Fixes #3370 - "canonical"-tag is missing in knowledge base

app/helpers/knowledge_base_helper.rb

@@ -11,7 +11,7 @@ module KnowledgeBaseHelper
     custom_address = knowledge_base.custom_address_uri
     return path if !custom_address
 
-    custom_path = path.gsub(%r{^/help}, custom_address.path || '').presence || '/'
+    custom_path = knowledge_base.custom_address_path(path)
     prefix      = full ? knowledge_base.custom_address_prefix(request) : ''
 
     "#{prefix}#{custom_path}"
@@ -61,4 +61,18 @@ module KnowledgeBaseHelper
   def dropdown_menu_direction
     system_locale_via_uri.dir == 'ltr' ? 'right' : 'left'
   end
+
+  def canonical_link_tag(knowledge_base, *objects)
+    path = kb_public_system_path(*objects)
+
+    tag :link, rel: 'canonical', href: knowledge_base.canonical_url(path)
+  end
+
+  def kb_public_system_path(*objects)
+    objects
+      .compact
+      .map { |elem| elem.translation.to_param }
+      .unshift(help_root_path)
+      .join('/')
+  end
 end

app/models/knowledge_base.rb

@@ -102,6 +102,29 @@ class KnowledgeBase < ApplicationModel
     "#{custom_address_uri.scheme}://#{host}#{port_string}"
   end
 
+  def custom_address_path(path)
+    uri = custom_address_uri
+
+    return path if !uri
+
+    custom_path  = custom_address_uri.path || ''
+    applied_path = path.gsub(%r{^/help}, custom_path)
+
+    applied_path.presence || '/'
+  end
+
+  def canonical_host
+    custom_address_uri&.host || Setting.get('fqdn')
+  end
+
+  def canonical_scheme_host
+    "#{Setting.get('http_type')}://#{canonical_host}"
+  end
+
+  def canonical_url(path)
+    "#{canonical_scheme_host}#{custom_address_path(path)}"
+  end
+
   def full_destroy!
     ChecksKbClientNotification.disable_in_all_classes!
 

app/views/layouts/knowledge_base.html.erb

@@ -13,6 +13,7 @@
 <meta name="viewport" content="width=device-width,initial-scale=1.0,viewport-fit=cover">
 <%= stylesheet_link_tag "knowledge_base.css", :media => 'all' %>
 <%= render 'knowledge_base/public/inline_stylesheet', knowledge_base: @knowledge_base, locale: system_locale_via_uri  %>
+<%= canonical_link_tag @knowledge_base, @category, @object %>
 
 <div class="wrapper js-wrapper">
   <%= render 'knowledge_base/public/top_banner', object: @object || @knowledge_base if editor? %>

spec/system/knowledge_base_public/canonical_link_spec.rb

@@ -0,0 +1,104 @@
+require 'rails_helper'
+
+RSpec.describe 'Public Knowledge Base canonical link', type: :system, current_user_id: 1, authenticated_as: false do
+  include_context 'basic Knowledge Base'
+
+  let(:path)          { '/path' }
+  let(:subdomain)     { 'subdomain.example.net' }
+  let(:locale)        { primary_locale.system_locale.locale }
+  let(:category_slug) { category.translations.first.to_param }
+  let(:answer_slug)   { published_answer.translations.first.to_param }
+
+  before do
+    published_answer
+    knowledge_base.update! custom_address: custom_address
+  end
+
+  shared_examples 'having canonical links on all pages' do
+    it 'includes canonical link on home page' do
+      visit help_root_path(locale)
+      expect(page).to have_canonical_url("#{prefix}/#{locale}")
+    end
+
+    it 'includes canonical link on category page' do
+      visit help_category_path(locale, category)
+      expect(page).to have_canonical_url("#{prefix}/#{locale}/#{category_slug}")
+    end
+
+    it 'includes canonical link on answer page' do
+      visit help_answer_path(locale, published_answer.category, published_answer)
+      expect(page).to have_canonical_url("#{prefix}/#{locale}/#{category_slug}/#{answer_slug}")
+    end
+  end
+
+  shared_examples 'core locations' do
+    let(:scheme) { ssl ? 'https' : 'http' }
+    before { Setting.set('http_type', scheme) }
+
+    context 'with custom domain' do
+      let(:custom_address) { subdomain }
+      let(:prefix) { "#{scheme}://#{subdomain}" }
+
+      it_behaves_like 'having canonical links on all pages'
+    end
+
+    context 'with custom path' do
+      let(:custom_address) { path }
+      let(:prefix) { "#{scheme}://#{Setting.get('fqdn')}#{path}" }
+
+      it_behaves_like 'having canonical links on all pages'
+    end
+
+    context 'with custom domain and path' do
+      let(:custom_address) { "#{subdomain}#{path}" }
+      let(:prefix) { "#{scheme}://#{subdomain}#{path}" }
+
+      it_behaves_like 'having canonical links on all pages'
+    end
+
+    context 'without custom address' do
+      let(:custom_address) { nil }
+      let(:prefix) { "#{scheme}://#{Setting.get('fqdn')}/help" }
+
+      it_behaves_like 'having canonical links on all pages'
+    end
+  end
+
+  context 'when SSL disabled' do
+    let(:ssl) { false }
+
+    include_examples 'core locations'
+  end
+
+  context 'when SSL enabled' do
+    let(:ssl) { true }
+
+    include_examples 'core locations'
+  end
+
+  matcher :have_canonical_url do |expected|
+    match do
+      return false if canonical_link_element.blank?
+
+      canonical_link_target == expected
+    end
+
+    failure_message do
+      return 'no canonical link found' if canonical_link_element.blank?
+
+      "expected canonical link pointing to \"#{expected}\", but found \"#{canonical_link_target}\" instead"
+    end
+
+    def canonical_link_element
+      return @canonical_link_element if defined?(@canonical_link_element)
+
+      @canonical_link_element = actual.first('head link[rel=canonical]', visible: :hidden, minimum: 0)
+    end
+
+    def canonical_link_target
+      @canonical_link_target ||= canonical_link_element[:href]
+    end
+
+    description { "have canonical tag with href of #{expected}" }
+  end
+end