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Open source (GPL) Java utilities maintained by Stephen Ostermiller with help from many contributors.
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/*
 * Input stream wrapper with a byte limit.
 * Copyright (C) 2004 Stephen Ostermiller
 * http://ostermiller.org/contact.pl?regarding=Java+Utilities
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * See COPYING.TXT for details.
 */
package com.Ostermiller.util;

import java.io.*;

/**
 * An input stream wrapper that will read only a set number of bytes from the
 * underlying stream.
 *
 * @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
 * @since ostermillerutils 1.04.00
 */
public class SizeLimitInputStream extends InputStream {

	/**
	 * The input stream that is being protected.
	 * All methods should be forwarded to it,
	 * after checking the size that has been read.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	protected InputStream in;

	/**
	 * The number of bytes to read at most from this
	 * Stream.  Read methods should
	 * check to ensure that bytesRead never
	 * exceeds maxBytesToRead.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	protected long maxBytesToRead = 0;

	/**
	 * The number of bytes that have been read
	 * from this stream.  Read methods should
	 * check to ensure that bytesRead never
	 * exceeds maxBytesToRead.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	protected long bytesRead = 0;

	/**
	 * The number of bytes that have been read
	 * from this stream since mark() was called.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	protected long bytesReadSinceMark = 0;

	/**
	 * The number of bytes the user has request
	 * to have been marked for reset.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	protected long markReadLimitBytes = -1;

	/**
	 * Get the number of bytes actually read
	 * from this stream.
	 *
	 * @return number of bytes that have already been taken from this stream.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public long getBytesRead(){
		return bytesRead;
	}

	/**
	 * Get the maximum number of bytes left to read
	 * before the limit (set in the constructor) is reached.
	 *
	 * @return The number of bytes that (at a maximum) are left to be taken from this stream.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public long getBytesLeft(){
		return maxBytesToRead - bytesRead;
	}

	/**
	 * Tell whether the number of bytes specified
	 * in the constructor have been read yet.
	 *
	 * @return true iff the specified number of bytes have all been read.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public boolean allBytesRead(){
		return getBytesLeft() == 0;
	}

	/**
	 * Get the number of total bytes (including bytes already read)
	 * that can be read from this stream (as set in the constructor).
	 * @return Maximum bytes that can be read until the size limit runs out
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public long getMaxBytesToRead(){
		return maxBytesToRead;
	}

	/**
	 * Create a new size limit input stream from
	 * another stream given a size limit.
	 *
	 * @param in The input stream.
	 * @param maxBytesToRead the max number of bytes to allow to be read from the underlying stream.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public SizeLimitInputStream(InputStream in, long maxBytesToRead){
		this.in = in;
		this.maxBytesToRead = maxBytesToRead;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public int read() throws IOException {
		if (bytesRead >= maxBytesToRead){
			return -1;
		}
		int b = in.read();
		if(b != -1){
			bytesRead++;
			bytesReadSinceMark++;
		}
		return b;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public int read(byte[] b) throws IOException {
		return this.read(b, 0, b.length);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public int read(byte[] b, int off, int len) throws IOException {
		if (bytesRead >= maxBytesToRead){
			return -1;
		}
		long bytesLeft = getBytesLeft();
		if (len > bytesLeft){
			len = (int)bytesLeft;
		}
		int bytesJustRead = in.read(b, off, len);
		bytesRead += bytesJustRead;
		bytesReadSinceMark += bytesJustRead;
		return bytesJustRead;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public long skip(long n) throws IOException {
		if (bytesRead >= maxBytesToRead){
			return -1;
		}
		long bytesLeft = getBytesLeft();
		if (n > bytesLeft){
			n = bytesLeft;
		}
		return in.skip(n);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public int available() throws IOException {
		int available = in.available();
		long bytesLeft = getBytesLeft();
		if (available > bytesLeft){
			available = (int)bytesLeft;
		}
		return available;
	}

	/**
	 * Close this stream and underlying streams.
	 * Calling this method may make data on the
	 * underlying stream unavailable.
	 * 
	 * Consider wrapping this stream in a NoCloseStream
	 * so that clients can
	 * call close() with no effect.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public void close() throws IOException {
		in.close();
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public void mark(int readlimit){
		if (in.markSupported()){
			markReadLimitBytes = readlimit;
			bytesReadSinceMark = 0;
			in.mark(readlimit);
		}
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public void reset() throws IOException {
		if (in.markSupported() && bytesReadSinceMark <= markReadLimitBytes){
			bytesRead -= bytesReadSinceMark;
			in.reset();
			bytesReadSinceMark = 0;
		}
	}

	/**
	 * {@inheritDoc}
	 */
	@Override public boolean markSupported(){
		return in.markSupported();
	}
}