/*
 *  RFC 1521 base64 encoding/decoding
 *
 *  Copyright (C) 2006-2010, Brainspark B.V.
 *
 *  This file is part of PolarSSL (http://www.polarssl.org)
 *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
 *
 *  All rights reserved.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  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.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

/* $Cambridge: exim/src/src/pdkim/base64.c,v 1.3 2009/12/07 13:05:07 tom Exp $ */


#include "base64.h"

static const unsigned char base64_enc_map[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', '+', '/'
};

static const unsigned char base64_dec_map[128] =
{
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127, 127, 127, 127, 127, 127, 127, 127,
    127, 127, 127,  62, 127, 127, 127,  63,  52,  53,
     54,  55,  56,  57,  58,  59,  60,  61, 127, 127,
    127,  64, 127, 127, 127,   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, 127, 127, 127, 127, 127, 127,  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, 127, 127, 127, 127, 127
};

/*
 * Encode a buffer into base64 format
 */
int base64_encode( unsigned char *dst, int *dlen,
                   const unsigned char *src, int  slen )
{
    int i, n;
    int C1, C2, C3;
    unsigned char *p;

    if( slen == 0 )
        return( 0 );

    n = (slen << 3) / 6;

    switch( (slen << 3) - (n * 6) )
    {
        case  2: n += 3; break;
        case  4: n += 2; break;
        default: break;
    }

    if( *dlen < n + 1 )
    {
        *dlen = n + 1;
        return( POLARSSL_ERR_BASE64_BUFFER_TOO_SMALL );
    }

    n = (slen / 3) * 3;

    for( i = 0, p = dst; i < n; i += 3 )
    {
        C1 = *src++;
        C2 = *src++;
        C3 = *src++;

        *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
        *p++ = base64_enc_map[(((C1 &  3) << 4) + (C2 >> 4)) & 0x3F];
        *p++ = base64_enc_map[(((C2 & 15) << 2) + (C3 >> 6)) & 0x3F];
        *p++ = base64_enc_map[C3 & 0x3F];
    }

    if( i < slen )
    {
        C1 = *src++;
        C2 = ((i + 1) < slen) ? *src++ : 0;

        *p++ = base64_enc_map[(C1 >> 2) & 0x3F];
        *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F];

        if( (i + 1) < slen )
             *p++ = base64_enc_map[((C2 & 15) << 2) & 0x3F];
        else *p++ = '=';

        *p++ = '=';
    }

    *dlen = p - dst;
    *p = 0;

    return( 0 );
}

/*
 * Decode a base64-formatted buffer
 */
int base64_decode( unsigned char *dst, int *dlen,
                   const unsigned char *src, int  slen )
{
    int i, j, n;
    unsigned long x;
    unsigned char *p;

    for( i = j = n = 0; i < slen; i++ )
    {
        if( ( slen - i ) >= 2 &&
            src[i] == '\r' && src[i + 1] == '\n' )
            continue;

        if( src[i] == '\n' )
            continue;

        if( src[i] == '=' && ++j > 2 )
            return( POLARSSL_ERR_BASE64_INVALID_CHARACTER );

        if( src[i] > 127 || base64_dec_map[src[i]] == 127 )
            return( POLARSSL_ERR_BASE64_INVALID_CHARACTER );

        if( base64_dec_map[src[i]] < 64 && j != 0 )
            return( POLARSSL_ERR_BASE64_INVALID_CHARACTER );

        n++;
    }

    if( n == 0 )
        return( 0 );

    n = ((n * 6) + 7) >> 3;

    if( *dlen < n )
    {
        *dlen = n;
        return( POLARSSL_ERR_BASE64_BUFFER_TOO_SMALL );
    }

   for( j = 3, n = x = 0, p = dst; i > 0; i--, src++ )
   {
        if( *src == '\r' || *src == '\n' )
            continue;

        j -= ( base64_dec_map[*src] == 64 );
        x  = (x << 6) | ( base64_dec_map[*src] & 0x3F );

        if( ++n == 4 )
        {
            n = 0;
            if( j > 0 ) *p++ = (unsigned char)( x >> 16 );
            if( j > 1 ) *p++ = (unsigned char)( x >>  8 );
            if( j > 2 ) *p++ = (unsigned char)( x       );
        }
    }

    *dlen = p - dst;

    return( 0 );
}
