Base64.java

/*
 * ====================
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright 2008-2009 Sun Microsystems, Inc. All rights reserved.
 *
 * The contents of this file are subject to the terms of the Common Development
 * and Distribution License("CDDL") (the "License").  You may not use this file
 * except in compliance with the License.
 *
 * You can obtain a copy of the License at
 * http://opensource.org/licenses/cddl1.php
 * See the License for the specific language governing permissions and limitations
 * under the License.
 *
 * When distributing the Covered Code, include this CDDL Header Notice in each file
 * and include the License file at http://opensource.org/licenses/cddl1.php.
 * If applicable, add the following below this CDDL Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
 * "Portions Copyrighted [year] [name of copyright owner]"
 * ====================
 */
package org.identityconnectors.common;

/**
 * Utility package for base64 encoding and decoding.
 *
 * @author Will Droste
 * @since 1.0
 */
public final class Base64 {

    /**
     * Never allow this to be instantiated.
     */
    private Base64() {
    }

    /**
     * Returns a String of base64-encoded characters to represent the specified
     * data array.
     *
     * @param data
     *            The array of bytes to encode.
     * @return A String containing base64-encoded characters.
     */
    static public String encode(byte[] data) {

        if (data == null) {
            return null;
        }

        char[] out = new char[((data.length + 2) / 3) * 4];

        //
        // 3 bytes encode to 4 chars. Output is always an even
        // multiple of 4 characters.
        //
        for (int i = 0, index = 0; i < data.length; i += 3, index += 4) {
            boolean quad = false;
            boolean trip = false;

            int val = (0xFF & (int) data[i]);
            val <<= 8;
            if ((i + 1) < data.length) {
                val |= (0xFF & (int) data[i + 1]);
                trip = true;
            }
            val <<= 8;
            if ((i + 2) < data.length) {
                val |= (0xFF & (int) data[i + 2]);
                quad = true;
            }
            out[index + 3] = alphabet[(quad ? (val & 0x3F) : 64)];
            val >>= 6;
            out[index + 2] = alphabet[(trip ? (val & 0x3F) : 64)];
            val >>= 6;
            out[index + 1] = alphabet[val & 0x3F];
            val >>= 6;
            out[index + 0] = alphabet[val & 0x3F];
        }
        return new String(out);
    }

    /**
     * Decodes a specified base64-encoded String and returns the resulting
     * bytes.
     *
     * @param encdata
     *            A String containing base64-encoded characters.
     * @return The base64-decoded array of bytes.
     */
    static public byte[] decode(String encdata) {

        if (encdata == null) {
            return null;
        }

        // convert to a char[]
        char[] data = encdata.toCharArray();

        // An empty string is a valid base64 encoded string.
        if (data.length == 0) {
            return new byte[0];
        }

        // check that length is a multiple of 4
        if (data.length % 4 != 0) {
            throw new RuntimeException("Data is not Base64 encoded.");
        }

        int len = ((data.length + 3) / 4) * 3;
        if (data[data.length - 1] == '=') {
            --len;
        }
        if (data[data.length - 2] == '=') {
            --len;
        }
        byte[] out = new byte[len];

        int shift = 0; // # of excess bits stored in accum
        int accum = 0; // excess bits
        int index = 0;

        for (int ix = 0; ix < data.length; ix++) {
            int value = codes[data[ix] & 0xFF]; // ignore high byte of char
            if (value >= 0) { // skip over non-code
                accum <<= 6; // bits shift up by 6 each time thru
                shift += 6; // loop, with new bits being put in
                accum |= value; // at the bottom.
                if (shift >= 8) { // whenever there are 8 or more shifted in,
                    shift -= 8; // write them out (from the top, leaving any
                    out[index++] = // excess at the bottom for next iteration.
                            (byte) ((accum >> shift) & 0xff);
                }
            } else {
                if (data[ix] != '=') {
                    throw new RuntimeException("Data is not Base64 encoded.");
                }
            }
        }
        if (index != out.length) {
            throw new RuntimeException("Data length mismatch.");
        }

        return out;
    }

    //
    // code characters for values 0..63
    //
    static private char[] alphabet =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=".toCharArray();

    //
    // lookup table for converting base64 characters to value in range 0..63
    //
    static private byte[] codes = new byte[256];

    static {
        for (int i = 0; i < 256; i++) {
            codes[i] = -1;
        }
        for (int i = 'A'; i <= 'Z'; i++) {
            codes[i] = (byte) (i - 'A');
        }
        for (int i = 'a'; i <= 'z'; i++) {
            codes[i] = (byte) (26 + i - 'a');
        }
        for (int i = '0'; i <= '9'; i++) {
            codes[i] = (byte) (52 + i - '0');
        }
        codes['+'] = 62;
        codes['/'] = 63;
    }
}