stringencoders - base64.js

base64.js

/*
 * Copyright (c) 2010 Nick Galbreath
 * http://code.google.com/p/stringencoders/source/browse/#svn/trunk/javascript
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
*/

/* base64 encode/decode compatible with window.btoa/atob
 *
 * window.atob/btoa is a Firefox extension to convert binary data (the "b")
 * to base64 (ascii, the "a").
 *
 * It is also found in Safari and Chrome.  It is not available in IE.
 *
 * if (!window.btoa) window.btoa = base64.encode
 * if (!window.atob) window.atob = base64.decode
 *
 * The original spec's for atob/btoa are a bit lacking
 * https://developer.mozilla.org/en/DOM/window.atob
 * https://developer.mozilla.org/en/DOM/window.btoa
 *
 * window.btoa and base64.encode takes a string where charCodeAt is [0,255]
 * If any character is not [0,255], then an exception is thrown.
 *
 * window.atob and base64.decode take a base64-encoded string
 * If the input length is not a multiple of 4, or contains invalid characters
 *   then an exception is thrown.
 */
base64 = {};
base64.PADCHAR = '=';
base64.ALPHA = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
base64.getbyte64 = function(s,i) {
    // This is oddly fast, except on Chrome/V8.
    //  Minimal or no improvement in performance by using a
    //   object with properties mapping chars to value (eg. 'A': 0)
    var idx = base64.ALPHA.indexOf(s.charAt(i));
    if (idx == -1) {
        throw "Cannot decode base64";
    }
    return idx;
}

base64.decode = function(s) {
    // convert to string
    s = "" + s;
    var getbyte64 = base64.getbyte64;
    var pads, i, b10;
    var imax = s.length
    if (imax == 0) {
        return s;
    }

    if (imax % 4 != 0) {
        throw "Cannot decode base64";
    }

    pads = 0
    if (s.charAt(imax -1) == base64.PADCHAR) {
        pads = 1;
        if (s.charAt(imax -2) == base64.PADCHAR) {
            pads = 2;
        }
        // either way, we want to ignore this last block
        imax -= 4;
    }

    var x = [];
    for (i = 0; i < imax; i += 4) {
        b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12) |
            (getbyte64(s,i+2) << 6) | getbyte64(s,i+3);
        x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff, b10 & 0xff));
    }

    switch (pads) {
    case 1:
        b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12) | (getbyte64(s,i+2) << 6)
        x.push(String.fromCharCode(b10 >> 16, (b10 >> 8) & 0xff));
        break;
    case 2:
        b10 = (getbyte64(s,i) << 18) | (getbyte64(s,i+1) << 12);
        x.push(String.fromCharCode(b10 >> 16));
        break;
    }
    return x.join('');
}

base64.getbyte = function(s,i) {
    var x = s.charCodeAt(i);
    if (x > 255) {
        throw "INVALID_CHARACTER_ERR: DOM Exception 5";
    }
    return x;
}


base64.encode = function(s) {
    if (arguments.length != 1) {
        throw "SyntaxError: Not enough arguments";
    }
    var padchar = base64.PADCHAR;
    var alpha   = base64.ALPHA;
    var getbyte = base64.getbyte;

    var i, b10;
    var x = [];

    // convert to string
    s = "" + s;

    var imax = s.length - s.length % 3;

    if (s.length == 0) {
        return s;
    }
    for (i = 0; i < imax; i += 3) {
        b10 = (getbyte(s,i) << 16) | (getbyte(s,i+1) << 8) | getbyte(s,i+2);
        x.push(alpha.charAt(b10 >> 18));
        x.push(alpha.charAt((b10 >> 12) & 0x3F));
        x.push(alpha.charAt((b10 >> 6) & 0x3f));
        x.push(alpha.charAt(b10 & 0x3f));
    }
    switch (s.length - imax) {
    case 1:
        b10 = getbyte(s,i) << 16;
        x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) +
               padchar + padchar);
        break;
    case 2:
        b10 = (getbyte(s,i) << 16) | (getbyte(s,i+1) << 8);
        x.push(alpha.charAt(b10 >> 18) + alpha.charAt((b10 >> 12) & 0x3F) +
               alpha.charAt((b10 >> 6) & 0x3f) + padchar);
        break;
    }
    return x.join('');
}