/*

 * base64.c - Base 64 encoding/decoding implementation

 * Copyright (C) 2006 Collabora Ltd.

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Lesser General Public

 * License as published by the Free Software Foundation; either

 * version 2.1 of the License, or (at your option) any later version.

 *

 * This library 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

 * Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public

 * License along with this library; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

 */

#include <ctype.h>

#include <string.h>

#include <glib.h>

#include "base64.h"

/*

|AAAA AABB|BBBB CCCC|CCDD DDDD|

0xFC = 1111 1100

0x03 = 0000 0011

0xF0 = 1111 0000

0x0F = 0000 1111

0xC0 = 1100 0000

0x3F = 0011 1111

3 input bytes = 4 output bytes;

2 input bytes = 2 output bytes;

1 input byte  = 1 output byte.

*/

static const gchar *encoding =

  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static const guint decoding[256] =

{

  /* ... */

   0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

   0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

   0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

   0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

   0, 0, 0,

  /* + */

  62,

  /* ... */

   0, 0, 0,

  /* / , 0-9 */

  63,

  52, 53, 54, 55, 56, 57, 58, 59, 60, 61,

  /* ... */

   0, 0, 0, 0, 0, 0, 0,

  /* A */

   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,

  /* ... */

   0, 0, 0, 0, 0, 0,

  /* a */

  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

};

#define GET_6_BITS_0(s) (((s)[0] & 0xFC) >> 2)

#define GET_6_BITS_1(s) (((s)[0] & 0x03) << 4) | \

                        (((s)[1] & 0xF0) >> 4)

#define GET_6_BITS_2(s) (((s)[1] & 0x0F) << 2) | \

                        (((s)[2] & 0xC0) >> 6)

#define GET_6_BITS_3(s) (((s)[2] & 0x3F) << 0)

#define GET_BYTE_0(s) (((decoding[(guchar)(s)[0]] & 0x3F) << 2) | \

                       ((decoding[(guchar)(s)[1]] & 0x30) >> 4))

#define GET_BYTE_1(s) (((decoding[(guchar)(s)[1]] & 0x0F) << 4) | \

                       ((decoding[(guchar)(s)[2]] & 0x3C) >> 2))

#define GET_BYTE_2(s) (((decoding[(guchar)(s)[2]] & 0x03) << 6) | \

                       ((decoding[(guchar)(s)[3]] & 0xFF) << 0))

gchar *_lm_base64_encode (const gchar *txt, gsize n)

{

  guint i;

  guint len;

  GString *tmp;

  GString *str = g_string_new_len (txt, n);

  len = str->len;

  /* TODO: calculate requisite output string length and allocate that big a

   * GString */

  tmp = g_string_new ("");

  for (i = 0; i < len; i += 3)

    {

      guint c1, c2, c3, c4;

      switch (i + 3 - len)

        {

        case 1:

          c1 = encoding[GET_6_BITS_0 (str->str + i)];

          c2 = encoding[GET_6_BITS_1 (str->str + i)];

          c3 = encoding[GET_6_BITS_2 (str->str + i)];

          c4 = '=';

          break;

        case 2:

          c1 = encoding[GET_6_BITS_0 (str->str + i)];

          c2 = encoding[GET_6_BITS_1 (str->str + i)];

          c3 = '=';

          c4 = '=';

          break;

        default:

          c1 = encoding[GET_6_BITS_0 (str->str + i)];

          c2 = encoding[GET_6_BITS_1 (str->str + i)];

          c3 = encoding[GET_6_BITS_2 (str->str + i)];

          c4 = encoding[GET_6_BITS_3 (str->str + i)];

        }

      g_string_append_printf (tmp, "%c%c%c%c", c1, c2, c3, c4);

    }

  return g_string_free (tmp, FALSE);

}

gchar *_lm_base64_decode (const gchar *str, gsize *len)

{

  guint i;

  GString *tmp;

  char group[4];

  guint filled = 0;

  *len = 0;

  for (i = 0; str[i]; i++)

    {

      if (str[i] != 'A' &&

          str[i] != '=' &&

          !isspace(str[i]) &&

          decoding[(guchar) str[i]] == 0)

        {

          g_debug ("bad character %x at byte %u", (guchar)str[i], i);

          return NULL;

        }

    }

  tmp = g_string_new ("");

  for (i = 0; str[i]; i++)

    {

      if (isspace(str[i]))

        continue;

      group[filled++] = str[i];

      if (filled == 4)

        {

          if (group[3] == '=')

            {

              if (group[2] == '=')

                {

                  g_string_append_c (tmp, GET_BYTE_0(group));

                }

              else

                {

                  g_string_append_c (tmp, GET_BYTE_0(group));

                  g_string_append_c (tmp, GET_BYTE_1(group));

                }

             }

           else

            {

              g_string_append_c (tmp, GET_BYTE_0(group));

              g_string_append_c (tmp, GET_BYTE_1(group));

              g_string_append_c (tmp, GET_BYTE_2(group));

            }

          filled = 0;

        }

    }

  if (filled)

    {

      g_debug ("insufficient padding at end of base64 string:\n%s", str);

      g_string_free (tmp, TRUE);

      return NULL;

    }

  *len = tmp->len;

  return g_string_free (tmp, FALSE);

}