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TwelveMonkeys Common I/O support classes.
There is a newer version: 3.12.0
/*
 * Copyright (c) 2008, Harald Kuhr
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * * Neither the name of the copyright holder nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.twelvemonkeys.io;

import com.twelvemonkeys.lang.Validate;

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

/**
 * An {@code InputStream} reading up to a specified number of bytes from an
 * underlying stream.
 *
 * @author Harald Kuhr
 * @version $Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/io/SubStream.java#2 $
 */
public final class SubStream extends FilterInputStream {
    private long bytesLeft;
    private int markLimit;

    /**
     * Creates a {@code SubStream} of the given {@code pStream}.
     *
     * @param pStream the underlying input stream
     * @param pLength maximum number of bytes to read drom this stream
     */
    public SubStream(final InputStream pStream, final long pLength) {
        super(Validate.notNull(pStream, "stream"));
        bytesLeft = pLength;
    }

    /**
     * Marks this stream as closed.
     * This implementation does not close the underlying stream.
     */
    @Override
    public void close() throws IOException {
        // NOTE: Do not close the underlying stream
        while (bytesLeft > 0) {
            //noinspection ResultOfMethodCallIgnored
            skip(bytesLeft);
        }
    }

    @Override
    public int available() throws IOException {
        return (int) Math.min(super.available(), bytesLeft);
    }

    @Override
    public void mark(int pReadLimit) {
        super.mark(pReadLimit);// This either succeeds or does nothing...
        markLimit = pReadLimit;
    }

    @Override
    public void reset() throws IOException {
        super.reset();// This either succeeds or throws IOException
        bytesLeft += markLimit;
    }

    @Override
    public int read() throws IOException {
        if (bytesLeft-- <= 0) {
            return -1;
        }
        return super.read();
    }

    @Override
    public final int read(byte[] pBytes) throws IOException {
        return read(pBytes, 0, pBytes.length);
    }

    @Override
    public int read(final byte[] pBytes, final int pOffset, final int pLength) throws IOException {
        if (bytesLeft <= 0) {
            return -1;
        }

        int read = super.read(pBytes, pOffset, (int) findMaxLen(pLength));
        bytesLeft = read < 0 ? 0 : bytesLeft - read;
        return read;
    }

    /**
     * Finds the maximum number of bytes we can read or skip, from this stream.
     *
     * @param pLength the requested length
     * @return the maximum number of bytes to read
     */
    private long findMaxLen(long pLength) {
        if (bytesLeft < pLength) {
            return (int) Math.max(bytesLeft, 0);
        }
        else {
            return pLength;
        }
    }

    @Override
    public long skip(long pLength) throws IOException {
        long skipped = super.skip(findMaxLen(pLength));// Skips 0 or more, never -1
        bytesLeft -= skipped;
        return skipped;
    }
}