func writeHeader(w xo.Writer, fields Fields) error { for _, f := range fields { buf, err := w.Reserve(len(f.Name) + len(f.Value) + 4) if err != nil { return err } n := copy(buf[0:], f.Name) n += copy(buf[n:], ": ") n += copy(buf[n:], f.Value) n += copy(buf[n:], "\r\n") if err := w.Commit(n); err != nil { return err } } _, err := w.Write(crlf) return err }