Avoid creating an in-memory copy of the log where possible.

This helps to avoid OOMs on low-memory devices.

bramble-android/src/main/java/org/briarproject/bramble/account/AndroidAccountManager.java

@@ -9,8 +9,10 @@ import org.briarproject.bramble.api.account.AccountManager;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 
 import java.io.File;
+import java.io.IOException;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -20,17 +22,21 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.GuardedBy;
 import javax.inject.Inject;
 
+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.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.IoUtils.deleteFileOrDir;
+import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.logFileOrDir;
 
 class AndroidAccountManager extends AccountManagerImpl
 		implements AccountManager {
 
 	private static final Logger LOG =
-			Logger.getLogger(AndroidAccountManager.class.getName());
+			getLogger(AndroidAccountManager.class.getName());
 
 	/**
 	 * Directories that shouldn't be deleted when deleting the user's account.
@@ -40,13 +46,16 @@ class AndroidAccountManager extends AccountManagerImpl
 
 	protected final Context appContext;
 	private final SharedPreferences prefs;
+	private final PersistentLogManager logManager;
 
 	@Inject
 	AndroidAccountManager(DatabaseConfig databaseConfig,
 			CryptoComponent crypto, IdentityManager identityManager,
-			SharedPreferences prefs, Application app) {
+			SharedPreferences prefs, PersistentLogManager logManager,
+			Application app) {
 		super(databaseConfig, crypto, identityManager);
 		this.prefs = prefs;
+		this.logManager = logManager;
 		appContext = app.getApplicationContext();
 	}
 
@@ -74,6 +83,7 @@ class AndroidAccountManager extends AccountManagerImpl
 				LOG.info("Contents of account directory after deleting:");
 				logFileOrDir(LOG, INFO, getDataDir());
 			}
+			replacePersistentLogger();
 		}
 	}
 
@@ -134,4 +144,13 @@ class AndroidAccountManager extends AccountManagerImpl
 	private void addIfNotNull(Set<File> files, @Nullable File file) {
 		if (file != null) files.add(file);
 	}
+
+	private void replacePersistentLogger() {
+		File logDir = appContext.getDir("log", MODE_PRIVATE);
+		try {
+			logManager.addLogHandler(logDir, getLogger(""));
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
 }

bramble-android/src/test/java/org/briarproject/bramble/account/AndroidAccountManagerTest.java

@@ -7,6 +7,7 @@ import android.content.pm.ApplicationInfo;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.jmock.Expectations;
 import org.jmock.lib.legacy.ClassImposteriser;
@@ -15,7 +16,9 @@ import org.junit.Before;
 import org.junit.Test;
 
 import java.io.File;
+import java.util.logging.Logger;
 
+import static android.content.Context.MODE_PRIVATE;
 import static junit.framework.Assert.assertFalse;
 import static junit.framework.Assert.assertTrue;
 import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
@@ -27,6 +30,8 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 			context.mock(SharedPreferences.class, "prefs");
 	private final SharedPreferences defaultPrefs =
 			context.mock(SharedPreferences.class, "defaultPrefs");
+	private final PersistentLogManager logManager =
+			context.mock(PersistentLogManager.class);
 	private final DatabaseConfig databaseConfig =
 			context.mock(DatabaseConfig.class);
 	private final CryptoComponent crypto = context.mock(CryptoComponent.class);
@@ -40,6 +45,7 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 	private final File testDir = getTestDirectory();
 	private final File keyDir = new File(testDir, "key");
 	private final File dbDir = new File(testDir, "db");
+	private final File logDir = new File(testDir, "log");
 
 	private AndroidAccountManager accountManager;
 
@@ -61,7 +67,7 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 			will(returnValue(app));
 		}});
 		accountManager = new AndroidAccountManager(databaseConfig, crypto,
-				identityManager, prefs, app) {
+				identityManager, prefs, logManager, app) {
 			@Override
 			SharedPreferences getDefaultSharedPreferences() {
 				return defaultPrefs;
@@ -109,10 +115,15 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 			will(returnValue(cacheDir));
 			oneOf(app).getExternalCacheDir();
 			will(returnValue(externalCacheDir));
+			oneOf(app).getDir("log", MODE_PRIVATE);
+			will(returnValue(logDir));
+			oneOf(logManager).addLogHandler(with(logDir),
+					with(any(Logger.class)));
 		}});
 
 		assertTrue(dbDir.mkdirs());
 		assertTrue(keyDir.mkdirs());
+		assertTrue(logDir.mkdirs());
 		assertTrue(codeCacheDir.mkdirs());
 		assertTrue(codeCacheFile.createNewFile());
 		assertTrue(libDir.mkdirs());
@@ -130,6 +141,7 @@ public class AndroidAccountManagerTest extends BrambleMockTestCase {
 
 		assertFalse(dbDir.exists());
 		assertFalse(keyDir.exists());
+		assertFalse(logDir.exists());
 		assertTrue(codeCacheDir.exists());
 		assertTrue(codeCacheFile.exists());
 		assertTrue(libDir.exists());

bramble-api/src/main/java/org/briarproject/bramble/api/StringMap.java

@@ -1,8 +1,16 @@
 package org.briarproject.bramble.api;
 
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
 import java.util.Hashtable;
 import java.util.Map;
 
+import javax.annotation.Nullable;
+
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
+@NotNullByDefault
 public abstract class StringMap extends Hashtable<String, String> {
 
 	protected StringMap(Map<String, String> m) {
@@ -52,4 +60,19 @@ public abstract class StringMap extends Hashtable<String, String> {
 	public void putLong(String key, long value) {
 		put(key, String.valueOf(value));
 	}
+
+	@Nullable
+	public byte[] getBytes(String key) {
+		String s = get(key);
+		if (s == null) return null;
+		try {
+			return fromHexString(s);
+		} catch (IllegalArgumentException e) {
+			return null;
+		}
+	}
+
+	public void putBytes(String key, byte[] value) {
+		put(key, toHexString(value));
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/StreamDecrypterFactory.java

@@ -19,4 +19,10 @@ public interface StreamDecrypterFactory {
 	 */
 	StreamDecrypter createContactExchangeStreamDecrypter(InputStream in,
 			SecretKey headerKey);
+
+	/**
+	 * Creates a {@link StreamDecrypter} for decrypting a log stream.
+	 */
+	StreamDecrypter createLogStreamDecrypter(InputStream in,
+			SecretKey headerKey);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/crypto/StreamEncrypterFactory.java

@@ -17,6 +17,12 @@ public interface StreamEncrypterFactory {
 	 * Creates a {@link StreamEncrypter} for encrypting a contact exchange
 	 * stream.
 	 */
-	StreamEncrypter createContactExchangeStreamDecrypter(OutputStream out,
+	StreamEncrypter createContactExchangeStreamEncrypter(OutputStream out,
+			SecretKey headerKey);
+
+	/**
+	 * Creates a {@link StreamEncrypter} for encrypting a log stream.
+	 */
+	StreamEncrypter createLogStreamEncrypter(OutputStream out,
 			SecretKey headerKey);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/logging/PersistentLogManager.java

@@ -0,0 +1,46 @@
+package org.briarproject.bramble.api.logging;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.Scanner;
+import java.util.logging.Handler;
+import java.util.logging.Logger;
+
+@NotNullByDefault
+public interface PersistentLogManager {
+
+	/**
+	 * The namespace of the (@link Settings) where the log key is stored.
+	 */
+	String LOG_SETTINGS_NAMESPACE = "log";
+
+	/**
+	 * The {@link Settings} key under which the log key is stored.
+	 */
+	String LOG_KEY_KEY = "logKey";
+
+	/**
+	 * Creates and returns a persistent log handler that stores its logs in
+	 * the given directory.
+	 */
+	Handler createLogHandler(File dir) throws IOException;
+
+	/**
+	 * Creates a persistent log handler that stores its logs in the given
+	 * directory and adds the handler to the given logger, replacing any
+	 * existing persistent log handler.
+	 */
+	void addLogHandler(File dir, Logger logger) throws IOException;
+
+	/**
+	 * Returns a {@link Scanner} for reading the persistent log entries stored
+	 * in the given directory.
+	 *
+	 * @param old True if the previous session's log should be loaded, or false
+	 * if the current session's log should be loaded
+	 */
+	Scanner getPersistedLog(File dir, boolean old) throws IOException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/transport/StreamReaderFactory.java

@@ -16,8 +16,13 @@ public interface StreamReaderFactory {
 
 	/**
 	 * Creates an {@link InputStream InputStream} for reading from a contact
-	 * exchangestream.
+	 * exchange stream.
 	 */
 	InputStream createContactExchangeStreamReader(InputStream in,
 			SecretKey headerKey);
+
+	/**
+	 * Creates an {@link InputStream} for reading from a log stream.
+	 */
+	InputStream createLogStreamReader(InputStream in, SecretKey headerKey);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/transport/StreamWriterFactory.java

@@ -9,15 +9,18 @@ import java.io.OutputStream;
 public interface StreamWriterFactory {
 
 	/**
-	 * Creates an {@link OutputStream OutputStream} for writing to a
-	 * transport stream
+	 * Creates a {@link StreamWriter} for writing to a transport stream.
 	 */
 	StreamWriter createStreamWriter(OutputStream out, StreamContext ctx);
 
 	/**
-	 * Creates an {@link OutputStream OutputStream} for writing to a contact
-	 * exchange stream.
+	 * Creates a {@link StreamWriter} for writing to a contact exchange stream.
 	 */
 	StreamWriter createContactExchangeStreamWriter(OutputStream out,
 			SecretKey headerKey);
+
+	/**
+	 * Creates a {@link StreamWriter} for writing to a log stream.
+	 */
+	StreamWriter createLogStreamWriter(OutputStream out, SecretKey headerKey);
 }

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java

@@ -13,6 +13,7 @@ import org.briarproject.bramble.identity.IdentityModule;
 import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.keyagreement.KeyAgreementModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
+import org.briarproject.bramble.logging.LoggingModule;
 import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.record.RecordModule;
@@ -41,6 +42,7 @@ import dagger.Module;
 		IoModule.class,
 		KeyAgreementModule.class,
 		LifecycleModule.class,
+		LoggingModule.class,
 		PluginModule.class,
 		PropertiesModule.class,
 		RecordModule.class,

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamDecrypterFactoryImpl.java

@@ -36,4 +36,10 @@ class StreamDecrypterFactoryImpl implements StreamDecrypterFactory {
 			SecretKey headerKey) {
 		return new StreamDecrypterImpl(in, cipherProvider.get(), 0, headerKey);
 	}
+
+	@Override
+	public StreamDecrypter createLogStreamDecrypter(InputStream in,
+			SecretKey headerKey) {
+		return createContactExchangeStreamDecrypter(in, headerKey);
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/crypto/StreamEncrypterFactoryImpl.java

@@ -51,7 +51,7 @@ class StreamEncrypterFactoryImpl implements StreamEncrypterFactory {
 	}
 
 	@Override
-	public StreamEncrypter createContactExchangeStreamDecrypter(
+	public StreamEncrypter createContactExchangeStreamEncrypter(
 			OutputStream out, SecretKey headerKey) {
 		AuthenticatedCipher cipher = cipherProvider.get();
 		byte[] streamHeaderNonce = new byte[STREAM_HEADER_NONCE_LENGTH];
@@ -60,4 +60,10 @@ class StreamEncrypterFactoryImpl implements StreamEncrypterFactory {
 		return new StreamEncrypterImpl(out, cipher, 0, null, streamHeaderNonce,
 				headerKey, frameKey);
 	}
+
+	@Override
+	public StreamEncrypter createLogStreamEncrypter(OutputStream out,
+			SecretKey headerKey) {
+		return createContactExchangeStreamEncrypter(out, headerKey);
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/logging/BriefLogFormatter.java

@@ -1,4 +1,4 @@
-package org.briarproject.briar.android.logging;
+package org.briarproject.bramble.logging;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
@@ -47,6 +47,7 @@ public class BriefLogFormatter extends Formatter {
 			sb.append('\n');
 			appendThrowable(sb, t);
 		}
+		sb.append('\n');
 		return sb.toString();
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/logging/FlushingStreamHandler.java

@@ -0,0 +1,43 @@
+package org.briarproject.bramble.logging;
+
+import java.io.OutputStream;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.logging.Formatter;
+import java.util.logging.LogRecord;
+import java.util.logging.StreamHandler;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+
+class FlushingStreamHandler extends StreamHandler {
+
+	private static final int FLUSH_DELAY_MS = 5_000;
+
+	private final ScheduledExecutorService scheduler;
+	private final Executor ioExecutor;
+	private final AtomicBoolean flushScheduled = new AtomicBoolean(false);
+
+	FlushingStreamHandler(ScheduledExecutorService scheduler,
+			Executor ioExecutor, OutputStream out, Formatter formatter) {
+		super(out, formatter);
+		this.scheduler = scheduler;
+		this.ioExecutor = ioExecutor;
+	}
+
+	@Override
+	public void publish(LogRecord record) {
+		super.publish(record);
+		if (!flushScheduled.getAndSet(true)) {
+			scheduler.schedule(this::scheduledFlush,
+					FLUSH_DELAY_MS, MILLISECONDS);
+		}
+	}
+
+	private void scheduledFlush() {
+		ioExecutor.execute(() -> {
+			flushScheduled.set(false);
+			flush();
+		});
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/logging/LoggingModule.java

@@ -0,0 +1,29 @@
+package org.briarproject.bramble.logging;
+
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
+
+import java.util.logging.Formatter;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class LoggingModule {
+
+	@Provides
+	Formatter provideFormatter() {
+		return new BriefLogFormatter();
+	}
+
+	@Provides
+	@Singleton
+	PersistentLogManager providePersistentLogManager(
+			LifecycleManager lifecycleManager,
+			PersistentLogManagerImpl persistentLogManager) {
+		lifecycleManager.registerOpenDatabaseHook(persistentLogManager);
+		return persistentLogManager;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/logging/PersistentLogManagerImpl.java

@@ -0,0 +1,177 @@
+package org.briarproject.bramble.logging;
+
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.OpenDatabaseHook;
+import org.briarproject.bramble.api.lifecycle.ShutdownManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.ByteArrayInputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.Scanner;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.logging.Formatter;
+import java.util.logging.Handler;
+import java.util.logging.Logger;
+import java.util.logging.StreamHandler;
+
+import javax.annotation.Nullable;
+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.util.LogUtils.logException;
+
+@ThreadSafe
+@NotNullByDefault
+class PersistentLogManagerImpl implements PersistentLogManager,
+		OpenDatabaseHook {
+
+	private static final Logger LOG =
+			getLogger(PersistentLogManagerImpl.class.getName());
+
+	private static final String LOG_FILE = "briar.log";
+	private static final String OLD_LOG_FILE = "briar.log.old";
+
+	private final ScheduledExecutorService scheduler;
+	private final Executor ioExecutor;
+	private final ShutdownManager shutdownManager;
+	private final DatabaseComponent db;
+	private final StreamReaderFactory streamReaderFactory;
+	private final StreamWriterFactory streamWriterFactory;
+	private final Formatter formatter;
+	private final SecretKey logKey;
+	private final AtomicReference<Integer> shutdownHookHandle =
+			new AtomicReference<>();
+
+	@Nullable
+	private volatile SecretKey oldLogKey = null;
+
+	@Inject
+	PersistentLogManagerImpl(
+			@Scheduler ScheduledExecutorService scheduler,
+			@IoExecutor Executor ioExecutor,
+			ShutdownManager shutdownManager,
+			DatabaseComponent db,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			Formatter formatter,
+			CryptoComponent crypto) {
+		this.scheduler = scheduler;
+		this.ioExecutor = ioExecutor;
+		this.shutdownManager = shutdownManager;
+		this.db = db;
+		this.streamReaderFactory = streamReaderFactory;
+		this.streamWriterFactory = streamWriterFactory;
+		this.formatter = formatter;
+		logKey = crypto.generateSecretKey();
+	}
+
+	@Override
+	public void onDatabaseOpened(Transaction txn) throws DbException {
+		Settings s = db.getSettings(txn, LOG_SETTINGS_NAMESPACE);
+		// Load the old log key, if any
+		byte[] oldKeyBytes = s.getBytes(LOG_KEY_KEY);
+		if (oldKeyBytes != null && oldKeyBytes.length == SecretKey.LENGTH) {
+			LOG.info("Loaded old log key");
+			oldLogKey = new SecretKey(oldKeyBytes);
+		}
+		// Store the current log key
+		s.putBytes(LOG_KEY_KEY, logKey.getBytes());
+		db.mergeSettings(txn, s, LOG_SETTINGS_NAMESPACE);
+	}
+
+	@Override
+	public Handler createLogHandler(File dir) throws IOException {
+		File logFile = new File(dir, LOG_FILE);
+		File oldLogFile = new File(dir, OLD_LOG_FILE);
+		if (oldLogFile.exists() && !oldLogFile.delete())
+			LOG.warning("Failed to delete old log file");
+		if (logFile.exists() && !logFile.renameTo(oldLogFile))
+			LOG.warning("Failed to rename log file");
+		try {
+			OutputStream out = new FileOutputStream(logFile);
+			StreamWriter writer =
+					streamWriterFactory.createLogStreamWriter(out, logKey);
+			StreamHandler handler = new FlushingStreamHandler(scheduler,
+					ioExecutor, writer.getOutputStream(), formatter);
+			// Flush the log and terminate the stream at shutdown
+			Runnable shutdownHook = () -> {
+				LOG.info("Shutting down");
+				handler.flush();
+				try {
+					writer.sendEndOfStream();
+				} catch (IOException e) {
+					logException(LOG, WARNING, e);
+				}
+			};
+			int handle = shutdownManager.addShutdownHook(shutdownHook);
+			// If a previous handler registered a shutdown hook, remove it
+			Integer oldHandle = shutdownHookHandle.getAndSet(handle);
+			if (oldHandle != null) {
+				shutdownManager.removeShutdownHook(oldHandle);
+			}
+			return handler;
+		} catch (SecurityException e) {
+			throw new IOException(e);
+		}
+	}
+
+	@Override
+	public void addLogHandler(File dir, Logger logger) throws IOException {
+		for (Handler h : logger.getHandlers()) {
+			if (h instanceof FlushingStreamHandler) logger.removeHandler(h);
+		}
+		logger.addHandler(createLogHandler(dir));
+	}
+
+	@Override
+	public Scanner getPersistedLog(File dir, boolean old)
+			throws IOException {
+		if (old) {
+			SecretKey oldLogKey = this.oldLogKey;
+			if (oldLogKey == null) {
+				LOG.info("Old log key has not been loaded");
+				return emptyScanner();
+			}
+			return getPersistedLog(new File(dir, OLD_LOG_FILE), oldLogKey);
+		} else {
+			return getPersistedLog(new File(dir, LOG_FILE), logKey);
+		}
+	}
+
+	private Scanner getPersistedLog(File logFile, SecretKey key)
+			throws IOException {
+		if (logFile.exists()) {
+			LOG.info("Reading log file");
+			InputStream in = new FileInputStream(logFile);
+			return new Scanner(streamReaderFactory.createLogStreamReader(in,
+					key));
+		} else {
+			LOG.info("Log file does not exist");
+			return emptyScanner();
+		}
+	}
+
+	private Scanner emptyScanner() {
+		return new Scanner(new ByteArrayInputStream(new byte[0]));
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/StreamReaderFactoryImpl.java

@@ -24,15 +24,21 @@ class StreamReaderFactoryImpl implements StreamReaderFactory {
 
 	@Override
 	public InputStream createStreamReader(InputStream in, StreamContext ctx) {
-		return new StreamReaderImpl(
-				streamDecrypterFactory.createStreamDecrypter(in, ctx));
+		return new StreamReaderImpl(streamDecrypterFactory
+				.createStreamDecrypter(in, ctx));
 	}
 
 	@Override
 	public InputStream createContactExchangeStreamReader(InputStream in,
 			SecretKey headerKey) {
-		return new StreamReaderImpl(
-				streamDecrypterFactory.createContactExchangeStreamDecrypter(in,
-						headerKey));
+		return new StreamReaderImpl(streamDecrypterFactory
+				.createContactExchangeStreamDecrypter(in, headerKey));
+	}
+
+	@Override
+	public InputStream createLogStreamReader(InputStream in,
+			SecretKey headerKey) {
+		return new StreamReaderImpl(streamDecrypterFactory
+				.createLogStreamDecrypter(in, headerKey));
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/transport/StreamWriterFactoryImpl.java

@@ -26,15 +26,21 @@ class StreamWriterFactoryImpl implements StreamWriterFactory {
 	@Override
 	public StreamWriter createStreamWriter(OutputStream out,
 			StreamContext ctx) {
-		return new StreamWriterImpl(
-				streamEncrypterFactory.createStreamEncrypter(out, ctx));
+		return new StreamWriterImpl(streamEncrypterFactory
+				.createStreamEncrypter(out, ctx));
 	}
 
 	@Override
 	public StreamWriter createContactExchangeStreamWriter(OutputStream out,
 			SecretKey headerKey) {
-		return new StreamWriterImpl(
-				streamEncrypterFactory.createContactExchangeStreamDecrypter(out,
-						headerKey));
+		return new StreamWriterImpl(streamEncrypterFactory
+				.createContactExchangeStreamEncrypter(out, headerKey));
+	}
+
+	@Override
+	public StreamWriter createLogStreamWriter(OutputStream out,
+			SecretKey headerKey) {
+		return new StreamWriterImpl(streamEncrypterFactory
+				.createLogStreamEncrypter(out, headerKey));
 	}
 }

briar-android/src/main/java/org/briarproject/bramble/account/BriarAccountManager.java

@@ -6,6 +6,7 @@ import android.content.SharedPreferences;
 import org.briarproject.bramble.api.crypto.CryptoComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.Localizer;
 import org.briarproject.briar.android.util.UiUtils;
@@ -17,8 +18,8 @@ class BriarAccountManager extends AndroidAccountManager {
 	@Inject
 	BriarAccountManager(DatabaseConfig databaseConfig, CryptoComponent crypto,
 			IdentityManager identityManager, SharedPreferences prefs,
-			Application app) {
-		super(databaseConfig, crypto, identityManager, prefs, app);
+			PersistentLogManager logManager, Application app) {
+		super(databaseConfig, crypto, identityManager, prefs, logManager, app);
 	}
 
 	@Override

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

@@ -20,6 +20,7 @@ import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.api.keyagreement.PayloadParser;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.settings.SettingsManager;
 import org.briarproject.bramble.api.system.AndroidExecutor;
@@ -56,6 +57,7 @@ import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager
 import org.briarproject.briar.api.test.TestDataCreator;
 
 import java.util.concurrent.Executor;
+import java.util.logging.Formatter;
 
 import javax.inject.Singleton;
 
@@ -165,6 +167,10 @@ public interface AndroidComponent
 
 	FeatureFlags featureFlags();
 
+	PersistentLogManager persistentLogManager();
+
+	Formatter formatter();
+
 	void inject(SignInReminderReceiver briarService);
 
 	void inject(BriarService briarService);

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

@@ -19,6 +19,7 @@ import org.acra.ReportingInteractionMode;
 import org.acra.annotation.ReportsCrashes;
 import org.briarproject.bramble.BrambleAndroidEagerSingletons;
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 import org.briarproject.briar.BriarCoreEagerSingletons;
 import org.briarproject.briar.BuildConfig;
 import org.briarproject.briar.R;
@@ -28,6 +29,8 @@ import org.briarproject.briar.android.reporting.BriarReportSenderFactory;
 import org.briarproject.briar.android.reporting.DevReportActivity;
 import org.briarproject.briar.android.util.UiUtils;
 
+import java.io.File;
+import java.io.IOException;
 import java.util.Collection;
 import java.util.logging.Handler;
 import java.util.logging.LogRecord;
@@ -36,6 +39,7 @@ import java.util.logging.Logger;
 import static android.app.ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND;
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
 import static org.acra.ReportField.ANDROID_VERSION;
 import static org.acra.ReportField.APP_VERSION_CODE;
@@ -54,6 +58,7 @@ import static org.acra.ReportField.REPORT_ID;
 import static org.acra.ReportField.STACK_TRACE;
 import static org.acra.ReportField.USER_APP_START_DATE;
 import static org.acra.ReportField.USER_CRASH_DATE;
+import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 
 @ReportsCrashes(
@@ -120,9 +125,19 @@ public class BriarApplicationImpl extends Application
 		rootLogger.addHandler(logHandler);
 		rootLogger.setLevel(IS_DEBUG_BUILD ? FINE : INFO);
 
+		applicationComponent = createApplicationComponent();
+
+		PersistentLogManager logManager =
+				applicationComponent.persistentLogManager();
+		File logDir = getDir("log", MODE_PRIVATE);
+		try {
+			rootLogger.addHandler(logManager.createLogHandler(logDir));
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+
 		LOG.info("Created");
 
-		applicationComponent = createApplicationComponent();
 		EmojiManager.install(new GoogleEmojiProvider());
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/activity/RequestCodes.java

@@ -16,5 +16,7 @@ public interface RequestCodes {
 	int REQUEST_KEYGUARD_UNLOCK = 12;
 	int REQUEST_ATTACH_IMAGE = 13;
 	int REQUEST_SAVE_ATTACHMENT = 14;
+	int REQUEST_EXPORT_LOG = 15;
+	int REQUEST_EXPORT_OLD_LOG = 16;
 
 }

briar-android/src/main/java/org/briarproject/briar/android/reporting/BriarReportPrimer.java

@@ -14,17 +14,21 @@ import android.os.Looper;
 import org.acra.builder.ReportBuilder;
 import org.acra.builder.ReportPrimer;
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
 import org.briarproject.briar.BuildConfig;
+import org.briarproject.briar.android.AndroidComponent;
 import org.briarproject.briar.android.BriarApplication;
-import org.briarproject.briar.android.logging.BriefLogFormatter;
 
 import java.io.File;
+import java.io.IOException;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.LinkedHashMap;
+import java.util.LinkedList;
 import java.util.Map;
+import java.util.Scanner;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.FutureTask;
@@ -37,6 +41,7 @@ import static android.bluetooth.BluetoothAdapter.SCAN_MODE_CONNECTABLE;
 import static android.bluetooth.BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE;
 import static android.content.Context.ACTIVITY_SERVICE;
 import static android.content.Context.CONNECTIVITY_SERVICE;
+import static android.content.Context.MODE_PRIVATE;
 import static android.content.Context.WIFI_P2P_SERVICE;
 import static android.content.Context.WIFI_SERVICE;
 import static android.net.ConnectivityManager.TYPE_MOBILE;
@@ -51,6 +56,8 @@ import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 public class BriarReportPrimer implements ReportPrimer {
 
+	private static final int MAX_PERSISTED_LOG_LINES = 1_000;
+
 	@Override
 	public void primeReport(@NonNull Context ctx,
 			@NonNull ReportBuilder builder) {
@@ -81,13 +88,23 @@ public class BriarReportPrimer implements ReportPrimer {
 			// Log
 			BriarApplication app =
 					(BriarApplication) ctx.getApplicationContext();
+			AndroidComponent appComponent = app.getApplicationComponent();
+			PersistentLogManager logManager =
+					appComponent.persistentLogManager();
+			Formatter formatter = appComponent.formatter();
+
 			StringBuilder sb = new StringBuilder();
-			Formatter formatter = new BriefLogFormatter();
 			for (LogRecord record : app.getRecentLogRecords()) {
-				sb.append(formatter.format(record)).append('\n');
+				sb.append(formatter.format(record));
 			}
 			customData.put("Log", sb.toString());
 
+			customData.put("Persisted log",
+					getPersistedLog(ctx, logManager, false));
+
+			customData.put("Previous persisted log",
+					getPersistedLog(ctx, logManager, true));
+
 			// System memory
 			Object o = ctx.getSystemService(ACTIVITY_SERVICE);
 			ActivityManager am = (ActivityManager) o;
@@ -252,6 +269,27 @@ public class BriarReportPrimer implements ReportPrimer {
 
 			return unmodifiableMap(customData);
 		}
+
+		private String getPersistedLog(Context ctx,
+				PersistentLogManager logManager, boolean old) {
+			File logDir = ctx.getDir("log", MODE_PRIVATE);
+			StringBuilder sb = new StringBuilder();
+			try {
+				Scanner scanner = logManager.getPersistedLog(logDir, old);
+				LinkedList<String> lines = new LinkedList<>();
+				int numLines = 0;
+				while (scanner.hasNextLine()) {
+					lines.add(scanner.nextLine());
+					if (numLines == MAX_PERSISTED_LOG_LINES) lines.pollFirst();
+					else numLines++;
+				}
+				scanner.close();
+				for (String line : lines) sb.append(line).append('\n');
+			} catch (IOException e) {
+				sb.append("Could not recover persisted log: ").append(e);
+			}
+			return sb.toString();
+		}
 	}
 
 	private static class SingleShotAndroidExecutor extends Thread {

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsActivity.java

@@ -1,18 +1,65 @@
 package org.briarproject.briar.android.settings;
 
+import android.content.Intent;
+import android.net.Uri;
 import android.os.Bundle;
 import android.view.MenuItem;
+import android.widget.Toast;
 
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.logging.PersistentLogManager;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
 
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.PrintWriter;
+import java.util.Scanner;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import androidx.annotation.RequiresApi;
 import androidx.appcompat.app.ActionBar;
 
+import static android.content.Intent.ACTION_CREATE_DOCUMENT;
+import static android.content.Intent.CATEGORY_OPENABLE;
+import static android.content.Intent.EXTRA_TITLE;
+import static android.os.Build.VERSION.SDK_INT;
+import static android.os.Environment.DIRECTORY_DOWNLOADS;
+import static android.os.Environment.getExternalStoragePublicDirectory;
+import static android.widget.Toast.LENGTH_LONG;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_EXPORT_LOG;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_EXPORT_OLD_LOG;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class SettingsActivity extends BriarActivity {
 
+	private static final Logger LOG =
+			getLogger(SettingsActivity.class.getName());
+
+	private static final String LOG_EXPORT_FILENAME = "briar-log.txt";
+
+	@Inject
+	@IoExecutor
+	Executor ioExecutor;
+
+	@Inject
+	PersistentLogManager logManager;
+
 	@Override
-	public void onCreate(Bundle bundle) {
+	public void onCreate(@Nullable Bundle bundle) {
 		super.onCreate(bundle);
 
 		ActionBar actionBar = getSupportActionBar();
@@ -37,4 +84,96 @@ public class SettingsActivity extends BriarActivity {
 		}
 		return false;
 	}
+
+	@Override
+	protected void onActivityResult(int request, int result,
+			@Nullable Intent data) {
+		super.onActivityResult(request, result, data);
+		if (request == REQUEST_EXPORT_LOG && result == RESULT_OK &&
+				data != null && data.getData() != null) {
+			exportLog(false, data.getData());
+		} else if (request == REQUEST_EXPORT_OLD_LOG && result == RESULT_OK &&
+				data != null && data.getData() != null) {
+			exportLog(true, data.getData());
+		}
+	}
+
+	private void exportLog(boolean old, Uri uri) {
+		copyLog(old, () -> getOutputStream(uri));
+	}
+
+	private void copyLog(boolean old, OutputStreamProvider osp) {
+		ioExecutor.execute(() -> {
+			try {
+				File logDir = getApplication().getDir("log", MODE_PRIVATE);
+				Scanner scanner = logManager.getPersistedLog(logDir, old);
+				if (!scanner.hasNextLine()) {
+					scanner.close();
+					runOnUiThreadUnlessDestroyed(() ->
+							Toast.makeText(getApplication(), "Log is empty",
+									LENGTH_LONG).show());
+					return;
+				}
+				PrintWriter w = new PrintWriter(osp.getOutputStream());
+				while (scanner.hasNextLine()) w.println(scanner.nextLine());
+				w.flush();
+				w.close();
+				scanner.close();
+				runOnUiThreadUnlessDestroyed(() ->
+						Toast.makeText(getApplication(), "Log exported",
+								LENGTH_LONG).show());
+			} catch (IOException e) {
+				logException(LOG, WARNING, e);
+				runOnUiThreadUnlessDestroyed(() ->
+						Toast.makeText(getApplication(), "Failed to export log",
+								LENGTH_LONG).show());
+			}
+		});
+	}
+
+	void onExportLogClick(boolean old) {
+		if (SDK_INT >= 19) {
+			Intent intent = getExportLogIntent();
+			int request = old ? REQUEST_EXPORT_OLD_LOG : REQUEST_EXPORT_LOG;
+			startActivityForResult(intent, request);
+		} else {
+			exportLog(old);
+		}
+	}
+
+	@RequiresApi(api = 19)
+	private Intent getExportLogIntent() {
+		Intent intent = new Intent(ACTION_CREATE_DOCUMENT);
+		intent.addCategory(CATEGORY_OPENABLE);
+		intent.setType("text/plain");
+		intent.putExtra(EXTRA_TITLE, LOG_EXPORT_FILENAME);
+		return intent;
+	}
+
+	private void exportLog(boolean old) {
+		File file = getLogOutputFile();
+		copyLog(old, () -> getOutputStream(file));
+	}
+
+	private File getLogOutputFile() {
+		File path = getExternalStoragePublicDirectory(DIRECTORY_DOWNLOADS);
+		//noinspection ResultOfMethodCallIgnored
+		path.mkdirs();
+		return new File(path, LOG_EXPORT_FILENAME);
+	}
+
+	private OutputStream getOutputStream(File file) throws IOException {
+		return new FileOutputStream(file);
+	}
+
+	private OutputStream getOutputStream(Uri uri) throws IOException {
+		OutputStream os =
+				getApplication().getContentResolver().openOutputStream(uri);
+		if (os == null) throw new IOException();
+		return os;
+	}
+
+	private interface OutputStreamProvider {
+		OutputStream getOutputStream() throws IOException;
+	}
 }

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsFragment.java

@@ -1,5 +1,6 @@
 package org.briarproject.briar.android.settings;
 
+import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
 import android.app.AlertDialog;
 import android.content.Context;
@@ -74,6 +75,7 @@ import static android.widget.Toast.LENGTH_SHORT;
 import static androidx.core.view.ViewCompat.LAYOUT_DIRECTION_LTR;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.plugin.Plugin.PREF_PLUGIN_ENABLE;
 import static org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_PREF_TOR_MOBILE;
 import static org.briarproject.bramble.api.plugin.TorConstants.DEFAULT_PREF_TOR_NETWORK;
@@ -133,7 +135,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 			"pref_key_tor_only_when_charging";
 
 	private static final Logger LOG =
-			Logger.getLogger(SettingsFragment.class.getName());
+			getLogger(SettingsFragment.class.getName());
 
 	private SettingsActivity listener;
 	private ListPreference language;
@@ -251,8 +253,25 @@ public class SettingsFragment extends PreferenceFragmentCompat
 						throw new RuntimeException("Boom!");
 					}
 			);
+			findPreference("pref_key_export_log").setOnPreferenceClickListener(
+					preference -> {
+						((SettingsActivity) requireActivity())
+								.onExportLogClick(false);
+						return true;
+					}
+			);
+			findPreference("pref_key_export_old_log")
+					.setOnPreferenceClickListener(
+							preference -> {
+								((SettingsActivity) requireActivity())
+										.onExportLogClick(true);
+								return true;
+							}
+					);
 		} else {
 			findPreference("pref_key_explode").setVisible(false);
+			findPreference("pref_key_export_log").setVisible(false);
+			findPreference("pref_key_export_old_log").setVisible(false);
 			findPreference("pref_key_test_data").setVisible(false);
 			PreferenceGroup testing =
 					findPreference("pref_key_explode").getParent();
@@ -331,6 +350,7 @@ public class SettingsFragment extends PreferenceFragmentCompat
 		return direction == LAYOUT_DIRECTION_LTR;
 	}
 
+	@SuppressLint("StringFormatInvalid")
 	private void setTorNetworkSummary(int torNetworkSetting) {
 		if (torNetworkSetting != PREF_TOR_NETWORK_AUTOMATIC) {
 			torNetwork.setSummary("%s");  // use setting value

briar-android/src/main/res/xml/settings.xml

@@ -227,6 +227,16 @@
 				android:targetPackage="@string/app_package"/>
 		</Preference>
 
+		<Preference
+			android:key="pref_key_export_log"
+			android:title="Export Current Log to SD Card"
+			app:iconSpaceReserved="false"/>
+
+		<Preference
+			android:key="pref_key_export_old_log"
+			android:title="Export Previous Log to SD Card"
+			app:iconSpaceReserved="false"/>
+
 		<Preference
 			android:key="pref_key_explode"
 			android:title="Crash"