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1   /*
2    * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package java.security;
27  
28  import java.io.IOException;
29  import java.io.EOFException;
30  import java.io.OutputStream;
31  import java.io.FilterOutputStream;
32  import java.io.PrintStream;
33  import java.io.ByteArrayOutputStream;
34  
35  /**
36   * A transparent stream that updates the associated message digest using
37   * the bits going through the stream.
38   *
39   * <p>To complete the message digest computation, call one of the
40   * {@code digest} methods on the associated message
41   * digest after your calls to one of this digest output stream's
42   * {@link #write(int) write} methods.
43   *
44   * <p>It is possible to turn this stream on or off (see
45   * {@link #on(boolean) on}). When it is on, a call to one of the
46   * {@code write} methods results in
47   * an update on the message digest.  But when it is off, the message
48   * digest is not updated. The default is for the stream to be on.
49   *
50   * @see MessageDigest
51   * @see DigestInputStream
52   *
53   * @author Benjamin Renaud
54   */
55  public class DigestOutputStream extends FilterOutputStream {
56  
57      private boolean on = true;
58  
59      /**
60       * The message digest associated with this stream.
61       */
62      protected MessageDigest digest;
63  
64      /**
65       * Creates a digest output stream, using the specified output stream
66       * and message digest.
67       *
68       * @param stream the output stream.
69       *
70       * @param digest the message digest to associate with this stream.
71       */
72      public DigestOutputStream(OutputStream stream, MessageDigest digest) {
73          super(stream);
74          setMessageDigest(digest);
75      }
76  
77      /**
78       * Returns the message digest associated with this stream.
79       *
80       * @return the message digest associated with this stream.
81       * @see #setMessageDigest(java.security.MessageDigest)
82       */
83      public MessageDigest getMessageDigest() {
84          return digest;
85      }
86  
87      /**
88       * Associates the specified message digest with this stream.
89       *
90       * @param digest the message digest to be associated with this stream.
91       * @see #getMessageDigest()
92       */
93      public void setMessageDigest(MessageDigest digest) {
94          this.digest = digest;
95      }
96  
97      /**
98       * Updates the message digest (if the digest function is on) using
99       * the specified byte, and in any case writes the byte
100      * to the output stream. That is, if the digest function is on
101      * (see {@link #on(boolean) on}), this method calls
102      * {@code update} on the message digest associated with this
103      * stream, passing it the byte {@code b}. This method then
104      * writes the byte to the output stream, blocking until the byte
105      * is actually written.
106      *
107      * @param b the byte to be used for updating and writing to the
108      * output stream.
109      *
110      * @exception IOException if an I/O error occurs.
111      *
112      * @see MessageDigest#update(byte)
113      */
114     public void write(int b) throws IOException {
115         out.write(b);
116         if (on) {
117             digest.update((byte)b);
118         }
119     }
120 
121     /**
122      * Updates the message digest (if the digest function is on) using
123      * the specified subarray, and in any case writes the subarray to
124      * the output stream. That is, if the digest function is on (see
125      * {@link #on(boolean) on}), this method calls {@code update}
126      * on the message digest associated with this stream, passing it
127      * the subarray specifications. This method then writes the subarray
128      * bytes to the output stream, blocking until the bytes are actually
129      * written.
130      *
131      * @param b the array containing the subarray to be used for updating
132      * and writing to the output stream.
133      *
134      * @param off the offset into {@code b} of the first byte to
135      * be updated and written.
136      *
137      * @param len the number of bytes of data to be updated and written
138      * from {@code b}, starting at offset {@code off}.
139      *
140      * @exception IOException if an I/O error occurs.
141      *
142      * @see MessageDigest#update(byte[], int, int)
143      */
144     public void write(byte[] b, int off, int len) throws IOException {
145         out.write(b, off, len);
146         if (on) {
147             digest.update(b, off, len);
148         }
149     }
150 
151     /**
152      * Turns the digest function on or off. The default is on.  When
153      * it is on, a call to one of the {@code write} methods results in an
154      * update on the message digest.  But when it is off, the message
155      * digest is not updated.
156      *
157      * @param on true to turn the digest function on, false to turn it
158      * off.
159      */
160     public void on(boolean on) {
161         this.on = on;
162     }
163 
164     /**
165      * Prints a string representation of this digest output stream and
166      * its associated message digest object.
167      */
168      public String toString() {
169          return "[Digest Output Stream] " + digest.toString();
170      }
171 }