discourse/lib/retrieve_title.rb

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# frozen_string_literal: true
module RetrieveTitle
CRAWL_TIMEOUT = 1
UNRECOVERABLE_ERRORS = [
Net::ReadTimeout,
FinalDestination::SSRFError,
FinalDestination::UrlEncodingError,
]
def self.crawl(url, max_redirects: nil, initial_https_redirect_ignore_limit: false)
fetch_title(
url,
max_redirects: max_redirects,
initial_https_redirect_ignore_limit: initial_https_redirect_ignore_limit,
)
rescue *UNRECOVERABLE_ERRORS
# ¯\_(ツ)_/¯
end
def self.extract_title(html, encoding = nil)
title = nil
return nil if html =~ /<title>/ && html !~ %r{</title>}
doc = nil
begin
doc = Nokogiri.HTML5(html, nil, encoding)
rescue ArgumentError
# invalid HTML (Eg: too many attributes, status tree too deep) - ignore
# Error in nokogumbo is not specialized, uses generic ArgumentError
# see: https://www.rubydoc.info/gems/nokogiri/Nokogiri/HTML5#label-Error+reporting
end
if doc
title = doc.at("title")&.inner_text
# A horrible hack - YouTube uses `document.title` to populate the title
# for some reason. For any other site than YouTube this wouldn't be worth it.
if title == "YouTube" && html =~ /document\.title *= *"(.*)";/
title = Regexp.last_match[1].sub(/ - YouTube\z/, "")
end
if !title && node = doc.at('meta[property="og:title"]')
title = node["content"]
end
end
if title.present?
title.gsub!(/\n/, " ")
title.gsub!(/ +/, " ")
title.strip!
return title
end
nil
end
private
def self.max_chunk_size(uri)
# Exception for sites that leave the title until very late.
if uri.host =~
/(^|\.)amazon\.(com|ca|co\.uk|es|fr|de|it|com\.au|com\.br|cn|in|co\.jp|com\.mx)\z/
return 500
end
return 300 if uri.host =~ /(^|\.)youtube\.com\z/ || uri.host =~ /(^|\.)youtu\.be\z/
return 50 if uri.host =~ /(^|\.)github\.com\z/
# default is 20k
20
end
# Fetch the beginning of a HTML document at a url
def self.fetch_title(url, max_redirects: nil, initial_https_redirect_ignore_limit: false)
fd =
FinalDestination.new(
url,
timeout: CRAWL_TIMEOUT,
stop_at_blocked_pages: true,
max_redirects: max_redirects,
initial_https_redirect_ignore_limit: initial_https_redirect_ignore_limit,
headers: {
Accept: "text/html,*/*",
},
)
current = nil
title = nil
encoding = nil
fd.get do |_response, chunk, uri|
unless Net::HTTPRedirection === _response
throw :done if uri.blank?
if current
current << chunk
else
current = chunk
end
if !encoding && content_type = _response["content-type"]&.strip&.downcase
if content_type =~ /charset="?([a-z0-9_-]+)"?/
encoding = Regexp.last_match(1)
encoding = nil if !Encoding.list.map(&:name).map(&:downcase).include?(encoding)
end
end
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max_size = max_chunk_size(uri) * 1024
title = extract_title(current, encoding)
throw :done if title || max_size < current.length
end
end
title
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end
end