discourse/app/jobs/regular/crawl_topic_link.rb

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require 'open-uri'
require 'nokogiri'
require 'excon'
module Jobs
class CrawlTopicLink < Jobs::Base
class ReadEnough < StandardError; end
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# Retrieve a header regardless of case sensitivity
def self.header_for(head, name)
header = head.headers.detect do |k, _|
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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)
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# If the site does not allow HEAD, just try the url
return uri if head.status == 405
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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
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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.
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return 80 if uri.host =~ /amazon\.(com|ca|co\.uk|es|fr|de|it|com\.au|com\.br|cn|in|co\.jp|com\.mx)$/
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# Default is 10k
10
end
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# Fetch the beginning of a HTML document at a url
def self.fetch_beginning(url)
# Never crawl in test mode
return if Rails.env.test?
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uri = final_uri(url)
return "" unless uri
result = ""
streamer = lambda do |chunk, _, _|
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result << chunk
# Using exceptions for flow control is really bad, but there really seems to
# be no sane way to get a stream to stop reading in Excon (or Net::HTTP for
# that matter!)
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raise ReadEnough.new if result.size > (CrawlTopicLink.max_chunk_size(uri) * 1024)
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end
Excon.get(uri.to_s, response_block: streamer, read_timeout: 20, headers: CrawlTopicLink.request_headers(uri))
result
rescue ReadEnough
result
end
def execute(args)
raise Discourse::InvalidParameters.new(:topic_link_id) unless args[:topic_link_id].present?
topic_link = TopicLink.find_by(id: args[:topic_link_id], internal: false, crawled_at: nil)
return if topic_link.blank?
# Look for a topic embed for the URL. If it exists, use its title and don't crawl
topic_embed = TopicEmbed.where(embed_url: topic_link.url).includes(:topic).references(:topic).first
# topic could be deleted, so skip
if topic_embed && topic_embed.topic
TopicLink.where(id: topic_link.id).update_all(['title = ?, crawled_at = CURRENT_TIMESTAMP', topic_embed.topic.title[0..255]])
return
end
begin
crawled = false
# Special case: Images
# If the link is to an image, put the filename as the title
if topic_link.url =~ /\.(jpg|gif|png)$/
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
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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
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end
end
end