Use text-only description in Open Graph tags

app/presenters/asciicast_page_presenter.rb

@@ -1,4 +1,6 @@
 class AsciicastPagePresenter
+  include ActionView::Helpers::SanitizeHelper
+  include ActionView::Helpers::TextHelper
 
   attr_reader :routes, :asciicast, :current_user, :policy, :playback_options
 
@@ -100,6 +102,14 @@ class AsciicastPagePresenter
     asciicast.description
   end
 
+  def short_text_description
+    if asciicast.description.present?
+      truncate(strip_tags(asciicast.description).gsub(/\n+/, ' '), length: 200)
+    else
+      "Recorded by #{asciicast.user.display_name}"
+    end
+  end
+
   def show_other_asciicasts_by_author?
     author.asciicast_count > 1
   end

app/views/asciicasts/_discovery_tags.html.erb

@@ -7,5 +7,5 @@
 <meta property="og:type" content="website" />
 <meta property="og:url" content="<%= asciicast_url(page.asciicast) %>" />
 <meta property="og:image" content="<%= asciicast_url(page.asciicast, format: :png) %>" />
-<meta property="og:description" content="<%= page.description %>" />
+<meta property="og:description" content="<%= page.short_text_description %>" />
 <meta property="og:site_name" content="asciinema.org" />