    001/*
    002 *  Licensed to the Apache Software Foundation (ASF) under one or more
    003 *  contributor license agreements.  See the NOTICE file distributed with
    004 *  this work for additional information regarding copyright ownership.
    005 *  The ASF licenses this file to You under the Apache License, Version 2.0
    006 *  (the "License"); you may not use this file except in compliance with
    007 *  the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 *
    017 */
    018package org.apache.commons.compress.utils;
    019
    020import java.io.FilterInputStream;
    021import java.io.IOException;
    022import java.io.InputStream;
    023
    024/**
    025 * A wrapper that overwrites {@link #skip} and delegates to {@link #read} instead.
    026 *
    027 * <p>Some implementations of {@link InputStream} implement {@link
    028 * InputStream#skip} in a way that throws an exception if the stream
    029 * is not seekable - {@link System#in System.in} is known to behave
    030 * that way. For such a stream it is impossible to invoke skip at all
    031 * and you have to read from the stream (and discard the data read)
    032 * instead. Skipping is potentially much faster than reading so we do
    033 * want to invoke {@code skip} when possible. We provide this class so
    034 * you can wrap your own {@link InputStream} in it if you encounter
    035 * problems with {@code skip} throwing an exception.</p>
    036 *
    037 * @since 1.17
    038 */
    039public class SkipShieldingInputStream extends FilterInputStream {
    040    private static final int SKIP_BUFFER_SIZE = 8192;
    041    // we can use a shared buffer as the content is discarded anyway
    042    private static final byte[] SKIP_BUFFER = new byte[SKIP_BUFFER_SIZE];
    043    public SkipShieldingInputStream(final InputStream in) {
    044        super(in);
    045    }
    046
    047    @Override
    048    public long skip(final long n) throws IOException {
    049        return n < 0 ? 0 : read(SKIP_BUFFER, 0, (int) Math.min(n, SKIP_BUFFER_SIZE));
    050    }
    051}