code: function (descriptor) {
          var methods = [];
          ACCEPTABLE_METHODS.forEach(function (method) {
              if (descriptor[method]) {
                  methods.push(method.toUpperCase());
              }
          });
          methods = methods.join(",");
          return function (request, response) {
              response.writeHead(200, {
                  "Content-Length": methods.length,
                  "Allow": methods
              });
              response.end(methods);
          };
      }
docs: Create a handler for the HTTP OPTIONS method based on the descriptor (which is a method name to callback map).
  This is only used of options is not provided by the user.
  
  @param {Object} descriptor A map of methods to their associated callbacks
  @return {Function} A function which will return a proper OPTIONS response
  @api private