Persist sessionStorage on disk.

webkit/dom_storage/session_storage_database.h

+// Copyright (c) 2012 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.
+
+#ifndef WEBKIT_DOM_STORAGE_SESSION_STORAGE_DATABASE_H_
+#define WEBKIT_DOM_STORAGE_SESSION_STORAGE_DATABASE_H_
+#pragma once
+
+#include "webkit/dom_storage/dom_storage_database.h"
+
+namespace leveldb {
+
+struct DB;
+struct WriteBatch;
+
+}  // namespace leveldb
+
+namespace dom_storage {
+
+// All DomStorageAreas for session storage share the same
+// SessionStorageDatabase.

[michaeln, 2012/04/12 01:48:46]

It'd be great if you carved this class out of the larger CL and put together
some unittests for it.

[marja, 2012/04/19 10:20:50]

I'll do that next...

+class SessionStorageDatabase :
+      public DomStorageDatabase,
+      public base::RefCountedThreadSafe<SessionStorageDatabase> {
+ public:
+  explicit SessionStorageDatabase(const FilePath& file_path);
+  virtual ~SessionStorageDatabase();
+
+  // Reads all the key, value pairs stored in the database and returns
+  // them. |result| is assumed to be empty and any duplicate keys will
+  // be overwritten. If the database exists on disk then it will be
+  // opened. If it does not exist then it will not be created and
+  // |result| will be unmodified.
+  virtual void ReadAllValues(int64 namespace_id,
+                             const GURL& origin,
+                             ValuesMap* result) OVERRIDE;
+
+  // Updates the backing database. Will remove all keys before updating
+  // the database if |clear_all_first| is set. Then all entries in
+  // |changes| will be examined - keys mapped to a null NullableString16
+  // will be removed and all others will be inserted/updated as appropriate.
+  virtual bool CommitChanges(int64 namespace_id,
+                             const GURL& origin,
+                             bool clear_all_first,
+                             const ValuesMap& changes) OVERRIDE;
+
+  // Creates a shallow copy of the map for the data associated with |origin| in
+  // |namespace_id| and associates it with |new_namespace_id|.
+  bool ShallowCopy(int64 namespace_id,

[michaeln, 2012/04/12 01:48:46]

See comment elsewhere about having CloneNamespace to do all areas in a single
batch

[marja, 2012/04/19 10:20:50]

Done.

+                   const GURL& origin,
+                   int64 new_namespace_id);
+
+  // Creates a deep copy of the map for the data associated with |origin| in
+  // |namespace_id|.
+  bool DeepCopy(int64 namespace_id, const GURL& origin);
+
+  // Deletes the data for |namespace_id| and |origin|.
+  void DeleteOrigin(int64 namespace_id, const GURL& origin);
+
+  // Deletes the data for |namespace_id|.
+  void DeleteNamespace(int64 namespace_id);
+
+  // Deletes possible leftover data from the previous run.
+  void DeleteLeftoverData();
+
+ private:
+  virtual bool LazyOpen(bool create_if_needed);
+  virtual bool IsOpen() const;
+
+  // Helper for reading all values belonging to the map |map_id| into |result|.
+  void ReadValuesInMap(const std::string& map_id, ValuesMap* result);
+
+  // Helper for creating a new map for |area_key|. |map_id| will hold the id of
+  // the created map. Retuns true if the creation succeeded, false otherwise.
+  bool CreateNewMap(const std::string& area_key,
+                    leveldb::WriteBatch* batch,
+                    std::string* map_id);
+
+  // Helper for writing values into a map.
+  void WriteValuesToMap(const std::string& map_id,
+                        const ValuesMap& values,
+                        leveldb::WriteBatch* batch);
+
+  // Helper for decreasing the ref count of a map.
+  void DecreaseRefCount(const std::string& map_id,
+                        leveldb::WriteBatch* batch);
+
+  // Helper for deleting all values in a map.
+  void DeleteValuesInMap(const std::string& map_id,
+                         leveldb::WriteBatch* batch);
+
+  // Helper for deleting data for |namespace_id| and |origin|.
+  void DeleteOrigin(const std::string& namespace_id,
+                    const std::string& origin,
+                    leveldb::WriteBatch* batch);
+
+  // Helper for deleting data for |namespace_id|.
+  void DeleteNamespace(const std::string& namespace_id,
+                       leveldb::WriteBatch* batch);
+
+  // Helper for debugging
+  void DumpData() const;
+
+  scoped_ptr<leveldb::DB> db_;
+};
+
+}  // namespace dom_storage
+
+#endif  // WEBKIT_DOM_STORAGE_SESSION_STORAGE_DATABASE_H_