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
15 package com.google.common.hash;
16
17 import static com.google.common.base.Preconditions.checkNotNull;
18
19 import com.google.common.annotations.Beta;
20 import java.io.FilterOutputStream;
21 import java.io.IOException;
22 import java.io.OutputStream;
23
24 /**
25 * An {@link OutputStream} that maintains a hash of the data written to it.
26 *
27 * @author Nick Piepmeier
28 * @since 16.0
29 */
30 @Beta
31 @ElementTypesAreNonnullByDefault
32 public final class HashingOutputStream extends FilterOutputStream {
33 private final Hasher hasher;
34
35 /**
36 * Creates an output stream that hashes using the given {@link HashFunction}, and forwards all
37 * data written to it to the underlying {@link OutputStream}.
38 *
39 * <p>The {@link OutputStream} should not be written to before or after the hand-off.
40 */
41 // TODO(user): Evaluate whether it makes sense to always piggyback the computation of a
42 // HashCode on an existing OutputStream, compared to creating a separate OutputStream that could
43 // be (optionally) be combined with another if needed (with something like
44 // MultiplexingOutputStream).
45 public HashingOutputStream(HashFunction hashFunction, OutputStream out) {
46 super(checkNotNull(out));
47 this.hasher = checkNotNull(hashFunction.newHasher());
48 }
49
50 @Override
51 public void write(int b) throws IOException {
52 hasher.putByte((byte) b);
53 out.write(b);
54 }
55
56 @Override
57 public void write(byte[] bytes, int off, int len) throws IOException {
58 hasher.putBytes(bytes, off, len);
59 out.write(bytes, off, len);
60 }
61
62 /**
63 * Returns the {@link HashCode} based on the data written to this stream. The result is
64 * unspecified if this method is called more than once on the same instance.
65 */
66 public HashCode hash() {
67 return hasher.hash();
68 }
69
70 // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
71 // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
72 // It should flush itself if necessary.
73 @Override
74 public void close() throws IOException {
75 out.close();
76 }
77 }