Go simple server example with decorator JSON handler pattern

server.go

package main

import (
	"context"
	"encoding/json"
	"errors"
	"net"
	"net/http"
	"os"
	"os/signal"
)


type Endpoints struct {
	Descr string `json:"description_field,omitempty"`
}

func (s *Endpoints) test(r *http.Request) (JsonResp, error) {
	return JsonResp{Status: 200, Body: Endpoints{Descr: r.PathValue("name")}}, nil
}

func main() {
	basectx := context.Background()

	ctx, stop := signal.NotifyContext(basectx, os.Interrupt)
	defer stop()

	// register
	handlers := http.NewServeMux()

	methods := &Endpoints{}
	handlers.HandleFunc("GET /test/{name}", DecorateJSON(methods.test))

	// setup server
	server := &http.Server{Addr: ":8080", Handler: handlers, BaseContext: func(l net.Listener) context.Context {
		return ctx
	}}

	go func() {
		<-ctx.Done()
		server.Shutdown(basectx)
	}()

	err := server.ListenAndServe()
	if err != nil && !errors.Is(err, http.ErrServerClosed) {
		panic(err)
	}
}

type JsonResp struct {
	Status int
	Body   any
}

type DecorateFunc func(r *http.Request) (JsonResp, error)

func DecorateJSON(fun DecorateFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		resp, err := fun(r)
		if err != nil {
			http.Error(w, "Internal server", http.StatusInternalServerError)
			return
		}

		//  RETURN JSON

		w.Header().Set("Content-type", "text/json")
		stringfied, err := json.MarshalIndent(resp.Body, "", " ")
		if err != nil {
			stringfied = []byte("Internal server error: failed to marshal JSON")
			resp.Status = http.StatusInternalServerError
		}

		w.WriteHeader(resp.Status)
		w.Write(stringfied)
	}
}