BASE64Decoder.java

package com.github.javautils.encrypt;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class BASE64Decoder extends CharacterDecoder {

    public BASE64Decoder() {
        decode_buffer = new byte[4];
    }

    protected int bytesPerAtom() {
        return 4;
    }

    protected int bytesPerLine() {
        return 72;
    }

    protected void decodeAtom(InputStream inputstream, OutputStream outputstream, int i)
            throws IOException {
        byte byte0 = -1;
        byte byte1 = -1;
        byte byte2 = -1;
        byte byte3 = -1;
        if (i < 2)
            throw new IOException("BASE64Decoder: Not enough bytes for an atom.");
        int j;
        do {
            j = inputstream.read();
            if (j == -1)
                throw new IOException("StreamExhausted");
        } while (j == 10 || j == 13);
        decode_buffer[0] = (byte) j;
        j = readFully(inputstream, decode_buffer, 1, i - 1);
        if (j == -1)
            throw new IOException("StreamExhausted");
        if (i > 3 && decode_buffer[3] == 61)
            i = 3;
        if (i > 2 && decode_buffer[2] == 61)
            i = 2;
        switch (i) {
            case 4: // '\004'
                byte3 = pem_convert_array[decode_buffer[3] & 0xff];
                // fall through

            case 3: // '\003'
                byte2 = pem_convert_array[decode_buffer[2] & 0xff];
                // fall through

            case 2: // '\002'
                byte1 = pem_convert_array[decode_buffer[1] & 0xff];
                byte0 = pem_convert_array[decode_buffer[0] & 0xff];
                // fall through

            default:
                switch (i) {
                    case 2: // '\002'
                        outputstream.write((byte) (byte0 << 2 & 0xfc | byte1 >>> 4 & 3));
                        break;

                    case 3: // '\003'
                        outputstream.write((byte) (byte0 << 2 & 0xfc | byte1 >>> 4 & 3));
                        outputstream.write((byte) (byte1 << 4 & 0xf0 | byte2 >>> 2 & 0xf));
                        break;

                    case 4: // '\004'
                        outputstream.write((byte) (byte0 << 2 & 0xfc | byte1 >>> 4 & 3));
                        outputstream.write((byte) (byte1 << 4 & 0xf0 | byte2 >>> 2 & 0xf));
                        outputstream.write((byte) (byte2 << 6 & 0xc0 | byte3 & 0x3f));
                        break;
                }
                break;
        }
    }

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

    static {
        pem_convert_array = new byte[256];
        for (int i = 0; i < 255; i++)
            pem_convert_array[i] = -1;

        for (int j = 0; j < pem_array.length; j++)
            pem_convert_array[pem_array[j]] = (byte) j;

    }
}