base64.js

/*
 * Copyright (c) 2012 Miles Shang <mail@mshang.ca>
 * 
 * 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.
 */

/*
 * Usage:
 * Set your settings:
 *   base64.settings.char62 = "-";
 *   base64.settings.char63 = "_";
 *   etc.
 * 
 * Then:
 * base64.encode(str) takes a string and returns the base64 encoding of it.
 * base64.decode(str) does the reverse.
 */

/* TODO:
 * Add a "padding_mandatory" flag to check for bad padding in the decoder.
 * Add test cases that throw errors.
 */

var base64 = new Object();

base64.settings = { // defaults
	"char62"        : "+",
	"char63"        : "/",
	"pad"           : "=",
	"ascii"         : false
};

/* 
 * Settings:
 * If "pad" is not null or undefined, then it will be used for encoding.
 *
 * If "ascii" is set to true, then the encoder
 * will assume that plaintext is in 8-bit chars (the standard). 
 * In this case, for every 3 chars in plaintext, you get 4 chars of base64.
 * Any non-8-bit chars will cause an error.
 * Otherwise, assume that all plaintext can be in the full range
 * of Javascript chars, i.e. 16 bits. Get 8 chars of base64 for 3 chars
 * of plaintext. Any possible JS string can be encoded.
 */

base64.encode = function (str) {
	this.char_set = 
		"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
		+ this.settings.char62 + this.settings.char63;
	
	var output = ""; // final output
	var buf = ""; // binary buffer
	for (var i = 0; i < str.length; ++i) {
		var c_num = str.charCodeAt(i);
		if (this.settings.ascii)
			if (c_num >= 256)
				throw "Not an 8-bit char.";
		var c_bin = c_num.toString(2);
		while (c_bin.length < (this.settings.ascii ? 8 : 16))
			c_bin = "0" + c_bin;
		buf += c_bin;
		
		while (buf.length >= 6) {
			var sextet = buf.slice(0, 6);
			buf = buf.slice(6);
			output += this.char_set.charAt(parseInt(sextet, 2));
		}
	}
	
	if (buf) { // not empty
		while (buf.length < 6) buf += "0";
		output += this.char_set.charAt(parseInt(buf, 2));
	}
	
	if (this.settings.pad)
		while (output.length % (this.settings.ascii ? 4 : 8) != 0)
			output += this.settings.pad;
	
	return output;
}

base64.decode = function (str) {
	this.char_set = 
		"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
		+ this.settings.char62 + this.settings.char63;
	
	var output = ""; // final output
	var buf = ""; // binary buffer
	var bits = (this.settings.ascii ? 8 : 16);
	for (var i = 0; i < str.length; ++i) {
		if (str[i] == this.settings.pad) break;
		var c_num = this.char_set.indexOf(str.charAt(i));
		if (c_num == -1) throw "Not base64.";
		var c_bin = c_num.toString(2);
		while (c_bin.length < 6) c_bin = "0" + c_bin;
		buf += c_bin;
		
		while (buf.length >= bits) {
			var octet = buf.slice(0, bits);
			buf = buf.slice(bits);
			output += String.fromCharCode(parseInt(octet, 2));
		}
	}
	return output;
}