require 'open-uri' require 'nokogiri' require 'excon' module Jobs class CrawlTopicLink < Jobs::Base class ReadEnough < Exception; end # Retrieve a header regardless of case sensitivity def self.header_for(head, name) header = head.headers.detect do |k, _| name == k.downcase end header[1] if header end def self.request_headers(uri) { "User-Agent" => "Mozilla/5.0 (Windows NT 6.2; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/32.0.1667.0 Safari/537.36", "Accept" => "text/html", "Host" => uri.host } end # Follow any redirects that might exist def self.final_uri(url, limit=5) return if limit < 0 uri = URI(url) return if uri.blank? || uri.host.blank? headers = CrawlTopicLink.request_headers(uri) head = Excon.head(url, read_timeout: 20, headers: headers) # If the site does not allow HEAD, just try the url return uri if head.status == 405 if head.status == 200 uri = nil unless header_for(head, 'content-type') =~ /text\/html/ return uri end location = header_for(head, 'location') if location location = "#{uri.scheme}://#{uri.host}#{location}" if location[0] == "/" return final_uri(location, limit - 1) end nil end def self.max_chunk_size(uri) # Amazon leaves the title until very late. Normally it's a bad idea to make an exception for # one host but amazon is a big one. return 80 if uri.host =~ /amazon\.(com|ca|co\.uk|es|fr|de|it|com\.au|com\.br|cn|in|co\.jp|com\.mx)$/ # Default is 10k 10 end # Fetch the beginning of a HTML document at a url def self.fetch_beginning(url) # Never crawl in test mode return if Rails.env.test? uri = final_uri(url) return "" unless uri result = "" streamer = lambda do |chunk, _, _| result << chunk # Using exceptions for flow control is really bad, but there really seems to # be no sane way to get a stream to stop reading in Excon (or Net::HTTP for # that matter!) raise ReadEnough.new if result.size > (CrawlTopicLink.max_chunk_size(uri) * 1024) end Excon.get(uri.to_s, response_block: streamer, read_timeout: 20, headers: CrawlTopicLink.request_headers(uri)) result rescue ReadEnough result end def execute(args) raise Discourse::InvalidParameters.new(:topic_link_id) unless args[:topic_link_id].present? topic_link = TopicLink.find_by(id: args[:topic_link_id], internal: false, crawled_at: nil) return if topic_link.blank? # Look for a topic embed for the URL. If it exists, use its title and don't crawl topic_embed = TopicEmbed.where(embed_url: topic_link.url).includes(:topic).references(:topic).first if topic_embed.present? TopicLink.where(id: topic_link.id).update_all(['title = ?, crawled_at = CURRENT_TIMESTAMP', topic_embed.topic.title[0..255]]) return end begin crawled = false # Special case: Images # If the link is to an image, put the filename as the title if topic_link.url =~ /\.(jpg|gif|png)$/ uri = URI(topic_link.url) filename = File.basename(uri.path) crawled = (TopicLink.where(id: topic_link.id).update_all(["title = ?, crawled_at = CURRENT_TIMESTAMP", filename]) == 1) end unless crawled # Fetch the beginning of the document to find the title result = CrawlTopicLink.fetch_beginning(topic_link.url) doc = Nokogiri::HTML(result) if doc title = doc.at('title').try(:inner_text) if title.present? title.gsub!(/\n/, ' ') title.gsub!(/ +/, ' ') title.strip! if title.present? crawled = (TopicLink.where(id: topic_link.id).update_all(['title = ?, crawled_at = CURRENT_TIMESTAMP', title[0..255]]) == 1) end end end end rescue Exception # If there was a connection error, do nothing ensure TopicLink.where(id: topic_link.id).update_all('crawled_at = CURRENT_TIMESTAMP') if !crawled && topic_link.present? end end end end