decodeinputstream.txt

MobilerRPC enables remote procedure calls between J2ME applications and java sevlet server.

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

public class DecodeInputStream extends InputStream
{
    static private final byte PAD = (byte)'=';
    static private byte[] REVERSE_ALPHABET = new byte[256];

    static
    {
        for(int i = 0; i < 256; i++)
        {
            REVERSE_ALPHABET[i] = -1;
        }
        for(int i = 'A'; i <= 'Z'; i++)
        {
            REVERSE_ALPHABET[i] = (byte)(i - 'A');
        }
        for(int i = 'a'; i <= 'z'; i++)
        {
            REVERSE_ALPHABET[i] = (byte)(i - 'a' + 26);
        }
        for(int i = '0'; i <= '9'; i++)
        {
            REVERSE_ALPHABET[i] = (byte)(i - '0' + 52);
        }
        REVERSE_ALPHABET['+'] = 62;
        REVERSE_ALPHABET['/'] = 63;
    }

    private InputStream in = null;
    private int[] decodeArray = new int[4];
    private int[] decodedArray = new int[3];
    private int decodedArrayIndex = 0;
    private int maxIndex = 0;
    private boolean eofFound = false;

    public DecodeInputStream(InputStream in)
    {
        this.in = in;
    }

    public int read() throws IOException
    {
        if(decodedArrayIndex >= maxIndex)
        {
            if(eofFound)
                return -1;

            int tmpIndex = 0;
            int padCount = 0;
            for(tmpIndex = 0; tmpIndex < 4;)
            {
                int b = in.read();
                if(b < 0)
                {
                    maxIndex = 0;
                    eofFound = true;
                    if(tmpIndex > 0)
                        throw new IOException("Invalid encoded stream.");
                    else
                        return -1;
                }
                b &= 0xFF;
                if(b == PAD)
                {
                    eofFound = true;
                    decodeArray[tmpIndex++] = 0;
                    padCount++;
                }
                else
                {
                    int decoded = REVERSE_ALPHABET[b];
                    if(decoded < 0)
                        continue;
                    else
                        decodeArray[tmpIndex++] = decoded;
                }
            }
            maxIndex = 3 - padCount;
            if(maxIndex <= 0)
            {
                maxIndex = 0;
                return -1;
            }
            decodedArrayIndex = 0;

            decode();
            decodeArray[0] = 0;
            decodeArray[1] = 0;
            decodeArray[2] = 0;
            decodeArray[3] = 0;
        }
        return decodedArray[decodedArrayIndex++];
    }

    public void close() throws IOException
    {
        in.close();
    }

    private void decode()
    {
        int a = decodeArray[0] << 18 | decodeArray[1] << 12 | decodeArray[2] << 6 | decodeArray[3];
        decodedArray[0] = (a >>> 16) & 0xFF;
        decodedArray[1] = (a >>> 8) & 0xFF;
        decodedArray[2] = a & 0xFF;
    }
}