PC World Komputer 1995 November/PCWK1195.iso/inne/win95/sieciowe/hotja32.lzh/hotjava/classsrc/java/util/base64decoder.java

Text File | 1995-08-11 | 5KB | 168 lines

/*
 * @(#)BASE64Decoder.java    1.1 95/03/16 Chuck McManis
 *
 * Copyright (c) 1995 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */
package java.util;

import java.io.OutputStream;
import java.io.InputStream;
import java.io.PrintStream;

/**
 * This class implements a BASE64 Character decoder as specified in RFC1113.
 *
 * This RFC is part of the Privacy Enhanced Mail (PEM) specification which
 * is published by the Internet Engineering Task Force (IETF). Unlike some
 * other encoding schemes there is nothing in this encoding that tells
 * the decoder where a buffer starts or stops, so to use it you will need
 * to isolate your encoded data into a single chunk and then feed them
 * this decoder. The simplest way to do that is to read all of the encoded
 * data into a string and then use:
 * <pre>
 *    byte    mydata[];
 *    BASE64Decoder base64 = new BASE64Decoder();
 *
 *    mydata = base64.decodeBuffer(bufferString);
 * </pre>
 * This will decode the String in <i>bufferString</i> and give you an array
 * of bytes in the array <i>myData</i>.
 *
 * On errors, this class throws a CEFormatException with the following detail
 * strings:
 * <pre>
 *    "BASE64Decoder: Bad Padding byte (2)."
 *    "BASE64Decoder: Bad Padding byte (1)."
 * </pre>
 *
 * @version    1.1, 16 Mar 1995
 * @author    Chuck McManis
 * @see        CharacterEncoder
 * @see        BASE64Decoder
 */

public class BASE64Decoder extends CharacterDecoder {

    /** This class has 3 bytes per atom */
    int bytesPerAtom() {
    return (3);
    }

    /** This class has 48 bytes per encoded line */
    int bytesPerLine() {
    return (48);
    }

    /**
     * This character array provides the character to value map
     * based on RFC1113.
     */
    private final static char pem_array[] = {
    //       0   1   2   3   4   5   6   7
        'A','B','C','D','E','F','G','H', // 0
        'I','J','K','L','M','N','O','P', // 1
        'Q','R','S','T','U','V','W','X', // 2
        'Y','Z','a','b','c','d','e','f', // 3
        'g','h','i','j','k','l','m','n', // 4
        'o','p','q','r','s','t','u','v', // 5
        'w','x','y','z','0','1','2','3', // 6
        '4','5','6','7','8','9','+','/'  // 7
    };

    byte decode_buffer[] = new byte[4];

    /**
     * Decode one BASE64 atom into 1, 2, or 3 bytes of data.
     */
    void decodeAtom(InputStream inStream, OutputStream outStream, int l) {
    int    i;
    byte    a = -1, b = -1, c = -1, d = -1;
    StringBuffer s = new StringBuffer(4);

    decode_buffer[0] = (byte) inStream.read();
    if (decode_buffer[0] == -1) {
        throw new CEStreamExhausted();
    }

    // check to see if we caught the trailing end of a <CR><LF>
    if (decode_buffer[0] == '\n') {
        i = inStream.read(decode_buffer, 0, 4);
    } else {
        i = inStream.read(decode_buffer, 1, 3);
    }
    if (i == -1) {
        throw new CEStreamExhausted();
    }

    for (i = 0; i < 64; i++) {
        if (decode_buffer[0] == pem_array[i]) {
        a = (byte) i;
        }
        if (decode_buffer[1] == pem_array[i]) {
        b = (byte) i;
        }
        if (decode_buffer[2] == pem_array[i]) {
        c = (byte) i;
        }
        if (decode_buffer[3] == pem_array[i]) {
        d = (byte) i;
        }
    }
    if ((l == 2) && (decode_buffer[3] != '=')) {
        throw new CEFormatException("BASE64Decoder: Bad Padding byte (2).");
    }
    if ((l == 1) &&
        ((decode_buffer[2] != '=') || (decode_buffer[3] != '='))) {
        throw new CEFormatException("BASE64Decoder: Bad Padding byte (1).");
    }

    for (i = 0; i < 4; i++) s.appendChar((char) decode_buffer[i]);
    switch (l) {
    case 1:
        outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
        break;
    case 2:
        outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
        outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
        break;
    case 3:
        outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
        outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
        outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );
        break;
    }
    return;
    }

    /**
     * decodeLineSuffix in this decoder simply finds the [newLine] and
     * positions us past it.
     */
    void decodeLineSuffix(InputStream inStream, OutputStream outStream) {
    int c;

    while (true) {
        c = inStream.read();
        if (c == -1) {
        throw new CEStreamExhausted();
        }
        if ((c == '\n') || (c == '\r')) {
        break;
        }
    }
    }
}