Add support for file attribute views in the union file system provider (#18)

* Add support for file attribute views in the union file system provider

Fixes #17 (crash with JetBrains JVM)

* Add file attribute tests

Author: amadornes

src/main/java/cpw/mods/niofs/union/UnionFileSystemProvider.java

@@ -6,9 +6,7 @@
 import java.net.URISyntaxException;
 import java.nio.channels.SeekableByteChannel;
 import java.nio.file.*;
-import java.nio.file.attribute.BasicFileAttributes;
-import java.nio.file.attribute.FileAttribute;
-import java.nio.file.attribute.FileAttributeView;
+import java.nio.file.attribute.*;
 import java.nio.file.spi.FileSystemProvider;
 import java.util.*;
 import java.util.function.BiPredicate;
@@ -205,7 +203,10 @@ public void checkAccess(final Path path, final AccessMode... modes) throws IOExc
 
     @Override
     public <V extends FileAttributeView> V getFileAttributeView(final Path path, final Class<V> type, final LinkOption... options) {
-        throw new UnsupportedOperationException();
+        if (path instanceof UnionPath && type == BasicFileAttributeView.class) {
+            return (V) new UnionBasicFileAttributeView(path, options);
+        }
+        return null;
     }
 
     @Override
@@ -231,4 +232,30 @@ void removeFileSystem(UnionFileSystem fs) {
             fileSystems.remove(fs.getKey());
         }
     }
+
+    private class UnionBasicFileAttributeView implements BasicFileAttributeView {
+
+        private final Path path;
+        private final LinkOption[] options;
+
+        public UnionBasicFileAttributeView(Path path, LinkOption[] options) {
+            this.path = path;
+            this.options = options;
+        }
+
+        @Override
+        public String name() {
+            return "union";
+        }
+
+        @Override
+        public BasicFileAttributes readAttributes() throws IOException {
+            return UnionFileSystemProvider.this.readAttributes(path, BasicFileAttributes.class, options);
+        }
+
+        @Override
+        public void setTimes(FileTime lastModifiedTime, FileTime lastAccessTime, FileTime createTime) {
+        }
+
+    }
 }

src/test/java/cpw/mods/niofs/union/TestUnionFS.java

@@ -4,6 +4,9 @@
 
 import java.io.IOException;
 import java.nio.file.*;
+import java.nio.file.attribute.BasicFileAttributeView;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileAttributeView;
 import java.nio.file.spi.FileSystemProvider;
 import java.util.List;
 import java.util.Map;
@@ -161,4 +164,50 @@ void testNested() {
         var input = assertDoesNotThrow(() -> Files.newInputStream(npath));
         var data = assertDoesNotThrow(() -> input.readAllBytes());
     }
+
+    @Test
+    void testFileAttributes() {
+        final var dir1 = Paths.get("src", "test", "resources", "dir1.zip").toAbsolutePath().normalize();
+        var fsp = (UnionFileSystemProvider)FileSystemProvider.installedProviders().stream().filter(fs-> fs.getScheme().equals("union")).findFirst().orElseThrow();
+        var ufs = fsp.newFileSystem((a,b) -> true, dir1);
+        var path = (UnionPath) ufs.getPath("subdir1");
+        var nonExistentPath = (UnionPath) ufs.getPath("non-existent-path");
+
+        // Non-union path
+        assertDoesNotThrow(() -> {
+            assertNull(fsp.getFileAttributeView(Paths.get("subdir1"), BasicFileAttributeView.class));
+        });
+        // Unsupported attribute view
+        assertDoesNotThrow(() -> {
+            assertNull(fsp.getFileAttributeView(path, FileAttributeView.class));
+        });
+        // Non-existent path w/ supported attribute view
+        assertThrows(NoSuchFileException.class, () -> {
+            var nonExistentView = assertDoesNotThrow(() -> {
+                var view = fsp.getFileAttributeView(nonExistentPath, BasicFileAttributeView.class);
+                assertNotNull(view);
+                return view;
+            });
+            nonExistentView.readAttributes();
+        });
+        // Non-existent path
+        assertThrows(NoSuchFileException.class, () -> {
+            ufs.readAttributes(nonExistentPath, BasicFileAttributes.class);
+        });
+
+        // Union path w/ supported attribute view
+        var validViewAttributes = assertDoesNotThrow(() -> {
+            var view = fsp.getFileAttributeView(path, BasicFileAttributeView.class);
+            assertNotNull(view);
+            return view.readAttributes();
+        });
+        // Known existing path
+        var validAttributes = assertDoesNotThrow(() -> {
+            var attributes = ufs.readAttributes(path, BasicFileAttributes.class);
+            assertNotNull(attributes);
+            return attributes;
+        });
+        // Ensure the attributes are the same through both methods
+        assertEquals(validAttributes, validViewAttributes);
+    }
 }