IO#ttyname

static VALUE
console_ttyname(VALUE io)
{
    int fd = rb_io_descriptor(io);
    if (!isatty(fd)) return Qnil;
# if defined _WIN32
    return rb_usascii_str_new_lit("con");
# elif defined HAVE_TTYNAME_R
    {
        char termname[1024], *tn = termname;
        size_t size = sizeof(termname);
        int e;
        if (ttyname_r(fd, tn, size) == 0)
            return rb_interned_str_cstr(tn);
        if ((e = errno) == ERANGE) {
            VALUE s = rb_str_new(0, size);
            while (1) {
                tn = RSTRING_PTR(s);
                size = rb_str_capacity(s);
                if (ttyname_r(fd, tn, size) == 0) {
                    return rb_str_to_interned_str(rb_str_resize(s, strlen(tn)));
                }
                if ((e = errno) != ERANGE) break;
                if ((size *= 2) >= INT_MAX/2) break;
                rb_str_resize(s, size);
            }
        }
        rb_syserr_fail_str(e, rb_sprintf("ttyname_r(%d)", fd));
        UNREACHABLE_RETURN(Qnil);
    }
# elif defined HAVE_TTYNAME
    {
        const char *tn = ttyname(fd);
        if (!tn) {
            int e = errno;
            rb_syserr_fail_str(e, rb_sprintf("ttyname(%d)", fd));
        }
        return rb_interned_str_cstr(tn);
    }
# else
#   error No ttyname function
# endif
}