Base64.java

package org.objectweb.jonas.security.realm.lib;

public class Base64 {

    private static char[] alphabet =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
        .toCharArray();

    private static 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;
    }



    public static 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;
    }

    public static byte[] decode(char[] data) {
        // as our input could contain non-BASE64 data (newlines,
        // whitespace of any sort, whatever) 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;
        for (int ix = 0; ix < data.length; ix++) {
            if ((data[ix] > 255) || codes[ data[ix] ] < 0) {
                --tempLen;  // ignore non-valid chars and padding
            }
        }
        // calculate required length:
        //  -- 3 bytes for every 4 valid base64 chars
        //  -- plus 2 bytes if there are 3 extra base64 chars,
        //     or plus 1 byte if there are 2 extra.

        int len = (tempLen / 4) * 3;
        if ((tempLen % 4) == 3) {
            len += 2;
        }
        if ((tempLen % 4) == 2) {
            len += 1;
        }

        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 = (data[ix] > 255) ? -1 : codes[ data[ix] ];

            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;
    }



}

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