Actually I don't really care about that, just don't want break the
interface requirement
in the doc it says "WriteAt writes len(p) bytes from p to the underlying
data stream at offset off. It returns the number of bytes written from p (0
<= n <= len(p)) and any error encountered that caused the write to stop
early."
but using binary.Write I lost that infomation. So what's the right way to
do it ? or just ignore it and return 0?
在 2016年12月16日星期五 UTC+8上午4:56:12，Tamás Gulácsi写道：
>
> 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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