Add ability to easily get the startTimestampMs of a session

firebase-crashlytics/src/androidTest/java/com/google/firebase/crashlytics/internal/persistence/CrashlyticsReportPersistenceTest.java

@@ -90,6 +90,17 @@ public void testListSortedOpenSessionIds_noOpenSessions() {
     assertTrue(openSessionIds.isEmpty());
   }
 
+  @Test
+  public void testPersistReports_getStartTimestampMillis() {
+    final String sessionId = "testSession";
+    final CrashlyticsReport testReport = makeTestReport(sessionId);
+
+    reportPersistence.persistReport(testReport);
+    assertEquals(
+        testReport.getSession().getStartedAt() * 1000,
+        reportPersistence.getStartTimestampMillis(sessionId));
+  }
+
   @Test
   public void testHasFinalizedReports() {
     final String sessionId = "testSession";

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/CrashlyticsController.java

@@ -37,7 +37,6 @@
 import java.io.FilenameFilter;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Date;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -168,14 +167,14 @@ synchronized void handleUncaughtException(
 
     // Capture the time that the crash occurs and close over it so that the time doesn't
     // reflect when we get around to executing the task later.
-    final Date time = new Date();
+    final long timestampMillis = System.currentTimeMillis();
 
     final Task<Void> handleUncaughtExceptionTask =
         backgroundWorker.submitTask(
             new Callable<Task<Void>>() {
               @Override
               public Task<Void> call() throws Exception {
-                final long timestampSeconds = getTimestampSeconds(time);
+                final long timestampSeconds = getTimestampSeconds(timestampMillis);
 
                 final String currentSessionId = getCurrentSessionId();
                 if (currentSessionId == null) {
@@ -190,7 +189,7 @@ public Task<Void> call() throws Exception {
                 reportingCoordinator.persistFatalEvent(
                     ex, thread, currentSessionId, timestampSeconds);
 
-                doWriteAppExceptionMarker(time.getTime());
+                doWriteAppExceptionMarker(timestampMillis);
 
                 doCloseSessions();
                 doOpenSession();
@@ -397,14 +396,14 @@ public Void call() throws Exception {
   void writeNonFatalException(@NonNull final Thread thread, @NonNull final Throwable ex) {
     // Capture and close over the current time, so that we get the exact call time,
     // rather than the time at which the task executes.
-    final Date time = new Date();
+    final long timestampMillis = System.currentTimeMillis();
 
     backgroundWorker.submit(
         new Runnable() {
           @Override
           public void run() {
             if (!isHandlingException()) {
-              long timestampSeconds = getTimestampSeconds(time);
+              long timestampSeconds = getTimestampSeconds(timestampMillis);
               final String currentSessionId = getCurrentSessionId();
               if (currentSessionId == null) {
                 Logger.getLogger()
@@ -661,11 +660,11 @@ private void finalizePreviousNativeSession(String previousSessionId) {
   }
 
   private static long getCurrentTimestampSeconds() {
-    return getTimestampSeconds(new Date());
+    return getTimestampSeconds(System.currentTimeMillis());
   }
 
-  private static long getTimestampSeconds(Date date) {
-    return date.getTime() / 1000;
+  private static long getTimestampSeconds(long timestampMillis) {
+    return timestampMillis / 1000;
   }
 
   // region Serialization to protobuf

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/CrashlyticsReportDataCapture.java

@@ -79,8 +79,8 @@ public CrashlyticsReportDataCapture(
     this.stackTraceTrimmingStrategy = stackTraceTrimmingStrategy;
   }
 
-  public CrashlyticsReport captureReportData(String identifier, long timestamp) {
-    return buildReportData().setSession(populateSessionData(identifier, timestamp)).build();
+  public CrashlyticsReport captureReportData(String identifier, long timestampSeconds) {
+    return buildReportData().setSession(populateSessionData(identifier, timestampSeconds)).build();
   }
 
   public Event captureEventData(
@@ -120,9 +120,9 @@ private CrashlyticsReport.Builder buildReportData() {
         .setPlatform(REPORT_ANDROID_PLATFORM);
   }
 
-  private CrashlyticsReport.Session populateSessionData(String identifier, long timestamp) {
+  private CrashlyticsReport.Session populateSessionData(String identifier, long timestampSeconds) {
     return CrashlyticsReport.Session.builder()
-        .setStartedAt(timestamp)
+        .setStartedAt(timestampSeconds)
         .setIdentifier(identifier)
         .setGenerator(GENERATOR)
         .setApp(populateSessionApplicationData())

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/SessionReportingCoordinator.java

@@ -88,8 +88,9 @@ public static SessionReportingCoordinator create(
   }
 
   @Override
-  public void onBeginSession(@NonNull String sessionId, long timestamp) {
-    final CrashlyticsReport capturedReport = dataCapture.captureReportData(sessionId, timestamp);
+  public void onBeginSession(@NonNull String sessionId, long timestampSeconds) {
+    final CrashlyticsReport capturedReport =
+        dataCapture.captureReportData(sessionId, timestampSeconds);
 
     reportPersistence.persistReport(capturedReport);
   }

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/persistence/CrashlyticsReportPersistence.java

@@ -59,6 +59,9 @@ public class CrashlyticsReportPersistence {
 
   private static final String REPORT_FILE_NAME = "report";
   private static final String USER_FILE_NAME = "user";
+  // We use the lastModified timestamp of this file to quickly store and access the startTime in ms
+  // of a session.
+  private static final String SESSION_START_TIMESTAMP_FILE_NAME = "start-time";
   private static final String EVENT_FILE_NAME_PREFIX = "event";
   private static final int EVENT_COUNTER_WIDTH = 10; // String width of maximum positive int value
   private static final String EVENT_COUNTER_FORMAT = "%0" + EVENT_COUNTER_WIDTH + "d";
@@ -110,6 +113,10 @@ public void persistReport(@NonNull CrashlyticsReport report) {
       final File sessionDirectory = prepareDirectory(getSessionDirectoryById(sessionId));
       final String json = TRANSFORM.reportToJson(report);
       writeTextFile(new File(sessionDirectory, REPORT_FILE_NAME), json);
+      writeTextFile(
+          new File(sessionDirectory, SESSION_START_TIMESTAMP_FILE_NAME),
+          "",
+          session.getStartedAt());
     } catch (IOException e) {
       Logger.getLogger().d("Could not persist report for session " + sessionId, e);
     }
@@ -177,6 +184,19 @@ public List<String> listSortedOpenSessionIds() {
     return openSessionIds;
   }
 
+  /**
+   * Gets the startTimestampMs of the given sessionId.
+   *
+   * @param sessionId
+   * @return startTimestampMs
+   */
+  public long getStartTimestampMillis(String sessionId) {
+    final File sessionDirectory = getSessionDirectoryById(sessionId);
+    final File sessionStartTimestampFile =
+        new File(sessionDirectory, SESSION_START_TIMESTAMP_FILE_NAME);
+    return sessionStartTimestampFile.lastModified();
+  }
+
   public boolean hasFinalizedReports() {
     return !getAllFinalizedReportFiles().isEmpty();
   }
@@ -489,6 +509,14 @@ private static void writeTextFile(File file, String text) throws IOException {
     }
   }
 
+  private static void writeTextFile(File file, String text, long lastModifiedTimestampSeconds)
+      throws IOException {
+    try (OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(file), UTF_8)) {
+      writer.write(text);
+      file.setLastModified(convertTimestampFromSecondsToMs(lastModifiedTimestampSeconds));
+    }
+  }
+
   @NonNull
   private static String readTextFile(@NonNull File file) throws IOException {
     final byte[] readBuffer = new byte[8192];
@@ -532,4 +560,8 @@ private static void recursiveDelete(@Nullable File file) {
     }
     file.delete();
   }
+
+  private static long convertTimestampFromSecondsToMs(long timestampSeconds) {
+    return timestampSeconds * 1000;
+  }
 }