json/include/nlohmann/detail/input/parser.hpp

#pragma once

#include <cassert> // assert
#include <cmath> // isfinite
#include <cstdint> // uint8_t
#include <functional> // function
#include <string> // string
#include <utility> // move

#include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/input/input_adapters.hpp>
#include <nlohmann/detail/input/json_sax.hpp>
#include <nlohmann/detail/input/lexer.hpp>
#include <nlohmann/detail/value_t.hpp>

namespace nlohmann
{
namespace detail
{
////////////
// parser //
////////////

/*!
@brief syntax analysis

This class implements a recursive decent parser.
*/
template<typename BasicJsonType>
class parser
{
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using lexer_t = lexer<BasicJsonType>;
    using token_type = typename lexer_t::token_type;

  public:
    enum class parse_event_t : uint8_t
    {
        /// the parser read `{` and started to process a JSON object
        object_start,
        /// the parser read `}` and finished processing a JSON object
        object_end,
        /// the parser read `[` and started to process a JSON array
        array_start,
        /// the parser read `]` and finished processing a JSON array
        array_end,
        /// the parser read a key of a value in an object
        key,
        /// the parser finished reading a JSON value
        value
    };

    using json_sax_t = json_sax<BasicJsonType>;

    using parser_callback_t =
        std::function<bool(int depth, parse_event_t event, BasicJsonType& parsed)>;

    /// a parser reading from an input adapter
    explicit parser(detail::input_adapter_t adapter,
                    const parser_callback_t cb = nullptr,
                    const bool allow_exceptions_ = true)
        : callback(cb), m_lexer(adapter), allow_exceptions(allow_exceptions_)
    {
        // read first token
        get_token();
    }

    /*!
    @brief public parser interface

    @param[in] strict      whether to expect the last token to be EOF
    @param[in,out] result  parsed JSON value

    @throw parse_error.101 in case of an unexpected token
    @throw parse_error.102 if to_unicode fails or surrogate error
    @throw parse_error.103 if to_unicode fails
    */
    void parse(const bool strict, BasicJsonType& result)
    {
        if (callback)
        {
            parse_internal(true, result);
            result.assert_invariant();

            // in strict mode, input must be completely read
            if (strict)
            {
                get_token();
                expect(token_type::end_of_input);
            }

            // in case of an error, return discarded value
            if (errored)
            {
                result = value_t::discarded;
                return;
            }

            // set top-level value to null if it was discarded by the callback
            // function
            if (result.is_discarded())
            {
                result = nullptr;
            }
        }
        else
        {
            json_sax_dom_parser<BasicJsonType> sdp(result, allow_exceptions);
            sax_parse_internal(&sdp);
            result.assert_invariant();

            // in strict mode, input must be completely read
            if (strict and (get_token() != token_type::end_of_input))
            {
                sdp.parse_error(m_lexer.get_position(),
                                m_lexer.get_token_string(),
                                exception_message(token_type::end_of_input));
            }

            // in case of an error, return discarded value
            if (sdp.is_errored())
            {
                result = value_t::discarded;
                return;
            }
        }
    }

    /*!
    @brief public accept interface

    @param[in] strict  whether to expect the last token to be EOF
    @return whether the input is a proper JSON text
    */
    bool accept(const bool strict = true)
    {
        json_sax_acceptor<BasicJsonType> sax_acceptor;

        if (not sax_parse_internal(&sax_acceptor))
        {
            return false;
        }

        // strict => last token must be EOF
        return not strict or (get_token() == token_type::end_of_input);
    }

    bool sax_parse(json_sax_t* sax)
    {
        return sax_parse_internal(sax);
    }

  private:
    /*!
    @brief the actual parser
    @throw parse_error.101 in case of an unexpected token
    @throw parse_error.102 if to_unicode fails or surrogate error
    @throw parse_error.103 if to_unicode fails
    */
    void parse_internal(bool keep, BasicJsonType& result)
    {
        // never parse after a parse error was detected
        assert(not errored);

        // start with a discarded value
        if (not result.is_discarded())
        {
            result.m_value.destroy(result.m_type);
            result.m_type = value_t::discarded;
        }

        switch (last_token)
        {
            case token_type::begin_object:
            {
                if (keep)
                {
                    if (callback)
                    {
                        keep = callback(depth++, parse_event_t::object_start, result);
                    }

                    if (not callback or keep)
                    {
                        // explicitly set result to object to cope with {}
                        result.m_type = value_t::object;
                        result.m_value = value_t::object;
                    }
                }

                // read next token
                get_token();

                // closing } -> we are done
                if (last_token == token_type::end_object)
                {
                    if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
                    {
                        result.m_value.destroy(result.m_type);
                        result.m_type = value_t::discarded;
                    }
                    break;
                }

                // parse values
                std::string key;
                BasicJsonType value;
                while (true)
                {
                    // store key
                    if (not expect(token_type::value_string))
                    {
                        return;
                    }
                    key = m_lexer.move_string();

                    bool keep_tag = false;
                    if (keep)
                    {
                        if (callback)
                        {
                            BasicJsonType k(key);
                            keep_tag = callback(depth, parse_event_t::key, k);
                        }
                        else
                        {
                            keep_tag = true;
                        }
                    }

                    // parse separator (:)
                    get_token();
                    if (not expect(token_type::name_separator))
                    {
                        return;
                    }

                    // parse and add value
                    get_token();
                    value.m_value.destroy(value.m_type);
                    value.m_type = value_t::discarded;
                    parse_internal(keep, value);

                    if (JSON_UNLIKELY(errored))
                    {
                        return;
                    }

                    if (keep and keep_tag and not value.is_discarded())
                    {
                        result.m_value.object->emplace(std::move(key), std::move(value));
                    }

                    // comma -> next value
                    get_token();
                    if (last_token == token_type::value_separator)
                    {
                        get_token();
                        continue;
                    }

                    // closing }
                    if (not expect(token_type::end_object))
                    {
                        return;
                    }
                    break;
                }

                if (keep and callback and not callback(--depth, parse_event_t::object_end, result))
                {
                    result.m_value.destroy(result.m_type);
                    result.m_type = value_t::discarded;
                }
                break;
            }

            case token_type::begin_array:
            {
                if (keep)
                {
                    if (callback)
                    {
                        keep = callback(depth++, parse_event_t::array_start, result);
                    }

                    if (not callback or keep)
                    {
                        // explicitly set result to array to cope with []
                        result.m_type = value_t::array;
                        result.m_value = value_t::array;
                    }
                }

                // read next token
                get_token();

                // closing ] -> we are done
                if (last_token == token_type::end_array)
                {
                    if (callback and not callback(--depth, parse_event_t::array_end, result))
                    {
                        result.m_value.destroy(result.m_type);
                        result.m_type = value_t::discarded;
                    }
                    break;
                }

                // parse values
                BasicJsonType value;
                while (true)
                {
                    // parse value
                    value.m_value.destroy(value.m_type);
                    value.m_type = value_t::discarded;
                    parse_internal(keep, value);

                    if (JSON_UNLIKELY(errored))
                    {
                        return;
                    }

                    if (keep and not value.is_discarded())
                    {
                        result.m_value.array->push_back(std::move(value));
                    }

                    // comma -> next value
                    get_token();
                    if (last_token == token_type::value_separator)
                    {
                        get_token();
                        continue;
                    }

                    // closing ]
                    if (not expect(token_type::end_array))
                    {
                        return;
                    }
                    break;
                }

                if (keep and callback and not callback(--depth, parse_event_t::array_end, result))
                {
                    result.m_value.destroy(result.m_type);
                    result.m_type = value_t::discarded;
                }
                break;
            }

            case token_type::literal_null:
            {
                result.m_type = value_t::null;
                break;
            }

            case token_type::value_string:
            {
                result.m_type = value_t::string;
                result.m_value = m_lexer.move_string();
                break;
            }

            case token_type::literal_true:
            {
                result.m_type = value_t::boolean;
                result.m_value = true;
                break;
            }

            case token_type::literal_false:
            {
                result.m_type = value_t::boolean;
                result.m_value = false;
                break;
            }

            case token_type::value_unsigned:
            {
                result.m_type = value_t::number_unsigned;
                result.m_value = m_lexer.get_number_unsigned();
                break;
            }

            case token_type::value_integer:
            {
                result.m_type = value_t::number_integer;
                result.m_value = m_lexer.get_number_integer();
                break;
            }

            case token_type::value_float:
            {
                result.m_type = value_t::number_float;
                result.m_value = m_lexer.get_number_float();

                // throw in case of infinity or NAN
                if (JSON_UNLIKELY(not std::isfinite(result.m_value.number_float)))
                {
                    if (allow_exceptions)
                    {
                        JSON_THROW(out_of_range::create(406, "number overflow parsing '" +
                                                        m_lexer.get_token_string() + "'"));
                    }
                    expect(token_type::uninitialized);
                }
                break;
            }

            case token_type::parse_error:
            {
                // using "uninitialized" to avoid "expected" message
                if (not expect(token_type::uninitialized))
                {
                    return;
                }
                break; // LCOV_EXCL_LINE
            }

            default:
            {
                // the last token was unexpected; we expected a value
                if (not expect(token_type::literal_or_value))
                {
                    return;
                }
                break; // LCOV_EXCL_LINE
            }
        }

        if (keep and callback and not callback(depth, parse_event_t::value, result))
        {
            result.m_value.destroy(result.m_type);
            result.m_type = value_t::discarded;
        }
    }

    bool sax_parse_internal(json_sax_t* sax)
    {
        switch (last_token)
        {
            case token_type::begin_object:
            {
                if (not sax->start_object())
                {
                    return false;
                }

                // read next token
                get_token();

                // closing } -> we are done
                if (JSON_UNLIKELY(last_token == token_type::end_object))
                {
                    return sax->end_object();
                }

                // parse values
                while (true)
                {
                    // parse key
                    if (JSON_UNLIKELY(last_token != token_type::value_string))
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                exception_message(token_type::value_string));
                    }
                    else
                    {
                        if (not sax->key(m_lexer.move_string()))
                        {
                            return false;
                        }
                    }

                    // parse separator (:)
                    get_token();
                    if (JSON_UNLIKELY(last_token != token_type::name_separator))
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                exception_message(token_type::name_separator));
                    }

                    // parse value
                    get_token();
                    if (not sax_parse_internal(sax))
                    {
                        return false;
                    }

                    // comma -> next value
                    get_token();
                    if (last_token == token_type::value_separator)
                    {
                        get_token();
                        continue;
                    }

                    // closing }
                    if (JSON_LIKELY(last_token == token_type::end_object))
                    {
                        return sax->end_object();
                    }
                    else
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                exception_message(token_type::end_object));
                    }
                }
            }

            case token_type::begin_array:
            {
                if (not sax->start_array())
                {
                    return false;
                }

                // read next token
                get_token();

                // closing ] -> we are done
                if (last_token == token_type::end_array)
                {
                    return sax->end_array();
                }

                // parse values
                while (true)
                {
                    // parse value
                    if (not sax_parse_internal(sax))
                    {
                        return false;
                    }

                    // comma -> next value
                    get_token();
                    if (last_token == token_type::value_separator)
                    {
                        get_token();
                        continue;
                    }

                    // closing ]
                    if (JSON_LIKELY(last_token == token_type::end_array))
                    {
                        return sax->end_array();
                    }
                    else
                    {
                        return sax->parse_error(m_lexer.get_position(),
                                                m_lexer.get_token_string(),
                                                exception_message(token_type::end_array));
                    }
                }
            }

            case token_type::value_float:
            {
                const auto res = m_lexer.get_number_float();

                if (JSON_UNLIKELY(not std::isfinite(res)))
                {
                    return sax->parse_error(m_lexer.get_position(),
                                            m_lexer.get_token_string(),
                                            "number overflow");
                }
                else
                {
                    return sax->number_float(res, m_lexer.move_string());
                }
            }

            case token_type::literal_false:
            {
                return sax->boolean(false);
            }

            case token_type::literal_null:
            {
                return sax->null();
            }

            case token_type::literal_true:
            {
                return sax->boolean(true);
            }

            case token_type::value_integer:
            {
                return sax->number_integer(m_lexer.get_number_integer());
            }

            case token_type::value_string:
            {
                return sax->string(m_lexer.move_string());
            }

            case token_type::value_unsigned:
            {
                return sax->number_unsigned(m_lexer.get_number_unsigned());
            }

            case token_type::parse_error:
            {
                // using "uninitialized" to avoid "expected" message
                return sax->parse_error(m_lexer.get_position(),
                                        m_lexer.get_token_string(),
                                        exception_message(token_type::uninitialized));
            }

            default: // the last token was unexpected
            {
                return sax->parse_error(m_lexer.get_position(),
                                        m_lexer.get_token_string(),
                                        exception_message(token_type::literal_or_value));
            }
        }
    }

    /// get next token from lexer
    token_type get_token()
    {
        return (last_token = m_lexer.scan());
    }

    /*!
    @throw parse_error.101 if expected token did not occur
    */
    bool expect(token_type t)
    {
        if (JSON_UNLIKELY(t != last_token))
        {
            errored = true;
            if (allow_exceptions)
            {
                JSON_THROW(parse_error::create(101, m_lexer.get_position(), exception_message(t)));
            }
            else
            {
                return false;
            }
        }

        return true;
    }

    std::string exception_message(const token_type expected)
    {
        std::string error_msg = "syntax error - ";
        if (last_token == token_type::parse_error)
        {
            error_msg += std::string(m_lexer.get_error_message()) + "; last read: '" +
                         m_lexer.get_token_string() + "'";
        }
        else
        {
            error_msg += "unexpected " + std::string(lexer_t::token_type_name(last_token));
        }

        if (expected != token_type::uninitialized)
        {
            error_msg += "; expected " + std::string(lexer_t::token_type_name(expected));
        }

        return error_msg;
    }

  private:
    /// current level of recursion
    int depth = 0;
    /// callback function
    const parser_callback_t callback = nullptr;
    /// the type of the last read token
    token_type last_token = token_type::uninitialized;
    /// the lexer
    lexer_t m_lexer;
    /// whether a syntax error occurred
    bool errored = false;
    /// whether to throw exceptions in case of errors
    const bool allow_exceptions = true;
};
}
}