Base64Utilities.java

package net.thesocialos.server.utils;

public class Base64Utilities {
	
	private static final char[] base64Chars = new char[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
			'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
			'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1',
			'2', '3', '4', '5', '6', '7', '8', '9', '+', '/' };
	/**
	 * An array mapping legal base 64 characters [a-zA-Z0-9$_] to their associated 6-bit values. The source indicies
	 * will be given by 7-bit ASCII characters, thus the array size needs to be 128 (actually 123 would suffice for the
	 * given set of characters in use).
	 */
	private static final byte[] base64Values = new byte[128];
	
	/**
	 * Initialize the base 64 encoder values.
	 */
	static {
		// Invert the mapping (i -> base64Chars[i])
		for (int i = 0; i < base64Chars.length; i++) {
			base64Values[base64Chars[i]] = (byte) i;
		}
	}
	
	/**
	 * Decode a base64 string into a byte array.
	 * 
	 * @param data
	 *            the encoded data.
	 * @return a byte array.
	 * @see #fromBase64(String)
	 */
	public static byte[] fromBase64(String data) {
		if (data == null) { return null; }
		
		int len = data.length();
		assert (len % 4) == 0;
		
		if (len == 0) { return new byte[0]; }
		
		char[] chars = new char[len];
		data.getChars(0, len, chars, 0);
		
		int olen = 3 * (len / 4);
		if (chars[len - 2] == '=') {
			--olen;
		}
		if (chars[len - 1] == '=') {
			--olen;
		}
		
		byte[] bytes = new byte[olen];
		
		int iidx = 0;
		int oidx = 0;
		while (iidx < len) {
			int c0 = base64Values[chars[iidx++] & 0xff];
			int c1 = base64Values[chars[iidx++] & 0xff];
			int c2 = base64Values[chars[iidx++] & 0xff];
			int c3 = base64Values[chars[iidx++] & 0xff];
			int c24 = (c0 << 18) | (c1 << 12) | (c2 << 6) | c3;
			
			bytes[oidx++] = (byte) (c24 >> 16);
			if (oidx == olen) {
				break;
			}
			bytes[oidx++] = (byte) (c24 >> 8);
			if (oidx == olen) {
				break;
			}
			bytes[oidx++] = (byte) c24;
		}
		
		return bytes;
	}
	
	/**
	 * Converts a byte array into a base 64 encoded string. Null is encoded as null, and an empty array is encoded as an
	 * empty string. Otherwise, the byte data is read 3 bytes at a time, with bytes off the end of the array padded with
	 * zeros. Each 24-bit chunk is encoded as 4 characters from the sequence [A-Za-z0-9$_]. If one of the size-bit
	 * source positions consists entirely of padding zeros, an '=' character is used instead.
	 * 
	 * @param data
	 *            a byte array, which may be null or empty
	 * @return a String
	 */
	public static String toBase64(byte[] data) {
		if (data == null) { return null; }
		
		int len = data.length;
		if (len == 0) { return ""; }
		
		int olen = 4 * ((len + 2) / 3);
		char[] chars = new char[olen];
		
		int iidx = 0;
		int oidx = 0;
		int charsLeft = len;
		while (charsLeft > 0) {
			int b0 = data[iidx++] & 0xff;
			int b1 = (charsLeft > 1) ? data[iidx++] & 0xff : 0;
			int b2 = (charsLeft > 2) ? data[iidx++] & 0xff : 0;
			int b24 = (b0 << 16) | (b1 << 8) | b2;
			
			int c0 = (b24 >> 18) & 0x3f;
			int c1 = (b24 >> 12) & 0x3f;
			int c2 = (b24 >> 6) & 0x3f;
			int c3 = b24 & 0x3f;
			
			chars[oidx++] = base64Chars[c0];
			chars[oidx++] = base64Chars[c1];
			chars[oidx++] = (charsLeft > 1) ? base64Chars[c2] : '=';
			chars[oidx++] = (charsLeft > 2) ? base64Chars[c3] : '=';
			
			charsLeft -= 3;
		}
		
		return new String(chars);
	}
}