common/prefs_interface.h

//
// Copyright (C) 2011 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#ifndef UPDATE_ENGINE_COMMON_PREFS_INTERFACE_H_
#define UPDATE_ENGINE_COMMON_PREFS_INTERFACE_H_

#include <stdint.h>

#include <string>
#include <vector>

namespace chromeos_update_engine {

// The prefs interface allows access to a persistent preferences
// store. The two reasons for providing this as an interface are
// testing as well as easier switching to a new implementation in the
// future, if necessary.

class PrefsInterface {
 public:
  // Observer class to be notified about key value changes.
  class ObserverInterface {
   public:
    virtual ~ObserverInterface() = default;

    // Called when the value is set for the observed |key|.
    virtual void OnPrefSet(std::string_view key) = 0;

    // Called when the observed |key| is deleted.
    virtual void OnPrefDeleted(std::string_view key) = 0;
  };

  virtual ~PrefsInterface() = default;

  // Gets a string |value| associated with |key|. Returns true on
  // success, false on failure (including when the |key| is not
  // present in the store).
  virtual bool GetString(std::string_view key, std::string* value) const = 0;

  // Associates |key| with a string |value|. Returns true on success,
  // false otherwise.
  virtual bool SetString(std::string_view key, std::string_view value) = 0;

  // Gets an int64_t |value| associated with |key|. Returns true on
  // success, false on failure (including when the |key| is not
  // present in the store).
  virtual bool GetInt64(std::string_view key, int64_t* value) const = 0;

  // Associates |key| with an int64_t |value|. Returns true on success,
  // false otherwise.
  virtual bool SetInt64(std::string_view key, const int64_t value) = 0;

  // Gets a boolean |value| associated with |key|. Returns true on
  // success, false on failure (including when the |key| is not
  // present in the store).
  virtual bool GetBoolean(std::string_view key, bool* value) const = 0;

  // Associates |key| with a boolean |value|. Returns true on success,
  // false otherwise.
  virtual bool SetBoolean(std::string_view key, const bool value) = 0;

  // Returns true if the setting exists (i.e. a file with the given key
  // exists in the prefs directory)
  virtual bool Exists(std::string_view key) const = 0;

  // Returns true if successfully deleted the file corresponding to
  // this key. Calling with non-existent keys does nothing.
  virtual bool Delete(std::string_view key) = 0;

  // Deletes the pref key from platform and given namespace subdirectories.
  // Keys are matched against end of pref keys in each namespace.
  // Returns true if all deletes were successful.
  virtual bool Delete(std::string_view pref_key,
                      const std::vector<std::string>& nss) = 0;

  // Creates a key which is part of a sub preference.
  static std::string CreateSubKey(const std::vector<std::string>& ns_with_key);

  // Returns a list of keys within the namespace.
  virtual bool GetSubKeys(std::string_view ns,
                          std::vector<std::string>* keys) const = 0;

  // Add an observer to watch whenever the given |key| is modified. The
  // OnPrefSet() and OnPrefDelete() methods will be called whenever any of the
  // Set*() methods or the Delete() method are called on the given key,
  // respectively.
  virtual void AddObserver(std::string_view key,
                           ObserverInterface* observer) = 0;

  // Remove an observer added with AddObserver(). The observer won't be called
  // anymore for future Set*() and Delete() method calls.
  virtual void RemoveObserver(std::string_view key,
                              ObserverInterface* observer) = 0;

  // create tmp_prefs to write to during checkpointing. Flush will replace prefs
  // with tmp_prefs
  virtual bool StartTransaction() = 0;

  // cancel any pending transaction by deleting tmp_prefs
  virtual bool CancelTransaction() = 0;

  // swap prefs with tmp_prefs checkpointing will use new tmp prefs to resume
  // updates, otherwise we fall back on old prefs
  virtual bool SubmitTransaction() = 0;

 protected:
  // Key separator used to create sub key and get file names,
  static const char kKeySeparator = '/';
};

}  // namespace chromeos_update_engine

#endif  // UPDATE_ENGINE_COMMON_PREFS_INTERFACE_H_