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 * 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

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 */

package java.security;

import java.nio.ByteBuffer;

import sun.security.jca.JCAUtil;

/**

 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)

 * for the {@code MessageDigest} class, which provides the functionality

 * of a message digest algorithm, such as MD5 or SHA. Message digests are

 * secure one-way hash functions that take arbitrary-sized data and output a

 * fixed-length hash value.

 *

 * <p> All the abstract methods in this class must be implemented by a

 * cryptographic service provider who wishes to supply the implementation

 * of a particular message digest algorithm.

 *

 * <p> Implementations are free to implement the Cloneable interface.

 *

 * @author Benjamin Renaud

 *

 *

 * @see MessageDigest

 */

public abstract class MessageDigestSpi {

    // for re-use in engineUpdate(ByteBuffer input)

    private byte[] tempArray;

    /**

     * Returns the digest length in bytes.

     *

     * <p>This concrete method has been added to this previously-defined

     * abstract class. (For backwards compatibility, it cannot be abstract.)

     *

     * <p>The default behavior is to return 0.

     *

     * <p>This method may be overridden by a provider to return the digest

     * length.

     *

     * @return the digest length in bytes.

     *

     * @since 1.2

     */

    protected int engineGetDigestLength() {

        return 0;

    }

    /**

     * Updates the digest using the specified byte.

     *

     * @param input the byte to use for the update.

     */

    protected abstract void engineUpdate(byte input);

    /**

     * Updates the digest using the specified array of bytes,

     * starting at the specified offset.

     *

     * @param input the array of bytes to use for the update.

     *

     * @param offset the offset to start from in the array of bytes.

     *

     * @param len the number of bytes to use, starting at

     * {@code offset}.

     */

    protected abstract void engineUpdate(byte[] input, int offset, int len);

    /**

     * Update the digest using the specified ByteBuffer. The digest is

     * updated using the {@code input.remaining()} bytes starting

     * at {@code input.position()}.

     * Upon return, the buffer's position will be equal to its limit;

     * its limit will not have changed.

     *

     * @param input the ByteBuffer

     * @since 1.5

     */

    protected void engineUpdate(ByteBuffer input) {

        if (input.hasRemaining() == false) {

            return;

        }

        if (input.hasArray()) {

            byte[] b = input.array();

            int ofs = input.arrayOffset();

            int pos = input.position();

            int lim = input.limit();

            engineUpdate(b, ofs + pos, lim - pos);

            input.position(lim);

        } else {

            int len = input.remaining();

            int n = JCAUtil.getTempArraySize(len);

            if ((tempArray == null) || (n > tempArray.length)) {

                tempArray = new byte[n];

            }

            while (len > 0) {

                int chunk = Math.min(len, tempArray.length);

                input.get(tempArray, 0, chunk);

                engineUpdate(tempArray, 0, chunk);

                len -= chunk;

            }

        }

    }

    /**

     * Completes the hash computation by performing final

     * operations such as padding. Once {@code engineDigest} has

     * been called, the engine should be reset (see

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

     * Resetting is the responsibility of the

     * engine implementor.

     *

     * @return the array of bytes for the resulting hash value.

     */

    protected abstract byte[] engineDigest();

    /**

     * Completes the hash computation by performing final

     * operations such as padding. Once {@code engineDigest} has

     * been called, the engine should be reset (see

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

     * Resetting is the responsibility of the

     * engine implementor.

     *

     * This method should be abstract, but we leave it concrete for

     * binary compatibility.  Knowledgeable providers should override this

     * method.

     *

     * @param buf the output buffer in which to store the digest

     *

     * @param offset offset to start from in the output buffer

     *

     * @param len number of bytes within buf allotted for the digest.

     * Both this default implementation and the SUN provider do not

     * return partial digests.  The presence of this parameter is solely

     * for consistency in our API's.  If the value of this parameter is less

     * than the actual digest length, the method will throw a DigestException.

     * This parameter is ignored if its value is greater than or equal to

     * the actual digest length.

     *

     * @return the length of the digest stored in the output buffer.

     *

     * @exception DigestException if an error occurs.

     *

     * @since 1.2

     */

    protected int engineDigest(byte[] buf, int offset, int len)

                                                throws DigestException {

        byte[] digest = engineDigest();

        if (len < digest.length)

                throw new DigestException("partial digests not returned");

        if (buf.length - offset < digest.length)

                throw new DigestException("insufficient space in the output "

                                          + "buffer to store the digest");

        System.arraycopy(digest, 0, buf, offset, digest.length);

        return digest.length;

    }

    /**

     * Resets the digest for further use.

     */

    protected abstract void engineReset();

    /**

     * Returns a clone if the implementation is cloneable.

     *

     * @return a clone if the implementation is cloneable.

     *

     * @exception CloneNotSupportedException if this is called on an

     * implementation that does not support {@code Cloneable}.

     */

    public Object clone() throws CloneNotSupportedException {

        if (this instanceof Cloneable) {

            return super.clone();

        } else {

            throw new CloneNotSupportedException();

        }

    }

}