android-platform-libcore/luni/src/main/java/java/util/zip/CheckedOutputStream.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 java.util.zip;

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

/**
 * The {@code CheckedOutputStream} class is used to maintain a running checksum
 * of all data written to a stream. The purpose of this checksum is to establish
 * data integrity, by publishing the checksum to other parties wanting to read
 * the non corrupted data.
 */
public class CheckedOutputStream extends java.io.FilterOutputStream {

    private final Checksum check;

    /**
     * Constructs a new {@code CheckedOutputStream} on {@code OutputStream}
     * {@code os}. The checksum is calculated using the algorithm implemented
     * by {@code csum}.
     *
     * @param os
     *            the output stream to calculate checksum for.
     * @param cs
     *            an entity implementing the checksum algorithm.
     */
    public CheckedOutputStream(OutputStream os, Checksum cs) {
        super(os);
        check = cs;
    }

    /**
     * Returns the checksum calculated on the stream read so far.
     *
     * @return the updated checksum.
     */
    public Checksum getChecksum() {
        return check;
    }

    /**
     * Writes the specified byte to the underlying stream. The checksum is
     * updated with {@code val}.
     *
     * @param val
     *            the data value to written to the output stream.
     * @throws IOException
     *             if an IO error has occurred.
     */
    @Override
    public void write(int val) throws IOException {
        out.write(val);
        check.update(val);
    }

    /**
     * Writes n bytes of data from {@code buf} starting at offset {@code off} to
     * the underlying stream. The checksum is updated with the bytes written.
     *
     * @param buf
     *            data written to the output stream.
     * @param off
     *            the offset to start reading the data from {@code buf} written
     *            to the output stream.
     * @param nbytes
     *            number of bytes to write to the output stream.
     * @throws IOException
     *             if an IO error has occurred.
     */
    @Override
    public void write(byte[] buf, int off, int nbytes) throws IOException {
        out.write(buf, off, nbytes);
        check.update(buf, off, nbytes);
    }
}