DigestInputStream


1   /*
2    * @(#)DigestInputStream.java   1.37 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.security;
9   
10  import java.io.IOException  ;
11  import java.io.EOFException  ;
12  import java.io.InputStream  ;
13  import java.io.FilterInputStream  ;
14  import java.io.PrintStream  ;
15  import java.io.ByteArrayInputStream  ;
16  
17  /**
18   * A transparent stream that updates the associated message digest using
19   * the bits going through the stream.
20   *
21   * <p>To complete the message digest computation, call one of the
22   * <code>digest</code> methods on the associated message
23   * digest after your calls to one of this digest input stream's
24   * {@link #read() read} methods.
25   *
26   * <p>It is possible to turn this stream on or off (see
27   * {@link #on(boolean) on}). When it is on, a call to one of the
28   * <code>read</code> methods
29   * results in an update on the message digest.  But when it is off,
30   * the message digest is not updated. The default is for the stream
31   * to be on.
32   *
33   * <p>Note that digest objects can compute only one digest (see
34   * {@link MessageDigest}),
35   * so that in order to compute intermediate digests, a caller should
36   * retain a handle onto the digest object, and clone it for each
37   * digest to be computed, leaving the orginal digest untouched.
38   *
39   * @see MessageDigest
40   *
41   * @see DigestOutputStream
42   *
43   * @version 1.37 03/12/19
44   * @author Benjamin Renaud
45   */
46  
47  public class DigestInputStream extends FilterInputStream   {
48  
49      /* NOTE: This should be made a generic UpdaterInputStream */
50  
51      /* Are we on or off? */
52      private boolean on = true;
53  
54      /**
55       * The message digest associated with this stream.
56       */
57      protected MessageDigest   digest;
58  
59      /**
60       * Creates a digest input stream, using the specified input stream
61       * and message digest.
62       *
63       * @param stream the input stream.
64       *
65       * @param digest the message digest to associate with this stream.
66       */
67      public DigestInputStream(InputStream   stream, MessageDigest   digest) {
68      super(stream);
69      setMessageDigest(digest);
70      }
71  
72      /**
73       * Returns the message digest associated with this stream.
74       *
75       * @return the message digest associated with this stream.
76       * @see #setMessageDigest(java.security.MessageDigest)
77       */
78      public MessageDigest   getMessageDigest() {
79      return digest;
80      }
81  
82      /**
83       * Associates the specified message digest with this stream.
84       *
85       * @param digest the message digest to be associated with this stream.
86       * @see #getMessageDigest()
87       */
88      public void setMessageDigest(MessageDigest   digest) {
89      this.digest = digest;
90      }
91  
92      /**
93       * Reads a byte, and updates the message digest (if the digest
94       * function is on).  That is, this method reads a byte from the
95       * input stream, blocking until the byte is actually read. If the
96       * digest function is on (see {@link #on(boolean) on}), this method
97       * will then call <code>update</code> on the message digest associated
98       * with this stream, passing it the byte read.
99       *
100      * @return the byte read.
101      *
102      * @exception IOException if an I/O error occurs.
103      *
104      * @see MessageDigest#update(byte)
105      */
106     public int read() throws IOException   {
107     int ch = in.read();
108     if (on && ch != -1) {
109         digest.update((byte)ch);
110     }
111     return ch;
112     }
113 
114     /**
115      * Reads into a byte array, and updates the message digest (if the
116      * digest function is on).  That is, this method reads up to
117      * <code>len</code> bytes from the input stream into the array
118      * <code>b</code>, starting at offset <code>off</code>. This method
119      * blocks until the data is actually
120      * read. If the digest function is on (see
121      * {@link #on(boolean) on}), this method will then call <code>update</code>
122      * on the message digest associated with this stream, passing it
123      * the data.
124      *
125      * @param b the array into which the data is read.
126      *
127      * @param off the starting offset into <code>b</code> of where the
128      * data should be placed.
129      *
130      * @param len the maximum number of bytes to be read from the input
131      * stream into b, starting at offset <code>off</code>.
132      *
133      * @return  the actual number of bytes read. This is less than
134      * <code>len</code> if the end of the stream is reached prior to
135      * reading <code>len</code> bytes. -1 is returned if no bytes were
136      * read because the end of the stream had already been reached when
137      * the call was made.
138      *
139      * @exception IOException if an I/O error occurs.
140      *
141      * @see MessageDigest#update(byte[], int, int)
142      */
143     public int read(byte[] b, int off, int len) throws IOException   {
144     int result = in.read(b, off, len);
145     if (on && result != -1) {
146         digest.update(b, off, result);
147     }
148     return result;
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>read</code> 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
158      * it off.
159      */
160     public void on(boolean on) {
161     this.on = on;
162     }
163 
164     /**
165      * Prints a string representation of this digest input stream and
166      * its associated message digest object.
167      */
168      public String   toString() {
169      return "[Digest Input Stream] " + digest.toString();
170      }
171 }
172 
173 
174 
175 
176
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