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	/*
	* Copyright (c) 1997, 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.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
	* @since 1.2
	*
	*
	* @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();
	}
	}
	}

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