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 {

		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)

		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{}