Feature: Notification API for Filesystem events

src/main/java/module-info.java

@@ -22,6 +22,7 @@
 	requires java.compiler;
 
 	exports org.cryptomator.cryptofs;
+	exports org.cryptomator.cryptofs.event;
 	exports org.cryptomator.cryptofs.common;
 	exports org.cryptomator.cryptofs.health.api;
 	exports org.cryptomator.cryptofs.migration;

src/main/java/org/cryptomator/cryptofs/CryptoFileSystemModule.java

@@ -10,6 +10,7 @@
 import org.cryptomator.cryptofs.attr.AttributeComponent;
 import org.cryptomator.cryptofs.attr.AttributeViewComponent;
 import org.cryptomator.cryptofs.dir.DirectoryStreamComponent;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
 import org.cryptomator.cryptofs.fh.OpenCryptoFileComponent;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -19,6 +20,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Optional;
+import java.util.function.Consumer;
 
 @Module(subcomponents = {AttributeComponent.class, AttributeViewComponent.class, OpenCryptoFileComponent.class, DirectoryStreamComponent.class})
 class CryptoFileSystemModule {
@@ -35,4 +37,17 @@ public Optional<FileStore> provideNativeFileStore(@PathToVault Path pathToVault)
 			return Optional.empty();
 		}
 	}
+
+	@Provides
+	@CryptoFileSystemScoped
+	public Consumer<FilesystemEvent> provideFilesystemEventConsumer(CryptoFileSystemProperties fsProps) {
+		var eventConsumer = fsProps.fsEventConsumner();
+		return event -> {
+			try {
+				eventConsumer.accept(event);
+			} catch (RuntimeException e) {
+				LOG.warn("Filesystem event consumer failed with exception when processing event {}", event, e);
+			}
+		};
+	}
 }

src/main/java/org/cryptomator/cryptofs/CryptoFileSystemProperties.java

@@ -9,6 +9,7 @@
 package org.cryptomator.cryptofs;
 
 import com.google.common.base.Strings;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
 import org.cryptomator.cryptolib.api.CryptorProvider;
 import org.cryptomator.cryptolib.api.MasterkeyLoader;
 
@@ -80,6 +81,15 @@ public class CryptoFileSystemProperties extends AbstractMap<String, Object> {
 
 	static final String DEFAULT_MASTERKEY_FILENAME = "masterkey.cryptomator";
 
+	/**
+	 * Key identifying the function to call for notifications.
+	 *
+	 * @since 2.9.0
+	 */
+	public static final String PROPERTY_NOTIFY_METHOD = "notificationConsumer";
+
+	static final Consumer<FilesystemEvent> DEFAULT_NOTIFY_METHOD = (FilesystemEvent e) -> {};
+
 	/**
 	 * Key identifying the filesystem flags.
 	 *
@@ -113,6 +123,7 @@ private CryptoFileSystemProperties(Builder builder) {
 				Map.entry(PROPERTY_FILESYSTEM_FLAGS, builder.flags), //
 				Map.entry(PROPERTY_VAULTCONFIG_FILENAME, builder.vaultConfigFilename), //
 				Map.entry(PROPERTY_MASTERKEY_FILENAME, builder.masterkeyFilename), //
+				Map.entry(PROPERTY_NOTIFY_METHOD, builder.eventConsumer), //
 				Map.entry(PROPERTY_MAX_CLEARTEXT_NAME_LENGTH, builder.maxCleartextNameLength), //
 				Map.entry(PROPERTY_SHORTENING_THRESHOLD, builder.shorteningThreshold), //
 				Map.entry(PROPERTY_CIPHER_COMBO, builder.cipherCombo) //
@@ -153,6 +164,10 @@ int shorteningThreshold() {
 		return (int) get(PROPERTY_SHORTENING_THRESHOLD);
 	}
 
+	Consumer<FilesystemEvent> fsEventConsumner() {
+		return (Consumer<FilesystemEvent>) get(PROPERTY_NOTIFY_METHOD);
+	}
+
 	@Override
 	public Set<Entry<String, Object>> entrySet() {
 		return entries;
@@ -208,6 +223,7 @@ public static class Builder {
 		private String masterkeyFilename = DEFAULT_MASTERKEY_FILENAME;
 		private int maxCleartextNameLength = DEFAULT_MAX_CLEARTEXT_NAME_LENGTH;
 		private int shorteningThreshold = DEFAULT_SHORTENING_THRESHOLD;
+		private Consumer<FilesystemEvent> eventConsumer = DEFAULT_NOTIFY_METHOD;
 
 		private Builder() {
 		}
@@ -220,6 +236,7 @@ private Builder(Map<String, ?> properties) {
 			checkedSet(Integer.class, PROPERTY_MAX_CLEARTEXT_NAME_LENGTH, properties, this::withMaxCleartextNameLength);
 			checkedSet(Integer.class, PROPERTY_SHORTENING_THRESHOLD, properties, this::withShorteningThreshold);
 			checkedSet(CryptorProvider.Scheme.class, PROPERTY_CIPHER_COMBO, properties, this::withCipherCombo);
+			checkedSet(Consumer.class, PROPERTY_NOTIFY_METHOD, properties, this::withFilesystemEventConsumer);
 		}
 
 		private <T> void checkedSet(Class<T> type, String key, Map<String, ?> properties, Consumer<T> setter) {
@@ -334,6 +351,21 @@ public Builder withMasterkeyFilename(String masterkeyFilename) {
 			return this;
 		}
 
+		/**
+		 * Sets the consumer for filesystem events
+		 *
+		 * @param eventConsumer the consumer to receive filesystem events
+		 * @return this
+		 * @since 2.8.0
+		 */
+		public Builder withFilesystemEventConsumer(Consumer<FilesystemEvent> eventConsumer) {
+			if (eventConsumer == null) {
+				throw new IllegalArgumentException("Parameter eventConsumer must not be null");
+			}
+			this.eventConsumer = eventConsumer;
+			return this;
+		}
+
 		/**
 		 * Validates the values and creates new {@link CryptoFileSystemProperties}.
 		 *

src/main/java/org/cryptomator/cryptofs/dir/C9rConflictResolver.java

@@ -6,6 +6,9 @@
 import com.google.common.io.RecursiveDeleteOption;
 import org.cryptomator.cryptofs.VaultConfig;
 import org.cryptomator.cryptofs.common.Constants;
+import org.cryptomator.cryptofs.event.ConflictResolutionFailedEvent;
+import org.cryptomator.cryptofs.event.ConflictResolvedEvent;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
 import org.cryptomator.cryptolib.api.Cryptor;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -18,6 +21,7 @@
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
+import java.util.function.Consumer;
 import java.util.stream.Stream;
 
 import static org.cryptomator.cryptofs.common.Constants.DIR_FILE_NAME;
@@ -33,14 +37,18 @@ class C9rConflictResolver {
 	private final Cryptor cryptor;
 	private final byte[] dirId;
 	private final int maxC9rFileNameLength;
+	private final Path cleartextPath;
 	private final int maxCleartextFileNameLength;
+	private final Consumer<FilesystemEvent> eventConsumer;
 
 	@Inject
-	public C9rConflictResolver(Cryptor cryptor, @Named("dirId") String dirId, VaultConfig vaultConfig) {
+	public C9rConflictResolver(Cryptor cryptor, @Named("dirId") String dirId, VaultConfig vaultConfig, Consumer<FilesystemEvent> eventConsumer, @Named("cleartextPath") Path cleartextPath) {
 		this.cryptor = cryptor;
 		this.dirId = dirId.getBytes(StandardCharsets.US_ASCII);
 		this.maxC9rFileNameLength = vaultConfig.getShorteningThreshold();
+		this.cleartextPath = cleartextPath;
 		this.maxCleartextFileNameLength = (maxC9rFileNameLength - 4) / 4 * 3 - 16; // math from FileSystemCapabilityChecker.determineSupportedCleartextFileNameLength()
+		this.eventConsumer = eventConsumer;
 	}
 
 	public Stream<Node> process(Node node) {
@@ -61,13 +69,15 @@ public Stream<Node> process(Node node) {
 				Path canonicalPath = node.ciphertextPath.resolveSibling(canonicalCiphertextFileName);
 				return resolveConflict(node, canonicalPath);
 			} catch (IOException e) {
-				LOG.error("Failed to resolve conflict for " + node.ciphertextPath, e);
+				eventConsumer.accept(new ConflictResolutionFailedEvent(cleartextPath.resolve(node.cleartextName), node.ciphertextPath.resolve(node.fullCiphertextFileName), e));
+				LOG.error("Failed to resolve conflict for {}", node.ciphertextPath, e);
 				return Stream.empty();
 			}
 		}
 	}
 
-	private Stream<Node> resolveConflict(Node conflicting, Path canonicalPath) throws IOException {
+	//visible for testing
+	Stream<Node> resolveConflict(Node conflicting, Path canonicalPath) throws IOException {
 		Path conflictingPath = conflicting.ciphertextPath;
 		if (resolveConflictTrivially(canonicalPath, conflictingPath)) {
 			Node resolved = new Node(canonicalPath);
@@ -111,6 +121,7 @@ private Node renameConflictingFile(Path canonicalPath, Path conflictingPath, Str
 		Node node = new Node(alternativePath);
 		node.cleartextName = alternativeCleartext;
 		node.extractedCiphertext = alternativeCiphertext;
+		eventConsumer.accept(new ConflictResolvedEvent(cleartextPath.resolve(cleartext), canonicalPath, cleartextPath.resolve(alternativeCleartext), alternativePath));
 		return node;
 	}
 

src/main/java/org/cryptomator/cryptofs/event/ConflictResolutionFailedEvent.java

@@ -0,0 +1,14 @@
+package org.cryptomator.cryptofs.event;
+
+import java.nio.file.Path;
+
+/**
+ * Emitted, if the conflict resolution inside an encrypted directory failed
+ *
+ * @param canonicalCleartextPath path of the canonical file within the cryptographic filesystem
+ * @param conflictingCiphertextPath path of the encrypted, conflicting file
+ * @param reason exception, why the resolution failed
+ */
+public record ConflictResolutionFailedEvent(Path canonicalCleartextPath, Path conflictingCiphertextPath, Exception reason) implements FilesystemEvent {
+
+}

src/main/java/org/cryptomator/cryptofs/event/ConflictResolvedEvent.java

@@ -0,0 +1,20 @@
+package org.cryptomator.cryptofs.event;
+
+import java.nio.file.Path;
+
+/**
+ * Emitted, if a conflict inside an encrypted directory was resolved.
+ * <p>
+ * A conflict exists, if two encrypted files with the same base64url string exist, but the second file has an arbitrary suffix before the file extension.
+ * The file <i>without</i> the suffix is called <b>canonical</b>.
+ * The file <i>with the suffix</i> is called <b>conflicting</b>
+ * On successful conflict resolution the conflicting file is renamed to the <b>resolved</b> file
+ *
+ * @param canonicalCleartextPath path of the canonical file within the cryptographic filesystem
+ * @param conflictingCiphertextPath path of the encrypted, conflicting file
+ * @param resolvedCleartextPath path of the resolved file within the cryptographic filesystem
+ * @param resolvedCiphertextPath path of the resolved, encrypted file
+ */
+public record ConflictResolvedEvent(Path canonicalCleartextPath, Path conflictingCiphertextPath, Path resolvedCleartextPath, Path resolvedCiphertextPath) implements FilesystemEvent {
+
+}

src/main/java/org/cryptomator/cryptofs/event/DecryptionFailedEvent.java

@@ -0,0 +1,15 @@
+package org.cryptomator.cryptofs.event;
+
+import org.cryptomator.cryptolib.api.AuthenticationFailedException;
+
+import java.nio.file.Path;
+
+/**
+ * Emitted, if a decryption operation fails.
+ *
+ * @param ciphertextPath path to the encrypted resource
+ * @param e thrown exception
+ */
+public record DecryptionFailedEvent(Path ciphertextPath, AuthenticationFailedException e) implements FilesystemEvent {
+
+}

src/main/java/org/cryptomator/cryptofs/event/FilesystemEvent.java

@@ -0,0 +1,27 @@
+package org.cryptomator.cryptofs.event;
+
+import java.util.function.Consumer;
+
+/**
+ * Common interface for all filesystem events.
+ * <p>
+ * Events are emitted via the notification method set in the properties during filesystem creation, see {@link org.cryptomator.cryptofs.CryptoFileSystemProperties.Builder#withFilesystemEventConsumer(Consumer)}.
+ * <p>
+ * To get a specific event type, use the enhanced switch pattern or typecasting in if-instance of, e.g.
+ * {@code
+ * FilesystemEvent fse;
+ * switch (fse) {
+ *   case DecryptionFailedEvent dfe -> //do stuff
+ *   case ConflictResolvedEvent cre -> //do other stuff
+ *   //other cases
+ * }
+ * if( fse instanceof DecryptionFailedEvent dfe) {
+ *   //do more stuff
+ * }
+ * }.
+ *
+ * @apiNote Events might have occured a long time ago in a galaxy far, far away... therefore, any feedback method is non-blocking and might fail due to changes in the filesystem.
+ */
+public sealed interface FilesystemEvent permits ConflictResolutionFailedEvent, ConflictResolvedEvent, DecryptionFailedEvent {
+
+}

src/main/java/org/cryptomator/cryptofs/fh/ChunkLoader.java

@@ -1,24 +1,34 @@
 package org.cryptomator.cryptofs.fh;
 
 import org.cryptomator.cryptofs.CryptoFileSystemStats;
+import org.cryptomator.cryptofs.event.DecryptionFailedEvent;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
 import org.cryptomator.cryptolib.api.AuthenticationFailedException;
 import org.cryptomator.cryptolib.api.Cryptor;
 
 import javax.inject.Inject;
+import javax.inject.Named;
 import java.io.IOException;
 import java.nio.ByteBuffer;
+import java.nio.file.Path;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
 
 @OpenFileScoped
 class ChunkLoader {
 
+	private final Consumer<FilesystemEvent> eventConsumer;
+	private final AtomicReference<Path> path;
 	private final Cryptor cryptor;
 	private final ChunkIO ciphertext;
 	private final FileHeaderHolder headerHolder;
 	private final CryptoFileSystemStats stats;
 	private final BufferPool bufferPool;
 
 	@Inject
-	public ChunkLoader(Cryptor cryptor, ChunkIO ciphertext, FileHeaderHolder headerHolder, CryptoFileSystemStats stats, BufferPool bufferPool) {
+	public ChunkLoader(Consumer<FilesystemEvent> eventConsumer, @CurrentOpenFilePath AtomicReference<Path> path, Cryptor cryptor, ChunkIO ciphertext, FileHeaderHolder headerHolder, CryptoFileSystemStats stats, BufferPool bufferPool) {
+		this.eventConsumer = eventConsumer;
+		this.path = path;
 		this.cryptor = cryptor;
 		this.ciphertext = ciphertext;
 		this.headerHolder = headerHolder;
@@ -42,6 +52,9 @@ public ByteBuffer load(Long chunkIndex) throws IOException, AuthenticationFailed
 				stats.addBytesDecrypted(cleartextBuf.remaining());
 			}
 			return cleartextBuf;
+		} catch (AuthenticationFailedException e) {
+			eventConsumer.accept(new DecryptionFailedEvent(path.get(), e));
+			throw e;
 		} finally {
 			bufferPool.recycle(ciphertextBuf);
 		}

src/main/java/org/cryptomator/cryptofs/fh/FileHeaderHolder.java

@@ -1,5 +1,8 @@
 package org.cryptomator.cryptofs.fh;
 
+import org.cryptomator.cryptofs.event.DecryptionFailedEvent;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
+import org.cryptomator.cryptolib.api.AuthenticationFailedException;
 import org.cryptomator.cryptolib.api.CryptoException;
 import org.cryptomator.cryptolib.api.Cryptor;
 import org.cryptomator.cryptolib.api.FileHeader;
@@ -13,20 +16,23 @@
 import java.nio.file.Path;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Consumer;
 
 @OpenFileScoped
 public class FileHeaderHolder {
 
 	private static final Logger LOG = LoggerFactory.getLogger(FileHeaderHolder.class);
 
+	private final Consumer<FilesystemEvent> eventConsumer;
 	private final Cryptor cryptor;
 	private final AtomicReference<Path> path;
 	private final AtomicReference<FileHeader> header = new AtomicReference<>();
 	private final AtomicReference<ByteBuffer> encryptedHeader = new AtomicReference<>();
 	private final AtomicBoolean isPersisted = new AtomicBoolean();
 
 	@Inject
-	public FileHeaderHolder(Cryptor cryptor, @CurrentOpenFilePath AtomicReference<Path> path) {
+	public FileHeaderHolder(Consumer<FilesystemEvent> eventConsumer, Cryptor cryptor, @CurrentOpenFilePath AtomicReference<Path> path) {
+		this.eventConsumer = eventConsumer;
 		this.cryptor = cryptor;
 		this.path = path;
 	}
@@ -75,6 +81,9 @@ FileHeader loadExisting(FileChannel ch) throws IOException {
 			isPersisted.set(true);
 			return existingHeader;
 		} catch (IllegalArgumentException | CryptoException e) {
+			if (e instanceof AuthenticationFailedException afe) {
+				eventConsumer.accept(new DecryptionFailedEvent(path.get(), afe));
+			}
 			throw new IOException("Unable to decrypt header of file " + path.get(), e);
 		}
 	}

src/test/java/org/cryptomator/cryptofs/CryptoFileSystemModuleTest.java

@@ -0,0 +1,35 @@
+package org.cryptomator.cryptofs;
+
+import org.cryptomator.cryptofs.event.ConflictResolutionFailedEvent;
+import org.cryptomator.cryptofs.event.FilesystemEvent;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+import java.nio.file.Path;
+import java.util.function.Consumer;
+
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class CryptoFileSystemModuleTest {
+
+	CryptoFileSystemModule inTest = new CryptoFileSystemModule();
+
+	@Test
+	void testEventConsumerIsDecorated() {
+		var p = Mockito.mock(Path.class);
+		var event = new ConflictResolutionFailedEvent(p, p, new RuntimeException());
+		var eventConsumer = (Consumer<FilesystemEvent>) mock(Consumer.class);
+		doThrow(new RuntimeException("fail")).when(eventConsumer).accept(event);
+		var props = mock(CryptoFileSystemProperties.class);
+		when(props.fsEventConsumner()).thenReturn(eventConsumer);
+
+		var decoratedConsumer = inTest.provideFilesystemEventConsumer(props);
+		Assertions.assertDoesNotThrow(() -> decoratedConsumer.accept(event));
+		verify(eventConsumer).accept(event);
+	}
+
+}