#ifndef CPP_JWT_BASE64_HPP
#define CPP_JWT_BASE64_HPP
#include <array>
#include <cassert>
#include "jwt/string_view.hpp"
namespace jwt {
// Returns the maximum number of bytes required to
// encode an input byte string of length `n` to base64.
inline constexpr
size_t encoding_size(size_t n)
{
return 4 * ((n + 2) / 3);
}
// Returns the maximum number of bytes required
// to store a decoded base64 byte string.
inline constexpr
size_t decoding_size(size_t n)
{
return n / 4 * 3;
}
/**
* Encoding map.
* A constexpr helper class for performing base64
* encoding on the input byte string.
*/
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',
'+','/',
};
};
/**
* Encodes a sequence of octet into base64 string.
* Returns std::string resized to contain only the
* encoded data (as usual without null terminator).
*
* The encoded string is atleast `encoding_size(input len)`
* in size.
*
* Arguments:
* @in : Input byte string to be encoded.
* @len : Length of the input byte string.
*/
std::string base64_encode(const char* in, size_t len)
{
std::string result;
const auto encoded_siz = encoding_size(len);
result.resize(encoded_siz);
constexpr static const EMap emap{};
int i = 0;
int j = 0;
for (; i < len - 2; i += 3) {
const auto first = in[i];
const auto second = in[i+1];
const auto third = in[i+2];
result[j++] = emap.at( (first >> 2) & 0x3F );
result[j++] = emap.at(((first & 0x03) << 4) | ((second & 0xF0) >> 4));
result[j++] = emap.at(((second & 0x0F) << 2) | ((third & 0xC0) >> 6));
result[j++] = emap.at( (third & 0x3F) );
}
switch (len % 3) {
case 2:
{
const auto first = in[i];
const auto second = in[i+1];
result[j++] = emap.at( (first >> 2) & 0x3F );
result[j++] = emap.at(((first & 0x03) << 4) | ((second & 0xF0) >> 4));
result[j++] = emap.at( (second & 0x0F) << 2 );
result[j++] = '=';
break;
}
case 1:
{
const auto first = in[i];
result[j++] = emap.at((first >> 2) & 0x3F);
result[j++] = emap.at((first & 0x03) << 4);
result[j++] = '=';
result[j++] = '=';
break;
}
case 0:
break;
};
result.resize(j);
return result;
}
//======================= Decoder ==========================
/**
* Decoding map.
* A helper constexpr class for providing interface
* to the decoding map for base64.
*/
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
};
};
/**
* Decodes octet of base64 encoded byte string.
*
* Returns a std::string with the decoded byte string.
*
* Arguments:
* @in : Encoded base64 byte string.
* @len : Length of the encoded input byte string.
*/
std::string base64_decode(const char* in, size_t len)
{
std::string result;
const auto decoded_siz = decoding_size(len);
result.resize(decoded_siz);
int i = 0;
size_t bytes_rem = len;
size_t bytes_wr = 0;
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 result;
const auto first = dmap.at(in[0]);
const auto second = dmap.at(in[1]);
const auto third = dmap.at(in[2]);
const 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;
}
bytes_wr = i;
switch(bytes_rem) {
case 4:
{
const auto third = dmap.at(in[2]);
const auto fourth = dmap.at(in[3]);
result[i + 2] = (third << 6) | fourth;
bytes_wr++;
//FALLTHROUGH
}
case 3:
{
const auto second = dmap.at(in[1]);
const auto third = dmap.at(in[2]);
result[i + 1] = (second << 4) | (third >> 2);
bytes_wr++;
//FALLTHROUGH
}
case 2:
{
const auto first = dmap.at(in[0]);
const auto second = dmap.at(in[1]);
result[i] = (first << 2) | (second >> 4);
bytes_wr++;
}
};
result.resize(bytes_wr);
return result;
}
/**
* Makes the base64 encoded byte string URL safe.
* Overwrites/skips few URL unsafe characters
* from the input sequence.
*
* Arguments:
* @data : Base64 encoded byte string.
* @len : Length of the base64 byte string.
*
* Returns:
* Length of the URL safe base64 encoded byte string.
*/
size_t base64_uri_encode(char* data, size_t len) noexcept
{
size_t i = 0;
size_t j = 0;
for (; i < len; ++i) {
switch (data[i]) {
case '+':
data[j++] = '-';
break;
case '/':
data[j++] = '_';
break;
case '=':
break;
default:
data[j++] = data[i];
};
}
return j;
}
/**
* Decodes an input URL safe base64 encoded byte string.
*
* NOTE: To be used only for decoding URL safe base64 encoded
* byte string.
*
* Arguments:
* @data : URL safe base64 encoded byte string.
* @len : Length of the input byte string.
*/
std::string base64_uri_decode(const char* data, size_t len)
{
std::string uri_dec;
uri_dec.resize(len + 4);
size_t i = 0;
for (; i < len; ++i)
{
switch (data[i]) {
case '-':
uri_dec[i] = '+';
break;
case '_':
uri_dec[i] = '/';
break;
default:
uri_dec[i] = data[i];
};
}
size_t trailer = 4 - (i % 4);
if (trailer && trailer < 4) {
while (trailer--) {
uri_dec[i++] = '=';
}
}
return base64_decode(uri_dec.c_str(), uri_dec.length());
}
} // END namespace jwt
#endif