func (w *wrapper) Write(b []byte) (int, error) {
	n, err := w.ResponseWriter.Write(b)
	w.written += n
	return n, err
}
Write wrapper to capture response size.
package httplog
import (
	"net/http"
	"time"
	"github.com/apex/log"
)
func New(h http.Handler) *Logger {
	return &Logger{Handler: h}
}
type Logger struct {
	http.Handler
}
type wrapper struct {
	http.ResponseWriter
	http.Flusher
	http.CloseNotifier
	written int
	status  int
}
func (w *wrapper) WriteHeader(code int) {
	w.status = code
	w.ResponseWriter.WriteHeader(code)
}