/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

/* $Id: SubInputStream.java 1610846 2014-07-15 20:44:18Z vhennebert $ */

package org.apache.xmlgraphics.util.io;

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

This class is a FilterInputStream descendant that reads from an underlying InputStream
up to a defined number of bytes or the end of the underlying stream. Closing this InputStream
will not result in the underlying InputStream to be closed, too.

This InputStream can be used to read chunks from a larger file of which the length is
known in advance.
/**
 * This class is a FilterInputStream descendant that reads from an underlying InputStream
 * up to a defined number of bytes or the end of the underlying stream. Closing this InputStream
 * will not result in the underlying InputStream to be closed, too.
 * <p>
 * This InputStream can be used to read chunks from a larger file of which the length is
 * known in advance.
 */
public class SubInputStream extends FilterInputStream {

    
Indicates the number of bytes remaining to be read from the underlying InputStream. /** Indicates the number of bytes remaining to be read from the underlying InputStream. */
    private long bytesToRead;

    
Indicates whether the underlying stream should be closed when the close() method is called. /**
     * Indicates whether the underlying stream should be closed when the {@link #close()} method
     * is called.
     */
    private boolean closeUnderlying;

    
Creates a new SubInputStream.
Params:
in – the InputStream to read from
maxLen – the maximum number of bytes to read from the underlying InputStream until
              the end-of-file is signalled.
closeUnderlying – true if the underlying stream should be closed when the close() method is called./**
     * Creates a new SubInputStream.
     * @param in the InputStream to read from
     * @param maxLen the maximum number of bytes to read from the underlying InputStream until
     *               the end-of-file is signalled.
     * @param closeUnderlying true if the underlying stream should be closed when the
     *               {@link #close()} method is called.
     */
    public SubInputStream(InputStream in, long maxLen, boolean closeUnderlying) {
        super(in);
        this.bytesToRead = maxLen;
        this.closeUnderlying = closeUnderlying;
    }

    
Creates a new SubInputStream. The underlying stream is not closed, when close() is called.
Params:
in – the InputStream to read from
maxLen – the maximum number of bytes to read from the underlying InputStream until
              the end-of-file is signalled./**
     * Creates a new SubInputStream. The underlying stream is not closed, when close() is called.
     * @param in the InputStream to read from
     * @param maxLen the maximum number of bytes to read from the underlying InputStream until
     *               the end-of-file is signalled.
     */
    public SubInputStream(InputStream in, long maxLen) {
        this(in, maxLen, false);
    }

    
{@inheritDoc} /** {@inheritDoc} */
    public int read() throws IOException {
        if (bytesToRead > 0) {
            int result = super.read();
            if (result >= 0) {
                bytesToRead--;
                return result;
            } else {
                return -1;
            }
        } else {
            return -1;
        }
    }

    
{@inheritDoc} /** {@inheritDoc} */
    public int read(byte[] b, int off, int len) throws IOException {
        if (bytesToRead == 0) {
            return -1;
        }
        int effRead = (int)Math.min(bytesToRead, len);
        //cast to int is safe because len can never be bigger than Integer.MAX_VALUE

        int result = super.read(b, off, effRead);
        if (result >= 0) {
            bytesToRead -= result;
        }
        return result;
    }

    
{@inheritDoc} /** {@inheritDoc} */
    public long skip(long n) throws IOException {
        long effRead = Math.min(bytesToRead, n);
        long result = super.skip(effRead);
        bytesToRead -= result;
        return result;
    }

    
{@inheritDoc} /** {@inheritDoc} */
    public void close() throws IOException {
        this.bytesToRead = 0;
        if (this.closeUnderlying) {
            super.close();
        }
    }
}