Save logs to disk.

briar-core/src/main/java/org/briarproject/briar/BriarCoreModule.java

@@ -6,6 +6,7 @@ import org.briarproject.briar.feed.DnsModule;
 import org.briarproject.briar.feed.FeedModule;
 import org.briarproject.briar.forum.ForumModule;
 import org.briarproject.briar.introduction.IntroductionModule;
+import org.briarproject.briar.logging.LoggingModule;
 import org.briarproject.briar.messaging.MessagingModule;
 import org.briarproject.briar.privategroup.PrivateGroupModule;
 import org.briarproject.briar.privategroup.invitation.GroupInvitationModule;
@@ -22,6 +23,7 @@ import dagger.Module;
 		ForumModule.class,
 		GroupInvitationModule.class,
 		IntroductionModule.class,
+		LoggingModule.class,
 		MessagingModule.class,
 		PrivateGroupModule.class,
 		SharingModule.class,

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

@@ -0,0 +1,64 @@
+package org.briarproject.briar.logging;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.TimeZone;
+import java.util.logging.Formatter;
+import java.util.logging.LogRecord;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.Locale.US;
+
+@ThreadSafe
+@NotNullByDefault
+public class BriefLogFormatter extends Formatter {
+
+	private final Object lock = new Object();
+	private final DateFormat dateFormat; // Locking: lock
+	private final Date date; // Locking: lock
+
+	public BriefLogFormatter() {
+		synchronized (lock) {
+			dateFormat = new SimpleDateFormat("MM-dd HH:mm:ss.SSS ", US);
+			dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
+			date = new Date();
+		}
+	}
+
+	@Override
+	public String format(LogRecord record) {
+		String dateString;
+		synchronized (lock) {
+			date.setTime(record.getMillis());
+			dateString = dateFormat.format(date);
+		}
+		StringBuilder sb = new StringBuilder(dateString);
+		sb.append(record.getLevel().getName().charAt(0)).append('/');
+		String tag = record.getLoggerName();
+		tag = tag.substring(tag.lastIndexOf('.') + 1);
+		sb.append(tag).append(": ");
+		sb.append(record.getMessage());
+		Throwable t = record.getThrown();
+		if (t != null) {
+			sb.append('\n');
+			appendThrowable(sb, t);
+		}
+		sb.append('\n');
+		return sb.toString();
+	}
+
+	private void appendThrowable(StringBuilder sb, Throwable t) {
+		sb.append(t);
+		for (StackTraceElement e : t.getStackTrace())
+			sb.append("\n        at ").append(e);
+		Throwable cause = t.getCause();
+		if (cause != null) {
+			sb.append("\n     Caused by: ");
+			appendThrowable(sb, cause);
+		}
+	}
+}

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

@@ -0,0 +1,23 @@
+package org.briarproject.briar.logging;
+
+import org.briarproject.briar.api.logging.PersistentLogManager;
+
+import java.util.logging.Formatter;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class LoggingModule {
+
+	@Provides
+	Formatter provideFormatter() {
+		return new BriefLogFormatter();
+	}
+
+	@Provides
+	PersistentLogManager providePersistentLogManager(
+			PersistentLogManagerImpl logManager) {
+		return logManager;
+	}
+}

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

@@ -0,0 +1,93 @@
+package org.briarproject.briar.logging;
+
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.lifecycle.ShutdownManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.briar.api.logging.PersistentLogManager;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Scanner;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.logging.Formatter;
+import java.util.logging.Handler;
+import java.util.logging.Logger;
+import java.util.logging.StreamHandler;
+
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.Collections.emptyList;
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static java.util.concurrent.TimeUnit.MINUTES;
+
+@ThreadSafe
+@NotNullByDefault
+class PersistentLogManagerImpl implements PersistentLogManager {
+
+	private static final Logger LOG =
+			Logger.getLogger(PersistentLogManagerImpl.class.getName());
+
+	private static final String LOG_FILE = "briar.log";
+	private static final String OLD_LOG_FILE = "briar.log.old";
+	private static final long FLUSH_INTERVAL_MS = MINUTES.toMillis(5);
+
+	private final ScheduledExecutorService scheduler;
+	private final Executor ioExecutor;
+	private final ShutdownManager shutdownManager;
+	private final Formatter formatter;
+
+	@Inject
+	PersistentLogManagerImpl(@Scheduler ScheduledExecutorService scheduler,
+			@IoExecutor Executor ioExecutor, ShutdownManager shutdownManager,
+			Formatter formatter) {
+		this.scheduler = scheduler;
+		this.ioExecutor = ioExecutor;
+		this.shutdownManager = shutdownManager;
+		this.formatter = formatter;
+	}
+
+	@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);
+			StreamHandler handler = new StreamHandler(out, formatter);
+			scheduler.scheduleWithFixedDelay(() ->
+							ioExecutor.execute(handler::flush),
+					FLUSH_INTERVAL_MS, FLUSH_INTERVAL_MS, MILLISECONDS);
+			shutdownManager.addShutdownHook(handler::flush);
+			return handler;
+		} catch (SecurityException e) {
+			throw new IOException(e);
+		}
+	}
+
+	@Override
+	public Collection<String> getPersistedLog(File dir) throws IOException {
+		File oldLogFile = new File(dir, OLD_LOG_FILE);
+		if (oldLogFile.exists()) {
+			LOG.info("Reading old log file");
+			List<String> lines = new ArrayList<>();
+			Scanner s = new Scanner(oldLogFile);
+			while (s.hasNextLine()) lines.add(s.nextLine());
+			s.close();
+			return lines;
+		} else {
+			LOG.info("Old log file does not exist");
+			return emptyList();
+		}
+	}
+}