Sample golang web server returning JSON objects

main.go

package main

import (
	"encoding/json"
	"log"
	"net/http"
	"strconv"
)

func ServeJSON(rw http.ResponseWriter, obj interface{}) {
	rw.Header().Add("content-type", "application/json")
	rw.WriteHeader(http.StatusOK)
	json.NewEncoder(rw).Encode(obj)
}

// plain struct
// remember only public fields are encoded
type Response1 struct {
	StatusCode int
	Status     string
	internalID int
}

func Serve1(rw http.ResponseWriter, req *http.Request) {
	resp := Response1{
		StatusCode: 10,
		Status:     "How do you do",
		internalID: 70,
	}

	ServeJSON(rw, resp)
}

// annotations
// json:something renames field
// json:,omitempty omits the field if the value is the zero value for that type (empty string, 0, etc)
type Response2 struct {
	StatusCode      int    `json:"code"`
	Status          string `json:"description"`
	ItemNumber      int    `json:"number,omitempty"`
	ItemDescription string `json:",omitempty"`
}

func Serve2(rw http.ResponseWriter, req *http.Request) {
	val := req.URL.Query()
	itemNr, _ := strconv.Atoi(val.Get("item"))

	ServeJSON(rw, Response2{
		StatusCode: 20, // will be 'code' when encoded
		// Status will be zero value when ommitted but will still be in output because of annotations
		ItemNumber: itemNr, // will be omitted by default because it is zero
		// ItemNumber shows up at "number" if service is queried with item
		// ItemDescription will also be zero value but will be omitted
	})
}

// Example of different ways to compose fields
type Response3 struct {
	Status     int
	Reasons    []string
	Keys       map[string]string
	LastResult Response1
	NextResult interface{}
}

func Serve3(rw http.ResponseWriter, req *http.Request) {
	ServeJSON(rw, Response3{
		Status:  200,
		Reasons: []string{"bing", "bang", "boom"},
		Keys: map[string]string{
			"a": "one",
			"b": "two",
		},
		LastResult: Response1{
			Status:     "hello",
			StatusCode: 201,
		},
		NextResult: []struct {
			Greeting string
			Language string
		}{
			{
				Greeting: "hello",
				Language: "english",
			},
			{
				Greeting: "bonjour",
				Language: "french",
			},
			{
				Greeting: "TO THE MOON 🚀🚀🚀",
				Language: "r/WallStreetBets",
			},
		},
	})
}

func main() {
	http.HandleFunc("/service1", Serve1)
	http.HandleFunc("/service2", Serve2)
	http.HandleFunc("/service3", Serve3)
	log.Println("serving at http://localhost:8080 . Try:")
	log.Println("http://localhost:8080/service1")
	log.Println("http://localhost:8080/service2")
	log.Println("http://localhost:8080/service2?item=300")
	log.Println("http://localhost:8080/service3")
	panic(http.ListenAndServe(":8080", nil))
}