mkstemp.c

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/*!
 * \file lib/gis/mkstemp.c
 *
 * \brief GIS Library - Temporary file functions.
 *
 * SPDX-FileCopyrightText: 2014 GRASS Development Team
 * SPDX-License-Identifier: GPL-2.0-or-later
 *
 * \author Glynn Clements
 */
 
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <grass/gis.h>
#include <grass/glocale.h>
 
#define MAX_REPLACE 5
 
static int next(char **replace, int num_replace)
{
    int i;
 
    for (i = 0; i < num_replace; i++) {
        char *p = replace[i];
 
        if (*p < 'z') {
            (*p)++;
            return 1;
        }
        else
            *p = 'a';
    }
 
    return 0;
}
 
static int G__mkstemp(char *template, int flags, int mode)
{
    char *replace[MAX_REPLACE];
    int num_replace = 0;
    char *ptr = template;
    int fd;
 
    while (num_replace < MAX_REPLACE) {
        char *p = strchr(ptr, 'X');
 
        if (!p)
            break;
        replace[num_replace++] = p;
        *p = 'a';
        ptr = p + 1;
    }
 
    if (!num_replace)
        return -1;
 
    for (;;) {
        if (!next(replace, num_replace))
            return -1;
 
        if (access(template, F_OK) == 0)
            continue;
 
        if (!flags)
            return 0;
 
        fd = open(template, flags, mode);
        if (fd < 0) {
            if (errno == EEXIST)
                continue;
            return -1;
        }
 
        return fd;
    }
 
    return -1;
}
 
/*!
 * \brief Opens a temporary file.
 *
 * This routine opens the file.
 *
 * The last two take the arguments "flags" and "mode". "flags" should be
 * O_WRONLY or O_RDWR, plus any other desired flags (e.g. O_APPEND).
 * "mode" is the file mode (0666 would be typical).
 *
 * The functions does not use the PID, although the caller can do so.
 *
 * In theory, up to 26^5 (= ~12 million) filenames will be attempted
 * until it finds one which doesn't exist.
 *
 * <b>Note:</b> <i>G_mktemp()</i> as such it is prone to race
 * conditions (some other process may create that file after G_mktemp()
 * returns).
 *
 * \return file name
 */
char *G_mktemp(char *template)
{
    return G__mkstemp(template, 0, 0) < 0 ? NULL : template;
}
 
/*!
 * \brief Returns a file descriptor.
 *
 * This routine opens the file and returns a descriptor.
 *
 * The last two take the arguments "flags" and "mode". "flags" should be
 * O_WRONLY or O_RDWR, plus any other desired flags (e.g. O_APPEND).
 * "mode" is the file mode (0666 would be typical).
 *
 * The functions does not use the PID, although the caller can do so.
 *
 * In theory, up to 26^5 (= ~12 million) filenames will be attempted
 * until it finds one which doesn't exist.
 *
 *
 * \return file descriptor
 */
int G_mkstemp(char *template, int flags, int mode)
{
 
    switch (flags & O_ACCMODE) {
    case O_RDONLY:
        G_fatal_error(_("Attempt to create read-only temporary file"));
        return -1;
    case O_WRONLY:
    case O_RDWR:
        break;
    default:
        G_fatal_error(_("Unrecognised access mode: %o"), flags & O_ACCMODE);
        return -1;
    }
 
    return G__mkstemp(template, flags | O_CREAT | O_EXCL, mode);
}
 
/*!
 * \brief Returns a file descriptor.
 *
 * This routine opens the file and returns a FILE*.
 *
 * The last two take the arguments "flags" and "mode". "flags" should be
 * O_WRONLY or O_RDWR, plus any other desired flags (e.g. O_APPEND).
 * "mode" is the file mode (0666 would be typical).
 *
 * The functions does not use the PID, although the caller can do so.
 *
 * In theory, up to 26^5 (= ~12 million) filenames will be attempted
 * until it finds one which doesn't exist.
 *
 * \return FILE*
 */
FILE *G_mkstemp_fp(char *template, int flags, int mode)
{
    const char *fmode = ((flags & O_ACCMODE) == O_RDWR)
                            ? ((flags & O_APPEND) ? "a+" : "w+")
                            : ((flags & O_APPEND) ? "a" : "w");
    int fd = G_mkstemp(template, flags, mode);
 
    if (fd < 0)
        return NULL;
    return fdopen(fd, fmode);
}