text: /*
   *  Copyright (C) 2014-2020 Savoir-faire Linux Inc.
   *
   *  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 <https://www.gnu.org/licenses/>.
   */
  
  #include "base64.h"
  
  #include <cstdint>
  #include <cstdlib>
  
  /* Mainly based on the following stackoverflow question:
   * http://stackoverflow.com/questions/342409/how-do-i-base64-encode-decode-in-c
   */
  static const char encoding_table[] = {
      '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', '+', '/'
  };
  
  static const size_t mod_table[] = { 0, 2, 1 };
  
  char *base64_encode(const uint8_t *input, size_t input_length,
                               char *output, size_t *output_length)
  {
      size_t i, j;
      size_t out_sz = *output_length;
      *output_length = 4 * ((input_length + 2) / 3);
      if (out_sz < *output_length || output == nullptr)
          return nullptr;
  
      for (i = 0, j = 0; i < input_length; ) {
          uint8_t octet_a = i < input_length ? input[i++] : 0;
          uint8_t octet_b = i < input_length ? input[i++] : 0;
          uint8_t octet_c = i < input_length ? input[i++] : 0;
  
          uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;
  
          output[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
          output[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
          output[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
          output[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
      }
  
      for (i = 0; i < mod_table[input_length % 3]; i++)
          output[*output_length - 1 - i] = '=';
  
      return output;
  }
  
  uint8_t *base64_decode(const char *input, size_t input_length,
                               uint8_t *output, size_t *output_length)
  {
      size_t i, j;
      uint8_t decoding_table[256];
  
      uint8_t c;
      for (c = 0; c < 64; c++)
          decoding_table[static_cast<int>(encoding_table[c])] = c;
  
      if (input_length % 4 != 0 || input_length < 2)
          return nullptr;
  
      size_t out_sz = *output_length;
      *output_length = input_length / 4 * 3;
      if (input[input_length - 1] == '=')
          (*output_length)--;
      if (input[input_length - 2] == '=')
          (*output_length)--;
  
      if (out_sz < *output_length || output == nullptr)
          return nullptr;
  
      for (i = 0, j = 0; i < input_length;) {
          uint8_t sextet_a = input[i] == '=' ? 0 & i++
              : decoding_table[static_cast<int>(input[i++])];
          uint8_t sextet_b = input[i] == '=' ? 0 & i++
              : decoding_table[static_cast<int>(input[i++])];
          uint8_t sextet_c = input[i] == '=' ? 0 & i++
              : decoding_table[static_cast<int>(input[i++])];
          uint8_t sextet_d = input[i] == '=' ? 0 & i++
              : decoding_table[static_cast<int>(input[i++])];
  
          uint32_t triple = (sextet_a << 3 * 6) +
                            (sextet_b << 2 * 6) +
                            (sextet_c << 1 * 6) +
                            (sextet_d << 0 * 6);
  
          if (j < *output_length)
              output[j++] = (triple >> 2 * 8) & 0xFF;
          if (j < *output_length)
              output[j++] = (triple >> 1 * 8) & 0xFF;
          if (j < *output_length)
              output[j++] = (triple >> 0 * 8) & 0xFF;
      }
  
      return output;
  }
  
  std::string
  base64_encode(const std::vector<uint8_t>::const_iterator begin,
                const std::vector<uint8_t>::const_iterator end)
  {
      size_t output_length = 4 * ((std::distance(begin, end) + 2) / 3);
      std::string out;
      out.resize(output_length);
      base64_encode(&(*begin), std::distance(begin, end),
                    &(*out.begin()), &output_length);
      out.resize(output_length);
      return out;
  }
  
  
  std::string
  base64_encode(const std::vector<unsigned char>& str)
  {
      return base64_encode(str.cbegin(), str.cend());
  }
  
  std::vector<unsigned char>
  base64_decode(const std::string& str)
  {
      size_t output_length = str.length() / 4 * 3 + 2;
      std::vector<uint8_t> output;
      output.resize(output_length);
      base64_decode(str.data(), str.size(), output.data(), &output_length);
      output.resize(output_length);
      return output;
  }
  