base64binary.js

/*
 Copyright (c) 2011, Daniel Guerrero
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 * Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above copyright
 notice, this list of conditions and the following disclaimer in the
 documentation and/or other materials provided with the distribution.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL DANIEL GUERRERO BE LIABLE FOR ANY
 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * Uses the new array typed in javascript to binary base64 encode/decode
 * at the moment just decodes a binary base64 encoded
 * into either an ArrayBuffer (decodeArrayBuffer)
 * or into an Uint8Array (decode)
 *
 * References:
 * https://developer.mozilla.org/en/JavaScript_typed_arrays/ArrayBuffer
 * https://developer.mozilla.org/en/JavaScript_typed_arrays/Uint8Array
 */
(function (exports) {
	//NOTE! we use '-' and not '+'
	//I did it so we can put '-' delimited strings
	var encodings = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-/=';

	Base64Binary = {

		/* will return a  Uint8Array type */
		decodeArrayBuffer: function (input) {
			var bytes = (input.length / 4) * 3;
			var ab = new ArrayBuffer(bytes);
			this.decode(input, ab);

			return ab;
		},

		decode: function (input, arrayBuffer) {
			//get last chars to see if are valid
			var lkey1 = encodings.indexOf(input.charAt(input.length - 1));
			var lkey2 = encodings.indexOf(input.charAt(input.length - 2));

			var bytes = (input.length / 4) * 3;
			if (lkey1 == 64) bytes--; //padding chars, so skip
			if (lkey2 == 64) bytes--; //padding chars, so skip

			var chr1, chr2, chr3;
			var enc1, enc2, enc3, enc4;
			var i = 0;
			var j = 0;

			var uarray = new Uint8Array(bytes);
			input = input.replace(/[^A-Za-z0-9\-\/\=]/g, "");

			for (i = 0; i < bytes; i += 3) {
				//get the 3 octects in 4 ascii chars
				enc1 = encodings.indexOf(input.charAt(j++));
				enc2 = encodings.indexOf(input.charAt(j++));
				enc3 = encodings.indexOf(input.charAt(j++));
				enc4 = encodings.indexOf(input.charAt(j++));

				chr1 = (enc1 << 2) | (enc2 >> 4);
				chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
				chr3 = ((enc3 & 3) << 6) | enc4;

				uarray[i] = chr1;
				if (enc3 != 64) uarray[i + 1] = chr2;
				if (enc4 != 64) uarray[i + 2] = chr3;
			}

			return uarray;
		},


		// Converts an ArrayBuffer directly to base64, without any intermediate 'convert to string then
		// use window.btoa' step. According to my tests, this appears to be a faster approach:
		// http://jsperf.com/encoding-xhr-image-data/5
		encode: function (arrayBuffer) {
			var base64 = ''

			var bytes = new Uint8Array(arrayBuffer)
			var byteLength = bytes.byteLength
			var byteRemainder = byteLength % 3
			var mainLength = byteLength - byteRemainder

			var a, b, c, d;
			var chunk;

			// Main loop deals with bytes in chunks of 3
			for (var i = 0; i < mainLength; i = i + 3) {
				// Combine the three bytes into a single integer
				chunk = (bytes[i] << 16) | (bytes[i + 1] << 8) | bytes[i + 2]

				// Use bitmasks to extract 6-bit segments from the triplet
				a = (chunk & 16515072) >> 18 // 16515072 = (2^6 - 1) << 18
				b = (chunk & 258048) >> 12 // 258048   = (2^6 - 1) << 12
				c = (chunk & 4032) >> 6 // 4032     = (2^6 - 1) << 6
				d = chunk & 63               // 63       = 2^6 - 1

				// Convert the raw binary segments to the appropriate ASCII encoding
				base64 += encodings[a] + encodings[b] + encodings[c] + encodings[d]
			}

			// Deal with the remaining bytes and padding
			if (byteRemainder == 1) {
				chunk = bytes[mainLength]

				a = (chunk & 252) >> 2 // 252 = (2^6 - 1) << 2

				// Set the 4 least significant bits to zero
				b = (chunk & 3) << 4 // 3   = 2^2 - 1

				base64 += encodings[a] + encodings[b] + '=='
			} else if (byteRemainder == 2) {
				chunk = (bytes[mainLength] << 8) | bytes[mainLength + 1]

				a = (chunk & 64512) >> 10 // 64512 = (2^6 - 1) << 10
				b = (chunk & 1008) >> 4 // 1008  = (2^6 - 1) << 4

				// Set the 2 least significant bits to zero
				c = (chunk & 15) << 2 // 15    = 2^4 - 1

				base64 += encodings[a] + encodings[b] + encodings[c] + '='
			}

			return base64
		}
	}

	exports.base64 = Base64Binary;
})(typeof exports === 'undefined' ? this[''] = {} : exports);