1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15package com.google.common.hash;
16
17import static com.google.common.base.Preconditions.checkArgument;
18import static com.google.common.base.Preconditions.checkNotNull;
19import static com.google.common.base.Preconditions.checkState;
20
21import java.io.Serializable;
22import java.security.MessageDigest;
23import java.security.NoSuchAlgorithmException;
24import java.util.Arrays;
25
26/**
27 * {@link HashFunction} adapter for {@link MessageDigest} instances.
28 *
29 * @author Kevin Bourrillion
30 * @author Dimitris Andreou
31 */
32final class MessageDigestHashFunction extends AbstractStreamingHashFunction
33    implements Serializable {
34  private final MessageDigest prototype;
35  private final int bytes;
36  private final boolean supportsClone;
37  private final String toString;
38
39  MessageDigestHashFunction(String algorithmName, String toString) {
40    this.prototype = getMessageDigest(algorithmName);
41    this.bytes = prototype.getDigestLength();
42    this.toString = checkNotNull(toString);
43    this.supportsClone = supportsClone();
44  }
45
46  MessageDigestHashFunction(String algorithmName, int bytes, String toString) {
47    this.toString = checkNotNull(toString);
48    this.prototype = getMessageDigest(algorithmName);
49    int maxLength = prototype.getDigestLength();
50    checkArgument(bytes >= 4 && bytes <= maxLength,
51        "bytes (%s) must be >= 4 and < %s", bytes, maxLength);
52    this.bytes = bytes;
53    this.supportsClone = supportsClone();
54  }
55
56  private boolean supportsClone() {
57    try {
58      prototype.clone();
59      return true;
60    } catch (CloneNotSupportedException e) {
61      return false;
62    }
63  }
64
65  @Override public int bits() {
66    return bytes * Byte.SIZE;
67  }
68
69  @Override public String toString() {
70    return toString;
71  }
72
73  private static MessageDigest getMessageDigest(String algorithmName) {
74    try {
75      return MessageDigest.getInstance(algorithmName);
76    } catch (NoSuchAlgorithmException e) {
77      throw new AssertionError(e);
78    }
79  }
80
81  @Override public Hasher newHasher() {
82    if (supportsClone) {
83      try {
84        return new MessageDigestHasher((MessageDigest) prototype.clone(), bytes);
85      } catch (CloneNotSupportedException e) {
86        // falls through
87      }
88    }
89    return new MessageDigestHasher(getMessageDigest(prototype.getAlgorithm()), bytes);
90  }
91
92  private static final class SerializedForm implements Serializable {
93    private final String algorithmName;
94    private final int bytes;
95    private final String toString;
96
97    private SerializedForm(String algorithmName, int bytes, String toString) {
98      this.algorithmName = algorithmName;
99      this.bytes = bytes;
100      this.toString = toString;
101    }
102
103    private Object readResolve() {
104      return new MessageDigestHashFunction(algorithmName, bytes, toString);
105    }
106
107    private static final long serialVersionUID = 0;
108  }
109
110  Object writeReplace() {
111    return new SerializedForm(prototype.getAlgorithm(), bytes, toString);
112  }
113
114  /**
115   * Hasher that updates a message digest.
116   */
117  private static final class MessageDigestHasher extends AbstractByteHasher {
118
119    private final MessageDigest digest;
120    private final int bytes;
121    private boolean done;
122
123    private MessageDigestHasher(MessageDigest digest, int bytes) {
124      this.digest = digest;
125      this.bytes = bytes;
126    }
127
128    @Override
129    protected void update(byte b) {
130      checkNotDone();
131      digest.update(b);
132    }
133
134    @Override
135    protected void update(byte[] b) {
136      checkNotDone();
137      digest.update(b);
138    }
139
140    @Override
141    protected void update(byte[] b, int off, int len) {
142      checkNotDone();
143      digest.update(b, off, len);
144    }
145
146    private void checkNotDone() {
147      checkState(!done, "Cannot re-use a Hasher after calling hash() on it");
148    }
149
150    @Override
151    public HashCode hash() {
152      checkNotDone();
153      done = true;
154      return (bytes == digest.getDigestLength())
155          ? HashCode.fromBytesNoCopy(digest.digest())
156          : HashCode.fromBytesNoCopy(Arrays.copyOf(digest.digest(), bytes));
157    }
158  }
159}
160