001/**
002 * Java Web Archive Toolkit - Software to read and validate ARC, WARC
003 * and GZip files. (http://jwat.org/)
004 * Copyright 2011-2012 Netarkivet.dk (http://netarkivet.dk/)
005 *
006 * Licensed under the Apache License, Version 2.0 (the "License");
007 * you may not use this file except in compliance with the License.
008 * You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.jwat.common;
019
020import java.io.FilterInputStream;
021import java.io.IOException;
022import java.io.InputStream;
023
024/**
025 * The standard <code>FileInputStream</code> has a known bug concerning it's
026 * skip method which does not correctly report the number of bytes skipped.
027 * This class provides a simple <code>InputStream</code> wrapper which ensures
028 * all skips are in turn done as reads.
029 *
030 * @author nicl
031 */
032public class InputStreamNoSkip extends FilterInputStream {
033
034    /** Buffer size to use when read skipping. */
035    public static final int SKIP_READ_BUFFER_SIZE = 8192;
036
037    /** Read buffer used by the skip method. */
038    protected byte[] skip_read_buffer = new byte[SKIP_READ_BUFFER_SIZE];
039
040    /**
041     * Construct a <code>InputStream</code> with the skip method
042     * overridden.
043     * @param in input stream to no skip on
044     */
045    public InputStreamNoSkip(InputStream in) {
046        super(in);
047    }
048
049    @Override
050    public long skip(long n) throws IOException {
051        long remaining = n;
052        long skipped = 0;
053        long readLast = 0;
054        while (remaining > 0 && readLast != -1) {
055            remaining -= readLast;
056            skipped += readLast;
057            readLast = read(skip_read_buffer, 0, (int) Math.min(remaining,
058                                                      SKIP_READ_BUFFER_SIZE));
059        }
060        return skipped;
061    }
062
063}