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

#pragma once

#include <array> // array
#include <cassert> // assert
#include <cstddef> // size_t
#include <cstdio> //FILE *
#include <cstring> // strlen
#include <istream> // istream
#include <iterator> // begin, end, iterator_traits, random_access_iterator_tag, distance, next
#include <memory> // shared_ptr, make_shared, addressof
#include <numeric> // accumulate
#include <string> // string, char_traits
#include <type_traits> // enable_if, is_base_of, is_pointer, is_integral, remove_pointer
#include <utility> // pair, declval

#include <nlohmann/detail/iterators/iterator_traits.hpp>
#include <nlohmann/detail/macro_scope.hpp>

namespace nlohmann
{
namespace detail
{
/// the supported input formats
enum class input_format_t { json, cbor, msgpack, ubjson, bson };

////////////////////
// input adapters //
////////////////////

/*!
Input adapter for stdio file access. This adapter read only 1 byte and do not use any
 buffer. This adapter is a very low level adapter.
*/
class file_input_adapter
{
  public:
    JSON_HEDLEY_NON_NULL(2)
    explicit file_input_adapter(std::FILE* f)  noexcept
        : m_file(f)
    {}

    // make class move-only
    file_input_adapter(const file_input_adapter&) = delete;
    file_input_adapter(file_input_adapter&&) = default;
    file_input_adapter& operator=(const file_input_adapter&) = delete;
    file_input_adapter& operator=(file_input_adapter&&) = delete;

    std::char_traits<char>::int_type get_character() noexcept
    {
        return std::fgetc(m_file);
    }

  private:
    /// the file pointer to read from
    std::FILE* m_file;
};


/*!
Input adapter for a (caching) istream. Ignores a UFT Byte Order Mark at
beginning of input. Does not support changing the underlying std::streambuf
in mid-input. Maintains underlying std::istream and std::streambuf to support
subsequent use of standard std::istream operations to process any input
characters following those used in parsing the JSON input.  Clears the
std::istream flags; any input errors (e.g., EOF) will be detected by the first
subsequent call for input from the std::istream.
*/
class input_stream_adapter
{
  public:
    ~input_stream_adapter()
    {
        // clear stream flags; we use underlying streambuf I/O, do not
        // maintain ifstream flags, except eof
        if (is)
        {
            is->clear(is->rdstate() & std::ios::eofbit);
        }
    }

    explicit input_stream_adapter(std::istream& i)
        : is(&i), sb(i.rdbuf())
    {}

    // delete because of pointer members
    input_stream_adapter(const input_stream_adapter&) = delete;
    input_stream_adapter& operator=(input_stream_adapter&) = delete;
    input_stream_adapter& operator=(input_stream_adapter&& rhs) = delete;

    input_stream_adapter(input_stream_adapter&& rhs) : is(rhs.is), sb(rhs.sb)
    {
        rhs.is = nullptr;
        rhs.sb = nullptr;
    }

    // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
    // ensure that std::char_traits<char>::eof() and the character 0xFF do not
    // end up as the same value, eg. 0xFFFFFFFF.
    std::char_traits<char>::int_type get_character()
    {
        auto res = sb->sbumpc();
        // set eof manually, as we don't use the istream interface.
        if (res == EOF)
        {
            is->clear(is->rdstate() | std::ios::eofbit);
        }
        return res;
    }

  private:
    /// the associated input stream
    std::istream* is = nullptr;
    std::streambuf* sb = nullptr;
};

/// input adapter for buffer input
class input_buffer_adapter
{
  public:
    input_buffer_adapter(const char* b, const std::size_t l) noexcept
        : cursor(b), limit(b == nullptr ? nullptr : (b + l))
    {}

    // delete because of pointer members
    input_buffer_adapter(const input_buffer_adapter&) = delete;
    input_buffer_adapter& operator=(input_buffer_adapter&) = delete;
    input_buffer_adapter(input_buffer_adapter&&) = default;
    input_buffer_adapter& operator=(input_buffer_adapter&&) = delete;

    std::char_traits<char>::int_type get_character() noexcept
    {
        if (JSON_HEDLEY_LIKELY(cursor < limit))
        {
            assert(cursor != nullptr and limit != nullptr);
            return std::char_traits<char>::to_int_type(*(cursor++));
        }

        return std::char_traits<char>::eof();
    }

  private:
    /// pointer to the current character
    const char* cursor;
    /// pointer past the last character
    const char* const limit;
};

template<typename WideStringType, size_t T>
struct wide_string_input_helper
{
    // UTF-32
    static void fill_buffer(const WideStringType& str,
                            size_t& current_wchar,
                            std::array<std::char_traits<char>::int_type, 4>& utf8_bytes,
                            size_t& utf8_bytes_index,
                            size_t& utf8_bytes_filled)
    {
        utf8_bytes_index = 0;

        if (current_wchar == str.size())
        {
            utf8_bytes[0] = std::char_traits<char>::eof();
            utf8_bytes_filled = 1;
        }
        else
        {
            // get the current character
            const auto wc = static_cast<unsigned int>(str[current_wchar++]);

            // UTF-32 to UTF-8 encoding
            if (wc < 0x80)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                utf8_bytes_filled = 1;
            }
            else if (wc <= 0x7FF)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xC0u | ((wc >> 6u) & 0x1Fu));
                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | (wc & 0x3Fu));
                utf8_bytes_filled = 2;
            }
            else if (wc <= 0xFFFF)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xE0u | ((wc >> 12u) & 0x0Fu));
                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((wc >> 6u) & 0x3Fu));
                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | (wc & 0x3Fu));
                utf8_bytes_filled = 3;
            }
            else if (wc <= 0x10FFFF)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xF0u | ((wc >> 18u) & 0x07u));
                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((wc >> 12u) & 0x3Fu));
                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | ((wc >> 6u) & 0x3Fu));
                utf8_bytes[3] = static_cast<std::char_traits<char>::int_type>(0x80u | (wc & 0x3Fu));
                utf8_bytes_filled = 4;
            }
            else
            {
                // unknown character
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                utf8_bytes_filled = 1;
            }
        }
    }
};

template<typename WideStringType>
struct wide_string_input_helper<WideStringType, 2>
{
    // UTF-16
    static void fill_buffer(const WideStringType& str,
                            size_t& current_wchar,
                            std::array<std::char_traits<char>::int_type, 4>& utf8_bytes,
                            size_t& utf8_bytes_index,
                            size_t& utf8_bytes_filled)
    {
        utf8_bytes_index = 0;

        if (current_wchar == str.size())
        {
            utf8_bytes[0] = std::char_traits<char>::eof();
            utf8_bytes_filled = 1;
        }
        else
        {
            // get the current character
            const auto wc = static_cast<unsigned int>(str[current_wchar++]);

            // UTF-16 to UTF-8 encoding
            if (wc < 0x80)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                utf8_bytes_filled = 1;
            }
            else if (wc <= 0x7FF)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xC0u | ((wc >> 6u)));
                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | (wc & 0x3Fu));
                utf8_bytes_filled = 2;
            }
            else if (0xD800 > wc or wc >= 0xE000)
            {
                utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xE0u | ((wc >> 12u)));
                utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((wc >> 6u) & 0x3Fu));
                utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | (wc & 0x3Fu));
                utf8_bytes_filled = 3;
            }
            else
            {
                if (current_wchar < str.size())
                {
                    const auto wc2 = static_cast<unsigned int>(str[current_wchar++]);
                    const auto charcode = 0x10000u + (((wc & 0x3FFu) << 10u) | (wc2 & 0x3FFu));
                    utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(0xF0u | (charcode >> 18u));
                    utf8_bytes[1] = static_cast<std::char_traits<char>::int_type>(0x80u | ((charcode >> 12u) & 0x3Fu));
                    utf8_bytes[2] = static_cast<std::char_traits<char>::int_type>(0x80u | ((charcode >> 6u) & 0x3Fu));
                    utf8_bytes[3] = static_cast<std::char_traits<char>::int_type>(0x80u | (charcode & 0x3Fu));
                    utf8_bytes_filled = 4;
                }
                else
                {
                    // unknown character
                    ++current_wchar;
                    utf8_bytes[0] = static_cast<std::char_traits<char>::int_type>(wc);
                    utf8_bytes_filled = 1;
                }
            }
        }
    }
};

template<typename WideStringType>
class wide_string_input_adapter
{
  public:
    explicit wide_string_input_adapter(const WideStringType& w) noexcept
        : str(w)
    {}

    std::char_traits<char>::int_type get_character() noexcept
    {
        // check if buffer needs to be filled
        if (utf8_bytes_index == utf8_bytes_filled)
        {
            fill_buffer<sizeof(typename WideStringType::value_type)>();

            assert(utf8_bytes_filled > 0);
            assert(utf8_bytes_index == 0);
        }

        // use buffer
        assert(utf8_bytes_filled > 0);
        assert(utf8_bytes_index < utf8_bytes_filled);
        return utf8_bytes[utf8_bytes_index++];
    }

  private:
    template<size_t T>
    void fill_buffer()
    {
        wide_string_input_helper<WideStringType, T>::fill_buffer(str, current_wchar, utf8_bytes, utf8_bytes_index, utf8_bytes_filled);
    }

    /// the wstring to process
    const WideStringType& str;

    /// index of the current wchar in str
    std::size_t current_wchar = 0;

    /// a buffer for UTF-8 bytes
    std::array<std::char_traits<char>::int_type, 4> utf8_bytes = {{0, 0, 0, 0}};

    /// index to the utf8_codes array for the next valid byte
    std::size_t utf8_bytes_index = 0;
    /// number of valid bytes in the utf8_codes array
    std::size_t utf8_bytes_filled = 0;
};

inline file_input_adapter input_adapter(std::FILE* file)
{
    return file_input_adapter(file);
}

inline input_stream_adapter input_adapter(std::istream& stream)
{
    return input_stream_adapter(stream);
}

inline input_stream_adapter input_adapter(std::istream&& stream)
{
    return input_stream_adapter(stream);
}

template<typename CharT,
         typename std::enable_if<
             std::is_pointer<CharT>::value and
             std::is_integral<typename std::remove_pointer<CharT>::type>::value and
             sizeof(typename std::remove_pointer<CharT>::type) == 1,
             int>::type = 0>
input_buffer_adapter input_adapter(CharT b, std::size_t l)
{
    return input_buffer_adapter(reinterpret_cast<const char*>(b), l);
}

template<typename CharT,
         typename std::enable_if<
             std::is_pointer<CharT>::value and
             std::is_integral<typename std::remove_pointer<CharT>::type>::value and
             sizeof(typename std::remove_pointer<CharT>::type) == 1,
             int>::type = 0>
input_buffer_adapter input_adapter(CharT b)
{
    return input_adapter(reinterpret_cast<const char*>(b),
                         std::strlen(reinterpret_cast<const char*>(b)));
}

template<class IteratorType,
         typename std::enable_if<
             std::is_same<typename iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value,
             int>::type = 0>
input_buffer_adapter input_adapter(IteratorType first, IteratorType last)
{
#ifndef NDEBUG
    // assertion to check that the iterator range is indeed contiguous,
    // see https://stackoverflow.com/a/35008842/266378 for more discussion
    const auto is_contiguous = std::accumulate(
                                   first, last, std::pair<bool, int>(true, 0),
                                   [&first](std::pair<bool, int> res, decltype(*first) val)
    {
        res.first &= (val == *(std::next(std::addressof(*first), res.second++)));
        return res;
    }).first;
    assert(is_contiguous);
#endif

    // assertion to check that each element is 1 byte long
    static_assert(
        sizeof(typename iterator_traits<IteratorType>::value_type) == 1,
        "each element in the iterator range must have the size of 1 byte");

    const auto len = static_cast<size_t>(std::distance(first, last));
    if (JSON_HEDLEY_LIKELY(len > 0))
    {
        // there is at least one element: use the address of first
        return input_buffer_adapter(reinterpret_cast<const char*>(&(*first)), len);
    }
    else
    {
        // the address of first cannot be used: use nullptr
        return input_buffer_adapter(nullptr, len);
    }
}

inline wide_string_input_adapter<std::wstring> input_adapter(const std::wstring& ws)
{
    return wide_string_input_adapter<std::wstring>(ws);
}


inline wide_string_input_adapter<std::u16string> input_adapter(const std::u16string& ws)
{
    return wide_string_input_adapter<std::u16string>(ws);
}

inline wide_string_input_adapter<std::u32string> input_adapter(const std::u32string& ws)
{
    return wide_string_input_adapter<std::u32string>(ws);
}

template<class ContiguousContainer, typename
         std::enable_if<not std::is_pointer<ContiguousContainer>::value and
                        std::is_base_of<std::random_access_iterator_tag, typename iterator_traits<decltype(std::begin(std::declval<ContiguousContainer const>()))>::iterator_category>::value,
                        int>::type = 0>
input_buffer_adapter input_adapter(const ContiguousContainer& c)
{
    return input_adapter(std::begin(c), std::end(c));
}


template<class T, std::size_t N>
input_buffer_adapter input_adapter(T (&array)[N])
{
    return input_adapter(std::begin(array), std::end(array));
}

// This class only handles inputs of input_buffer_adapter type.
// It's required so that expressions like {ptr, len} can be implicitely casted
// to the correct adapter.
class span_input_adapter
{
  public:
    template<typename CharT,
             typename std::enable_if<
                 std::is_pointer<CharT>::value and
                 std::is_integral<typename std::remove_pointer<CharT>::type>::value and
                 sizeof(typename std::remove_pointer<CharT>::type) == 1,
                 int>::type = 0>
    span_input_adapter(CharT b, std::size_t l)
        : ia(reinterpret_cast<const char*>(b), l) {}

    template<typename CharT,
             typename std::enable_if<
                 std::is_pointer<CharT>::value and
                 std::is_integral<typename std::remove_pointer<CharT>::type>::value and
                 sizeof(typename std::remove_pointer<CharT>::type) == 1,
                 int>::type = 0>
    span_input_adapter(CharT b)
        : span_input_adapter(reinterpret_cast<const char*>(b),
                             std::strlen(reinterpret_cast<const char*>(b))) {}

    template<class IteratorType,
             typename std::enable_if<
                 std::is_same<typename iterator_traits<IteratorType>::iterator_category, std::random_access_iterator_tag>::value,
                 int>::type = 0>
    span_input_adapter(IteratorType first, IteratorType last)
        : ia(input_adapter(first, last)) {}

    template<class T, std::size_t N>
    span_input_adapter(T (&array)[N])
        : span_input_adapter(std::begin(array), std::end(array)) {}

    /// input adapter for contiguous container
    template<class ContiguousContainer, typename
             std::enable_if<not std::is_pointer<ContiguousContainer>::value and
                            std::is_base_of<std::random_access_iterator_tag, typename iterator_traits<decltype(std::begin(std::declval<ContiguousContainer const>()))>::iterator_category>::value,
                            int>::type = 0>
    span_input_adapter(const ContiguousContainer& c)
        : span_input_adapter(std::begin(c), std::end(c)) {}

    input_buffer_adapter&& get()
    {
        return std::move(ia);
    }

  private:
    input_buffer_adapter ia;
};
}  // namespace detail
}  // namespace nlohmann