src/main/java/org/eclipse/mdm/openatfx/mdf/mdf4/ATBLOCK.java - mdmbl/org.eclipse.mdm.openatfx.mdf - Git at Google

 /********************************************************************************
  * Copyright (c) 2015-2018 Contributors to the Eclipse Foundation
  *
  * See the NOTICE file(s) distributed with this work for additional
  * information regarding copyright ownership.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0 which is available at
  * http://www.eclipse.org/legal/epl-2.0.
  *
  * SPDX-License-Identifier: EPL-2.0
  *
  ********************************************************************************/


 package org.eclipse.mdm.openatfx.mdf.mdf4;

 import static java.lang.Math.min;
 import static java.nio.file.StandardOpenOption.CREATE_NEW;

 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.channels.SeekableByteChannel;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.security.DigestInputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;

 import org.asam.ods.T_ExternalReference;

 /**
  * <p>
  * THE ATTACHMENT BLOCK <code>ATBLOCK</code>
  * </p>
  * The data section of the ATBLOCK contains attachments (binary data)
  *
  * @author Christian Rechner, Tobias Leemann
  */
 class ATBLOCK extends BLOCK {

 	public static String BLOCK_ID = "##AT";

 	private long lnkAtNext;

 	private long lnkTxFilename;

 	private long lnkTxMIMEtype;

 	private long lnkMdComment;

 	private int flags;

 	private int creatorIndex;

 	private byte[] md5CheckSum;

 	private long origSize;

 	private long embeddedSize;

 	/**
 	 * Constructor.
 	 *
 	 * @param sbc
 	 *            The byte channel pointing to the MDF file.
 	 * @param pos
 	 *            The position of the block within the MDF file.
 	 */
 	private ATBLOCK(SeekableByteChannel sbc, long pos) {
 		super(sbc, pos);
 	}

 	public long getLnkAtNext() {
 		return lnkAtNext;
 	}

 	public void setLnkAtNext(long lnkAtNext) {
 		this.lnkAtNext = lnkAtNext;
 	}

 	public long getLnkTxFilename() {
 		return lnkTxFilename;
 	}

 	public void setLnkTxFilename(long lnkTxFilename) {
 		this.lnkTxFilename = lnkTxFilename;
 	}

 	public long getLnkTxMIMEtype() {
 		return lnkTxMIMEtype;
 	}

 	public void setLnkTxMIMEtype(long lnkTxMIMEtype) {
 		this.lnkTxMIMEtype = lnkTxMIMEtype;
 	}

 	public long getLnkMdComment() {
 		return lnkMdComment;
 	}

 	public void setLnkMdComment(long lnkMdComment) {
 		this.lnkMdComment = lnkMdComment;
 	}

 	public int getFlags() {
 		return flags;
 	}

 	public void setFlags(int flags) {
 		this.flags = flags;
 	}

 	public int getCreatorIndex() {
 		return creatorIndex;
 	}

 	public void setCreatorIndex(int creatorIndex) {
 		this.creatorIndex = creatorIndex;
 	}

 	public byte[] getMd5CheckSum() {
 		return md5CheckSum;
 	}

 	public void setMd5CheckSum(byte[] md5CheckSum) {
 		this.md5CheckSum = md5CheckSum;
 	}

 	public long getOrigSize() {
 		return origSize;
 	}

 	public void setOrigSize(long origSize) {
 		this.origSize = origSize;
 	}

 	public long getEmbeddedSize() {
 		return embeddedSize;
 	}

 	public void setEmbeddedSize(long embeddedSize) {
 		this.embeddedSize = embeddedSize;
 	}

 	public ATBLOCK getAtNextBlock() throws IOException {
 		if (lnkAtNext > 0) {
 			return ATBLOCK.read(sbc, lnkAtNext);
 		}
 		return null;
 	}

 	public TXBLOCK getTxFilennameBlock() throws IOException {
 		if (lnkTxFilename > 0) {
 			return TXBLOCK.read(sbc, lnkTxFilename);
 		}
 		return null;
 	}

 	public TXBLOCK getTxMIMETypeBlock() throws IOException {
 		if (lnkTxMIMEtype > 0) {
 			return TXBLOCK.read(sbc, lnkTxMIMEtype);
 		}
 		return null;
 	}

 	public TXBLOCK getTxCommentBlock() throws IOException {
 		if (lnkMdComment > 0) {
 			return TXBLOCK.read(sbc, lnkMdComment);
 		}
 		return null;
 	}

 	public MDBLOCK getMdCommentBlock() throws IOException {
 		if (lnkMdComment > 0) {
 			return MDBLOCK.read(sbc, lnkMdComment);
 		}
 		return null;
 	}

 	/**
 	 * {@inheritDoc}
 	 */
 	@Override
 	public String toString() {
 		return "DTBLOCK [pos=" + getPos() + "]";
 	}

 	/**
 	 * Reads a SDBLOCK from the channel starting at current channel position.
 	 *
 	 * @param channel
 	 *            The channel to read from.
 	 * @param pos
 	 *            The position
 	 * @return The block data.
 	 * @throws IOException
 	 *             The exception.
 	 */
 	public static ATBLOCK read(SeekableByteChannel channel, long pos) throws IOException {
 		ATBLOCK block = new ATBLOCK(channel, pos);

 		// read block header
 		ByteBuffer bb = ByteBuffer.allocate(24 + 32 + 40); // 24 Head 32 Links
 															// 40 Data
 		bb.order(ByteOrder.LITTLE_ENDIAN);
 		channel.position(pos);
 		channel.read(bb);
 		bb.rewind();

 		// CHAR 4: Block type identifier
 		block.setId(MDF4Util.readCharsISO8859(bb, 4));
 		if (!block.getId().equals(BLOCK_ID)) {
 			throw new IOException("Wrong block type - expected '" + BLOCK_ID + "', found '" + block.getId() + "'");
 		}

 		// BYTE 4: Reserved used for 8-Byte alignment
 		bb.get(new byte[4]);

 		// UINT64: Length of block
 		block.setLength(MDF4Util.readUInt64(bb));

 		// UINT64: Number of links
 		block.setLinkCount(MDF4Util.readUInt64(bb));

 		// LINK 1 Pointer to next ATBLOCK (NIL allowed)
 		block.setLnkAtNext(MDF4Util.readLink(bb));

 		// LINK 1 Pointer to Text Block with Filename (NIL allowed)
 		block.setLnkTxFilename(MDF4Util.readLink(bb));

 		// LINK 1 Pointer to Text Block with MIME Type (TXBLOCK) (NIL allowed)
 		block.setLnkTxMIMEtype(MDF4Util.readLink(bb));

 		// LINK 1 Pointer to comment Block MDBLOCK (NIL allowed)
 		block.setLnkMdComment(MDF4Util.readLink(bb));

 		// UINT16 flags
 		block.setFlags(MDF4Util.readUInt16(bb));

 		// UINT16 Creator Index
 		block.setCreatorIndex(MDF4Util.readUInt16(bb));

 		// BYTE 4: Reserved used for 8-Byte alignment
 		bb.get(new byte[4]);

 		// BYTE 16: MD5 Checksum
 		byte[] md5sum = new byte[16];
 		bb.get(md5sum);
 		block.setMd5CheckSum(md5sum);

 		// UINT64 OriginalSize
 		block.setOrigSize(MDF4Util.readUInt64(bb));

 		// UINT64 EmbeddedSize
 		block.setEmbeddedSize(MDF4Util.readUInt64(bb));

 		return block;
 	}

 	/**
 	 * Converts this AT Block and all linked one into dedicated
 	 * external links, where each embedded file is written to disc.
 	 *
 	 * @param target  the working directory
 	 * @param subDir  name of the target sub directory for exporting embedded files, may be empty
 	 * @return  all external links, neither null nor empty
 	 * @throws IOException  in case of errors
 	 */
 	public T_ExternalReference[] toExtRefs(Path target, String subDir) throws IOException {
 		List<T_ExternalReference> extRefs = new ArrayList<>();
 		ATBLOCK block = this;

 		int count = 0;
 		while (block != null) {
 			boolean embedded = (block.flags & 1) != 0;

 			Path file;
 			if (embedded) {
 				file = block.exportEmbedded(subDir.isEmpty() ? target : target.resolve(subDir), ++count);
 			} else {
 				file = block.getFilePath(target, true);
 			}

 			block.checkMD5(file);

 			extRefs.add(new T_ExternalReference(block.getDescription(), block.getMimeType(file),
 					target.relativize(file).toString()));
 			block = block.getAtNextBlock();
 		}

 		return extRefs.stream().toArray(T_ExternalReference[]::new);
 	}

 	/**
 	 * Returns the file MIME type if available.
 	 *
 	 * @return  the MIME type, may be empty but not null
 	 * @throws IOException  in case of errors
 	 */
 	private String getMimeType(Path file) throws IOException {
 		String value = Files.probeContentType(file);
 		if (lnkTxMIMEtype > 0) {
 			value = getTxMIMETypeBlock().getTxData();
 		}

 		return value == null ? "application/octet-stream" : value.trim();
 	}

 	/**
 	 * Returns the file description if available.
 	 *
 	 * @return  the file description, may be empty but not null
 	 * @throws IOException  in case of errors
 	 */
 	private String getDescription() throws IOException {
 		if (lnkMdComment < 1) {
 			return "";
 		}

 		String value = null;
 		try {
 			value = getMdCommentBlock().getMdData();
 		} catch (IOException e) {
 			value = getTxCommentBlock().getTxData();
 		}

 		return value == null ? "" : value.trim();
 	}

 	/**
 	 * Exports given embedded stream into given file.
 	 *
 	 * @param target  the target file path, not null and must not exist yet
 	 * @param id  the internal files count, used to index files whose name is unknown
 	 * @return  the newly created file path, not null
 	 * @throws IOException  in case of errors
 	 */
 	private Path exportEmbedded(Path target, int id) throws IOException {
 		if ((flags & 1) == 0) {
 			throw new IllegalStateException("file is not embedded");
 		}

 		Path file;
 		if (lnkTxFilename > 0) {
 			file = getFilePath(target, false);
 		} else {
 			file = target.resolve("embedded_" + id + ".bin");
 		}

 		Files.createDirectories(file.getParent());
 		EmbeddedStream embeddedStream = new EmbeddedStream(sbc, getPos() + 96, getEmbeddedSize());
 		boolean compressed = (flags & 1 << 1) != 0;
 		if (compressed) {
 			unzip(embeddedStream, file);
 		} else {
 			Files.copy(embeddedStream, file);
 		}

 		return file;
 	}

 	/**
 	 * Exports given compressed embedded inputs stream into given file target.
 	 *
 	 * @param embeddedStream  the embedded input stream, not null
 	 * @param target  the target file path, not null and must not exist yet
 	 * @throws IOException  in case of errors
 	 */
 	private void unzip(EmbeddedStream embeddedStream, Path target) throws IOException {
 		try (InputStream is = embeddedStream; OutputStream os = Files.newOutputStream(target, CREATE_NEW)) {
 			Inflater inflater =  new Inflater();

 			byte[] writeBuffer = new byte[8192];
 			byte[] readBuffer = new byte[8192];
 			int written;
 			int read = 0;
 			while(read > -1 && !inflater.finished()) {
 				while(inflater.needsInput() && (read = is.read(readBuffer)) > 0) {
 					// feed iflater as long as it needs input and as long as there is data available
 					inflater.setInput(readBuffer, 0, read);
 				}

 				while ((written = inflater.inflate(writeBuffer)) > 0) {
 					// write decompressed bytes as long inflater is satisfied
 					os.write(writeBuffer, 0, written);
 				}
 			}

 			os.flush();
 		} catch (DataFormatException e) {
 			throw new IOException("failed to decompress embedded file", e);
 		}
 	}

 	/**
 	 * Returns the file path.
 	 *
 	 * @param target  the working directory
 	 * @param exists  if true, the returned file path must exist
 	 * @return  the target file path, not null
 	 * @throws IOException  in case of errors
 	 */
 	private Path getFilePath(Path target, boolean exists) throws IOException {
 		if (lnkTxFilename < 1) {
 			throw new IllegalStateException("file name TXBLOCK is not set");
 		}

 		TXBLOCK fileNameTX = getTxFilennameBlock();
 		Path file = Paths.get(fileNameTX.getTxData());
 		if (!file.isAbsolute()) {
 			file = target.resolve(fileNameTX.getTxData());
 		}

 		if (exists && !file.toFile().exists()) {
 			throw new IOException("file '" + file + "' not found.");
 		}

 		return file;
 	}

 	/**
 	 * Compares calculated MD5 checksum with the stored one.
 	 *
 	 * @param file  the file path, not null
 	 * @throws IOException  in case of errors
 	 */
 	private void checkMD5(Path file) throws IOException {
 		if ((flags & 1 << 2) == 0) {
 			// checksum is not available => skip!
 			return;
 		}
 		try {
 			MessageDigest md = MessageDigest.getInstance("MD5");
 			try (DigestInputStream is = new DigestInputStream(Files.newInputStream(file), md)) {
 				byte[] buffer = new byte[1024];
 				while (is.read(buffer) != -1);
 				byte[] calculated = is.getMessageDigest().digest();
 				if (!Arrays.equals(calculated, getMd5CheckSum())) {
 					throw new IOException("checksum validation failed for file '" + file + "'");
 				}
 			}
 		} catch (NoSuchAlgorithmException e) {
 			throw new IOException("checksum algorithm 'MD5' not found.");
 		}
 	}

 	/**
 	 * Embedded input stream implementation.
 	 */
 	private static final class EmbeddedStream extends InputStream {

 		private final SeekableByteChannel sbc;
 		private final long length0;

 		private long current = 0;

 		/**
 		 * Constructor.
 		 *
 		 * @param sbc  the channel source for byte access, not null
 		 * @param start  the channel position this stream internally starts from
 		 * @param length  the number of bytes this stream will provide
 		 * @throws IOException  in case of errors
 		 */
 		public EmbeddedStream(SeekableByteChannel sbc, long start, long length) throws IOException {
 			this.sbc = sbc;
 			this.length0 = length;

 			sbc.position(start);
 		}

 		/**
 		 * {@inheritDoc}
 		 */
 		@Override
 		public int read() throws IOException {
 			if (current >= length0) {
 				return -1;
 			}

 			ByteBuffer buffer = ByteBuffer.allocate(1);
 			int read = sbc.read(buffer);
 			if (read > 0) {
 				current += read;
 				buffer.rewind();
 				return buffer.getInt();
 			} else {
 				return -1;
 			}
 		}

 		/**
 		 * {@inheritDoc}
 		 */
 		@Override
 		public int read(byte[] bytes) throws IOException {
 			if (current >= length0) {
 				return -1;
 			}

 			int read = (int) min(sbc.read(ByteBuffer.wrap(bytes)), length0 - current);
 			if (read > 0) {
 				current += read;
 				return read;
 			} else {
 				return -1;
 			}
 		}

 		/**
 		 * {@inheritDoc}
 		 */
 		@Override
 		public int read(byte[] bytes, int offset, int length) throws IOException {
 			if (current >= length0) {
 				return -1;
 			}

 			int read = (int) min(sbc.read(ByteBuffer.wrap(bytes, offset, length)), length0 - current);
 			if (read > 0) {
 				current += read;
 				return read;
 			} else {
 				return -1;
 			}
 		}

 	}
 }
	/********************************************************************************
	* Copyright (c) 2015-2018 Contributors to the Eclipse Foundation
	*
	* See the NOTICE file(s) distributed with this work for additional
	* information regarding copyright ownership.
	*
	* This program and the accompanying materials are made available under the
	* terms of the Eclipse Public License v. 2.0 which is available at
	* http://www.eclipse.org/legal/epl-2.0.
	*
	* SPDX-License-Identifier: EPL-2.0
	*
	********************************************************************************/


	package org.eclipse.mdm.openatfx.mdf.mdf4;

	import static java.lang.Math.min;
	import static java.nio.file.StandardOpenOption.CREATE_NEW;

	import java.io.IOException;
	import java.io.InputStream;
	import java.io.OutputStream;
	import java.nio.ByteBuffer;
	import java.nio.ByteOrder;
	import java.nio.channels.SeekableByteChannel;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.security.DigestInputStream;
	import java.security.MessageDigest;
	import java.security.NoSuchAlgorithmException;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.List;
	import java.util.zip.DataFormatException;
	import java.util.zip.Inflater;

	import org.asam.ods.T_ExternalReference;

	/**
	* <p>
	* THE ATTACHMENT BLOCK <code>ATBLOCK</code>
	* </p>
	* The data section of the ATBLOCK contains attachments (binary data)
	*
	* @author Christian Rechner, Tobias Leemann
	*/
	class ATBLOCK extends BLOCK {

	public static String BLOCK_ID = "##AT";

	private long lnkAtNext;

	private long lnkTxFilename;

	private long lnkTxMIMEtype;

	private long lnkMdComment;

	private int flags;

	private int creatorIndex;

	private byte[] md5CheckSum;

	private long origSize;

	private long embeddedSize;

	/**
	* Constructor.
	*
	* @param sbc
	* The byte channel pointing to the MDF file.
	* @param pos
	* The position of the block within the MDF file.
	*/
	private ATBLOCK(SeekableByteChannel sbc, long pos) {
	super(sbc, pos);
	}

	public long getLnkAtNext() {
	return lnkAtNext;
	}

	public void setLnkAtNext(long lnkAtNext) {
	this.lnkAtNext = lnkAtNext;
	}

	public long getLnkTxFilename() {
	return lnkTxFilename;
	}

	public void setLnkTxFilename(long lnkTxFilename) {
	this.lnkTxFilename = lnkTxFilename;
	}

	public long getLnkTxMIMEtype() {
	return lnkTxMIMEtype;
	}

	public void setLnkTxMIMEtype(long lnkTxMIMEtype) {
	this.lnkTxMIMEtype = lnkTxMIMEtype;
	}

	public long getLnkMdComment() {
	return lnkMdComment;
	}

	public void setLnkMdComment(long lnkMdComment) {
	this.lnkMdComment = lnkMdComment;
	}

	public int getFlags() {
	return flags;
	}

	public void setFlags(int flags) {
	this.flags = flags;
	}

	public int getCreatorIndex() {
	return creatorIndex;
	}

	public void setCreatorIndex(int creatorIndex) {
	this.creatorIndex = creatorIndex;
	}

	public byte[] getMd5CheckSum() {
	return md5CheckSum;
	}

	public void setMd5CheckSum(byte[] md5CheckSum) {
	this.md5CheckSum = md5CheckSum;
	}

	public long getOrigSize() {
	return origSize;
	}

	public void setOrigSize(long origSize) {
	this.origSize = origSize;
	}

	public long getEmbeddedSize() {
	return embeddedSize;
	}

	public void setEmbeddedSize(long embeddedSize) {
	this.embeddedSize = embeddedSize;
	}

	public ATBLOCK getAtNextBlock() throws IOException {
	if (lnkAtNext > 0) {
	return ATBLOCK.read(sbc, lnkAtNext);
	}
	return null;
	}

	public TXBLOCK getTxFilennameBlock() throws IOException {
	if (lnkTxFilename > 0) {
	return TXBLOCK.read(sbc, lnkTxFilename);
	}
	return null;
	}

	public TXBLOCK getTxMIMETypeBlock() throws IOException {
	if (lnkTxMIMEtype > 0) {
	return TXBLOCK.read(sbc, lnkTxMIMEtype);
	}
	return null;
	}

	public TXBLOCK getTxCommentBlock() throws IOException {
	if (lnkMdComment > 0) {
	return TXBLOCK.read(sbc, lnkMdComment);
	}
	return null;
	}

	public MDBLOCK getMdCommentBlock() throws IOException {
	if (lnkMdComment > 0) {
	return MDBLOCK.read(sbc, lnkMdComment);
	}
	return null;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public String toString() {
	return "DTBLOCK [pos=" + getPos() + "]";
	}

	/**
	* Reads a SDBLOCK from the channel starting at current channel position.
	*
	* @param channel
	* The channel to read from.
	* @param pos
	* The position
	* @return The block data.
	* @throws IOException
	* The exception.
	*/
	public static ATBLOCK read(SeekableByteChannel channel, long pos) throws IOException {
	ATBLOCK block = new ATBLOCK(channel, pos);

	// read block header
	ByteBuffer bb = ByteBuffer.allocate(24 + 32 + 40); // 24 Head 32 Links
	// 40 Data
	bb.order(ByteOrder.LITTLE_ENDIAN);
	channel.position(pos);
	channel.read(bb);
	bb.rewind();

	// CHAR 4: Block type identifier
	block.setId(MDF4Util.readCharsISO8859(bb, 4));
	if (!block.getId().equals(BLOCK_ID)) {
	throw new IOException("Wrong block type - expected '" + BLOCK_ID + "', found '" + block.getId() + "'");
	}

	// BYTE 4: Reserved used for 8-Byte alignment
	bb.get(new byte[4]);

	// UINT64: Length of block
	block.setLength(MDF4Util.readUInt64(bb));

	// UINT64: Number of links
	block.setLinkCount(MDF4Util.readUInt64(bb));

	// LINK 1 Pointer to next ATBLOCK (NIL allowed)
	block.setLnkAtNext(MDF4Util.readLink(bb));

	// LINK 1 Pointer to Text Block with Filename (NIL allowed)
	block.setLnkTxFilename(MDF4Util.readLink(bb));

	// LINK 1 Pointer to Text Block with MIME Type (TXBLOCK) (NIL allowed)
	block.setLnkTxMIMEtype(MDF4Util.readLink(bb));

	// LINK 1 Pointer to comment Block MDBLOCK (NIL allowed)
	block.setLnkMdComment(MDF4Util.readLink(bb));

	// UINT16 flags
	block.setFlags(MDF4Util.readUInt16(bb));

	// UINT16 Creator Index
	block.setCreatorIndex(MDF4Util.readUInt16(bb));

	// BYTE 4: Reserved used for 8-Byte alignment
	bb.get(new byte[4]);

	// BYTE 16: MD5 Checksum
	byte[] md5sum = new byte[16];
	bb.get(md5sum);
	block.setMd5CheckSum(md5sum);

	// UINT64 OriginalSize
	block.setOrigSize(MDF4Util.readUInt64(bb));

	// UINT64 EmbeddedSize
	block.setEmbeddedSize(MDF4Util.readUInt64(bb));

	return block;
	}

	/**
	* Converts this AT Block and all linked one into dedicated
	* external links, where each embedded file is written to disc.
	*
	* @param target the working directory
	* @param subDir name of the target sub directory for exporting embedded files, may be empty
	* @return all external links, neither null nor empty
	* @throws IOException in case of errors
	*/
	public T_ExternalReference[] toExtRefs(Path target, String subDir) throws IOException {
	List<T_ExternalReference> extRefs = new ArrayList<>();
	ATBLOCK block = this;

	int count = 0;
	while (block != null) {
	boolean embedded = (block.flags & 1) != 0;

	Path file;
	if (embedded) {
	file = block.exportEmbedded(subDir.isEmpty() ? target : target.resolve(subDir), ++count);
	} else {
	file = block.getFilePath(target, true);
	}

	block.checkMD5(file);

	extRefs.add(new T_ExternalReference(block.getDescription(), block.getMimeType(file),
	target.relativize(file).toString()));
	block = block.getAtNextBlock();
	}

	return extRefs.stream().toArray(T_ExternalReference[]::new);
	}

	/**
	* Returns the file MIME type if available.
	*
	* @return the MIME type, may be empty but not null
	* @throws IOException in case of errors
	*/
	private String getMimeType(Path file) throws IOException {
	String value = Files.probeContentType(file);
	if (lnkTxMIMEtype > 0) {
	value = getTxMIMETypeBlock().getTxData();
	}

	return value == null ? "application/octet-stream" : value.trim();
	}

	/**
	* Returns the file description if available.
	*
	* @return the file description, may be empty but not null
	* @throws IOException in case of errors
	*/
	private String getDescription() throws IOException {
	if (lnkMdComment < 1) {
	return "";
	}

	String value = null;
	try {
	value = getMdCommentBlock().getMdData();
	} catch (IOException e) {
	value = getTxCommentBlock().getTxData();
	}

	return value == null ? "" : value.trim();
	}

	/**
	* Exports given embedded stream into given file.
	*
	* @param target the target file path, not null and must not exist yet
	* @param id the internal files count, used to index files whose name is unknown
	* @return the newly created file path, not null
	* @throws IOException in case of errors
	*/
	private Path exportEmbedded(Path target, int id) throws IOException {
	if ((flags & 1) == 0) {
	throw new IllegalStateException("file is not embedded");
	}

	Path file;
	if (lnkTxFilename > 0) {
	file = getFilePath(target, false);
	} else {
	file = target.resolve("embedded_" + id + ".bin");
	}

	Files.createDirectories(file.getParent());
	EmbeddedStream embeddedStream = new EmbeddedStream(sbc, getPos() + 96, getEmbeddedSize());
	boolean compressed = (flags & 1 << 1) != 0;
	if (compressed) {
	unzip(embeddedStream, file);
	} else {
	Files.copy(embeddedStream, file);
	}

	return file;
	}

	/**
	* Exports given compressed embedded inputs stream into given file target.
	*
	* @param embeddedStream the embedded input stream, not null
	* @param target the target file path, not null and must not exist yet
	* @throws IOException in case of errors
	*/
	private void unzip(EmbeddedStream embeddedStream, Path target) throws IOException {
	try (InputStream is = embeddedStream; OutputStream os = Files.newOutputStream(target, CREATE_NEW)) {
	Inflater inflater = new Inflater();

	byte[] writeBuffer = new byte[8192];
	byte[] readBuffer = new byte[8192];
	int written;
	int read = 0;
	while(read > -1 && !inflater.finished()) {
	while(inflater.needsInput() && (read = is.read(readBuffer)) > 0) {
	// feed iflater as long as it needs input and as long as there is data available
	inflater.setInput(readBuffer, 0, read);
	}

	while ((written = inflater.inflate(writeBuffer)) > 0) {
	// write decompressed bytes as long inflater is satisfied
	os.write(writeBuffer, 0, written);
	}
	}

	os.flush();
	} catch (DataFormatException e) {
	throw new IOException("failed to decompress embedded file", e);
	}
	}

	/**
	* Returns the file path.
	*
	* @param target the working directory
	* @param exists if true, the returned file path must exist
	* @return the target file path, not null
	* @throws IOException in case of errors
	*/
	private Path getFilePath(Path target, boolean exists) throws IOException {
	if (lnkTxFilename < 1) {
	throw new IllegalStateException("file name TXBLOCK is not set");
	}

	TXBLOCK fileNameTX = getTxFilennameBlock();
	Path file = Paths.get(fileNameTX.getTxData());
	if (!file.isAbsolute()) {
	file = target.resolve(fileNameTX.getTxData());
	}

	if (exists && !file.toFile().exists()) {
	throw new IOException("file '" + file + "' not found.");
	}

	return file;
	}

	/**
	* Compares calculated MD5 checksum with the stored one.
	*
	* @param file the file path, not null
	* @throws IOException in case of errors
	*/
	private void checkMD5(Path file) throws IOException {
	if ((flags & 1 << 2) == 0) {
	// checksum is not available => skip!
	return;
	}
	try {
	MessageDigest md = MessageDigest.getInstance("MD5");
	try (DigestInputStream is = new DigestInputStream(Files.newInputStream(file), md)) {
	byte[] buffer = new byte[1024];
	while (is.read(buffer) != -1);
	byte[] calculated = is.getMessageDigest().digest();
	if (!Arrays.equals(calculated, getMd5CheckSum())) {
	throw new IOException("checksum validation failed for file '" + file + "'");
	}
	}
	} catch (NoSuchAlgorithmException e) {
	throw new IOException("checksum algorithm 'MD5' not found.");
	}
	}

	/**
	* Embedded input stream implementation.
	*/
	private static final class EmbeddedStream extends InputStream {

	private final SeekableByteChannel sbc;
	private final long length0;

	private long current = 0;

	/**
	* Constructor.
	*
	* @param sbc the channel source for byte access, not null
	* @param start the channel position this stream internally starts from
	* @param length the number of bytes this stream will provide
	* @throws IOException in case of errors
	*/
	public EmbeddedStream(SeekableByteChannel sbc, long start, long length) throws IOException {
	this.sbc = sbc;
	this.length0 = length;

	sbc.position(start);
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public int read() throws IOException {
	if (current >= length0) {
	return -1;
	}

	ByteBuffer buffer = ByteBuffer.allocate(1);
	int read = sbc.read(buffer);
	if (read > 0) {
	current += read;
	buffer.rewind();
	return buffer.getInt();
	} else {
	return -1;
	}
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public int read(byte[] bytes) throws IOException {
	if (current >= length0) {
	return -1;
	}

	int read = (int) min(sbc.read(ByteBuffer.wrap(bytes)), length0 - current);
	if (read > 0) {
	current += read;
	return read;
	} else {
	return -1;
	}
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public int read(byte[] bytes, int offset, int length) throws IOException {
	if (current >= length0) {
	return -1;
	}

	int read = (int) min(sbc.read(ByteBuffer.wrap(bytes, offset, length)), length0 - current);
	if (read > 0) {
	current += read;
	return read;
	} else {
	return -1;
	}
	}

	}
	}