code: function (req) {
      var keys = Object.keys(req.headers)
  
      var values = keys.map(function (key) {
        return req.headers[key]
      })
  
      var headers = req.method + req.url + keys.join() + values.join()
  
      // startline: [method] [url] HTTP/1.1\r\n = 12
      // endline: \r\n = 2
      // every header + \r\n = * 2
      // add 2 for each combined header
      return new Buffer(headers).length + (keys.length * 2) + 2 + 12 + 2
    }
docs: quickly calculates the header size in bytes for a given array of headers