Add dom_storage::SessionStorageDatabase.

webkit/dom_storage/session_storage_database.h

Index: webkit/dom_storage/session_storage_database.h
diff --git a/webkit/dom_storage/session_storage_database.h b/webkit/dom_storage/session_storage_database.h
new file mode 100644
index 0000000000000000000000000000000000000000..c2e05c89f88d7efaeea13444338b8192c03659a2
--- /dev/null
+++ b/webkit/dom_storage/session_storage_database.h
@@ -0,0 +1,162 @@
+// 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 {
+
+class DB;
+class WriteBatch;
+
+}  // namespace leveldb

[michaeln, 2012/04/25 08:32:12]

style nit: generally we forward declare more in a more condensed less verbose
way

namespace leveldb {
class DB;
class WriteBatch;
}

[marja, 2012/04/25 15:44:27]

Done.

+
+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,

[michaeln, 2012/04/25 08:32:12]

Since this class works with multiple object types (unlike the simpler
single-origin-only DomStorageDatabase), maybe these method names could be
modified to more consistently reflect what they're operating on. Maybe...

ReadAreaValues
CommitAreaChanges
CloneNamespace
DeepCopyArea
ResetArea (ie. DisaccociateMap)
DeleteArea (ie. DeleteOrigin)
DeleteNamespace
DeleteAll (ie. DeleteLeftoverData)

Where 'area' refers to stuff for <namespace_id, origin>.

[marja, 2012/04/25 15:44:27]

Done.

+                     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);

[michaeln, 2012/04/25 08:32:12]

consider calling this CloneNamespace to be more consistent with naming on other
classes... namespaces are cloned, areas are copied (shallow | deep).

[marja, 2012/04/25 15:44:27]

Done.

+
+  // 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|.
+  bool DeleteOrigin(int64 namespace_id, const GURL& origin);
+
+  // Deletes the data for |namespace_id|.
+  bool DeleteNamespace(int64 namespace_id);
+
+  // Deletes possible leftover data from the previous run.
+  bool DeleteLeftoverData();

[michaeln, 2012/04/25 08:32:12]

Feels like it might be premature to add this method. Consider leaving it out for
now and revisiting when integrating with the higher level chrome level logic to
do session restore. Or maybe simplify the impl and call the method DeleteAll().

[marja, 2012/04/25 15:44:27]

Done (deleted it).

+
+ private:
+  friend class base::RefCountedThreadSafe<SessionStorageDatabase>;
+  friend class SessionStorageDatabaseTest;
+
+  ~SessionStorageDatabase();
+
+  bool LazyOpen(bool create_if_needed);
+  leveldb::Status TryToOpen(const FilePath& file_path, leveldb::DB** db);
+  bool IsOpen() const;
+
+  // For checking consistency invariants. Returns |ok|, for chaining.
+  bool ConsistencyCheck(bool ok);
+  // For checking database errors. If a database error occurs, the data is
+  // deleted and the database is not accessed during this run. Returns |ok|, for
+  // chaining.
+  bool DatabaseErrorCheck(bool ok);
+
+  // 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.
+  bool 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.
+  bool 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.
+  bool DecreaseRefCount(const std::string& map_id,
+                        int decrease,
+                        leveldb::WriteBatch* batch);
+
+  // Helper for deleting all values in a map.
+  bool ClearMap(const std::string& map_id, leveldb::WriteBatch* batch);
+
+  // Helper for deleting data for |namespace_id| and |origin|.
+  bool DeleteOrigin(const std::string& namespace_id,
+                    const std::string& origin,
+                    leveldb::WriteBatch* batch);
+
+  // Helper functions for creating the keys needed for the schema.
+  static std::string NamespaceStartKey(const std::string& namespace_id);
+  static std::string NamespaceStartKey(int64 namespace_id,
+                                       int64 namespace_offset);
+  static std::string NamespaceKey(const std::string& namespace_id,
+                                  const std::string& origin);
+  static std::string NamespaceKey(int64 namespace_id,
+                                  int64 namespace_offset,
+                                  const GURL& origin);
+  static std::string NamespacePrefix();
+  static std::string MapRefCountKey(const std::string& map_id);
+  static std::string MapKey(const std::string& map_id, const std::string& key);
+  static std::string MapPrefix();
+  static std::string NextNamespaceIdKey();
+  static std::string NextMapIdKey();
+
+  scoped_ptr<leveldb::DB> db_;
+  FilePath file_path_;
+
+  // True if a database error has occurred (e.g., cannot read data).
+  bool db_error_;
+  // True if the database is in an inconsistent state.
+  bool is_inconsistent_;
+
+  // 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_