Then I should deal with the encoding of all the envelope fields. This
envelope seems to be simple, but i got a more complicated one in the real
dev works.
在 2016年12月16日星期五 UTC+8上午10:44:27，ma...@influxdb.com写道：
>
>
>
> On Thursday, December 15, 2016 at 6:05:53 PM UTC-8, Peng Wang wrote:
>>
>> 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
>>>> }
>>>>
>>>
>>>
>>
> You know the size of Envelope, so you can write it to a local byte slice
> first and then pass that byte slice to w.Write.
>
> https://play.golang.org/p/WZmxCjgQVm
>
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