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 excpetion.</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(InputStream in) {
044        super(in);
045    }
046
047    @Override
048    public long skip(long n) throws IOException {
049        return n < 0 ? 0 : read(SKIP_BUFFER, 0, (int) Math.min(n, SKIP_BUFFER_SIZE));
050    }
051}