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

This helps to avoid OOMs on low-memory devices.

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

@@ -5,7 +5,7 @@ import org.briarproject.bramble.api.settings.Settings;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.List;
+import java.util.Scanner;
 import java.util.logging.Handler;
 import java.util.logging.Logger;
 
@@ -36,11 +36,11 @@ public interface PersistentLogManager {
 	void addLogHandler(File dir, Logger logger) throws IOException;
 
 	/**
-	 * Loads and returns the persistent log entries stored in the given
+	 * Returns a {@link Scanner} for reading the persistent log entries stored
-	 * directory, or an empty list if no log entries are found.
+	 * 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
 	 */
-	List<String> getPersistedLog(File dir, boolean old) throws IOException;
+	Scanner getPersistedLog(File dir, boolean old) throws IOException;
 }

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

@@ -16,14 +16,13 @@ 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.LinkedList;
-import java.util.List;
 import java.util.Scanner;
 import java.util.concurrent.Executor;
 import java.util.concurrent.ScheduledExecutorService;
@@ -37,7 +36,6 @@ import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
-import static java.util.Collections.emptyList;
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -52,7 +50,6 @@ class PersistentLogManagerImpl implements PersistentLogManager,
 
 	private static final String LOG_FILE = "briar.log";
 	private static final String OLD_LOG_FILE = "briar.log.old";
-	private static final int MAX_LINES_TO_RETURN = 10_000;
 
 	private final ScheduledExecutorService scheduler;
 	private final Executor ioExecutor;
@@ -147,13 +144,13 @@ class PersistentLogManagerImpl implements PersistentLogManager,
 	}
 
 	@Override
-	public List<String> getPersistedLog(File dir, boolean old)
+	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 emptyList();
+				return emptyScanner();
 			}
 			return getPersistedLog(new File(dir, OLD_LOG_FILE), oldLogKey);
 		} else {
@@ -161,31 +158,20 @@ class PersistentLogManagerImpl implements PersistentLogManager,
 		}
 	}
 
-	private List<String> getPersistedLog(File logFile, SecretKey key)
+	private Scanner getPersistedLog(File logFile, SecretKey key)
 			throws IOException {
 		if (logFile.exists()) {
 			LOG.info("Reading log file");
-			LinkedList<String> lines = new LinkedList<>();
-			int numLines = 0;
 			InputStream in = new FileInputStream(logFile);
-			//noinspection TryFinallyCanBeTryWithResources
+			return new Scanner(streamReaderFactory.createLogStreamReader(in,
-			try {
+					key));
-				InputStream reader = streamReaderFactory
-						.createLogStreamReader(in, key);
-				Scanner s = new Scanner(reader);
-				while (s.hasNextLine()) {
-					lines.add(s.nextLine());
-					if (numLines == MAX_LINES_TO_RETURN) lines.poll();
-					else numLines++;
-				}
-				s.close();
-				return lines;
-			} finally {
-				in.close();
-			}
 		} else {
 			LOG.info("Log file does not exist");
-			return emptyList();
+			return emptyScanner();
 		}
 	}
+
+	private Scanner emptyScanner() {
+		return new Scanner(new ByteArrayInputStream(new byte[0]));
+	}
 }

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

@@ -26,7 +26,9 @@ 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;
@@ -54,6 +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) {
@@ -271,9 +275,16 @@ public class BriarReportPrimer implements ReportPrimer {
 			File logDir = ctx.getDir("log", MODE_PRIVATE);
 			StringBuilder sb = new StringBuilder();
 			try {
-				for (String line : logManager.getPersistedLog(logDir, old)) {
+				Scanner scanner = logManager.getPersistedLog(logDir, old);
-					sb.append(line).append('\n');
+				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);
 			}

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

@@ -19,7 +19,7 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.io.PrintWriter;
-import java.util.List;
+import java.util.Scanner;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
@@ -106,18 +106,19 @@ public class SettingsActivity extends BriarActivity {
 		ioExecutor.execute(() -> {
 			try {
 				File logDir = getApplication().getDir("log", MODE_PRIVATE);
-				List<String> lines = logManager.getPersistedLog(logDir, old);
+				Scanner scanner = logManager.getPersistedLog(logDir, old);
-				if (lines.isEmpty()) {
+				if (!scanner.hasNextLine()) {
+					scanner.close();
 					runOnUiThreadUnlessDestroyed(() ->
 							Toast.makeText(getApplication(), "Log is empty",
 									LENGTH_LONG).show());
 					return;
 				}
 				PrintWriter w = new PrintWriter(osp.getOutputStream());
-				for (String line : lines) {
+				while (scanner.hasNextLine()) w.println(scanner.nextLine());
-					w.println(line);
+				w.flush();
-				}
 				w.close();
+				scanner.close();
 				runOnUiThreadUnlessDestroyed(() ->
 						Toast.makeText(getApplication(), "Log exported",
 								LENGTH_LONG).show());