001/*
002 * Copyright (C) 2011 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.hash;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018
019import com.google.common.annotations.Beta;
020import java.io.FilterOutputStream;
021import java.io.IOException;
022import java.io.OutputStream;
023
024/**
025 * An {@link OutputStream} that maintains a hash of the data written to it.
026 *
027 * @author Nick Piepmeier
028 * @since 16.0
029 */
030@Beta
031public final class HashingOutputStream extends FilterOutputStream {
032  private final Hasher hasher;
033
034  /**
035   * Creates an output stream that hashes using the given {@link HashFunction}, and forwards all
036   * data written to it to the underlying {@link OutputStream}.
037   *
038   * <p>The {@link OutputStream} should not be written to before or after the hand-off.
039   */
040  // TODO(user): Evaluate whether it makes sense to always piggyback the computation of a
041  // HashCode on an existing OutputStream, compared to creating a separate OutputStream that could
042  // be (optionally) be combined with another if needed (with something like
043  // MultiplexingOutputStream).
044  public HashingOutputStream(HashFunction hashFunction, OutputStream out) {
045    super(checkNotNull(out));
046    this.hasher = checkNotNull(hashFunction.newHasher());
047  }
048
049  @Override
050  public void write(int b) throws IOException {
051    hasher.putByte((byte) b);
052    out.write(b);
053  }
054
055  @Override
056  public void write(byte[] bytes, int off, int len) throws IOException {
057    hasher.putBytes(bytes, off, len);
058    out.write(bytes, off, len);
059  }
060
061  /**
062   * Returns the {@link HashCode} based on the data written to this stream. The result is
063   * unspecified if this method is called more than once on the same instance.
064   */
065  public HashCode hash() {
066    return hasher.hash();
067  }
068
069  // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
070  // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
071  // It should flush itself if necessary.
072  @Override
073  public void close() throws IOException {
074    out.close();
075  }
076}