t.Fatal("should fail")
	} else if err.(*OpError).Err != ErrWriteToConnected {
		t.Fatalf("should fail as ErrWriteToConnected: %v", err)
	}
	if _, err = c.(*UnixConn).WriteTo(b, raddr); err == nil {
		t.Fatal("should fail")
	} else if err.(*OpError).Err != ErrWriteToConnected {
		t.Fatalf("should fail as ErrWriteToConnected: %v", err)
	}
	if _, _, err = c.(*UnixConn).WriteMsgUnix(b, nil, raddr); err == nil {

	if c.fd.isConnected {
		return 0, ErrWriteToConnected
	}
	if addr == nil {
		return 0, errMissingAddress
	}
	sa, err := addr.sockaddr(c.fd.family)
	if err != nil {
		return 0, err
	}
	return c.fd.writeTo(b, sa)
}

func (c *IPConn) writeMsg(b, oob []byte, addr *IPAddr) (n, oobn int, err error) {
	if c.fd.isConnected {
		return 0, 0, ErrWriteToConnected
	}
	if addr == nil {

		t.Fatal("should fail")
	}
	if err != nil && err.(*OpError).Err != ErrWriteToConnected {
		t.Fatalf("should fail as ErrWriteToConnected: %v", err)
	}
	_, err = c.(*UDPConn).WriteTo(b, ra)
	if err == nil {
		t.Fatal("should fail")
	}
	if err != nil && err.(*OpError).Err != ErrWriteToConnected {
		t.Fatalf("should fail as ErrWriteToConnected: %v", err)
	}
	_, err = c.Write(b)
	if err != nil {
		t.Fatal(err)

		addr = netip.AddrPortFrom(ip, uint16(sa.Port))
	}
	return
}

func (c *UDPConn) writeTo(b []byte, addr *UDPAddr) (int, error) {
	if c.fd.isConnected {
		return 0, ErrWriteToConnected
	}
	if addr == nil {
		return 0, errMissingAddress
	}

	switch c.fd.family {
	case syscall.AF_INET:
		sa, err := ipToSockaddrInet4(addr.IP, addr.Port)
		if err != nil {
			return 0, err

			addr = &UnixAddr{Name: sa.Name, Net: sotypeToNet(c.fd.sotype)}
		}
	}
	return
}

func (c *UnixConn) writeTo(b []byte, addr *UnixAddr) (int, error) {
	if c.fd.isConnected {
		return 0, ErrWriteToConnected
	}
	if addr == nil {
		return 0, errMissingAddress
	}
	if addr.Net != sotypeToNet(c.fd.sotype) {
		return 0, syscall.EAFNOSUPPORT
	}
	sa := &syscall.SockaddrUnix{Name: addr.Name}

		return nil
	case *os.SyscallError:
		nestedErr = err.Err
		goto third
	}
	switch nestedErr {
	case errCanceled, ErrClosed, errMissingAddress, errTimeout, os.ErrDeadlineExceeded, ErrWriteToConnected, io.ErrUnexpectedEOF:
		return nil
	}
	return fmt.Errorf("unexpected type on 2nd nested level: %T", nestedErr)

third:
	if isPlatformError(nestedErr) {
		return nil
	}

	// For connection setup and write operations.
	errMissingAddress = errors.New("missing address")

	// For both read and write operations.
	errCanceled         = canceledError{}
	ErrWriteToConnected = errors.New("use of WriteTo with pre-connected connection")
)

// canceledError lets us return the same error string we have always
// returned, while still being Is context.Canceled.
type canceledError struct{}

		{"Dialer.FallbackDelay", Field, 5},
		{"Dialer.KeepAlive", Field, 3},
		{"Dialer.LocalAddr", Field, 1},
		{"Dialer.Resolver", Field, 8},
		{"Dialer.Timeout", Field, 1},
		{"ErrClosed", Var, 16},
		{"ErrWriteToConnected", Var, 0},
		{"Error", Type, 0},
		{"FileConn", Func, 0},
		{"FileListener", Func, 0},
		{"FilePacketConn", Func, 0},
		{"FlagBroadcast", Const, 0},
		{"FlagLoopback", Const, 0},