base64.h

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/*
 Copyright (c) 2026 - SD-Innovation S.A.S. - FRANCE
*/
 
/*
ver: 2.x.x - build: 2026-04-28
*/
 
/*
The zlib License

Copyright (c) 2026 SD-Innovation S.A.S. 

This software is provided ‘as-is’, without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.

3. This notice may not be removed or altered from any source
distribution.

*/
 
#pragma once
 
#include <optional>
#include <span>
#include <string>
#include <vector>
 
namespace sdi_toolBox::desktop::utils
{
//--------------------------------------------------------------
class Base64
{
  public:
  Base64() = delete;
 
 
  [[nodiscard]] static std::string encode(std::span<const std::uint8_t> data);
 
  [[nodiscard]] static std::string encode(std::string_view text);
 
 
  [[nodiscard]] static std::optional<std::vector<std::uint8_t>> decode(std::string_view input);
 
  [[nodiscard]] static std::optional<std::string> decode_to_string(std::string_view input);
 
 
  private:
 
  [[nodiscard]] static std::optional<std::uint8_t> decode_char(char c) noexcept;
 
 
  static constexpr std::string_view ENCODE_LOOKUP = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 
  static constexpr char PADDING_CAR = '=';
 
};
//--------------------------------------------------------------
 
//--------------------------------------------------------------
/* Encode binary data to Base64 string */
inline std::string Base64::encode(const std::span<const std::uint8_t> data)
{
  std::string result;
  result.reserve(((data.size() + 2) / 3) * 4);
 
  for (std::size_t i = 0; i < data.size(); i += 3)
  {
    const std::uint32_t b0 = data[i];
    const std::uint32_t b1 = (i + 1 < data.size()) ? data[i + 1] : 0u;
    const std::uint32_t b2 = (i + 2 < data.size()) ? data[i + 2] : 0u;
 
    const std::uint32_t triple = (b0 << 16) | (b1 << 8) | b2;
 
    result += ENCODE_LOOKUP[(triple >> 18) & 0x3F];
    result += ENCODE_LOOKUP[(triple >> 12) & 0x3F];
    result += (i + 1 < data.size()) ? ENCODE_LOOKUP[(triple >> 6) & 0x3F] : PADDING_CAR;
    result += (i + 2 < data.size()) ? ENCODE_LOOKUP[(triple >> 0) & 0x3F] : PADDING_CAR;
  }
 
  return result;
}
//--------------------------------------------------------------
/* Encode a text string to Base64 string */
inline std::string Base64::encode(const std::string_view text)
{
  return encode(std::span(reinterpret_cast<const std::uint8_t *>(text.data()), text.size()));
}
//--------------------------------------------------------------
/* Decode a Base64 string to binary data (returns std::nullopt if invalid) */
inline std::optional<std::vector<std::uint8_t>> Base64::decode(const std::string_view input)
{
  if (input.size() % 4 != 0)
    return std::nullopt;
 
  if (input.empty())
    return std::vector<std::uint8_t>{};
 
  // Validate padding: '=' is only allowed in the last group, in position 2 or 3
  // Valid forms: "xxx=" or "xx=="
  for (std::size_t i = 0; i < input.size() - 4; ++i)
  {
    if (input[i] == PADDING_CAR)
      return std::nullopt;     // '=' found outside the last group
  }
 
  const std::string_view last = input.substr(input.size() - 4);
  // "xx==" : positions 0,1 must be valid chars, positions 2,3 must be '='
  // "xxx=" : positions 0,1,2 must be valid chars, position 3 must be '='
  // "xxxx" : all positions must be valid chars
  if (last[2] == PADDING_CAR && last[3] != PADDING_CAR)
    return std::nullopt;     // "xx=x" is invalid
 
  std::vector<std::uint8_t> result;
  result.reserve((input.size() / 4) * 3);
 
  for (std::size_t i = 0; i < input.size(); i += 4)
  {
    const auto v0 = decode_char(input[i]);
    const auto v1 = decode_char(input[i + 1]);
    const auto v2 = input[i + 2] == PADDING_CAR ? std::optional<std::uint8_t>{ 0 } : decode_char(input[i + 2]);
    const auto v3 = input[i + 3] == PADDING_CAR ? std::optional<std::uint8_t>{ 0 } : decode_char(input[i + 3]);
 
    if (!v0 || !v1 || !v2 || !v3)
      return std::nullopt;
 
    const std::uint32_t triple =
      (static_cast<std::uint32_t>(*v0) << 18) |
      (static_cast<std::uint32_t>(*v1) << 12) |
      (static_cast<std::uint32_t>(*v2) << 6) |
      (static_cast<std::uint32_t>(*v3));
 
    result.push_back(static_cast<std::uint8_t>((triple >> 16) & 0xFF));
    if (input[i + 2] != PADDING_CAR)
      result.push_back(static_cast<std::uint8_t>((triple >> 8) & 0xFF));
    if (input[i + 3] != PADDING_CAR)
      result.push_back(static_cast<std::uint8_t>((triple >> 0) & 0xFF));
  }
 
  return result;
}
//--------------------------------------------------------------
/* Decode a Base64 string to a text string (returns std::nullopt if invalid) */
inline std::optional<std::string> Base64::decode_to_string(const std::string_view input)
{
  const auto bytes = decode(input);
  if (!bytes)
    return std::nullopt;
  return std::string(reinterpret_cast<const char *>(bytes->data()), bytes->size());
}
//--------------------------------------------------------------
/* Helper to decode a single Base64 character to its 6-bit value (returns std::nullopt if invalid) */
inline std::optional<std::uint8_t> Base64::decode_char(const char c) noexcept
{
  if (c >= 'A' && c <= 'Z')
    return static_cast<std::uint8_t>(c - 'A');
  if (c >= 'a' && c <= 'z')
    return static_cast<std::uint8_t>(c - 'a' + 26);
  if (c >= '0' && c <= '9')
    return static_cast<std::uint8_t>(c - '0' + 52);
  if (c == '+')
    return 62;
  if (c == '/')
    return 63;
  return std::nullopt;
}
//--------------------------------------------------------------
}     // namespace sdi_toolBox::desktop::utils