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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2015 DiffPlug.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.common.hash;

import static com.google.common.base.Preconditions.checkNotNull;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.annotation.CheckReturnValue;

import com.google.common.annotations.Beta;

/**
 * An {@link OutputStream} that maintains a hash of the data written to it.
 *
 * @author Nick Piepmeier
 * @since 16.0
 */
@Beta
public final class HashingOutputStream extends FilterOutputStream {
	private final Hasher hasher;

	/**
	 * Creates an output stream that hashes using the given {@link HashFunction}, and forwards all
	 * data written to it to the underlying {@link OutputStream}.
	 *
	 * The {@link OutputStream} should not be written to before or after the hand-off.
	 */
	// TODO(user): Evaluate whether it makes sense to always piggyback the computation of a
	// HashCode on an existing OutputStream, compared to creating a separate OutputStream that could
	// be (optionally) be combined with another if needed (with something like
	// MultiplexingOutputStream).
	public HashingOutputStream(HashFunction hashFunction, OutputStream out) {
		super(checkNotNull(out));
		this.hasher = checkNotNull(hashFunction.newHasher());
	}

	@Override
	public void write(int b) throws IOException {
		hasher.putByte((byte) b);
		out.write(b);
	}

	@Override
	public void write(byte[] bytes, int off, int len) throws IOException {
		hasher.putBytes(bytes, off, len);
		out.write(bytes, off, len);
	}

	/**
	 * Returns the {@link HashCode} based on the data written to this stream. The result is
	 * unspecified if this method is called more than once on the same instance.
	 */
	@CheckReturnValue
	public HashCode hash() {
		return hasher.hash();
	}

	// Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
	// it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
	// It should flush itself if necessary.
	@Override
	public void close() throws IOException {
		out.close();
	}
}