code: function createHeaderGetter(str) {
    var header = str.toLowerCase()
  
    return headerGetter
  
    function headerGetter(req, res) {
      // set appropriate Vary header
      res.vary(str)
  
      // multiple headers get joined with comma by node.js core
      return (req.headers[header] || '').split(/ *, */)
    }
  }
docs: Create a getter for the given header name.