/*
 * 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
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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;
    }
}