Add support for structured data and more OpenGraph tags to link cards (mastodon#16938)

Save preview cards under their canonical URL

Increase max redirects to follow from 2 to 3

Author: Gargron

app/lib/link_details_extractor.rb

@@ -0,0 +1,200 @@
+# frozen_string_literal: true
+
+class LinkDetailsExtractor
+  include ActionView::Helpers::TagHelper
+
+  class StructuredData
+    def initialize(data)
+      @data = data
+    end
+
+    def headline
+      json['headline']
+    end
+
+    def description
+      json['description']
+    end
+
+    def image
+      obj = first_of_value(json['image'])
+
+      return obj['url'] if obj.is_a?(Hash)
+
+      obj
+    end
+
+    def date_published
+      json['datePublished']
+    end
+
+    def date_modified
+      json['dateModified']
+    end
+
+    def author_name
+      author['name']
+    end
+
+    def author_url
+      author['url']
+    end
+
+    def publisher_name
+      publisher['name']
+    end
+
+    private
+
+    def author
+      first_of_value(json['author']) || {}
+    end
+
+    def publisher
+      first_of_value(json['publisher']) || {}
+    end
+
+    def first_of_value(arr)
+      arr.is_a?(Array) ? arr.first : arr
+    end
+
+    def json
+      @json ||= Oj.load(@data)
+    end
+  end
+
+  def initialize(original_url, html, html_charset)
+    @original_url = Addressable::URI.parse(original_url)
+    @html         = html
+    @html_charset = html_charset
+  end
+
+  def to_preview_card_attributes
+    {
+      title: title || '',
+      description: description || '',
+      image_remote_url: image,
+      type: type,
+      width: width || 0,
+      height: height || 0,
+      html: html || '',
+      provider_name: provider_name || '',
+      provider_url: provider_url || '',
+      author_name: author_name || '',
+      author_url: author_url || '',
+      embed_url: embed_url || '',
+    }
+  end
+
+  def type
+    player_url.present? ? :video : :link
+  end
+
+  def html
+    player_url.present? ? content_tag(:iframe, src: player_url, width: width, height: height, allowtransparency: 'true', scrolling: 'no', frameborder: '0') : nil
+  end
+
+  def width
+    opengraph_tag('twitter:player:width')
+  end
+
+  def height
+    opengraph_tag('twitter:player:height')
+  end
+
+  def title
+    structured_data&.headline || opengraph_tag('og:title') || document.xpath('//title').map(&:content).first
+  end
+
+  def description
+    structured_data&.description || opengraph_tag('og:description') || meta_tag('description')
+  end
+
+  def image
+    valid_url_or_nil(opengraph_tag('og:image'))
+  end
+
+  def canonical_url
+    valid_url_or_nil(opengraph_tag('og:url') || link_tag('canonical'), same_origin_only: true) || @original_url.to_s
+  end
+
+  def provider_name
+    structured_data&.publisher_name || opengraph_tag('og:site_name')
+  end
+
+  def provider_url
+    valid_url_or_nil(host_to_url(opengraph_tag('og:site')))
+  end
+
+  def author_name
+    structured_data&.author_name || opengraph_tag('og:author') || opengraph_tag('og:author:username')
+  end
+
+  def author_url
+    structured_data&.author_url
+  end
+
+  def embed_url
+    valid_url_or_nil(opengraph_tag('twitter:player:stream'))
+  end
+
+  private
+
+  def player_url
+    valid_url_or_nil(opengraph_tag('twitter:player'))
+  end
+
+  def host_to_url(str)
+    return if str.blank?
+
+    str.start_with?(/https?:\/\//) ? str : "http://#{str}"
+  end
+
+  def valid_url_or_nil(str, same_origin_only: false)
+    return if str.blank?
+
+    url = @original_url + Addressable::URI.parse(str)
+
+    return if url.host.blank? || !%w(http https).include?(url.scheme) || (same_origin_only && url.host != @original_url.host)
+
+    url.to_s
+  rescue Addressable::URI::InvalidURIError
+    nil
+  end
+
+  def link_tag(name)
+    document.xpath("//link[@rel=\"#{name}\"]").map { |link| link['href'] }.first
+  end
+
+  def opengraph_tag(name)
+    document.xpath("//meta[@property=\"#{name}\" or @name=\"#{name}\"]").map { |meta| meta['content'] }.first
+  end
+
+  def meta_tag(name)
+    document.xpath("//meta[@name=\"#{name}\"]").map { |meta| meta['content'] }.first
+  end
+
+  def structured_data
+    @structured_data ||= begin
+      json_ld = document.xpath('//script[@type="application/ld+json"]').map(&:content).first
+      json_ld.present? ? StructuredData.new(json_ld) : nil
+    end
+  end
+
+  def document
+    @document ||= Nokogiri::HTML(@html, nil, encoding)
+  end
+
+  def encoding
+    @encoding ||= begin
+      guess = detector.detect(@html, @html_charset)
+      guess&.fetch(:confidence, 0).to_i > 60 ? guess&.fetch(:encoding, nil) : nil
+    end
+  end
+
+  def detector
+    @detector ||= CharlockHolmes::EncodingDetector.new.tap do |detector|
+      detector.strip_tags = true
+    end
+  end
+end

app/lib/request.rb

@@ -94,7 +94,7 @@ def valid_url?(url)
     end
 
     def http_client
-      HTTP.use(:auto_inflate).timeout(TIMEOUT.dup).follow(max_hops: 2)
+      HTTP.use(:auto_inflate).timeout(TIMEOUT.dup).follow(max_hops: 3)
     end
   end
 

app/services/fetch_link_card_service.rb

@@ -13,12 +13,12 @@ class FetchLinkCardService < BaseService
   }iox
 
   def call(status)
-    @status = status
-    @url    = parse_urls
+    @status       = status
+    @original_url = parse_urls
 
-    return if @url.nil? || @status.preview_cards.any?
+    return if @original_url.nil? || @status.preview_cards.any?
 
-    @url = @url.to_s
+    @url = @original_url.to_s
 
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
@@ -31,7 +31,7 @@ def call(status)
 
     attach_card if @card&.persisted?
   rescue HTTP::Error, OpenSSL::SSL::SSLError, Addressable::URI::InvalidURIError, Mastodon::HostValidationError, Mastodon::LengthValidationError => e
-    Rails.logger.debug "Error fetching link #{@url}: #{e}"
+    Rails.logger.debug "Error fetching link #{@original_url}: #{e}"
     nil
   end
 
@@ -47,6 +47,12 @@ def html
     return @html if defined?(@html)
 
     Request.new(:get, @url).add_headers('Accept' => 'text/html', 'User-Agent' => Mastodon::Version.user_agent + ' Bot').perform do |res|
+      # We follow redirects, and ideally we want to save the preview card for
+      # the destination URL and not any link shortener in-between, so here
+      # we set the URL to the one of the last response in the redirect chain
+      @url  = res.request.uri.to_s.to_s
+      @card = PreviewCard.find_or_initialize_by(url: @url) if @card.url != @url
+
       if res.code == 200 && res.mime_type == 'text/html'
         @html_charset = res.charset
         @html = res.body_with_limit
@@ -63,12 +69,15 @@ def attach_card
   end
 
   def parse_urls
-    if @status.local?
-      urls = @status.text.scan(URL_PATTERN).map { |array| Addressable::URI.parse(array[1]).normalize }
-    else
-      html  = Nokogiri::HTML(@status.text)
-      links = html.css('a')
-      urls  = links.filter_map { |a| Addressable::URI.parse(a['href']) unless skip_link?(a) }.filter_map(&:normalize)
+    urls = begin
+      if @status.local?
+        @status.text.scan(URL_PATTERN).map { |array| Addressable::URI.parse(array[1]).normalize }
+      else
+        document = Nokogiri::HTML(@status.text)
+        links    = document.css('a')
+
+        links.filter_map { |a| Addressable::URI.parse(a['href']) unless skip_link?(a) }.filter_map(&:normalize)
+      end
     end
 
     urls.reject { |uri| bad_url?(uri) }.first
@@ -79,18 +88,16 @@ def bad_url?(uri)
     uri.host.blank? || TagManager.instance.local_url?(uri.to_s) || !%w(http https).include?(uri.scheme)
   end
 
-  # rubocop:disable Naming/MethodParameterName
-  def mention_link?(a)
+  def mention_link?(anchor)
     @status.mentions.any? do |mention|
-      a['href'] == ActivityPub::TagManager.instance.url_for(mention.account)
+      anchor['href'] == ActivityPub::TagManager.instance.url_for(mention.account)
     end
   end
 
-  def skip_link?(a)
+  def skip_link?(anchor)
     # Avoid links for hashtags and mentions (microformats)
-    a['rel']&.include?('tag') || a['class']&.match?(/u-url|h-card/) || mention_link?(a)
+    anchor['rel']&.include?('tag') || anchor['class']&.match?(/u-url|h-card/) || mention_link?(anchor)
   end
-  # rubocop:enable Naming/MethodParameterName
 
   def attempt_oembed
     service         = FetchOEmbedService.new
@@ -139,42 +146,14 @@ def attempt_oembed
   def attempt_opengraph
     return if html.nil?
 
-    detector = CharlockHolmes::EncodingDetector.new
-    detector.strip_tags = true
-
-    guess      = detector.detect(@html, @html_charset)
-    encoding   = guess&.fetch(:confidence, 0).to_i > 60 ? guess&.fetch(:encoding, nil) : nil
-    page       = Nokogiri::HTML(@html, nil, encoding)
-    player_url = meta_property(page, 'twitter:player')
-
-    if player_url && !bad_url?(Addressable::URI.parse(player_url))
-      @card.type   = :video
-      @card.width  = meta_property(page, 'twitter:player:width') || 0
-      @card.height = meta_property(page, 'twitter:player:height') || 0
-      @card.html   = content_tag(:iframe, nil, src: player_url,
-                                               width: @card.width,
-                                               height: @card.height,
-                                               allowtransparency: 'true',
-                                               scrolling: 'no',
-                                               frameborder: '0')
-    else
-      @card.type = :link
-    end
-
-    @card.title            = meta_property(page, 'og:title').presence || page.at_xpath('//title')&.content || ''
-    @card.description      = meta_property(page, 'og:description').presence || meta_property(page, 'description') || ''
-    @card.image_remote_url = (Addressable::URI.parse(@url) + meta_property(page, 'og:image')).to_s if meta_property(page, 'og:image')
-
-    return if @card.title.blank? && @card.html.blank?
-
-    @card.save_with_optional_image!
-  end
+    link_details_extractor = LinkDetailsExtractor.new(@url, @html, @html_charset)
 
-  def meta_property(page, property)
-    page.at_xpath("//meta[contains(concat(' ', normalize-space(@property), ' '), ' #{property} ')]")&.attribute('content')&.value || page.at_xpath("//meta[@name=\"#{property}\"]")&.attribute('content')&.value
+    @card = PreviewCard.find_or_initialize_by(url: link_details_extractor.canonical_url) if link_details_extractor.canonical_url != @card.url
+    @card.assign_attributes(link_details_extractor.to_preview_card_attributes)
+    @card.save_with_optional_image! unless @card.title.blank? && @card.html.blank?
   end
 
   def lock_options
-    { redis: Redis.current, key: "fetch:#{@url}", autorelease: 15.minutes.seconds }
+    { redis: Redis.current, key: "fetch:#{@original_url}", autorelease: 15.minutes.seconds }
   end
 end

spec/lib/link_details_extractor_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+RSpec.describe LinkDetailsExtractor do
+  let(:original_url) { '' }
+  let(:html) { '' }
+  let(:html_charset) { nil }
+
+  subject { described_class.new(original_url, html, html_charset) }
+
+  describe '#canonical_url' do
+    let(:original_url) { 'https://foo.com/article?bar=baz123' }
+
+    context 'when canonical URL points to another host' do
+      let(:html) { '<!doctype html><link rel="canonical" href="https://bar.com/different-article" />' }
+
+      it 'ignores the canonical URLs' do
+        expect(subject.canonical_url).to eq original_url
+      end
+    end
+
+    context 'when canonical URL points to the same host' do
+      let(:html) { '<!doctype html><link rel="canonical" href="https://foo.com/article" />' }
+
+      it 'ignores the canonical URLs' do
+        expect(subject.canonical_url).to eq 'https://foo.com/article'
+      end
+    end
+  end
+end

spec/services/fetch_link_card_service_spec.rb

@@ -1,7 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe FetchLinkCardService, type: :service do
-  subject { FetchLinkCardService.new }
+  subject { described_class.new }
 
   before do
     stub_request(:get, 'http://example.xn--fiqs8s/').to_return(request_fixture('idn.txt'))