1 files changed, 34 insertions, 0 deletions
diff --git a/lib/banzai/filter/absolute_link_filter.rb b/lib/banzai/filter/absolute_link_filter.rb
new file mode 100644
index 00000000000..1ec6201523f
--- /dev/null
+++ b/lib/banzai/filter/absolute_link_filter.rb
@@ -0,0 +1,34 @@
+require 'uri'
+
+module Banzai
+  module Filter
+    # HTML filter that converts relative urls into absolute ones.
+    class AbsoluteLinkFilter < HTML::Pipeline::Filter
+      def call
+        return doc unless context[:only_path] == false
+
+        doc.search('a.gfm').each do |el|
+          process_link_attr el.attribute('href')
+        end
+
+        doc
+      end
+
+      protected
+
+      def process_link_attr(html_attr)
+        return if html_attr.blank?
+        return if html_attr.value.start_with?('//')
+
+        uri = URI(html_attr.value)
+        html_attr.value = absolute_link_attr(uri) if uri.relative?
+      rescue URI::Error
+        # noop
+      end
+
+      def absolute_link_attr(uri)
+        URI.join(Gitlab.config.gitlab.url, uri).to_s
+      end
+    end
+  end
+end