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 "base/file_path.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "third_party/leveldatabase/src/include/leveldb/status.h"
+#include "webkit/dom_storage/dom_storage_types.h"
+
+class GURL;
+
+namespace leveldb {
+
+struct DB;
+struct WriteBatch;
+
+}  // namespace leveldb
+
+namespace dom_storage {
+
+// SessionStorageDatabase holds the data from multiple namespaces and multiple
+// origins. All DomStorageAreas for session storage share the same
+// SessionStorageDatabase.
+class SessionStorageDatabase :
+      public base::RefCountedThreadSafe<SessionStorageDatabase> {
+ public:
+  explicit SessionStorageDatabase(const FilePath& file_path);
+
+  // 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.
+  void ReadAllValues(int64 namespace_id,
+                     const GURL& origin,
+                     ValuesMap* result);
+
+  // 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.
+  bool CommitChanges(int64 namespace_id,
+                     const GURL& origin,
+                     bool clear_all_first,
+                     const ValuesMap& changes);
+
+  // Creates shallow copies of the maps for |namespace_id| and associates them
+  // with |new_namespace_id|.
+  bool ShallowCopyNamespace(int64 namespace_id, 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);
+
+  // Breaks the association of (|namespace_id|, |origin|) and its map.
+  bool DisassociateMap(int64 namespace_id, const GURL& origin);
+
+  // Deletes the data for |namespace_id| and |origin|.
+  void DeleteOrigin(int64 namespace_id, const GURL& origin);

[michaeln, 2012/04/22 22:50:01]

Might be useful to have this method invoked as a consequence of
DomStorageArea::DeleteOrigin() being called?

[marja, 2012/05/11 12:18:32]

Done.

+
+  // Deletes the data for |namespace_id|.
+  void DeleteNamespace(int64 namespace_id);
+
+  // Deletes possible leftover data from the previous run.
+  void DeleteLeftoverData();
+
+ private:
+  friend class base::RefCountedThreadSafe<SessionStorageDatabase>;
+  ~SessionStorageDatabase();
+
+  bool LazyOpen(bool create_if_needed);
+  leveldb::Status TryToOpen(const FilePath& file_path, leveldb::DB** db);
+  bool IsOpen() const;
+
+  // Helper for reading the contents of the map |map_id| into |result|. If
+  // |only_keys| is true, only keys are aread from the database and the values
+  // in |result| will be empty.
+  void ReadMap(const std::string& map_id, ValuesMap* result, bool only_keys);
+
+  // 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 reading the next namespace id.
+  bool GetNextNamespaceId(int64* next_namespace_id);
+
+  // Helper for keeping the next namespace id up to date when adding new
+  // namespaces.
+  void UpdateNextNamespaceId(int64 namespace_id, leveldb::WriteBatch* batch);
+
+  // Helper for reading the ref count of a map.
+  bool GetRefCount(const std::string& map_key, int64* ref_count);
+
+  // 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 ClearMap(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();
+
+  // Helper for ensuring that the database is in a consistent state.
+  bool CheckConsistency();
+
+  scoped_ptr<leveldb::DB> db_;
+
+  FilePath file_path_;
+  bool failed_to_open_;
+
+  // On startup, we read the next ununsed namespace id from the database. It
+  // will be the offset for namespace ids. The actual id of a namespace in the
+  // database will be: id passed to the API function + namespace_offset_.
+  int64 namespace_offset_;
+
+  DISALLOW_COPY_AND_ASSIGN(SessionStorageDatabase);
+};
+
+}  // namespace dom_storage
+
+#endif  // WEBKIT_DOM_STORAGE_SESSION_STORAGE_DATABASE_H_