base64.java

本文档讲解了OTA的概念

/**
 * Copyright (C) 2003-2005 Funambol
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package com.ultrapower.tools;

/**
 * @version $Id: Base64.java,v 1.3.4.2 2005/04/14 18:31:05 nichele Exp $
 *
 * Just repackaged into sync4j.framework.tools
 */
public class Base64 {
    private static final byte[] encodingTable = {
        (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',
        (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',
        (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U',
        (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',
        (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',
        (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',
        (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u',
        (byte)'v',
        (byte)'w', (byte)'x', (byte)'y', (byte)'z',
        (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6',
        (byte)'7', (byte)'8', (byte)'9',
        (byte)'+', (byte)'/'
    };

    /**
     * encode the input data producong a base 64 encoded byte array.
     *
     * @return a byte array containing the base 64 encoded data.
     */
    public static byte[] encode(
    byte[]	data) {
        byte[]	bytes;

        int modulus = data.length % 3;
        if (modulus == 0) {
            bytes = new byte[4 * data.length / 3];
        }
        else {
            bytes = new byte[4 * ((data.length / 3) + 1)];
        }

        int dataLength = (data.length - modulus);
        int a1, a2, a3;
        for (int i = 0, j = 0; i < dataLength; i += 3, j += 4) {
            a1 = data[i] & 0xff;
            a2 = data[i + 1] & 0xff;
            a3 = data[i + 2] & 0xff;

            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];
            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];
            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];
            bytes[j + 3] = encodingTable[a3 & 0x3f];
        }

                /*
                 * process the tail end.
                 */
        int	b1, b2, b3;
        int	d1, d2;

        switch (modulus) {
            case 0:		/* nothing left to do */
                break;
            case 1:
                d1 = data[data.length - 1] & 0xff;
                b1 = (d1 >>> 2) & 0x3f;
                b2 = (d1 << 4) & 0x3f;

                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = (byte)'=';
                bytes[bytes.length - 1] = (byte)'=';
                break;
            case 2:
                d1 = data[data.length - 2] & 0xff;
                d2 = data[data.length - 1] & 0xff;

                b1 = (d1 >>> 2) & 0x3f;
                b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
                b3 = (d2 << 2) & 0x3f;

                bytes[bytes.length - 4] = encodingTable[b1];
                bytes[bytes.length - 3] = encodingTable[b2];
                bytes[bytes.length - 2] = encodingTable[b3];
                bytes[bytes.length - 1] = (byte)'=';
                break;
        }

        return bytes;
    }

    /*
     * set up the decoding table.
     */
    private static final byte[] decodingTable;

    static {
        decodingTable = new byte[128];

        for (int i = 0; i < 128; i++) {
            decodingTable[i] = (byte) -1;
        }

        for (int i = 'A'; i <= 'Z'; i++) {
            decodingTable[i] = (byte)(i - 'A');
        }

        for (int i = 'a'; i <= 'z'; i++) {
            decodingTable[i] = (byte)(i - 'a' + 26);
        }

        for (int i = '0'; i <= '9'; i++) {
            decodingTable[i] = (byte)(i - '0' + 52);
        }

        decodingTable['+'] = 62;
        decodingTable['/'] = 63;
    }

    /**
     * decode the base 64 encoded input data.
     *
     * @return a byte array representing the decoded data.
     */
    public static byte[] decode(byte[]	data) {

        byte[]	bytes;
        byte	b1, b2, b3, b4;

        data = discardNonBase64Bytes(data);

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

        for (int i = 0, j = 0; i < data.length - 4; i += 4, j += 3) {
            b1 = decodingTable[data[i]];
            b2 = decodingTable[data[i + 1]];
            b3 = decodingTable[data[i + 2]];
            b4 = decodingTable[data[i + 3]];

            bytes[j] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte)((b3 << 6) | b4);
        }

        if (data[data.length - 2] == '=') {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];

            bytes[bytes.length - 1] = (byte)((b1 << 2) | (b2 >> 4));
        }
        else if (data[data.length - 1] == '=') {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];

            bytes[bytes.length - 2] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte)((b2 << 4) | (b3 >> 2));
        }
        else {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            b4 = decodingTable[data[data.length - 1]];

            bytes[bytes.length - 3] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte)((b3 << 6) | b4);
        }

        return bytes;
    }

    /**
     * decode the base 64 encoded String data.
     *
     * @return a byte array representing the decoded data.
     */
    public static byte[] decode(String	data) {
        byte[]	bytes;
        byte	b1, b2, b3, b4;

        data = discardNonBase64Chars(data);

        if (data.charAt(data.length() - 2) == '=') {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];
        }
        else if (data.charAt(data.length() - 1) == '=') {
            bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];
        }
        else {
            bytes = new byte[((data.length() / 4) * 3)];
        }

        for (int i = 0, j = 0; i < data.length() - 4; i += 4, j += 3) {
            b1 = decodingTable[data.charAt(i)];
            b2 = decodingTable[data.charAt(i + 1)];
            b3 = decodingTable[data.charAt(i + 2)];
            b4 = decodingTable[data.charAt(i + 3)];

            bytes[j] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte)((b3 << 6) | b4);
        }

        if (data.charAt(data.length() - 2) == '=') {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];

            bytes[bytes.length - 1] = (byte)((b1 << 2) | (b2 >> 4));
        }
        else if (data.charAt(data.length() - 1) == '=') {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];

            bytes[bytes.length - 2] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte)((b2 << 4) | (b3 >> 2));
        }
        else {
            b1 = decodingTable[data.charAt(data.length() - 4)];
            b2 = decodingTable[data.charAt(data.length() - 3)];
            b3 = decodingTable[data.charAt(data.length() - 2)];
            b4 = decodingTable[data.charAt(data.length() - 1)];

            bytes[bytes.length - 3] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte)((b3 << 6) | b4);
        }

        return bytes;
    }

    // --------------------------------------------------------- Private Methods

    /**
     * Discards any characters outside of the base64 alphabet (see page 25 of RFC 2045)
     * "Any characters outside of the base64 alphabet are to be ignored in base64
     * encoded data."
     *
     * @param data the base64 encoded data
     * @return the data, less non-base64 characters.
     */
    private static byte[] discardNonBase64Bytes(byte[] data) {
        byte temp[] = new byte[data.length];
        int bytesCopied = 0;

        for (int i = 0; i < data.length; i++) {
            if (isValidBase64Byte(data[i])) {
                temp[bytesCopied++] = data[i];
            }
        }

        byte newData[] = new byte[bytesCopied];

        System.arraycopy(temp, 0, newData, 0, bytesCopied);

        return newData;
    }

    /**
     * Discards any characters outside of the base64 alphabet (see page 25 of RFC 2045)
     * "Any characters outside of the base64 alphabet are to be ignored in base64
     * encoded data."
     *
     * @param data the base64 encoded data
     * @return the data, less non-base64 characters.
     */
    private static String discardNonBase64Chars(String data) {

        StringBuffer sb = new StringBuffer();

        int length = data.length();

        for (int i = 0; i < length; i++) {
            if (isValidBase64Byte((byte)(data.charAt(i)))) {
                sb.append(data.charAt(i));
            }
        }

        return sb.toString();
    }

    /**
     * Checks is the given byte is in base64 alphabet
     * @param b the byte to check
     * @return boolean true if the byte is in base64 alphabet
     */
    private static boolean isValidBase64Byte(byte b) {
        if (b == '=') {
            return true;
        } else if (b < 0 || b >= 128) {
            return false;
        } else if (decodingTable[b] == -1) {
            return false;
        }
        return true;
    }

}