base64.hh

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/*
 * libkeepass - KeePass key database importer/exporter
 * Copyright (C) 2014 Christian Kindahl
 * Copyright (C) 2024 Dominik Krümpelmann
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
#include <algorithm>
#include <locale>
#include <string>
#include <string_view>
#include <type_traits>
 
#include "exception.hh"
 
namespace keepass {
 
template <typename InputIterator>
std::string base64_encode(InputIterator first, InputIterator last) {
  static const std::string kBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                     "abcdefghijklmnopqrstuvwxyz"
                                     "0123456789+/";
 
  std::string dst;
 
  while (first != last) {
    auto c0 = static_cast<uint8_t>(*first++);
    if (first == last) {
      dst.push_back(kBase64[static_cast<std::string::size_type>(c0 >> 2)]);
      dst.push_back(kBase64[static_cast<std::string::size_type>(((c0 & 0x3) << 4))]);
      dst.push_back('=');
      dst.push_back('=');
    } else {
      auto c1 = static_cast<uint8_t>(*first++);
      if (first == last) {
        dst.push_back(kBase64[static_cast<std::string::size_type>(c0 >> 2)]);
        dst.push_back(kBase64[static_cast<std::string::size_type>(((c0 & 0x3) << 4) | (c1 >> 4))]);
        dst.push_back(kBase64[static_cast<std::string::size_type>(((c1 & 0xf) << 2))]);
        dst.push_back('=');
      } else {
        auto c2 = static_cast<uint8_t>(*first++);
        dst.push_back(kBase64[static_cast<std::string::size_type>(c0 >> 2)]);
        dst.push_back(kBase64[static_cast<std::string::size_type>(((c0 & 0x3) << 4) | (c1 >> 4))]);
        dst.push_back(kBase64[static_cast<std::string::size_type>(((c1 & 0xf) << 2) | (c2 >> 6))]);
        dst.push_back(kBase64[static_cast<std::string::size_type>(c2 & 0x3f)]);
      }
    }
  }
 
  return dst;
}
 
template <typename OutputIterator, typename Type>
void base64_decode(std::string_view src, OutputIterator result) {
  static const std::string kBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                     "abcdefghijklmnopqrstuvwxyz"
                                     "0123456789+/";
 
  std::string src_trimmed;
  std::copy_if(src.begin(), src.end(), std::back_inserter<std::string>(src_trimmed),
               [](char c) { return !std::isspace(c, std::locale::classic()); });
 
  if (src_trimmed.size() % 4 != 0)
    throw FormatError("Base64 data must be a multiple of four in size.");
 
  uint32_t bits24 = 0;
  std::size_t i = 0;
 
  for (char c : src_trimmed) {
    if (c == '=') {
      *result = static_cast<Type>(bits24 >> 16);
      ++result;
      if (i > 2) {
        *result = static_cast<Type>((bits24 >> 8) & 0xff);
        ++result;
      }
      if (i > 3) {
        *result = static_cast<Type>(bits24 & 0xff);
        ++result;
      }
      break;
    }
 
    std::size_t v = kBase64.find(c);
    if (v == std::string::npos)
      throw FormatError("Illegal character in base64 stream.");
 
    bits24 |= static_cast<uint32_t>(v) << (18 - i++ * 6);
    if (i == 4) {
      *result = static_cast<Type>(bits24 >> 16);
      ++result;
      *result = static_cast<Type>((bits24 >> 8) & 0xff);
      ++result;
      *result = static_cast<Type>(bits24 & 0xff);
      ++result;
 
      bits24 = 0;
      i = 0;
    }
  }
}
 
inline std::string base64_encode(const std::string& src) {
  return base64_encode(src.begin(), src.end());
}
 
inline std::string base64_decode(std::string_view src) {
  std::string dst;
  base64_decode<std::back_insert_iterator<std::string>, char>(src, std::back_inserter(dst));
  return dst;
}
 
} // namespace keepass