1 files changed, 56 insertions, 0 deletions
diff --git a/lib/banzai/filter/wiki_link_filter.rb b/lib/banzai/filter/wiki_link_filter.rb
new file mode 100644
index 00000000000..06d10c98501
--- /dev/null
+++ b/lib/banzai/filter/wiki_link_filter.rb
@@ -0,0 +1,56 @@
+require 'uri'
+
+module Banzai
+  module Filter
+    # HTML filter that "fixes" relative links to files in a repository.
+    #
+    # Context options:
+    #   :project_wiki
+    class WikiLinkFilter < HTML::Pipeline::Filter
+
+      def call
+        return doc unless project_wiki?
+
+        doc.search('a:not(.gfm)').each do |el|
+          process_link_attr el.attribute('href')
+        end
+
+        doc
+      end
+
+      protected
+
+      def project_wiki?
+        !context[:project_wiki].nil?
+      end
+
+      def process_link_attr(html_attr)
+        return if html_attr.blank? || file_reference?(html_attr)
+
+        uri = URI(html_attr.value)
+        if uri.relative? && uri.path.present?
+          html_attr.value = rebuild_wiki_uri(uri).to_s
+        end
+      rescue URI::Error
+        # noop
+      end
+
+      def rebuild_wiki_uri(uri)
+        uri.path = ::File.join(project_wiki_base_path, uri.path)
+        uri
+      end
+
+      def file_reference?(html_attr)
+        !File.extname(html_attr.value).blank?
+      end
+
+      def project_wiki
+        context[:project_wiki]
+      end
+
+      def project_wiki_base_path
+        project_wiki && project_wiki.wiki_base_path
+      end
+    end
+  end
+end