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.checkNotNull;
18
19import com.google.common.annotations.Beta;
20
21import java.io.FilterOutputStream;
22import java.io.IOException;
23import java.io.OutputStream;
24
25/**
26 * An {@link OutputStream} that maintains a hash of the data written to it.
27 *
28 * @author Nick Piepmeier
29 * @since 16.0
30 */
31@Beta
32public 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 public void write(int b) throws IOException {
51    hasher.putByte((byte) b);
52    out.write(b);
53  }
54
55  @Override public void write(byte[] bytes, int off, int len) throws IOException {
56    hasher.putBytes(bytes, off, len);
57    out.write(bytes, off, len);
58  }
59
60  /**
61   * Returns the {@link HashCode} based on the data written to this stream. The result is
62   * unspecified if this method is called more than once on the same instance.
63   */
64  public HashCode hash() {
65    return hasher.hash();
66  }
67
68  // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
69  // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
70  // It should flush itself if necessary.
71  @Override public void close() throws IOException {
72    out.close();
73  }
74}
75