nghttp2/src/base64.h

/*
 * nghttp2 - HTTP/2 C Library
 *
 * Copyright (c) 2013 Tatsuhiro Tsujikawa
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
#ifndef BASE64_H
#define BASE64_H

#include "nghttp2_config.h"

#include <string>

namespace nghttp2 {

namespace base64 {

template <typename InputIt> std::string encode(InputIt first, InputIt last) {
  static constexpr char CHAR_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', '+', '/',
  };
  std::string res;
  size_t len = last - first;
  if (len == 0) {
    return res;
  }
  size_t r = len % 3;
  res.resize((len + 2) / 3 * 4);
  auto j = last - r;
  auto p = std::begin(res);
  while (first != j) {
    uint32_t n = static_cast<uint8_t>(*first++) << 16;
    n += static_cast<uint8_t>(*first++) << 8;
    n += static_cast<uint8_t>(*first++);
    *p++ = CHAR_TABLE[n >> 18];
    *p++ = CHAR_TABLE[(n >> 12) & 0x3fu];
    *p++ = CHAR_TABLE[(n >> 6) & 0x3fu];
    *p++ = CHAR_TABLE[n & 0x3fu];
  }

  if (r == 2) {
    uint32_t n = static_cast<uint8_t>(*first++) << 16;
    n += static_cast<uint8_t>(*first++) << 8;
    *p++ = CHAR_TABLE[n >> 18];
    *p++ = CHAR_TABLE[(n >> 12) & 0x3fu];
    *p++ = CHAR_TABLE[(n >> 6) & 0x3fu];
    *p++ = '=';
  } else if (r == 1) {
    uint32_t n = static_cast<uint8_t>(*first++) << 16;
    *p++ = CHAR_TABLE[n >> 18];
    *p++ = CHAR_TABLE[(n >> 12) & 0x3fu];
    *p++ = '=';
    *p++ = '=';
  }
  return res;
}

template <typename InputIt>
InputIt next_decode_input(InputIt first, InputIt last, const int *tbl) {
  for (; first != last; ++first) {
    if (tbl[static_cast<size_t>(*first)] != -1 || *first == '=') {
      break;
    }
  }
  return first;
}

template <typename InputIt> std::string decode(InputIt first, InputIt last) {
  static constexpr int INDEX_TABLE[] = {
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57,
      58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0,  1,  2,  3,  4,  5,  6,
      7,  8,  9,  10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
      25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
      37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1};
  auto len = last - first;
  if (len % 4 != 0) {
    return "";
  }
  std::string res;
  res.resize(len / 4 * 3);

  auto p = std::begin(res);
  for (; first != last;) {
    uint32_t n = 0;
    for (int i = 1; i <= 4; ++i, ++first) {
      auto idx = INDEX_TABLE[static_cast<size_t>(*first)];
      if (idx == -1) {
        if (i <= 2) {
          return "";
        }
        if (i == 3) {
          if (*first == '=' && *(first + 1) == '=' && first + 2 == last) {
            *p++ = n >> 16;
            res.resize(p - std::begin(res));
            return res;
          }
          return "";
        }
        if (*first == '=' && first + 1 == last) {
          *p++ = n >> 16;
          *p++ = n >> 8 & 0xffu;
          res.resize(p - std::begin(res));
          return res;
        }
        return "";
      }

      n += idx << (24 - i * 6);
    }

    *p++ = n >> 16;
    *p++ = n >> 8 & 0xffu;
    *p++ = n & 0xffu;
  }

  return res;
}

} // namespace base64

} // namespace nghttp2

#endif // BASE64_H