Separate serialization and error handling from the actual api handling logic in golang

handler.go

type handlerFunc func(w http.ResponseWriter, r *http.Request) (interface{}, error)

func handle(fn handlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Add("Content-Type", "application/json")
		i, err := fn(w, r)

		if err != nil {
			handleError(w, err, http.StatusInternalServerError)
			return
		}

		json.NewEncoder(w).Encode(i)
	}
}

func handleError(w http.ResponseWriter, err error, code int) {
	fmt.Fprintln(os.Stderr, err.Error())

	w.WriteHeader(code)
	json.NewEncoder(w).Encode(struct {
		Error      string `json:"error"`
		StatusCode int    `json:"status_code"`
	}{
		Error:      err.Error(),
		StatusCode: code,
	})
}

// see an example usage: https://github.com/mhewedy/mego/blob/e77fff47c4b9a19965246a29c818c3d316b462b3/mego-api/api/routes.go

https://github.com/mhewedy/mego/blob/e77fff47c4b9a19965246a29c818c3d316b462b3/mego-api/api/routes.go