2016. december 15., csütörtök 17:36:47 UTC+1 időpontban 彭望 a következőt
írta:
>
> Hi all, I'm doing a simple message serialization, message defines like
> below:
> type Envelope struct {
> Magic uint32
> DataSize uint32
> }
>
> type Message struct {
> Envelope
> Data []byte
> }
>
> and I want to implement the io.WriterTo interface for Message
> func (m *Message) WriteTo(w io.Writer) (n int64, err error) {
> err = binary.Write(w, binary.BigEndian, &m.Envelope)
> if err != nil {
> // here, how should I return a proper n? Since w maybe
> *net.TCPConn and binary.Write maybe write 1 bytes and peer has dropped the
> connection.
> return 0, fmt.Errorf("Write message envelope error: %s", err)
> }
>
> // multiple lines skipped
> }
>
If you really want to know the number of bytes written, wrap w in a
counting writer, which counts the bytes written.
> type countingWriter struct {
> w io.Writer
> N int64
> }
> func (w *countingWriter) Write(p []byte) (int, error) {
> n, err := w.w.Write(p)
> w.N += int64(n)
> return n, err
> }
>
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