Use modified time to detect sync changes. Can not use md5 checksum to detect changes in zip file.

MyTracks/src/com/google/android/apps/mytracks/io/drive/SendDriveAsyncTask.java

@@ -90,14 +90,16 @@ public class SendDriveAsyncTask extends AbstractSendAsyncTask {
       String driveId = track.getDriveId();
       if (driveId != null && !driveId.equals("")) {
         File driveFile = drive.files().get(driveId).execute();
-        if (SyncUtils.isValid(driveFile, folderId) && SyncUtils.updateDriveFile(
-            drive, driveFile, context, myTracksProviderUtils, track, false)) {
+        if (driveFile != null && updateDriveFile(drive, driveFile, folderId, track)) {
           addPermission(drive, driveFile);
           return true;
         }
+
+        // clear sync state
         SyncUtils.updateTrack(myTracksProviderUtils, track, null);
       }
 
+      // insert new drive file
       File file = SyncUtils.insertDriveFile(
           drive, folderId, context, myTracksProviderUtils, track, false);
       if (file == null) {
@@ -119,6 +121,29 @@ public class SendDriveAsyncTask extends AbstractSendAsyncTask {
       return retryTask();
     }
   }
+  
+  /**
+   * Updates a drive file using info from a track. Returns true if successful.
+   * 
+   * @param drive the drive
+   * @param driveFile the drive file
+   * @param folderId the folder id of the drive file
+   * @param track the track
+   */
+  private boolean updateDriveFile(Drive drive, File driveFile, String folderId, Track track)
+      throws IOException {
+    if (!SyncUtils.isValid(driveFile, folderId)) {
+      return false;
+    }
+    long driveModifiedTime = driveFile.getModifiedDate().getValue();
+    long modifiedTime = track.getModifiedTime();
+
+    if (driveModifiedTime != modifiedTime) {
+      return SyncUtils.updateDriveFile(
+          drive, driveFile, context, myTracksProviderUtils, track, true);
+    }
+    return true;
+  }
 
   @Override
   protected void invalidateToken() {}

MyTracks/src/com/google/android/apps/mytracks/io/sync/SyncUtils.java

@@ -47,13 +47,9 @@ import android.database.Cursor;
 import android.os.Bundle;
 import android.util.Log;
 
-import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
-import java.io.InputStream;
-import java.security.MessageDigest;
-import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.Locale;
 
@@ -372,25 +368,14 @@ public class SyncUtils {
 
     try {
       file = SyncUtils.getTempFile(context, myTracksProviderUtils, track, true);
-
       if (file == null) {
         Log.e(TAG, "Unable to update drive file. File is null for track " + track.getName());
         return false;
       }
 
       String title = track.getName() + "." + KmzTrackExporter.KMZ_EXTENSION;
-      File updatedFile;
-      String digest = md5(file);
-      if (digest != null && digest.equals(driveFile.getMd5Checksum())) {
-        if (title.equals(driveFile.getTitle())) {
-          updatedFile = driveFile;
-        } else {
-          // Only update the title
-          updatedFile = updateDriveFile(drive, driveFile, title, null, canRetry);
-        }
-      } else {
-        updatedFile = updateDriveFile(drive, driveFile, title, file, canRetry);
-      }
+      File updatedFile = updateDriveFile(drive, driveFile, title, file, canRetry);
+
       if (updatedFile == null) {
         Log.e(
             TAG, "Unable to update drive file. Updated file is null for track " + track.getName());
@@ -513,52 +498,4 @@ public class SyncUtils {
         : "");
     myTracksProviderUtils.updateTrack(track);
   }
-
-  /**
-   * Gets the md5 digest for a file.
-   * 
-   * @param file the file
-   */
-  public static String md5(java.io.File file) {
-    if (file == null) {
-      return null;
-    }
-    InputStream in = null;
-    byte[] digest;
-    try {
-      in = new FileInputStream(file);
-      MessageDigest digester = MessageDigest.getInstance("MD5");
-      byte[] bytes = new byte[8192];
-      int byteCount;
-      while ((byteCount = in.read(bytes)) > 0) {
-        digester.update(bytes, 0, byteCount);
-      }
-      digest = digester.digest();
-
-      StringBuilder builder = new StringBuilder(digest.length * 2);
-      for (byte b : digest) {
-        if ((b & 0xFF) < 0x10) {
-          builder.append("0");
-        }
-        builder.append(Integer.toHexString(b & 0xFF));
-      }
-      return builder.toString();
-
-    } catch (IOException e) {
-      Log.e(TAG, "IOException", e);
-      return null;
-    } catch (NoSuchAlgorithmException e) {
-      Log.e(TAG, "NoSuchAlgorithmException", e);
-      return null;
-    } finally {
-      if (in != null) {
-        try {
-          in.close();
-        } catch (IOException e) {
-          Log.e(TAG, "Unable to close inputstream", e);
-          return null;
-        }
-      }
-    }
-  }
 }