/*

 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.

 * 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

 * published by the Free Software Foundation.  Oracle designates this

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

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.security;

import java.io.IOException;

import java.io.EOFException;

import java.io.InputStream;

import java.io.FilterInputStream;

import java.io.PrintStream;

import java.io.ByteArrayInputStream;

/**

 * 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} methods on the associated message

 * digest after your calls to one of this digest input stream's

 * {@link #read() read} 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 read} 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.

 *

 * <p>Note that digest objects can compute only one digest (see

 * {@link MessageDigest}),

 * so that in order to compute intermediate digests, a caller should

 * retain a handle onto the digest object, and clone it for each

 * digest to be computed, leaving the original digest untouched.

 *

 * @see MessageDigest

 *

 * @see DigestOutputStream

 *

 * @author Benjamin Renaud

 * @since 1.2

 */

public class DigestInputStream extends FilterInputStream {

    /* NOTE: This should be made a generic UpdaterInputStream */

    /* Are we on or off? */

    private boolean on = true;

    /**

     * The message digest associated with this stream.

     */

    protected MessageDigest digest;

    /**

     * Creates a digest input stream, using the specified input stream

     * and message digest.

     *

     * @param stream the input stream.

     *

     * @param digest the message digest to associate with this stream.

     */

    public DigestInputStream(InputStream 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;

    }

    /**

     * Reads a byte, and updates the message digest (if the digest

     * function is on).  That is, this method reads a byte from the

     * input stream, blocking until the byte is actually read. If the

     * digest function is on (see {@link #on(boolean) on}), this method

     * will then call {@code update} on the message digest associated

     * with this stream, passing it the byte read.

     *

     * @return the byte read.

     *

     * @exception IOException if an I/O error occurs.

     *

     * @see MessageDigest#update(byte)

     */

    public int read() throws IOException {

        int ch = in.read();

        if (on && ch != -1) {

            digest.update((byte)ch);

        }

        return ch;

    }

    /**

     * Reads into a byte array, and updates the message digest (if the

     * digest function is on).  That is, this method reads up to

     * {@code len} bytes from the input stream into the array

     * {@code b}, starting at offset {@code off}. This method

     * blocks until the data is actually

     * read. If the digest function is on (see

     * {@link #on(boolean) on}), this method will then call {@code update}

     * on the message digest associated with this stream, passing it

     * the data.

     *

     * @param b the array into which the data is read.

     *

     * @param off the starting offset into {@code b} of where the

     * data should be placed.

     *

     * @param len the maximum number of bytes to be read from the input

     * stream into b, starting at offset {@code off}.

     *

     * @return  the actual number of bytes read. This is less than

     * {@code len} if the end of the stream is reached prior to

     * reading {@code len} bytes. -1 is returned if no bytes were

     * read because the end of the stream had already been reached when

     * the call was made.

     *

     * @exception IOException if an I/O error occurs.

     *

     * @see MessageDigest#update(byte[], int, int)

     */

    public int read(byte[] b, int off, int len) throws IOException {

        int result = in.read(b, off, len);

        if (on && result != -1) {

            digest.update(b, off, result);

        }

        return result;

    }

    /**

     * Turns the digest function on or off. The default is on.  When

     * it is on, a call to one of the {@code read} 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 input stream and

     * its associated message digest object.

     */

     public String toString() {

         return "[Digest Input Stream] " + digest.toString();

     }

}