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encode.c

/* ----------------------------------------------------------------------------
 *
    VDE_OVER_NS 
      (C) 2007 Daniele Lacamera

    Derived from:
    NSTX -- tunneling network-packets over DNS

     (C) 2000 by Florian Heinz and Julien Oster

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License version 2, as 
    published by the Free Software Foundation.

    This program 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 General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

  -------------------------------------------------------------------------- */

#include <string.h>
#include <stdlib.h>

unsigned char map[] = 
            "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_1234567890";
unsigned char *revmap = NULL;

void init_revmap (void)
{
   unsigned int i;
   
   revmap = malloc(256);
   
   for (i = 0; i < strlen((char*)map); i++)
     revmap[map[i]] = i;
}
   
const unsigned char *
nstx_encode(const unsigned char *data, int len) {
   int i = 0, off = 1, cut = 0;
   static unsigned char *buf = NULL;
   
   if (len % 3)
     cut = 3 - len%3;
   
   buf = realloc(buf, ((len+2)/3)*4+2);
   buf[0] = map[cut];
   while (i < len) {
      buf[off + 0] = map[(data[i] & 252) >> 2];
      buf[off + 1] = map[((data[i] & 3) << 4) | ((data[i+1] & 240) >> 4)];
      buf[off + 2] = map[((data[i+1] & 15) << 2 ) | ((data[i+2] & 192) >> 6)];
      buf[off + 3] = map[(data[i+2] & 63)];
      i += 3;
      off += 4;
   }
   buf[off] = '\0';
   
   return buf;
}

const unsigned char *
nstx_decode(const unsigned char *data, int *rlen) {
   int i = 0, off = 1;
   int len;
   static unsigned char *buf = NULL;
   
   if (!revmap)
     init_revmap();
   
   len = strlen((char*)data);

   buf = realloc(buf, ((len+3)/4)*3);
   
   while (off+3 < len) {
      buf[i+0] = (revmap[data[off]]<<2)|((revmap[data[off+1]]&48)>>4);
      buf[i+1] = ((revmap[data[off+1]]&15)<<4)|((revmap[data[off+2]]&60)>>2);
      buf[i+2] = ((revmap[data[off+2]]&3)<<6)|(revmap[data[off+3]]);
      i += 3;
      off += 4;
   }
   *rlen = i - revmap[data[0]];
   
   return buf;
}

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