1  /*!
  2   * uid-safe
  3   * Copyright(c) 2014 Jonathan Ong
  4   * Copyright(c) 2015-2017 Douglas Christopher Wilson
  5   * MIT Licensed
  6   */
  7  
  8  'use strict'
  9  
 10  /**
 11   * Module dependencies.
 12   * @private
 13   */
 14  
 15  var randomBytes = require('random-bytes')
 16  
 17  /**
 18   * Module variables.
 19   * @private
 20   */
 21  
 22  var EQUAL_END_REGEXP = /=+$/
 23  var PLUS_GLOBAL_REGEXP = /\+/g
 24  var SLASH_GLOBAL_REGEXP = /\//g
 25  
 26  /**
 27   * Module exports.
 28   * @public
 29   */
 30  
 31  module.exports = uid
 32  module.exports.sync = uidSync
 33  
 34  /**
 35   * Create a unique ID.
 36   *
 37   * @param {number} length
 38   * @param {function} [callback]
 39   * @return {Promise}
 40   * @public
 41   */
 42  
 43  function uid (length, callback) {
 44    // validate callback is a function, if provided
 45    if (callback !== undefined && typeof callback !== 'function') {
 46      throw new TypeError('argument callback must be a function')
 47    }
 48  
 49    // require the callback without promises
 50    if (!callback && !global.Promise) {
 51      throw new TypeError('argument callback is required')
 52    }
 53  
 54    if (callback) {
 55      // classic callback style
 56      return generateUid(length, callback)
 57    }
 58  
 59    return new Promise(function executor (resolve, reject) {
 60      generateUid(length, function onUid (err, str) {
 61        if (err) return reject(err)
 62        resolve(str)
 63      })
 64    })
 65  }
 66  
 67  /**
 68   * Create a unique ID sync.
 69   *
 70   * @param {number} length
 71   * @return {string}
 72   * @public
 73   */
 74  
 75  function uidSync (length) {
 76    return toString(randomBytes.sync(length))
 77  }
 78  
 79  /**
 80   * Generate a unique ID string.
 81   *
 82   * @param {number} length
 83   * @param {function} callback
 84   * @private
 85   */
 86  
 87  function generateUid (length, callback) {
 88    randomBytes(length, function (err, buf) {
 89      if (err) return callback(err)
 90      callback(null, toString(buf))
 91    })
 92  }
 93  
 94  /**
 95   * Change a Buffer into a string.
 96   *
 97   * @param {Buffer} buf
 98   * @return {string}
 99   * @private
100   */
101  
102  function toString (buf) {
103    return buf.toString('base64')
104      .replace(EQUAL_END_REGEXP, '')
105      .replace(PLUS_GLOBAL_REGEXP, '-')
106      .replace(SLASH_GLOBAL_REGEXP, '_')
107  }