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3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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   *
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24   */
25  
26  package java.security;
27  
28  import java.nio.ByteBuffer;
29  
30  import sun.security.jca.JCAUtil;
31  
32  /**
33   * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
34   * for the {@code MessageDigest} class, which provides the functionality
35   * of a message digest algorithm, such as MD5 or SHA. Message digests are
36   * secure one-way hash functions that take arbitrary-sized data and output a
37   * fixed-length hash value.
38   *
39   * <p> All the abstract methods in this class must be implemented by a
40   * cryptographic service provider who wishes to supply the implementation
41   * of a particular message digest algorithm.
42   *
43   * <p> Implementations are free to implement the Cloneable interface.
44   *
45   * @author Benjamin Renaud
46   *
47   *
48   * @see MessageDigest
49   */
50  
51  public abstract class MessageDigestSpi {
52  
53      // for re-use in engineUpdate(ByteBuffer input)
54      private byte[] tempArray;
55  
56      /**
57       * Returns the digest length in bytes.
58       *
59       * <p>This concrete method has been added to this previously-defined
60       * abstract class. (For backwards compatibility, it cannot be abstract.)
61       *
62       * <p>The default behavior is to return 0.
63       *
64       * <p>This method may be overridden by a provider to return the digest
65       * length.
66       *
67       * @return the digest length in bytes.
68       *
69       * @since 1.2
70       */
71      protected int engineGetDigestLength() {
72          return 0;
73      }
74  
75      /**
76       * Updates the digest using the specified byte.
77       *
78       * @param input the byte to use for the update.
79       */
80      protected abstract void engineUpdate(byte input);
81  
82      /**
83       * Updates the digest using the specified array of bytes,
84       * starting at the specified offset.
85       *
86       * @param input the array of bytes to use for the update.
87       *
88       * @param offset the offset to start from in the array of bytes.
89       *
90       * @param len the number of bytes to use, starting at
91       * {@code offset}.
92       */
93      protected abstract void engineUpdate(byte[] input, int offset, int len);
94  
95      /**
96       * Update the digest using the specified ByteBuffer. The digest is
97       * updated using the {@code input.remaining()} bytes starting
98       * at {@code input.position()}.
99       * Upon return, the buffer's position will be equal to its limit;
100      * its limit will not have changed.
101      *
102      * @param input the ByteBuffer
103      * @since 1.5
104      */
105     protected void engineUpdate(ByteBuffer input) {
106         if (input.hasRemaining() == false) {
107             return;
108         }
109         if (input.hasArray()) {
110             byte[] b = input.array();
111             int ofs = input.arrayOffset();
112             int pos = input.position();
113             int lim = input.limit();
114             engineUpdate(b, ofs + pos, lim - pos);
115             input.position(lim);
116         } else {
117             int len = input.remaining();
118             int n = JCAUtil.getTempArraySize(len);
119             if ((tempArray == null) || (n > tempArray.length)) {
120                 tempArray = new byte[n];
121             }
122             while (len > 0) {
123                 int chunk = Math.min(len, tempArray.length);
124                 input.get(tempArray, 0, chunk);
125                 engineUpdate(tempArray, 0, chunk);
126                 len -= chunk;
127             }
128         }
129     }
130 
131     /**
132      * Completes the hash computation by performing final
133      * operations such as padding. Once {@code engineDigest} has
134      * been called, the engine should be reset (see
135      * {@link #engineReset() engineReset}).
136      * Resetting is the responsibility of the
137      * engine implementor.
138      *
139      * @return the array of bytes for the resulting hash value.
140      */
141     protected abstract byte[] engineDigest();
142 
143     /**
144      * Completes the hash computation by performing final
145      * operations such as padding. Once {@code engineDigest} has
146      * been called, the engine should be reset (see
147      * {@link #engineReset() engineReset}).
148      * Resetting is the responsibility of the
149      * engine implementor.
150      *
151      * This method should be abstract, but we leave it concrete for
152      * binary compatibility.  Knowledgeable providers should override this
153      * method.
154      *
155      * @param buf the output buffer in which to store the digest
156      *
157      * @param offset offset to start from in the output buffer
158      *
159      * @param len number of bytes within buf allotted for the digest.
160      * Both this default implementation and the SUN provider do not
161      * return partial digests.  The presence of this parameter is solely
162      * for consistency in our API's.  If the value of this parameter is less
163      * than the actual digest length, the method will throw a DigestException.
164      * This parameter is ignored if its value is greater than or equal to
165      * the actual digest length.
166      *
167      * @return the length of the digest stored in the output buffer.
168      *
169      * @exception DigestException if an error occurs.
170      *
171      * @since 1.2
172      */
173     protected int engineDigest(byte[] buf, int offset, int len)
174                                                 throws DigestException {
175 
176         byte[] digest = engineDigest();
177         if (len < digest.length)
178                 throw new DigestException("partial digests not returned");
179         if (buf.length - offset < digest.length)
180                 throw new DigestException("insufficient space in the output "
181                                           + "buffer to store the digest");
182         System.arraycopy(digest, 0, buf, offset, digest.length);
183         return digest.length;
184     }
185 
186     /**
187      * Resets the digest for further use.
188      */
189     protected abstract void engineReset();
190 
191     /**
192      * Returns a clone if the implementation is cloneable.
193      *
194      * @return a clone if the implementation is cloneable.
195      *
196      * @exception CloneNotSupportedException if this is called on an
197      * implementation that does not support {@code Cloneable}.
198      */
199     public Object clone() throws CloneNotSupportedException {
200         if (this instanceof Cloneable) {
201             return super.clone();
202         } else {
203             throw new CloneNotSupportedException();
204         }
205     }
206 }