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/*

 * realpath.c -- canonicalize pathname by removing symlinks

 * Copyright (C) 1993 Rick Sladkey <jrs@world.std.com>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU Library Public License as published by

 * the Free Software Foundation; either version 2, or (at your option)

 * any later version.

 *

 * 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 Library Public License for more details.

 */

#ifdef HAVE_CONFIG_H

#include <config.h>

#endif

#include <sys/types.h>

#include <unistd.h>

#include <stdio.h>

#include <string.h>

#include <strings.h>

#include <limits.h>                             /* for PATH_MAX */

#include <sys/param.h>                  /* for MAXPATHLEN */

#include <errno.h>

#include <sys/stat.h>                   /* for S_IFLNK */

#ifndef PATH_MAX

#ifdef _POSIX_VERSION

#define PATH_MAX _POSIX_PATH_MAX

#else

#ifdef MAXPATHLEN

#define PATH_MAX MAXPATHLEN

#else

#define PATH_MAX 1024

#endif

#endif

#endif

#define MAX_READLINKS 32

#ifdef __STDC__

char *realpath(const char *path, char resolved_path[])

#else

char *realpath(path, resolved_path)

const char *path;

char resolved_path[];

#endif

{

        char copy_path[PATH_MAX];

        char link_path[PATH_MAX];

        char got_path[PATH_MAX];

        char *new_path = got_path;

        char *max_path;

        int readlinks = 0;

        int n;

        /* Make a copy of the source path since we may need to modify it. */

        if (strlen(path) >= PATH_MAX - 2) {

                __set_errno(ENAMETOOLONG);

                return NULL;

        }

        strcpy(copy_path, path);

        path = copy_path;

        max_path = copy_path + PATH_MAX - 2;

        /* If it's a relative pathname use getwd for starters. */

        if (*path != '/') {

                /* Ohoo... */

#define HAVE_GETCWD

#ifdef HAVE_GETCWD

                getcwd(new_path, PATH_MAX - 1);

#else

                getwd(new_path);

#endif

                new_path += strlen(new_path);

                if (new_path[-1] != '/')

                        *new_path++ = '/';

        } else {

                *new_path++ = '/';

                path++;

        }

        /* Expand each slash-separated pathname component. */

        while (*path != '\0') {

                /* Ignore stray "/". */

                if (*path == '/') {

                        path++;

                        continue;

                }

                if (*path == '.') {

                        /* Ignore ".". */

                        if (path[1] == '\0' || path[1] == '/') {

                                path++;

                                continue;

                        }

                        if (path[1] == '.') {

                                if (path[2] == '\0' || path[2] == '/') {

                                        path += 2;

                                        /* Ignore ".." at root. */

                                        if (new_path == got_path + 1)

                                                continue;

                                        /* Handle ".." by backing up. */

                                        while ((--new_path)[-1] != '/');

                                        continue;

                                }

                        }

                }

                /* Safely copy the next pathname component. */

                while (*path != '\0' && *path != '/') {

                        if (path > max_path) {

                                __set_errno(ENAMETOOLONG);

                                return NULL;

                        }

                        *new_path++ = *path++;

                }

#ifdef S_IFLNK

                /* Protect against infinite loops. */

                if (readlinks++ > MAX_READLINKS) {

                        __set_errno(ELOOP);

                        return NULL;

                }

                /* See if latest pathname component is a symlink. */

                *new_path = '\0';

                n = readlink(got_path, link_path, PATH_MAX - 1);

                if (n < 0) {

                        /* EINVAL means the file exists but isn't a symlink. */

                        if (errno != EINVAL) {

                                /* Make sure it's null terminated. */

                                *new_path = '\0';

                                strcpy(resolved_path, got_path);

                                return NULL;

                        }

                } else {

                        /* Note: readlink doesn't add the null byte. */

                        link_path[n] = '\0';

                        if (*link_path == '/')

                                /* Start over for an absolute symlink. */

                                new_path = got_path;

                        else

                                /* Otherwise back up over this component. */

                                while (*(--new_path) != '/');

                        /* Safe sex check. */

                        if (strlen(path) + n >= PATH_MAX - 2) {

                                __set_errno(ENAMETOOLONG);

                                return NULL;

                        }

                        /* Insert symlink contents into path. */

                        strcat(link_path, path);

                        strcpy(copy_path, link_path);

                        path = copy_path;

                }

#endif                                                  /* S_IFLNK */

                *new_path++ = '/';

        }

        /* Delete trailing slash but don't whomp a lone slash. */

        if (new_path != got_path + 1 && new_path[-1] == '/')

                new_path--;

        /* Make sure it's null terminated. */

        *new_path = '\0';

        strcpy(resolved_path, got_path);

        return resolved_path;

}