From 4e4673234645abce10074e55f2155b5eb666dd96 Mon Sep 17 00:00:00 2001
From: Dan Ungureanu <dan@ungureanu.me>
Date: Mon, 22 Mar 2021 19:41:42 +0200
Subject: [PATCH] FEATURE: Implement browser update in crawler view (#12448)

browser-update script does not work correctly in some very old browsers
because the contents of <noscript> is not accessible in JavaScript.
For these browsers, the server can display the crawler page and add the
browser update notice.

Simply loading the browser-update script in the crawler view is not a
solution because that means all crawlers will also see it.
---
 app/controllers/application_controller.rb |  7 ++++++-
 app/views/layouts/crawler.html.erb        |  7 ++++++-
 config/site_settings.yml                  |  5 +++++
 lib/crawler_detection.rb                  |  8 ++++++++
 spec/components/crawler_detection_spec.rb | 16 ++++++++++++++++
 5 files changed, 41 insertions(+), 2 deletions(-)
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 039f5d7c934..e2c4be1ad66 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -56,12 +56,17 @@ class ApplicationController < ActionController::Base
     SiteSetting.enable_escaped_fragments? && params.key?("_escaped_fragment_")
   end
 
+  def show_browser_update?
+    @show_browser_update ||= CrawlerDetection.show_browser_update?(request.user_agent)
+  end
+  helper_method :show_browser_update?
+
   def use_crawler_layout?
     @use_crawler_layout ||=
       request.user_agent &&
       (request.content_type.blank? || request.content_type.include?('html')) &&
       !['json', 'rss'].include?(params[:format]) &&
-      (has_escaped_fragment? || params.key?("print") ||
+      (has_escaped_fragment? || params.key?("print") || show_browser_update? ||
       CrawlerDetection.crawler?(request.user_agent, request.headers["HTTP_VIA"])
       )
   end
diff --git a/app/views/layouts/crawler.html.erb b/app/views/layouts/crawler.html.erb
index 8848af5cf4e..4e0a7e7bdd4 100644
--- a/app/views/layouts/crawler.html.erb
+++ b/app/views/layouts/crawler.html.erb
@@ -16,7 +16,9 @@
     <%= theme_lookup("head_tag") %>
     <%= render_google_universal_analytics_code %>
     <%= yield :head %>
-
+    <% if show_browser_update? %>
+      <style>.buorg {position:absolute; z-index:111111; width:100%; top:0px; left:0px; background:#FDF2AB; text-align:left; font-family: sans-serif; color:#000; font-size: 14px;} .buorg div {padding: 8px;} .buorg a, .buorg a:visited {color:#E25600; text-decoration: underline;} @media print { .buorg { display: none !important; } }</style>
+    <% end %>
     <%= build_plugin_html 'server:before-head-close-crawler' %>
   </head>
   <body class="crawler">
@@ -67,6 +69,9 @@
     </footer>
     <%= theme_lookup("footer") %>
     <%= theme_lookup("body_tag") %>
+    <% if show_browser_update? %>
+      <div class="buorg"><div><%= I18n.t("js.browser_update").html_safe %></div></div>
+    <% end %>
   </body>
   <%= yield :after_body %>
 </html>
diff --git a/config/site_settings.yml b/config/site_settings.yml
index a2baeccf36e..c3c2801e1ff 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -1539,6 +1539,11 @@ security:
     default: "rss|bot|spider|crawler|facebook|archive|wayback|ping|monitor|lighthouse"
     type: list
     list_type: compact
+  browser_update_user_agents:
+    hidden: true
+    default: "MSIE 6|MSIE 7|MSIE 8|MSIE 9"
+    type: list
+    list_type: compact
   crawler_check_bypass_agents:
     hidden: true
     default: "cubot"
diff --git a/lib/crawler_detection.rb b/lib/crawler_detection.rb
index 36fb61b63e5..0b90dc0acb6 100644
--- a/lib/crawler_detection.rb
+++ b/lib/crawler_detection.rb
@@ -37,6 +37,14 @@ module CrawlerDetection
 
   end
 
+  def self.show_browser_update?(user_agent)
+    return false if SiteSetting.browser_update_user_agents.blank?
+
+    @browser_update_matchers ||= {}
+    matcher = @browser_update_matchers[SiteSetting.browser_update_user_agents] ||= to_matcher(SiteSetting.browser_update_user_agents)
+    user_agent.match?(matcher)
+  end
+
   # Given a user_agent that returns true from crawler?, should its request be allowed?
   def self.allow_crawler?(user_agent)
     return true if SiteSetting.allowed_crawler_user_agents.blank? &&
diff --git a/spec/components/crawler_detection_spec.rb b/spec/components/crawler_detection_spec.rb
index c5f2a2056b9..58d7926b138 100644
--- a/spec/components/crawler_detection_spec.rb
+++ b/spec/components/crawler_detection_spec.rb
@@ -69,6 +69,22 @@ describe CrawlerDetection do
 
   end
 
+  describe 'show_browser_update?' do
+    it 'always returns false if setting is empty' do
+      SiteSetting.browser_update_user_agents = ""
+
+      expect(CrawlerDetection.show_browser_update?('Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0)')).to eq(false)
+      expect(CrawlerDetection.show_browser_update?('Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/6.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E)')).to eq(false)
+    end
+
+    it 'returns true if setting matches user agent' do
+      SiteSetting.browser_update_user_agents = "MSIE 6|MSIE 7|MSIE 8|MSIE 9"
+
+      expect(CrawlerDetection.show_browser_update?('Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0)')).to eq(false)
+      expect(CrawlerDetection.show_browser_update?('Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/6.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E)')).to eq(true)
+    end
+  end
+
   describe 'allow_crawler?' do
     it 'returns true if allowlist and blocklist are blank' do
       expect(CrawlerDetection.allow_crawler?('Googlebot/2.1 (+http://www.google.com/bot.html)')).to eq(true)
