base64.java

一个非常好的ssh客户端实现

/******************************************************************************
 *
 * Copyright (c) 1999-2003 AppGate Network Security AB. All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code as
 * defined in and that are subject to the MindTerm Public Source License,
 * Version 2.0, (the 'License'). You may not use this file except in compliance
 * with the License.
 * 
 * You should have received a copy of the MindTerm Public Source License
 * along with this software; see the file LICENSE.  If not, write to
 * AppGate Network Security AB, Otterhallegatan 2, SE-41118 Goteborg, SWEDEN
 *
 *****************************************************************************/

package com.mindbright.util;

public final class Base64 {

    private final static int[] fromBase64 = {
	-1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, -1, -1, -1, -1, -1,
	-1, -1, -1, 62, -1, -1, -1, 63,
	52, 53, 54, 55, 56, 57, 58, 59,
	60, 61, -1, -1, -1, -1, -1, -1,
	-1,  0,  1,  2,  3,  4,  5,  6,
	7,  8,  9, 10, 11, 12, 13, 14,
	15, 16, 17, 18, 19, 20, 21, 22,
	23, 24, 25, -1, -1, -1, -1, -1,
	-1, 26, 27, 28, 29, 30, 31, 32,
	33, 34, 35, 36, 37, 38, 39, 40,
	41, 42, 43, 44, 45, 46, 47, 48,
	49, 50, 51, -1, -1, -1, -1, -1
    };

    private final static byte[] toBase64 = {
	// 'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
	   65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80,
	// 'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',
	   81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 97, 98, 99,100,101,102,
	// 'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',
	   103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,
	// 'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/'
	   119,120,121,122, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 43, 47, (byte)'='
    };

    private final static int PAD_CHAR = 64;

    public static byte[] encode(byte[] data) {
	return encode(data, 0, data.length);
    }

    public static byte[] encode(byte[] data, int offset, int length) {
	byte[] encoded;
	int x1, x2, x3, x4;
	int i, j, r, n;

	r       = length % 3;
	n       = offset + (length - r);
	encoded = new byte[((length / 3) * 4) + (r != 0 ? 4 : 0)];

	for(i = offset, j = 0; i < n; i += 3, j += 4) {
	    x1 = (data[i] & 0xfc) >> 2;
	    x2 = (((data[i    ] & 0x03) << 4) | ((data[i + 1] & 0xf0) >> 4));
	    x3 = (((data[i + 1] & 0x0f) << 2) | ((data[i + 2] & 0xc0) >> 6));
	    x4 = (data[i + 2] & 0x3f);
	    encoded[j    ] = toBase64[x1];
	    encoded[j + 1] = toBase64[x2];
	    encoded[j + 2] = toBase64[x3];
	    encoded[j + 3] = toBase64[x4];
	}

	if(r != 0) {
	    x1 = (data[i] & 0xfc) >> 2;
	    x2 = (data[i] & 0x03) << 4;
	    x3 = PAD_CHAR;
	    x4 = PAD_CHAR;
	    if(r == 2) {
		x2 |= ((data[i + 1] & 0xf0) >> 4);
		x3 = (data[i + 1] & 0x0f) << 2;
	    }
	    encoded[j++] = toBase64[x1];
	    encoded[j++] = toBase64[x2];
	    encoded[j++] = toBase64[x3];
	    encoded[j++] = toBase64[x4];
	}

	return encoded;
    }

    public static byte[] decode(byte[] data) {
	return decode(data, 0, data.length);
    }

    public static byte[] decode(byte[] encoded, int offset, int length) {
	byte[] data;
	int i, j, n, v = 0, c, bits = 0;

	n    = offset + length;
	data = new byte[(length * 3) / 4];

	for(i = offset, j = 0; i < n; i++) {
	    c = fromBase64[encoded[i]];
	    if(c < 0) {
		if(encoded[i] == toBase64[PAD_CHAR])
		    break;
		continue;
	    }
	    v = (v << 6) | c;
	    bits += 6;
	    if(bits >= 8) {
		bits -= 8;
		data[j++] = (byte) ((v >> bits) & 0xff);
	    }
	}

	if(data.length > j) {
	    byte[] tmp = new byte[j];
	    System.arraycopy(data, 0, tmp, 0, j);
	    data = tmp;
	}

	return data;
    }

}