1 files changed, 57 insertions, 0 deletions
diff --git a/lib/banzai/filter/attributes_filter.rb b/lib/banzai/filter/attributes_filter.rb
new file mode 100644
index 00000000000..1cf7155b80e
--- /dev/null
+++ b/lib/banzai/filter/attributes_filter.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module Banzai
+  module Filter
+    # Looks for attributes that are specified for an element.  Follows the basic syntax laid out
+    # in https://github.com/jgm/commonmark-hs/blob/master/commonmark-extensions/test/attributes.md
+    # For example,
+    #   ![](http://example.com/image.jpg){width=50%}
+    #
+    # However we currently have the following limitations:
+    # - only support images
+    # - only support the `width` and `height` attributes
+    # - attributes can not span multiple lines
+    # - unsupported attributes are thrown away
+    class AttributesFilter < HTML::Pipeline::Filter
+      CSS   = 'img'
+      XPATH = Gitlab::Utils::Nokogiri.css_to_xpath(CSS).freeze
+
+      ATTRIBUTES_PATTERN = %r{\A(?<matched>\{(?<attributes>.{1,100})\})}.freeze
+      WIDTH_HEIGHT_REGEX = %r{\A(?<name>height|width)="?(?<size>[\w%]{1,10})"?\z}.freeze
+      VALID_SIZE_REGEX   = %r{\A\d{1,4}(%|px)?\z}.freeze
+
+      def call
+        return doc unless Feature.enabled?(:markdown_image_attributes, group)
+
+        doc.xpath(XPATH).each do |img|
+          sibling = img.next
+          next unless sibling && sibling.text? && sibling.content.first == '{'
+
+          match = sibling.content.match(ATTRIBUTES_PATTERN)
+          next unless match && match[:attributes]
+
+          match[:attributes].split(' ').each do |attribute|
+            next unless attribute.match?(WIDTH_HEIGHT_REGEX)
+
+            attribute_match = attribute.match(WIDTH_HEIGHT_REGEX)
+            img[attribute_match[:name].to_sym] = attribute_match[:size] if valid_size?(attribute_match[:size])
+          end
+
+          sibling.content = sibling.content.sub(match[:matched], '')
+        end
+
+        doc
+      end
+
+      private
+
+      def valid_size?(size)
+        size.match?(VALID_SIZE_REGEX)
+      end
+
+      def group
+        context[:group] || context[:project]&.group
+      end
+    end
+  end
+end