(OVERRIDDEN_HEADER) if guardian.is_admin? && !is_api?
      render plain: overridden
      return
    end
    if SiteSetting.allow_index_in_robots_txt?
      @robots_info = self.class.fetch_default_robots_info
      render :index, content_type: 'text/plain'
    else
      render :no_index, content_type: 'text/plain'
    end
  end

  # If you are hosting Discourse in a subfolder, you will need to create your robots.txt
  # in the root of your web server with the appropriate paths. This method will return
  # JSON that can be used by a script to create a robots.txt that works well with your
  # existing site.
  def builder
    result = self.class.fetch_default_robots_info
    overridden = SiteSetting.overridden_robots_txt
    result[:overridden] = overridden if overridden.present?
    render json: result
  end

  def self.fetch_default_robots_info
    deny_paths = DISALLOWED_PATHS.map { |p| Discourse.base_uri + p }
    deny_all = [ "#{Discourse.base_uri}/" ]

    result = {
      header: "# See http://www.robotstxt.org/robotstxt.html for documentation on how to use the robots.txt file",
      agents: []
    }

    if SiteSetting.whitelisted_crawler_user_agents.present?
      SiteSetting.whitelisted_crawler_user_agents.split('|').each do |agent|
        result[:agents] << { name: agent, disallow: deny_paths }
      end

      result[:agents] << { name: '*', disallow: deny_all }
    elsif SiteSetting.blacklisted_crawler_user_agents.present?
      result[:agents] << { name: '*', disallow: deny_paths }
      SiteSetting.blacklisted_crawler_user_agents.split('|').each do |agent|
        result[:agents] << { name: agent, disallow: deny_all }
      end
    else
      result[:agents] << { name: '*', disallow: deny_paths }
    end

    if SiteSetting.slow_down_crawler_user_agents.present?
      SiteSetting.slow_down_crawler_user_agents.split('|').each do |agent|
        result[:agents] << {
          name: agent,
          delay: SiteSetting.slow_down_crawler_rate,
          disallow: deny_paths
        }
      end
    end

    result
  end
end