CountdownInputStream.java

/* Copyright (c) 2001-2011, The HSQL Development Group
 * 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.
 *
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 * 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
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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package org.hsqldb.lib;

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

// fredt@users - 1.9.0 corrected read(byte[], int, int)

/**
 * Counts down from a specified value the number of bytes actually read
 * from the wrapped InputStream. <p>
 *
 * Returns minus one (-1) early from readXXX methods if the count
 * down reaches zero (0) before the end of the wrapped InputStream
 * is encountered. <p>
 *
 * This class is especially useful when a fixed number of bytes is to be read
 * from an InputStream that is in turn to be used as the source for an
 * {@link java.io.InputStreamReader InputStreamReader}.
 *
 * @author boucherb@users
 * @version 2.1.1
 * @since 1.9.0
 */
public final class CountdownInputStream extends InputStream {

    private long        m_count;
    private InputStream m_input;

    public CountdownInputStream(final InputStream is) {
        m_input = is;
    }

    public int read() throws IOException {

        if (m_count <= 0) {
            return -1;
        }

        final int b = m_input.read();

        if (b >= 0) {
            m_count--;
        }

        return b;
    }

    public int read(final byte[] buf) throws IOException {

        if (buf == null) {
            throw new NullPointerException();
        } 

        if (m_count <= 0) {
            return -1;
        }

        int len = buf.length;

        if (len > m_count) {
            len = (int) m_count;
        }

        final int r = m_input.read(buf, 0, len);

        if (r > 0) {
            m_count -= r;
        }

        return r;
    }

    public int read(final byte[] buf, final int off,
                    int len) throws IOException {

        if (buf == null) {
            throw new NullPointerException();
        } 

        if (m_count <= 0) {
            return -1;
        }

        if (len > m_count) {
            len = (int) m_count;
        }

        final int r = m_input.read(buf, off, len);

        if (r > 0) {
            m_count -= r;
        }

        return r;
    }

    public void close() throws IOException {
        m_input.close();
    }

    public int available() throws IOException {
        return Math.min(m_input.available(),
                        (int) Math.min(Integer.MAX_VALUE, m_count));
    }

    public long skip(long count) throws IOException {
        return (count <= 0) ? 0
                            : m_input.skip(Math.min(m_count, count));
    }

    public long getCount() {
        return m_count;
    }

    public void setCount(long count) {
        m_count = count;
    }
}