annotate json/json11/json11.hpp @ 66:6f160dee1192

Instead of using separate values and b64values entries in JSON serialisations, allow numeric arrays to be replaced by b64 variants wherever they appear (discriminating by type). Also rename values to featureValues in feature throughout, as values turns out to be a hazardous name in a JS context. Finally use Array instead of Text for array encoding (seems clearer).

/* 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.)
 */

/* 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.
 */

#pragma once

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

namespace json11 {

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
    Json(std::nullptr_t) noexcept;  // NUL
    Json(double value);             // NUMBER
    Json(int value);                // NUMBER
    Json(bool value);               // BOOL
    Json(const std::string &value); // STRING
    Json(std::string &&value);      // STRING
    Json(const char * value);       // STRING
    Json(const array &values);      // ARRAY
    Json(array &&values);           // ARRAY
    Json(const object &values);     // OBJECT
    Json(object &&values);          // OBJECT

    // Implicit constructor: anything with a to_json() function.
    template <class T, class = decltype(&T::to_json)>
    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, typename M::key_type>::value
        && std::is_constructible<Json, typename M::mapped_type>::value,
            int>::type = 0>
    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, typename V::value_type>::value,
            int>::type = 0>
    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.
    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 nullptr;
        }
    }
    // Parse multiple objects, concatenated or separated by whitespace
    static std::vector<Json> parse_multi(
        const std::string & in,
        std::string & err,
        JsonParse strategy = JsonParse::STANDARD);

    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