/*      $OpenBSD: copy.c,v 1.6 2025/05/31 14:04:09 deraadt Exp $ */
/*
 * Copyright (c) 2021 Claudio Jeker <claudio@openbsd.org>
 *
 * 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 <sys/types.h>

#include <err.h>
#include <fcntl.h>
#include <unistd.h>

#include "extern.h"

#define _MAXBSIZE (64 * 1024)

/*
 * Return true if all bytes in buffer are zero.
 * A buffer of zero length is also considered a zero buffer.
 */
static int
iszero(const void *b, size_t len)
{
        const unsigned char *c = b;

        for (; len > 0; len--) {
                if (*c++ != '\0')
                        return 0;
        }
        return 1;
}

static int
copy_internal(int fromfd, int tofd)
{
        char buf[_MAXBSIZE];
        ssize_t r, w;

        while ((r = read(fromfd, buf, sizeof(buf))) > 0) {
                if (iszero(buf, sizeof(buf))) {
                        if (lseek(tofd, r, SEEK_CUR) == -1)
                                return -1;
                } else {
                        w = write(tofd, buf, r);
                        if (r != w || w == -1)
                                return -1;
                }
        }
        if (r == -1)
                return -1;
        if (ftruncate(tofd, lseek(tofd, 0, SEEK_CUR)) == -1)
                return -1;
        return 0;
}

void
copy_file(int rootfd, const char *basedir_abs, const struct flist *f)
{
        int fromfd, tofd, dfd;

        dfd = open(basedir_abs, O_RDONLY | O_DIRECTORY);
        if (dfd == -1)
                err(ERR_FILE_IO, "%s: open", basedir_abs);

        fromfd = openat(dfd, f->path, O_RDONLY | O_NOFOLLOW);
        if (fromfd == -1)
                err(ERR_FILE_IO, "%s/%s: openat", basedir_abs, f->path);
        close(dfd);

        tofd = openat(rootfd, f->path,
            O_WRONLY | O_NOFOLLOW | O_TRUNC | O_CREAT | O_EXCL,
            0600);
        if (tofd == -1)
                err(ERR_FILE_IO, "%s: openat", f->path);

        if (copy_internal(fromfd, tofd) == -1)
                err(ERR_FILE_IO, "%s: copy file", f->path);

        close(fromfd);
        close(tofd);
}