001    /* DigestOutputStream.java --- An output stream tied to a message digest
002       Copyright (C) 1999, 2004, 2005  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.security;
040    
041    import java.io.FilterOutputStream;
042    import java.io.IOException;
043    import 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     */
057    public 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    }