/*      $OpenBSD: symlinks.c,v 1.7 2021/09/02 21:06:06 deraadt Exp $ */
/*
 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <assert.h>
#include <stdint.h>
#include <stdlib.h>
#include <limits.h>
#include <unistd.h>

#include "extern.h"

/*
 * Allocate space for a readlink(2) invocation.
 * Returns NULL on failure or a buffer otherwise.
 * The buffer must be passed to free() by the caller.
 */
char *
symlink_read(const char *path)
{
        char    *buf = NULL;
        size_t   sz;
        ssize_t  nsz = 0;
        void    *pp;

        for (sz = PATH_MAX; ; sz *= 2) {
                if ((pp = realloc(buf, sz + 1)) == NULL) {
                        ERR("realloc");
                        free(buf);
                        return NULL;
                }
                buf = pp;

                if ((nsz = readlink(path, buf, sz)) == -1) {
                        ERR("%s: readlink", path);
                        free(buf);
                        return NULL;
                } else if (nsz == 0) {
                        ERRX("%s: empty link", path);
                        free(buf);
                        return NULL;
                } else if ((size_t)nsz < sz)
                        break;
        }

        assert(buf != NULL);
        assert(nsz > 0);
        buf[nsz] = '\0';
        return buf;
}

/*
 * Allocate space for a readlinkat(2) invocation.
 * Returns NULL on failure or a buffer otherwise.
 * The buffer must be passed to free() by the caller.
 */
char *
symlinkat_read(int fd, const char *path)
{
        char    *buf = NULL;
        size_t   sz;
        ssize_t  nsz = 0;
        void    *pp;

        for (sz = PATH_MAX; ; sz *= 2) {
                if ((pp = realloc(buf, sz + 1)) == NULL) {
                        ERR("realloc");
                        free(buf);
                        return NULL;
                }
                buf = pp;

                if ((nsz = readlinkat(fd, path, buf, sz)) == -1) {
                        ERR("%s: readlinkat", path);
                        free(buf);
                        return NULL;
                } else if (nsz == 0) {
                        ERRX("%s: empty link", path);
                        free(buf);
                        return NULL;
                } else if ((size_t)nsz < sz)
                        break;
        }

        assert(buf != NULL);
        assert(nsz > 0);
        buf[nsz] = '\0';
        return buf;
}