sinatra.rb

def provides(*types)
        types = [types] unless types.kind_of? Array
        types.map!{|t| mime_type(t)}

        condition {
          matching_types = (request.accept & types)
          unless matching_types.empty?
            response.headers['Content-Type'] = matching_types.first
            true
          else
            false
          end
        }
      end