001/* DigestOutputStream.java --- An output stream tied to a message digest
002   Copyright (C) 1999, 2004, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.security;
040
041import java.io.FilterOutputStream;
042import java.io.IOException;
043import java.io.OutputStream;
044
045/**
046 * DigestOutputStream is a class that ties an OutputStream with a
047 * MessageDigest. The Message Digest is used by the class to update it
048 * self as bytes are written to the OutputStream.
049 *
050 * The updating to the digest depends on the on flag which is set to
051 * true by default that tells the class to update the data in the
052 * message digest.
053 *
054 * @version 0.0
055 * @author Mark Benvenuto (ivymccough@worldnet.att.net)
056 */
057public class DigestOutputStream extends FilterOutputStream
058{
059  /**
060   * The message digest for the DigestOutputStream
061   */
062  protected MessageDigest digest;
063
064  //Manages the on flag
065  private boolean state = true;
066
067  /**
068   * Constructs a new DigestOutputStream.  It associates a
069   * MessageDigest with the stream to compute the stream as data is
070   * written.
071   *
072   * @param stream An OutputStream to associate this stream with
073   * @param digest A MessageDigest to hash the stream with
074   */
075  public DigestOutputStream(OutputStream stream, MessageDigest digest)
076  {
077    super(stream);
078    this.digest = digest;
079  }
080
081  /**
082   * Returns the MessageDigest associated with this DigestOutputStream
083   *
084   * @return The MessageDigest used to hash this stream
085   */
086  public MessageDigest getMessageDigest()
087  {
088    return digest;
089  }
090
091  /**
092   * Sets the current MessageDigest to current parameter
093   *
094   * @param digest A MessageDigest to associate with this stream
095   */
096  public void setMessageDigest(MessageDigest digest)
097  {
098    this.digest = digest;
099  }
100
101
102  /**
103   * Updates the hash if the on flag is true and then writes a byte to
104   * the underlying output stream.
105   *
106   * @param b A byte to write to the output stream
107   *
108   * @exception IOException if the underlying output stream 
109   * cannot write the byte, this is thrown.
110   */
111  public void write(int b) throws IOException
112  {
113    if (state)
114      digest.update((byte) b);
115
116    out.write(b);
117  }
118
119  /**
120   * Updates the hash if the on flag is true and then writes the bytes
121   * to the underlying output stream.
122   *
123   * @param b Bytes to write to the output stream
124   * @param off Offset to start to start at in array
125   * @param len Length of data to write
126   *
127   * @exception IOException if the underlying output stream 
128   * cannot write the bytes, this is thrown.
129   */
130  public void write(byte[]b, int off, int len) throws IOException
131  {
132    if (state)
133      digest.update(b, off, len);
134
135    out.write(b, off, len);
136  }
137
138  /**
139   * Sets the flag specifying if this DigestOutputStream updates the
140   * digest in the write() methods. The default is on;
141   *
142   * @param on True means it digests stream, false means it does not
143   */
144  public void on(boolean on)
145  {
146    state = on;
147  }
148
149  /**
150   * Converts the output stream and underlying message digest to a string.
151   *
152   * @return A string representing the output stream and message digest.
153   */
154  public String toString()
155  {
156    return "[Digest Output Stream] " + digest.toString();
157  }
158}