/* MacInputStream.java -- 
   Copyright (C) 2003, 2006 Free Software Foundation, Inc.

This file is a part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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or based on this library.  If you modify this library, you may extend
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package gnu.javax.crypto.mac;

import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;

/**
 * A filtering input stream that computes a MAC (message authentication code)
 * over all data read from the stream.
 */
public class MacInputStream extends FilterInputStream
{

  // Field.
  // ------------------------------------------------------------------------

  /**
   * The digesting state. The MAC is updated only if this flag is true.
   */
  private boolean digesting;

  /**
   * The MAC being updated.
   */
  private IMac mac;

  // Constructor.
  // ------------------------------------------------------------------------

  /**
   * Creates a new MacInputStream. The stream is initially set to digest
   * data written, the <i>mac</i> argument must have already been initialized,
   * and the <i>mac</i> argument is <b>not</b> cloned.
   *
   * @param in The underlying input stream.
   * @param mac The mac instance to use.
   */
  public MacInputStream(InputStream in, IMac mac)
  {
    super(in);
    if (mac == null)
      throw new NullPointerException();
    this.mac = mac;
    digesting = true;
  }

  // Instance methods.
  // ------------------------------------------------------------------------

  /**
   * Returns the MAC this stream is updating.
   *
   * @return The MAC.
   */
  public IMac getMac()
  {
    return mac;
  }

  /**
   * Sets the MAC this stream is updating, which must have already been
   * initialized. The argument is not cloned by this method.
   *
   * @param mac The new MAC.
   * @throws NullPointerException If the argument is null.
   */
  public void setMac(IMac mac)
  {
    if (mac == null)
      throw new NullPointerException();
    this.mac = mac;
  }

  /**
   * Turns the digesting state on or off. When off, the MAC will not be
   * updated when data is written to the stream.
   *
   * @param flag The new digesting state.
   */
  public void on(boolean flag)
  {
    digesting = flag;
  }

  public int read() throws IOException
  {
    int i = in.read();
    if (digesting && i != -1)
      mac.update((byte) i);
    return i;
  }

  public int read(byte[] buf, int off, int len) throws IOException
  {
    int i = in.read(buf, off, len);
    if (digesting && i != -1)
      mac.update(buf, off, i);
    return i;
  }
}