base/prefs/json_pref_store.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_PREFS_JSON_PREF_STORE_H_
   6 #define BASE_PREFS_JSON_PREF_STORE_H_
   7
   8 #include <set>
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/callback_forward.h"
  13 #include "base/compiler_specific.h"
  14 #include "base/files/file_path.h"
  15 #include "base/files/important_file_writer.h"
  16 #include "base/memory/scoped_ptr.h"
  17 #include "base/memory/weak_ptr.h"
  18 #include "base/message_loop/message_loop_proxy.h"
  19 #include "base/observer_list.h"
  20 #include "base/prefs/base_prefs_export.h"
  21 #include "base/prefs/persistent_pref_store.h"
  22 #include "base/threading/non_thread_safe.h"
  23
  24 class PrefFilter;
  25
  26 namespace base {
  27 class DictionaryValue;
  28 class FilePath;
  29 class SequencedTaskRunner;
  30 class SequencedWorkerPool;
  31 class Value;
  32 }
  33
  34 // A writable PrefStore implementation that is used for user preferences.
  35 class BASE_PREFS_EXPORT JsonPrefStore
  36     : public PersistentPrefStore,
  37       public base::ImportantFileWriter::DataSerializer,
  38       public base::SupportsWeakPtr<JsonPrefStore>,
  39       public base::NonThreadSafe {
  40  public:
  41   struct ReadResult;
  42
  43   // Returns instance of SequencedTaskRunner which guarantees that file
  44   // operations on the same file will be executed in sequenced order.
  45   static scoped_refptr<base::SequencedTaskRunner> GetTaskRunnerForFile(
  46       const base::FilePath& pref_filename,
  47       base::SequencedWorkerPool* worker_pool);
  48
  49   // Same as the constructor below with no alternate filename.
  50   JsonPrefStore(
  51       const base::FilePath& pref_filename,
  52       const scoped_refptr<base::SequencedTaskRunner>& sequenced_task_runner,
  53       scoped_ptr<PrefFilter> pref_filter);
  54
  55   // |sequenced_task_runner| must be a shutdown-blocking task runner, ideally
  56   // created by the GetTaskRunnerForFile() method above.
  57   // |pref_filename| is the path to the file to read prefs from.
  58   // |pref_alternate_filename| is the path to an alternate file which the
  59   // desired prefs may have previously been written to. If |pref_filename|
  60   // doesn't exist and |pref_alternate_filename| does, |pref_alternate_filename|
  61   // will be moved to |pref_filename| before the read occurs.
  62   JsonPrefStore(
  63       const base::FilePath& pref_filename,
  64       const base::FilePath& pref_alternate_filename,
  65       const scoped_refptr<base::SequencedTaskRunner>& sequenced_task_runner,
  66       scoped_ptr<PrefFilter> pref_filter);
  67
  68   // PrefStore overrides:
  69   virtual bool GetValue(const std::string& key,
  70                         const base::Value** result) const OVERRIDE;
  71   virtual void AddObserver(PrefStore::Observer* observer) OVERRIDE;
  72   virtual void RemoveObserver(PrefStore::Observer* observer) OVERRIDE;
  73   virtual bool HasObservers() const OVERRIDE;
  74   virtual bool IsInitializationComplete() const OVERRIDE;
  75
  76   // PersistentPrefStore overrides:
  77   virtual bool GetMutableValue(const std::string& key,
  78                                base::Value** result) OVERRIDE;
  79   virtual void SetValue(const std::string& key, base::Value* value) OVERRIDE;
  80   virtual void SetValueSilently(const std::string& key,
  81                                 base::Value* value) OVERRIDE;
  82   virtual void RemoveValue(const std::string& key) OVERRIDE;
  83   virtual bool ReadOnly() const OVERRIDE;
  84   virtual PrefReadError GetReadError() const OVERRIDE;
  85   // Note this method may be asynchronous if this instance has a |pref_filter_|
  86   // in which case it will return PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE.
  87   // See details in pref_filter.h.
  88   virtual PrefReadError ReadPrefs() OVERRIDE;
  89   virtual void ReadPrefsAsync(ReadErrorDelegate* error_delegate) OVERRIDE;
  90   virtual void CommitPendingWrite() OVERRIDE;
  91   virtual void ReportValueChanged(const std::string& key) OVERRIDE;
  92
  93   // Just like RemoveValue(), but doesn't notify observers. Used when doing some
  94   // cleanup that shouldn't otherwise alert observers.
  95   void RemoveValueSilently(const std::string& key);
  96
  97   // Registers |on_next_successful_write| to be called once, on the next
  98   // successful write event of |writer_|.
  99   void RegisterOnNextSuccessfulWriteCallback(
 100       const base::Closure& on_next_successful_write);
 101
 102  private:
 103   virtual ~JsonPrefStore();
 104
 105   // This method is called after the JSON file has been read.  It then hands
 106   // |value| (or an empty dictionary in some read error cases) to the
 107   // |pref_filter| if one is set. It also gives a callback pointing at
 108   // FinalizeFileRead() to that |pref_filter_| which is then responsible for
 109   // invoking it when done. If there is no |pref_filter_|, FinalizeFileRead()
 110   // is invoked directly.
 111   void OnFileRead(scoped_ptr<ReadResult> read_result);
 112
 113   // ImportantFileWriter::DataSerializer overrides:
 114   virtual bool SerializeData(std::string* output) OVERRIDE;
 115
 116   // This method is called after the JSON file has been read and the result has
 117   // potentially been intercepted and modified by |pref_filter_|.
 118   // |initialization_successful| is pre-determined by OnFileRead() and should
 119   // be used when reporting OnInitializationCompleted().
 120   // |schedule_write| indicates whether a write should be immediately scheduled
 121   // (typically because the |pref_filter_| has already altered the |prefs|) --
 122   // this will be ignored if this store is read-only.
 123   void FinalizeFileRead(bool initialization_successful,
 124                         scoped_ptr<base::DictionaryValue> prefs,
 125                         bool schedule_write);
 126
 127   const base::FilePath path_;
 128   const base::FilePath alternate_path_;
 129   const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
 130
 131   scoped_ptr<base::DictionaryValue> prefs_;
 132
 133   bool read_only_;
 134
 135   // Helper for safely writing pref data.
 136   base::ImportantFileWriter writer_;
 137
 138   scoped_ptr<PrefFilter> pref_filter_;
 139   ObserverList<PrefStore::Observer, true> observers_;
 140
 141   scoped_ptr<ReadErrorDelegate> error_delegate_;
 142
 143   bool initialized_;
 144   bool filtering_in_progress_;
 145   PrefReadError read_error_;
 146
 147   std::set<std::string> keys_need_empty_value_;
 148
 149   DISALLOW_COPY_AND_ASSIGN(JsonPrefStore);
 150 };
 151
 152 #endif  // BASE_PREFS_JSON_PREF_STORE_H_