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/**
 * Java Web Archive Toolkit - Software to read and validate ARC, WARC
 * and GZip files. (http://jwat.org/)
 * Copyright 2011-2012 Netarkivet.dk (http://netarkivet.dk/)
 *
 * 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 org.jwat.common;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * The standard FileInputStream has a known bug concerning it's
 * skip method which does not correctly report the number of bytes skipped.
 * This class provides a simple InputStream wrapper which ensures
 * all skips are in turn done as reads.
 *
 * @author nicl
 */
public class InputStreamNoSkip extends FilterInputStream {

    /** Buffer size to use when read skipping. */
    public static final int SKIP_READ_BUFFER_SIZE = 8192;

    /** Read buffer used by the skip method. */
    protected byte[] skip_read_buffer = new byte[SKIP_READ_BUFFER_SIZE];

    /**
     * Construct a InputStream with the skip method
     * overridden.
     * @param in input stream to no skip on
     */
    public InputStreamNoSkip(InputStream in) {
        super(in);
    }

    @Override
    public long skip(long n) throws IOException {
        long remaining = n;
        long skipped = 0;
        long readLast = 0;
        while (remaining > 0 && readLast != -1) {
            remaining -= readLast;
            skipped += readLast;
            readLast = read(skip_read_buffer, 0, (int) Math.min(remaining,
                                                      SKIP_READ_BUFFER_SIZE));
        }
        return skipped;
    }

}