/*
 * Copyright (c) 1996, 1998 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Portions Copyright (c) 1995 by International Business Machines, Inc.
 *
 * International Business Machines, Inc. (hereinafter called IBM) grants
 * permission under its copyrights to use, copy, modify, and distribute this
 * Software with or without fee, provided that the above copyright notice and
 * all paragraphs of this notice appear in all copies, and that the name of IBM
 * not be used in connection with the marketing of any product incorporating
 * the Software or modifications thereof, without specific, written prior
 * permission.
 *
 * To the extent it has a right to do so, IBM grants an immunity from suit
 * under its patents, if any, for the use, sale or manufacture of products to
 * the extent that such products are used for performing Domain Name System
 * dynamic updates in TCP/IP networks by means of the Software.  No immunity is
 * granted for any product per se or for any other function of any product.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", AND IBM DISCLAIMS ALL WARRANTIES,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE.  IN NO EVENT SHALL IBM BE LIABLE FOR ANY SPECIAL,
 * DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE, EVEN
 * IF IBM IS APPRISED OF THE POSSIBILITY OF SUCH DAMAGES.
 */

#include "bson-compat.h"
#include "bson-macros.h"
#include "bson-types.h"

#define Assert(Cond) \
   if (!(Cond))      \
   abort ()

static const char Base64[] =
   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char Pad64 = '=';

/* (From RFC1521 and draft-ietf-dnssec-secext-03.txt)
 * The following encoding technique is taken from RFC 1521 by Borenstein
 * and Freed.  It is reproduced here in a slightly edited form for
 * convenience.
 *
 * A 65-character subset of US-ASCII is used, enabling 6 bits to be
 * represented per printable character. (The extra 65th character, "=",
 * is used to signify a special processing function.)
 *
 * The encoding process represents 24-bit groups of input bits as output
 * strings of 4 encoded characters. Proceeding from left to right, a
 * 24-bit input group is formed by concatenating 3 8-bit input groups.
 * These 24 bits are then treated as 4 concatenated 6-bit groups, each
 * of which is translated into a single digit in the base64 alphabet.
 *
 * Each 6-bit group is used as an index into an array of 64 printable
 * characters. The character referenced by the index is placed in the
 * output string.
 *
 *                       Table 1: The Base64 Alphabet
 *
 *    Value Encoding  Value Encoding  Value Encoding  Value Encoding
 *        0 A            17 R            34 i            51 z
 *        1 B            18 S            35 j            52 0
 *        2 C            19 T            36 k            53 1
 *        3 D            20 U            37 l            54 2
 *        4 E            21 V            38 m            55 3
 *        5 F            22 W            39 n            56 4
 *        6 G            23 X            40 o            57 5
 *        7 H            24 Y            41 p            58 6
 *        8 I            25 Z            42 q            59 7
 *        9 J            26 a            43 r            60 8
 *       10 K            27 b            44 s            61 9
 *       11 L            28 c            45 t            62 +
 *       12 M            29 d            46 u            63 /
 *       13 N            30 e            47 v
 *       14 O            31 f            48 w         (pad) =
 *       15 P            32 g            49 x
 *       16 Q            33 h            50 y
 *
 * Special processing is performed if fewer than 24 bits are available
 * at the end of the data being encoded.  A full encoding quantum is
 * always completed at the end of a quantity.  When fewer than 24 input
 * bits are available in an input group, zero bits are added (on the
 * right) to form an integral number of 6-bit groups.  Padding at the
 * end of the data is performed using the '=' character.
 *
 * Since all base64 input is an integral number of octets, only the
 * following cases can arise:
 *
 *     (1) the final quantum of encoding input is an integral
 *         multiple of 24 bits; here, the final unit of encoded
 *    output will be an integral multiple of 4 characters
 *    with no "=" padding,
 *     (2) the final quantum of encoding input is exactly 8 bits;
 *         here, the final unit of encoded output will be two
 *    characters followed by two "=" padding characters, or
 *     (3) the final quantum of encoding input is exactly 16 bits;
 *         here, the final unit of encoded output will be three
 *    characters followed by one "=" padding character.
 */

static ssize_t
b64_ntop (uint8_t const *src, size_t srclength, char *target, size_t targsize)
{
   size_t datalength = 0;
   uint8_t input[3];
   uint8_t output[4];
   size_t i;

   while (2 < srclength) {
      input[0] = *src++;
      input[1] = *src++;
      input[2] = *src++;
      srclength -= 3;

      output[0] = input[0] >> 2;
      output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
      output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
      output[3] = input[2] & 0x3f;
      Assert (output[0] < 64);
      Assert (output[1] < 64);
      Assert (output[2] < 64);
      Assert (output[3] < 64);

      if (datalength + 4 > targsize) {
         return -1;
      }
      target[datalength++] = Base64[output[0]];
      target[datalength++] = Base64[output[1]];
      target[datalength++] = Base64[output[2]];
      target[datalength++] = Base64[output[3]];
   }

   /* Now we worry about padding. */
   if (0 != srclength) {
      /* Get what's left. */
      input[0] = input[1] = input[2] = '\0';

      for (i = 0; i < srclength; i++) {
         input[i] = *src++;
      }
      output[0] = input[0] >> 2;
      output[1] = ((input[0] & 0x03) << 4) + (input[1] >> 4);
      output[2] = ((input[1] & 0x0f) << 2) + (input[2] >> 6);
      Assert (output[0] < 64);
      Assert (output[1] < 64);
      Assert (output[2] < 64);

      if (datalength + 4 > targsize) {
         return -1;
      }
      target[datalength++] = Base64[output[0]];
      target[datalength++] = Base64[output[1]];

      if (srclength == 1) {
         target[datalength++] = Pad64;
      } else {
         target[datalength++] = Base64[output[2]];
      }
      target[datalength++] = Pad64;
   }

   if (datalength >= targsize) {
      return -1;
   }
   target[datalength] = '\0'; /* Returned value doesn't count \0. */
   return datalength;
}
