/* MessageDigestAdapter.java -- 
   Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

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it under the terms of the GNU General Public License as published by
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General Public License for more details.

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USA

Linking this library statically or dynamically with other modules is
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permission to link this library with independent modules to produce an
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package gnu.java.security.jce.hash;

import gnu.java.security.hash.IMessageDigest;
import gnu.java.security.hash.HashFactory;

import java.security.DigestException;
import java.security.MessageDigestSpi;

/**
 * The implementation of a generic {@link java.security.MessageDigest} adapter
 * class to wrap GNU hash instances.
 * <p>
 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>) for
 * the {@link java.security.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 the {@link MessageDigestSpi} class are
 * implemented by this class and all its sub-classes.
 * <p>
 * All the implementations which subclass this object, and which are serviced by
 * the GNU provider implement the {@link Cloneable} interface.
 */
class MessageDigestAdapter
    extends MessageDigestSpi
    implements Cloneable
{
  /** Our underlying hash instance. */
  private IMessageDigest adaptee;

  /**
   * Trivial protected constructor.
   * 
   * @param mdName the canonical name of the hash algorithm.
   */
  protected MessageDigestAdapter(String mdName)
  {
    this(HashFactory.getInstance(mdName));
  }

  /**
   * Private constructor for cloning purposes.
   * 
   * @param adaptee a clone of the underlying hash algorithm instance.
   */
  private MessageDigestAdapter(IMessageDigest adaptee)
  {
    super();

    this.adaptee = adaptee;
  }

  public Object clone()
  {
    return new MessageDigestAdapter((IMessageDigest) adaptee.clone());
  }

  public int engineGetDigestLength()
  {
    return adaptee.hashSize();
  }

  public void engineUpdate(byte input)
  {
    adaptee.update(input);
  }

  public void engineUpdate(byte[] input, int offset, int len)
  {
    adaptee.update(input, offset, len);
  }

  public byte[] engineDigest()
  {
    return adaptee.digest();
  }

  public int engineDigest(byte[] buf, int offset, int len)
      throws DigestException
  {
    int result = adaptee.hashSize();
    if (len < result)
      throw new DigestException();

    byte[] md = adaptee.digest();
    System.arraycopy(md, 0, buf, offset, result);
    return result;
  }

  public void engineReset()
  {
    adaptee.reset();
  }
}