Current doc says
ReadFrom reads data from r until EOF or error. The return value n is the
> number of bytes read. Any error except io.EOF encountered during the read
> is also returned.
WriteTo writes data to w until there's no more data to write or when an
> error occurs. The return value n is the number of bytes written. Any error
> encountered during the write is also returned.
Note that io.EOF is explicitly ignored in ReadFrom but it's a bit vague
about how io.EOF should be handled in WriteTo. Should we return io.EOF or
ignore it? An example
type dataSource struct {
// implementation details
}
func (src *dataSource) WriteTo(w io.Writer) (nn int64, err error) {
buf := make([]byte, 32*1024)
for {
nr, er := src.internalRead(buf) // assume internalRead gets data
from some internal source
if nr > 0 {
nw, ew := w.Write(buf[:nr])
nn += int64(nw)
if ew != nil {
err = ew
break
}
}
if er != nil {
// What if er == io.EOF here? Shall we ignore it?
err = er
break
}
}
}
Since WriteTo can be used by io.Copy as a shortcut and io.Copy ignores
io.EOF, I tend to think WriteTo should also ignore io.EOF. If so, the doc
of io.WriteTo probably needs to be more explicit and consistent with
io.ReadFrom.
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