include POST params and/or JSON params in Golang HTTP log output

verbose_golang_http.go

// just an extension of the default Negroni logger
// https://github.com/codegangsta/negroni/blob/c7477ad8e330bef55bf1ebe300cf8aa67c492d1b/logger.go

// USAGE
// import (
// "github.com/gorilla/mux"
// "github.com/codegangsta/negroni"
// "github.com/kr/pretty"
// )
// router := mux.NewRouter()
// negroniRouter := negroni.New(NewLogger())
// negroniRouter.UseHandler(router)
// negroniRouter.Run(fmt.Sprintf(":8080"))

// # OUTPUT FOR application/json
// [VerboseHttpLogger] Started POST, /blogs, application/json
// [VerboseHttpLogger] JSON: map[string]interface {}{
//     "myJsonKey": "myJsonValue",
// }
// [VerboseHttpLogger] Completed 201 Accepted in 4.568037ms
//
// # ----------------------------------
//
// # OUTPUT FOR application/x-www-form-urlencoded
// [VerboseHttpLogger] Started POST, /blogs, application/x-www-form-urlencoded
// [VerboseHttpLogger] urlencoded-Form: url.Values{
//     "myFieldName": {"someValue"},
// }
// [VerboseHttpLogger] Completed 201 Accepted in 4.568037ms


type VerboseHttpLogger struct {
	*log.Logger
}

func NewLogger() *VerboseHttpLogger {
	return &VerboseHttpLogger{log.New(os.Stdout, "[VerboseHttpLogger] ", 0)}
}

func (l *VerboseHttpLogger) ServeHTTP(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	start := time.Now()
	contentType := r.Header.Get("Content-Type")
	l.Printf("Started %s, %s, %s", r.Method, r.URL.Path, contentType)

	r.ParseForm()

	if r.Body != nil {
		bodyBytes, _ := ioutil.ReadAll(r.Body)
		r.Body.Close()
		r.Body = ioutil.NopCloser(bytes.NewBuffer(bodyBytes))

		if contentType == "application/x-www-form-urlencoded" {
			l.Printf("urlencoded-Form: %# v\n", pretty.Formatter(r.Form))
		} else if contentType == "application/json" {
			var data map[string]interface{}
			json.Unmarshal(bodyBytes, &data)
			l.Printf("JSON: %# v\n", pretty.Formatter(data))
		}
	}

	next(rw, r)

	res := rw.(negroni.ResponseWriter)
	l.Printf("Completed %v %s in %v", res.Status(), http.StatusText(res.Status()), time.Since(start))
}