/*
 * Copyright (C) 2013 The Guava Authors
 *
 * 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 com.google.common.annotations.Beta;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

An InputStream that maintains a hash of the data read from it. 
Author:
Qian Huang
Since:
16.0/**
 * An {@link InputStream} that maintains a hash of the data read from it.
 *
 * @author Qian Huang
 * @since 16.0
 */
@Beta
public final class HashingInputStream extends FilterInputStream {
  private final Hasher hasher;

  
Creates an input stream that hashes using the given HashFunction and delegates all data read from it to the underlying InputStream. 
The InputStream should not be read from before or after the hand-off. /**
   * Creates an input stream that hashes using the given {@link HashFunction} and delegates all data
   * read from it to the underlying {@link InputStream}.
   *
   * <p>The {@link InputStream} should not be read from before or after the hand-off.
   */
  public HashingInputStream(HashFunction hashFunction, InputStream in) {
    super(checkNotNull(in));
    this.hasher = checkNotNull(hashFunction.newHasher());
  }

  
Reads the next byte of data from the underlying input stream and updates the hasher with the
byte read.
/**
   * Reads the next byte of data from the underlying input stream and updates the hasher with the
   * byte read.
   */
  @Override
  @CanIgnoreReturnValue
  public int read() throws IOException {
    int b = in.read();
    if (b != -1) {
      hasher.putByte((byte) b);
    }
    return b;
  }

  
Reads the specified bytes of data from the underlying input stream and updates the hasher with
the bytes read.
/**
   * Reads the specified bytes of data from the underlying input stream and updates the hasher with
   * the bytes read.
   */
  @Override
  @CanIgnoreReturnValue
  public int read(byte[] bytes, int off, int len) throws IOException {
    int numOfBytesRead = in.read(bytes, off, len);
    if (numOfBytesRead != -1) {
      hasher.putBytes(bytes, off, numOfBytesRead);
    }
    return numOfBytesRead;
  }

  
mark() is not supported for HashingInputStream
Returns:
false always/**
   * mark() is not supported for HashingInputStream
   *
   * @return {@code false} always
   */
  @Override
  public boolean markSupported() {
    return false;
  }

  
mark() is not supported for HashingInputStream /** mark() is not supported for HashingInputStream */
  @Override
  public void mark(int readlimit) {}

  
reset() is not supported for HashingInputStream.
Throws:
IOException – this operation is not supported/**
   * reset() is not supported for HashingInputStream.
   *
   * @throws IOException this operation is not supported
   */
  @Override
  public void reset() throws IOException {
    throw new IOException("reset not supported");
  }

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