json_file_value_serializer.h

// 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 BASE_JSON_JSON_FILE_VALUE_SERIALIZER_H_
#define BASE_JSON_JSON_FILE_VALUE_SERIALIZER_H_

#include <string>

#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/file_path.h"
#include "base/values.h"

class BASE_EXPORT JSONFileValueSerializer : public base::ValueSerializer {
 public:
  // json_file_patch is the path of a file that will be source of the
  // deserialization or the destination of the serialization.
  // When deserializing, the file should exist, but when serializing, the
  // serializer will attempt to create the file at the specified location.
  explicit JSONFileValueSerializer(const base::FilePath& json_file_path)
    : json_file_path_(json_file_path),
      allow_trailing_comma_(false) {}

  virtual ~JSONFileValueSerializer() {}

  // DO NOT USE except in unit tests to verify the file was written properly.
  // We should never serialize directly to a file since this will block the
  // thread. Instead, serialize to a string and write to the file you want on
  // the file thread.
  //
  // Attempt to serialize the data structure represented by Value into
  // JSON.  If the return value is true, the result will have been written
  // into the file whose name was passed into the constructor.
  virtual bool Serialize(const Value& root) OVERRIDE;

  // Equivalent to Serialize(root) except binary values are omitted from the
  // output.
  bool SerializeAndOmitBinaryValues(const Value& root);

  // Attempt to deserialize the data structure encoded in the file passed
  // in to the constructor into a structure of Value objects.  If the return
  // value is NULL, and if |error_code| is non-null, |error_code| will
  // contain an integer error code (either JsonFileError or JsonParseError).
  // If |error_message| is non-null, it will be filled in with a formatted
  // error message including the location of the error if appropriate.
  // The caller takes ownership of the returned value.
  virtual Value* Deserialize(int* error_code,
                             std::string* error_message) OVERRIDE;

  // This enum is designed to safely overlap with JSONReader::JsonParseError.
  enum JsonFileError {
    JSON_NO_ERROR = 0,
    JSON_ACCESS_DENIED = 1000,
    JSON_CANNOT_READ_FILE,
    JSON_FILE_LOCKED,
    JSON_NO_SUCH_FILE
  };

  // File-specific error messages that can be returned.
  static const char* kAccessDenied;
  static const char* kCannotReadFile;
  static const char* kFileLocked;
  static const char* kNoSuchFile;

  // Convert an error code into an error message.  |error_code| is assumed to
  // be a JsonFileError.
  static const char* GetErrorMessageForCode(int error_code);

  void set_allow_trailing_comma(bool new_value) {
    allow_trailing_comma_ = new_value;
  }

 private:
  bool SerializeInternal(const Value& root, bool omit_binary_values);

  base::FilePath json_file_path_;
  bool allow_trailing_comma_;

  // A wrapper for file_util::ReadFileToString which returns a non-zero
  // JsonFileError if there were file errors.
  int ReadFileToString(std::string* json_string);

  DISALLOW_IMPLICIT_CONSTRUCTORS(JSONFileValueSerializer);
};

#endif  // BASE_JSON_JSON_FILE_VALUE_SERIALIZER_H_