I’m trying to create a function that duplicates a file given a file descriptor and a file name:

int filedup(int fd1, char *fname)
{
    int fd;
    size_t  rd;
    char    buff;
    
    if (fd1 < 0 || fd1 > OPEN_MAX)
        return (-1);
    if (!validfname(fname))
        return (-1);
    fd = open(fname, O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if (fd == -1)
        return (-1);
    rd = read(fd1, &buff, 1);
    while (rd > 0)
    {
        write(fd, &buff, 1);
        rd = read(fd1, &buff, 1);
    }
    close(fd);
    return (0);
}
int main(void)
{
    int fd;

    fd = open("/tmp/tmp", O_RDWR | O_CREAT | O_TRUNC, 0644);
    if (fd == -1)
        return (-1);
    putstr_fd(strdup("hello world\n"), fd); 
    filedup(fd, "tmp");
    close(fd);
    return (0);
}

I tried to debug it, and the problem was rd == 0 even though the file contains data.

$ cat ./tmp
$ (nothing)

I’m not sure what’s the problem ? what am i doing wrong ?