code: function sendOptionsResponse(res, methods) {
    var options = Object.create(null)
  
    // build unique method map
    for (var i = 0; i < methods.length; i++) {
      options[methods[i]] = true
    }
  
    // construct the allow list
    var allow = Object.keys(options).sort().join(', ')
  
    // send response
    res.setHeader('Allow', allow)
    res.setHeader('Content-Length', Buffer.byteLength(allow))
    res.setHeader('Content-Type', 'text/plain')
    res.setHeader('X-Content-Type-Options', 'nosniff')
    res.end(allow)
  }
docs: Send an OPTIONS response.
  
  @private