/*
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 * without modification, are permitted provided that the following 
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 *  distribution.
 *  
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 * contributors may be used to endorse or promote products derived 
 * from this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any 
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND 
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 */

package examples.rmisocfac;

import java.io.*;

class XorInputStream extends FilterInputStream {
  
   /*
    * The byte being used to "decrypt" each byte of data.
    */
    private final byte pattern;
  
    /*
     * Constructs an input stream that uses the specified pattern
     * to "decrypt" each byte of data.
     */
    public XorInputStream(InputStream in, byte pattern) {
        super(in);
	this.pattern = pattern;
    }
  
    /*
     * Reads in a byte and xor's the byte with the pattern.
     * Returns the byte.
     */
    public int read() throws IOException {
        int b = in.read();
        //If not end of file or an error, truncate b to one byte
	if (b != -1)
	  b = (b ^ pattern) & 0xFF;
                     
	return b;
    }
  
    /*
     * Reads up to len bytes
     */
    public int read(byte b[], int off, int len) throws IOException {
        int numBytes = in.read(b, off, len);

	if (numBytes <= 0)
	    return numBytes;

        for(int i = 0; i < numBytes; i++) {
	    b[off + i] = (byte)((b[off + i] ^ pattern) & 0xFF);
        }
	
	return numBytes;
    }
}