path: root/src/vfs/tar/tar-internal.c

/*
   Virtual File System: GNU Tar file system.

   Copyright (C) 2023
   Free Software Foundation, Inc.

   Written by:
   Andrew Borodin <aborodin@vmail.ru>, 2023

   This file is part of the Midnight Commander.

   The Midnight Commander 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 3 of the License,
   or (at your option) any later version.

   The Midnight Commander 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, see <http://www.gnu.org/licenses/>.
 */

/**
 * \file
 * \brief Source: Virtual File System: GNU Tar file system
 * \author Andrew Borodin
 * \date 2022
 */

#include <config.h>

#include <ctype.h>              /* isspace() */
#include <inttypes.h>           /* uintmax_t */
#include <stdint.h>             /* UINTMAX_MAX, etc */

#include "lib/global.h"
#include "lib/widget.h"         /* message() */
#include "lib/vfs/vfs.h"        /* mc_read() */

#include "tar-internal.h"

/*** global variables ****************************************************************************/

/*** file scope macro definitions ****************************************************************/

/* Log base 2 of common values. */
#define LG_8 3
#define LG_64 6
#define LG_256 8

/*** file scope type declarations ****************************************************************/

/*** forward declarations (file scope functions) *************************************************/

/*** file scope variables ************************************************************************/

/* Base 64 digits; see RFC 2045 Table 1.  */
static char const base_64_digits[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', '+', '/'
};

/* Table of base 64 digit values indexed by unsigned chars.
   The value is 64 for unsigned chars that are not base 64 digits. */
static char base64_map[1 + (unsigned char) (-1)];

/* --------------------------------------------------------------------------------------------- */
/*** file scope functions ************************************************************************/
/* --------------------------------------------------------------------------------------------- */

static gboolean
tar_short_read (size_t status, tar_super_t * archive)
{
    size_t left;                /* bytes left */
    char *more;                 /* pointer to next byte to read */

    more = archive->record_start->buffer + status;
    left = record_size - status;

    while (left % BLOCKSIZE != 0 || (left != 0 && status != 0))
    {
        if (status != 0)
        {
            ssize_t r;

            r = mc_read (archive->fd, more, left);
            if (r == -1)
                return FALSE;

            status = (size_t) r;
        }

        if (status == 0)
            break;

        left -= status;
        more += status;
    }

    record_end = archive->record_start + (record_size - left) / BLOCKSIZE;

    return TRUE;
}

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

static gboolean
tar_flush_read (tar_super_t * archive)
{
    size_t status;

    status = mc_read (archive->fd, archive->record_start->buffer, record_size);
    if (status == record_size)
        return TRUE;

    return tar_short_read (status, archive);
}

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

/**  Flush the current buffer from the archive.
 */
static gboolean
tar_flush_archive (tar_super_t * archive)
{
    record_start_block += record_end - archive->record_start;
    current_block = archive->record_start;
    record_end = archive->record_start + blocking_factor;

    return tar_flush_read (archive);
}

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

static off_t
tar_seek_archive (tar_super_t * archive, off_t size)
{
    off_t start, offset;
    off_t nrec, nblk;
    off_t skipped;

    skipped = (blocking_factor - (current_block - archive->record_start)) * BLOCKSIZE;
    if (size <= skipped)
        return 0;

    /* Compute number of records to skip */
    nrec = (size - skipped) / record_size;
    if (nrec == 0)
        return 0;

    start = tar_current_block_ordinal (archive);

    offset = mc_lseek (archive->fd, nrec * record_size, SEEK_CUR);
    if (offset < 0)
        return offset;

#if 0
    if ((offset % record_size) != 0)
    {
        message (D_ERROR, MSG_ERROR, _("tar: mc_lseek not stopped at a record boundary"));
        return -1;
    }
#endif

    /* Convert to number of records */
    offset /= BLOCKSIZE;
    /* Compute number of skipped blocks */
    nblk = offset - start;

    /* Update buffering info */
    record_start_block = offset - blocking_factor;
    current_block = record_end;

    return nblk;
}

/* --------------------------------------------------------------------------------------------- */
/*** public functions ****************************************************************************/
/* --------------------------------------------------------------------------------------------- */

void
tar_base64_init (void)
{
    size_t i;

    memset (base64_map, 64, sizeof base64_map);
    for (i = 0; i < 64; i++)
        base64_map[(int) base_64_digits[i]] = i;
}

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

void
tar_assign_string (char **string, char *value)
{
    g_free (*string);
    *string = value;
}

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

void
tar_assign_string_dup (char **string, const char *value)
{
    g_free (*string);
    *string = g_strdup (value);
}

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

void
tar_assign_string_dup_n (char **string, const char *value, size_t n)
{
    g_free (*string);
    *string = g_strndup (value, n);
}

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

/**
 * Convert buffer at @where0 of size @digs from external format to intmax_t.
 * @digs must be positive.
 * If @type is non-NULL, data are of type @type.
 * The buffer must represent a value in the range -@minval through @maxval;
 * if the mathematically correct result V would be greater than INTMAX_MAX,
 * return a negative integer V such that (uintmax_t) V yields the correct result.
 * If @octal_only, allow only octal numbers instead of the other GNU extensions.
 *
 * Result is -1 if the field is invalid.
 */
#if !(INTMAX_MAX <= UINTMAX_MAX && - (INTMAX_MIN + 1) <= UINTMAX_MAX)
#error "tar_from_header() internally represents intmax_t as uintmax_t + sign"
#endif
#if !(UINTMAX_MAX / 2 <= INTMAX_MAX)
#error "tar_from_header() returns intmax_t to represent uintmax_t"
#endif
intmax_t
tar_from_header (const char *where0, size_t digs, char const *type, intmax_t minval,
                 uintmax_t maxval, gboolean octal_only)
{
    uintmax_t value = 0;
    uintmax_t uminval = minval;
    uintmax_t minus_minval = -uminval;
    const char *where = where0;
    char const *lim = where + digs;
    gboolean negative = FALSE;

    /* Accommodate buggy tar of unknown vintage, which outputs leading
       NUL if the previous field overflows. */
    if (*where == '\0')
        where++;

    /* Accommodate older tars, which output leading spaces. */
    while (TRUE)
    {
        if (where == lim)
            return (-1);

        if (!isspace ((unsigned char) *where))
            break;

        where++;
    }

    if (isodigit (*where))
    {
        char const *where1 = where;
        gboolean overflow = FALSE;

        while (TRUE)
        {
            value += *where++ - '0';
            if (where == lim || !isodigit (*where))
                break;
            overflow |= value != (value << LG_8 >> LG_8);
            value <<= LG_8;
        }

        /* Parse the output of older, unportable tars, which generate
           negative values in two's complement octal. If the leading
           nonzero digit is 1, we can't recover the original value
           reliably; so do this only if the digit is 2 or more. This
           catches the common case of 32-bit negative time stamps. */
        if ((overflow || maxval < value) && *where1 >= 2 && type != NULL)
        {
            /* Compute the negative of the input value, assuming two's complement. */
            int digit;

            digit = (*where1 - '0') | 4;
            overflow = FALSE;
            value = 0;
            where = where1;

            while (TRUE)
            {
                value += 7 - digit;
                where++;
                if (where == lim || !isodigit (*where))
                    break;
                digit = *where - '0';
                overflow |= value != (value << LG_8 >> LG_8);
                value <<= LG_8;
            }

            value++;
            overflow |= value == 0;

            if (!overflow && value <= minus_minval)
                negative = TRUE;
        }

        if (overflow)
            return (-1);
    }
    else if (octal_only)
    {
        /* Suppress the following extensions. */
    }
    else if (*where == '-' || *where == '+')
    {
        /* Parse base-64 output produced only by tar test versions
           1.13.6 (1999-08-11) through 1.13.11 (1999-08-23).
           Support for this will be withdrawn in future tar releases. */
        int dig;

        negative = *where++ == '-';

        while (where != lim && (dig = base64_map[(unsigned char) *where]) < 64)
        {
            if (value << LG_64 >> LG_64 != value)
                return (-1);
            value = (value << LG_64) | dig;
            where++;
        }
    }
    else if (where <= lim - 2 && (*where == '\200'      /* positive base-256 */
                                  || *where == '\377' /* negative base-256 */ ))
    {
        /* Parse base-256 output.  A nonnegative number N is
           represented as (256**DIGS)/2 + N; a negative number -N is
           represented as (256**DIGS) - N, i.e. as two's complement.
           The representation guarantees that the leading bit is
           always on, so that we don't confuse this format with the
           others (assuming ASCII bytes of 8 bits or more). */

        int signbit;
        uintmax_t topbits;

        signbit = *where & (1 << (LG_256 - 2));
        topbits =
            (((uintmax_t) - signbit) << (CHAR_BIT * sizeof (uintmax_t) - LG_256 - (LG_256 - 2)));

        value = (*where++ & ((1 << (LG_256 - 2)) - 1)) - signbit;

        while (TRUE)
        {
            value = (value << LG_256) + (unsigned char) *where++;
            if (where == lim)
                break;

            if (((value << LG_256 >> LG_256) | topbits) != value)
                return (-1);
        }

        negative = signbit != 0;
        if (negative)
            value = -value;
    }

    if (where != lim && *where != '\0' && !isspace ((unsigned char) *where))
        return (-1);

    if (value <= (negative ? minus_minval : maxval))
        return tar_represent_uintmax (negative ? -value : value);

    return (-1);
}

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

off_t
off_from_header (const char *p, size_t s)
{
    /* Negative offsets are not allowed in tar files, so invoke
       from_header with minimum value 0, not TYPE_MINIMUM (off_t). */
    return tar_from_header (p, s, "off_t", 0, TYPE_MAXIMUM (off_t), FALSE);
}

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

/**
 * Return the location of the next available input or output block.
 * Return NULL for EOF.
 */
union block *
tar_find_next_block (tar_super_t * archive)
{
    if (current_block == record_end)
    {
        if (hit_eof)
            return NULL;

        if (!tar_flush_archive (archive))
        {
            message (D_ERROR, MSG_ERROR, _("Inconsistent tar archive"));
            return NULL;
        }

        if (current_block == record_end)
        {
            hit_eof = TRUE;
            return NULL;
        }
    }

    return current_block;
}

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

/**
 * Indicate that we have used all blocks up thru @block.
 */
gboolean
tar_set_next_block_after (union block * block)
{
    while (block >= current_block)
        current_block++;

    /* Do *not* flush the archive here. If we do, the same argument to tar_set_next_block_after()
       could mean the next block (if the input record is exactly one block long), which is not
       what is intended.  */

    return !(current_block > record_end);
}

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

/**
 * Compute and return the block ordinal at current_block.
 */
off_t
tar_current_block_ordinal (const tar_super_t * archive)
{
    return record_start_block + (current_block - archive->record_start);
}

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

/**
 * Skip over @size bytes of data in blocks in the archive.
 */
gboolean
tar_skip_file (tar_super_t * archive, off_t size)
{
    union block *x;
    off_t nblk;

    nblk = tar_seek_archive (archive, size);
    if (nblk >= 0)
        size -= nblk * BLOCKSIZE;

    while (size > 0)
    {
        x = tar_find_next_block (archive);
        if (x == NULL)
            return FALSE;

        tar_set_next_block_after (x);
        size -= BLOCKSIZE;
    }

    return TRUE;
}

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