socket?

static VALUE
rb_file_socket_p(VALUE obj, VALUE fname)
{
#ifndef S_ISSOCK
#  ifdef _S_ISSOCK
#    define S_ISSOCK(m) _S_ISSOCK(m)
#  else
#    ifdef _S_IFSOCK
#      define S_ISSOCK(m) ((m & S_IFMT) == _S_IFSOCK)
#    else
#      ifdef S_IFSOCK
#        define S_ISSOCK(m) ((m & S_IFMT) == S_IFSOCK)
#      endif
#    endif
#  endif
#endif

#ifdef S_ISSOCK
    struct stat st;

    if (rb_stat(fname, &st) < 0) return Qfalse;
    if (S_ISSOCK(st.st_mode)) return Qtrue;

#endif
    return Qfalse;
}