idxIRRBase64.java

package jeffaschenk.commons.frameworks.cnxidx.utility.ldap;

/**
 * Provides encoding of raw bytes to base64-encoded characters, and
 * decoding of base64 characters to raw bytes.
 * <p/>
 * Permission to remove original Gnu Public License granted by original author,
 * Kevin Kelly, on June 13, 2001.
 *
 * @author jeff.schenk
 * @version 1.2
 * Developed 2001
 */

public class idxIRRBase64 {

    /**
     * returns an array of base64-encoded characters to represent the
     * passed data array.
     *
     * @param data the array of bytes to encode
     * @return char[] base64-coded character array.
     */
    static public char[] encode(byte[] data) {
        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 out;
    }

    /**
     * Decodes a BASE-64 encoded stream to recover the original
     * data. White space before and after will be trimmed away,
     * but no other manipulation of the input will be performed.
     * <p/>
     * As of version 1.2 this method will properly handle input
     * containing junk characters (newlines and the like) rather
     * than throwing an error. It does this by pre-parsing the
     * input and generating from that a count of VALID input
     * characters.
     *
     * @param data the array of bytes to decode.
     * @return byte[] Decoded byte array.
     * @throws Error due to miscalculation.
     */
    static public byte[] decode(char[] data)
            throws Error {
        // as our input could contain non-BASE64 data (newlines
        // and other silly human-prettifications) we must first
        // adjust our count of USABLE data so that...
        // (a) we don't misallocate the output array, and (b)
        // think that we miscalculated our data length just
        // because of extraneous throw-away junk
        int tempLen = data.length;        // start with everything we've got
        for (int ix = 0; ix < data.length; ix++) {
            int value = codes[data[ix] & 0xFF]; // ignore
            if ((value < 0) && (data[ix] != 61)) // 61 is the '=' symbol (a padding null byte)
            {
                --tempLen;        // aha, found some useless stuff to ignore!
            }
        }
        int len = ((tempLen + 3) / 4) * 3;        // calculate length based on what remains!
        if (tempLen > 0 && data[tempLen - 1] == '=') --len;
        if (tempLen > 1 && data[tempLen - 2] == '=') --len;
        byte[] out = new byte[len];


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

        // we now go through the entire array (NOT using the 'tempLen' value)
        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);
                }
            }
            // we will also have skipped processing a padding null byte ('=') here;
            // these are used ONLY for padding to an even length and do not legally
            // occur as encoded data. for this reason we can ignore the fact that
            // no index++ operation occurs in that special case: the out[] array is
            // initialized to all-zero bytes to start with and that works to our
            // advantage in this combination.
        }

        // if there is STILL something wrong we just have to throw up now!
        if (index != out.length) {
            throw new Error("Miscalculated data length (wrote " + index + " instead of " + out.length + ")");
        }

        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;
    }

} ///:~ End of idxIRRBase64 Class.