Merge branch '2292-contact-mailbox-download-worker' into 'master'

Mailbox download worker for a contact's mailbox

Closes #2292

See merge request briar/briar!1658

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

@@ -22,10 +22,21 @@ interface ConnectivityChecker {
 	 * the check succeeds. If a check is already running then the observer is
 	 * called when the check succeeds. If a connectivity check has recently
 	 * succeeded then the observer is called immediately.
+	 * <p>
+	 * Observers are removed after being called, or when the checker is
+	 * {@link #destroy() destroyed}.
 	 */
 	void checkConnectivity(MailboxProperties properties,
 			ConnectivityObserver o);
 
+	/**
+	 * Removes an observer that was added via
+	 * {@link #checkConnectivity(MailboxProperties, ConnectivityObserver)}. If
+	 * there are no remaining observers and a connectivity check is running
+	 * then the check will be cancelled.
+	 */
+	void removeObserver(ConnectivityObserver o);
+
 	interface ConnectivityObserver {
 		void onConnectivityCheckSucceeded();
 	}

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

@@ -80,8 +80,7 @@ abstract class ConnectivityCheckerImpl implements ConnectivityChecker {
 						> CONNECTIVITY_CHECK_FRESHNESS_MS) {
 					// The last connectivity check is stale, start a new one
 					connectivityObservers.add(o);
-					ApiCall task =
+					ApiCall task = createConnectivityCheckTask(properties);
-							createConnectivityCheckTask(properties);
 					connectivityCheck = mailboxApiCaller.retryWithBackoff(task);
 				} else {
 					// The last connectivity check is fresh
@@ -108,4 +107,16 @@ abstract class ConnectivityCheckerImpl implements ConnectivityChecker {
 			o.onConnectivityCheckSucceeded();
 		}
 	}
+
+	@Override
+	public void removeObserver(ConnectivityObserver o) {
+		synchronized (lock) {
+			if (destroyed) return;
+			connectivityObservers.remove(o);
+			if (connectivityObservers.isEmpty() && connectivityCheck != null) {
+				connectivityCheck.cancel();
+				connectivityCheck = null;
+			}
+		}
+	}
 }

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

@@ -5,8 +5,6 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
 
-import java.io.IOException;
-
 import javax.annotation.concurrent.ThreadSafe;
 
 @ThreadSafe
@@ -24,16 +22,11 @@ class ContactMailboxConnectivityChecker extends ConnectivityCheckerImpl {
 	@Override
 	ApiCall createConnectivityCheckTask(MailboxProperties properties) {
 		if (properties.isOwner()) throw new IllegalArgumentException();
-		return new SimpleApiCall() {
+		return new SimpleApiCall(() -> {
-			@Override
+			if (!mailboxApi.checkStatus(properties)) throw new ApiException();
-			void tryToCallApi() throws IOException, ApiException {
+			// Call the observers and cache the result
-				if (!mailboxApi.checkStatus(properties)) {
+			onConnectivityCheckSucceeded(clock.currentTimeMillis());
-					throw new ApiException();
+		});
-				}
-				// Call the observers and cache the result
-				onConnectivityCheckSucceeded(clock.currentTimeMillis());
-			}
-		};
 	}
 
 }

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

@@ -0,0 +1,241 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.Cancellable;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.mailbox.ConnectivityChecker.ConnectivityObserver;
+import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
+import org.briarproject.bramble.mailbox.MailboxApi.MailboxFile;
+import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
+import org.briarproject.bramble.mailbox.TorReachabilityMonitor.TorReachabilityObserver;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@ThreadSafe
+@NotNullByDefault
+class ContactMailboxDownloadWorker implements MailboxWorker,
+		ConnectivityObserver, TorReachabilityObserver {
+
+	/**
+	 * When the worker is started it waits for a connectivity check, then
+	 * starts its first download cycle: checking the inbox, downloading and
+	 * deleting any files, and checking again until the inbox is empty.
+	 * <p>
+	 * The worker then waits for our Tor hidden service to be reachable before
+	 * starting its second download cycle. This ensures that if a contact
+	 * tried and failed to connect to our hidden service before it was
+	 * reachable, and therefore uploaded a file to the mailbox instead, we'll
+	 * find the file in the second download cycle.
+	 */
+	private enum State {
+		CREATED,
+		CONNECTIVITY_CHECK,
+		DOWNLOAD_CYCLE_1,
+		WAITING_FOR_TOR,
+		DOWNLOAD_CYCLE_2,
+		FINISHED,
+		DESTROYED
+	}
+
+	private static final Logger LOG =
+			getLogger(ContactMailboxDownloadWorker.class.getName());
+
+	private final ConnectivityChecker connectivityChecker;
+	private final TorReachabilityMonitor torReachabilityMonitor;
+	private final MailboxApiCaller mailboxApiCaller;
+	private final MailboxApi mailboxApi;
+	private final MailboxFileManager mailboxFileManager;
+	private final MailboxProperties mailboxProperties;
+	private final Object lock = new Object();
+
+	@GuardedBy("lock")
+	private State state = State.CREATED;
+
+	@GuardedBy("lock")
+	@Nullable
+	private Cancellable apiCall = null;
+
+	ContactMailboxDownloadWorker(
+			ConnectivityChecker connectivityChecker,
+			TorReachabilityMonitor torReachabilityMonitor,
+			MailboxApiCaller mailboxApiCaller,
+			MailboxApi mailboxApi,
+			MailboxFileManager mailboxFileManager,
+			MailboxProperties mailboxProperties) {
+		if (mailboxProperties.isOwner()) throw new IllegalArgumentException();
+		this.connectivityChecker = connectivityChecker;
+		this.torReachabilityMonitor = torReachabilityMonitor;
+		this.mailboxApiCaller = mailboxApiCaller;
+		this.mailboxApi = mailboxApi;
+		this.mailboxFileManager = mailboxFileManager;
+		this.mailboxProperties = mailboxProperties;
+	}
+
+	@Override
+	public void start() {
+		LOG.info("Started");
+		synchronized (lock) {
+			// Don't allow the worker to be reused
+			if (state != State.CREATED) throw new IllegalStateException();
+			state = State.CONNECTIVITY_CHECK;
+		}
+		// Avoid leaking observer in case destroy() is called concurrently
+		// before observer is added
+		connectivityChecker.checkConnectivity(mailboxProperties, this);
+		boolean destroyed;
+		synchronized (lock) {
+			destroyed = state == State.DESTROYED;
+		}
+		if (destroyed) connectivityChecker.removeObserver(this);
+	}
+
+	@Override
+	public void destroy() {
+		LOG.info("Destroyed");
+		Cancellable apiCall;
+		synchronized (lock) {
+			state = State.DESTROYED;
+			apiCall = this.apiCall;
+			this.apiCall = null;
+		}
+		if (apiCall != null) apiCall.cancel();
+		connectivityChecker.removeObserver(this);
+		torReachabilityMonitor.removeObserver(this);
+	}
+
+	@Override
+	public void onConnectivityCheckSucceeded() {
+		LOG.info("Connectivity check succeeded");
+		synchronized (lock) {
+			if (state != State.CONNECTIVITY_CHECK) return;
+			state = State.DOWNLOAD_CYCLE_1;
+			// Start first download cycle
+			apiCall = mailboxApiCaller.retryWithBackoff(
+					new SimpleApiCall(this::apiCallListInbox));
+		}
+	}
+
+	private void apiCallListInbox() throws IOException, ApiException {
+		synchronized (lock) {
+			if (state == State.DESTROYED) return;
+		}
+		LOG.info("Listing inbox");
+		List<MailboxFile> files = mailboxApi.getFiles(mailboxProperties,
+				requireNonNull(mailboxProperties.getInboxId()));
+		if (files.isEmpty()) onDownloadCycleFinished();
+		else downloadNextFile(new LinkedList<>(files));
+	}
+
+	private void onDownloadCycleFinished() {
+		boolean addObserver = false;
+		synchronized (lock) {
+			if (state == State.DOWNLOAD_CYCLE_1) {
+				LOG.info("First download cycle finished");
+				state = State.WAITING_FOR_TOR;
+				addObserver = true;
+			} else if (state == State.DOWNLOAD_CYCLE_2) {
+				LOG.info("Second download cycle finished");
+				state = State.FINISHED;
+			}
+		}
+		if (addObserver) {
+			// Avoid leaking observer in case destroy() is called concurrently
+			// before observer is added
+			torReachabilityMonitor.addOneShotObserver(this);
+			boolean destroyed;
+			synchronized (lock) {
+				destroyed = state == State.DESTROYED;
+			}
+			if (destroyed) torReachabilityMonitor.removeObserver(this);
+		}
+	}
+
+	private void downloadNextFile(Queue<MailboxFile> queue) {
+		synchronized (lock) {
+			if (state == State.DESTROYED) return;
+			MailboxFile file = queue.remove();
+			apiCall = mailboxApiCaller.retryWithBackoff(
+					new SimpleApiCall(() -> apiCallDownloadFile(file, queue)));
+		}
+	}
+
+	private void apiCallDownloadFile(MailboxFile file,
+			Queue<MailboxFile> queue) throws IOException, ApiException {
+		synchronized (lock) {
+			if (state == State.DESTROYED) return;
+		}
+		LOG.info("Downloading file");
+		File tempFile = mailboxFileManager.createTempFileForDownload();
+		try {
+			mailboxApi.getFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()),
+					file.name, tempFile);
+		} catch (IOException | ApiException e) {
+			if (!tempFile.delete()) {
+				LOG.warning("Failed to delete temporary file");
+			}
+			throw e;
+		}
+		mailboxFileManager.handleDownloadedFile(tempFile);
+		deleteFile(file, queue);
+	}
+
+	private void deleteFile(MailboxFile file, Queue<MailboxFile> queue) {
+		synchronized (lock) {
+			if (state == State.DESTROYED) return;
+			apiCall = mailboxApiCaller.retryWithBackoff(
+					new SimpleApiCall(() -> apiCallDeleteFile(file, queue)));
+		}
+	}
+
+	private void apiCallDeleteFile(MailboxFile file, Queue<MailboxFile> queue)
+			throws IOException, ApiException {
+		synchronized (lock) {
+			if (state == State.DESTROYED) return;
+		}
+		try {
+			mailboxApi.deleteFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()), file.name);
+		} catch (TolerableFailureException e) {
+			// Catch this so we can continue to the next file
+			logException(LOG, INFO, e);
+		}
+		if (queue.isEmpty()) {
+			// List the inbox again to check for files that may have arrived
+			// while we were downloading
+			synchronized (lock) {
+				if (state == State.DESTROYED) return;
+				apiCall = mailboxApiCaller.retryWithBackoff(
+						new SimpleApiCall(this::apiCallListInbox));
+			}
+		} else {
+			downloadNextFile(queue);
+		}
+	}
+
+	@Override
+	public void onTorReachable() {
+		LOG.info("Our Tor hidden service is reachable");
+		synchronized (lock) {
+			if (state != State.WAITING_FOR_TOR) return;
+			state = State.DOWNLOAD_CYCLE_2;
+			// Start second download cycle
+			apiCall = mailboxApiCaller.retryWithBackoff(
+					new SimpleApiCall(this::apiCallListInbox));
+		}
+	}
+}

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

@@ -24,6 +24,8 @@ interface MailboxApiCaller {
 	 * Asynchronously calls the given API call on the {@link IoExecutor},
 	 * automatically retrying at increasing intervals until the API call
 	 * returns false or retries are cancelled.
+	 * <p>
+	 * This method is safe to call while holding a lock.
 	 *
 	 * @return A {@link Cancellable} that can be used to cancel any future
 	 * retries.

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

@@ -0,0 +1,23 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * A worker that downloads files from a contact's mailbox.
+ */
+@ThreadSafe
+@NotNullByDefault
+interface MailboxWorker {
+
+	/**
+	 * Asynchronously starts the worker.
+	 */
+	void start();
+
+	/**
+	 * Destroys the worker and cancels any pending tasks or retries.
+	 */
+	void destroy();
+}

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

@@ -16,17 +16,20 @@ import static org.briarproject.bramble.util.LogUtils.logException;
  * Convenience class for making simple API calls that don't return values.
  */
 @NotNullByDefault
-public abstract class SimpleApiCall implements ApiCall {
+class SimpleApiCall implements ApiCall {
 
 	private static final Logger LOG = getLogger(SimpleApiCall.class.getName());
 
-	abstract void tryToCallApi()
+	private final Attempt attempt;
-			throws IOException, ApiException, TolerableFailureException;
+
+	SimpleApiCall(Attempt attempt) {
+		this.attempt = attempt;
+	}
 
 	@Override
 	public boolean callApi() {
 		try {
-			tryToCallApi();
+			attempt.tryToCallApi();
 			return false; // Succeeded, don't retry
 		} catch (IOException | ApiException e) {
 			logException(LOG, WARNING, e);
@@ -36,4 +39,17 @@ public abstract class SimpleApiCall implements ApiCall {
 			return false; // Failed tolerably, don't retry
 		}
 	}
+
+	interface Attempt {
+
+		/**
+		 * Makes a single attempt to call an API endpoint. If this method
+		 * throws an {@link IOException} or an {@link ApiException}, the call
+		 * will be retried. If it throws a {@link TolerableFailureException}
+		 * or returns without throwing an exception, the call will not be
+		 * retried.
+		 */
+		void tryToCallApi()
+				throws IOException, ApiException, TolerableFailureException;
+	}
 }

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

@@ -38,6 +38,12 @@ interface TorReachabilityMonitor {
 	 */
 	void addOneShotObserver(TorReachabilityObserver o);
 
+	/**
+	 * Removes an observer that was added via
+	 * {@link #addOneShotObserver(TorReachabilityObserver)}.
+	 */
+	void removeObserver(TorReachabilityObserver o);
+
 	interface TorReachabilityObserver {
 
 		void onTorReachable();

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

@@ -87,6 +87,14 @@ class TorReachabilityMonitorImpl
 		if (callNow) o.onTorReachable();
 	}
 
+	@Override
+	public void removeObserver(TorReachabilityObserver o) {
+		synchronized (lock) {
+			if (destroyed) return;
+			observers.remove(o);
+		}
+	}
+
 	@Override
 	public void eventOccurred(Event e) {
 		if (e instanceof TransportActiveEvent) {

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

@@ -187,6 +187,32 @@ public class ConnectivityCheckerImplTest extends BrambleMockTestCase {
 		checker.onConnectivityCheckSucceeded(now);
 	}
 
+	@Test
+	public void testCheckIsCancelledWhenObserverIsRemoved() {
+		ConnectivityCheckerImpl checker = createChecker();
+
+		// When checkConnectivity() is called a check should be started
+		context.checking(new Expectations() {{
+			oneOf(clock).currentTimeMillis();
+			will(returnValue(now));
+			oneOf(mailboxApiCaller).retryWithBackoff(apiCall);
+			will(returnValue(task));
+		}});
+
+		checker.checkConnectivity(properties, observer1);
+
+		// When the observer is removed the check should be cancelled
+		context.checking(new Expectations() {{
+			oneOf(task).cancel();
+		}});
+
+		checker.removeObserver(observer1);
+
+		// If the check runs anyway (cancellation came too late) the observer
+		// should not be called
+		checker.onConnectivityCheckSucceeded(now);
+	}
+
 	private ConnectivityCheckerImpl createChecker() {
 
 		return new ConnectivityCheckerImpl(clock, mailboxApiCaller) {

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

@@ -0,0 +1,215 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.mailbox.MailboxFileId;
+import org.briarproject.bramble.api.mailbox.MailboxProperties;
+import org.briarproject.bramble.mailbox.MailboxApi.MailboxFile;
+import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.CaptureArgumentAction;
+import org.jmock.Expectations;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.File;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.mailbox.MailboxConstants.CLIENT_SUPPORTS;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getMailboxProperties;
+import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.junit.Assert.assertFalse;
+
+public class ContactMailboxDownloadWorkerTest extends BrambleMockTestCase {
+
+	private final ConnectivityChecker connectivityChecker =
+			context.mock(ConnectivityChecker.class);
+	private final TorReachabilityMonitor torReachabilityMonitor =
+			context.mock(TorReachabilityMonitor.class);
+	private final MailboxApiCaller mailboxApiCaller =
+			context.mock(MailboxApiCaller.class);
+	private final MailboxApi mailboxApi = context.mock(MailboxApi.class);
+	private final MailboxFileManager mailboxFileManager =
+			context.mock(MailboxFileManager.class);
+
+	private final MailboxProperties mailboxProperties =
+			getMailboxProperties(false, CLIENT_SUPPORTS);
+	private final long now = System.currentTimeMillis();
+	private final MailboxFile file1 =
+			new MailboxFile(new MailboxFileId(getRandomId()), now - 1);
+	private final MailboxFile file2 =
+			new MailboxFile(new MailboxFileId(getRandomId()), now);
+	private final List<MailboxFile> files = asList(file1, file2);
+
+	private File testDir, tempFile;
+	private ContactMailboxDownloadWorker worker;
+
+	@Before
+	public void setUp() {
+		testDir = getTestDirectory();
+		tempFile = new File(testDir, "temp");
+		worker = new ContactMailboxDownloadWorker(connectivityChecker,
+				torReachabilityMonitor, mailboxApiCaller, mailboxApi,
+				mailboxFileManager, mailboxProperties);
+	}
+
+	@After
+	public void tearDown() {
+		deleteTestDirectory(testDir);
+	}
+
+	@Test
+	public void testChecksConnectivityWhenStartedAndRemovesObserverWhenDestroyed() {
+		// When the worker is started it should start a connectivity check
+		context.checking(new Expectations() {{
+			oneOf(connectivityChecker).checkConnectivity(
+					with(mailboxProperties), with(worker));
+		}});
+
+		worker.start();
+
+		// When the worker is destroyed it should remove the connectivity
+		// and reachability observers
+		context.checking(new Expectations() {{
+			oneOf(connectivityChecker).removeObserver(worker);
+			oneOf(torReachabilityMonitor).removeObserver(worker);
+		}});
+
+		worker.destroy();
+	}
+
+	@Test
+	public void testDownloadsFilesWhenConnectivityCheckSucceeds()
+			throws Exception {
+		// When the worker is started it should start a connectivity check
+		context.checking(new Expectations() {{
+			oneOf(connectivityChecker).checkConnectivity(
+					with(mailboxProperties), with(worker));
+		}});
+
+		worker.start();
+
+		// When the connectivity check succeeds, a list-inbox task should be
+		// started for the first download cycle
+		AtomicReference<ApiCall> listTask = new AtomicReference<>(null);
+		context.checking(new Expectations() {{
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(listTask, ApiCall.class, 0));
+		}});
+
+		worker.onConnectivityCheckSucceeded();
+
+		// When the list-inbox tasks runs and finds some files to download,
+		// it should start a download task for the first file
+		AtomicReference<ApiCall> downloadTask = new AtomicReference<>(null);
+		context.checking(new Expectations() {{
+			oneOf(mailboxApi).getFiles(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()));
+			will(returnValue(files));
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(downloadTask, ApiCall.class, 0));
+		}});
+
+		assertFalse(listTask.get().callApi());
+
+		// When the first download task runs it should download the file to the
+		// location provided by the file manager and start a delete task
+		AtomicReference<ApiCall> deleteTask = new AtomicReference<>(null);
+		context.checking(new Expectations() {{
+			oneOf(mailboxFileManager).createTempFileForDownload();
+			will(returnValue(tempFile));
+			oneOf(mailboxApi).getFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()),
+					file1.name, tempFile);
+			oneOf(mailboxFileManager).handleDownloadedFile(tempFile);
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(deleteTask, ApiCall.class, 0));
+		}});
+
+		assertFalse(downloadTask.get().callApi());
+
+		// When the first delete task runs it should delete the file, ignore
+		// the tolerable failure, and start a download task for the next file
+		context.checking(new Expectations() {{
+			oneOf(mailboxApi).deleteFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()), file1.name);
+			will(throwException(new TolerableFailureException()));
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(downloadTask, ApiCall.class, 0));
+		}});
+
+		assertFalse(deleteTask.get().callApi());
+
+		// When the second download task runs it should download the file to
+		// the location provided by the file manager and start a delete task
+		context.checking(new Expectations() {{
+			oneOf(mailboxFileManager).createTempFileForDownload();
+			will(returnValue(tempFile));
+			oneOf(mailboxApi).getFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()),
+					file2.name, tempFile);
+			oneOf(mailboxFileManager).handleDownloadedFile(tempFile);
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(deleteTask, ApiCall.class, 0));
+		}});
+
+		assertFalse(downloadTask.get().callApi());
+
+		// When the second delete task runs it should delete the file and
+		// start a list-inbox task to check for files that may have arrived
+		// since the first download cycle started
+		context.checking(new Expectations() {{
+			oneOf(mailboxApi).deleteFile(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()), file2.name);
+			will(throwException(new TolerableFailureException()));
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(listTask, ApiCall.class, 0));
+		}});
+
+		assertFalse(deleteTask.get().callApi());
+
+		// When the list-inbox tasks runs and finds no more files to download,
+		// it should add a Tor reachability observer
+		context.checking(new Expectations() {{
+			oneOf(mailboxApi).getFiles(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()));
+			will(returnValue(emptyList()));
+			oneOf(torReachabilityMonitor).addOneShotObserver(worker);
+		}});
+
+		assertFalse(listTask.get().callApi());
+
+		// When the reachability observer is called, a list-inbox task should
+		// be started for the second download cycle
+		context.checking(new Expectations() {{
+			oneOf(mailboxApiCaller).retryWithBackoff(with(any(ApiCall.class)));
+			will(new CaptureArgumentAction<>(listTask, ApiCall.class, 0));
+		}});
+
+		worker.onTorReachable();
+
+		// When the list-inbox tasks runs and finds no more files to download,
+		// it should finish the second download cycle
+		context.checking(new Expectations() {{
+			oneOf(mailboxApi).getFiles(mailboxProperties,
+					requireNonNull(mailboxProperties.getInboxId()));
+			will(returnValue(emptyList()));
+		}});
+
+		assertFalse(listTask.get().callApi());
+
+		// When the worker is destroyed it should remove the connectivity
+		// and reachability observers
+		context.checking(new Expectations() {{
+			oneOf(connectivityChecker).removeObserver(worker);
+			oneOf(torReachabilityMonitor).removeObserver(worker);
+		}});
+
+		worker.destroy();
+	}
+}