Golang HTTP Handler request/response logger

logger.go

func logger(prefix string, h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		// Save a copy of this request for debugging.
		requestDump, err := httputil.DumpRequest(r, false)
		if err != nil {
			log.Println(err)
		}
		log.Println(prefix, string(requestDump))

		rec := httptest.NewRecorder()
		h.ServeHTTP(rec, r)

		dump, err := httputil.DumpResponse(rec.Result(), false)
		if err != nil {
			log.Fatal(err)
		}
		log.Println(prefix, string(dump))

		// we copy the captured response headers to our new response
		for k, v := range rec.Header() {
			w.Header()[k] = v
		}

		// grab the captured response body
		data := rec.Body.Bytes()

		w.Write(data)
	}
}

If you want to also keep the status code,

w.WriteHeader(rec.Code)

Note that I'm not 100% sure this is the correct way to do this.

w.WriteHeader(rec.Code) needs to be called before w.Write(data).