Merge changes from topic "stats-migration"

* changes:
  Add null check when list directory
  [MS82.2] Add a rewriteSingle method that takes two timestamps

core/java/android/net/netstats/NetworkStatsDataMigrationUtils.java

@@ -52,6 +52,7 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.net.ProtocolException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Set;
@@ -161,9 +162,12 @@ public class NetworkStatsDataMigrationUtils {
     @NonNull
     private static ArrayList<File> getPlatformFileListForPrefix(@NonNull @Prefix String prefix) {
         final ArrayList<File> list = new ArrayList<>();
-        final File platformFiles = new File(getPlatformBaseDir(), "netstats");
+        final File platformFiles = getPlatformBaseDir();
         if (platformFiles.exists()) {
-            for (String name : platformFiles.list()) {
+            final String[] files = platformFiles.list();
+            if (files == null) return list;
+            Arrays.sort(files);
+            for (String name : files) {
                 // Skip when prefix doesn't match.
                 if (!name.startsWith(prefix + ".")) continue;
 

core/java/com/android/internal/util/FileRotator.java

@@ -16,6 +16,7 @@
 
 package com.android.internal.util;
 
+import android.annotation.NonNull;
 import android.os.FileUtils;
 import android.util.Log;
 
@@ -281,6 +282,20 @@ public class FileRotator {
         }
     }
 
+    /**
+     * Process a single file atomically, with the given start and end timestamps.
+     * If a file with these exact start and end timestamps does not exist, a new
+     * empty file will be written.
+     */
+    public void rewriteSingle(@NonNull Rewriter rewriter, long startTimeMillis, long endTimeMillis)
+            throws IOException {
+        final FileInfo info = new FileInfo(mPrefix);
+
+        info.startMillis = startTimeMillis;
+        info.endMillis = endTimeMillis;
+        rewriteSingle(rewriter, info.build());
+    }
+
     /**
      * Read any rotated data that overlap the requested time range.
      */