use if net.OpError.Err == syscall.EIPE, but net.OpError.Err never eq to syscall.EPIPE

[xiaotushaoxia]

    broker := func(to, from *net.TCPConn) {
        written, err := io.Copy(to, from)
        if err != nil {
            // If the socket we are writing to is shutdown with
            // SHUT_WR, forward it to the other end of the pipe:
            if err, ok := err.(*net.OpError); ok && err.Err == syscall.EPIPE {
                _ = from.CloseRead()
            }
        }
        _ = to.CloseWrite()
        event <- written
    }

net.OpError.Err is *os.SyscallError, os.SyscallError.Err can not be syscall.Errno

maybe this is expected behavior

    broker := func(to, from *net.TCPConn) {
        written, err := io.Copy(to, from)
        if err != nil {
            // If the socket we are writing to is shutdown with
            // SHUT_WR, forward it to the other end of the pipe:
            var errno syscall.Errno
            if errors.As(err, &errno) && errno == syscall.EPIPE {
                _ = from.CloseRead()
            }
        }
        _ = to.CloseWrite()
        event <- written
    }