/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * particular file as subject to the "Classpath" exception as provided

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 */

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

 *

 * @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();

     }

}