Merge branch '2292-mailbox-file-manager' into 'master'

Add mailbox plugin and file manager for downloads

See merge request briar/briar!1655

bramble-api/src/main/java/org/briarproject/bramble/api/connection/ConnectionManager.java

@@ -16,6 +16,17 @@ public interface ConnectionManager {
 	 */
 	void manageIncomingConnection(TransportId t, TransportConnectionReader r);
 
+	/**
+	 * Manages an incoming connection from a contact via a mailbox.
+	 * <p>
+	 * This method does not mark the tag as recognised until after the data
+	 * has been read from the {@link TransportConnectionReader}, at which
+	 * point the {@link TagController} is called to decide whether the tag
+	 * should be marked as recognised.
+	 */
+	void manageIncomingConnection(TransportId t, TransportConnectionReader r,
+			TagController c);
+
 	/**
 	 * Manages an incoming connection from a contact over a duplex transport.
 	 */
@@ -46,4 +57,21 @@ public interface ConnectionManager {
 	 */
 	void manageOutgoingConnection(PendingContactId p, TransportId t,
 			DuplexTransportConnection d);
+
+	/**
+	 * An interface for controlling whether a tag should be marked as
+	 * recognised.
+	 */
+	interface TagController {
+		/**
+		 * This method is only called if a tag was read from the corresponding
+		 * {@link TransportConnectionReader} and recognised.
+		 *
+		 * @param exception True if an exception was thrown while reading from
+		 * the {@link TransportConnectionReader}, after successfully reading
+		 * and recognising the tag.
+		 * @return True if the tag should be marked as recognised.
+		 */
+		boolean shouldMarkTagAsRecognised(boolean exception);
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxConstants.java

@@ -1,5 +1,7 @@
 package org.briarproject.bramble.api.mailbox;
 
+import org.briarproject.bramble.api.plugin.TransportId;
+
 import static java.util.concurrent.TimeUnit.HOURS;
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_FRAME_LENGTH;
 import static org.briarproject.bramble.api.transport.TransportConstants.MAX_PAYLOAD_LENGTH;
@@ -8,6 +10,11 @@ import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENG
 
 public interface MailboxConstants {
 
+	/**
+	 * The transport ID of the mailbox plugin.
+	 */
+	TransportId ID = new TransportId("org.briarproject.bramble.mailbox");
+
 	/**
 	 * The maximum length of a file that can be uploaded to or downloaded from
 	 * a mailbox.

bramble-api/src/main/java/org/briarproject/bramble/api/mailbox/MailboxDirectory.java

@@ -0,0 +1,22 @@
+package org.briarproject.bramble.api.mailbox;
+
+import java.io.File;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Annotation for injecting the {@link File directory} where the Mailbox plugin
+ * should store its state.
+ */
+@Qualifier
+@Target({FIELD, METHOD, PARAMETER})
+@Retention(RUNTIME)
+public @interface MailboxDirectory {
+}

bramble-core/src/main/java/org/briarproject/bramble/connection/Connection.java

@@ -54,7 +54,7 @@ abstract class Connection {
 		}
 	}
 
-	private byte[] readTag(InputStream in) throws IOException {
+	byte[] readTag(InputStream in) throws IOException {
 		byte[] tag = new byte[TAG_LENGTH];
 		read(in, tag);
 		return tag;

bramble-core/src/main/java/org/briarproject/bramble/connection/ConnectionManagerImpl.java

@@ -67,7 +67,15 @@ class ConnectionManagerImpl implements ConnectionManager {
 			TransportConnectionReader r) {
 		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
 				connectionRegistry, streamReaderFactory, streamWriterFactory,
-				syncSessionFactory, transportPropertyManager, t, r));
+				syncSessionFactory, transportPropertyManager, t, r, null));
+	}
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			TransportConnectionReader r, TagController c) {
+		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, t, r, c));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingSimplexSyncConnection.java

@@ -1,7 +1,9 @@
 package org.briarproject.bramble.connection;
 
+import org.briarproject.bramble.api.connection.ConnectionManager.TagController;
 import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 import org.briarproject.bramble.api.plugin.TransportId;
@@ -15,6 +17,8 @@ import org.briarproject.bramble.api.transport.StreamWriterFactory;
 
 import java.io.IOException;
 
+import javax.annotation.Nullable;
+
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
@@ -23,6 +27,8 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 
 	private final TransportId transportId;
 	private final TransportConnectionReader reader;
+	@Nullable
+	private final TagController tagController;
 
 	IncomingSimplexSyncConnection(KeyManager keyManager,
 			ConnectionRegistry connectionRegistry,
@@ -30,33 +36,50 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 			StreamWriterFactory streamWriterFactory,
 			SyncSessionFactory syncSessionFactory,
 			TransportPropertyManager transportPropertyManager,
-			TransportId transportId, TransportConnectionReader reader) {
+			TransportId transportId,
+			TransportConnectionReader reader,
+			@Nullable TagController tagController) {
 		super(keyManager, connectionRegistry, streamReaderFactory,
 				streamWriterFactory, syncSessionFactory,
 				transportPropertyManager);
 		this.transportId = transportId;
 		this.reader = reader;
+		this.tagController = tagController;
 	}
 
 	@Override
 	public void run() {
 		// Read and recognise the tag
-		StreamContext ctx = recogniseTag(reader, transportId);
+		byte[] tag;
+		StreamContext ctx;
+		try {
+			tag = readTag(reader.getInputStream());
+			// If we have a tag controller, defer marking the tag as recognised
+			if (tagController == null) {
+				ctx = keyManager.getStreamContext(transportId, tag);
+			} else {
+				ctx = keyManager.getStreamContextOnly(transportId, tag);
+			}
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			return;
+		}
 		if (ctx == null) {
 			LOG.info("Unrecognised tag");
-			onError(false);
+			onError();
 			return;
 		}
 		ContactId contactId = ctx.getContactId();
 		if (contactId == null) {
 			LOG.warning("Received rendezvous stream, expected contact");
-			onError(true);
+			onError(tag);
 			return;
 		}
 		if (ctx.isHandshakeMode()) {
 			// TODO: Support handshake mode for contacts
 			LOG.warning("Received handshake tag, expected rotation mode");
-			onError(true);
+			onError(tag);
 			return;
 		}
 		try {
@@ -65,15 +88,33 @@ class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
 					LOG.info("Ignoring priority for simplex connection");
 			// Create and run the incoming session
 			createIncomingSession(ctx, reader, handler).run();
+			// Success
+			markTagAsRecognisedIfRequired(false, tag);
 			reader.dispose(false, true);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
-			onError(true);
+			onError(tag);
 		}
 	}
 
-	private void onError(boolean recognised) {
-		disposeOnError(reader, recognised);
+	private void onError() {
+		disposeOnError(reader, false);
+	}
+
+	private void onError(byte[] tag) {
+		markTagAsRecognisedIfRequired(true, tag);
+		disposeOnError(reader, true);
+	}
+
+	private void markTagAsRecognisedIfRequired(boolean exception, byte[] tag) {
+		if (tagController != null &&
+				tagController.shouldMarkTagAsRecognised(exception)) {
+			try {
+				keyManager.markTagAsRecognised(transportId, tag);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		}
 	}
 }
 

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxFileManager.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.io.File;
+import java.io.IOException;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+@ThreadSafe
+@NotNullByDefault
+interface MailboxFileManager {
+
+	/**
+	 * Creates an empty file for storing a download.
+	 */
+	File createTempFileForDownload() throws IOException;
+
+	/**
+	 * Handles a file that has been downloaded. The file should be created
+	 * with {@link #createTempFileForDownload()}.
+	 */
+	void handleDownloadedFile(File f);
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxFileManagerImpl.java

@@ -0,0 +1,174 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventListener;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.mailbox.MailboxDirectory;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.api.plugin.file.FileConstants.PROP_PATH;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@ThreadSafe
+@NotNullByDefault
+class MailboxFileManagerImpl implements MailboxFileManager, EventListener {
+
+	private static final Logger LOG =
+			getLogger(MailboxFileManagerImpl.class.getName());
+
+	// Package access for testing
+	static final String DOWNLOAD_DIR_NAME = "downloads";
+
+	private final Executor ioExecutor;
+	private final PluginManager pluginManager;
+	private final ConnectionManager connectionManager;
+	private final LifecycleManager lifecycleManager;
+	private final File mailboxDir;
+	private final EventBus eventBus;
+	private final CountDownLatch orphanLatch = new CountDownLatch(1);
+
+	@Inject
+	MailboxFileManagerImpl(@IoExecutor Executor ioExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			LifecycleManager lifecycleManager,
+			@MailboxDirectory File mailboxDir,
+			EventBus eventBus) {
+		this.ioExecutor = ioExecutor;
+		this.pluginManager = pluginManager;
+		this.connectionManager = connectionManager;
+		this.lifecycleManager = lifecycleManager;
+		this.mailboxDir = mailboxDir;
+		this.eventBus = eventBus;
+	}
+
+	@Override
+	public File createTempFileForDownload() throws IOException {
+		// Wait for orphaned files to be handled before creating new files
+		try {
+			orphanLatch.await();
+		} catch (InterruptedException e) {
+			throw new IOException(e);
+		}
+		File downloadDir = createDirectoryIfNeeded(DOWNLOAD_DIR_NAME);
+		return File.createTempFile("mailbox", ".tmp", downloadDir);
+	}
+
+	private File createDirectoryIfNeeded(String name) throws IOException {
+		File dir = new File(mailboxDir, name);
+		//noinspection ResultOfMethodCallIgnored
+		dir.mkdirs();
+		if (!dir.isDirectory()) {
+			throw new IOException("Failed to create directory '" + name + "'");
+		}
+		return dir;
+	}
+
+	@Override
+	public void handleDownloadedFile(File f) {
+		// We shouldn't reach this point until the plugin has been started
+		SimplexPlugin plugin =
+				(SimplexPlugin) requireNonNull(pluginManager.getPlugin(ID));
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_PATH, f.getAbsolutePath());
+		TransportConnectionReader reader = plugin.createReader(p);
+		if (reader == null) {
+			LOG.warning("Failed to create reader for downloaded file");
+			return;
+		}
+		TransportConnectionReader decorated = new MailboxFileReader(reader, f);
+		LOG.info("Reading downloaded file");
+		connectionManager.manageIncomingConnection(ID, decorated,
+				exception -> isHandlingComplete(exception, true));
+	}
+
+	private boolean isHandlingComplete(boolean exception, boolean recognised) {
+		// If we've successfully read the file then we're done
+		if (!exception && recognised) return true;
+		// If the app is shutting down we may get spurious IO exceptions
+		// due to executors being shut down. Leave the file in the download
+		// directory and we'll try to read it again at the next startup
+		return !lifecycleManager.getLifecycleState().isAfter(RUNNING);
+	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
+			if (t.getTransportId().equals(ID)) {
+				ioExecutor.execute(this::handleOrphanedFiles);
+				eventBus.removeListener(this);
+			}
+		}
+	}
+
+	/**
+	 * This method is called at startup, as soon as the plugin is started, to
+	 * handle any files that were left in the download directory at the last
+	 * shutdown.
+	 */
+	@IoExecutor
+	private void handleOrphanedFiles() {
+		try {
+			File downloadDir = createDirectoryIfNeeded(DOWNLOAD_DIR_NAME);
+			File[] orphans = downloadDir.listFiles();
+			// Now that we've got the list of orphans, new files can be created
+			orphanLatch.countDown();
+			if (orphans != null) for (File f : orphans) handleDownloadedFile(f);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+
+	private class MailboxFileReader implements TransportConnectionReader {
+
+		private final TransportConnectionReader delegate;
+		private final File file;
+
+		private MailboxFileReader(TransportConnectionReader delegate,
+				File file) {
+			this.delegate = delegate;
+			this.file = file;
+		}
+
+		@Override
+		public InputStream getInputStream() throws IOException {
+			return delegate.getInputStream();
+		}
+
+		@Override
+		public void dispose(boolean exception, boolean recognised)
+				throws IOException {
+			delegate.dispose(exception, recognised);
+			if (isHandlingComplete(exception, recognised)) {
+				LOG.info("Deleting downloaded file");
+				if (!file.delete()) {
+					LOG.warning("Failed to delete downloaded file");
+				}
+			}
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxModule.java

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.client.ClientHelper;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.mailbox.MailboxManager;
 import org.briarproject.bramble.api.mailbox.MailboxSettingsManager;
@@ -34,6 +35,8 @@ public class MailboxModule {
 		MailboxUpdateValidator mailboxUpdateValidator;
 		@Inject
 		MailboxUpdateManager mailboxUpdateManager;
+		@Inject
+		MailboxFileManager mailboxFileManager;
 	}
 
 	@Provides
@@ -101,4 +104,14 @@ public class MailboxModule {
 		}
 		return mailboxUpdateManager;
 	}
+
+	@Provides
+	@Singleton
+	MailboxFileManager provideMailboxFileManager(FeatureFlags featureFlags,
+			EventBus eventBus, MailboxFileManagerImpl mailboxFileManager) {
+		if (featureFlags.shouldEnableMailbox()) {
+			eventBus.addListener(mailboxFileManager);
+		}
+		return mailboxFileManager;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/AbstractRemovableDrivePlugin.java

@@ -67,6 +67,7 @@ abstract class AbstractRemovableDrivePlugin implements SimplexPlugin {
 	public void start() {
 		callback.mergeLocalProperties(
 				new TransportProperties(singletonMap(PROP_SUPPORTED, "true")));
+		callback.pluginStateChanged(ACTIVE);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FilePlugin.java

@@ -11,6 +11,7 @@ import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.OutputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
@@ -29,11 +30,6 @@ abstract class FilePlugin implements SimplexPlugin {
 	protected final PluginCallback callback;
 	protected final long maxLatency;
 
-	protected abstract void writerFinished(File f, boolean exception);
-
-	protected abstract void readerFinished(File f, boolean exception,
-			boolean recognised);
-
 	FilePlugin(PluginCallback callback, long maxLatency) {
 		this.callback = callback;
 		this.maxLatency = maxLatency;
@@ -50,9 +46,8 @@ abstract class FilePlugin implements SimplexPlugin {
 		String path = p.get(PROP_PATH);
 		if (isNullOrEmpty(path)) return null;
 		try {
-			File file = new File(path);
-			FileInputStream in = new FileInputStream(file);
-			return new FileTransportReader(file, in, this);
+			FileInputStream in = new FileInputStream(path);
+			return new TransportInputStreamReader(in);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
 			return null;
@@ -70,8 +65,8 @@ abstract class FilePlugin implements SimplexPlugin {
 				LOG.info("Failed to create file");
 				return null;
 			}
-			FileOutputStream out = new FileOutputStream(file);
-			return new FileTransportWriter(file, out, this);
+			OutputStream out = new FileOutputStream(file);
+			return new TransportOutputStreamWriter(this, out);
 		} catch (IOException e) {
 			logException(LOG, WARNING, e);
 			return null;

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FileTransportReader.java

@@ -1,39 +0,0 @@
-package org.briarproject.bramble.plugin.file;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportConnectionReader;
-
-import java.io.File;
-import java.io.InputStream;
-import java.util.logging.Logger;
-
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.IoUtils.tryToClose;
-
-@NotNullByDefault
-class FileTransportReader implements TransportConnectionReader {
-
-	private static final Logger LOG =
-			Logger.getLogger(FileTransportReader.class.getName());
-
-	private final File file;
-	private final InputStream in;
-	private final FilePlugin plugin;
-
-	FileTransportReader(File file, InputStream in, FilePlugin plugin) {
-		this.file = file;
-		this.in = in;
-		this.plugin = plugin;
-	}
-
-	@Override
-	public InputStream getInputStream() {
-		return in;
-	}
-
-	@Override
-	public void dispose(boolean exception, boolean recognised) {
-		tryToClose(in, LOG, WARNING);
-		plugin.readerFinished(file, exception, recognised);
-	}
-}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FileTransportWriter.java

@@ -1,54 +0,0 @@
-package org.briarproject.bramble.plugin.file;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
-
-import java.io.File;
-import java.io.OutputStream;
-import java.util.logging.Logger;
-
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.IoUtils.tryToClose;
-
-@NotNullByDefault
-class FileTransportWriter implements TransportConnectionWriter {
-
-	private static final Logger LOG =
-			Logger.getLogger(FileTransportWriter.class.getName());
-
-	private final File file;
-	private final OutputStream out;
-	private final FilePlugin plugin;
-
-	FileTransportWriter(File file, OutputStream out, FilePlugin plugin) {
-		this.file = file;
-		this.out = out;
-		this.plugin = plugin;
-	}
-
-	@Override
-	public long getMaxLatency() {
-		return plugin.getMaxLatency();
-	}
-
-	@Override
-	public int getMaxIdleTime() {
-		return plugin.getMaxIdleTime();
-	}
-
-	@Override
-	public boolean isLossyAndCheap() {
-		return plugin.isLossyAndCheap();
-	}
-
-	@Override
-	public OutputStream getOutputStream() {
-		return out;
-	}
-
-	@Override
-	public void dispose(boolean exception) {
-		tryToClose(out, LOG, WARNING);
-		plugin.writerFinished(file, exception);
-	}
-}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/MailboxPlugin.java

@@ -0,0 +1,73 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.ConnectionHandler;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.PluginException;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.util.Collection;
+
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+
+@NotNullByDefault
+class MailboxPlugin extends FilePlugin {
+
+	MailboxPlugin(PluginCallback callback, long maxLatency) {
+		super(callback, maxLatency);
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public int getMaxIdleTime() {
+		// Unused for simplex transports
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void start() throws PluginException {
+		callback.pluginStateChanged(ACTIVE);
+	}
+
+	@Override
+	public void stop() throws PluginException {
+	}
+
+	@Override
+	public State getState() {
+		return ACTIVE;
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return 0;
+	}
+
+	@Override
+	public boolean shouldPoll() {
+		return false;
+	}
+
+	@Override
+	public int getPollingInterval() {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void poll(
+			Collection<Pair<TransportProperties, ConnectionHandler>> properties) {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public boolean isLossyAndCheap() {
+		return false;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/MailboxPluginFactory.java

@@ -0,0 +1,39 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+
+@NotNullByDefault
+public class MailboxPluginFactory implements SimplexPluginFactory {
+
+	private static final long MAX_LATENCY = DAYS.toMillis(14);
+
+	@Inject
+	MailboxPluginFactory() {
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public long getMaxLatency() {
+		return MAX_LATENCY;
+	}
+
+	@Nullable
+	@Override
+	public SimplexPlugin createPlugin(PluginCallback callback) {
+		return new MailboxPlugin(callback, MAX_LATENCY);
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/mailbox/MailboxFileManagerImplTest.java

@@ -0,0 +1,194 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionManager.TagController;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.CaptureArgumentAction;
+import org.briarproject.bramble.test.RunAction;
+import org.jmock.Expectations;
+import org.jmock.lib.action.DoAllAction;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.File;
+import java.util.concurrent.Executor;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
+import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.STOPPING;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.ID;
+import static org.briarproject.bramble.api.plugin.file.FileConstants.PROP_PATH;
+import static org.briarproject.bramble.mailbox.MailboxFileManagerImpl.DOWNLOAD_DIR_NAME;
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class MailboxFileManagerImplTest extends BrambleMockTestCase {
+
+	private final Executor ioExecutor = context.mock(Executor.class);
+	private final PluginManager pluginManager =
+			context.mock(PluginManager.class);
+	private final ConnectionManager connectionManager =
+			context.mock(ConnectionManager.class);
+	private final LifecycleManager lifecycleManager =
+			context.mock(LifecycleManager.class);
+	private final EventBus eventBus = context.mock(EventBus.class);
+	private final SimplexPlugin plugin = context.mock(SimplexPlugin.class);
+	private final TransportConnectionReader transportConnectionReader =
+			context.mock(TransportConnectionReader.class);
+
+	private File mailboxDir;
+	private MailboxFileManagerImpl manager;
+
+	@Before
+	public void setUp() {
+		mailboxDir = getTestDirectory();
+		manager = new MailboxFileManagerImpl(ioExecutor, pluginManager,
+				connectionManager, lifecycleManager, mailboxDir, eventBus);
+	}
+
+	@After
+	public void tearDown() {
+		deleteTestDirectory(mailboxDir);
+	}
+
+	@Test
+	public void testHandlesOrphanedFilesAtStartup() throws Exception {
+		// Create an orphaned file, left behind at the previous shutdown
+		File downloadDir = new File(mailboxDir, DOWNLOAD_DIR_NAME);
+		//noinspection ResultOfMethodCallIgnored
+		downloadDir.mkdirs();
+		File orphan = new File(downloadDir, "orphan");
+		assertTrue(orphan.createNewFile());
+
+		TransportProperties props = new TransportProperties();
+		props.put(PROP_PATH, orphan.getAbsolutePath());
+
+		// When the plugin becomes active the orphaned file should be handled
+		context.checking(new Expectations() {{
+			oneOf(ioExecutor).execute(with(any(Runnable.class)));
+			will(new RunAction());
+			oneOf(eventBus).removeListener(manager);
+			oneOf(pluginManager).getPlugin(ID);
+			will(returnValue(plugin));
+			oneOf(plugin).createReader(props);
+			will(returnValue(transportConnectionReader));
+			oneOf(connectionManager).manageIncomingConnection(with(ID),
+					with(any(TransportConnectionReader.class)),
+					with(any(TagController.class)));
+		}});
+
+		manager.eventOccurred(new TransportActiveEvent(ID));
+	}
+
+	@Test
+	public void testDeletesFileWhenReadSucceeds() throws Exception {
+		expectCheckForOrphans();
+		manager.eventOccurred(new TransportActiveEvent(ID));
+
+		File f = manager.createTempFileForDownload();
+		AtomicReference<TransportConnectionReader> reader =
+				new AtomicReference<>(null);
+		AtomicReference<TagController> controller = new AtomicReference<>(null);
+
+		expectPassFileToConnectionManager(f, reader, controller);
+		manager.handleDownloadedFile(f);
+
+		// The read is successful, so the tag controller should allow the tag
+		// to be marked as read and the reader should delete the file
+		context.checking(new Expectations() {{
+			oneOf(transportConnectionReader).dispose(false, true);
+		}});
+
+		assertTrue(controller.get().shouldMarkTagAsRecognised(false));
+		reader.get().dispose(false, true);
+		assertFalse(f.exists());
+	}
+
+	@Test
+	public void testDeletesFileWhenTagIsNotRecognised() throws Exception {
+		testDeletesFile(false, RUNNING, false);
+	}
+
+	@Test
+	public void testDeletesFileWhenReadFails() throws Exception {
+		testDeletesFile(true, RUNNING, false);
+	}
+
+	@Test
+	public void testDoesNotDeleteFileWhenTagIsNotRecognisedAtShutdown()
+			throws Exception {
+		testDeletesFile(false, STOPPING, true);
+	}
+
+	@Test
+	public void testDoesNotDeleteFileWhenReadFailsAtShutdown()
+			throws Exception {
+		testDeletesFile(true, STOPPING, true);
+	}
+
+	private void testDeletesFile(boolean recognised, LifecycleState state,
+			boolean fileExists) throws Exception {
+		expectCheckForOrphans();
+		manager.eventOccurred(new TransportActiveEvent(ID));
+
+		File f = manager.createTempFileForDownload();
+		AtomicReference<TransportConnectionReader> reader =
+				new AtomicReference<>(null);
+		AtomicReference<TagController> controller = new AtomicReference<>(null);
+
+		expectPassFileToConnectionManager(f, reader, controller);
+		manager.handleDownloadedFile(f);
+
+		context.checking(new Expectations() {{
+			oneOf(transportConnectionReader).dispose(true, recognised);
+			oneOf(lifecycleManager).getLifecycleState();
+			will(returnValue(state));
+		}});
+
+		reader.get().dispose(true, recognised);
+		assertEquals(fileExists, f.exists());
+	}
+
+	private void expectCheckForOrphans() {
+		context.checking(new Expectations() {{
+			oneOf(ioExecutor).execute(with(any(Runnable.class)));
+			will(new RunAction());
+			oneOf(eventBus).removeListener(manager);
+		}});
+	}
+
+	private void expectPassFileToConnectionManager(File f,
+			AtomicReference<TransportConnectionReader> reader,
+			AtomicReference<TagController> controller) {
+		TransportProperties props = new TransportProperties();
+		props.put(PROP_PATH, f.getAbsolutePath());
+
+		context.checking(new Expectations() {{
+			oneOf(pluginManager).getPlugin(ID);
+			will(returnValue(plugin));
+			oneOf(plugin).createReader(props);
+			will(returnValue(transportConnectionReader));
+			oneOf(connectionManager).manageIncomingConnection(with(ID),
+					with(any(TransportConnectionReader.class)),
+					with(any(TagController.class)));
+			will(new DoAllAction(
+					new CaptureArgumentAction<>(reader,
+							TransportConnectionReader.class, 1),
+					new CaptureArgumentAction<>(controller,
+							TagController.class, 2)
+			));
+		}});
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/plugin/file/RemovableDriveIntegrationTestComponent.java

@@ -13,6 +13,7 @@ import org.briarproject.bramble.system.DefaultWakefulIoExecutorModule;
 import org.briarproject.bramble.system.TimeTravelModule;
 import org.briarproject.bramble.test.TestDatabaseConfigModule;
 import org.briarproject.bramble.test.TestFeatureFlagModule;
+import org.briarproject.bramble.test.TestMailboxDirectoryModule;
 import org.briarproject.bramble.test.TestSecureRandomModule;
 
 import javax.inject.Singleton;
@@ -27,6 +28,7 @@ import dagger.Component;
 		DefaultWakefulIoExecutorModule.class,
 		TestDatabaseConfigModule.class,
 		TestFeatureFlagModule.class,
+		TestMailboxDirectoryModule.class,
 		RemovableDriveIntegrationTestModule.class,
 		RemovableDriveModule.class,
 		TestSecureRandomModule.class,

bramble-core/src/test/java/org/briarproject/bramble/test/BrambleCoreIntegrationTestModule.java

@@ -13,6 +13,7 @@ import dagger.Module;
 		DefaultWakefulIoExecutorModule.class,
 		TestDatabaseConfigModule.class,
 		TestFeatureFlagModule.class,
+		TestMailboxDirectoryModule.class,
 		TestPluginConfigModule.class,
 		TestSecureRandomModule.class,
 		TimeTravelModule.class

bramble-core/src/test/java/org/briarproject/bramble/test/TestMailboxDirectoryModule.java

@@ -0,0 +1,18 @@
+package org.briarproject.bramble.test;
+
+import org.briarproject.bramble.api.mailbox.MailboxDirectory;
+
+import java.io.File;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class TestMailboxDirectoryModule {
+
+	@Provides
+	@MailboxDirectory
+	File provideMailboxDirectory() {
+		return new File("mailbox");
+	}
+}

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -14,6 +14,7 @@ import org.briarproject.bramble.api.crypto.PublicKey;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.mailbox.MailboxDirectory;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.BluetoothConstants;
 import org.briarproject.bramble.api.plugin.LanTcpConstants;
@@ -27,6 +28,7 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reporting.DevConfig;
 import org.briarproject.bramble.plugin.bluetooth.AndroidBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.file.AndroidRemovableDrivePluginFactory;
+import org.briarproject.bramble.plugin.file.MailboxPluginFactory;
 import org.briarproject.bramble.plugin.tcp.AndroidLanTcpPluginFactory;
 import org.briarproject.bramble.plugin.tor.AndroidTorPluginFactory;
 import org.briarproject.bramble.util.AndroidUtils;
@@ -63,6 +65,7 @@ import org.briarproject.briar.api.test.TestAvatarCreator;
 
 import java.io.File;
 import java.security.GeneralSecurityException;
+import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
@@ -76,7 +79,6 @@ import dagger.Provides;
 import static android.content.Context.MODE_PRIVATE;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Arrays.asList;
-import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_CONTROL_PORT;
@@ -156,6 +158,13 @@ public class AppModule {
 		return new AndroidDatabaseConfig(dbDir, keyDir, keyStrengthener);
 	}
 
+	@Provides
+	@Singleton
+	@MailboxDirectory
+	File provideMailboxDirectory(Application app) {
+		return app.getDir("mailbox", MODE_PRIVATE);
+	}
+
 	@Provides
 	@Singleton
 	@TorDirectory
@@ -190,7 +199,7 @@ public class AppModule {
 	PluginConfig providePluginConfig(AndroidBluetoothPluginFactory bluetooth,
 			AndroidTorPluginFactory tor, AndroidLanTcpPluginFactory lan,
 			AndroidRemovableDrivePluginFactory drive,
-			FeatureFlags featureFlags) {
+			MailboxPluginFactory mailbox, FeatureFlags featureFlags) {
 		@NotNullByDefault
 		PluginConfig pluginConfig = new PluginConfig() {
 
@@ -201,8 +210,10 @@ public class AppModule {
 
 			@Override
 			public Collection<SimplexPluginFactory> getSimplexFactories() {
-				if (SDK_INT >= 19) return singletonList(drive);
-				else return emptyList();
+				List<SimplexPluginFactory> simplex = new ArrayList<>();
+				if (featureFlags.shouldEnableMailbox()) simplex.add(mailbox);
+				if (SDK_INT >= 19) simplex.add(drive);
+				return simplex;
 			}
 
 			@Override

briar-headless/src/main/java/org/briarproject/briar/headless/HeadlessModule.kt

@@ -6,6 +6,7 @@ import dagger.Provides
 import org.briarproject.bramble.account.AccountModule
 import org.briarproject.bramble.api.FeatureFlags
 import org.briarproject.bramble.api.db.DatabaseConfig
+import org.briarproject.bramble.api.mailbox.MailboxDirectory
 import org.briarproject.bramble.api.plugin.PluginConfig
 import org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_CONTROL_PORT
 import org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_SOCKS_PORT
@@ -71,6 +72,12 @@ internal class HeadlessModule(private val appDir: File) {
         return HeadlessDatabaseConfig(dbDir, keyDir)
     }
 
+    @Provides
+    @MailboxDirectory
+    internal fun provideMailboxDirectory(): File {
+        return File(appDir, "mailbox")
+    }
+
     @Provides
     @TorDirectory
     internal fun provideTorDirectory(): File {

briar-headless/src/test/java/org/briarproject/briar/headless/HeadlessTestModule.kt

@@ -5,6 +5,7 @@ import dagger.Module
 import dagger.Provides
 import org.briarproject.bramble.account.AccountModule
 import org.briarproject.bramble.api.db.DatabaseConfig
+import org.briarproject.bramble.api.mailbox.MailboxDirectory
 import org.briarproject.bramble.api.plugin.PluginConfig
 import org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_CONTROL_PORT
 import org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_SOCKS_PORT
@@ -68,6 +69,12 @@ internal class HeadlessTestModule(private val appDir: File) {
         return HeadlessDatabaseConfig(dbDir, keyDir)
     }
 
+    @Provides
+    @MailboxDirectory
+    internal fun provideMailboxDirectory(): File {
+        return File(appDir, "mailbox")
+    }
+
     @Provides
     @TorSocksPort
     internal fun provideTorSocksPort(): Int = DEFAULT_SOCKS_PORT