base.h

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#ifndef JWT_CPP_BASE_H
#define JWT_CPP_BASE_H
 
#include <array>
#include <stdexcept>
#include <string>
 
#ifdef __has_cpp_attribute
#if __has_cpp_attribute(fallthrough)
#define JWT_FALLTHROUGH [[fallthrough]]
#endif
#endif
 
#ifndef JWT_FALLTHROUGH
#define JWT_FALLTHROUGH
#endif
 
namespace jwt
{
namespace alphabet
{
struct base64
{
    static const std::array<char, 64>& data()
    {
        static constexpr std::array<char, 64> data{
            {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
             'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
             'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
             'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'}};
        return data;
    }
    static const std::string& fill()
    {
        static std::string fill{"="};
        return fill;
    }
};
struct base64url
{
    static const std::array<char, 64>& data()
    {
        static constexpr std::array<char, 64> data{
            {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
             'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
             'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
             'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_'}};
        return data;
    }
    static const std::string& fill()
    {
        static std::string fill{"%3d"};
        return fill;
    }
};
} // namespace alphabet
 
class base
{
  public:
    template <typename T> static std::string encode(const std::string& bin)
    {
        return encode(bin, T::data(), T::fill());
    }
    template <typename T> static std::string decode(const std::string& base)
    {
        return decode(base, T::data(), T::fill());
    }
    template <typename T> static std::string pad(const std::string& base)
    {
        return pad(base, T::fill());
    }
    template <typename T> static std::string trim(const std::string& base)
    {
        return trim(base, T::fill());
    }
 
  private:
    static std::string encode(const std::string& bin, const std::array<char, 64>& alphabet,
                              const std::string& fill)
    {
        size_t size = bin.size();
        std::string res;
 
        // clear incomplete bytes
        size_t fast_size = size - size % 3;
        for (size_t i = 0; i < fast_size;)
        {
            uint32_t octet_a = static_cast<unsigned char>(bin[i++]);
            uint32_t octet_b = static_cast<unsigned char>(bin[i++]);
            uint32_t octet_c = static_cast<unsigned char>(bin[i++]);
 
            uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;
 
            res += alphabet[(triple >> 3 * 6) & 0x3F];
            res += alphabet[(triple >> 2 * 6) & 0x3F];
            res += alphabet[(triple >> 1 * 6) & 0x3F];
            res += alphabet[(triple >> 0 * 6) & 0x3F];
        }
 
        if (fast_size == size)
            return res;
 
        size_t mod = size % 3;
 
        uint32_t octet_a = fast_size < size ? static_cast<unsigned char>(bin[fast_size++]) : 0;
        uint32_t octet_b = fast_size < size ? static_cast<unsigned char>(bin[fast_size++]) : 0;
        uint32_t octet_c = fast_size < size ? static_cast<unsigned char>(bin[fast_size++]) : 0;
 
        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;
 
        switch (mod)
        {
            case 1:
                res += alphabet[(triple >> 3 * 6) & 0x3F];
                res += alphabet[(triple >> 2 * 6) & 0x3F];
                res += fill;
                res += fill;
                break;
            case 2:
                res += alphabet[(triple >> 3 * 6) & 0x3F];
                res += alphabet[(triple >> 2 * 6) & 0x3F];
                res += alphabet[(triple >> 1 * 6) & 0x3F];
                res += fill;
                break;
            default: break;
        }
 
        return res;
    }
 
    static std::string decode(const std::string& base, const std::array<char, 64>& alphabet,
                              const std::string& fill)
    {
        size_t size = base.size();
 
        size_t fill_cnt = 0;
        while (size > fill.size())
        {
            if (base.substr(size - fill.size(), fill.size()) == fill)
            {
                fill_cnt++;
                size -= fill.size();
                if (fill_cnt > 2)
                    throw std::runtime_error("Invalid input: too much fill");
            }
            else
                break;
        }
 
        if ((size + fill_cnt) % 4 != 0)
            throw std::runtime_error("Invalid input: incorrect total size");
 
        size_t out_size = size / 4 * 3;
        std::string res;
        res.reserve(out_size);
 
        auto get_sextet = [&](size_t offset)
        {
            for (size_t i = 0; i < alphabet.size(); i++)
            {
                if (alphabet[i] == base[offset])
                    return static_cast<uint32_t>(i);
            }
            throw std::runtime_error("Invalid input: not within alphabet");
        };
 
        size_t fast_size = size - size % 4;
        for (size_t i = 0; i < fast_size;)
        {
            uint32_t sextet_a = get_sextet(i++);
            uint32_t sextet_b = get_sextet(i++);
            uint32_t sextet_c = get_sextet(i++);
            uint32_t sextet_d = get_sextet(i++);
 
            uint32_t triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) +
                              (sextet_d << 0 * 6);
 
            res += static_cast<char>((triple >> 2 * 8) & 0xFFU);
            res += static_cast<char>((triple >> 1 * 8) & 0xFFU);
            res += static_cast<char>((triple >> 0 * 8) & 0xFFU);
        }
 
        if (fill_cnt == 0)
            return res;
 
        uint32_t triple = (get_sextet(fast_size) << 3 * 6) + (get_sextet(fast_size + 1) << 2 * 6);
 
        switch (fill_cnt)
        {
            case 1:
                triple |= (get_sextet(fast_size + 2) << 1 * 6);
                res += static_cast<char>((triple >> 2 * 8) & 0xFFU);
                res += static_cast<char>((triple >> 1 * 8) & 0xFFU);
                break;
            case 2: res += static_cast<char>((triple >> 2 * 8) & 0xFFU); break;
            default: break;
        }
 
        return res;
    }
 
    static std::string pad(const std::string& base, const std::string& fill)
    {
        std::string padding;
        switch (base.size() % 4)
        {
            case 1: padding += fill; JWT_FALLTHROUGH;
            case 2: padding += fill; JWT_FALLTHROUGH;
            case 3: padding += fill; JWT_FALLTHROUGH;
            default: break;
        }
 
        return base + padding;
    }
 
    static std::string trim(const std::string& base, const std::string& fill)
    {
        auto pos = base.find(fill);
        return base.substr(0, pos);
    }
};
} // namespace jwt
 
#endif