/*
 ** Copyright (C) 2013-2022 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
 ** Copyright (C) 1998-2013 Sourcefire, Inc.
 **
 ** Written by Patrick Mullen <pmullen@sourcefire.com>
 ** 9/11/2013 - Changed uint32_t to size_t
 **
 ** 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.  You may not use, modify or
 ** distribute this program under any other version of the GNU General
 ** Public License.
 **
 ** 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.
 */

#ifdef HAVE_CONFIG_H
#include "clamav-config.h"
#endif

#include "sf_base64decode.h"

// clang-format off
uint8_t sf_decode64tab[256] = {
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,62 ,100,100,100, 63,
         52, 53, 54, 55, 56, 57, 58, 59, 60, 61,100,100,100, 99,100,100,
        100,  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, 25,100,100,100,100,100,
        100, 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, 51,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,
        100,100,100,100,100,100,100,100,100,100,100,100,100,100,100,100};
// clang-format on

/* base64decode assumes the input data terminates with '=' and/or at the end of the input buffer
 * at inbuf_size.  If extra characters exist within inbuf before inbuf_size is reached, it will
 * happily decode what it can and skip over what it can't.  This is consistent with other decoders
 * out there.  So, either terminate the string, set inbuf_size correctly, or at least be sure the
 * data is valid up until the point you care about.  Note base64 data does NOT have to end with
 * '=' and won't if the number of bytes of input data is evenly divisible by 3.
*/
int sf_base64decode(uint8_t *inbuf, size_t inbuf_size, uint8_t *outbuf, size_t outbuf_size, size_t *bytes_written)
{
    uint8_t *cursor, *endofinbuf;
    uint8_t *outbuf_ptr;
    uint8_t base64data[4], *base64data_ptr; /* temporary holder for current base64 chunk */
    uint8_t tableval_a, tableval_b, tableval_c, tableval_d;

    size_t n;
    size_t max_base64_chars; /* The max number of decoded base64 chars that fit into outbuf */

    int error = 0;

    /* This algorithm will waste up to 4 bytes but we really don't care.
      At the end we're going to copy the exact number of bytes requested. */
    max_base64_chars = (outbuf_size / 3) * 4 + 4; /* 4 base64 bytes gives 3 data bytes, plus
                                                    an extra 4 to take care of any rounding */

    base64data_ptr = base64data;
    endofinbuf     = inbuf + inbuf_size;

    /* Strip non-base64 chars from inbuf and decode */
    n              = 0;
    *bytes_written = 0;
    cursor         = inbuf;
    outbuf_ptr     = outbuf;
    while ((cursor < endofinbuf) && (n < max_base64_chars)) {
        if (sf_decode64tab[*cursor] != 100) {
            *base64data_ptr++ = *cursor;
            n++; /* Number of base64 bytes we've stored */
            if (!(n % 4)) {
                /* We have four databytes upon which to operate */

                if ((base64data[0] == '=') || (base64data[1] == '=')) {
                    /* Error in input data */
                    error = 1;
                    break;
                }

                /* retrieve values from lookup table */
                tableval_a = sf_decode64tab[base64data[0]];
                tableval_b = sf_decode64tab[base64data[1]];
                tableval_c = sf_decode64tab[base64data[2]];
                tableval_d = sf_decode64tab[base64data[3]];

                if (*bytes_written < outbuf_size) {
                    *outbuf_ptr++ = (tableval_a << 2) | (tableval_b >> 4);
                    (*bytes_written)++;
                }

                if ((base64data[2] != '=') && (*bytes_written < outbuf_size)) {
                    *outbuf_ptr++ = (tableval_b << 4) | (tableval_c >> 2);
                    (*bytes_written)++;
                } else {
                    break;
                }

                if ((base64data[3] != '=') && (*bytes_written < outbuf_size)) {
                    *outbuf_ptr++ = (tableval_c << 6) | tableval_d;
                    (*bytes_written)++;
                } else {
                    break;
                }

                /* Reset our decode pointer for the next group of four */
                base64data_ptr = base64data;
            }
        }
        cursor++;
    }

    if (error)
        return (-1);
    else
        return (0);
}
