Add SimpleCache index file heuristics

net/disk_cache/simple/simple_index_file.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/disk_cache/simple/simple_index_file.h"
 
 #include "base/file_util.h"
 #include "base/hash.h"
 #include "base/logging.h"
 #include "base/pickle.h"
@@ skipping 48 matching lines @@
 
 bool SimpleIndexFile::IndexMetadata::CheckIndexMetadata() {
   return number_of_entries_ <= kMaxEntiresInIndex &&
       magic_number_ == disk_cache::kSimpleIndexMagicNumber &&
       version_ == disk_cache::kSimpleVersion;
 }
 
 // static
 scoped_ptr<SimpleIndex::EntrySet> SimpleIndexFile::LoadFromDisk(
     const base::FilePath& index_filename) {
+  // Only load if the index is not stale.
+  if (SimpleIndexFile::IsIndexFileStale(index_filename))
+    return scoped_ptr<SimpleIndex::EntrySet>(NULL);
   std::string contents;
   if(!file_util::ReadFileToString(index_filename, &contents)) {
     LOG(WARNING) << "Could not read Simple Index file.";
     return scoped_ptr<SimpleIndex::EntrySet>(NULL);
   }
 
   return SimpleIndexFile::Deserialize(contents.data(), contents.size());
 }
 
 // static
@@ skipping 75 matching lines @@
     LOG(ERROR) << "Could not write Simple Cache index to temporary file: "
                << temp_filename.value();
     file_util::Delete(temp_filename, /* recursive = */ false);
     return;
   }
   // Swap temp and index_file.
   bool result = file_util::ReplaceFile(temp_filename, index_filename);
   DCHECK(result);
 }
 
+// static
+bool SimpleIndexFile::IsIndexFileStale(const base::FilePath& index_filename) {
+  base::PlatformFileInfo dir_info;
+  base::PlatformFileInfo index_info;
+  if (!file_util::GetFileInfo(index_filename.DirName(), &dir_info))
+    return false;
+  DCHECK(dir_info.is_directory);
+  if (!file_util::GetFileInfo(index_filename, &index_info))
+    return false;
+
+  // Index file last_modified must be equal to the directory last_modified since
+  // the last operation we do is ReplaceFile in the
+  // SimpleIndexFile::WriteToDisk().
+  // If not true, we need to restore the index.
+  return index_info.last_modified >= dir_info.last_modified;
+}
+
 }  // namespace disk_cache