Implement an initial extension settings API.

chrome/browser/extensions/extension_settings_storage.h

Index: chrome/browser/extensions/extension_settings_storage.h
diff --git a/chrome/browser/extensions/extension_settings_storage.h b/chrome/browser/extensions/extension_settings_storage.h
new file mode 100644
index 0000000000000000000000000000000000000000..a0ec66680324734b453c286d1a8a247f54409298
--- /dev/null
+++ b/chrome/browser/extensions/extension_settings_storage.h
@@ -0,0 +1,83 @@
+// Copyright (c) 2011 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_H_
+#pragma once
+
+#include "base/values.h"
+
+// Interface for extension settings storage classes.
+//
+// All asynchrous methods *must* run in a message loop, i.e. the callbacks may
+// not be run from the calling method, but must be PostTask'ed (whether to
+// one's own thread or to e.g. the FILE thread).
+class ExtensionSettingsStorage {
+ public:
+  // Asynchronous results of Set/Get/Remove.  Exactly one of OnSuccess or
+  // OnFailure will eventually be called.
+  // Callback objects will be deleted after running.
+  class Callback {
+   public:
+    virtual ~Callback() {}
+
+    // Indicates the storage operation was successful.  Settings value will be
+    // non-NULL.  Ownership is passed to the callback.
+    virtual void OnSuccess(DictionaryValue* settings) = 0;
+
+    // Indicates the storage operation failed.  Messages describes the failure.
+    virtual void OnFailure(const std::string& message) = 0;
+  };
+
+  virtual ~ExtensionSettingsStorage() {}
+
+  // The different types of extension settings storage.
+  enum Type {
+    NONE,
+    NOOP,
+    LEVELDB
+  };
+
+  // Destroys this settings storage object.  This is needed as a separate
+  // interface method as opposed to just using the destructor, since
+  // destruction may need to be done asynchronously (e.g. on the FILE thread).
+  virtual void DestroyEventually() = 0;

[Matt Perry, 2011/06/23 19:14:11]

nit: name this DeleteSoon to be consistent with other cases like this.

[not at google - send to devlin, 2011/06/27 08:51:02]

Done.

+
+  // Gets a single value from storage.  Callback with a dictionary mapping the
+  // key to its value, if any.
+  virtual void Get(const std::string& key, Callback* callback) = 0;
+
+  // Gets multiple values from storage.  Callback with a dictionary mapping
+  // each key to its value, if any.
+  virtual void Get(const ListValue& keys, Callback* callback) = 0;
+
+  // Gets all values from storage.  Callback with a dictionary mapping every
+  // key to its value.
+  virtual void Get(Callback* callback) = 0;
+
+  // Sets a single key to a new value.  Callback with a dictionary mapping the
+  // key to its new value; on success, this is guaranteed to be the given key
+  // to the given new value.
+  virtual void Set(const std::string& key, const Value& value,
+      Callback* callback) = 0;
+
+  // Sets multiple keys to new values. Callback with a dictionary mapping each
+  // key to its new value; on success, this is guaranteed to be each given key
+  // to its given new value.
+  virtual void Set(const DictionaryValue& values, Callback* callback) = 0;
+
+  // Removes a key from the map.  Callback with a dictionary mapping the key
+  // to its new value; on success, this will be an empty map.
+  virtual void Remove(const std::string& key, Callback* callback) = 0;
+
+  // Removes multiple keys from the map.  Callback with a dictionary mapping
+  // each key to its new value; on success, this will be an empty map.
+  virtual void Remove(const ListValue& keys, Callback* callback) = 0;
+
+  // Clears the storage.  Callback with a dictionary mapping every key in
+  // storage to its value; on success, this will be an empty map.
+  virtual void Clear(Callback *callback) = 0;
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_STORAGE_H_