/*

 * Copyright (c) Ian F. Darwin 1986-1995.

 * Software written by Ian F. Darwin and others;

 * maintained 1995-present by Christos Zoulas and others.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice immediately at the beginning of the file, without modification,

 *    this list of conditions, and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR

 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 */

/*

 * is_tar() -- figure out whether file is a tar archive.

 *

 * Stolen (by the author!) from the file_public domain tar program:

 * Public Domain version written 26 Aug 1985 John Gilmore (ihnp4!hoptoad!gnu).

 *

 * @(#)list.c 1.18 9/23/86 Public Domain - gnu

 *

 * Comments changed and some code/comments reformatted

 * for file command by Ian Darwin.

 */

#include "file.h"

#ifndef lint

FILE_RCSID("@(#)$File: is_tar.c,v 1.50 2022/12/26 17:31:14 christos Exp $")

#endif

#include "magic.h"

#include <string.h>

#include <ctype.h>

#include "tar.h"

#define isodigit(c) ( ((c) >= '0') && ((c) <= '7') )

file_private int is_tar(const unsigned char *, size_t);

file_private int from_oct(const char *, size_t);  /* Decode octal number */

static const char tartype[][32] = { /* should be equal to messages */

  "tar archive",      /* found in ../magic/Magdir/archive */

  "POSIX tar archive",

  "POSIX tar archive (GNU)",  /*  */

};

file_protected int

file_is_tar(struct magic_set *ms, const struct buffer *b)

{

  const unsigned char *buf = CAST(const unsigned char *, b->fbuf);

  size_t nbytes = b->flen;

  /*

   * Do the tar test first, because if the first file in the tar

   * archive starts with a dot, we can confuse it with an nroff file.

   */

  int tar;

  int mime = ms->flags & MAGIC_MIME;

  if ((ms->flags & (MAGIC_APPLE|MAGIC_EXTENSION)) != 0)

    return 0;

  tar = is_tar(buf, nbytes);

  if (tar < 1 || tar > 3)

    return 0;

  if (mime == MAGIC_MIME_ENCODING)

    return 1;

  if (file_printf(ms, "%s", mime ? "application/x-tar" :

      tartype[tar - 1]) == -1)

    return -1;

  return 1;

}

/*

 * Return

 *  0 if the checksum is bad (i.e., probably not a tar archive),

 *  1 for old UNIX tar file,

 *  2 for Unix Std (POSIX) tar file,

 *  3 for GNU tar file.

 */

file_private int

is_tar(const unsigned char *buf, size_t nbytes)

{

  static const char gpkg_match[] = "/gpkg-1";

  const union record *header = RCAST(const union record *,

      RCAST(const void *, buf));

  size_t i;

  int sum, recsum;

  const unsigned char *p, *ep;

  const char *nulp;

  if (nbytes < sizeof(*header))

    return 0;

  /* If the file looks like Gentoo GLEP 78 binary package (GPKG),

   * don't waste time on further checks and fall back to magic rules.

   */

  nulp = CAST(const char *,

      memchr(header->header.name, 0, sizeof(header->header.name)));

  if (nulp != NULL && nulp >= header->header.name + sizeof(gpkg_match) &&

      memcmp(nulp - sizeof(gpkg_match) + 1, gpkg_match,

      sizeof(gpkg_match)) == 0)

      return 0;

  recsum = from_oct(header->header.chksum, sizeof(header->header.chksum));

  sum = 0;

  p = header->charptr;

  ep = header->charptr + sizeof(*header);

  while (p < ep)

    sum += *p++;

  /* Adjust checksum to count the "chksum" field as blanks. */

  for (i = 0; i < sizeof(header->header.chksum); i++)

    sum -= header->header.chksum[i];

  sum += ' ' * sizeof(header->header.chksum);

  if (sum != recsum)

    return 0; /* Not a tar archive */

  if (strncmp(header->header.magic, GNUTMAGIC,

      sizeof(header->header.magic)) == 0)

    return 3;   /* GNU Unix Standard tar archive */

  if (strncmp(header->header.magic, TMAGIC,

      sizeof(header->header.magic)) == 0)

    return 2;   /* Unix Standard tar archive */

  return 1;     /* Old fashioned tar archive */

}

/*

 * Quick and dirty octal conversion.

 *

 * Result is -1 if the field is invalid (all blank, or non-octal).

 */

file_private int

from_oct(const char *where, size_t digs)

{

  int value;

  if (digs == 0)

    return -1;

  while (isspace(CAST(unsigned char, *where))) { /* Skip spaces */

    where++;

    if (digs-- == 0)

      return -1;   /* All blank field */

  }

  value = 0;

  while (digs > 0 && isodigit(*where)) { /* Scan til non-octal */

    value = (value << 3) | (*where++ - '0');

    digs--;

  }

  if (digs > 0 && *where && !isspace(CAST(unsigned char, *where)))

    return -1;     /* Ended on non-(space/NUL) */

  return value;

}