/*
 * @(#)DigestOutputStream.java	1.28 00/02/02
 *
 * Copyright 1996-2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package java.security;

import java.io.IOException;
import java.io.EOFException;
import java.io.OutputStream;
import java.io.FilterOutputStream;
import java.io.PrintStream;
import java.io.ByteArrayOutputStream;

/**
 * A transparent stream that updates the associated message digest using
 * the bits going through the stream.
 *
 * <p>To complete the message digest computation, call one of the
 * <code>digest</code> methods on the associated message
 * digest after your calls to one of this digest ouput stream's
 * {@link #write(int) write} methods.
 *
 * <p>It is possible to turn this stream on or off (see
 * {@link #on(boolean) on}). When it is on, a call to one of the
 * <code>write</code> methods results in
 * an update on the message digest.  But when it is off, the message
 * digest is not updated. The default is for the stream to be on.
 *
 * @see MessageDigest
 * @see DigestInputStream
 *
 * @version 1.28 00/02/02
 * @author Benjamin Renaud
 */
public class DigestOutputStream extends FilterOutputStream {

    private boolean on = true;

    /**
     * The message digest associated with this stream.
     */
    protected MessageDigest digest;

    /**
     * Creates a digest output stream, using the specified output stream
     * and message digest.
     *
     * @param stream the output stream.
     *
     * @param digest the message digest to associate with this stream.
     */
    public DigestOutputStream(OutputStream stream, MessageDigest digest) {
	super(stream);
	setMessageDigest(digest);
    }

    /**
     * Returns the message digest associated with this stream.
     *
     * @return the message digest associated with this stream.
     * @see #setMessageDigest(java.security.MessageDigest)
     */
    public MessageDigest getMessageDigest() {
	return digest;
    }

    /**
     * Associates the specified message digest with this stream.
     *
     * @param digest the message digest to be associated with this stream.
     * @see #getMessageDigest()
     */
    public void setMessageDigest(MessageDigest digest) {
	this.digest = digest;
    }

    /**
     * Updates the message digest (if the digest function is on) using
     * the specified byte, and in any case writes the byte
     * to the output stream. That is, if the digest function is on
     * (see {@link #on(boolean) on}), this method calls
     * <code>update</code> on the message digest associated with this
     * stream, passing it the byte <code>b</code>. This method then
     * writes the byte to the output stream, blocking until the byte
     * is actually written.
     *
     * @param b the byte to be used for updating and writing to the
     * output stream.
     *
     * @exception IOException if an I/O error occurs.
     *
     * @see MessageDigest#update(byte)
     */
    public void write(int b) throws IOException {
	if (on) {
	    digest.update((byte)b);
	}
	out.write(b);
    }

    /**
     * Updates the message digest (if the digest function is on) using
     * the specified subarray, and in any case writes the subarray to
     * the output stream. That is, if the digest function is on (see
     * {@link #on(boolean) on}), this method calls <code>update</code>
     * on the message digest associated with this stream, passing it
     * the subarray specifications. This method then writes the subarray
     * bytes to the output stream, blocking until the bytes are actually
     * written.
     *
     * @param b the array containing the subarray to be used for updating
     * and writing to the output stream.
     *
     * @param off the offset into <code>b</code> of the first byte to
     * be updated and written.
     *
     * @param len the number of bytes of data to be updated and written
     * from <code>b</code>, starting at offset <code>off</code>.
     *
     * @exception IOException if an I/O error occurs.
     *
     * @see MessageDigest#update(byte[], int, int)
     */
    public void write(byte[] b, int off, int len) throws IOException {
	if (on) {
	    digest.update(b, off, len);
	}
	out.write(b, off, len);
    }

    /**
     * Turns the digest function on or off. The default is on.  When
     * it is on, a call to one of the <code>write</code> methods results in an
     * update on the message digest.  But when it is off, the message
     * digest is not updated.
     *
     * @param on true to turn the digest function on, false to turn it
     * off.
     */
    public void on(boolean on) {
	this.on = on;
    }

    /**
     * Prints a string representation of this digest output stream and
     * its associated message digest object.
     */
     public String toString() {
	 return "[Digest Output Stream] " + digest.toString();
     }
}