itextpdf-master/itext/src/main/java/com/itextpdf/text/io/WindowRandomAccessSource.java
/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2022 iText Group NV
 * Authors: Kevin Day, Bruno Lowagie, et al.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License version 3
 * as published by the Free Software Foundation with the addition of the
 * following permission added to Section 15 as permitted in Section 7(a):
 * FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
 * ITEXT GROUP. ITEXT GROUP DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
 * OF THIRD PARTY RIGHTS.
 *
 * 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 Affero General License for more
 * details. You should have received a copy of the GNU Affero General License
 * along with this program; if not, see http://www.gnu.org/licenses or write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA, 02110-1301 USA, or download the license from the following URL:
 * http://itextpdf.com/terms-of-use/
 *
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General License.
 *
 * In accordance with Section 7(b) of the GNU Affero General License, a covered
 * work must retain the producer line in every PDF that is created or
 * manipulated using iText.
 *
 * You can be released from the requirements of the license by purchasing a
 * commercial license. Buying such a license is mandatory as soon as you develop
 * commercial activities involving the iText software without disclosing the
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 *
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 */
package com.itextpdf.text.io;

import java.io.IOException;

/**
 * A RandomAccessSource that wraps another RandomAccessSouce and provides a window of it at a specific offset and over
 * a specific length.  Position 0 becomes the offset position in the underlying source.
 * @since 5.3.5
 */
public class WindowRandomAccessSource implements RandomAccessSource {
	/**
	 * The source
	 */
	private final RandomAccessSource source;
	
	/**
	 * The amount to offset the source by
	 */
	private final long offset;
	
	/**
	 * The length
	 */
	private final long length;
	
	/**
	 * Constructs a new OffsetRandomAccessSource that extends to the end of the underlying source
	 * @param source the source
	 * @param offset the amount of the offset to use
	 */
	public WindowRandomAccessSource(RandomAccessSource source, long offset) {
		this(source, offset, source.length() - offset);
	}

	/**
	 * Constructs a new OffsetRandomAccessSource with an explicit length
	 * @param source the source
	 * @param offset the amount of the offset to use
	 * @param length the number of bytes to be included in this RAS
	 */
	public WindowRandomAccessSource(RandomAccessSource source, long offset, long length) {
		this.source = source;
		this.offset = offset;
		this.length = length;
	}
	
	/**
	 * {@inheritDoc}
	 * Note that the position will be adjusted to read from the corrected location in the underlying source
	 */
	public int get(long position) throws IOException {
		if (position >= length) return -1;
		return source.get(offset + position);
	}

	/**
	 * {@inheritDoc}
	 * Note that the position will be adjusted to read from the corrected location in the underlying source
	 */
	public int get(long position, byte[] bytes, int off, int len) throws IOException {
		if (position >= length) 
			return -1;
		
		long toRead = Math.min(len, length - position);
		return source.get(offset + position, bytes, off, (int)toRead);
	}

	/**
	 * {@inheritDoc}
	 * Note that the length will be adjusted to read from the corrected location in the underlying source
	 */
	public long length() {
		return length;
	}

	/**
	 * {@inheritDoc}
	 */
	public void close() throws IOException {
		source.close();
	}

}
