Add jHDF info to written files

jhdf/src/main/java/io/jhdf/HdfFile.java

@@ -59,9 +59,8 @@ public class HdfFile implements Group, AutoCloseable {
 	private static final Logger logger = LoggerFactory.getLogger(HdfFile.class);
 
 	static {
-		final String versionStr = HdfFile.class.getPackage().getImplementationVersion();
-		if (versionStr != null) {
-			logger.info("jHDF version: {}", HdfFile.class.getPackage().getImplementationVersion());
+		if (JhdfInfo.VERSION != null) {
+			logger.info("jHDF version: {}", JhdfInfo.VERSION);
 		} else {
 			logger.warn("Using development version of jHDF");
 		}

jhdf/src/main/java/io/jhdf/JhdfInfo.java

@@ -0,0 +1,27 @@
+/*
+ * This file is part of jHDF. A pure Java library for accessing HDF5 files.
+ *
+ * http://jhdf.io
+ *
+ * Copyright (c) 2024 James Mudd
+ *
+ * MIT License see 'LICENSE' file
+ */
+package io.jhdf;
+
+import java.nio.ByteOrder;
+
+public final class JhdfInfo {
+
+	private JhdfInfo() {
+		throw new AssertionError("No instances of JhdfInfo");
+	}
+
+	public static final String VERSION = JhdfInfo.class.getPackage().getImplementationVersion();
+
+	public static final String OS = System.getProperty("os.name");
+
+	public static final String ARCH = System.getProperty("os.arch");
+
+	public static final String BYTE_ORDER = ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_ENDIAN) ? "LE" : "BE";
+}

jhdf/src/main/java/io/jhdf/Superblock.java

@@ -447,7 +447,7 @@ public SuperblockV2V3() {
 			baseAddressByte = 0;
 			superblockExtensionAddress = Constants.UNDEFINED_ADDRESS;
 			endOfFileAddress = 500; // TODO
-			rootGroupObjectHeaderAddress = 48;
+			rootGroupObjectHeaderAddress = WritableHdfFile.ROOT_GROUP_ADDRESS;
 		}
 
 		private SuperblockV2V3(FileChannel fc, final long address) {

jhdf/src/main/java/io/jhdf/WritableHdfFile.java

@@ -24,7 +24,9 @@
 
 import java.io.File;
 import java.io.IOException;
+import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
 import java.util.Iterator;
@@ -36,7 +38,7 @@ public class WritableHdfFile implements WritableGroup, AutoCloseable {
 
 	private static final Logger logger = LoggerFactory.getLogger(WritableHdfFile.class);
 
-	private static final long ROOT_GROUP_ADDRESS = 48;
+	public static final long ROOT_GROUP_ADDRESS = 64;
 
 	private final Path path;
 	private final FileChannel fileChannel;
@@ -73,6 +75,7 @@ private void flush() {
 		logger.info("Flushing to disk [{}]...", path.toAbsolutePath());
 		try {
 			rootGroup.write(hdfFileChannel, ROOT_GROUP_ADDRESS);
+			hdfFileChannel.write(getJHdfInfo());
 			long endOfFile = hdfFileChannel.getFileChannel().size();
 			hdfFileChannel.write(superblock.toBuffer(endOfFile), 0L);
 			logger.info("Flushed to disk [{}] file is [{}] bytes", path.toAbsolutePath(), endOfFile);
@@ -81,6 +84,11 @@ private void flush() {
 		}
 	}
 
+	private ByteBuffer getJHdfInfo() {
+		final String info = "jHDF - " + JhdfInfo.VERSION + " - " + JhdfInfo.OS + " - " + JhdfInfo.ARCH + " - " + JhdfInfo.BYTE_ORDER;
+		return ByteBuffer.wrap(info.getBytes(StandardCharsets.UTF_8));
+	}
+
 	@Override
 	public WritiableDataset putDataset(String name, Object data) {
 		return rootGroup.putDataset(name, data);