json11.h

/* Copyright (c) 2013 Dropbox, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

/* json11
 *
 * json11 is a tiny JSON library for C++11, providing JSON parsing and
 * serialization.
 *
 * The core object provided by the library is json11::Json. A Json object
 * represents any JSON value: null, bool, number (int or double), string
 * (std::string), array (std::vector), or object (std::map).
 *
 * Json objects act like values: they can be assigned, copied, moved, compared
 * for equality or order, etc. There are also helper methods Json::dump, to
 * serialize a Json to a string, and Json::parse (static) to parse a std::string
 * as a Json object.
 *
 * Internally, the various types of Json object are represented by the JsonValue
 * class hierarchy.
 *
 * A note on numbers - JSON specifies the syntax of number formatting but not
 * its semantics, so some JSON implementations distinguish between integers and
 * floating-point numbers, while some don't. In json11, we choose the latter.
 * Because some JSON implementations (namely Javascript itself) treat all
 * numbers as the same type, distinguishing the two leads to JSON that will be
 * *silently* changed by a round-trip through those implementations. Dangerous!
 * To avoid that risk, json11 stores all numbers as double internally, but also
 * provides integer helpers.
 *
 * Fortunately, double-precision IEEE754 ('double') can precisely store any
 * integer in the range +/-2^53, which includes every 'int' on most systems.
 * (Timestamps often use int64 or long long to avoid the Y2038K problem; a
 * double storing microseconds since some epoch will be exact for +/- 275
 * years.)
 */
#pragma once

#include <initializer_list>
#include <map>
#include <memory>
#include <string>
#include <utility>
#include <vector>

namespace json11_internal_lightgbm {

enum JsonParse { STANDARD, COMMENTS };

class JsonValue;

class Json final {
 public:
  // Types
  enum Type { NUL, NUMBER, BOOL, STRING, ARRAY, OBJECT };

  // Array and object typedefs
  typedef std::vector<Json> array;
  typedef std::map<std::string, Json> object;

  // Constructors for the various types of JSON value.
  Json() noexcept;                          // NUL
  explicit Json(std::nullptr_t) noexcept;   // NUL
  explicit Json(double value);              // NUMBER
  explicit Json(int value);                 // NUMBER
  explicit Json(bool value);                // BOOL
  explicit Json(const std::string &value);  // STRING
  explicit Json(std::string &&value);       // STRING
  explicit Json(const char *value);         // STRING
  explicit Json(const array &values);       // ARRAY
  explicit Json(array &&values);            // ARRAY
  explicit Json(const object &values);      // OBJECT
  explicit Json(object &&values);           // OBJECT

  // Implicit constructor: anything with a to_json() function.
  template <class T, class = decltype(&T::to_json)>
  explicit Json(const T &t) : Json(t.to_json()) {}

  // Implicit constructor: map-like objects (std::map, std::unordered_map, etc)
  template <
      class M,
      typename std::enable_if<
          std::is_constructible<
              std::string, decltype(std::declval<M>().begin()->first)>::value &&
              std::is_constructible<
                  Json, decltype(std::declval<M>().begin()->second)>::value,
          int>::type = 0>
  explicit Json(const M &m) : Json(object(m.begin(), m.end())) {}

  // Implicit constructor: vector-like objects (std::list, std::vector,
  // std::set, etc)
  template <class V, typename std::enable_if<
                         std::is_constructible<
                             Json, decltype(*std::declval<V>().begin())>::value,
                         int>::type = 0>
  explicit Json(const V &v) : Json(array(v.begin(), v.end())) {}

  // This prevents Json(some_pointer) from accidentally producing a bool. Use
  // Json(bool(some_pointer)) if that behavior is desired.
  explicit Json(void *) = delete;

  // Accessors
  Type type() const;

  bool is_null() const { return type() == NUL; }
  bool is_number() const { return type() == NUMBER; }
  bool is_bool() const { return type() == BOOL; }
  bool is_string() const { return type() == STRING; }
  bool is_array() const { return type() == ARRAY; }
  bool is_object() const { return type() == OBJECT; }

  // Return the enclosed value if this is a number, 0 otherwise. Note that
  // json11 does not distinguish between integer and non-integer numbers -
  // number_value() and int_value() can both be applied to a NUMBER-typed
  // object.
  double number_value() const;
  int int_value() const;

  // Return the enclosed value if this is a boolean, false otherwise.
  bool bool_value() const;
  // Return the enclosed string if this is a string, "" otherwise.
  const std::string &string_value() const;
  // Return the enclosed std::vector if this is an array, or an empty vector
  // otherwise.
  const array &array_items() const;
  // Return the enclosed std::map if this is an object, or an empty map
  // otherwise.
  const object &object_items() const;

  // Return a reference to arr[i] if this is an array, Json() otherwise.
  const Json &operator[](size_t i) const;
  // Return a reference to obj[key] if this is an object, Json() otherwise.
  const Json &operator[](const std::string &key) const;

  // Serialize.
  void dump(std::string *out) const;
  std::string dump() const {
    std::string out;
    dump(&out);
    return out;
  }

  // Parse. If parse fails, return Json() and assign an error message to err.
  static Json parse(const std::string &in, std::string *err,
                    JsonParse strategy = JsonParse::STANDARD);
  static Json parse(const char *in, std::string *err,
                    JsonParse strategy = JsonParse::STANDARD) {
    if (in) {
      return parse(std::string(in), err, strategy);
    } else {
      *err = "null input";
      return Json(nullptr);
    }
  }
  // Parse multiple objects, concatenated or separated by whitespace
  static std::vector<Json> parse_multi(
      const std::string &in, std::string::size_type *parser_stop_pos,
      std::string *err, JsonParse strategy = JsonParse::STANDARD);

  static inline std::vector<Json> parse_multi(
      const std::string &in, std::string *err,
      JsonParse strategy = JsonParse::STANDARD) {
    std::string::size_type parser_stop_pos;
    return parse_multi(in, &parser_stop_pos, err, strategy);
  }

  bool operator==(const Json &rhs) const;
  bool operator<(const Json &rhs) const;
  bool operator!=(const Json &rhs) const { return !(*this == rhs); }
  bool operator<=(const Json &rhs) const { return !(rhs < *this); }
  bool operator>(const Json &rhs) const { return (rhs < *this); }
  bool operator>=(const Json &rhs) const { return !(*this < rhs); }

  /* has_shape(types, err)
   *
   * Return true if this is a JSON object and, for each item in types, has a
   * field of the given type. If not, return false and set err to a descriptive
   * message.
   */
  typedef std::initializer_list<std::pair<std::string, Type>> shape;
  bool has_shape(const shape &types, std::string *err) const;

 private:
  std::shared_ptr<JsonValue> m_ptr;
};

// Internal class hierarchy - JsonValue objects are not exposed to users of this
// API.
class JsonValue {
 protected:
  friend class Json;
  friend class JsonInt;
  friend class JsonDouble;
  virtual Json::Type type() const = 0;
  virtual bool equals(const JsonValue *other) const = 0;
  virtual bool less(const JsonValue *other) const = 0;
  virtual void dump(std::string *out) const = 0;
  virtual double number_value() const;
  virtual int int_value() const;
  virtual bool bool_value() const;
  virtual const std::string &string_value() const;
  virtual const Json::array &array_items() const;
  virtual const Json &operator[](size_t i) const;
  virtual const Json::object &object_items() const;
  virtual const Json &operator[](const std::string &key) const;
  virtual ~JsonValue() {}
};

}  // namespace json11_internal_lightgbm