Fix IOUtils#fsync on Windows fsyncing directories

libs/core/src/main/java/org/elasticsearch/core/internal/io/IOUtils.java

@@ -24,6 +24,7 @@
 import java.nio.file.FileVisitResult;
 import java.nio.file.FileVisitor;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
 import java.nio.file.attribute.BasicFileAttributes;
@@ -249,6 +250,7 @@ public FileVisitResult visitFileFailed(final Path file, final IOException exc) t
     }
 
     // TODO: replace with constants class if needed (cf. org.apache.lucene.util.Constants)
+    private static final boolean WINDOWS = System.getProperty("os.name").startsWith("Windows");
     private static final boolean LINUX = System.getProperty("os.name").startsWith("Linux");
     private static final boolean MAC_OS_X = System.getProperty("os.name").startsWith("Mac OS X");
 
@@ -263,6 +265,14 @@ public FileVisitResult visitFileFailed(final Path file, final IOException exc) t
      *                   systems and operating systems allow to fsync on a directory)
      */
     public static void fsync(final Path fileToSync, final boolean isDir) throws IOException {
+        if (isDir && WINDOWS) {
+            // opening a directory on Windows fails, directories can not be fsynced there
+            if (Files.exists(fileToSync) == false) {
+                // yet do not suppress trying to fsync directories that do not exist
+                throw new NoSuchFileException(fileToSync.toString());
+            }
+            return;
+        }
         try (FileChannel file = FileChannel.open(fileToSync, isDir ? StandardOpenOption.READ : StandardOpenOption.WRITE)) {
             try {
                 file.force(true);

libs/core/src/test/java/org/elasticsearch/core/internal/io/IOUtilsTests.java

@@ -19,6 +19,7 @@
 
 import org.apache.lucene.mockfile.FilterFileSystemProvider;
 import org.apache.lucene.mockfile.FilterPath;
+import org.apache.lucene.util.Constants;
 import org.elasticsearch.common.CheckedConsumer;
 import org.elasticsearch.common.io.PathUtils;
 import org.elasticsearch.test.ESTestCase;
@@ -27,14 +28,20 @@
 import java.io.IOException;
 import java.io.OutputStream;
 import java.net.URI;
+import java.nio.channels.FileChannel;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.AccessDeniedException;
 import java.nio.file.FileSystem;
 import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.OpenOption;
 import java.nio.file.Path;
+import java.nio.file.attribute.FileAttribute;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
+import java.util.Set;
 import java.util.function.Function;
 
 import static org.hamcrest.Matchers.arrayWithSize;
@@ -214,6 +221,43 @@ public void testFsyncDirectory() throws Exception {
         // no exception
     }
 
+    private static final class AccessDeniedWhileOpeningDirectoryFileSystem extends FilterFileSystemProvider {
+
+        AccessDeniedWhileOpeningDirectoryFileSystem(final FileSystem delegate) {
+            super("access_denied://", Objects.requireNonNull(delegate));
+        }
+
+        @Override
+        public FileChannel newFileChannel(
+                final Path path,
+                final Set<? extends OpenOption> options,
+                final FileAttribute<?>... attrs) throws IOException {
+            if (Files.isDirectory(path)) {
+                throw new AccessDeniedException(path.toString());
+            }
+            return delegate.newFileChannel(path, options, attrs);
+        }
+
+    }
+
+    public void testFsyncAccessDeniedOpeningDirectory() throws Exception {
+        final Path path = createTempDir().toRealPath();
+        final FileSystem fs = new AccessDeniedWhileOpeningDirectoryFileSystem(path.getFileSystem()).getFileSystem(URI.create("file:///"));
+        final Path wrapped = new FilterPath(path, fs);
+        if (Constants.WINDOWS) {
+            // no exception, we early return and do not even try to open the directory
+            IOUtils.fsync(wrapped, true);
+        } else {
+            expectThrows(AccessDeniedException.class, () -> IOUtils.fsync(wrapped, true));
+        }
+    }
+
+    public void testFsyncNonExistentDirectory() throws Exception {
+        final Path dir = FilterPath.unwrap(createTempDir()).toRealPath();
+        final Path nonExistentDir = dir.resolve("non-existent");
+        expectThrows(NoSuchFileException.class, () -> IOUtils.fsync(nonExistentDir, true));
+    }
+
     public void testFsyncFile() throws IOException {
         final Path path = createTempDir().toRealPath();
         final Path subPath = path.resolve(randomAlphaOfLength(8));