Base64 encoder decoder + Stack allocator

include/jwt/base64.hpp

@@ -0,0 +1,183 @@
+#ifndef CPP_JWT_BASE64_HPP
+#define CPP_JWT_BASE64_HPP
+
+#include <array>
+#include <cassert>
+
+namespace jwt {
+
+/*
+ * Encoding map.
+ */
+class EMap
+{
+public:
+  constexpr EMap() = default;
+
+public:
+  constexpr char at(size_t pos) const noexcept
+  {
+    assert (pos < chars_.size());
+    return chars_.at(pos);
+  }
+
+private:
+  std::array<char, 64> chars_ = {
+    '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 base64_encode(const char* in, size_t len)
+{
+  std::string result;
+  result.resize(128);
+
+  constexpr static const EMap bmap{};
+
+  int i = 0;
+
+  for (; i < len - 2; i += 3) {
+    auto first  = in[i];
+    auto second = in[i+1];
+    auto third  = in[i+2];
+
+    result[i]     = bmap.at( (first >> 2) & 0x3F                           );
+    result[i + 1] = bmap.at(((first  & 0x03) << 4) | ((second & 0xF0) >> 4));
+    result[i + 2] = bmap.at(((second & 0x0F) << 2) | ((third  & 0xC0) >> 6));
+    result[i + 3] = bmap.at(                          (third  & 0x3F)      );
+  }
+
+  switch (len % 3) {
+  case 2:
+  {
+    auto first  = in[i];
+    auto second = in[i+1];
+
+    result[i]     = bmap.at( (first >> 2) & 0x3F                          );
+    result[i + 1] = bmap.at(((first & 0x03) << 4) | ((second & 0xF0) >> 4));
+    result[i + 2] = bmap.at(                         (second & 0x0F) << 2 );
+    result[i + 3] = '=';
+    break;
+  }
+  case 1:
+  {
+    auto& first = in[i];
+
+    result[i]     = bmap.at((first >> 2) & 0x3F                          );
+    result[i + 1] = bmap.at((first & 0x03) << 4                          );
+    result[i + 2] = '=';
+    result[i + 3] = '=';
+    break;
+  }
+  case 0:
+    break;
+  };
+
+  return result;
+}
+
+
+
+//======================= Decoder ==========================
+
+/*
+ * Decoding map.
+ */
+class DMap
+{
+public:
+  constexpr DMap() = default;
+
+public:
+  constexpr char at(size_t pos) const noexcept
+  {
+    assert (pos < map_.size());
+    return map_[pos];
+  }
+
+private:
+  std::array<char, 256> map_ = {
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, //   0-15
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, //  16-31
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, //  32-47
+    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, //  48-63
+    -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, //  64-79
+    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, //  80-95
+    -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, //  96-111
+    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1, // 112-127
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 128-143
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 144-159
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 160-175
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 176-191
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 192-207
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 208-223
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 224-239
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1  // 240-255
+  };
+};
+
+
+std::string base64_decode(const char* in, size_t len)
+{
+  std::string result;
+  result.resize(128);
+  int i = 0;
+  size_t bytes_rem = len;
+
+  constexpr static const DMap dmap{};
+
+  while (dmap.at(in[bytes_rem - 1]) == -1) { bytes_rem--; }
+
+  while (bytes_rem > 4)
+  {
+    // Error case in input
+    if (dmap.at(*in) == -1) return;
+
+    auto first  = dmap.at(in[0]);
+    auto second = dmap.at(in[1]);
+    auto third  = dmap.at(in[2]);
+    auto fourth = dmap.at(in[3]);
+
+    result[i]     = (first  << 2) | (second >> 4);
+    result[i + 1] = (second << 4) | (third >> 2);
+    result[i + 2] = (third  << 6) | fourth;
+
+    bytes_rem -= 4;
+    i += 3;
+    in += 4;
+  }
+
+  switch(bytes_rem) {
+  case 4:
+  {
+    auto third  = dmap.at(in[2]);
+    auto fourth = dmap.at(in[3]);
+    result[i + 2] = (third << 6) | fourth;
+    //FALLTHROUGH
+  }
+  case 3:
+  {
+    auto second = dmap.at(in[1]);
+    auto third  = dmap.at(in[2]);
+    result[i + 1] = (second << 4) | (third >> 2);
+    //FALLTHROUGH
+  }
+  case 2:
+  {
+    auto first  = dmap.at(in[0]);
+    auto second = dmap.at(in[1]);
+    result[i] = (first << 2) | (second >> 4);
+  }
+  };
+
+  return result;
+}
+
+} // END namespace jwt
+
+
+#endif