NewId vs NewSequentialId与另一个uuid源（javascript）结合使用

Question

我需要在我的服务器端代码以及客户端代码（在浏览器中）创建UID。我目前使用NewID（）作为我的默认值，但是当在客户端（在浏览器中）创建对象时，我使用uuid.js.我是否更有可能将NewSequentialId（）与我的默认值（在服务器端创建对象时使用）进行冲突？

仅供参考，这是uuid.js代码，因为我无法回想起我下载的位置。

//     uuid.js
//
//     Copyright (c) 2010-2012 Robert Kieffer
//     MIT License - http://opensource.org/licenses/mit-license.php

(function() {
  var _global = this;

  // Unique ID creation requires a high quality random # generator.  We feature
  // detect to determine the best RNG source, normalizing to a function that
  // returns 128-bits of randomness, since that's what's usually required
  var _rng;

  // Node.js crypto-based RNG - http://nodejs.org/docs/v0.6.2/api/crypto.html
  //
  // Moderately fast, high quality
  if (typeof(require) == 'function') {
    try {
      var _rb = require('crypto').randomBytes;
      _rng = _rb && function() {return _rb(16);};
    } catch(e) {}
  }

  if (!_rng && _global.crypto && crypto.getRandomValues) {
    // WHATWG crypto-based RNG - http://wiki.whatwg.org/wiki/Crypto
    //
    // Moderately fast, high quality
    var _rnds8 = new Uint8Array(16);
    _rng = function whatwgRNG() {
      crypto.getRandomValues(_rnds8);
      return _rnds8;
    };
  }

  if (!_rng) {
    // Math.random()-based (RNG)
    //
    // If all else fails, use Math.random().  It's fast, but is of unspecified
    // quality.
    var  _rnds = new Array(16);
    _rng = function() {
      for (var i = 0, r; i < 16; i++) {
        if ((i & 0x03) === 0) r = Math.random() * 0x100000000;
        _rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
      }

      return _rnds;
    };
  }

  // Buffer class to use
  var BufferClass = typeof(Buffer) == 'function' ? Buffer : Array;

  // Maps for number <-> hex string conversion
  var _byteToHex = [];
  var _hexToByte = {};
  for (var i = 0; i < 256; i++) {
    _byteToHex[i] = (i + 0x100).toString(16).substr(1);
    _hexToByte[_byteToHex[i]] = i;
  }

  // **`parse()` - Parse a UUID into it's component bytes**
  function parse(s, buf, offset) {
    var i = (buf && offset) || 0, ii = 0;

    buf = buf || [];
    s.toLowerCase().replace(/[0-9a-f]{2}/g, function(oct) {
      if (ii < 16) { // Don't overflow!
        buf[i + ii++] = _hexToByte[oct];
      }
    });

    // Zero out remaining bytes if string was short
    while (ii < 16) {
      buf[i + ii++] = 0;
    }

    return buf;
  }

  // **`unparse()` - Convert UUID byte array (ala parse()) into a string**
  function unparse(buf, offset) {
    var i = offset || 0, bth = _byteToHex;
    return  bth[buf[i++]] + bth[buf[i++]] +
            bth[buf[i++]] + bth[buf[i++]] + '-' +
            bth[buf[i++]] + bth[buf[i++]] + '-' +
            bth[buf[i++]] + bth[buf[i++]] + '-' +
            bth[buf[i++]] + bth[buf[i++]] + '-' +
            bth[buf[i++]] + bth[buf[i++]] +
            bth[buf[i++]] + bth[buf[i++]] +
            bth[buf[i++]] + bth[buf[i++]];
  }

  // **`v1()` - Generate time-based UUID**
  //
  // Inspired by https://github.com/LiosK/UUID.js
  // and http://docs.python.org/library/uuid.html

  // random #'s we need to init node and clockseq
  var _seedBytes = _rng();

  // Per 4.5, create and 48-bit node id, (47 random bits + multicast bit = 1)
  var _nodeId = [
    _seedBytes[0] | 0x01,
    _seedBytes[1], _seedBytes[2], _seedBytes[3], _seedBytes[4], _seedBytes[5]
  ];

  // Per 4.2.2, randomize (14 bit) clockseq
  var _clockseq = (_seedBytes[6] << 8 | _seedBytes[7]) & 0x3fff;

  // Previous uuid creation time
  var _lastMSecs = 0, _lastNSecs = 0;

  // See https://github.com/broofa/node-uuid for API details
  function v1(options, buf, offset) {
    var i = buf && offset || 0;
    var b = buf || [];

    options = options || {};

    var clockseq = options.clockseq != null ? options.clockseq : _clockseq;

    // UUID timestamps are 100 nano-second units since the Gregorian epoch,
    // (1582-10-15 00:00).  JSNumbers aren't precise enough for this, so
    // time is handled internally as 'msecs' (integer milliseconds) and 'nsecs'
    // (100-nanoseconds offset from msecs) since unix epoch, 1970-01-01 00:00.
    var msecs = options.msecs != null ? options.msecs : new Date().getTime();

    // Per 4.2.1.2, use count of uuid's generated during the current clock
    // cycle to simulate higher resolution clock
    var nsecs = options.nsecs != null ? options.nsecs : _lastNSecs + 1;

    // Time since last uuid creation (in msecs)
    var dt = (msecs - _lastMSecs) + (nsecs - _lastNSecs)/10000;

    // Per 4.2.1.2, Bump clockseq on clock regression
    if (dt < 0 && options.clockseq == null) {
      clockseq = clockseq + 1 & 0x3fff;
    }

    // Reset nsecs if clock regresses (new clockseq) or we've moved onto a new
    // time interval
    if ((dt < 0 || msecs > _lastMSecs) && options.nsecs == null) {
      nsecs = 0;
    }

    // Per 4.2.1.2 Throw error if too many uuids are requested
    if (nsecs >= 10000) {
      throw new Error('uuid.v1(): Can\'t create more than 10M uuids/sec');
    }

    _lastMSecs = msecs;
    _lastNSecs = nsecs;
    _clockseq = clockseq;

    // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
    msecs += 12219292800000;

    // `time_low`
    var tl = ((msecs & 0xfffffff) * 10000 + nsecs) % 0x100000000;
    b[i++] = tl >>> 24 & 0xff;
    b[i++] = tl >>> 16 & 0xff;
    b[i++] = tl >>> 8 & 0xff;
    b[i++] = tl & 0xff;

    // `time_mid`
    var tmh = (msecs / 0x100000000 * 10000) & 0xfffffff;
    b[i++] = tmh >>> 8 & 0xff;
    b[i++] = tmh & 0xff;

    // `time_high_and_version`
    b[i++] = tmh >>> 24 & 0xf | 0x10; // include version
    b[i++] = tmh >>> 16 & 0xff;

    // `clock_seq_hi_and_reserved` (Per 4.2.2 - include variant)
    b[i++] = clockseq >>> 8 | 0x80;

    // `clock_seq_low`
    b[i++] = clockseq & 0xff;

    // `node`
    var node = options.node || _nodeId;
    for (var n = 0; n < 6; n++) {
      b[i + n] = node[n];
    }

    return buf ? buf : unparse(b);
  }

  // **`v4()` - Generate random UUID**

  // See https://github.com/broofa/node-uuid for API details
  function v4(options, buf, offset) {
    // Deprecated - 'format' argument, as supported in v1.2
    var i = buf && offset || 0;

    if (typeof(options) == 'string') {
      buf = options == 'binary' ? new BufferClass(16) : null;
      options = null;
    }
    options = options || {};

    var rnds = options.random || (options.rng || _rng)();

    // Per 4.4, set bits for version and `clock_seq_hi_and_reserved`
    rnds[6] = (rnds[6] & 0x0f) | 0x40;
    rnds[8] = (rnds[8] & 0x3f) | 0x80;

    // Copy bytes to buffer, if provided
    if (buf) {
      for (var ii = 0; ii < 16; ii++) {
        buf[i + ii] = rnds[ii];
      }
    }

    return buf || unparse(rnds);
  }

  // Export public API
  var uuid = v4;
  uuid.v1 = v1;
  uuid.v4 = v4;
  uuid.parse = parse;
  uuid.unparse = unparse;
  uuid.BufferClass = BufferClass;

  if (typeof define === 'function' && define.amd) {
    // Publish as AMD module
    define(function() {return uuid;});
  } else if (typeof(module) != 'undefined' && module.exports) {
    // Publish as node.js module
    module.exports = uuid;
  } else {
    // Publish as global (in browsers)
    var _previousRoot = _global.uuid;

    // **`noConflict()` - (browser only) to reset global 'uuid' var**
    uuid.noConflict = function() {
      _global.uuid = _previousRoot;
      return uuid;
    };

    _global.uuid = uuid;
  }
}).call(this);

Answer 1

这实际上是一个非常有趣的问题，有很多级别。

首先，值得注意的是uuid.js支持两种不同形式的id。 uuid.v4()使用随机数创建ID，而uuid.v1()根据时间戳创建ID。 id的“版本”实际上是在id本身中编码的，这保证了理论上v4 id不会与v1 id冲突。这是RFC4122的一部分，即UUID规范。

值得注意的是，对于v1 id，每个id源应该具有唯一的“node id”，也在id中编码，这保证了由该源创建的id序列的唯一性。对于可以访问保证唯一值（例如设备的MAC地址）的id源，这很有效。但是，uuid.js无法访问此类值，因此会为其节点ID生成随机值。这会带来生成与服务器使用的节点ID匹配的节点ID的风险。节点id是48位值，意味着节点id冲突的可能性是281,474,976,710,656：1。所以，这是一个机会，但它非常低。

......但这些都不重要！

事实证明，即使NewSequentialID()生成表面上与v1 ID类似的ID，Microsoft for whatever reasons也决定交换ID中的各个字段，从而破坏了RFC4122的兼容性。这意味着，根据序列号，ID可能看起来像有效的v1 ID，也可能看起来不是有效的v4 ID，或者只是无效的UUID。即如果你想谈论uuid碰撞的可能性，使用NewSequentialID()会对工作产生影响。

在最后一期中，我不确定是否有一种简单的方法来量化碰撞风险。在一天结束时，UUID是128位值，这意味着可以从中获取 HUGE 数字空间。除了最苛刻的要求之外，您可能还可以。但是，与使用符合RFC的UUID源的情况相比，碰撞风险会增加。

[FWIW，你的uuid.js来自the node-uuid project（*咳嗽*说作者）。]