HORIZON PROJECT

/*!

 * vary

 * Copyright(c) 2014-2017 Douglas Christopher Wilson

 * MIT Licensed

 */

'use strict'

/**

 * Module exports.

 */

module.exports = vary

module.exports.append = append

/**

 * RegExp to match field-name in RFC 7230 sec 3.2

 *

 * field-name    = token

 * token         = 1*tchar

 * tchar         = "!" / "#" / "$" / "%" / "&" / "'" / "*"

 *               / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"

 *               / DIGIT / ALPHA

 *               ; any VCHAR, except delimiters

 */

var FIELD_NAME_REGEXP = /^[!#$%&'*+\-.^_`|~0-9A-Za-z]+$/

/**

 * Append a field to a vary header.

 *

 * @param {String} header

 * @param {String|Array} field

 * @return {String}

 * @public

 */

function append (header, field) {

  if (typeof header !== 'string') {

    throw new TypeError('header argument is required')

  }

  if (!field) {

    throw new TypeError('field argument is required')

  }

  // get fields array

  var fields = !Array.isArray(field)

    ? parse(String(field))

    : field

  // assert on invalid field names

  for (var j = 0; j < fields.length; j++) {

    if (!FIELD_NAME_REGEXP.test(fields[j])) {

      throw new TypeError('field argument contains an invalid header name')

    }

  }

  // existing, unspecified vary

  if (header === '*') {

    return header

  }

  // enumerate current values

  var val = header

  var vals = parse(header.toLowerCase())

  // unspecified vary

  if (fields.indexOf('*') !== -1 || vals.indexOf('*') !== -1) {

    return '*'

  }

  for (var i = 0; i < fields.length; i++) {

    var fld = fields[i].toLowerCase()

    // append value (case-preserving)

    if (vals.indexOf(fld) === -1) {

      vals.push(fld)

      val = val

        ? val + ', ' + fields[i]

        : fields[i]

    }

  }

  return val

}

/**

 * Parse a vary header into an array.

 *

 * @param {String} header

 * @return {Array}

 * @private

 */

function parse (header) {

  var end = 0

  var list = []

  var start = 0

  // gather tokens

  for (var i = 0, len = header.length; i < len; i++) {

    switch (header.charCodeAt(i)) {

      case 0x20: /*   */

        if (start === end) {

          start = end = i + 1

        }

        break

      case 0x2c: /* , */

        list.push(header.substring(start, end))

        start = end = i + 1

        break

      default:

        end = i + 1

        break

    }

  }

  // final token

  list.push(header.substring(start, end))

  return list

}

/**

 * Mark that a request is varied on a header field.

 *

 * @param {Object} res

 * @param {String|Array} field

 * @public

 */

function vary (res, field) {

  if (!res || !res.getHeader || !res.setHeader) {

    // quack quack

    throw new TypeError('res argument is required')

  }

  // get existing header

  var val = res.getHeader('Vary') || ''

  var header = Array.isArray(val)

    ? val.join(', ')

    : String(val)

  // set new header

  if ((val = append(header, field))) {

    res.setHeader('Vary', val)

  }

}