mash: Add a simple, temporary preferences store.

components/filesystem/public/cpp/prefs/filesystem_json_pref_store.h

+// Copyright 2016 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 COMPONENTS_FILESYSTEM_PUBLIC_CPP_PREFS_FILESYSTEM_JSON_PREF_STORE_H_
+#define COMPONENTS_FILESYSTEM_PUBLIC_CPP_PREFS_FILESYSTEM_JSON_PREF_STORE_H_
+
+#include <stdint.h>
+
+#include <set>
+#include <string>
+
+#include "base/callback_forward.h"
+#include "base/compiler_specific.h"
+#include "base/files/file_path.h"
+#include "base/gtest_prod_util.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
+#include "base/prefs/base_prefs_export.h"
+#include "base/prefs/persistent_pref_store.h"
+#include "base/prefs/pref_filter.h"
+#include "base/threading/non_thread_safe.h"
+#include "components/filesystem/public/interfaces/directory.mojom.h"
+#include "components/filesystem/public/interfaces/file.mojom.h"
+#include "components/filesystem/public/interfaces/file_system.mojom.h"
+#include "components/filesystem/public/interfaces/types.mojom.h"
+#include "mojo/public/cpp/bindings/binding.h"
+
+class PrefFilter;
+
+namespace base {
+class Clock;
+class DictionaryValue;
+class FilePath;
+class JsonPrefStoreLossyWriteTest;
+class Value;
+}
+
+namespace filesystem {
+
+// A forked, hack'n'slashed copy of base::JsonPrefStore which writes its
+// preference data to the mojo filesystem instead of the real
+// filesystem. Unlike base::JsonPrefStore, this class can safely be used inside
+// a sandboxed process.
+//
+// In the long run, we'll want to replace the current base::PrefService code
+// with something very different, especially since this component hard punts on
+// all the hard things that the preference service does (enterprise management,
+// parental controls, extension integration, etc.) and its interface is really
+// not optimal for a mojoified world--there are a few places where we assume
+// that writing to disk is synchronous...but it no longer is!
+//
+// Removing this class is a part of crbug.com/580652.
+class FilesystemJsonPrefStore
+    : public PersistentPrefStore,
+      public filesystem::FileSystemClient,
+      public base::SupportsWeakPtr<FilesystemJsonPrefStore>,
+      public base::NonThreadSafe {
+ public:
+  struct ReadResult;
+
+  FilesystemJsonPrefStore(const std::string& pref_filename,
+                          filesystem::FileSystemPtr filesystem,
+                          scoped_ptr<PrefFilter> pref_filter);
+
+  // PrefStore overrides:
+  bool GetValue(const std::string& key,
+                const base::Value** result) const override;
+  void AddObserver(PrefStore::Observer* observer) override;
+  void RemoveObserver(PrefStore::Observer* observer) override;
+  bool HasObservers() const override;
+  bool IsInitializationComplete() const override;
+
+  // PersistentPrefStore overrides:
+  bool GetMutableValue(const std::string& key, base::Value** result) override;
+  void SetValue(const std::string& key,
+                scoped_ptr<base::Value> value,
+                uint32_t flags) override;
+  void SetValueSilently(const std::string& key,
+                        scoped_ptr<base::Value> value,
+                        uint32_t flags) override;
+  void RemoveValue(const std::string& key, uint32_t flags) override;
+  bool ReadOnly() const override;
+  PrefReadError GetReadError() const override;
+  // Note this method may be asynchronous if this instance has a |pref_filter_|
+  // in which case it will return PREF_READ_ERROR_ASYNCHRONOUS_TASK_INCOMPLETE.
+  // See details in pref_filter.h.
+  PrefReadError ReadPrefs() override;
+  void ReadPrefsAsync(ReadErrorDelegate* error_delegate) override;
+  void CommitPendingWrite() override;
+  void SchedulePendingLossyWrites() override;
+  void ReportValueChanged(const std::string& key, uint32_t flags) override;
+
+  // FileSystemClient overrides:
+  void OnFileSystemShutdown() override;
+
+  // Just like RemoveValue(), but doesn't notify observers. Used when doing some
+  // cleanup that shouldn't otherwise alert observers.
+  void RemoveValueSilently(const std::string& key, uint32_t flags);
+
+ private:
+  friend class base::JsonPrefStoreLossyWriteTest;
+
+  ~FilesystemJsonPrefStore() override;
+
+  // This method is called after the JSON file has been read.  It then hands
+  // |value| (or an empty dictionary in some read error cases) to the
+  // |pref_filter| if one is set. It also gives a callback pointing at
+  // FinalizeFileRead() to that |pref_filter_| which is then responsible for
+  // invoking it when done. If there is no |pref_filter_|, FinalizeFileRead()
+  // is invoked directly.
+  void OnFileRead(scoped_ptr<ReadResult> read_result);
+
+  // This method is called after the JSON file has been read and the result has
+  // potentially been intercepted and modified by |pref_filter_|.
+  // |schedule_write| indicates whether a write should be immediately scheduled
+  // (typically because the |pref_filter_| has already altered the |prefs|) --
+  // this will be ignored if this store is read-only.
+  void FinalizeFileRead(scoped_ptr<base::DictionaryValue> prefs,
+                        bool schedule_write);
+
+  // Schedule a write with the file writer as long as |flags| doesn't contain
+  // WriteablePrefStore::LOSSY_PREF_WRITE_FLAG.
+  void ScheduleWrite(uint32_t flags);
+
+  // Actually performs a write. Unlike the //base version of this class, we
+  // don't use the ImportantFileWriter and instead write using the mojo
+  // filesystem API.
+  void PerformWrite();
+
+  // Opens the filesystem and calls |callback| when completed, whether
+  // successfully or unsuccessfully.
+  void OpenFilesystem(base::Closure callback);
+
+  // Callback method which verifies that there were no errors on opening the
+  // filesystem, and if there aren't, invokes the passed in callback.
+  void OnOpenFilesystem(base::Closure callback, FileError err);
+
+  // Asynchronous implementation details of PerformWrite().
+  void OnTempFileWriteStart();
+  void OnTempFileOpened(FileError err);
+  void OnTempFileWrite(FileError err, uint32_t num_bytes_written);
+  void OnTempFileClosed(FileError err);
+  void OnTempFileRenamed(FileError err);
+
+  // Asynchronous implementation details of ReadPrefsAsync().
+  void OnPreferencesReadStart();
+  void OnPreferencesFileOpened(FileError err);
+  void OnPreferencesFileRead(FileError err, mojo::Array<uint8_t> contents);
+
+  const std::string path_;
+  mojo::Binding<filesystem::FileSystemClient> binding_;
+  filesystem::FileSystemPtr filesystem_;
+
+  // |directory_| is only bound after the first attempt to access the
+  // |filesystem. See OpenFilesystem().
+  DirectoryPtr directory_;
+
+  FilePtr preferences_file_;
+  FilePtr temporary_file_;
+
+  scoped_ptr<base::DictionaryValue> prefs_;
+
+  bool read_only_;
+
+  scoped_ptr<PrefFilter> pref_filter_;
+  base::ObserverList<PrefStore::Observer, true> observers_;
+
+  scoped_ptr<ReadErrorDelegate> error_delegate_;
+
+  bool initialized_;
+  bool filtering_in_progress_;
+  bool pending_lossy_write_;
+  PrefReadError read_error_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilesystemJsonPrefStore);
+};
+
+}  // namespace filesystem
+
+#endif  // COMPONENTS_FILESYSTEM_PUBLIC_CPP_PREFS_FILESYSTEM_JSON_PREF_STORE_H_