/*

 * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

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 */

package java.util.zip;

import java.io.FilterInputStream;

import java.io.InputStream;

import java.io.IOException;

/**

 * An input stream that also maintains a checksum of the data being read.

 * The checksum can then be used to verify the integrity of the input data.

 *

 * @see         Checksum

 * @author      David Connelly

 * @since 1.1

 */

public class CheckedInputStream extends FilterInputStream {

    private Checksum cksum;

    /**

     * Creates an input stream using the specified Checksum.

     * @param in the input stream

     * @param cksum the Checksum

     */

    public CheckedInputStream(InputStream in, Checksum cksum) {

        super(in);

        this.cksum = cksum;

    }

    /**

     * Reads a byte. Will block if no input is available.

     * @return the byte read, or -1 if the end of the stream is reached.

     * @throws    IOException if an I/O error has occurred

     */

    public int read() throws IOException {

        int b = in.read();

        if (b != -1) {

            cksum.update(b);

        }

        return b;

    }

    /**

     * Reads into an array of bytes. If {@code len} is not zero, the method

     * blocks until some input is available; otherwise, no

     * bytes are read and {@code 0} is returned.

     * @param buf the buffer into which the data is read

     * @param off the start offset in the destination array {@code b}

     * @param len the maximum number of bytes read

     * @return    the actual number of bytes read, or -1 if the end

     *            of the stream is reached.

     * @throws     NullPointerException If {@code buf} is {@code null}.

     * @throws     IndexOutOfBoundsException If {@code off} is negative,

     * {@code len} is negative, or {@code len} is greater than

     * {@code buf.length - off}

     * @throws    IOException if an I/O error has occurred

     */

    public int read(byte[] buf, int off, int len) throws IOException {

        len = in.read(buf, off, len);

        if (len != -1) {

            cksum.update(buf, off, len);

        }

        return len;

    }

    /**

     * Skips specified number of bytes of input.

     * @param n the number of bytes to skip

     * @return the actual number of bytes skipped

     * @throws    IOException if an I/O error has occurred

     */

    public long skip(long n) throws IOException {

        byte[] buf = new byte[512];

        long total = 0;

        while (total < n) {

            long len = n - total;

            len = read(buf, 0, len < buf.length ? (int)len : buf.length);

            if (len == -1) {

                return total;

            }

            total += len;

        }

        return total;

    }

    /**

     * Returns the Checksum for this input stream.

     * @return the Checksum value

     */

    public Checksum getChecksum() {

        return cksum;

    }

}