include/nlohmann/detail/output/binary_writer.hpp - develop - githubmirror/json

include/nlohmann/detail/output/binary_writer.hpp
1 922 строки74 KB
Niels Lohmann
Do not write BJData ndarrays whose size overflows std::size_t (#5362)
05 авг 2026, 14:44
05 авг 2026, 14:449a091d2
//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++
// |  |  |__   |  |  | | | |  version 3.12.0
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

#pragma once

#include <algorithm> // reverse
#include <array> // array
#include <map> // map
#include <cmath> // isnan, isinf
#include <cstdint> // uint8_t, uint16_t, uint32_t, uint64_t
#include <cstring> // memcpy
#include <limits> // numeric_limits
#include <string> // string
#include <utility> // move
#include <vector> // vector

#include <nlohmann/detail/input/binary_reader.hpp>
#include <nlohmann/detail/macro_scope.hpp>
#include <nlohmann/detail/output/output_adapters.hpp>
#include <nlohmann/detail/string_concat.hpp>

NLOHMANN_JSON_NAMESPACE_BEGIN
namespace detail
{

/// how to encode BJData
enum class bjdata_version_t
{
    draft2,
    draft3,
};

///////////////////
// binary writer //
///////////////////

/*!
@brief serialization to CBOR and MessagePack values
*/
template<typename BasicJsonType, typename CharType>
class binary_writer
{
    using string_t = typename BasicJsonType::string_t;
    using binary_t = typename BasicJsonType::binary_t;
    using number_float_t = typename BasicJsonType::number_float_t;

  public:
    /*!
    @brief create a binary writer

    @param[in] adapter  output adapter to write to
    */
    explicit binary_writer(output_adapter_t<CharType> adapter) : oa(std::move(adapter))
    {
        JSON_ASSERT(oa);
    }

    /*!
    @param[in] j  JSON value to serialize
    @pre       j.type() == value_t::object
    */
    void write_bson(const BasicJsonType& j)
    {
        switch (j.type())
        {
            case value_t::object:
            {
                write_bson_object(*j.m_data.m_value.object);
                break;
            }

            case value_t::null:
            case value_t::array:
            case value_t::string:
            case value_t::boolean:
            case value_t::number_integer:
            case value_t::number_unsigned:
            case value_t::number_float:
            case value_t::binary:
            case value_t::discarded:
            default:
            {
                JSON_THROW(type_error::create(317, concat("to serialize to BSON, top-level type must be object, but is ", j.type_name()), &j));
            }
        }
    }

    /*!
    @param[in] j  JSON value to serialize
    */
    void write_cbor(const BasicJsonType& j)
    {
        switch (j.type())
        {
            case value_t::null:
            {
                oa->write_character(to_char_type(0xF6));
                break;
            }

            case value_t::boolean:
            {
                oa->write_character(j.m_data.m_value.boolean
                                    ? to_char_type(0xF5)
                                    : to_char_type(0xF4));
                break;
            }

            case value_t::number_integer:
            {
                if (j.m_data.m_value.number_integer >= 0)
                {
                    // CBOR does not differentiate between positive signed
                    // integers and unsigned integers. Therefore, we used the
                    // code from the value_t::number_unsigned case here.
                    if (j.m_data.m_value.number_integer <= 0x17)
                    {
                        write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint8_t>::max)())
                    {
                        oa->write_character(to_char_type(0x18));
                        write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint16_t>::max)())
                    {
                        oa->write_character(to_char_type(0x19));
                        write_number(static_cast<std::uint16_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint32_t>::max)())
                    {
                        oa->write_character(to_char_type(0x1A));
                        write_number(static_cast<std::uint32_t>(j.m_data.m_value.number_integer));
                    }
                    else
                    {
                        oa->write_character(to_char_type(0x1B));
                        write_number(static_cast<std::uint64_t>(j.m_data.m_value.number_integer));
                    }
                }
                else
                {
                    // The conversions below encode the sign in the first
                    // byte, and the value is converted to a positive number.
                    const auto positive_number = -1 - j.m_data.m_value.number_integer;
                    if (j.m_data.m_value.number_integer >= -24)
                    {
                        write_number(static_cast<std::uint8_t>(0x20 + positive_number));
                    }
                    else if (positive_number <= (std::numeric_limits<std::uint8_t>::max)())
                    {
                        oa->write_character(to_char_type(0x38));
                        write_number(static_cast<std::uint8_t>(positive_number));
                    }
                    else if (positive_number <= (std::numeric_limits<std::uint16_t>::max)())
                    {
                        oa->write_character(to_char_type(0x39));
                        write_number(static_cast<std::uint16_t>(positive_number));
                    }
                    else if (positive_number <= (std::numeric_limits<std::uint32_t>::max)())
                    {
                        oa->write_character(to_char_type(0x3A));
                        write_number(static_cast<std::uint32_t>(positive_number));
                    }
                    else
                    {
                        oa->write_character(to_char_type(0x3B));
                        write_number(static_cast<std::uint64_t>(positive_number));
                    }
                }
                break;
            }

            case value_t::number_unsigned:
            {
                if (j.m_data.m_value.number_unsigned <= 0x17)
                {
                    write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_unsigned));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    oa->write_character(to_char_type(0x18));
                    write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_unsigned));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    oa->write_character(to_char_type(0x19));
                    write_number(static_cast<std::uint16_t>(j.m_data.m_value.number_unsigned));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    oa->write_character(to_char_type(0x1A));
                    write_number(static_cast<std::uint32_t>(j.m_data.m_value.number_unsigned));
                }
                else
                {
                    oa->write_character(to_char_type(0x1B));
                    write_number(static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned));
                }
                break;
            }

            case value_t::number_float:
            {
                if (std::isnan(j.m_data.m_value.number_float))
                {
                    // NaN is 0xf97e00 in CBOR
                    oa->write_character(to_char_type(0xF9));
                    oa->write_character(to_char_type(0x7E));
                    oa->write_character(to_char_type(0x00));
                }
                else if (std::isinf(j.m_data.m_value.number_float))
                {
                    // Infinity is 0xf97c00, -Infinity is 0xf9fc00
                    oa->write_character(to_char_type(0xf9));
                    oa->write_character(j.m_data.m_value.number_float > 0 ? to_char_type(0x7C) : to_char_type(0xFC));
                    oa->write_character(to_char_type(0x00));
                }
                else
                {
                    write_compact_float(j.m_data.m_value.number_float, detail::input_format_t::cbor);
                }
                break;
            }

            case value_t::string:
            {
                // step 1: write control byte and the string length
                const auto N = j.m_data.m_value.string->size();
                if (N <= 0x17)
                {
                    write_number(static_cast<std::uint8_t>(0x60 + N));
                }
                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    oa->write_character(to_char_type(0x78));
                    write_number(static_cast<std::uint8_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    oa->write_character(to_char_type(0x79));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    oa->write_character(to_char_type(0x7A));
                    write_number(static_cast<std::uint32_t>(N));
                }
                // LCOV_EXCL_START
                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    oa->write_character(to_char_type(0x7B));
                    write_number(static_cast<std::uint64_t>(N));
                }
                // LCOV_EXCL_STOP

                // step 2: write the string
                oa->write_characters(
                    reinterpret_cast<const CharType*>(j.m_data.m_value.string->c_str()),
                    j.m_data.m_value.string->size());
                break;
            }

            case value_t::array:
            {
                // step 1: write control byte and the array size
                const auto N = j.m_data.m_value.array->size();
                if (N <= 0x17)
                {
                    write_number(static_cast<std::uint8_t>(0x80 + N));
                }
                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    oa->write_character(to_char_type(0x98));
                    write_number(static_cast<std::uint8_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    oa->write_character(to_char_type(0x99));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    oa->write_character(to_char_type(0x9A));
                    write_number(static_cast<std::uint32_t>(N));
                }
                // LCOV_EXCL_START
                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    oa->write_character(to_char_type(0x9B));
                    write_number(static_cast<std::uint64_t>(N));
                }
                // LCOV_EXCL_STOP

                // step 2: write each element
                for (const auto& el : *j.m_data.m_value.array)
                {
                    write_cbor(el);
                }
                break;
            }

            case value_t::binary:
            {
                if (j.m_data.m_value.binary->has_subtype())
                {
                    if (j.m_data.m_value.binary->subtype() <= (std::numeric_limits<std::uint8_t>::max)())
                    {
                        write_number(static_cast<std::uint8_t>(0xd8));
                        write_number(static_cast<std::uint8_t>(j.m_data.m_value.binary->subtype()));
                    }
                    else if (j.m_data.m_value.binary->subtype() <= (std::numeric_limits<std::uint16_t>::max)())
                    {
                        write_number(static_cast<std::uint8_t>(0xd9));
                        write_number(static_cast<std::uint16_t>(j.m_data.m_value.binary->subtype()));
                    }
                    else if (j.m_data.m_value.binary->subtype() <= (std::numeric_limits<std::uint32_t>::max)())
                    {
                        write_number(static_cast<std::uint8_t>(0xda));
                        write_number(static_cast<std::uint32_t>(j.m_data.m_value.binary->subtype()));
                    }
                    else if (j.m_data.m_value.binary->subtype() <= (std::numeric_limits<std::uint64_t>::max)())
                    {
                        write_number(static_cast<std::uint8_t>(0xdb));
                        write_number(static_cast<std::uint64_t>(j.m_data.m_value.binary->subtype()));
                    }
                }

                // step 1: write control byte and the binary array size
                const auto N = j.m_data.m_value.binary->size();
                if (N <= 0x17)
                {
                    write_number(static_cast<std::uint8_t>(0x40 + N));
                }
                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    oa->write_character(to_char_type(0x58));
                    write_number(static_cast<std::uint8_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    oa->write_character(to_char_type(0x59));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    oa->write_character(to_char_type(0x5A));
                    write_number(static_cast<std::uint32_t>(N));
                }
                // LCOV_EXCL_START
                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    oa->write_character(to_char_type(0x5B));
                    write_number(static_cast<std::uint64_t>(N));
                }
                // LCOV_EXCL_STOP

                // step 2: write each element
                oa->write_characters(
                    reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
                    N);

                break;
            }

            case value_t::object:
            {
                // step 1: write control byte and the object size
                const auto N = j.m_data.m_value.object->size();
                if (N <= 0x17)
                {
                    write_number(static_cast<std::uint8_t>(0xA0 + N));
                }
                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    oa->write_character(to_char_type(0xB8));
                    write_number(static_cast<std::uint8_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    oa->write_character(to_char_type(0xB9));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    oa->write_character(to_char_type(0xBA));
                    write_number(static_cast<std::uint32_t>(N));
                }
                // LCOV_EXCL_START
                else if (N <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    oa->write_character(to_char_type(0xBB));
                    write_number(static_cast<std::uint64_t>(N));
                }
                // LCOV_EXCL_STOP

                // step 2: write each element
                for (const auto& el : *j.m_data.m_value.object)
                {
                    write_cbor(el.first);
                    write_cbor(el.second);
                }
                break;
            }

            case value_t::discarded:
            default:
                break;
        }
    }

    /*!
    @param[in] j  JSON value to serialize
    */
    void write_msgpack(const BasicJsonType& j)
    {
        switch (j.type())
        {
            case value_t::null: // nil
            {
                oa->write_character(to_char_type(0xC0));
                break;
            }

            case value_t::boolean: // true and false
            {
                oa->write_character(j.m_data.m_value.boolean
                                    ? to_char_type(0xC3)
                                    : to_char_type(0xC2));
                break;
            }

            case value_t::number_integer:
            {
                if (j.m_data.m_value.number_integer >= 0)
                {
                    // MessagePack does not differentiate between positive
                    // signed integers and unsigned integers. Therefore, we used
                    // the code from the value_t::number_unsigned case here.
                    if (j.m_data.m_value.number_unsigned < 128)
                    {
                        // positive fixnum
                        write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                    {
                        // uint 8
                        oa->write_character(to_char_type(0xCC));
                        write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                    {
                        // uint 16
                        oa->write_character(to_char_type(0xCD));
                        write_number(static_cast<std::uint16_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                    {
                        // uint 32
                        oa->write_character(to_char_type(0xCE));
                        write_number(static_cast<std::uint32_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint64_t>::max)())
                    {
                        // uint 64
                        oa->write_character(to_char_type(0xCF));
                        write_number(static_cast<std::uint64_t>(j.m_data.m_value.number_integer));
                    }
                }
                else
                {
                    if (j.m_data.m_value.number_integer >= -32)
                    {
                        // negative fixnum
                        write_number(static_cast<std::int8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer >= (std::numeric_limits<std::int8_t>::min)() &&
                             j.m_data.m_value.number_integer <= (std::numeric_limits<std::int8_t>::max)())
                    {
                        // int 8
                        oa->write_character(to_char_type(0xD0));
                        write_number(static_cast<std::int8_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer >= (std::numeric_limits<std::int16_t>::min)() &&
                             j.m_data.m_value.number_integer <= (std::numeric_limits<std::int16_t>::max)())
                    {
                        // int 16
                        oa->write_character(to_char_type(0xD1));
                        write_number(static_cast<std::int16_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer >= (std::numeric_limits<std::int32_t>::min)() &&
                             j.m_data.m_value.number_integer <= (std::numeric_limits<std::int32_t>::max)())
                    {
                        // int 32
                        oa->write_character(to_char_type(0xD2));
                        write_number(static_cast<std::int32_t>(j.m_data.m_value.number_integer));
                    }
                    else if (j.m_data.m_value.number_integer >= (std::numeric_limits<std::int64_t>::min)() &&
                             j.m_data.m_value.number_integer <= (std::numeric_limits<std::int64_t>::max)())
                    {
                        // int 64
                        oa->write_character(to_char_type(0xD3));
                        write_number(static_cast<std::int64_t>(j.m_data.m_value.number_integer));
                    }
                }
                break;
            }

            case value_t::number_unsigned:
            {
                if (j.m_data.m_value.number_unsigned < 128)
                {
                    // positive fixnum
                    write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    // uint 8
                    oa->write_character(to_char_type(0xCC));
                    write_number(static_cast<std::uint8_t>(j.m_data.m_value.number_integer));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    // uint 16
                    oa->write_character(to_char_type(0xCD));
                    write_number(static_cast<std::uint16_t>(j.m_data.m_value.number_integer));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    // uint 32
                    oa->write_character(to_char_type(0xCE));
                    write_number(static_cast<std::uint32_t>(j.m_data.m_value.number_integer));
                }
                else if (j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    // uint 64
                    oa->write_character(to_char_type(0xCF));
                    write_number(static_cast<std::uint64_t>(j.m_data.m_value.number_integer));
                }
                break;
            }

            case value_t::number_float:
            {
                write_compact_float(j.m_data.m_value.number_float, detail::input_format_t::msgpack);
                break;
            }

            case value_t::string:
            {
                // step 1: write control byte and the string length
                const auto N = j.m_data.m_value.string->size();
                if (N <= 31)
                {
                    // fixstr
                    write_number(static_cast<std::uint8_t>(0xA0 | N));
                }
                else if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    // str 8
                    oa->write_character(to_char_type(0xD9));
                    write_number(static_cast<std::uint8_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    // str 16
                    oa->write_character(to_char_type(0xDA));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    // str 32
                    oa->write_character(to_char_type(0xDB));
                    write_number(static_cast<std::uint32_t>(N));
                }

                // step 2: write the string
                oa->write_characters(
                    reinterpret_cast<const CharType*>(j.m_data.m_value.string->c_str()),
                    j.m_data.m_value.string->size());
                break;
            }

            case value_t::array:
            {
                // step 1: write control byte and the array size
                const auto N = j.m_data.m_value.array->size();
                if (N <= 15)
                {
                    // fixarray
                    write_number(static_cast<std::uint8_t>(0x90 | N));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    // array 16
                    oa->write_character(to_char_type(0xDC));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    // array 32
                    oa->write_character(to_char_type(0xDD));
                    write_number(static_cast<std::uint32_t>(N));
                }

                // step 2: write each element
                for (const auto& el : *j.m_data.m_value.array)
                {
                    write_msgpack(el);
                }
                break;
            }

            case value_t::binary:
            {
                // step 0: determine if the binary type has a set subtype to
                // determine whether to use the ext or fixext types
                const bool use_ext = j.m_data.m_value.binary->has_subtype();

                // step 1: write control byte and the byte string length
                const auto N = j.m_data.m_value.binary->size();
                if (N <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    std::uint8_t output_type{};
                    bool fixed = true;
                    if (use_ext)
                    {
                        switch (N)
                        {
                            case 1:
                                output_type = 0xD4; // fixext 1
                                break;
                            case 2:
                                output_type = 0xD5; // fixext 2
                                break;
                            case 4:
                                output_type = 0xD6; // fixext 4
                                break;
                            case 8:
                                output_type = 0xD7; // fixext 8
                                break;
                            case 16:
                                output_type = 0xD8; // fixext 16
                                break;
                            default:
                                output_type = 0xC7; // ext 8
                                fixed = false;
                                break;
                        }

                    }
                    else
                    {
                        output_type = 0xC4; // bin 8
                        fixed = false;
                    }

                    oa->write_character(to_char_type(output_type));
                    if (!fixed)
                    {
                        write_number(static_cast<std::uint8_t>(N));
                    }
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    const std::uint8_t output_type = use_ext
                                                     ? 0xC8 // ext 16
                                                     : 0xC5; // bin 16

                    oa->write_character(to_char_type(output_type));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    const std::uint8_t output_type = use_ext
                                                     ? 0xC9 // ext 32
                                                     : 0xC6; // bin 32

                    oa->write_character(to_char_type(output_type));
                    write_number(static_cast<std::uint32_t>(N));
                }

                // step 1.5: if this is an ext type, write the subtype
                if (use_ext)
                {
                    write_number(static_cast<std::int8_t>(j.m_data.m_value.binary->subtype()));
                }

                // step 2: write the byte string
                oa->write_characters(
                    reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
                    N);

                break;
            }

            case value_t::object:
            {
                // step 1: write control byte and the object size
                const auto N = j.m_data.m_value.object->size();
                if (N <= 15)
                {
                    // fixmap
                    write_number(static_cast<std::uint8_t>(0x80 | (N & 0xF)));
                }
                else if (N <= (std::numeric_limits<std::uint16_t>::max)())
                {
                    // map 16
                    oa->write_character(to_char_type(0xDE));
                    write_number(static_cast<std::uint16_t>(N));
                }
                else if (N <= (std::numeric_limits<std::uint32_t>::max)())
                {
                    // map 32
                    oa->write_character(to_char_type(0xDF));
                    write_number(static_cast<std::uint32_t>(N));
                }

                // step 2: write each element
                for (const auto& el : *j.m_data.m_value.object)
                {
                    write_msgpack(el.first);
                    write_msgpack(el.second);
                }
                break;
            }

            case value_t::discarded:
            default:
                break;
        }
    }

    /*!
    @param[in] j  JSON value to serialize
    @param[in] use_count   whether to use '#' prefixes (optimized format)
    @param[in] use_type    whether to use '$' prefixes (optimized format)
    @param[in] add_prefix  whether prefixes need to be used for this value
    @param[in] use_bjdata  whether write in BJData format, default is false
    @param[in] bjdata_version  which BJData version to use, default is draft2
    */
    void write_ubjson(const BasicJsonType& j, const bool use_count,
                      const bool use_type, const bool add_prefix = true,
                      const bool use_bjdata = false, const bjdata_version_t bjdata_version = bjdata_version_t::draft2)
    {
        const bool bjdata_draft3 = use_bjdata && bjdata_version == bjdata_version_t::draft3;

        switch (j.type())
        {
            case value_t::null:
            {
                if (add_prefix)
                {
                    oa->write_character(to_char_type('Z'));
                }
                break;
            }

            case value_t::boolean:
            {
                if (add_prefix)
                {
                    oa->write_character(j.m_data.m_value.boolean
                                        ? to_char_type('T')
                                        : to_char_type('F'));
                }
                break;
            }

            case value_t::number_integer:
            {
                write_number_with_ubjson_prefix(j.m_data.m_value.number_integer, add_prefix, use_bjdata);
                break;
            }

            case value_t::number_unsigned:
            {
                write_number_with_ubjson_prefix(j.m_data.m_value.number_unsigned, add_prefix, use_bjdata);
                break;
            }

            case value_t::number_float:
            {
                write_number_with_ubjson_prefix(j.m_data.m_value.number_float, add_prefix, use_bjdata);
                break;
            }

            case value_t::string:
            {
                if (add_prefix)
                {
                    oa->write_character(to_char_type('S'));
                }
                write_number_with_ubjson_prefix(j.m_data.m_value.string->size(), true, use_bjdata);
                oa->write_characters(
                    reinterpret_cast<const CharType*>(j.m_data.m_value.string->c_str()),
                    j.m_data.m_value.string->size());
                break;
            }

            case value_t::array:
            {
                if (add_prefix)
                {
                    oa->write_character(to_char_type('['));
                }

                bool prefix_required = true;
                if (use_type && !j.m_data.m_value.array->empty())
                {
                    JSON_ASSERT(use_count);
                    const CharType first_prefix = ubjson_prefix(j.front(), use_bjdata);
                    const bool same_prefix = std::all_of(j.begin() + 1, j.end(),
                                                         [this, first_prefix, use_bjdata](const BasicJsonType & v)
                    {
                        return ubjson_prefix(v, use_bjdata) == first_prefix;
                    });

                    std::vector<CharType> bjdx = {'[', '{', 'S', 'H', 'T', 'F', 'N', 'Z'}; // excluded markers in bjdata optimized type

                    if (same_prefix && !(use_bjdata && std::find(bjdx.begin(), bjdx.end(), first_prefix) != bjdx.end()))
                    {
                        prefix_required = false;
                        oa->write_character(to_char_type('$'));
                        oa->write_character(first_prefix);
                    }
                }

                if (use_count)
                {
                    oa->write_character(to_char_type('#'));
                    write_number_with_ubjson_prefix(j.m_data.m_value.array->size(), true, use_bjdata);
                }

                for (const auto& el : *j.m_data.m_value.array)
                {
                    write_ubjson(el, use_count, use_type, prefix_required, use_bjdata, bjdata_version);
                }

                if (!use_count)
                {
                    oa->write_character(to_char_type(']'));
                }

                break;
            }

            case value_t::binary:
            {
                if (add_prefix)
                {
                    oa->write_character(to_char_type('['));
                }

                if (use_type && (bjdata_draft3 || !j.m_data.m_value.binary->empty()))
                {
                    JSON_ASSERT(use_count);
                    oa->write_character(to_char_type('$'));
                    oa->write_character(bjdata_draft3 ? 'B' : 'U');
                }

                if (use_count)
                {
                    oa->write_character(to_char_type('#'));
                    write_number_with_ubjson_prefix(j.m_data.m_value.binary->size(), true, use_bjdata);
                }

                if (use_type)
                {
                    oa->write_characters(
                        reinterpret_cast<const CharType*>(j.m_data.m_value.binary->data()),
                        j.m_data.m_value.binary->size());
                }
                else
                {
                    for (size_t i = 0; i < j.m_data.m_value.binary->size(); ++i)
                    {
                        oa->write_character(to_char_type(bjdata_draft3 ? 'B' : 'U'));
                        oa->write_character(to_char_type(j.m_data.m_value.binary->data()[i]));
                    }
                }

                if (!use_count)
                {
                    oa->write_character(to_char_type(']'));
                }

                break;
            }

            case value_t::object:
            {
                if (use_bjdata && j.m_data.m_value.object->size() == 3 && j.m_data.m_value.object->find("_ArrayType_") != j.m_data.m_value.object->end() && j.m_data.m_value.object->find("_ArraySize_") != j.m_data.m_value.object->end() && j.m_data.m_value.object->find("_ArrayData_") != j.m_data.m_value.object->end())
                {
                    if (!write_bjdata_ndarray(*j.m_data.m_value.object, use_count, use_type, bjdata_version))  // decode bjdata ndarray in the JData format (https://github.com/NeuroJSON/jdata)
                    {
                        break;
                    }
                }

                if (add_prefix)
                {
                    oa->write_character(to_char_type('{'));
                }

                bool prefix_required = true;
                if (use_type && !j.m_data.m_value.object->empty())
                {
                    JSON_ASSERT(use_count);
                    const CharType first_prefix = ubjson_prefix(j.front(), use_bjdata);
                    const bool same_prefix = std::all_of(j.begin(), j.end(),
                                                         [this, first_prefix, use_bjdata](const BasicJsonType & v)
                    {
                        return ubjson_prefix(v, use_bjdata) == first_prefix;
                    });

                    std::vector<CharType> bjdx = {'[', '{', 'S', 'H', 'T', 'F', 'N', 'Z'}; // excluded markers in bjdata optimized type

                    if (same_prefix && !(use_bjdata && std::find(bjdx.begin(), bjdx.end(), first_prefix) != bjdx.end()))
                    {
                        prefix_required = false;
                        oa->write_character(to_char_type('$'));
                        oa->write_character(first_prefix);
                    }
                }

                if (use_count)
                {
                    oa->write_character(to_char_type('#'));
                    write_number_with_ubjson_prefix(j.m_data.m_value.object->size(), true, use_bjdata);
                }

                for (const auto& el : *j.m_data.m_value.object)
                {
                    write_number_with_ubjson_prefix(el.first.size(), true, use_bjdata);
                    oa->write_characters(
                        reinterpret_cast<const CharType*>(el.first.c_str()),
                        el.first.size());
                    write_ubjson(el.second, use_count, use_type, prefix_required, use_bjdata, bjdata_version);
                }

                if (!use_count)
                {
                    oa->write_character(to_char_type('}'));
                }

                break;
            }

            case value_t::discarded:
            default:
                break;
        }
    }

  private:
    //////////
    // BSON //
    //////////

    /*!
    @return The size of a BSON document entry header, including the id marker
            and the entry name size (and its null-terminator).
    */
    static std::size_t calc_bson_entry_header_size(const string_t& name, const BasicJsonType& j)
    {
        const auto it = name.find(static_cast<typename string_t::value_type>(0));
        if (JSON_HEDLEY_UNLIKELY(it != BasicJsonType::string_t::npos))
        {
            JSON_THROW(out_of_range::create(409, concat("BSON key cannot contain code point U+0000 (at byte ", std::to_string(it), ")"), &j));
        }

        static_cast<void>(j);
        return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;
    }

    /*!
    @brief Checks that @a size fits into the 32-bit length field used by BSON
    @return The size as a signed 32-bit integer
    @throw out_of_range.412 if @a size exceeds the range of std::int32_t
    */
    static std::int32_t to_bson_length(const std::size_t size)
    {
        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::int32_t>(size)))
        {
            JSON_THROW(out_of_range::create(412, concat("BSON length ", std::to_string(size), " exceeds maximum of ", std::to_string((std::numeric_limits<std::int32_t>::max)())), nullptr));
        }

        return static_cast<std::int32_t>(size);
    }

    /*!
    @brief Writes the given @a element_type and @a name to the output adapter
    */
    void write_bson_entry_header(const string_t& name,
                                 const std::uint8_t element_type)
    {
        oa->write_character(to_char_type(element_type));
        oa->write_characters(
            reinterpret_cast<const CharType*>(name.c_str()),
            name.size() + 1u);
    }

    /*!
    @brief Writes a BSON element with key @a name and boolean value @a value
    */
    void write_bson_boolean(const string_t& name,
                            const bool value)
    {
        write_bson_entry_header(name, 0x08);
        oa->write_character(value ? to_char_type(0x01) : to_char_type(0x00));
    }

    /*!
    @brief Writes a BSON element with key @a name and double value @a value
    */
    void write_bson_double(const string_t& name,
                           const double value)
    {
        write_bson_entry_header(name, 0x01);
        write_number<double>(value, true);
    }

    /*!
    @return The size of the BSON-encoded string in @a value
    */
    static std::size_t calc_bson_string_size(const string_t& value)
    {
        return sizeof(std::int32_t) + value.size() + 1ul;
    }

    /*!
    @brief Writes a BSON element with key @a name and string value @a value
    */
    void write_bson_string(const string_t& name,
                           const string_t& value)
    {
        write_bson_entry_header(name, 0x02);

        write_number<std::int32_t>(to_bson_length(value.size() + 1ul), true);
        oa->write_characters(
            reinterpret_cast<const CharType*>(value.c_str()),
            value.size() + 1);
    }

    /*!
    @brief Writes a BSON element with key @a name and null value
    */
    void write_bson_null(const string_t& name)
    {
        write_bson_entry_header(name, 0x0A);
    }

    /*!
    @return The size of the BSON-encoded integer @a value
    */
    static std::size_t calc_bson_integer_size(const std::int64_t value)
    {
        return (std::numeric_limits<std::int32_t>::min)() <= value && value <= (std::numeric_limits<std::int32_t>::max)()
               ? sizeof(std::int32_t)
               : sizeof(std::int64_t);
    }

    /*!
    @brief Writes a BSON element with key @a name and integer @a value
    */
    void write_bson_integer(const string_t& name,
                            const std::int64_t value)
    {
        if ((std::numeric_limits<std::int32_t>::min)() <= value && value <= (std::numeric_limits<std::int32_t>::max)())
        {
            write_bson_entry_header(name, 0x10); // int32
            write_number<std::int32_t>(static_cast<std::int32_t>(value), true);
        }
        else
        {
            write_bson_entry_header(name, 0x12); // int64
            write_number<std::int64_t>(static_cast<std::int64_t>(value), true);
        }
    }

    /*!
    @return The size of the BSON-encoded unsigned integer @a value
    */
    static constexpr std::size_t calc_bson_unsigned_size(const std::uint64_t value) noexcept
    {
        return (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
               ? sizeof(std::int32_t)
               : sizeof(std::int64_t);
    }

    /*!
    @brief Writes a BSON element with key @a name and unsigned @a value
    */
    void write_bson_unsigned(const string_t& name,
                             const std::uint64_t value)
    {
        if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
        {
            write_bson_entry_header(name, 0x10 /* int32 */);
            write_number<std::int32_t>(static_cast<std::int32_t>(value), true);
        }
        else if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
        {
            write_bson_entry_header(name, 0x12 /* int64 */);
            write_number<std::int64_t>(static_cast<std::int64_t>(value), true);
        }
        else
        {
            write_bson_entry_header(name, 0x11 /* uint64 */);
            write_number<std::uint64_t>(value, true);
        }
    }

    /*!
    @brief Writes a BSON element with key @a name and object @a value
    */
    void write_bson_object_entry(const string_t& name,
                                 const typename BasicJsonType::object_t& value)
    {
        write_bson_entry_header(name, 0x03); // object
        write_bson_object(value);
    }

    /*!
    @return The size of the BSON-encoded array @a value
    */
    static std::size_t calc_bson_array_size(const typename BasicJsonType::array_t& value)
    {
        std::size_t array_index = 0ul;

        const std::size_t embedded_document_size = std::accumulate(std::begin(value), std::end(value), static_cast<std::size_t>(0), [&array_index](std::size_t result, const typename BasicJsonType::array_t::value_type & el)
        {
            return result + calc_bson_element_size(std::to_string(array_index++), el);
        });

        return sizeof(std::int32_t) + embedded_document_size + 1ul;
    }

    /*!
    @return The size of the BSON-encoded binary array @a value
    */
    static std::size_t calc_bson_binary_size(const typename BasicJsonType::binary_t& value)
    {
        return sizeof(std::int32_t) + value.size() + 1ul;
    }

    /*!
    @brief Writes a BSON element with key @a name and array @a value
    */
    void write_bson_array(const string_t& name,
                          const typename BasicJsonType::array_t& value)
    {
        write_bson_entry_header(name, 0x04); // array
        write_number<std::int32_t>(to_bson_length(calc_bson_array_size(value)), true);

        std::size_t array_index = 0ul;

        for (const auto& el : value)
        {
            write_bson_element(std::to_string(array_index++), el);
        }

        oa->write_character(to_char_type(0x00));
    }

    /*!
    @brief Writes a BSON element with key @a name and binary value @a value
    */
    void write_bson_binary(const string_t& name,
                           const binary_t& value)
    {
        write_bson_entry_header(name, 0x05);

        write_number<std::int32_t>(to_bson_length(value.size()), true);
        write_number(value.has_subtype() ? static_cast<std::uint8_t>(value.subtype()) : static_cast<std::uint8_t>(0x00));

        oa->write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
    }

    /*!
    @brief Calculates the size necessary to serialize the JSON value @a j with its @a name
    @return The calculated size for the BSON document entry for @a j with the given @a name.
    */
    static std::size_t calc_bson_element_size(const string_t& name,
            const BasicJsonType& j)
    {
        const auto header_size = calc_bson_entry_header_size(name, j);
        switch (j.type())
        {
            case value_t::object:
                return header_size + calc_bson_object_size(*j.m_data.m_value.object);

            case value_t::array:
                return header_size + calc_bson_array_size(*j.m_data.m_value.array);

            case value_t::binary:
                return header_size + calc_bson_binary_size(*j.m_data.m_value.binary);

            case value_t::boolean:
                return header_size + 1ul;

            case value_t::number_float:
                return header_size + 8ul;

            case value_t::number_integer:
                return header_size + calc_bson_integer_size(j.m_data.m_value.number_integer);

            case value_t::number_unsigned:
                return header_size + calc_bson_unsigned_size(j.m_data.m_value.number_unsigned);

            case value_t::string:
                return header_size + calc_bson_string_size(*j.m_data.m_value.string);

            case value_t::null:
                return header_size + 0ul;

            // LCOV_EXCL_START
            case value_t::discarded:
            default:
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert)
                return 0ul;
                // LCOV_EXCL_STOP
        }
    }

    /*!
    @brief Serializes the JSON value @a j to BSON and associates it with the
           key @a name.
    @param name The name to associate with the JSON entity @a j within the
                current BSON document
    */
    void write_bson_element(const string_t& name,
                            const BasicJsonType& j)
    {
        switch (j.type())
        {
            case value_t::object:
                return write_bson_object_entry(name, *j.m_data.m_value.object);

            case value_t::array:
                return write_bson_array(name, *j.m_data.m_value.array);

            case value_t::binary:
                return write_bson_binary(name, *j.m_data.m_value.binary);

            case value_t::boolean:
                return write_bson_boolean(name, j.m_data.m_value.boolean);

            case value_t::number_float:
                return write_bson_double(name, j.m_data.m_value.number_float);

            case value_t::number_integer:
                return write_bson_integer(name, j.m_data.m_value.number_integer);

            case value_t::number_unsigned:
                return write_bson_unsigned(name, j.m_data.m_value.number_unsigned);

            case value_t::string:
                return write_bson_string(name, *j.m_data.m_value.string);

            case value_t::null:
                return write_bson_null(name);

            // LCOV_EXCL_START
            case value_t::discarded:
            default:
                JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert)
                return;
                // LCOV_EXCL_STOP
        }
    }

    /*!
    @brief Calculates the size of the BSON serialization of the given
           JSON-object @a j.
    @param[in] value  JSON value to serialize
    @pre       value.type() == value_t::object
    */
    static std::size_t calc_bson_object_size(const typename BasicJsonType::object_t& value)
    {
        const std::size_t document_size = std::accumulate(value.begin(), value.end(), static_cast<std::size_t>(0),
                                          [](size_t result, const typename BasicJsonType::object_t::value_type & el)
        {
            return result += calc_bson_element_size(el.first, el.second);
        });

        return sizeof(std::int32_t) + document_size + 1ul;
    }

    /*!
    @param[in] value  JSON value to serialize
    @pre       value.type() == value_t::object
    */
    void write_bson_object(const typename BasicJsonType::object_t& value)
    {
        write_number<std::int32_t>(to_bson_length(calc_bson_object_size(value)), true);

        for (const auto& el : value)
        {
            write_bson_element(el.first, el.second);
        }

        oa->write_character(to_char_type(0x00));
    }

    //////////
    // CBOR //
    //////////

    static constexpr CharType get_cbor_float_prefix(float /*unused*/)
    {
        return to_char_type(0xFA);  // Single-Precision Float
    }

    static constexpr CharType get_cbor_float_prefix(double /*unused*/)
    {
        return to_char_type(0xFB);  // Double-Precision Float
    }

    /////////////
    // MsgPack //
    /////////////

    static constexpr CharType get_msgpack_float_prefix(float /*unused*/)
    {
        return to_char_type(0xCA);  // float 32
    }

    static constexpr CharType get_msgpack_float_prefix(double /*unused*/)
    {
        return to_char_type(0xCB);  // float 64
    }

    ////////////
    // UBJSON //
    ////////////

    // UBJSON: write number (floating point)
    template<typename NumberType, typename std::enable_if<
                 std::is_floating_point<NumberType>::value, int>::type = 0>
    void write_number_with_ubjson_prefix(const NumberType n,
                                         const bool add_prefix,
                                         const bool use_bjdata)
    {
        if (add_prefix)
        {
            oa->write_character(get_ubjson_float_prefix(n));
        }
        write_number(n, use_bjdata);
    }

    // UBJSON: write number (unsigned integer)
    template<typename NumberType, typename std::enable_if<
                 std::is_unsigned<NumberType>::value, int>::type = 0>
    void write_number_with_ubjson_prefix(const NumberType n,
                                         const bool add_prefix,
                                         const bool use_bjdata)
    {
        if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int8_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('i'));  // int8
            }
            write_number(static_cast<std::uint8_t>(n), use_bjdata);
        }
        else if (n <= (std::numeric_limits<std::uint8_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('U'));  // uint8
            }
            write_number(static_cast<std::uint8_t>(n), use_bjdata);
        }
        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int16_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('I'));  // int16
            }
            write_number(static_cast<std::int16_t>(n), use_bjdata);
        }
        else if (use_bjdata && n <= static_cast<uint64_t>((std::numeric_limits<uint16_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('u'));  // uint16 - bjdata only
            }
            write_number(static_cast<std::uint16_t>(n), use_bjdata);
        }
        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('l'));  // int32
            }
            write_number(static_cast<std::int32_t>(n), use_bjdata);
        }
        else if (use_bjdata && n <= static_cast<uint64_t>((std::numeric_limits<uint32_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('m'));  // uint32 - bjdata only
            }
            write_number(static_cast<std::uint32_t>(n), use_bjdata);
        }
        else if (n <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('L'));  // int64
            }
            write_number(static_cast<std::int64_t>(n), use_bjdata);
        }
        else if (use_bjdata && n <= (std::numeric_limits<uint64_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('M'));  // uint64 - bjdata only
            }
            write_number(static_cast<std::uint64_t>(n), use_bjdata);
        }
        else
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('H'));  // high-precision number
            }

            const auto number = BasicJsonType(n).dump();
            write_number_with_ubjson_prefix(number.size(), true, use_bjdata);
            for (std::size_t i = 0; i < number.size(); ++i)
            {
                oa->write_character(to_char_type(static_cast<std::uint8_t>(number[i])));
            }
        }
    }

    // UBJSON: write number (signed integer)
    template < typename NumberType, typename std::enable_if <
                   std::is_signed<NumberType>::value&&
                   !std::is_floating_point<NumberType>::value, int >::type = 0 >
    void write_number_with_ubjson_prefix(const NumberType n,
                                         const bool add_prefix,
                                         const bool use_bjdata)
    {
        if ((std::numeric_limits<std::int8_t>::min)() <= n && n <= (std::numeric_limits<std::int8_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('i'));  // int8
            }
            write_number(static_cast<std::int8_t>(n), use_bjdata);
        }
        else if (static_cast<std::int64_t>((std::numeric_limits<std::uint8_t>::min)()) <= n && n <= static_cast<std::int64_t>((std::numeric_limits<std::uint8_t>::max)()))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('U'));  // uint8
            }
            write_number(static_cast<std::uint8_t>(n), use_bjdata);
        }
        else if ((std::numeric_limits<std::int16_t>::min)() <= n && n <= (std::numeric_limits<std::int16_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('I'));  // int16
            }
            write_number(static_cast<std::int16_t>(n), use_bjdata);
        }
        else if (use_bjdata && (static_cast<std::int64_t>((std::numeric_limits<std::uint16_t>::min)()) <= n && n <= static_cast<std::int64_t>((std::numeric_limits<std::uint16_t>::max)())))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('u'));  // uint16 - bjdata only
            }
            write_number(static_cast<uint16_t>(n), use_bjdata);
        }
        else if ((std::numeric_limits<std::int32_t>::min)() <= n && n <= (std::numeric_limits<std::int32_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('l'));  // int32
            }
            write_number(static_cast<std::int32_t>(n), use_bjdata);
        }
        else if (use_bjdata && (static_cast<std::int64_t>((std::numeric_limits<std::uint32_t>::min)()) <= n && n <= static_cast<std::int64_t>((std::numeric_limits<std::uint32_t>::max)())))
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('m'));  // uint32 - bjdata only
            }
            write_number(static_cast<uint32_t>(n), use_bjdata);
        }
        else if ((std::numeric_limits<std::int64_t>::min)() <= n && n <= (std::numeric_limits<std::int64_t>::max)())
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('L'));  // int64
            }
            write_number(static_cast<std::int64_t>(n), use_bjdata);
        }
        // LCOV_EXCL_START
        else
        {
            if (add_prefix)
            {
                oa->write_character(to_char_type('H'));  // high-precision number
            }

            const auto number = BasicJsonType(n).dump();
            write_number_with_ubjson_prefix(number.size(), true, use_bjdata);
            for (std::size_t i = 0; i < number.size(); ++i)
            {
                oa->write_character(to_char_type(static_cast<std::uint8_t>(number[i])));
            }
        }
        // LCOV_EXCL_STOP
    }

    /*!
    @brief determine the type prefix of container values
    */
    CharType ubjson_prefix(const BasicJsonType& j, const bool use_bjdata) const noexcept
    {
        switch (j.type())
        {
            case value_t::null:
                return 'Z';

            case value_t::boolean:
                return j.m_data.m_value.boolean ? 'T' : 'F';

            case value_t::number_integer:
            {
                if ((std::numeric_limits<std::int8_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::int8_t>::max)())
                {
                    return 'i';
                }
                if ((std::numeric_limits<std::uint8_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint8_t>::max)())
                {
                    return 'U';
                }
                if ((std::numeric_limits<std::int16_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::int16_t>::max)())
                {
                    return 'I';
                }
                if (use_bjdata && ((std::numeric_limits<std::uint16_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint16_t>::max)()))
                {
                    return 'u';
                }
                if ((std::numeric_limits<std::int32_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::int32_t>::max)())
                {
                    return 'l';
                }
                if (use_bjdata && ((std::numeric_limits<std::uint32_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::uint32_t>::max)()))
                {
                    return 'm';
                }
                if ((std::numeric_limits<std::int64_t>::min)() <= j.m_data.m_value.number_integer && j.m_data.m_value.number_integer <= (std::numeric_limits<std::int64_t>::max)())
                {
                    return 'L';
                }
                // anything else is treated as a high-precision number
                return 'H'; // LCOV_EXCL_LINE
            }

            case value_t::number_unsigned:
            {
                if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int8_t>::max)()))
                {
                    return 'i';
                }
                if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::uint8_t>::max)()))
                {
                    return 'U';
                }
                if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int16_t>::max)()))
                {
                    return 'I';
                }
                if (use_bjdata && j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::uint16_t>::max)()))
                {
                    return 'u';
                }
                if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
                {
                    return 'l';
                }
                if (use_bjdata && j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::uint32_t>::max)()))
                {
                    return 'm';
                }
                if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
                {
                    return 'L';
                }
                if (use_bjdata && j.m_data.m_value.number_unsigned <= (std::numeric_limits<std::uint64_t>::max)())
                {
                    return 'M';
                }
                // anything else is treated as a high-precision number
                return 'H'; // LCOV_EXCL_LINE
            }

            case value_t::number_float:
                return get_ubjson_float_prefix(j.m_data.m_value.number_float);

            case value_t::string:
                return 'S';

            case value_t::array: // fallthrough
            case value_t::binary:
                return '[';

            case value_t::object:
                return '{';

            case value_t::discarded:
            default:  // discarded values
                return 'N';
        }
    }

    static constexpr CharType get_ubjson_float_prefix(float /*unused*/)
    {
        return 'd';  // float 32
    }

    static constexpr CharType get_ubjson_float_prefix(double /*unused*/)
    {
        return 'D';  // float 64
    }

    /*!
    @return false if the object is successfully converted to a bjdata ndarray, true if the type or size is invalid
    */
    bool write_bjdata_ndarray(const typename BasicJsonType::object_t& value, const bool use_count, const bool use_type, const bjdata_version_t bjdata_version)
    {
        std::map<string_t, CharType> bjdtype = {{"uint8", 'U'},  {"int8", 'i'},  {"uint16", 'u'}, {"int16", 'I'},
            {"uint32", 'm'}, {"int32", 'l'}, {"uint64", 'M'}, {"int64", 'L'}, {"single", 'd'}, {"double", 'D'},
            {"char", 'C'}, {"byte", 'B'}
        };

        string_t key = "_ArrayType_";
        // use get<string_t>() instead of static_cast<string_t> to avoid an
        // ambiguous conversion under explicit instantiation on C++17 (see #4825)
        auto it = bjdtype.find(value.at(key).template get<string_t>());
        if (it == bjdtype.end())
        {
            return true;
        }
        CharType dtype = it->second;

        key = "_ArraySize_";
        std::size_t len = (value.at(key).empty() ? 0 : 1);
        for (const auto& el : value.at(key))
        {
            // a dimension is read as an unsigned value below, so anything that
            // is not a non-negative integer is rejected: a non-integer entry
            // would pun unrelated bytes as the dimension, and a negative one
            // would wrap into a nonsensical length
            if (!el.is_number_integer() || (!el.is_number_unsigned() && el.template get<std::int64_t>() < 0))
            {
                return true;
            }

            // a dimension that does not fit into std::size_t, or a product that
            // overflows it, would wrap around and could match the size of
            // _ArrayData_ by accident; the resulting header announces an
            // element count that no reader can honor (the binary reader rejects
            // it with out_of_range.408), so encode as a plain object instead
            const auto dim = el.template get<std::uint64_t>();
            if (!value_in_range_of<std::size_t>(dim))
            {
                return true;
            }
            const auto dim_size = static_cast<std::size_t>(dim);
            if (dim_size != 0 && len > (std::numeric_limits<std::size_t>::max)() / dim_size)
            {
                return true;
            }
            len *= dim_size;
        }

        key = "_ArrayData_";
        if (value.at(key).size() != len)
        {
            return true;
        }

        // every element is written below as the number kind dtype names, so it
        // has to actually be a number of that category: an element of any other
        // type would reinterpret unrelated bytes, e.g. a string's heap pointer,
        // as that number. Such an object falls back to a plain object encoding.
        // dtype names the wire type, not the storage type: whether an integer
        // is held as number_integer or number_unsigned depends on how the value
        // was built (parsing stores non-negative integers as unsigned, the C++
        // API stores int literals as signed), so both are accepted here and the
        // writes below go through get<>, which reads the member that is active.
        const bool ndarray_is_float = (dtype == 'd' || dtype == 'D');
        for (const auto& el : value.at(key))
        {
            if (ndarray_is_float ? !el.is_number_float() : !el.is_number_integer())
            {
                return true;
            }
        }

        oa->write_character('[');
        oa->write_character('$');
        oa->write_character(dtype);
        oa->write_character('#');

        key = "_ArraySize_";
        write_ubjson(value.at(key), use_count, use_type, true,  true, bjdata_version);

        key = "_ArrayData_";
        if (dtype == 'U' || dtype == 'C' || dtype == 'B')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::uint8_t>(el.template get<std::uint64_t>()), true);
            }
        }
        else if (dtype == 'i')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::int8_t>(el.template get<std::int64_t>()), true);
            }
        }
        else if (dtype == 'u')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::uint16_t>(el.template get<std::uint64_t>()), true);
            }
        }
        else if (dtype == 'I')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::int16_t>(el.template get<std::int64_t>()), true);
            }
        }
        else if (dtype == 'm')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::uint32_t>(el.template get<std::uint64_t>()), true);
            }
        }
        else if (dtype == 'l')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<std::int32_t>(el.template get<std::int64_t>()), true);
            }
        }
        else if (dtype == 'M')
        {
            for (const auto& el : value.at(key))
            {
                write_number(el.template get<std::uint64_t>(), true);
            }
        }
        else if (dtype == 'L')
        {
            for (const auto& el : value.at(key))
            {
                write_number(el.template get<std::int64_t>(), true);
            }
        }
        else if (dtype == 'd')
        {
            for (const auto& el : value.at(key))
            {
                write_number(static_cast<float>(el.template get<double>()), true);
            }
        }
        else if (dtype == 'D')
        {
            for (const auto& el : value.at(key))
            {
                write_number(el.template get<double>(), true);
            }
        }
        return false;
    }

    ///////////////////////
    // Utility functions //
    ///////////////////////

    /*
    @brief write a number to output input
    @param[in] n number of type @a NumberType
    @param[in] OutputIsLittleEndian Set to true if output data is
                                 required to be little endian
    @tparam NumberType the type of the number

    @note This function needs to respect the system's endianness, because bytes
          in CBOR, MessagePack, and UBJSON are stored in network order (big
          endian) and therefore need reordering on little endian systems.
          On the other hand, BSON and BJData use little endian and should reorder
          on big endian systems.
    */
    template<typename NumberType>
    void write_number(const NumberType n, const bool OutputIsLittleEndian = false)
    {
        // step 1: write the number to an array of length NumberType
        std::array<CharType, sizeof(NumberType)> vec{};
        std::memcpy(vec.data(), &n, sizeof(NumberType));

        // step 2: write the array to output (with possible reordering)
        if (is_little_endian != OutputIsLittleEndian)
        {
            // reverse byte order prior to conversion if necessary
            std::reverse(vec.begin(), vec.end());
        }

        oa->write_characters(vec.data(), sizeof(NumberType));
    }

    void write_compact_float(const number_float_t n, detail::input_format_t format)
    {
#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wfloat-equal"
#endif
        if (!std::isfinite(n) || ((static_cast<double>(n) >= static_cast<double>(std::numeric_limits<float>::lowest()) &&
                                   static_cast<double>(n) <= static_cast<double>((std::numeric_limits<float>::max)()) &&
                                   static_cast<double>(static_cast<float>(n)) == static_cast<double>(n))))
        {
            oa->write_character(format == detail::input_format_t::cbor
                                ? get_cbor_float_prefix(static_cast<float>(n))
                                : get_msgpack_float_prefix(static_cast<float>(n)));
            write_number(static_cast<float>(n));
        }
        else
        {
            oa->write_character(format == detail::input_format_t::cbor
                                ? get_cbor_float_prefix(n)
                                : get_msgpack_float_prefix(n));
            write_number(n);
        }
#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif
    }

  public:
    // The following to_char_type functions are implement the conversion
    // between uint8_t and CharType. In case CharType is not unsigned,
    // such a conversion is required to allow values greater than 128.
    // See <https://github.com/nlohmann/json/issues/1286> for a discussion.
    template < typename C = CharType,
               enable_if_t < std::is_signed<C>::value && std::is_signed<char>::value > * = nullptr >
    static constexpr CharType to_char_type(std::uint8_t x) noexcept
    {
        return *reinterpret_cast<char*>(&x);
    }

    template < typename C = CharType,
               enable_if_t < std::is_signed<C>::value && std::is_unsigned<char>::value > * = nullptr >
    static CharType to_char_type(std::uint8_t x) noexcept
    {
        // The std::is_trivial trait is deprecated in C++26. The replacement is to use
        // std::is_trivially_copyable and std::is_trivially_default_constructible.
        // However, some older library implementations support std::is_trivial
        // but not all the std::is_trivially_* traits.
        // Since detecting full support across all libraries is difficult,
        // we use std::is_trivial unless we are using a standard where it has been deprecated.
        // For more details, see: https://github.com/nlohmann/json/pull/4775#issuecomment-2884361627
#ifdef JSON_HAS_CPP_26
        static_assert(std::is_trivially_copyable<CharType>::value, "CharType must be trivially copyable");
        static_assert(std::is_trivially_default_constructible<CharType>::value, "CharType must be trivially default constructible");
#else
        static_assert(std::is_trivial<CharType>::value, "CharType must be trivial");
#endif

        static_assert(sizeof(std::uint8_t) == sizeof(CharType), "size of CharType must be equal to std::uint8_t");
        CharType result;
        std::memcpy(&result, &x, sizeof(x));
        return result;
    }

    template<typename C = CharType,
             enable_if_t<std::is_unsigned<C>::value>* = nullptr>
    static constexpr CharType to_char_type(std::uint8_t x) noexcept
    {
        return x;
    }

    template < typename InputCharType, typename C = CharType,
               enable_if_t <
                   std::is_signed<C>::value &&
                   std::is_signed<char>::value &&
                   std::is_same<char, typename std::remove_cv<InputCharType>::type>::value
                   > * = nullptr >
    static constexpr CharType to_char_type(InputCharType x) noexcept
    {
        return x;
    }

  private:
    /// whether we can assume little endianness
    const bool is_little_endian = little_endianness();

    /// the output
    output_adapter_t<CharType> oa = nullptr;
};

}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END