/* DigestInputStream.java --- An Input stream tied to a message digest
   Copyright (C) 1999 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., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

As a special exception, if you link this library with other files to
produce an executable, this library does not by itself cause the
resulting executable to be covered by the GNU General Public License.
This exception does not however invalidate any other reasons why the
executable file might be covered by the GNU General Public License. */

package java.security;
//import java.security.MessageDigest;
import java.io.InputStream;
import java.io.FilterInputStream;
import java.io.IOException;

/**
   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, len);

    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();
  }
}