itextpdf-master/itext/src/main/java/com/itextpdf/text/io/GetBufferedRandomAccessSource.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
 * source code of your own applications. These activities include: offering paid
 * services to customers as an ASP, serving PDFs on the fly in a web
 * application, shipping iText with a closed source product.
 *
 * For more information, please contact iText Software Corp. at this address:
 * sales@itextpdf.com
 */
package com.itextpdf.text.io;

import java.io.IOException;

/**
 * @since 5.3.5
 */
public class GetBufferedRandomAccessSource implements RandomAccessSource {
	/**
	 * The source
	 */
	private final RandomAccessSource source;
	
	private final byte[] getBuffer;
	private long getBufferStart = -1;
	private long getBufferEnd = -1;
	
	/**
	 * Constructs a new OffsetRandomAccessSource
	 * @param source the source
	 */
	public GetBufferedRandomAccessSource(RandomAccessSource source) {
		this.source = source;
		
		this.getBuffer = new byte[(int)Math.min(Math.max(source.length()/4, 1), (long)4096)];
		this.getBufferStart = -1;
		this.getBufferEnd = -1;

	}

	/**
	 * {@inheritDoc}
	 */
	public int get(long position) throws IOException {
		if (position < getBufferStart || position > getBufferEnd){
			int count = source.get(position, getBuffer, 0, getBuffer.length);
			if (count == -1)
				return -1;
			getBufferStart = position;
			getBufferEnd = position + count - 1;
		}
		int bufPos = (int)(position-getBufferStart);
		return 0xff & getBuffer[bufPos];
	}

	/**
	 * {@inheritDoc}
	 */
	public int get(long position, byte[] bytes, int off, int len) throws IOException {
		return source.get(position, bytes, off, len);
	}

	/**
	 * {@inheritDoc}
	 */
	public long length() {
		return source.length();
	}

	/**
	 * Does nothing - the underlying source is not closed
	 */
	public void close() throws IOException {
		source.close();
		getBufferStart = -1;
		getBufferEnd = -1;
	}

}
