umber' && err.statusCode >= 400 && err.statusCode < 600) {
    return err.statusCode
  }

  return undefined
}

/**
 * Get resource name for the request.
 *
 * This is typically just the original pathname of the request
 * but will fallback to "resource" is that cannot be determined.
 *
 * @param {IncomingMessage} req
 * @return {string}
 * @private
 */

function getResourceName (req) {
  try {
    return parseUrl.original(req).pathname
  } catch (e) {
    return 'resource'
  }
}

/**
 * Get status code from response.
 *
 * @param {OutgoingMessage} res
 * @return {number}
 * @private
 */

function getResponseStatusCode (res) {
  var status = res.statusCode

  // default status code to 500 if outside valid range
  if (typeof status !== 'number' || status < 400 || status > 599) {
    status = 500
  }

  return status
}

/**
 * Determine if the response headers have been sent.
 *
 * @param {object} res
 * @returns {boolean}
 * @private
 */

function headersSent (res) {
  return typeof res.headersSent !== 'boolean'
    ? Boolean(res._header)
    : res.headersSent
}

/**
 * Send response.
 *
 * @param {IncomingMessage} req
 * @param {OutgoingMessage} res
 * @param {number} status
 * @param {object} headers
 * @param {string} message
 * @private
 */

function send (req, res, status, headers, message) {
  function write () {
    // response body
    var body = createHtmlDocument(message)

    // response status
    res.statusCode = status

    if (req.httpVersionMajor < 2) {
      res.statusMessage = statuses.message[status]
    }

    // remove any content headers
    res.removeHeader('Content-Encoding')
    res.removeHeader('Content-Language')
    res.removeHeader('Content-Range')

    // response headers
    setHeaders(res, headers)

    // security headers
    res.setHeader('Content-Security-Policy', "default-src 'none'")
    res.setHeader('X-Content-Type-Options', 'nosniff')

    // standard headers
    res.setHeader('Content-Type', 'text/html; charset=utf-8')
    res.setHeader('Content-Length', Buffer.byteLength(body, 'utf8'))

    if (req.method === 'HEAD') {
      res.end()
      return
    }

    res.end(body, 'utf8')
  }

  if (isFinished(req)) {
    write()
    return
  }

  // unpipe everything from the request
  unpipe(req)

  // flush the request
  onFinished(req, write)
  req.resume()
}

/**
 * Set response headers from an object.
 *
 * @param {OutgoingMessage} res
 * @param {object} headers
 * @private
 */

function setHeaders (res, headers) {
  if (!headers) {
    return
  }

  var keys = Object.keys(headers)
  for (var i = 0; i < keys.length; i++) {
    var key = keys[i]
    res.setHeader(key, headers[key])
  }
}
