/* DigestInputStream.java --- An Input stream tied to a message digest
   Copyright (C) 1999, 2003, 2004, 2005  Free Software Foundation, Inc.

This file is 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, 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; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, 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
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
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exception statement from your version. */


package java.security;

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

/**
 * DigestInputStream is a class that ties an InputStream with a 
 * MessageDigest. The Message Digest is used by the class to 
 * update it self as bytes are read from the InputStream.
 *
 * The updating to the digest depends on the on flag which is set
 * to true by default to tell the class to update the data
 * in the message digest.
 *
 * @version 0.0
 * @author Mark Benvenuto (ivymccough@worldnet.att.net)
 */
public class DigestInputStream extends FilterInputStream
{
  /**
   * The message digest for the DigestInputStream 
   */
  protected MessageDigest digest;

  //Manages the on flag
  private boolean state = true;

  /**
   * Constructs a new DigestInputStream.
   * It associates a MessageDigest with the stream to 
   * compute the stream as data is written.
   *
   * @param stream An InputStream to associate this stream with
   * @param digest A MessageDigest to hash the stream with
   */
  public DigestInputStream(InputStream stream, MessageDigest digest)
  {
    super(stream);
    //this.in = stream;
    this.digest = digest;
  }

  /**
   * Returns the MessageDigest associated with this DigestInputStream 
   *
   * @return The MessageDigest used to hash this stream
   */
  public MessageDigest getMessageDigest()
  {
    return digest;
  }

  /**
   * Sets the current MessageDigest to current parameter
   *
   * @param digest A MessageDigest to associate with this stream
   */
  public void setMessageDigest(MessageDigest digest)
  {
    this.digest = digest;
  }

  /** 
   * Reads a byte from the input stream and updates the digest.
   * This method reads the underlying input stream and if the 
   * on flag is true then updates the message digest.
   *
   * @return Returns a byte from the input stream, -1 is returned to indicate that 
   * the end of stream was reached before this read call
   *
   * @throws IOException if an IO error occurs in the underlying input stream,
   * this error is thrown
   */
  public int read() throws IOException
  {
    int temp = in.read();

    if (state == true && temp != -1)
      digest.update((byte) temp);

    return temp;
  }

  /** 
   * Reads bytes from the input stream and updates the digest.
   * This method reads the underlying input stream and if the 
   * on flag is true then updates the message digest.
   *
   * @param b a byte array to store the data from the input stream
   * @param off an offset to start at in the array
   * @param len length of data to read
   * @return Returns count of bytes read, -1 is returned to indicate that 
   * the end of stream was reached before this read call
   *
   * @throws IOException if an IO error occurs in the underlying input stream,
   * this error is thrown
   */
  public int read(byte[]b, int off, int len) throws IOException
  {
    int temp = in.read(b, off, len);

    if (state == true && temp != -1)
      digest.update(b, off, temp);

    return temp;
  }

  /**
   * Sets the flag specifing if this DigestInputStream updates the
   * digest in the write() methods. The default is on;
   *
   * @param on True means it digests stream, false means it does not
   */
  public void on(boolean on)
  {
    state = on;
  }

  /**
   * Converts the input stream and underlying message digest to a string.
   *
   * @return A string representing the input stream and message digest.
   */
  public String toString()
  {
    return "[Digest Input Stream] " + digest.toString();
  }
}