Check JSON middleware

json_middleware.go

package main

import (
	"time"
	"net/http"
	"log"
	"io/ioutil"
	"encoding/json"
	router "github.com/go-chi/chi"
	routermw "github.com/go-chi/chi/middleware"
	"bytes"
)

func withJsonCheck(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r == nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("nil??"))
			return // Doesn't serve next

		}

		// TODO also check req headers content-type

		raw, err := ioutil.ReadAll(r.Body)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("error reader"))
			return // Doesn't serve next
		}

		s := string(raw)

		if s == "" {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("not valid JSON (empty) :("))
			return // Doesn't serve next
		}

		if s == "{}" {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("not valid JSON (empty obj) :("))
			return // Doesn't serve next
		}

		var ignore interface{}

		err = json.Unmarshal(raw, &ignore)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("not valid JSON (unmarshal) :("))
			return // Doesn't serve next
		}

		r.Body = ioutil.NopCloser(bytes.NewBuffer(raw)) // Must set body for next

		h.ServeHTTP(w, r) // Valid json -> serve next MW
	})
}

func home(w http.ResponseWriter, r *http.Request) {
	raw, err := ioutil.ReadAll(r.Body)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		w.Write([]byte("error in handler"))
		return
	}

	w.Write([]byte("hey i got valid json!\n"))
	w.Write(raw)
}

func main() {
	r := router.NewRouter()

	r.Use(routermw.Logger)
	r.Use(routermw.Recoverer)

	// JSON check
	r.Use(withJsonCheck)

	r.Post(`/`, home)

	srv := http.Server{
		Addr:              `localhost:8080`,
		Handler:           r,
		WriteTimeout:      time.Second * 30,
		ReadHeaderTimeout: time.Second * 30,
		IdleTimeout:       time.Second * 30,
		ReadTimeout:       time.Second * 30,
	}

	log.Printf("Listening address '%v'\n", srv.Addr)

	srv.ListenAndServe()

}