header.c

/*
 * uzlib  -  tiny deflate/inflate library (deflate, gzip, zlib)
 *
 * Copyright (c) 2003 by Joergen Ibsen / Jibz
 * All Rights Reserved
 *
 * http://www.ibsensoftware.com/
 *
 * Copyright (c) 2014-2018 by Paul Sokolovsky
 *
 * Optimised for MicroPython:
 * Copyright (c) 2023 by Jim Mussared
 *
 * This software is provided 'as-is', without any express
 * or implied warranty.  In no event will the authors be
 * held liable for any damages arising from the use of
 * this software.
 *
 * Permission is granted to anyone to use this software
 * for any purpose, including commercial applications,
 * and to alter it and redistribute it freely, subject to
 * the following restrictions:
 *
 * 1. The origin of this software must not be
 *    misrepresented; you must not claim that you
 *    wrote the original software. If you use this
 *    software in a product, an acknowledgment in
 *    the product documentation would be appreciated
 *    but is not required.
 *
 * 2. Altered source versions must be plainly marked
 *    as such, and must not be misrepresented as
 *    being the original software.
 *
 * 3. This notice may not be removed or altered from
 *    any source distribution.
 */

#include "uzlib.h"

#define FTEXT    1
#define FHCRC    2
#define FEXTRA   4
#define FNAME    8
#define FCOMMENT 16

void tinf_skip_bytes(uzlib_uncomp_t *d, int num);
uint16_t tinf_get_uint16(uzlib_uncomp_t *d);

void tinf_skip_bytes(uzlib_uncomp_t *d, int num)
{
    while (num--) uzlib_get_byte(d);
}

uint16_t tinf_get_uint16(uzlib_uncomp_t *d)
{
    unsigned int v = uzlib_get_byte(d);
    v = (uzlib_get_byte(d) << 8) | v;
    return v;
}

int uzlib_parse_zlib_gzip_header(uzlib_uncomp_t *d, int *wbits)
{
    /* -- check format -- */
    unsigned char cmf = uzlib_get_byte(d);
    unsigned char flg = uzlib_get_byte(d);

    /* check for gzip id bytes */
    if (cmf == 0x1f && flg == 0x8b) {
        /* check method is deflate */
        if (uzlib_get_byte(d) != 8) return UZLIB_DATA_ERROR;

        /* get flag byte */
        flg = uzlib_get_byte(d);

        /* check that reserved bits are zero */
        if (flg & 0xe0) return UZLIB_DATA_ERROR;

        /* -- find start of compressed data -- */

        /* skip rest of base header of 10 bytes */
        tinf_skip_bytes(d, 6);

        /* skip extra data if present */
        if (flg & FEXTRA)
        {
           unsigned int xlen = tinf_get_uint16(d);
           tinf_skip_bytes(d, xlen);
        }

        /* skip file name if present */
        if (flg & FNAME) { while (uzlib_get_byte(d)); }

        /* skip file comment if present */
        if (flg & FCOMMENT) { while (uzlib_get_byte(d)); }

        /* check header crc if present */
        if (flg & FHCRC)
        {
           /*unsigned int hcrc =*/ tinf_get_uint16(d);

            // TODO: Check!
    //       if (hcrc != (tinf_crc32(src, start - src) & 0x0000ffff))
    //          return UZLIB_DATA_ERROR;
        }

        /* initialize for crc32 checksum */
        d->checksum_type = UZLIB_CHKSUM_CRC;
        d->checksum = ~0;

        /* gzip does not include the window size in the header, as it is expected that a
           compressor will use wbits=15 (32kiB).*/
        *wbits = 15;

        return UZLIB_HEADER_GZIP;
    } else {
       /* check checksum */
       if ((256*cmf + flg) % 31) return UZLIB_DATA_ERROR;

       /* check method is deflate */
       if ((cmf & 0x0f) != 8) return UZLIB_DATA_ERROR;

       /* check window size is valid */
       if ((cmf >> 4) > 7) return UZLIB_DATA_ERROR;

       /* check there is no preset dictionary */
       if (flg & 0x20) return UZLIB_DATA_ERROR;

       /* initialize for adler32 checksum */
       d->checksum_type = UZLIB_CHKSUM_ADLER;
       d->checksum = 1;

       *wbits = (cmf >> 4) + 8;

        return UZLIB_HEADER_ZLIB;
    }
}