Base64以及在URL中的应用

https://en.wikipedia.org/wiki/Base64 https://github.com/dankogai/js-base64 Base64.encodeURI(‘小飼弾’); // 5bCP6aO85by- ‘小飼弾’.toBase64(true); // 5bCP6aO85by- 在URL中的应用 Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java持久化系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。此时，采用Base64编码不仅比较简短，同时也具有不可读性，即所编码的数据不会被人用肉眼所直接看到。 然而，标准的Base64并不适合直接放在URL里传输，因为URL编码器会把标准Base64中的/和+字符变为形如%XX的形式，而这些%号在存入数据库时还需要再进行转换，因为ANSI SQL中已将%号用作通配符。 为解决此问题，可采用一种用于URL的改进Base64编码，它不在末尾填充=号，并将标准Base64中的+和/分别改成了-和_，这样就免去了在URL编解码和数据库存储时所要作的转换，避免了编码信息长度在此过程中的增加，并统一了数据库、表单等处对象标识符的格式。 另有一种用于正则表达式的改进Base64变种，它将+和/改成了!和-，因为+，*以及前面在IRCu中用到的[和]在正则表达式中都可能具有特殊含义。 此外还有一些变种，它们将+/改为_-或._（用作编程语言中的标识符名称）或.-（用于XML中的Nmtoken）甚至_:（用于XML中的Name）。

/*
 *  base64.js
 *
 *  Licensed under the BSD 3-Clause License.
 *    http://opensource.org/licenses/BSD-3-Clause
 *
 *  References:
 *    http://en.wikipedia.org/wiki/Base64
 */
;(function (global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined'
        ? module.exports = factory(global)
        : typeof define === 'function' && define.amd
        ? define(factory) : factory(global)
}((
    typeof self !== 'undefined' ? self
        : typeof window !== 'undefined' ? window
        : typeof global !== 'undefined' ? global
: this
), function(global) {
    'use strict';
    // existing version for noConflict()
    var _Base64 = global.Base64;
    var version = "2.4.5";
    // if node.js, we use Buffer
    var buffer;
    if (typeof module !== 'undefined' && module.exports) {
        try {
            buffer = require('buffer').Buffer;
        } catch (err) {}
    }
    // constants
    var b64chars
        = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    var b64tab = function(bin) {
        var t = {};
        for (var i = 0, l = bin.length; i < l; i++) t[bin.charAt(i)] = i;
        return t;
    }(b64chars);
    var fromCharCode = String.fromCharCode;
    // encoder stuff
    var cb_utob = function(c) {
        if (c.length < 2) {
            var cc = c.charCodeAt(0);
            return cc < 0x80 ? c
                : cc < 0x800 ? (fromCharCode(0xc0  (cc >>> 6))
                                + fromCharCode(0x80  (cc & 0x3f)))
                : (fromCharCode(0xe0  ((cc >>> 12) & 0x0f))
                   + fromCharCode(0x80  ((cc >>>  6) & 0x3f))
                   + fromCharCode(0x80  ( cc         & 0x3f)));
        } else {
            var cc = 0x10000
                + (c.charCodeAt(0) - 0xD800) * 0x400
                + (c.charCodeAt(1) - 0xDC00);
            return (fromCharCode(0xf0  ((cc >>> 18) & 0x07))
                    + fromCharCode(0x80  ((cc >>> 12) & 0x3f))
                    + fromCharCode(0x80  ((cc >>>  6) & 0x3f))
                    + fromCharCode(0x80  ( cc         & 0x3f)));
        }
    };
    var re_utob = /[\uD800-\uDBFF][\uDC00-\uDFFFF][^\x00-\x7F]/g;
    var utob = function(u) {
        return u.replace(re_utob, cb_utob);
    };
    var cb_encode = function(ccc) {
        var padlen = [0, 2, 1][ccc.length % 3],
        ord = ccc.charCodeAt(0) << 16
             ((ccc.length > 1 ? ccc.charCodeAt(1) : 0) << 8)
             ((ccc.length > 2 ? ccc.charCodeAt(2) : 0)),
        chars = [
            b64chars.charAt( ord >>> 18),
            b64chars.charAt((ord >>> 12) & 63),
            padlen >= 2 ? '=' : b64chars.charAt((ord >>> 6) & 63),
            padlen >= 1 ? '=' : b64chars.charAt(ord & 63)
        ];
        return chars.join('');
    };
    var btoa = global.btoa ? function(b) {
        return global.btoa(b);
    } : function(b) {
        return b.replace(/[\s\S]{1,3}/g, cb_encode);
    };
    var _encode = buffer ?
        buffer.from && Uint8Array && buffer.from !== Uint8Array.from
        ? function (u) {
            return (u.constructor === buffer.constructor ? u : buffer.from(u))
                .toString('base64')
        }
        :  function (u) {
            return (u.constructor === buffer.constructor ? u : new  buffer(u))
                .toString('base64')
        }
        : function (u) { return btoa(utob(u)) }
    ;
    var encode = function(u, urisafe) {
        return !urisafe
            ? _encode(String(u))
            : _encode(String(u)).replace(/[+\/]/g, function(m0) {
                return m0 == '+' ? '-' : '_';
            }).replace(/=/g, '');
    };
    var encodeURI = function(u) { return encode(u, true) };
    // decoder stuff
    var re_btou = new RegExp([
        '[\xC0-\xDF][\x80-\xBF]',
        '[\xE0-\xEF][\x80-\xBF]{2}',
        '[\xF0-\xF7][\x80-\xBF]{3}'
    ].join(''), 'g');
    var cb_btou = function(cccc) {
        switch(cccc.length) {
        case 4:
            var cp = ((0x07 & cccc.charCodeAt(0)) << 18)
                    ((0x3f & cccc.charCodeAt(1)) << 12)
                    ((0x3f & cccc.charCodeAt(2)) <<  6)
                     (0x3f & cccc.charCodeAt(3)),
            offset = cp - 0x10000;
            return (fromCharCode((offset  >>> 10) + 0xD800)
                    + fromCharCode((offset & 0x3FF) + 0xDC00));
        case 3:
            return fromCharCode(
                ((0x0f & cccc.charCodeAt(0)) << 12)
                     ((0x3f & cccc.charCodeAt(1)) << 6)
                      (0x3f & cccc.charCodeAt(2))
            );
        default:
            return  fromCharCode(
                ((0x1f & cccc.charCodeAt(0)) << 6)
                      (0x3f & cccc.charCodeAt(1))
            );
        }
    };
    var btou = function(b) {
        return b.replace(re_btou, cb_btou);
    };
    var cb_decode = function(cccc) {
        var len = cccc.length,
        padlen = len % 4,
        n = (len > 0 ? b64tab[cccc.charAt(0)] << 18 : 0)
             (len > 1 ? b64tab[cccc.charAt(1)] << 12 : 0)
             (len > 2 ? b64tab[cccc.charAt(2)] <<  6 : 0)
             (len > 3 ? b64tab[cccc.charAt(3)]       : 0),
        chars = [
            fromCharCode( n >>> 16),
            fromCharCode((n >>>  8) & 0xff),
            fromCharCode( n         & 0xff)
        ];
        chars.length -= [0, 0, 2, 1][padlen];
        return chars.join('');
    };
    var atob = global.atob ? function(a) {
        return global.atob(a);
    } : function(a){
        return a.replace(/[\s\S]{1,4}/g, cb_decode);
    };
    var _decode = buffer ?
        buffer.from && Uint8Array && buffer.from !== Uint8Array.from
        ? function(a) {
            return (a.constructor === buffer.constructor
                    ? a : buffer.from(a, 'base64')).toString();
        }
        : function(a) {
            return (a.constructor === buffer.constructor
                    ? a : new buffer(a, 'base64')).toString();
        }
        : function(a) { return btou(atob(a)) };
    var decode = function(a){
        return _decode(
            String(a).replace(/[-_]/g, function(m0) { return m0 == '-' ? '+' : '/' })
                .replace(/[^A-Za-z0-9\+\/]/g, '')
        );
    };
    var noConflict = function() {
        var Base64 = global.Base64;
        global.Base64 = _Base64;
        return Base64;
    };
    // export Base64
    global.Base64 = {
        VERSION: version,
        atob: atob,
        btoa: btoa,
        fromBase64: decode,
        toBase64: encode,
        utob: utob,
        encode: encode,
        encodeURI: encodeURI,
        btou: btou,
        decode: decode,
        noConflict: noConflict
    };
    // if ES5 is available, make Base64.extendString() available
    if (typeof Object.defineProperty === 'function') {
        var noEnum = function(v){
            return {value:v,enumerable:false,writable:true,configurable:true};
        };
        global.Base64.extendString = function () {
            Object.defineProperty(
                String.prototype, 'fromBase64', noEnum(function () {
                    return decode(this)
                }));
            Object.defineProperty(
                String.prototype, 'toBase64', noEnum(function (urisafe) {
                    return encode(this, urisafe)
                }));
            Object.defineProperty(
                String.prototype, 'toBase64URI', noEnum(function () {
                    return encode(this, true)
                }));
        };
    }
    //
    // export Base64 to the namespace
    //
    if (global['Meteor']) { // Meteor.js
        Base64 = global.Base64;
    }
    // module.exports and AMD are mutually exclusive.
    // module.exports has precedence.
    if (typeof module !== 'undefined' && module.exports) {
        module.exports.Base64 = global.Base64;
    }
    else if (typeof define === 'function' && define.amd) {
        // AMD. Register as an anonymous module.
        define([], function(){ return global.Base64 });
    }
    // that's it!
    return {Base64: global.Base64}
}));