openproject/app/views/common/list_attachments.json.erb

<%= attachments.select { |a| a.readable? and a.visible? }
               .map { |a| { :content_type => CGI::escape_html(a.content_type),
                            :filename =>     CGI::escape_html(a.filename),
                            :description =>  CGI::escape_html(a.description),
                            :url => url_for(:controller => 'attachments', :action => 'show', :id => a, :filename => a.filename),
                            :is_image => !!a.image? # doing the !! as image? for whatever reason returns null or a number
                          }
                    }.to_json.html_safe %>