js Base64编码与解码

Base64编码与解码

1. 系统自带的
   js系统自带的base64二进制转为字符为atob(),字符转为二进制函数为btoa(),但是实际使用时在对一些base64加密的字符解密时出现错误，不符合我的要求。使用网上的一些用js写的base64函数的效果不错。

参考资料
js中的atob解决中文乱码 http://blog.csdn.net/abxn2002/article/details/50887594
js中的atob和btoa的使用 http://blog.csdn.net/hsany330/article/details/52575518

2. 原理

3. base64

   var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
   var base64DecodeChars = new Array(
       -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
       -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
       -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
       52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
       -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
       15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
       -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
       41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
   
   function base64encode(str) {
       var out, i, len;
       var c1, c2, c3;
   
       len = str.length;
       i = 0;
       out = "";
       while(i < len) {
       c1 = str.charCodeAt(i++) & 0xff;
       if(i == len)
       {
           out += base64EncodeChars.charAt(c1 >> 2);
           out += base64EncodeChars.charAt((c1 & 0x3) << 4);
           out += "==";
           break;
       }
       c2 = str.charCodeAt(i++);
       if(i == len)
       {
           out += base64EncodeChars.charAt(c1 >> 2);
           out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
           out += base64EncodeChars.charAt((c2 & 0xF) << 2);
           out += "=";
           break;
       }
       c3 = str.charCodeAt(i++);
       out += base64EncodeChars.charAt(c1 >> 2);
       out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
       out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));
       out += base64EncodeChars.charAt(c3 & 0x3F);
       }
       return out;
   }
   
   function base64decode(str) {
       var c1, c2, c3, c4;
       var i, len, out;
   
       len = str.length;
       i = 0;
       out = "";
       while(i < len) {
       /* c1 */
       do {
           c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
       } while(i < len && c1 == -1);
       if(c1 == -1)
           break;
   
       /* c2 */
       do {
           c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
       } while(i < len && c2 == -1);
       if(c2 == -1)
           break;
   
       out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
   
       /* c3 */
       do {
           c3 = str.charCodeAt(i++) & 0xff;
           if(c3 == 61)
           return out;
           c3 = base64DecodeChars[c3];
       } while(i < len && c3 == -1);
       if(c3 == -1)
           break;
   
       out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
   
       /* c4 */
       do {
           c4 = str.charCodeAt(i++) & 0xff;
           if(c4 == 61)
           return out;
           c4 = base64DecodeChars[c4];
       } while(i < len && c4 == -1);
       if(c4 == -1)
           break;
       out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
       }
       return out;
   }
   
   function utf16to8(str) {
       var out, i, len, c;
   
       out = "";
       len = str.length;
       for(i = 0; i < len; i++) {
       c = str.charCodeAt(i);
       if ((c >= 0x0001) && (c <= 0x007F)) {
           out += str.charAt(i);
       } else if (c > 0x07FF) {
           out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));
           out += String.fromCharCode(0x80 | ((c >>  6) & 0x3F));
           out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
       } else {
           out += String.fromCharCode(0xC0 | ((c >>  6) & 0x1F));
           out += String.fromCharCode(0x80 | ((c >>  0) & 0x3F));
       }
       }
       return out;
   }
   
   function utf8to16(str) {
       var out, i, len, c;
       var char2, char3;
   
       out = "";
       len = str.length;
       i = 0;
       while(i < len) {
       c = str.charCodeAt(i++);
       switch(c >> 4)
       { 
         case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
           // 0xxxxxxx
           out += str.charAt(i-1);
           break;
         case 12: case 13:
           // 110x xxxx   10xx xxxx
           char2 = str.charCodeAt(i++);
           out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
           break;
         case 14:
           // 1110 xxxx  10xx xxxx  10xx xxxx
           char2 = str.charCodeAt(i++);
           char3 = str.charCodeAt(i++);
           out += String.fromCharCode(((c & 0x0F) << 12) |
                          ((char2 & 0x3F) << 6) |
                          ((char3 & 0x3F) << 0));
           break;
       }
       }
   
       return out;
   }
   
   function CharToHex(str) {
       var out, i, len, c, h;
       out = "";
       len = str.length;
       i = 0;
       while(i < len) 
       {
           c = str.charCodeAt(i++);
           h = c.toString(16);
           if(h.length < 2)
               h = "0" + h;
           
           out += "\\x" + h + " ";
           if(i > 0 && i % 8 == 0)
               out += "\r\n";
       }
   
       return out;
   }
   
   function doEncode() {
       var src = document.getElementById('src').value;
       document.getElementById('dest').value = base64encode(utf16to8(src));
   }
   
   function doDecode() {
       var src = document.getElementById('src').value;
       var opts = document.getElementById('opt');
   
       if(opts.checked)
       {
           document.getElementById('dest').value = CharToHex(base64decode(src));
       }
       else
       {
           document.getElementById('dest').value = utf8to16(base64decode(src));
       }
   }    
   

参考资料
base64算法 http://www.cnblogs.com/ricksun/archive/2012/08/27/2658654.html
base64算法 http://files.cnblogs.com/files/mofish/base64.js
base64算法 http://www.cnblogs.com/pengchengzhong/p/6027663.html
base64原理 http://www.cnblogs.com/chengmo/archive/2014/05/18/3735917.html