course_link_validator.rb

# frozen_string_literal: true

#
# Copyright (C) 2014 - present Instructure, Inc.
#
# This file is part of Canvas.
#
# Canvas is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, version 3 of the License.
#
# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.

require "nokogiri"

class CourseLinkValidator
  TAG = "link_validation"

  # retrieves the validation job
  def self.current_progress(course)
    Progress.where(tag: TAG, context_type: "Course", context_id: course.id).last
  end

  # creates a new validation job
  def self.queue_course(course)
    progress = current_progress(course)
    return progress if progress&.pending?

    progress ||= Progress.new(tag: TAG, context: course)
    progress.reset!
    progress.process_job(self, :process, {})
    progress
  end

  def self.process(progress)
    validator = new(progress.context)
    validator.check_course(progress)
    progress.set_results({ issues: validator.issues, completed_at: Time.now.utc, version: 2 })
  rescue
    report_id = Canvas::Errors.capture_exception(:course_link_validation, $ERROR_INFO)[:error_report]
    progress.workflow_state = "failed"
    progress.set_results({ error_report_id: report_id, completed_at: Time.now.utc })
  end

  attr_accessor :course, :domain_regex, :issues, :visited_urls

  def initialize(course)
    self.course = course
    domain = course.root_account.domain
    self.domain_regex = %r{\w+:?//#{domain}/} if domain
    self.issues = []
    self.visited_urls = {}
  end

  # ****************************************************************
  # this is where the magic happens
  def check_course(progress)
    # Course card image
    if course.image_url.present?
      find_invalid_link(course.image_url) do |link|
        issues << { name: I18n.t("Course Card Image"), type: :course_card_image,
                    content_url: "/courses/#{course.id}/settings",
                    invalid_links: [link.merge(image: true)] }
      end
      progress.update_completion! 1
    end

    # Syllabus
    find_invalid_links(course.syllabus_body) do |links|
      issues << { name: I18n.t(:syllabus, "Course Syllabus"), type: :syllabus,
                  content_url: "/courses/#{course.id}/assignments/syllabus" }.merge(invalid_links: links)
    end
    progress.update_completion! 5

    # Assessment questions
    course.assessment_questions.active.each do |aq|
      next if aq.assessment_question_bank.deleted?

      check_question(aq)
    end
    progress.update_completion! 15

    # Assignments
    course.assignments.active.each do |assignment|
      next if assignment.quiz || assignment.discussion_topic

      find_invalid_links(assignment.description) do |links|
        issues << { name: assignment.title, type: :assignment,
                    content_url: "/courses/#{course.id}/assignments/#{assignment.id}" }.merge(invalid_links: links)
      end
    end
    progress.update_completion! 25

    # Calendar events
    course.calendar_events.active.each do |event|
      find_invalid_links(event.description) do |links|
        issues << { name: event.title, type: :calendar_event,
                    content_url: "/courses/#{course.id}/calendar_events/#{event.id}" }.merge(invalid_links: links)
      end
    end
    progress.update_completion! 35

    # Discussion topics
    course.discussion_topics.active.each do |topic|
      find_invalid_links(topic.message) do |links|
        issues << { name: topic.title, type: :discussion_topic,
                    content_url: "/courses/#{course.id}/discussion_topics/#{topic.id}" }.merge(invalid_links: links)
      end
    end
    progress.update_completion! 55

    # External URL Module items (almost forgot about these)
    invalid_module_links = {}
    course.context_module_tags.not_deleted.where(content_type: "ExternalUrl").preload(:context_module).each do |ct|
      find_invalid_link(ct.url) do |invalid_link|
        (invalid_module_links[ct.context_module] ||= []) << invalid_link.merge(link_text: ct.title)
      end
    end
    invalid_module_links.each do |mod, links|
      issues << { name: mod.name, type: :module,
                  content_url: "/courses/#{course.id}/modules#module_#{mod.id}" }.merge(invalid_links: links)
    end

    progress.update_completion! 65

    # Quizzes
    course.quizzes.active.each do |quiz|
      find_invalid_links(quiz.description) do |links|
        issues << { name: quiz.title, type: :quiz,
                    content_url: "/courses/#{course.id}/quizzes/#{quiz.id}" }.merge(invalid_links: links)
      end
      quiz.quiz_questions.active.each do |qq|
        check_question(qq)
      end
    end
    progress.update_completion! 85

    # Wiki pages
    course.wiki_pages.not_deleted.each do |page|
      find_invalid_links(page.body) do |links|
        issues << { name: page.title, type: :wiki_page,
                    content_url: "/courses/#{course.id}/pages/#{page.url}" }.merge(invalid_links: links)
      end
    end
    progress.update_completion! 99
  end

  def check_question(question)
    # Assessment/Quiz Questions

    links = []
    %i[question_text correct_comments_html incorrect_comments_html neutral_comments_html more_comments_html].each do |field|
      find_invalid_links(question.question_data[field]) do |field_links|
        links += field_links
      end
    end

    (question.question_data[:answers] || []).each do |answer|
      %i[html comments_html left_html].each do |field|
        find_invalid_links(answer[field]) do |field_links|
          links += field_links
        end
      end
    end

    if links.any?
      hash = { name: question.question_data[:question_name] }.merge(invalid_links: links)
      case question
      when AssessmentQuestion
        hash[:type] = :assessment_question
        hash[:content_url] = "/courses/#{course.id}/question_banks/#{question.assessment_question_bank_id}#question_#{question.id}_question_text"
      when Quizzes::QuizQuestion
        hash[:type] = :quiz_question
        hash[:content_url] = "/courses/#{course.id}/quizzes/#{question.quiz_id}/take?preview=1#question_#{question.id}"
      end
      issues << hash
    end
  end

  # pretty much copied from ImportedHtmlConverter
  def find_invalid_links(html)
    links = []
    doc = Nokogiri::HTML5(html || "")
    attrs = %w[href src data value]

    doc.search("*").each do |node|
      attrs.each do |attr|
        url = node[attr]
        next unless url.present?

        if attr == "value" && !(node["name"] && node["name"] == "src")
          next
        end

        find_invalid_link(url) do |invalid_link|
          link_text = node.text.presence
          invalid_link[:link_text] = link_text if link_text
          invalid_link[:image] = true if node.name == "img"
          links << invalid_link
        end
      end
    end

    yield links if links.any?
  end

  # yields a hash containing the url and an error type if the url is invalid
  def find_invalid_link(url)
    return if url.start_with?("mailto:")

    unless (result = visited_urls[url])
      begin
        if ImportedHtmlConverter.relative_url?(url) || (domain_regex && url.match(domain_regex))
          result = if valid_route?(url)
                     if url.match(%r{/courses/(\d+)}) && course.id.to_s != $1
                       :course_mismatch
                     else
                       check_object_status(url)
                     end
                   else
                     :unreachable
                   end
        else
          unless reachable_url?(url)
            result = :unreachable
          end
        end
      rescue URI::Error
        result = :unparsable
      end
      result ||= :success
      visited_urls[url] = result
    end

    unless result == :success
      invalid_link = { url: url, reason: result }
      yield invalid_link
    end
  end

  # checks against the Rails routes to see if the url matches anything
  def valid_route?(url)
    path = URI.parse(url).path
    path = ActionDispatch::Journey::Router::Utils.normalize_path(path)

    @route_set ||= ::Rails.application.routes.set.routes.select { |r| r.verb == "GET" }
    @route_set.any? { |r| r.path.match(path) } || (!Pathname(path).each_filename.include?("..") && Rails.root.join("public", path.delete_prefix("/")).file?)
  end

  # makes sure that links to course objects exist and are in a visible state
  def check_object_status(url, object: nil)
    return :missing_item unless valid_route?(url)
    return :missing_item if url.include?("/test_error")

    object ||= Context.find_asset_by_url(url)
    unless object
      return :missing_item unless [nil, "syllabus"].include?(url.match(%r{/courses/\d+/\w+/(.+)})&.[](1))
      return :missing_item if url.include?("/media_objects_iframe/")

      return nil
    end
    if object.deleted?
      return :deleted
    end

    case object
    when Attachment
      return :unpublished_item if object.locked?
    when Quizzes::Quiz
      return :unpublished_item if object.workflow_state == "created" || object.workflow_state == "unpublished"
    else
      return :unpublished_item if object.workflow_state == "unpublished"
    end
    nil
  rescue
    :missing_item
  end

  # whitelisted hosts will never be flagged as unavailable
  def whitelisted?(url)
    @whitelist ||= Setting.get("link_validator_whitelisted_hosts", "").split(",")
    return false if @whitelist.empty?

    host = URI.parse(url).host
    @whitelist.include?(host)
  rescue URI::InvalidURIError
    false
  end

  # ping the url and make sure we get a 200
  def reachable_url?(url)
    return true if whitelisted?(url)

    @unavailable_photo_redirect_pattern ||= Regexp.new(Setting.get("unavailable_photo_redirect_pattern", "yimg\\.com/.+/photo_unavailable.png$"))
    redirect_proc = lambda do |response|
      # flickr does a redirect to this file when a photo is deleted/not found;
      # treat this as a broken image instead of following the redirect
      url = response["Location"]
      raise RuntimeError("photo unavailable") if url&.match?(@unavailable_photo_redirect_pattern)
    end

    begin
      response = CanvasHttp.head(url, { "Accept-Encoding" => "gzip" }, redirect_limit: 9, redirect_spy: redirect_proc)
      if %w[404 405].include?(response.code)
        response = CanvasHttp.get(url, { "Accept-Encoding" => "gzip" }, redirect_limit: 9, redirect_spy: redirect_proc) do
          # don't read the response body
        end
      end

      case response.code
      when /^2/, "401", "403", "429", "503"
        # we accept unauthorized and forbidden codes here because sometimes servers refuse to serve our requests
        # and someone can link to a site that requires authentication anyway - doesn't necessarily make it invalid
        true
      else
        false
      end
    rescue
      false
    end
  end
end