nntpchan/contrib/backends/nntpchan-daemon/libnntpchan/base64.cpp

#include <nntpchan/base64.hpp>

// taken from i2pd
namespace i2p
{
namespace data
{
static void iT64Build(void);

/*
*
* BASE64 Substitution Table
* -------------------------
*
* Direct Substitution Table
*/

static const char T64[64] = {'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', '+', '/'};

/*
* Reverse Substitution Table (built in run time)
*/

static char iT64[256];
static int isFirstTime = 1;

/*
* Padding
*/

static char P64 = '=';

/*
*
* ByteStreamToBase64
* ------------------
*
* Converts binary encoded data to BASE64 format.
*
*/
static size_t                                   /* Number of bytes in the encoded buffer */
    ByteStreamToBase64(const uint8_t *InBuffer, /* Input buffer, binary data */
                       size_t InCount,          /* Number of bytes in the input buffer */
                       char *OutBuffer,         /* output buffer */
                       size_t len               /* length of output buffer */
                       )

{
  unsigned char *ps;
  unsigned char *pd;
  unsigned char acc_1;
  unsigned char acc_2;
  int i;
  int n;
  int m;
  size_t outCount;

  ps = (unsigned char *)InBuffer;
  n = InCount / 3;
  m = InCount % 3;
  if (!m)
    outCount = 4 * n;
  else
    outCount = 4 * (n + 1);
  if (outCount > len)
    return 0;
  pd = (unsigned char *)OutBuffer;
  for (i = 0; i < n; i++)
  {
    acc_1 = *ps++;
    acc_2 = (acc_1 << 4) & 0x30;
    acc_1 >>= 2; /* base64 digit #1 */
    *pd++ = T64[acc_1];
    acc_1 = *ps++;
    acc_2 |= acc_1 >> 4; /* base64 digit #2 */
    *pd++ = T64[acc_2];
    acc_1 &= 0x0f;
    acc_1 <<= 2;
    acc_2 = *ps++;
    acc_1 |= acc_2 >> 6; /* base64 digit #3 */
    *pd++ = T64[acc_1];
    acc_2 &= 0x3f; /* base64 digit #4 */
    *pd++ = T64[acc_2];
  }
  if (m == 1)
  {
    acc_1 = *ps++;
    acc_2 = (acc_1 << 4) & 0x3f; /* base64 digit #2 */
    acc_1 >>= 2;                 /* base64 digit #1 */
    *pd++ = T64[acc_1];
    *pd++ = T64[acc_2];
    *pd++ = P64;
    *pd++ = P64;
  }
  else if (m == 2)
  {
    acc_1 = *ps++;
    acc_2 = (acc_1 << 4) & 0x3f;
    acc_1 >>= 2; /* base64 digit #1 */
    *pd++ = T64[acc_1];
    acc_1 = *ps++;
    acc_2 |= acc_1 >> 4; /* base64 digit #2 */
    *pd++ = T64[acc_2];
    acc_1 &= 0x0f;
    acc_1 <<= 2; /* base64 digit #3 */
    *pd++ = T64[acc_1];
    *pd++ = P64;
  }

  return outCount;
}

/*
*
* Base64ToByteStream
* ------------------
*
* Converts BASE64 encoded data to binary format. If input buffer is
* not properly padded, buffer of negative length is returned
*
*/
static ssize_t                               /* Number of output bytes */
    Base64ToByteStream(const char *InBuffer, /* BASE64 encoded buffer */
                       size_t InCount,       /* Number of input bytes */
                       uint8_t *OutBuffer,   /* output buffer length */
                       size_t len            /* length of output buffer */
                       )
{
  unsigned char *ps;
  unsigned char *pd;
  unsigned char acc_1;
  unsigned char acc_2;
  int i;
  int n;
  int m;
  size_t outCount;

  if (isFirstTime)
    iT64Build();
  n = InCount / 4;
  m = InCount % 4;
  if (InCount && !m)
    outCount = 3 * n;
  else
  {
    outCount = 0;
    return 0;
  }

  ps = (unsigned char *)(InBuffer + InCount - 1);
  while (*ps-- == P64)
    outCount--;
  ps = (unsigned char *)InBuffer;

  if (outCount > len)
    return -1;
  pd = OutBuffer;
  auto endOfOutBuffer = OutBuffer + outCount;
  for (i = 0; i < n; i++)
  {
    acc_1 = iT64[*ps++];
    acc_2 = iT64[*ps++];
    acc_1 <<= 2;
    acc_1 |= acc_2 >> 4;
    *pd++ = acc_1;
    if (pd >= endOfOutBuffer)
      break;

    acc_2 <<= 4;
    acc_1 = iT64[*ps++];
    acc_2 |= acc_1 >> 2;
    *pd++ = acc_2;
    if (pd >= endOfOutBuffer)
      break;

    acc_2 = iT64[*ps++];
    acc_2 |= acc_1 << 6;
    *pd++ = acc_2;
  }

  return outCount;
}

static size_t Base64EncodingBufferSize(const size_t input_size)
{
  auto d = div(input_size, 3);
  if (d.rem)
    d.quot++;
  return 4 * d.quot;
}

/*
*
* iT64
* ----
* Reverse table builder. P64 character is replaced with 0
*
*
*/

static void iT64Build()
{
  int i;
  isFirstTime = 0;
  for (i = 0; i < 256; i++)
    iT64[i] = -1;
  for (i = 0; i < 64; i++)
    iT64[(int)T64[i]] = i;
  iT64[(int)P64] = 0;
}
}
}

namespace nntpchan
{
std::string B64Encode(const uint8_t *data, const std::size_t l)
{
  std::string out;
  out.resize(i2p::data::Base64EncodingBufferSize(l));
  i2p::data::ByteStreamToBase64(data, l, &out[0], out.size());
  return out;
}

bool B64Decode(const std::string &data, std::vector<uint8_t> &out)
{
  out.resize(data.size());
  if (i2p::data::Base64ToByteStream(data.c_str(), data.size(), &out[0], out.size()) == -1)
    return false;
  out.shrink_to_fit();
  return true;
}
}